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Nanowire Electronics: From Nanoscale to Macroscale
Abstract
Semiconductor nanowires have attracted extensive interest as one of the best-defined classes of nanoscale building blocks for the bottom-up assembly of functional electronic and optoelectronic devices over the past two decades. The article provides a comprehensive review of the continuing efforts in exploring semiconductor nanowires for the assembly of functional nanoscale electronics and macroelectronics. Specifically, we start with a brief overview of the synthetic control of various semiconductor nanowires and nanowire heterostructures with precisely controlled physical dimension, chemical composition, heterostructure interface, and electronic properties to define the material foundation for nanowire electronics. We then summarize a series of assembly strategies developed for creating well-ordered nanowire arrays with controlled spatial position, orientation, and density, which are essential for constructing increasingly complex electronic devices and circuits from synthetic semiconductor nanowires. Next, we review the fundamental electronic properties and various single nanowire transistor concepts. Combining the designable electronic properties and controllable assembly approaches, we then discuss a series of nanoscale devices and integrated circuits assembled from nanowire building blocks, as well as a unique design of solution-processable nanowire thin-film transistors for high-performance large-area flexible electronics. Last, we conclude with a brief perspective on the standing challenges and future opportunities.
... In practical, heuristic corrections to Anderson's rule have found success in specific systems, such as the 60:40 rule for the GaAs/AlGaAs system. The band offsets are determined by the difference in electron affinity added with the band gap of the two semiconductors 1 and 2 as follows [31]: ...
... This model reveals a very good agreement with experimental outcomes of AlAs/GaAs value for Al 0.30 Ga 0.7 As/GaAs assuming ΔE V /ΔE g = 1/3. Furthermore, most of the simpler and useful theories of heterojunction band alignment proposed are based on transitivity, and it appears to be verified within experimental uncertainties in lattice-matched heterostructure systems [31]. However, the theoretical and experimental band offsets change for the different proposed approaches and each of the theoretical methods experiences challenges to predict the band offset reliably when applied for all semiconductor heterostructures combinations. ...
... Spatially localized interface states may generate at the terminal interface of the semiconductor at typical semiconductor−dielectric or semiconductor−metal interfaces (figure 5(g)), which leads to band bending as well as interface modification. The energy-level diagrams could in principle be constructed by joining semiconductor band structure diagrams with molecular orbital diagrams for the interface between organic molecules or materials, and the inorganic semiconductor (figure 5(h)) [31]. ...
The demand for advanced electronic and optoelectronic devices has driven significant research and development efforts toward exploring emerging semiconductor materials with enhanced performance characteristics. II-VI semiconductors have been studied extensively owing to their wide bandgap characteristics, which enable high electron mobility, excellent thermal stability, and resistance to radiation damage. These properties make them well-suited for a range of applications, including solar cells, light-emitting diodes (LEDs), photodetectors, lasers, sensors, and field effect transistors (FETs). In II-VI compounds, both ionic and covalent bonds exist with a higher electronegative nature of the VI-group elements than II-group elements. This existing ionic behavior strongly influences the binding of valence band electrons rather strongly to the lattice atoms. Thus, the II-VI semiconductors such as CdS, CdTe, ZnS, ZnSe, and CdSe possess wide tunable bandgaps (~0.02 to ≥ 4.0 eV) and high absorption coefficients of approximately 106 cm-1, setting them apart from other semiconductors formed by a covalent bond with closely equal atomic weights. This review article delves into the physics of II-VI semiconductor homo/heterojunctions, and the steps involved in device fabrication including lithography, etching, metallization, stability (oxidation and passivation) and polymerization together with several doping strategies. Furthermore, this review explores the process for tuning the distinct physical and chemical properties and a substantial advancement in electronic, and optoelectronic devices, including tools, cutting-edge equipment, and instrumentations. This comprehensive review provides detailed insights into the potential and technological progress of II-VI wide bandgap semiconductor device technology including experienced challenges and prospects.
... For this purpose, the c-Si layer can be created by performing a solid phase epitaxy (SPE) of an a-Si layer, touching through holes down to the bottom seeding sites on the c-Si wafer surface, followed by a conventional top-down lithography and etching procedure to pattern the ultrathin 1D fin or NW channels [47,48]. However, the SPE formation of mono-like c-Si demands a high annealing temperature of > 800 • C for achieving a lateral epitaxy growth rate of <100 nm/min [49]; hence, instead of the top-down etching formation approach, these ultrathin 1D channels can be directly generated from a low-temperature bottom-up catalytic growth strategy, commonly led by nanoscale metal droplets, by consuming gaseous or solid phase precursors [50,51]. As shown in the right side of Figure 1, the catalytic growth of SiNWs or nanowhiskers, mediated by metallic particles, was discovered more than half a century ago [50][51][52][53][54][55], but their potential applications in nanoscale electronics were not fully recognized until the end of the 1990s, thanks to the development of more powerful and convenient characterization or observation tools and more sophisticated manipulation techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and film deposition equipment and so on [50,54,[56][57][58]. ...
... However, the SPE formation of mono-like c-Si demands a high annealing temperature of > 800 • C for achieving a lateral epitaxy growth rate of <100 nm/min [49]; hence, instead of the top-down etching formation approach, these ultrathin 1D channels can be directly generated from a low-temperature bottom-up catalytic growth strategy, commonly led by nanoscale metal droplets, by consuming gaseous or solid phase precursors [50,51]. As shown in the right side of Figure 1, the catalytic growth of SiNWs or nanowhiskers, mediated by metallic particles, was discovered more than half a century ago [50][51][52][53][54][55], but their potential applications in nanoscale electronics were not fully recognized until the end of the 1990s, thanks to the development of more powerful and convenient characterization or observation tools and more sophisticated manipulation techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and film deposition equipment and so on [50,54,[56][57][58]. Catalytic growth of SiNWs is best known as a high-yielding, low-cost fabrication method capable of producing various ultrathin NW structures with high crystallinity and at relatively low temperatures. ...
... However, the SPE formation of mono-like c-Si demands a high annealing temperature of > 800 • C for achieving a lateral epitaxy growth rate of <100 nm/min [49]; hence, instead of the top-down etching formation approach, these ultrathin 1D channels can be directly generated from a low-temperature bottom-up catalytic growth strategy, commonly led by nanoscale metal droplets, by consuming gaseous or solid phase precursors [50,51]. As shown in the right side of Figure 1, the catalytic growth of SiNWs or nanowhiskers, mediated by metallic particles, was discovered more than half a century ago [50][51][52][53][54][55], but their potential applications in nanoscale electronics were not fully recognized until the end of the 1990s, thanks to the development of more powerful and convenient characterization or observation tools and more sophisticated manipulation techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and film deposition equipment and so on [50,54,[56][57][58]. Catalytic growth of SiNWs is best known as a high-yielding, low-cost fabrication method capable of producing various ultrathin NW structures with high crystallinity and at relatively low temperatures. ...
Quasi-one-dimensional (1D) semiconducting nanowires (NWs), with excellent electrostatic control capability, are widely regarded as advantageous channels for the fabrication of high-performance microelectronics, memories, and sensors. For example, the latest Si field-effect-transistor (FET) technology nodes, < N5 nm, use horizontally-stacked SiNWs or nanosheet channels in a gate-all-around (GAA) configuration. However, further scaling of the top-down etching fabrication is reaching physical limits, necessitating the development of new fabrication or integration technologies in monolithic three dimensional (3D) architecture to push Moore’s law forward. These new capabilities are also critical, for implementing of more advanced non von Neumann paradigms of in-memory and neuromorphic computing. For this, a versatile and highly controllable low-temperature growth integration of orderly 1D SiNW channels is desired, as it will provide an alternative or complementary new route to fabricate a multilayer of Si CMOS logics/memories in a fully 3D stacked manner. In this study, we assess the evolution and recent progress of catalytic growth strategies for ultrathin 1D channels in-plane or planar NWs, and revisit the key mechanisms and technological milestones in geometry, lattice quality, line-shape, position, and composition controls. We aim to eventually establish a reliable catalytic growth integration strategy, suitable for the fabrication of GAA FETs and the implementation of a monolithic 3D integration architecture. Finally, we also present a summary and perspectives on the current challenges and future opportunities of monolithic growth integration of NW electronics in 3D architecture.
... In recent decades, the research of materials at nanoscale has experienced exponential growth, revealing quantum phenomena in the macroscopic world. With a two-dimensional quantum confinement, the nanowires exhibit an exceptional itinerant ferromagnetism [10,11] and perform a crucial building-block role in nanoelectronics [12]. In this article, we report a real-space tight-binding study on the electronic band structure of nanowires built by cubically arranged atoms with interactions up to third neighbors. ...
... Green's function (12) can be rewritten as [13] ...
The flat electronic band has remarkable relevance in the strongly correlated phenomena mainly due to its reduced kinetic energy in comparison to the many-body potential energy. The formation of such bands in cubically structured nanowires is addressed in this article by means of a new independent channel method and a generalized convolution theorem developed for the Green’s function including the first, second, and third neighbor interactions. A real-space renormalization method is further applied to address macroscopic-length aperiodic nanowires. We also determined the appearance condition of these flat bands, as well as their degeneracy and robustness in the face of perturbations, such as structural dislocations. Finally, the possible experimental detection of this flat band via the electronic specific heat is analyzed.
... The revolution in information technology over the past half-century has enabled the growth of cylindrical quantum wires with axial heterostructure, like metal-organic epitaxy, molecular beam epitaxy (MBE), chemical lithography [1][2][3][4][5][6][7][8], etc. Theoretical and experimental techniques can easily reveal the fundamental physical mechanisms of carrier transmission inside cylindrical quantum wires due to their periodic nature and the quantum confinement effect [9]. Many applications, from the nanoscale to the macroscale, are made possible by the advantages of axial CQWRs heterostructures, and they also help to better understand the mechanism of the one-dimensional movement of carriers [10,11]. For electronic transmission applications, such as solar cells, where the nanowire geometry can benefit cell performance and carrier efficiency, the axial CQWRs Heterostructures are of special interest [12,13], nanowire transistors [14], nanowire lasers [15], energy conversion, harvesting and storage [16], etc. Tubular semiconductor-based nano-heterosystems consisting of two periodically alternating CQWRs are interesting because they direct the electron density along a one-dimensional cylindrical structure. ...
In this paper, we have studied a theoretical and numerical investigation of the electronic properties of finite cylindrical quantum wires (CQWRs), constituted by the periodic alteration of two semiconductor materials of CQWRs GaAs/AlGaAs in the axial direction, the structure sandwiched between two substrates GaAs. The electronic band structure and the electronic transmission spectrum are obtained by means of Green’s function approach, taking into account the impact of connection barriers. Our results reveal that the electronic energy levels of CQWRs consist of alternating passbands and bandgaps. The coincidence of incoming electronic waves with these discrete electronic energy levels leads to electron transport during the CQWRs superlattice. We employed an effective mass model dependent on the cell position in the axial direction to solve the Schrodinger equation. This model was adjusted to reflect variations in the confining potentials while accounting for changes in the radial direction. When the radius of the structure is relatively small the electronic states tend towards higher energies due to geometrical confinement. On the other hand, as the radius increases, the passbands and bandgaps move to lower energies. Similarly, the pseudogaps turn into full gaps, and their width increases, and this feature is also observed when the number of cells increases. This property is due to the interaction between the neighboring electrons and the eigenstates of the CQWRs. In addition, the passbands and band gaps shift to high energy when the barrier concentration increases, and the width of band gaps increases also. Finally, we have demonstrated the theoretical design of an optoelectronic device for filtering electronic waves by geometrical and physical parameters, whose electronic band structure of this finite CQWRs superlattice can be controlled.
... One-dimensional (1D) nanomaterials, such as CNTs and carbon nanofibers, exhibit linear structures and offer high aspect ratios, mechanical strength, and electrical conductivity. [87,88] Two-dimensional (2D) nanomaterials, such as graphene and graphene oxide, exhibit a planar sheet-like structure with exceptional electrical conductivity and large surface area. [89] They have been extensively explored in the development of flexible and transparent conductive electrodes and biosensors. ...
The past few decades have witnessed the rapid advancement and broad applications of flexible bioelectronics, in wearable and implantable electronics, brain–computer interfaces, neural science and technology, clinical diagnosis, treatment, etc. It is noteworthy that soft and elastic conductive hydrogels, owing to their multiple similarities with biological tissues in terms of mechanics, electronics, water‐rich, and biological functions, have successfully bridged the gap between rigid electronics and soft biology. Multifunctional hydrogel bioelectronics, emerging as a new generation of promising material candidates, have authentically established highly compatible and reliable, high‐quality bioelectronic interfaces, particularly in bioelectronic recording and stimulation. This review summarizes the material basis and design principles involved in constructing hydrogel bioelectronic interfaces, and systematically discusses the fundamental mechanism and unique advantages in bioelectrical interfacing with the biological surface. Furthermore, an overview of the state‐of‐the‐art manufacturing strategies for hydrogel bioelectronic interfaces with enhanced biocompatibility and integration with the biological system is presented. This review finally exemplifies the unprecedented advancement and impetus toward bioelectronic recording and stimulation, especially in implantable and integrated hydrogel bioelectronic systems, and concludes with a perspective expectation for hydrogel bioelectronics in clinical and biomedical applications.
... The development of efficient manufacturing techniques, particularly at the nanoscale, has always been an arduous task. Despite advancements in technology, it remains difficult to discover an affordable and replicable method for creating nanoscale structures [1,2]. Scientists are intrigued by the possibility of manipulating the properties of materials by selecting and interacting with individual particles. ...
... As one-dimensional materials, nanorods are key elements in a broad range of devices, such as nanoelectronics [1,2], biomedical sensors [3], and optical devices [4]. To use nanorods in practical applications, a key challenge is to align the nanorods on the pre-patterned electrodes. ...
Dielectrophoresis is a potential candidate for aligning nanorods on electrodes, in which the interplay between electric fields and microfluidics is critically associated with its yield. Despite much of previous work on dielectrophoresis, the impact of frequency modulation on dielectrophoresis-driven nanorod self-assembly is insufficiently understood. In this work, we systematically explore the frequency dependence of the self-alignment of silicon nanorod using a microfluidic channel. We vary the frequency from 1kHz to 1000 kHz and analyze the resulting alignments in conjunction with numerical analysis. Our experiment reveals an optimal alignment yield at approximately 100 kHz, followed by a decrease in alignment efficiency. The nanorod self-alignments are influenced by multiple consequences, including the trapping effect, induced electrical double layer, electrohydrodynamic flow, and particle detachment. This study provides insights into the impact of frequency modulation of electric fields on the alignment of silicon nanorods using dielectrophoresis, broadening its use in various future nanotechnology applications.
... These nanostructures are well-known for their peculiar geometry providing remarkable optical [20] and electronic properties. [21] Decoration of the NWs with nanoparticles and QDs is the well-known approach used to tailor optical absorption, provide fast interfacial charge carriers transfer and their efficient separation via proper bandgap engineering aimed at optimization of the semiconductor NW-based device performance. [22] This strategy was employed for the development of flexible photodetectors [23] and advanced flexible image sensors. ...
Carbon dots (CDs) are promising nanostructures in the field of photonics owing to the ease of fabrication, tunable and efficient emission. Gallium phosphide (GaP) nanowires are known for high surface area, optical density, waveguiding, resonant optical properties but lacking the luminescence due to the indirect bandgap. Here, hybrid photonic structures – GaP nanowires decorated with the CDs are fabricated and studied. Feasible drop‐casting deposition technique allows fabrication of dense vertical structures exhibiting efficient photoluminescence. Deposition of the CDs over the nanowires does not affect their luminescent properties demonstrating tolerance of the approach toward the surface aggregation. Tuning of the emission spectrum is obtained via variation of the excitation wavelength and CDs’ synthesis protocol. The structures emitting throughout the visible range are obtained. Analysis of the photoluminescence of an individual structure demonstrates the most intense and fast recombination processes at the ends of a nanowire. It is shown that the luminescence of the CDs’ covering a nanowire acting as a Fabry–Perot cavity is enhanced up to a factor of 3 governed by the Purcell effect. The obtained results unveil a path for fabrication of novel photonic devices via decoration of optically dense nanowires with CDs for enhanced and directed broadband emission.
... The recent discovery of atomically thin two-dimensional (2D) materials, has revolutionized materials science by enabling nanoscale quantum effects [1,2]. Over the past few decades, 2D materials have garnered substantial research interest due to their remarkable properties and the immense potential they hold for applications across diverse fields, ranging from electronics and energy storage to medicine [3][4][5][6]. ...
This study computationally investigates the thermoelectric properties of two-dimensional tetragonal Silicene (T-Si) using a tight binding model. The effects of external factors such as bias voltage, magnetic field, and chemical potential on the thermoelectric performance are analyzed through transport coefficients calculated using the Kubo formula and Green’s function method. The intrinsic gapless T-Si exhibits tunable electronic structure and thermoelectric properties under these external fields. The results demonstrate that the bias voltage reduces thermoelectric performance due to opening a band gap, while the magnetic field and chemical doping enhance it based on the increasing carrier concentration. The specific heat exhibits a Schottky anomaly peak which its position and intensity modulated by the external fields. Electrical conductivity displays pronounced tuning across temperature ranges under the influence of the fields. The positions, intensities, and magnitudes of power factor, figure of merit, and Seebeck coefficient peaks are sensitively dependent on external parameters. The findings indicate that optimizing the electronic and thermal properties of T-Si using external controlled parameters provides pathways for enhancing the thermoelectric efficiency for thermal energy harvesting applications.
... Nanowires exhibit unique electronic and optical properties due to their small dimensions and high aspect ratio as well as quantum confinement effects, making them suitable for multiple applications in different fields including electronics, photonics, and sensing [1][2][3][4][5][6][7][8][9]. III-V semiconductor compounds, such as indium arsenide (InAs), are particularly attractive for high-speed electronic devices due to their low electron effective mass and high carrier mobility [3,7]. ...
... Nanowire-based polarized photodetectors have gained significant recognition for their compact device size, exceptional conversion efficiency, adjustable light absorption coefficient, and wide spectral range. [22][23][24][25][26][27][28][29] This is particularly important in the context of industrial market demand for device integration and miniaturization. Searching for new polarization-sensitive low-dimensional materials has long been a research frontier. ...
Perpendicular optical reversal of the linear dichroism transition has promising applications in polarization-sensitive optoelectronic devices. We perform a systematical study on the in-plane optical anisotropy of quasi-one-dimensional PdBr2 by using combined measurements of the angle-resolved polarized Raman spectroscopy (ARPRS) and anisotropic optical absorption spectrum. The analyses of ARPRS data validate the anisotropic Raman properties of the PdBr2 flake. And anisotropic optical absorption spectrum of PdBr2 nanoflake demonstrates distinct optical linear dichroism reversal. Photodetector constructed by PdBr2 nanowire exhibits high responsivity of 747 A⋅W⁻¹ and specific detectivity of 5.8 × 10¹² Jones. And the photodetector demonstrates prominent polarization-sensitive photoresponsivity under 405-nm light irradiation with large photocurrent anisotropy ratio of 1.56, which is superior to those of most of previously reported quasi-one-dimensional counterparts. Our study offers fundamental insights into the strong optical anisotropy exhibited by PdBr2, establishing it as a promising candidate for miniaturization and integration trends of polarization-related applications.
... Semiconductor nanowires (NWs) formed using bottom-up crystal growth techniques have attracted considerable interest because of their unique properties and potential for various applications in electronic [1][2][3][4] and photonic devices [5][6][7], and quantum information processing [8,9]. In particular, InPbased heterostructured NWs are promising for photonic devices, because they have a direct band gap compatible with the telecom band [10,11]. ...
We carried out in-situ annealing of InP Nanowires (NWs) in a metal-organic vapor phase epitaxial (MOVPE) growth reactor to control and reduce the tip size of InP NWs. InP NWs were grown by selective-area (SA) MOVPE on partially masked (111)A InP substrates, and annealing was successively applied in tertiarybutylphosphine (TBP) ambient. Initially, InP NWs had a hexagonal cross-section with {11-2} facets vertical to the substrates; they became tapered, and edges were rounded by annealing. By appropriately selecting the annealing temperature and initial NW diameter, the tip size of the NW was reduced and NWs with a tip size of 20nm were successfully formed. Subsequently, a thin InAsP layer was grown on the annealed NWs and their photoluminescence was investigated at low temperatures. The characterization results indicated the formation of InAsP quantum dots (QDs) emitting in the telecom band. Our approach is useful for reducing the size of NWs and for the controlled formation of InAsP QDs embedded in InP NWs in photonic devices compatible with telecom bands.
... Semiconductor-heterostructure-based science and technology have made remarkable development in various fields from basic research to practical applications [1][2][3]. Because of the one-dimension structure with a nanoscale diameter [4], semiconductor nanowires have shown high potential applications in many research fields including electronics [5], photonics [6], photoelectrochemistry [7], etc [8][9][10]. In contrast to the film-based structure, a nanowire-based structure grown by bottom-up approach has exhibited high capability to form a dislocation-free interface for latticemismatch heterostructures [11][12][13][14][15]. ...
Nanowire-based structure has attracted much interest for its high potential applications in fundamental research and technology. Due to the inadequate understanding of nanowire growth and structural control, optoelectronic property still needs to be improved for nanowire-based optical devices working in telecom band range. Here we report enhancement of the optoelectronic property of InP/InAs heterostructure nanowire light emitting diodes with telecom-band electroluminescence. Due to a high leakage current, nanowire-based devices have shown a low open-circuit voltage of 0.084 V. We clarify that the high leakage current is caused by a conductive thin shell layer on nanowire sidewalls. By a surface wet etching, these nanowire-based devices show a low leakage current and exhibits an open-circuit voltage of 0.412 V. These results indicate an improved optoelectronic performance of InP/InAs nanowire light emitting diodes by enhanced understanding of nanowire growth and structural control. This work paves the way for high-performance nanowire-based optoelectronic devices working in telecom band range.
... Changes in physical properties at the nanoscale can be used to tailor the performance of semiconductor nanostructure devices. Semiconductor nanowires are attractive constituents for electronic devices in many applications, including energyharvesting photovoltaics (Haverkort et al., 2018;, light-emitting diodes (Gudiksen et al., 2002;Gibson et al., 2019;Barrigó n et al., 2019;Motohisa et al., 2019) and electronics (Memisevic et al., 2017;Tomioka et al., 2012;Jia et al., 2019). ...
Developing semiconductor devices requires a fast and reliable source of strain information with high spatial resolution and strain sensitivity. This work investigates the strain in an axially heterostructured 180 nm-diameter GaInP nanowire with InP segments of varying lengths down to 9 nm, simultaneously probing both materials. Scanning X-ray diffraction (XRD) is compared with Bragg projection ptychography (BPP), a fast single-projection method. BPP offers a sufficient spatial resolution to reveal fine details within the largest segments, unlike scanning XRD. The spatial resolution affects the quantitative accuracy of the strain maps, where BPP shows much-improved agreement with an elastic 3D finite element model compared with scanning XRD. The sensitivity of BPP to small deviations from the Bragg condition is systematically investigated. The experimental confirmation of the model suggests that the large lattice mismatch of 1.52% is accommodated without defects.
... Although NiAl-LDH can theoretically produce both CO and CH 4 because of its sufficient reduction potentials, it only promotes CO as the CO 2 reduction product in practice. The band edge potential values of NiAl-LDH and TiO 2 represent a type II (staggered) energy band structure [62]. Assuming that the current ternary hybrid NiAl-LDH@TiO 2 /Ti 3 C 2 system follows a traditional type II charge transfer mechanism, the photoreduction reaction should occur at the CB of TiO 2 , while the photooxidation reaction should occur at the VB of NiAl-LDH. ...
... The band edge potential values of CoAl-LDH and TiO 2 indicate a staggered or type II energy band alignment [54]. Assuming that the developed CoAl-LDH/TiO 2 /Ti 3 C 2 hybrid photocatalyst follows a traditional type II mechanism, the photoreduction reaction should occur at the CB of TiO 2 , while the photooxidation reaction should occur at the VB of CoAl-LDH. ...
... We investigated the use of GaN hollow nanowire lasers standing on sapphire substrate as tiny generators of vector beams with azimuthal polarization (Figure 1 and Figure 2). Nanowires 23,24,25 have promising optical and electrical characteristics. Various nanowire light sources 26,27 have been developed so far. ...
We fabricated GaN based hollow nanowires standing upright on a sapphire substrate by the sublimation method and found that they exhibit laser oscillation at room temperature. These very long, hollow, nano-sized structures cannot be fabricated by other means. Furthermore, we determined the condition under which the fundamental mode is azimuthally polarized by investigating the dispersion of the hollow structure. Examination of the measured emission properties indicates that the hollow nanowire operates as a topological, vector-beam, light source.
... To introduce nanowire devices into the mainstream planar electronic architecture, technologically and economically feasible approaches must be developed for rationally assembling nanowires into planar arrays with consistent orientations and precise positions for scaledup device integration. [9,10] In contrast to the various conventional post-growth assembly strategies, [11,12] advanced surface-guided mechanisms have been proposed for generating self-oriented planar nanowires via onestep growth. For example, the principle of lattice-matching epitaxy was first used to produce oriented planar nanowires (e.g., GaN, [13] ZnO, [14] and GaAs [15] ) on well-cut flat crystalline substrates, with the nanowires inheriting their orientation from the crystallographic symmetry of the substrates. ...
The simultaneous control of the orientation and position of organic semiconductor nanowires remains a major challenge when integrating them into monolithic devices. In this study, tris(8‐hydroxyquinoline)aluminum(III) (Alq3) molecules are self‐assembled into single‐crystalline nanowires with consistent orientation and predictable positions by selective‐area graphoepitaxial growth. The nanowire orientation is determined by parallel nanogrooves on a periodically modified faceted sapphire surface, and the position is simultaneously defined using a shadow mask. Computational fluid dynamics simulations showed that the mass flow field over the sapphire surface is tailored by the mask, resulting in preferential nanowire nucleation around the hole centers and leaving sufficient free space for the subsequent growth. Accordingly, the number, length, and density of the nanowires can be controlled by adjusting the mask layout. The good alignment and predictable positions of these nanowires facilitated their subsequent device integration, eliminating laborious assembly steps and potential damage after nanowire growth. Measurements from an in situ integrated two‐terminal device based on the Alq3 nanowires revealed that the nanowires exhibit a remarkable negative differential resistance and fast photoresponse in the UV region. Overall, selective‐area graphoepitaxial growth provides a versatile protocol for fabricating site‐ and orientation‐controlled organic semiconductor nanowires for the monolithic fabrication of nanowire‐based devices.
... Nanowires (NW) have gained a great deal of attention in the last decades due to their fascinating properties, e.g., large surface-to-volume ratio [1,2], quantum confinement of charge carriers [3,4], and high carrier mobility [5]. These properties, if controlled on demand, can be used to engineer building blocks of functional devices at the nanoscale, finding applications in, e.g., optoelectronics [6,7], electronics [6,8], and photovoltaics [9][10][11]. To this end, control of the dimensions, crystal orientation, crystal phase, and density of crystal defects is crucial. ...
The broad and fascinating properties of nanowires and their synthesis have attracted great attention as building blocks for functional devices at the nanoscale. Silicon and germanium are highly interesting materials due to their compatibility with standard CMOS technology. Their combination provides optimal templates for quantum applications, for which nanowires need to be of high quality, with carefully designed dimensions, crystal phase, and orientation. In this work, we present a detailed study on the growth kinetics of silicon (length 0.1–1 μm, diameter 10–60 nm) and germanium (length 0.06–1 μm, diameter 10–500 nm) nanowires grown by chemical vapor deposition applying the vapour–liquid–solid growth method catalysed by gold. The effects of temperature, partial pressure of the precursor gas, and different carrier gases are analysed via scanning electron microscopy. Argon as carrier gas enhances the growth rate at higher temperatures (120 nm/min for Ar and 48 nm/min H2), while hydrogen enhances it at lower temperatures (35 nm/min for H2 and 22 nm/min for Ar) due to lower heat capacity. Both materials exhibit two growth regimes as a function of the temperature. The tapering rate is about ten times lower for silicon nanowires than for germanium ones. Finally, we identify the optimal conditions for nucleation in the nanowire growth process.
... For instance, detecting the spin current can be accomplished by simply measuring a half-integer quantized conductance plateau, without the need of sophisticated techniques, such as an external magnetic field or top-gate bias 2,11,15 . Furthermore, benefiting from the potential to precisely control and monitor spin transport in a single-spin channel, these 1D magnetic systems can be utilized for versatile applications, including spin-qubit quantum computer 27 , spin filter [28][29][30][31] , and magnetic random access memory 32,33 . ...
Precise manipulation and monitoring spin transport in one-dimensional (1D) systems is a long-sought goal in the field of nano-spintronics. Based on first-principles calculations, we report the observation of half-integer conductance quantization in the Cobalt-fulvalene sandwich nanowire. Compared with a pure monatomic Cobalt wire, the introduction of fulvalene molecules leads to three important features: Firstly, the strong coupling between the fulvalene and the Cobalt prevents the contamination of the ambient air, ensuring both chemical and physical stabilities; Secondly, the fulvalene symmetry-selectively filters out most of the d -type orbitals of the Cobalt while leaving a single d -type orbital to form an open spin channel around the Fermi level, which offers a mechanism to achieve the observed half-integer conductance; Thirdly, it maintains a superexchange coupling between adjacent Co atoms to achieve a high Curie temperature. Spin transport calculations show that this half-metallic nanowire can serve as a perfect spin filter or a spin valve device, thus revealing the potential of Cobalt-fulvalene sandwich nanowire as a promising building block of high-performance spintronics technology.
Self-powered wide band gap semiconductors ultraviolet (UV) photodetectors based on one-dimensional (1D) micro/nanowires have attracted considerable attention on account of their wide potential applications. Here, amorphous Ga2O3 was sputtered onto...
Nanostructured materials present improved thermoelectric properties due to non-trivial effects at the nanoscale. However, the characterization of individual nanostructures, especially from the thermal point of view, is still an unsolved topic. This work presents the complete structural, morphological, and thermoelectrical evaluation of the selfsame individual bottom-up integrated nanowire employing an innovative micro-machined device compatible with transmission electron microscopy whose fabrication is also discussed. Thanks to a design that arranges the nanostructured samples completely suspended, detailed structural analysis using transmission electron microscopy is enabled. In the same device architecture, electrical collectors and isolated heaters are available at both ends of the trenches for thermoelectrical measurements of the nanowire i.e. thermal and electrical properties simultaneously. This allows the direct measurement of the nanowire power factor. Furthermore, micro-Raman thermometry measurements were performed to evaluate the thermal conductivity of the same suspended silicon nanowire. A thermal profile of the self-heating nanowire could be spatially resolved and used to compute the thermal conductivity. In this work, heavily-doped silicon nanowires were grown on this microdevices yielding a thermal conductivity of 30.8 ± 1.7 W Km-1 and a power factor of 2.8 mW mK-2 at an average nanowire temperature of 400 K. Notably, no thermal contact resistance was observed between the nanowire and the bulk, confirming the epitaxial attachment. The device presented here shows remarkable utility in the challenging thermoelectrical characterization of integrated nanostructures and in the development of multiple devices such as thermoelectric generators.
The present work deals with the study of the effect of temperature on the Raman spectroscopy and electrical properties of the silicon nanowires. The nanowires are fabricated through silver assisted electrochemical etching process. Prior to these studies, the fabricated nanowires are characterized through field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), and X-ray diffraction (XRD) measurements. FESEM reveals the vertical alignment of the nanowires. FETEM indicates the materials to be highly crystalline, which is also complemented by the XRD result. Raman peak is blue-shifted with a decrease of temperature suggesting lattice disturbance at low temperature. Temperature-dependent current-voltage (I-V) measurements are fitted with Cheung’s model and the characteristic parameters viz. ideality factor (n), barrier height (ϕb), and series resistance (Rs) are estimated from the fitted plots. At lower temperatures, the value of n highly deviates from the ideal value of unity and is 23.42 at 110 K. The materials are observed to obey space charge limited conduction (SCLC) to trap charge limit current (TCLC) with increasing bias at lower temperatures.
This comprehensive review examines the immense capacity of nanowires, nanostructures characterized by unbounded dimensions, to profoundly transform the field of biomedicine. Nanowires, which are created by combining several materials using techniques such as electrospinning and vapor deposition, possess distinct mechanical, optical, and electrical properties. As a result, they are well-suited for use in nanoscale electronic devices, drug delivery systems, chemical sensors, and other applications. The utilization of techniques such as the vapor-liquid-solid (VLS) approach and template-assisted approaches enables the achievement of precision in synthesis. This precision allows for the customization of characteristics, which in turn enables the capability of intracellular sensing and accurate drug administration. Nanowires exhibit potential in biomedical imaging, neural interfacing, and tissue engineering, despite obstacles related to biocompatibility and scalable manufacturing. They possess multifunctional capabilities that have the potential to greatly influence the intersection of nanotechnology and healthcare. Surmounting present obstacles has the potential to unleash the complete capabilities of nanowires, leading to significant improvements in diagnostics, biosensing, regenerative medicine, and next-generation point-of-care medicines.
Flexible and stretchable thin-film transistors (TFTs) are crucial in skin-like electronics for wearable and implantable applications. Such electronics are usually constrained in performance owing to a lack of high-mobility and stretchable semiconducting channels. Tellurium, a rising semiconductor with superior charge carrier mobilities, has been limited by its intrinsic brittleness and anisotropy. Here, we achieve highly oriented arrays of tellurium nanowires (TeNWs) on various substrates with wafer-scale scalability by a facile lock-and-shear strategy. Such an assembly approach mimics the alignment process of the trailing tentacles of a swimming jellyfish. We further apply these TeNW arrays in high-mobility TFTs and logic gates with improved flexibility and stretchability. More specifically, mobilities over 100 square centimeters per volt per second and on/off ratios of ~10 ⁴ are achieved in TeNW-TFTs. The TeNW-TFTs on polyethylene terephthalate can sustain an omnidirectional bending strain of 1.3% for more than 1000 cycles. Furthermore, TeNW-TFTs on an elastomeric substrate can withstand a unidirectional strain of 40% with no performance degradation.
The development of artificial light-harvesting systems based on long-range ordered ultrathin organic nanomaterials (i.e., below 3 nm), which were assembled from stimuli-responsive sequence-controlled biomimetic polymers, remains challenging. Herein, we report the self-assembly of azobenzene-containing amphiphilic ternary alternating peptoids to construct photo-responsive ultrathin peptoids nanoribbons (UTPNRs) with a thickness of ~2.3 nm and the length in several micrometers. The pendants hydrophobic conjugate stacking mechanism explained the formation of one-dimensional ultrathin nanostructures, whose thickness was highly dependent on the length of side groups. The photo-isomerization of azobenzene moiety endowed the aggregates with a reversible morphology transformation from UTPNRs to spherical micelles (46.5 nm), upon the alternative irradiation with ultraviolet and visible light. Donor of 4-(2-hydroxyethylamino)-7-nitro-2,1,3-benzoxadiazole (NBD) and acceptor of rhodamine B (RB) were introduced onto the hydrophobic and hydrophilic regions, respectively, to generate photo-controllable artificial light-harvesting systems. Compared with the spheres-based systems, the obtained NBD-UTPNRs@RB composite proved a higher energy transfer efficiency (90.6%) and a lower requirement of RB acceptors in water. A proof-of-concept use as fluorescent writable ink demonstrated the potential of UTPNRs on information encryption.
We fabricated GaN-based hollow nanowires standing upright on a sapphire substrate by the sublimation method and found that they exhibit laser oscillation at room temperature. These very long, hollow, nanosized structures cannot be fabricated by other means. Furthermore, we determined the condition under which the fundamental mode is azimuthally polarized by investigating the dispersion of the hollow structure. Examination of the measured emission properties indicates that the hollow nanowire operates as a topological, vector-beam light source.
Despite substantial advancements in n-type 1D and 2D nanostructures, achieving p-type field-effect transistors (FETs) using 1D nanostructures remains a formidable challenge due to surface defects and doping limitations. This study presents a scalable approach for fabricating the p-type homojunction (p/p+) CuI nanoribbons (CuI NRs) with enhanced charge injection. Characterization of iodide-exposed (I-rich) CuI thin films reveals improved crystallinity and significantly higher carrier concentration compared with pristine CuI thin films. Leveraging the unique carrier tuning property of CuI, localized iodine exposure facilitated by electron beam lithography at the source/drain electrode interface of CuI NRs leads to the formation of a homojunction CuI NR. The homojunction CuI NR p-type FETs exhibits performance improvements, with three-orders of magnitude lower contact resistance and high mobility (5.6 cm2V–1s–1) with an on/off ratio of 104. Temperature-dependent studies reveal the presence of shallow traps and a reduced Schottky barrier height in the homojunction CuI NR FETs, contributing to efficient charge transfer at the metal–semiconductor interface. These findings establish CuI NR as a promising material for developing reliable p-type semiconductor devices. The fabrication of homojunction CuI NRs represents a significant advancement in the field of 1D nanostructures, holding immense potential for cost-effective and scalable device fabrication.
Exploitation of low‐dimensional metal‐oxide semiconductor nanowires (MOS NWs) with peculiar and radial coaxial architectures is of great significance for constructing nanoscale, high‐performance, multi‐module integrable functional electronic products. Here, highly ordered In2O3@ZnO coaxial NW arrays (CNWA) using a simple and economical electrospinning technique are synthesized and assembled into field‐effect transistors (FETs). Featuring strong carrier effusion efficiency at the In2O3@ZnO circular heterogeneous interface, the field effect mobility (εFE) gets an intrinsic improvement and can reach as high as 202.3 cm² V‒1 s‒1 for high‐k‐based CNWA FETs, which exceeds the performance of oxide‐based FETs devices reported by far. Furthermore, the unique structural advantages endowing In2O3@ZnO CNWA FETs with excellent optoelectronic coupling capabilities are identified, for which further optoelectronic detection and artificial photonic synaptic devices are constructed and functional simulations are implemented. This work offers new insights in designing optoelectronics and artificial synapses to process and recognize information for neuromorphic computing and artificial intelligence applications.
High thermal conductivity and ambipolar mobility are highly desirable for semiconductors in electronics and have been observed in bulk boron arsenide (BAs). In this work, we explore the scaling behavior of a monolayer hydrogenated BAs field-effect transistor (ML H-BAs FET) by employing ab initio quantum transport methods. Both the armchair- and zigzag-directed ML H-BAs FETs can well satisfy the requirements of the International Technology Roadmap for Semiconductors even if the gate length is scaled down to 2∼3 nm for high-performance applications. The excellent n- and p−type symmetry of bulk BAs is well preserved in the ML H-BAs FET along with the zigzag direction but is lost in the armchair direction. However, such asymmetry can be suppressed by applying uniaxial compressive strain owing to the broken valence band degeneracy. Our findings provide important theoretical insights into transport symmetry and the scaling behavior of ML H-BAs FETs.
The development of high‐reactive single‐atom catalysts (SACs) based on long‐range‐ordered ultrathin organic nanomaterials (UTONMs) (i.e., below 3 nm) provides a significant tactic for the advancement in hydrogen evolution reactions (HER) but remains challenging. Herein, photo‐responsive ultrathin peptoid nanobelts (UTPNBs) with a thickness of ≈2.2 nm and micron‐scaled length are generated using the self‐assembly of azobenzene‐containing amphiphilic ternary alternating peptoids. The pendants hydrophobic conjugate stacking mechanism reveals the formation of 1D ultralong UTPNBs, whose thickness is dictated by the length of side groups that are linked to peptoid backbones. The photo‐responsive feature is demonstrated by a reversible morphological transformation from UTPNBs to nanospheres (21.5 nm) upon alternative irradiation with UV and visible lights. Furthermore, the electrocatalyst performance of these aggregates co‐decorated with nitrogen‐rich ligand of terpyridine (TE) and uniformly‐distributed atomic platinum (Pt) is evaluated toward HER, with a photo‐controllable electrocatalyst activity that highly depended on both the presence of Pt element and structural characteristic of substrates. The Pt‐based SACs using TE‐modified UTPNBs as support exhibit a favorable electrocatalytic capacity with an overpotential of ≈28 mV at a current density of 10 mA cm⁻². This work presents a promising strategy to fabricate stimuli‐responsive UTONMs‐based catalysts with controllable HER catalytic performance.
The sky is the limit with regards to the societal impact nanomaterials can have on the lives. However, in this study, it is shown that their potential is out of this world. The planet Mars has an abundant source of calcium sulfate minerals and in this work, it is shown that these deposits can be the basis of transformative nanomaterials to potentially support future space endeavors. Vitally, the methods applied are low cost and require no specialized instruments of great expertise, strengthening the potential involvement of nanotechnology in sustaining Martian inhabitation. Through a scalable eco‐friendly liquid processing technique performed on two common terrestrial gypsum, this simple method presented a cost‐efficient procedure to yield suspensions of large aspect ratio anhydrite nanobelts with long‐term stability that are characterized through scanning electron microscopy and Raman spectroscopy. Transmission electron microscopy shows nanobelts to have a mesocrystal structure, with distinct nanoparticle constituents making up the lattice. Unexpectedly, anhydrite nanobelts have remarkable electronic properties, namely a bandgap that is easily tuned between semiconducting (≈2.2 eV) and insulating (≈4 eV) behaviors through dimensional control measured via atomic force microscopy. To demonstrate the application potential of the nanobelts; optoelectronic, electrochemical, and nanocomposite measurements are made.
In the past decade, there has been tremendous progress in integrating chalcogenide phase-change materials (PCMs) on the silicon photonic platform for non-volatile memory to neuromorphic in-memory computing applications. Especially, these non von Neumann computational elements and systems benefit from mass manufacturing of silicon photonic integrated circuits (PICs) on 8-inch wafers using 130-nm complementary metal-oxide semiconductor (CMOS) line. Chip manufacturing based on the deep-ultraviolet (DUV) lithography and electron-beam lithography (EBL) enable rapid prototyping of PICs, which can be integrated with high-quality PCMs based on the wafer-scale sputtering technique as a back-end-of-line (BEOL) process. In this article, we overview recent advances of waveguide integrated PCM memory cells, functional devices, and neuromorphic systems, with an emphasis on fabrication and integration processes to attain the state-of-the-art device performance. After a short overview of PCM based photonic devices, we discuss the materials properties of the functional layer as well as the progress on the light guiding layer, namely, the silicon and germanium waveguide platforms. Next, we discuss the cleanroom fabrication flow of waveguide devices integrated with thin films and nanowires, silicon waveguide and plasmonic microheaters for electrothermal switching of PCMs and mixed-mode operation. Finally, the fabrication of photonic and photonic-electronic neuromorphic computing systems is reviewed. These systems consist arrays of PCM memory elements for associative learning, matrix-vector multiplication, and pattern recognition. With large-scale integration, neuromorphic photonic computing paradigm holds the promise to outperform digital electronic accelerators by taking the advantages of ultra-high bandwidth, high speed, and energy efficient operation in running machine learning algorithms.
The field of nanowire (NW) technology represents an exciting and steadily growing research area with applications in ultra-sensitive mass and force sensing. Existing detection methods for NW deflection and oscillation include optical and field emission approaches. However, they are challenging for detecting small diameter NWs because of the heating produced by the laser beam and the impact of the high electric field. Alternatively, the deflection of a NW can be detected indirectly by co-resonantly coupling the NW to a cantilever and measuring it using a scanning probe microscope. Here, we prove experimentally that co-resonantly coupled devices are sensitive to small force derivatives similar to standalone NWs. We detect force derivatives as small as 10⁻⁹ N/m with a bandwidth of 1 Hz at room temperature. Furthermore, the measured hybrid vibration modes show clear signatures of avoided crossing. The detection technique presented in this work verifies a major step in boosting NW-based force and mass sensing.
Metal oxide field‐effect transistors (MOFETs) represent a promising technology for applications in existing but alsoemerging large‐area electronics. Simultaneously, the rise of 1D nanomaterials with unique properties, represented by nanofibers (NFs), has also energized research. Thus, developing 1D nanofiber networks (NFNs) to act as the potential building blocks for use in fundamental elements of transistors is considered to be a promising approach torealize high‐performance 1D electronics. However, high processing temperatures and disordered nanofiber distribution represent two remaining technical challenges. Here, electrospun highly aligned IGZO (a‐IGZO) nanofiber arrays with low‐thermal‐budget of 350 °C and impressive device characteristics are achieved, including a μFE of 5.63 cm2 V –1 s –1 and superior on/off current ratio of ≈107. When ALD‐derived high‐k HfAlOx thin films are employed as gate dielectrics, the source/drain voltage (VDS) can be substantially reduced by ten times to a range of only 03 V, along with a three times improvement in mobility to a respectable value of 15.9 cm2 V –1 s –1 . Successful integrations of logic operation, sensor, and flexible devices implies the potential prospect of a‐IGZO NFN FETs in multifunctional electronics. The strategy for combining cryogenic processes and parallel arrays provides a feasible and reliable route in building future low‐power, high‐performance flexible electronics.
Nanoengineering the composition and morphology of functional nanoparticles endows them to perform multiple tasks and functions. An intriguing strategy for creating multifunctional nanomaterials involves the construction of core–shell nanostructures, which have enabled promising applications in biomedicine, energy, sensing, and catalysis. Here, a straightforward nanoengineering approach is presented utilizing liquid metal nanoparticles and galvanic replacement to create diverse core–shell nanostructures. Controlled nanostructures including liquid metal core‐gold nanoparticle shell (LM@Au), gold nanoparticle core‐gallium oxide shell (Au@Ga oxide), and hollow Ga oxide nanoparticles are successfully fabricated. Remarkably, these investigations reveal that LM@Au exhibits exceptional photothermal performance, achieving an impressive conversion efficiency of 65.9%, which is five times that of gold nanoparticles. By leveraging the high photothermal conversion efficiency and excellent biocompatibility of LM@Au, its promising application in hyperthermia cancer therapy is demonstrated. This simple yet powerful nanoengineering strategy opens new avenues for the controlled synthesis of complex core–shell nanostructures, advancing various fields beyond biomedicine.
Nanowires (NWs) of III-V semiconductor materials have been of interest to researchers for the last two decades. Knowledge of the subband spectrum of charge carriers in NWs and NW-based structures is very important for current applications. The electronic subband spectrum in NWs is currently known in detail, while for holes it is found with significant simplifications. One or more of the following crucial features are usually neglected: the real NW cross section shape, the crystal orientation of the NW, an accounting for the real anisotropic Hamiltonian of the bulk host material, and contributions that are due to the lack of an inversion center in the crystal lattice. Here we present a detailed calculation of hole subbands in GaAs NWs with the [111] orientation with a zinc blende crystal lattice, taking into account all the above four features. The spectrum of hole subbands based on the 4×4 Luttinger Hamiltonian is numerically calculated taking into account two main contributions arising from the lack of inversion symmetry (the Td point group) in the lattice of the host crystal. Accounting for these contributions leads to the appearance of spin splitting only for some subbands, in accordance with symmetry considerations. However, a significant rearrangement also occurs in the spectrum of nonsplit subbands. The hole densities are visualized, and it is shown that the contribution of terms with Td symmetry significantly changes the structure of the multicomponent wave function. Thus, taking into account the lack of an inversion center is essential for the spectrum of hole subbands and wave functions in GaAs NWs. This can be more pronounced for NWs of III-V materials constituted by heavy elements, such as InSb, where spin-orbit interaction is stronger. The effect of a transverse electric field leading to so-called Rashba spin splitting is considered as well.
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Gallium nitride (GaN) all-around (wrap) gate vertical nanowire (V-NW) field-effect transistors (FETs) are favorable for enhanced electrostatic control of the gate and selectivity for normally on/off operation. In this work, GaN V-NW FETs with a Schottky barrier gate (V-NW MESFETs), were fabricated for the first time. A nanofabrication process with comprehensive description of all processing steps is reported. It was validated with the demonstration of GaN V-NW MESFETs consisting of an array of 900 (30 × 30) GaN NWs with the narrowest until now reported diameter of 100 nm and all-around gate length of 250 nm. The GaN NWs were formed by a top-down approach, which combines conventional nanopatterning techniques and anisotropic wet etching of an initial GaN epilayer, grown by plasma assisted molecular beam epitaxy on a sapphire (0001) substrate. DC I-V characteristics exhibited normally-off operation and threshold voltage of +0.4 V, due to electron depletion region from the all-around Schottky barrier. A maximum drain-source current density (J ds) of 330 A cm-2 and maximum transconductance (g m) of 285 S cm-2 were obtained from I-V measurements. The results and directions for further optimization were discussed.
Simultaneous epitaxial growth of film and nanowire array on a substrate is of both scientific significance and practical importance for nanoscale optoelectronics. Nevertheless, in situ building conducting connection between individually isolated nanowires grown on insulating substrates is still challenging. Herein, we demonstrate a novel and facile strategy for the simultaneous epitaxial growth of nonpolar a-plane ZnO film and obliquely aligned nanowire array on Au-coated r-plane sapphire substrate. The morphology, structure, components, and optical properties of the as-synthesized ZnO nanostructures were investigated using field-emission scanning electron microscopy, X-ray diffraction, field-emission transmission electron microscopy, energy-dispersive spectroscopy, X-ray photo-electron spectroscopy, and photoluminescence spectroscopy. A cooperative growth mechanism is proposed: Au-catalyzed vapor transport initiates the co-occurrence of nonpolar a-plane and polar c-plane ZnO nuclei, and subsequently, the non-upward directed Au catalyst helps the nonpolar a-plane ZnO nuclei develop into a ZnO conductive film at the bottom and zinc self-catalyzed vapor-liquid-solid growth helps the polar c-plane ZnO nuclei develop simultaneously into obliquely aligned nanowire arrays. The proposed strategy realized in situ synthesis of nanowires with conductive connection and it can benefit the application of ZnO nanowires in optoelectronics.
The formation of twin plane superlattices in group III-V semiconductor nanowires (NWs) is analyzed by considering two dimensional nucleation using surface and twinning energies, obtained by performing electronic structure calculations within density functional theory. The calculations for GaP, GaAs, InP, and InAs demonstrate that surface energies strongly depend on the growth conditions such as temperature and pressure during the epitaxial growth. Furthermore, the calculated twinning energies are found to be much smaller than previously estimated values by the dissociation width of edge dislocations, which lead to smaller segment lengths. We also find that the nonlinear relationship between segment length and NW diameter depending on constituent elements is due to the difference in twinning energies. These results imply that twinning formation as well as surface stability are crucial for the formation of twin plane superlattices in group III-V semiconductor NWs.
Developing uncooled photodetectors at mid-wavelength infrared (MWIR) is critical for various applications including remote sensing, heat seeking, spectroscopy, and more. In this study, we demonstrate room-temperature operation of nanowire-based photodetectors at MWIR composed of vertical selective-area InAsSb nanowire photoabsorber arrays on large bandgap InP substrate with nanoscale plasmonic gratings. We accomplish this by significantly suppressing the nonradiative recombination at the InAsSb nanowire surfaces by introducing ex-situ conformal Al2O3 passivation shells. Transient simulations estimate an extremely low surface recombination velocity on the order of 103 cm/s. We further achieve room-temperature photoluminescence emission from InAsSb nanowires, spanning the entire MWIR regime from 3 µm to 5 µm. A dry-etching process is developed to expose only the top nanowire facets for metal contacts, with the sidewalls conformally covered by Al2O3 shells, allowing for a higher internal quantum efficiency. Based on these techniques, we fabricate nanowire photodetectors with an optimized pitch and diameter and demonstrate room-temperature spectral response with MWIR detection signatures up to 3.4 µm. The results of this work indicate that uncooled focal plane arrays at MWIR on low-cost InP substrates can be designed with nanostructured absorbers for highly compact and fully integrated detection platforms.
In the era of miniaturization, the one-dimensional nanostructures presented numerous possibilities to realize operational nanosensors and devices by tuning their electrical transport properties. Upon size reduction, the physical properties of materials become extremely challenging to characterize and understand due to the complex interplay among structures, surface properties, strain effects, distribution of grains, and their internal coupling mechanism. In this report, we demonstrate the fabrication of a single metal-carbon composite nanowire inside a diamond-anvil-cell and examine the in situ pressure-driven electrical transport properties. The nanowire manifests a rapid and reversible pressure dependence of the strong nonlinear electrical conductivity with significant zero-bias differential conduction revealing a quantum tunneling dominant carrier transport mechanism. We fully rationalize our observations on the basis of a metal-carbon framework in a highly compressed nanowire corroborating a quantum-tunneling boundary, in addition to a classical percolation boundary that exists beyond the percolation threshold. The structural phase progressions were monitored to evidence the pressure-induced shape reconstruction of the metallic grains and modification of their intergrain interactions for successful explanation of the electrical transport behavior. The pronounced sensitivity of electrical conductivity to an external pressure stimulus provides a rationale to design low-dimensional advanced pressure sensing devices.
In this paper experimental results on study of optical properties of Si wafers with surface textures in form of Si random pyramids, Si nanowire arrays, and pyramidal Si combined with Si nanowire arrays are presented. It is shown that the use of the metal-assisted chemical etching method allows to fabricate an array of Si nanowires, and a complex structure composed of Si pyramids with nanotextured side faces which possess a high degree of anti-reflecting ability. Experimental results of the absorbance and reflectance spectra measuring demonstrated that in comparison with other textures, the structures with nanotextured pyramids' side faces exhibit the highest absorption (~ 98 %) and lowest reflection values (~ 1 %) in all range of wavelength (300-1100 nm). The concept of a complex structure combining the advantages of pyramids and Si nanowires to achieve the omnidirectional light absorption and overcome the directional dependence of photovoltaic performance is discussed.
The Langmuir-Blodgett (LB) technique is a way of making supra-molecular assembly in ultrathin films with a controlled layered structure and crystal parameter, which have many envisioned technological applications for optical and molecular electronic devices as well as signal processing and transformation. Probably LB technique is the best method to manipulate materials at molecular level and provides a scope to realize the molecular electronics in reality. In this review article, we have discussed about the general introduction of LB technique and recent development on LB and related system including (i) LB methodology, (ii) characterizations of LB films, (iii) LB films and molecular electronics, (iv) historical review of LB films, (v) research and applications including fundamental research and application towards devices.
Thermoelectric micro/nanogenerators (µTEGs) are potential candidates as energy harvesters to power IoT sensors. This study reports on a thermoelectric micro/nanogenerator with a planar architecture built by silicon micromachining technologies that uses silicon-germanium (SiGe) nanowire (NW) arrays as thermoelectric material. The growth of bottom-up NW arrays by means of Chemical Vapour Deposition - Vapour Liquid Solid growth (CVD-VLS) and their monolithic integration into prefabricated microplatforms are presented. It is shown that SiGe NWs based µTEGs can harvest 7.1 μW/cm² without any additional heat exchanger, when there is a waste heat source available at a temperature of 200 °C. Since the required power density for many sensing applications is in the range of 10–100 μW/cm² the results obtained in this work are close to meet expectations.
On-chip metal inductors that revolutionized radio frequency electronics in the 1990s suffer from an inherent limitation in their scalability in state-of-the-art radio frequency integrated circuits. This is because the inductance density values for conventional metal inductors, which result from magnetic inductance alone, are limited by the laws of electromagnetic induction. Here, we report inductors made of intercalated graphene that uniquely exploit the relatively large kinetic inductance and high conductivity of the material to achieve both small form-factors and high inductance values, a combination that has proved difficult to attain so far. Our two-turn spiral inductors based on bromine-intercalated multilayer graphene exhibit a 1.5-fold higher inductance density, leading to a one-third area reduction, compared to conventional inductors, while providing undiminished Q-factors of up to 12. This purely material-enabled technique provides an attractive solution to the longstanding scaling problem of on-chip inductors and opens an unconventional path for the development of ultra-compact wireless communication systems. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
The electrical and optical properties of low dimensional nanostructures depend critically on size and geometry and may differ distinctly from those of their bulk counterparts. In particular, ultra-thin semiconducting layers as well as nanowires have already proven the feasibility to realize and study quantum size effects enabling novel ultra-scaled devices. Further, plasmonic metal nanostructures attracted recently a lot of attention because of appealing near-field mediated enhancement effects. Thus, combining metal and semiconducting constituents in quasi 1D heterostructures will pave the way for ultra-scaled systems and high-performance devices with exceptional electrical, optical and plasmonic functionality. This paper reports on the sophisticated fabrication and structural properties of axial and radial, Al-Ge and Al-Si nanowire heterostructures, synthesized by a thermally induced exchange reaction of single-crystalline Ge-Si core-shell nanowires and Al pads. This enables a self-aligned metallic contact formation to Ge segments beyond lithographic limitations as well as ultra-thin semiconducting layers wrapped around monocrystalline Al core nanowires. High-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and µ-Raman measurements proved the composition and perfect crystallinity of these metal-semiconductor nanowire heterostructures. This exemplary selective replacement of Ge by Al represents a general approach for the elaboration of radial and axial metal-semiconductor heterostructures in various Ge-semiconductor heterostructures.
Wide-gap semiconductors are excellent candidates for next-generation optoelectronic devices, including tunable emitters and detectors. ZnSe nanowire-based devices show great promise in blue emission applications, since they can be easily and reproducibly fabricated. However, their utility is limited by deep level defect states that inhibit optoelectronic device performance. The primary objective of this work is to show how the performance of ZnSe nanowire devices improves when nanowires are subjected to a post-growth anneal treatment in a zinc-rich atmosphere. We use low temperature photoluminescence spectroscopy to determine the primary recombination mechanisms and associated defect states. We then characterize the electronic properties of ZnSe nanowire field effect transistors fabricated from both as-grown and Zn-annealed nanowires, and measure an order-of-magnitude improvement to the electrical conductivity and mobility after the annealing treatment. We show that annealing reduces the concentration of zinc vacancies, which are responsible for strong compensation and high amounts of scattering in the as-grown nanowires.
Surface states that induce depletion regions are commonly believed to control the transport of charged carriers through semiconductor nanowires. However, direct, localized optical and electrical measurements of ZnO nanowires show that native point defects inside the nanowire bulk and created at metal-semiconductor interfaces are electrically-active and play a dominant role electronically - altering the semiconductor doping, the carrier density along the wire length, and the injection of charge into the wire. We used depth-resolved cathodoluminescence spectroscopy to measure the densities of multiple point defects inside ZnO nanowires, substitutional Cu on Zn sites, zinc vacancy, and oxygen vacancy defects, showing that their densities varied strongly both radially and lengthwise for tapered wires. These defect profiles and their variation with wire diameter produce trap-assisted tunneling and acceptor trapping of free carriers, the balance of which determines the low contact resistivity (2.6 x 10-3 Ω-cm-2) ohmic, Schottky (Φ > 0.35 eV) or blocking nature of Pt contacts to a single nano- / microwire. We show how these defects can now be manipulated by ion beam methods and nanowire design, opening new avenues to control nanowire charge injection and transport.
The fabrication of nanowire (NW)‐based flexible electronics including wearable energy storage devices, flexible displays, electrical sensors, and health monitors has received great attention both in fundamental research and market requirements in our daily lives. Other than a disordered state after synthesis, NWs with designed and hierarchical structures would not only optimize the intrinsic performance, but also create new physical and chemical properties, and integration of individual NWs into well‐defined structures over large areas is one of the most promising strategies to optimize the performance of NW‐based flexible electronics. Here, the recent developments and achievements made in the field of flexible electronics composed of integrated NW structures are presented. The different assembly strategies for the construction of 1D, 2D, and 3D NW assemblies, especially the NW coassembly process for 2D NW assemblies, are comprehensively discussed. The improvements of different NW assemblies on flexible electronics structure and performance are described in detail to elucidate the advantages of well‐defined NW assemblies. Finally, a short summary and outlook for future challenges and perspectives in this field are presented. Directional assembly of nanowires into 1D, 2D, and 3D assemblies toward flexible electronic devices benefits many potential applications. 1D assemblies with fiber structures can be used as flexible electronics for textiles, 2D assemblies can be used as transparent electrodes or units for logic circuits, and 3D assemblies can be used in the fabrication of pressure sensors or high‐performance energy storage devices.
In this work, laser scribing is used to obtain a monolithic series connection between adjacent silicon nanowire radial junction (SiNW RJ) solar cells on the same glass substrate. The SiNW RJ solar cells have been deposited in a low‐temperature plasma‐enhanced chemical vapor deposition (PECVD) reactor in a single pump‐down process. The crystalline SiNWs have been grown by plasma‐assisted vapor‐liquid‐solid method using tin (Sn) metal drops as a growth catalyst. A detailed study of the laser scribing step P2 is performed for better selective removal of the SiNW RJs. The laser scribed spots are characterized by scanning electron microscopy (SEM) and Raman spectroscopy mapping. In addition, a silver grid is optimized and inkjet printed on top of the mini‐modules for better device performance. Based on that, a very good performance of the SiNW RJ mini‐modules is achieved with an energy conversion efficiency over 4% and power generation in the active area of 10 cm2. This work presents a break‐through in the modularization of the SiNW RJ solar cells and demonstrates the potential of the silicon nanowire devices for industrial applications as well as their compatibility with industrial fabrication processes. This letter reports on high performance large area silicon nanowire radial junction mini‐modules with energy conversion efficiency of 5% obtained with seven cells connected in series on the same glass substrate with total active area of 10 cm2. The performance is achieved after detailed study and optimization of the P2 laser scribing step and ink‐jet printing of the silver grid.
Molecular transistors operating in the quantum tunneling regime represent potential electronic building blocks for future integrated circuits. However, due to their complex fabrication processes and poor stability, traditional molecular transistors can only operate stably at cryogenic temperatures. Here, through a combined experimental and theoretical investigation, we demonstrate a new design of vertical molecular tunneling transistors, with stable switching operations up to room temperature, formed from cross-plane graphene/self-assembled monolayer (SAM)/gold heterostructures. We show that vertical molecular junctions formed from pseudo- p -bis((4-(acetylthio)phenyl)ethynyl)- p -[2,2]cyclophane (PCP) SAMs exhibit destructive quantum interference (QI) effects, which are absent in 1,4-bis(((4-acetylthio)phenyl)ethynyl)benzene (OPE3) SAMs. Consequently, the zero-bias differential conductance of the former is only about 2% of the latter, resulting in an enhanced on-off current ratio for (PCP) SAMs. Field-effect control is achieved using an ionic liquid gate, whose strong vertical electric field penetrates through the graphene layer and tunes the energy levels of the SAMs. The resulting on-off current ratio achieved in PCP SAMs can reach up to ~330, about one order of magnitude higher than that of OPE3 SAMs. The demonstration of molecular junctions with combined QI effect and gate tunability represents a critical step toward functional devices in future molecular-scale electronics.
Achieving gate control with atomic precision, which is crucial to the transistor performance at the smallest size scale, remains a challenge. Here we report a new class of aromatic‐ring molecular nanotransistors based on graphene‐molecule‐graphene single‐molecule junctions by using an ionic liquid gate for the first time. Both experimental phenomena and theoretical calculations prove that this ionic liquid gate can effectively modulate the alignment between molecular frontier orbitals and the Fermi energy level of graphene electrodes, thus tuning the charge transport properties of the junctions. In addition, with a small gate voltage (|VG| ≤ 1.5 V) ambipolar charge transport in electrochemically inactive molecular systems (EG > 3.5 eV) is realized. These results offer a useful way to build high‐performance single‐molecule transistors, thus promoting the prospects for molecularly‐engineered electronic devices.
Intentional impurity addition is a crucial aspect for III-V nanowire growth. In this study, we demonstrated the effect of the Sn addition on GaAs nanowires growth by metal-organic chemical vapor deposition. With increasing the TESn flow rate, the nanowire axial growth was suppressed while the nanowire lateral growth was promoted, as well as planar defects were increased. Systematic electron microscopy characterizations suggested that the Sn addition tuned the catalyst composition, changed the vapor-solid-liquid surface energies and hindered the Ga atoms diffusion on nanowire sidewalls, which are responsible for the observed changes in morphology and structural quality of grown GaAs nanowires. This study contributes to understanding the role of impurity dopants on III-V nanowires growth, which will be of benefit for the design and fabrication of future nanowire-based devices.
A major obstacle for the applications of single‐walled carbon nanotubes (SWNTs) in electronic devices is their structural diversity, ending in SWNTs with diverse electrical properties. Catalytic chemical vapor deposition has shown great promise in directly synthesizing high‐quality SWNTs with a high selectivity to specific chirality (n, m). During the growth process, the tube–catalyst interface plays crucial roles in regulating the SWNT nucleation thermodynamics and growth kinetics, ultimately governing the SWNT chirality distribution. Starting with the introduction of SWNT growth modes, this review seeks to extend the knowledge about chirality‐selective synthesis by clarifying the energetically favored SWNT cap nucleation and the threshold step for SWNT growth, which describes how the tube–catalyst interface affects both the nucleus energy and the new carbon atom incorporation. Such understandings are subsequently applied to interpret the (n, m) specific growth achieved on a variety of templates, such as SWNT segments or predefined molecular seeds, transition metal (Fe, Co and Ni)‐containing catalysts at low reaction temperatures, W‐based alloy catalysts, and metal carbides at relatively high reaction temperatures. The up to date achievements on chirality‐controlled synthesis of SWNTs is summarized and the remaining major challenges existing in the SWNT synthesis field are discussed.
Co@NiSe2 electrode materials were synthesized via a simple hydrothermal method by using nickel foam in situ as the backbone and subsequently characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and a specific surface area analyzer. Results show that the Co@NiSe2 electrode exhibits a nanowire structure and grows uniformly on the nickel foam base. These features make the electrode show a relatively high specific surface area and electrical conductivity, and thus exhibit excellent electrochemical performance. The obtained electrode has a high specific capacitance of 3167.6 F·g−1 at a current density of 1 A·g−1. To enlarge the potential window and increase the energy density, an asymmetric supercapacitor was assembled by using a Co@NiSe2 electrode and activated carbon acting as positive and negative electrodes, respectively. The prepared asymmetrical supercapacitor functions stably under the potential window of 0–1.6 V. The asymmetric supercapacitor can deliver a high energy density of 50.0 Wh·kg−1 at a power density of 779.0 W·kg−1. Moreover, the prepared asymmetric supercapacitor exhibits a good rate performance and cycle stability.
Although various synthesis and characterization strategies have been employed for the synthesis of crystalline nanowires, there is very little work done on development of low-dimensional amorphous semiconductors. This paper presents a simple strategy to grow amorphous InSb (a-InSb) nanowires (NWs) in a chemical vapor deposition (CVD) system. The NWs were grown on Si substrate coated with indium film and the lack of crystallinity in the as-grown stoichiometric NWs was ascertained by Raman spectroscopy and electron transport measurements. A model proposed to explain the amorphous NW growth mechanism takes into account the fact that NW growth was carried out at the high temperature ramp-up rate of 75 ∘C/min. This high rate is believed to affect the growth kinematics and determine the arrangement of atoms in the growing NW. Raman spectrum of the as-grown sample shows a broad peak around 155 cm−1, indicative of the presence of high density of homopolar Sb-Sb bonds in the amorphous matrix. It was also found that high intensity laser light induces localized crystallization of the NW, most likely due to radiation-stimulated diffusion of defects in a-InSb. The nonlinear trend of the current-voltage characteristics for individually contacted a-InSb NWs was analyzed to prove that the non-linearity is not induced by Schottky contacts. At high bias fields, space charge limited conduction was the proposed electron transport mechanism. Post-growth annealing of the as-grown a-InSb NWs was found to be very effective in causing the NWs to undergo a phase transition from amorphous to crystalline.
This paper reports on gate-all-around (GAA) silicon (Si) nanowire (NW) field-effect transistors (FETs) built in a lateral configuration, which represent the ultimate scaling limit of triple-gate finFET devices and allow a less disruptive CMOS scaling path in terms of processing and circuit layout design. We address several of their critical technological challenges, looking in particular at doping strategies. A comprehensive review of junctionless vs. inversion-mode type of transistors is here presented, evaluating the impact on the devices' operation mode and on device properties such as: variability, reliability, noise, DC and analog/RF performance. We also discuss the potential for further manufacturable co-integration options.
We report the realization of defect-free InAsSb nanowires (NW) arrays on Si substrates by selective-area metal-organic chemical vapor deposition. The influences of growth temperature and morphology of patterned Si/SiO2 substrates on the formation of InAsSb NW arrays are studied. It is found that both the morphology and the yield of NW arrays are sensitive to the growth conditions. By optimizing the growth conditions, high quality InAsSb NW arrays, which exhibit a pure zinc-blende crystal structure without any defects are achieved. In addition, the back-gated FET devices based on the as-grown NWs are fabricated, which show an electron mobility of 2000 cm2.V-1.s-1 at room temperature.
When the first transistors were built in the late 1940s, few could predict their widespread adoption and the capabilities of the integrated circuits that would evolve from those initial discoveries.
The nano-bio interface generated by integrating semiconductor nanomaterials with living cells could serve as a platform for facilitating energy and signal transfer between non-living materials and living systems for applications in energy and the life sciences. This review presents recent advances in one-dimensional nanomaterial-biosystem interfaces and applications from chemical conversion and energy production to electrophysiology. First, we introduce representative types of nanowire-biosystem interfaces and their design principles. Second, we present nanomaterial-bacteria hybrids for solar-to-chemical CO2 reduction. Third, we introduce nano-bio hybrid electrodes for energy production, especially for biofuel cells. Fourth, we present semiconductor nanowire-embedded nanoelectronics interfaced with living cells and tissue for electrophysiological signal recordings. Last, we provide a brief summary of the progress on energy and signal transfer at the nano-bio interface, as well as our perspectives on the challenges and future directions in this interesting field.
Single nanowires have a broad range of applications in nano-electronics, nano-mechanics, and nano-photonics, but, to date, no technique can produce single sub-20 nm wide nanowires with electrical connections in a scalable fashion. In this work, we combine conventional optical and crack lithographies to generate single nanowire devices with controllable and predictable dimensions and placement, and with electrical contacts to the individual nanowires. We demonstrate nanowires made of gold, platinum, palladium, tungsten, tin, and metal oxides. We have used conventional i-line stepper lithography with a nominal resolution of 365 nm to define crack lithography structures in a shadow mask for large-scale manufacturing of sub-20 nm wide nanowires, which is a 20-fold improvement over the resolution that is possible with the utilized stepper lithography. Overall, the proposed method represents an effective approach to generate single nanowire devices with useful applications in electrochemistry, photonics, gas-, and bio-sensing.
This work presents a Raman spectroscopy study of Hg1−xCdxSe alloys grown on GaSb (2 1 1) substrates by molecular beam epitaxy. For the Raman spectra of Hg1−xCdxSe (0 ≤ x ≤ 0.6) measured with low laser excitation intensity, no sample damage is observed and the Raman spectra are dominated by the HgSe-like phonon modes. However, with a higher laser excitation intensity, material damage in the form of void formation is observed due to Hg loss and the resultant Raman spectra are dominated by CdSe-like phonon modes. For a constant laser excitation intensity the material damage was found to increase with increasing Cd content due to weakening of the Hg-Se bond in the presence of Cd. A separate Raman study undertaken on the cross-section of a compositionally graded HgCdSe sample clearly indicates that the integrated Raman intensity exhibits an essentially linear dependence on Cd content for the composition range, 0.30 ≤ x ≤ 0.45. The results of this study provide a useful guide for the development of any thermal procedure to be used in any detector fabrication process, as well as indicating that Raman spectroscopy has the potential to be developed into a general purpose tool capable of assessing HgCdSe compositional uniformity.
If single-molecule, room-temperature, quantum interference (QI) effects could be translated into massively parallel arrays of molecules located between planar electrodes, QI-controlled molecular transistors would become available as buildingblocks for future electronic devices. Here, we demonstrate unequivocal signatures of room-temperature QI in vertical tunneling transistors, formed from self-assembled monolayers (SAMs), with stable room-temperature switch-
ing operations. As a result of constructive QI effects, the conductances of the junctions formed from anthanthrene-based molecules with two different connectivities differ by a factor of 34, which can further increase to 173 by controlling the molecule-electrode interface with different terminal groups. Field-effect control is achieved using an ionic liquid gate, whose strong vertical electric field penetrates through the graphene layer and tunes the energy levels of the SAMs. The resulting room-temperature on-off current ratio of the lowest-conductance SAMs can reach up to 306, about one order of magnitude higher than that of the highest-conductance SAMs.
In this paper experimental results on study of optical properties of Si wafers with surface textures in form of Si random pyramids, Si nanowire arrays, and pyramidal Si combined with Si nanowire arrays are presented. It is shown that the use of the metal-assisted chemical etching method allows to fabricate an array of Si nanowires, and a complex structure composed of Si pyramids with nanotextured side faces which possess a high degree of anti-reflecting ability. Experimental results of the absorbance and reflectance spectra measuring demonstrated that in comparison with other textures, the structures with nanotextured pyramids' side faces exhibit the highest absorption (~ 98 %) and lowest reflection values (~ 1 %) in all range of wavelength (300-1100 nm). The concept of a complex structure combining the advantages of pyramids and Si nanowires to achieve the omnidirectional light absorption and overcome the directional dependence of photovoltaic performance is discussed.
Using capacitance, conductance and noise measurements, we investigate the trapping behavior at the surface and in the core of triangular-shaped one-dimensional (1D) array of GaN nanowire gate-all-around field effect transistor (GAA FET), fabricated via a top-down process. The surface traps in such a low dimensional device play a crucial role in determining the device performance. The estimated surface trap density rapidly decreases with increasing frequency, ranging from 6.07 × 10¹² cm⁻²·eV⁻¹ at 1 kHz to 1.90 × 10¹¹ cm⁻²·eV⁻¹ at 1 MHz, respectively. The noise results reveal that the power spectral density increases with gate voltage and clearly exhibits 1/f-noise signature in the accumulation region (Vgs > Vth = 3.4 V) for all frquencies. In the surface depletion region (1.5 V < Vgs < Vth), the device is governed by 1/f at lower frequencies and 1/f² noise at frequencies higher than ~ 5 kHz. The 1/f² noise characteristics is attributed to additional generation–recombination (G–R), mostly caused by the electron trapping/detrapping process through deep traps located in the surface depletion region of the nanowire. The cutoff frequency for the 1/f² noise characteristics further shifts to lower frequency of 10²–10³ Hz when the device operates in deep-subthreshold region (Vgs < 1.5 V). In this regime, the electron trapping/detrapping process through deep traps expands into the totally depleted nanowire core and the G–R noise prevails in the entire nanowire channel. © 2019, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature.
The high-crystalline indium oxide (In2O3) nanowires were deposited by chemical vapor deposition (CVD) method on Si (111) substrates using C and In2O3 powders as the raw materials. The morphology, microstructures and the valences analysis of In2O3 nanowires were characterized by XRD, SEM, EDS, XPS and TEM techniques. The length and density of In2O3 nanowires can be effectively controlled by adjusting the experimental parameters. The optimal growth condition is obtained, namely the Au catalyst thickness of 12 nm, growth temperature of 1050 °C and Ar flow rate of 200 sccm. The cubic bixbyite structure as pure In2O3 (space group I a3¯) as well as large amounts of oxygen vacancies can be observed in the deposited In2O3 nanowires. The photoluminescence (PL) spectrum shows an ultraviolet emission peak located at 390.6 nm and two luminescence peaks located at 423.6 nm and 436.5 nm, which can be attributed to the near-band-edge emission and the presence of oxygen vacancy defects in the In2O3 nanowires, respectively.
We investigate the low-temperature transport in 8-nm-diam Si junctionless nanowire field-effect transistors fabricated by top down techniques with a wraparound gate and two different phosphorus doping concentrations. First we extract the intrinsic gate capacitance of the device geometry from a device that demonstrates Coulomb blockade at 12 mK with over 500 Coulomb peaks across a gate-voltage range of 6 V indicating the formation of an island in the entire 150-nm-long nanowire channel. In two other devices, made from silicon on insulator wafers that were doped to an activated dopant concentration of Si:P 4×1019 and 2×1020cm−3, we observe quantum interference and use the extracted gate coupling to determine the mean free paths from the dominant energy scale on the gate-voltage axis. For the higher doped device, the analysis yields a mean free path of 4±2nm, which is on the order of the average spacing of phosphorus atoms and suggests scattering on unactivated or activated dopants. For the device with an implanted phosphorus density of 4×1019cm−3, the quantum interference effects suggest a mean free path of 10±2nm, which is comparable to the nanowire width, and thus allows for coherent formation of transversal modes. The results suggest that the low-temperature mobility is limited by scattering on phosphorus dopants rather than the expected surface roughness scattering for nanowires with diameters larger than or comparable to the Fermi wavelength. A temperature-dependent analysis of universal conductance fluctuations indicates a phase-coherence length greater than the nanowire length for temperatures below 1.9 K, and decoherence from one-dimensional electron-electron interactions dominates transport for higher temperatures. Our measurements, therefore, provide insight into scattering and dephasing mechanisms in technologically relevant silicon device geometries, which will help with future design choices with regard to, e.g., doping density.
SiC nanowire aerogel (SNA) with highly porous 3D nanowire architecture was synthesized by polymer pyrolysis chemical vapor deposition (PPCVD) process to deposit SiC nanowires in the pores of carbon foam, followed by high temperature oxidation of carbon foam. The microstructure of the prepared SNA was characterized by SEM,TEMand a large number of interweaving SiC nanowires with a diameter of 80-100 nmand a length of hundreds of micrometers form the highly porous 3D nanowire architecture of SNA. The prepared SNA possesses the performance combination of ultra-low density (30±7mg · cm ⁻³ ), high-temperature oxidation resistance (750 °C), noncombustible and fire resistance property in the fire, excellent thermal insulating property (0.03W · m ⁻¹ · k ⁻¹ at room temperature in He) and compressive strength of 0.11 MPa, which is applicable as high-temperature heat insulator, ceramic matrix composite, high temperature flue gas filter, fire-proofing material and catalyst carrier.
Bioelectronics for healthcare that monitor the health information on users in real time have stepped into the limelight as crucial electronic devices for the future due to the increased demand for "point-of-care" testing, which is defined as medical diagnostic testing at the time and place of patient care. In contrast to traditional diagnostic testing, which is generally conducted at medical institutions with diagnostic instruments and requires a long time for specimen analysis, point-of-care testing can be accomplished personally at the bedside, and health information on users can be monitored in real time. Advances in materials science and device technology have enabled next-generation electronics, including flexible, stretchable, and biocompatible electronic devices, bringing the commercialization of personalized healthcare devices increasingly within reach, e.g., wearable bioelectronics attached to the body that monitor the health information on users in real time. Additionally, the monitoring of harmful factors in the environment surrounding the user, such as air pollutants, chemicals, and ultraviolet light, is also important for health maintenance because such factors can have short- and long-term detrimental effects on the human body. The precise detection of chemical species from both the human body and the surrounding environment is crucial for personal health care because of the abundant information that such factors can provide when determining a person's health condition. In this respect, sensor applications based on an organic-transistor platform have various advantages, including signal amplification, molecular design capability, low cost, and mechanical robustness (e.g., flexibility and stretchability). This Account covers recent progress in organic transistor-based chemical sensors that detect various chemical species in the human body or the surrounding environment, which will be the core elements of wearable electronic devices. There has been considerable effort to develop high-performance chemical sensors based on organic-transistor platforms through material design and device engineering. Various experimental approaches have been adopted to develop chemical sensors with high sensitivity, selectivity, and stability, including the synthesis of new materials, structural engineering, surface functionalization, and device engineering. In this Account, we first provide a brief introduction to the operating principles of transistor-based chemical sensors. Then we summarize the progress in the fabrication of transistor-based chemical sensors that detect chemical species from the human body (e.g., molecules in sweat, saliva, urine, tears, etc.). We then highlight examples of chemical sensors for detecting harmful chemicals in the environment surrounding the user (e.g., nitrogen oxides, sulfur dioxide, volatile organic compounds, liquid-phase organic solvents, and heavy metal ions). Finally, we conclude this Account with a perspective on the wearable bioelectronics, especially focusing on organic electronic materials and devices.
We have demonstrated the epitaxial growth of AlGaN nanowires on Al coated Si (0 0 1) substrate. The as-grown nanowires feature diameters of >200 nm and relatively uniform height distribution. AlGaN nanowires with emission wavelengths from 340 nm to 288 nm have been successfully achieved by varying Al/Ga beam equivalent pressure ratio and growth temperature. Detailed structural characterization suggests that AlGaN nanowires grown on Al template are free of dislocations. We have further demonstrated functional AlGaN nanowire deep ultraviolet (DUV) light emitting diodes, which exhibit a turn-on voltage of 7 V and a single peak EL emission at 288 nm. The realization of high quality AlGaN nanostructures on reflective Al template provides a promising approach for achieving high efficiency DUV light emitters.
The van der Waals epitaxy of functional materials provides an interesting and efficient way to manipulate the electrical properties of various hybrid two-dimensional (2D) systems. Here we show the controlled epitaxial assembly of semiconducting one-dimensional (1D) atomic chains, AuCN, on graphene and investigate the electrical properties of 1D/2D van der Waals heterostructures. AuCN nanowire assembly is tuned by different growth conditions, although the epitaxial alignment between AuCN chains and graphene remains unchanged. The switching of the preferred nanowire growth axis indicates that diffusion kinetics affects the nanowire formation process. Semiconducting AuCN chains endow the 1D/2D hybrid system with a strong responsivity to photons with an energy above 2.7 eV, which is consistent with the bandgap of AuCN. A large UV response (responsivity ~ 10^4 A/W) was observed under illumination using 3.1 eV (400 nm) photons. Our study clearly demonstrates that 1D chain-structured semiconductors can play a crucial role as a component in multifunctional van der Waals heterostructures
Anisotropy in crystal growth of III-V semiconductor nanowires can be enhanced by the assistance of a liquid particle. During the past decades, selected scientific works have reported a controlled change in the nanowire growth direction by manipulation of the assisting droplet. Although these results are interesting from an engineering point of view, a detailed understanding of the process is necessary in order to rationally design complex nanostructures. In this letter, we utilize our understanding of the growth-assisting droplet to control the morphology and direction of gold-assisted wurtzite-phase InAs nanowires, using controlled droplet displacement followed by resumed growth. By confining the droplet to the nanowire sidewall using zincblende inclusions as barriers, epitaxial growth of horizontal branches from existing nanowires is demonstrated. This is done by tailoring droplet wetting of the nanowire and using identical conditions for the nanowire "stem" and branch growth. This work demonstrates the importance of the droplet dynamics and wetting stability, along with the benefits of crystallographic control, for understanding the growth along different directions. Controlled branched growth is one way to achieve designed nanowire networks.
Limited by the Boltzmann distribution of electrons, the sub-threshold swing (SS) of conventional MOSFETs cannot be less than 60 mV dec-1. This limitation hinders the reduction of power dissipation of the devices. Herein, we present high-performance In2O3 nanowire (NW) negative capacitance field-effect transistors (NC-FETs) by introducing ferroelectric P(VDF-TrFE) layer in the gate dielectric stack. The fabricated devices exhibit the excellent gate modulation with the high saturation current density of 550 μA μm-1 and outstanding SS value less than 60 mV dec-1 for over 4 decades of channel current. The assembled inverter circuit can demonstrate the impressive voltage gain of 25 and cut-off frequency of over 10 MHz. By utilizing the self-aligned fabrication scheme, the device can be ultimately scaled down to below 100 nm channel length. The devices with 200 nm channel length exhibits the best performances, in which a high on/off current ratio of >10^7, a large output current density of 960 μA μm-1 and a small SS value of 42 mV dec-1 are obtained at the same time. All these would not only evidently demonstrate the potency of NW NC-FETs for the facilitation to break through Boltzmann limit in nanoelectronics, but also open up a new avenue to low-power transistors for portable products.
Considering the demand of III-V multigate (MUG) transistors for next-generation CMOS technologies, a compact model is required to test their performance in different circuits. The low effective mass and highly confined geometry of these MUG devices demand the use of computationally expensive coupled Poisson-Schrödinger (PS) solver for terminal charges and surface potential. In this paper, we propose an approximation, which decouples the PS equations and enables the development of a computationally efficient analytical model. The surface potential and semiconductor charge equations for III-V low effective mass channel cylindrical nanowire (NW) transistors are derived using the proposed approximation. The proposed model is physics-based and does not include any empirical parameters. The accuracy of the model is verified across NWs of different sizes and materials using the data from the 2-D PS solver and found to be accurate. IEEE
Low dimensional heterostructures have potential applications in information, sensing, and energy-related technologies. In order to obtain high-quality low dimensional heterostructures, an essential method is tuning chemical composition in a single nanostructure to obtain two or multiple components with well-matched electronic band structures. Here, we present a tutorial review of a unique chemical vapor growth approach with in situ switchable solid chemical sources that can build composition-modulated chalcogenide heterostructures in one-dimensional nanowires, quasi one-dimensional nanobelts and two-dimensional atomic layered nanosheets in a controlled manner. This approach has generated a large variety of heterostructures that not only exhibit gradient distribution in chemical composition, but also show sharp interfaces. Diverse integrated photonic and optoelectronic devices are enabled by the composition-modulated heterostructures based on chalcogenides or other material systems.
We report the growth, structural, and electrical characterization of epitaxial, strained SixGe1−x-Ge-Si core-double-shell nanowire heterostructures designed to provide quantum confinement of holes and electrons in the compressively strained Ge and tensile-strained Si shells, respectively. The growth utilizes the vapor-liquid-solid growth mechanism for the SixGe1−x core, followed by a sequence of in-situ ultra-high-vacuum chemical vapor deposition for the epitaxial Ge and Si shell growth. Using a combination of micro-Raman spectroscopy on individual nanowires and lattice dynamic theory, we determine a large compressive (tensile) hydrostatic strain of up to −0.9% (0.67%) in the Ge (Si) shell. We demonstrate p- and n-type metal-oxide-semiconductor field-effect transistors using SixGe1−x-Ge-Si core-double-shell nanowires as channel and observe a 500% (20%) enhancement of the average hole (electron) mobility compared to control devices using Si nanowires, due to an increased hole (electron) mobility in the compressively strained Ge (tensile strained Si) shell. An analysis of the hole transport provides the valence band offset in the core-double-shell nanowire heterostructures.
We report the growth control of ZnO nanowire arrays to fasten the growth rate and reduce the defects by a microwave-assisted hydrothermal method for dye-sensitized solar cells (DSSCs). After optimization of the growth parameters during the hydrothermal synthesis, fast length growth rate and a flat upper surface with low defects are obtained. It is found that rather low concentration of the raw materials of hexamethylenetetramine (HMTA) is necessary to avoid the brush defects on the nanowires arrays, which is also helpful to reach the maximum length growth rate up to 6.0 μm per hour. When used as the photoanode in DSSCs, these nanowires show high power conversion efficiency which is attributed to the enlarged internal surface area to increase dye adsorption on the photoanode to improve the light harvest. So this work shows an efficient method to obtain ZnO nanowires with low defects for DSSCs.
Heat dissipation is the key issue for the scaling of metal-oxide-semiconductor field-effect transistors (MOSFETs). Boltzmann distribution of electrons imposes the physical limit on subthreshold swing (SS) hampering the abating of switching energy and the augmenting of devices density. Negative capacitance effect is proposed to rescue MOSFETs from ‘Boltzmann tyranny’. Herein, we report the first In2O3 nanowires (NWs)-transistors with SS values in the sub-60 mV/dec region, which utilize ferroelectric P(VDF-TrFE) as the dielectric layer. The ultra-low SS down to ~10 mV/dec is observed, and the SS spans over 5 orders of magnitude in drain current. Meanwhile, the high on/off ratio more than 108 and a transconductance (gm) of 2.3 μS are obtained simultaneously at Vd = 0.1V. The results can be understood by the “voltage amplification” effect induced by negative capacitance effect. Moreover, the steep slope FETs based inverters indicate a high voltage gain of 41.6. Besides the NOR and NAND gates, the Schmitt trigger inverters containing only one steep slope FET are demonstrated. This work demonstrate an avenue for low-power circuits design with steep subthreshold swing.
The realization of an innovative label- and PCR-free silicon nanowires (NWs) optical biosensor for direct genome detection is demonstrated. The system is based on the cooperative hybridization to selectively capture DNA and on the optical emission of quantum confined carriers in Si NWs whose quenching is used as detection mechanism. The Si NW platform was tested with Hepatitis B virus (HBV) complete genome and it was able to reach a remarkable Limit of Detection (LoD) of 2 copies/reaction for the synthetic genome and 20 copies/reaction for the genome extracted from human blood. These results are even better than those obtained with the gold standard real time PCR method in the genome analysis. The Si NWs sensor showed high sensitivity and specificity, easy detection method and low manufacturing cost fully compatible with standard silicon process technology. All these points are key factors for the future development a new class of genetic point of care devices reliable, fast, low cost, easy to use for self-testing including the developing countries.
In 2006, the group of Dr C.M. Lieber pioneered the field of nanowire sensors by fabricating devices for the ultra-sensitive label-free detection of biological macromolecules. Since then, nanowire sensors have demonstrated their ability to detect cancer-associated analytes in peripheral blood, tumor tissue, and the exhaled breath of cancer patients. These innovative developments have marked a new era with unprecedented detection performance, capable of addressing crucial needs such as cancer diagnosis and monitoring disease progression and patient response to therapy. The ability of nanowire sensors to identify molecular features of patient tumor represents a first step toward precision medicine, and their integration into portable devices has the potential to revolutionize cancer diagnosis and patient monitoring.
Semiconductor nanowires (NWs) are promising for realizing various on‐chip nonlinear optical devices, due to their nanoscale lateral confinement and strong light–matter interaction. However, high‐intensity pulsed pump lasers are typically needed to exploit their optical nonlinearity because light couples poorly with nanometric‐size wires. Here, microwatts continuous‐wave light pumped second harmonic generation (SHG) in AlGaAs NWs is demonstrated by integrating them with silicon planar photonic crystal cavities. Light–NW coupling is enhanced effectively by the extremely localized cavity mode at the subwavelength scale. Strong SHG is obtained even with a continuous‐wave laser excitation with a pump power down to W, and the cavity‐enhancement factor is estimated around 150. Additionally, in the integrated device, the NW's SHG is more than two orders of magnitude stronger than third harmonic generations in the silicon slab, though the NW only couples with less than 1% of the cavity mode. This significantly reduced power requirement of NW's nonlinear frequency conversion would promote NW‐based building blocks for nonlinear optics, especially in chip‐integrated coherent light sources, entangled photon pairs and signal processing devices. Microwatts (W) continuous‐wave laser pumped second harmonic generations (SHGs) in AlGaAs nanowires (NWs) are demonstrated by integrating them with photonic crystal nanocavities, which might promote NW‐based on‐chip nonlinear optics. The SHG enhancement factor by the strongly localized cavity mode is estimated to be around 150.
Two-dimensional semiconductors (2DSCs) have attracted considerable attention as atomically thin channel materials for field-effect transistors. Each layer in 2DSCs consists of a single- or few-atom-thick, covalently bonded lattice, in which all carriers are confined in their atomically thin channel with superior gate controllability and greatly suppressed OFF-state current, in contrast to typical bulk semiconductors plagued by short channel effects and heat generation from static power. Additionally, 2DSCs are free of surface dangling bonds that plague traditional semiconductors, and hence exhibit excellent electronic properties at the limit of single atom thickness. Therefore, 2DSCs can offer significant potential for the ultimate transistor scaling to single atomic body thickness. Earlier studies of graphene transistors have been limited by the zero bandgap and low ON–OFF ratio of graphene, and transition metal dichalcogenide (TMDC) devices are typically plagued by insufficient carrier mobility. To this end, considerable efforts have been devoted towards searching for new 2DSCs with optimum electronic properties. Within a relatively short period of time, a large number of 2DSCs have been demonstrated to exhibit unprecedented characteristics or unique functionalities. Here we review the recent efforts and progress in exploring novel 2DSCs beyond graphene and TMDCs for ultra-thin body transistors, discussing the merits, limits and prospects of each material.
Recent years have seen a rapid expansion of research into photonic and plasmonic nanowire waveguides for both fundamental studies and technological applications, because of their ability to propagate and process optical signals in tightly confined light fields with high speed and low power, space and material requirements. This comprehensive review summarizes recent advances in the fabrication, characterization and applications of both photonic and plasmonic NW waveguides, with a special focus on the comparative discussion of their differences and similarities in mechanisms and properties, strengths and limitations in performance, and how they can work together in hybrid devices with performances and applications that neither can achieve individually. We also provided an outlook of the future opportunities and directions in this exciting field.
We report an experimental study on quasi-one-dimensional Al-Ge-Al nanowire (NW) heterostructures featuring unmatched photoconductive gains exceeding 10^7 and responsivities as high as 10 A/µW in the visible wavelength regime. Our observations are attributed to the presence of GeOx related hole-trapping states at the NW surface and can be described by a photogating effect in accordance with previous studies on low-dimensional nanostructures. Utilizing an ultrascaled photodetector device operating in the quantum ballistic transport regime at room temperature we demonstrate for the first time that individual current channels can be addressed directly by laser irradiation. The resulting quantization of the photocurrent represents the ultimate limit of photodetectors, allowing for advanced concepts including highly resolved imaging, light effect transistors and single photon detectors with practically zero off-state current.