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AFM Manipulation of Gold Nanowires To Build Electrical Circuits
Abstract
We introduce Scanning-Probe-Assisted Nanowire Circuitry (SPANC) as a new method to fabricate electrodes for the characterization of electrical transport properties at the nanoscale. SPANC uses an atomic force microscope manipulating nanowires to create complex and highly conductive nanostructures (paths) that work as nanoelectrodes allowing connectivity and electrical characterization of other nanoobjects. The paths are formed by the spontaneous cold welding of gold nanowires upon mechanical contact leading to an excellent contact resistance of 9 /junction. SPANC is an easy to use and cost-effective technique that fabricates clean nanodevices. Hence, this new method can complement and/or be an alternative to other well-established methods to fabricate nanocircuits such as Electron Beam Lithography (EBL). The circuits made by SPANC are easily reconfigurable and their fabrication does not require the use of polymers and chemicals. In this work, we present a few examples that illustrate the capabilities of this method, allowing robust device fabrication and electrical characterization of several nanoobjects with sizes down to 10 nm, well below the current smallest size able to be contacted in a device using the standard available technology (30 nm). Importantly, we also provide the first experimental determination of the sheet resistance of thin antimonene flakes.
... It is instructive to compare the mentioned results with the case of graphene, where a linear increase of the sheet conductance (the inverse of the sheet resistance) has been observed with the number of layers [38,39] in contrast with our case, where it remains constant. We compare the sheet resistance (ρ2D = 1200 ± 300 Ω sq -1 ) with that obtained following the same procedure for FL graphene [37], ρ2D-G = 670 ± 60 Ω sq -1 . Graphene has 4 Dirac cones, with intervalley scattering typically suppressed by long-range scattering potentials. ...
... We contacted the FL antimonene flakes deposited on SiO2/Si substrates using gold nanowire electrodes through the SPANC technique [37]. Briefly, we deposited gold nanowires on the substrates with FL antimonene flakes and assembled them into nanoelectrodes by AFM manipulation. ...
Antimonene -a single layer of antimony atoms- and its few layer forms are among the latest additions to the 2D mono-elemental materials family. Numerous predictions and experimental evidence of its remarkable properties including (opto)electronic, energetic or biomedical, among others, together with its robustness under ambient conditions, have attracted the attention of the scientific community. However, experimental evidence of its electrical properties is still lacking. Here, we characterized the electronic properties of mechanically exfoliated flakes of few-layer (FL) antimonene of different thicknesses (∼ 2–40 nm) through photoemission electron microscopy, kelvin probe force microscopy and transport measurements, which allows us to estimate a sheet resistance of ∼ 1200 Ω sq⁻¹ and a mobility of ∼ 150 cm²V⁻¹s⁻¹ in ambient conditions, independent of the flake thickness. Alternatively, our theoretical calculations indicate that topologically protected surface states (TPSS) should play a key role in the electronic properties of FL antimonene, which supports our experimental findings. We anticipate our work will trigger further experimental studies on TPSS in FL antimonene thanks to its simple structure and significant stability in ambient environments.
... It is instructive to compare the mentioned results with the case of graphene, where a linear increase of the sheet conductance (the inverse of the sheet resistance) has been observed with the number of layers [38,39] in contrast with our case, where it remains constant. We compare the sheet resistance (ρ2D = 1200 ± 300 Ω sq -1 ) with that obtained following the same procedure for FL graphene [37], ρ2D-G = 670 ± 60 Ω sq -1 . Graphene has 4 Dirac cones, with intervalley scattering typically suppressed by long-range scattering potentials. ...
... We contacted the FL antimonene flakes deposited on SiO2/Si substrates using gold nanowire electrodes through the SPANC technique [37]. Briefly, we deposited gold nanowires on the substrates with FL antimonene flakes and assembled them into nanoelectrodes by AFM manipulation. ...
Antimonene -- a single layer of antimony atoms -- and its few layer forms are among the latest additions to the 2D mono-elemental materials family. Numerous predictions and experimental evidence of its remarkable properties including (opto)electronic, energetic or biomedical, among others, together with its robustness under ambient conditions, have attracted the attention of the scientific community. However, experimental evidence of its electrical properties is still lacking. Here, we characterized the electronic properties of mechanically exfoliated flakes of few-layer (FL) antimonene of different thicknesses (~ 2-40 nm) through photoemission electron microscopy, kelvin probe force microscopy and transport measurements, which allows us to estimate a sheet resistance of ~ 1200 $\Omega$sq$^{-1}$ and a mobility of ~ 150 cm$^2$V$^{-1}$s$^{-1}$ in ambient conditions, independent of the flake thickness. Alternatively, our theoretical calculations indicate that topologically protected surface states (TPSS) should play a key role in the electronic properties of FL antimonene, which supports our experimental findings. We anticipate our work will trigger further experimental studies on TPSS in FL antimonene thanks to its simple structure and significant stability in ambient environments.
... Bow-tie antennas are deposited to increase light absorption in the horizontal configuration, as well as increase the efficiency in collecting the radiation 53,54 . Device fabrication of traditional vertical free-standing NWs 55 requires a time-consuming transfer and alignment procedure by nano-manipulation 56,57 or transfer printing 41,58 . In contrast, this method is inherently wafer scalable 59 , as the horizontal NW arrays can be straightforwardly processed into receivers on the as-grown substrate. ...
Terahertz (THz) radiation will play a pivotal role in wireless communications, sensing, spectroscopy and imaging technologies in the decades to come. THz emitters and receivers should thus be simplified in their design and miniaturized to become a commodity. In this work we demonstrate scalable photoconductive THz receivers based on horizontally-grown InAs nanowires (NWs) embedded in a bow-tie antenna that work at room temperature. The NWs provide a short photoconductivity lifetime while conserving high electron mobility. The large surface-to-volume ratio also ensures low dark current and thus low thermal noise, compared to narrow-bandgap bulk devices. By engineering the NW morphology, the NWs exhibit greatly different photoconductivity lifetimes, enabling the receivers to detect THz photons via both direct and integrating sampling modes. The broadband NW receivers are compatible with gating lasers across the entire range of telecom wavelengths (1.2–1.6 μm) and thus are ideal for inexpensive all-optical fibre-based THz time-domain spectroscopy and imaging systems. The devices are deterministically positioned by lithography and thus scalable to the wafer scale, opening the path for a new generation of commercial THz receivers.
... where R L2 , R L3 represent the resistance of W1 of length L 2 and L 3 , respectively. In this circuit, the contacts between the probe nanowires and sample nanowire are always in the head-to-side manner 21 . Therefore, the R C-Ag could be considered as equal in Eq. (15)~ (17). ...
Nanowires have emerged as promising one-dimensional materials with which to construct various nanocircuits and nanosensors. However, measuring the electrical properties of individual nanowires directly remains challenging because of their small size, thereby hindering the comprehensive understanding of nanowire-based device performance. A crucial factor in achieving reliable electrical characterization is establishing well-determined contact conditions between the nanowire sample and the electrodes, which becomes particularly difficult for soft nanowires. Introduced here is a novel technique for measuring the conductivity of an individual nanowire with the aid of automated nanomanipulation using an atomic force microscope. In this method, two nanowire segments cut from the same silver nanowire are positioned onto a pair of gold electrodes, serving as flexible nanoprobes to establish controllable contact with the sample. By changing the contact points along the nanowire sample, conductivity measurements can be performed on different regions, thereby eliminating the influence of contact resistance by analyzing multiple current–voltage curves. Using this approach, the resistivity of a 100-nm-diameter silver nanowire is determined to be 3.49 × 10−8 Ω m.
... Currently, the two most popular means of micro/nanooperation are AFM and SEM. With its high resolution, precise motion, and good repeatability, AFM allows precise operations such as assembling carbon nanotubes and single-molecule viruses, [9][10][11] but it cannot image and operate simultaneously, and the control strategy of its post-observation motion and its limited scanning range restrict its operational efficiency. Meanwhile, SEM is used widely in microscopic and nanoscopic operation and characterization, resulting in continuous innovation and improvement in those areas. ...
Because of their unique mechanical and electrical properties, zinc oxide (ZnO) nanowires are used widely in microscopic and nanoscopic devices and structures, but characterizing them remains challenging. In this paper, two pick-up strategies are proposed for characterizing the electrical properties of ZnO nanowires using SEM equipped with a nanomanipulator. To pick up nanowires efficiently, direct sampling is compared with electrification fusing, and experiments show that direct sampling is more stable while electrification fusing is more efficient. ZnO nanowires have cut-off properties, and good Schottky contact with the tungsten probes was established. In piezoelectric experiments, the maximum piezoelectric voltage generated by an individual ZnO nanowire was 0.07 V, and its impedance decreased with increasing input signal frequency until it became stable. This work offers a technical reference for the pick-up and construction of nanomaterials and nanogeneration technology.
... Recently, owing to the high resolution, versatility, and reproducibility, Atomic Force Microscopy (AFM)-based nanofabrication techniques emerged as one of the most prominent nanofabrication approaches. Since its discovery in 1986 by Binnig et al. [1], AFM has been widely adopted: initially for sample surface investigation down to the atomic resolution [2,3], and lately for nanolithography [4,5] and nanofunctionalization [6] purposes. These nanofabrication approaches, generally known as Scanning Probe Lithography (SPL) [4,7], are based on the use of AFM probes to directly fabricate nanostructures on the sample surface through various mechanisms, opening up a wide range of possible applications [8]. ...
In recent years, Atomic Force Microscope (AFM)-based nanolithography techniques have emerged as a very powerful approach for the machining of countless types of nanostructures. However, the conventional AFM-based nanolithography methods suffer from low efficiency, low rate of patterning, and high complexity of execution. In this frame, we first developed an easy and effective nanopatterning technique, termed Pulse-Atomic Force Lithography (P-AFL), with which we were able to pattern 2.5D nanogrooves on a thin polymer layer. Indeed, for the first time, we patterned nanogrooves with either constant or varying depth profiles, with sub-nanometre resolution, high accuracy, and reproducibility. In this paper, we present the results on the investigation of the effects of P-AFL parameters on 2.5D nanostructures’ morphology. We considered three main P-AFL parameters, i.e., the pulse’s amplitude (setpoint), the pulses’ width, and the distance between the following indentations (step), and we patterned arrays of grooves after a precise and well-established variation of the aforementioned parameters. Optimizing the nanolithography process, in terms of patterning time and nanostructures quality, we realized unconventional shape nanostructures with high accuracy and fidelity. Finally, a scanning electron microscope was used to confirm that P-AFL does not induce any damage on AFM tips used to pattern the nanostructures.
... When dealing with molecular nanomaterials such as CNTs, both the study of their individualized physicochemistry [13] and the manufacture of nanodevices requires their manipulation at the nanoscale [14]. This procedure involves positional modification, controlled deformation, and nano-electrical connection [15,16]. ...
Nanomanipulation of molecular materials such as carbon nanotubes (CNTs) or new covalent organic frameworks (COFs) is key not only for the study of their fundamental physicochemical properties, but also for building and probing nanodevices. Therefore, we have investigated the tribological properties of oxidized MWCNTs (ox-MWCNTs) and their hybridization with COF building blocks ([email protected]) adsorbed on a mica surface. We used the AFM tip to apply torsional forces on individual nanotubes. Depending on the manipulation parameters, the lateral displacements of the AFM tip slide and/or bend nanotubes enabling the direct quantification of the nanotube-mica adhesion. We found striking changes in the behaviour of the lateral force needed to manipulate each carbon nanotube variant which indicates an increased adhesion of [email protected] with respect to ox-MWCNTs (∼10x). In addition, the use of the AFM tip as a mobile electrode enabled the measurement of electrical transport through individual nanotubes that revealed a rectifying behaviour of the [email protected] with high resistivity, which was in contrast with the near ohmic performance of ox-MWCNTs.
... Compared with other nanolithography technologies mentioned above, the cost-effective AFM lithography exhibits many advantages in process simplicity and resolution [12], and can be used to make patterns on a variety of materials [13], thanks to the unique combined scanning, manipulating and imaging capabilities of ultrasharp AFM probes with a typical tip radius below 10 nm [14,15]. It can be applied to achieve nanoscale features such as nanodots [16], nanowire [17], nanofluidics [18], and two-dimensional (2D)/threedimensional (3D) nanopatterns [19][20][21][22][23] on a variety of materials, which includes polymers [24], silicon [25], metals [26], and 2D materials [27,28]. Meanwhile, the wide usage of polymers in diverse applications such as opto/micro-electronics, sensors, and data storage has promoted the innovation of polymer nanolithography [16]. ...
Electric-field-assisted atomic force microscope (E-AFM) nanolithography is a novel polymer-patterning technique that has diverse applications. E-AFM uses a biased AFM tip with conductive coatings to make patterns with little probe-sample interaction, which thereby avoids the tip wear that is a major issue for contact-mode AFM-based lithography, which usually requires a high probe-sample contact force to fabricate nanopatterns; however, the relatively large tip radius and large tip-sample separation limit its capacity to fabricate high-resolution nanopatterns. In this paper, we developed a contact mode E-AFM nanolithography approach to achieve high-resolution nanolithography of poly (methyl methacrylate) (PMMA) using a conductive AFM probe with a low stiffness (~0.16 N/m). The nanolithography process generates features by biasing the AFM probe across a thin polymer film on a metal substrate. A small constant force (0.5-1 nN) applied on the AFM tip helps engage the tip-film contact, which enhances nanomachining resolution. This E-AFM nanolithography approach enables high-resolution nanopatterning with feature width down to ~16 nm, which is less than one half of the nominal tip radius of the employed conductive AFM probes.
... The past several decades have witnessed a tremendous advancement in precision manipulation techniques that exploit optics (1,2), magnetics (3,4), electrical fields (5,6), atomic force microscopy (7,8), and acoustofluidics (9)(10)(11)(12)(13)(14) for assorted applications in biology, chemistry, medicine, and micro/nanosystems (15)(16)(17)(18). Among them, acoustofluidicsbased precision manipulation techniques have garnered considerable interest (16,(19)(20)(21)(22)(23)(24) because of their versatility, simplicity, low power requirement, and contactless nature (10,11,25,26). ...
Acoustic black holes offer superior capabilities for slowing down and trapping acoustic waves for various applications such as metastructures, energy harvesting, and vibration and noise control. However, no studies have considered the linear and nonlinear effects of acoustic black holes on micro/nanoparticles in fluids. This study presents acoustofluidic black holes (AFBHs) that leverage controlled interactions between AFBH-trapped acoustic wave energy and particles in droplets to enable versatile particle manipulation functionalities, such as translation, concentration, and patterning of particles. We investigated the AFBH-enabled wave energy trapping and wavelength shrinking effects, as well as the trapped wave energy–induced acoustic radiation forces on particles and acoustic streaming in droplets. This study not only fills the gap between the emerging fields of acoustofluidics and acoustic black holes but also leads to a class of AFBH-based in-droplet particle manipulation toolsets with great potential for many applications, such as biosensing, point-of-care testing, and drug screening.
... The electrical interconnection of functional nanomaterials frequently implies the construction of a conductive nanojunction. The conventional choices to accomplish this assignment are scanning electron microscope (SEM)-based methods (electron beam-induced deposition (EBID) [7] and Joule heating fusion [8]) and transmission electron microscopy (TEM) or atomic force microscope (AFM)-based approaches (cold welding [9,10] and spot welding [11]). ...
Nanointerconnection has been selected as a promising method in the post-Moore era to realize device miniaturization and integration. Even with many advances, the existing nanojoining methods still need further developments to meet the three-dimensional nanostructure construction requirements of the next-generation devices. Here, we proposed an efficient silver (Ag)-filled nanotube fabrication method and realized the controllable melting and ultrafine flow of the encapsulated silver at a subfemtogram (0.83 fg/s) level, which presents broad application prospects in the interconnection of materials in the nanometer or even subnanometer. We coated Ag nanowire with polyvinylpyrrolidone (PVP) to obtain core–shell nanostructures instead of the conventional well-established nanotube filling or direct synthesis technique, thus overcoming obstacles such as low filling rate, discontinuous metalcore, and limited filling length. Electromigration and thermal gradient force were figured out as the dominant forces for the controllable flow of molten silver. The conductive amorphous carbonaceous shell formed by pyrolyzing the insulative PVP layer was also verified by energy dispersive spectroscopy (EDS), which enabled the continued outflow of the internal Ag. Finally, a reconfigurable nanointerconnection experiment was implemented, which opens the way for interconnection error correction in the fabrication of nanoelectronic devices.
... Nowadays, there are several methods to realize the manipulation of micro-nano particles, such as atomic force microscope (AFM) [5][6][7], magnetic tweezers [8,9] and optical tweezers [10][11][12]. However, the methods either are unable to implement large-area manipulation or easily damage samples. ...
Micro-nano particle manipulation methods in liquid environments have been widely used in the fields such as medicine, biology and material science. Nevertheless, the methods usually rely on pre-prepared physical microfluidic channels. In this work, virtual electrodes based on the optically induced dielectrophoresis (ODEP) method were used as virtual microchannels instead of traditional physical microfluidic channels. Virtual microchannels with different shapes were implemented by the designs of projected light patterns, which made the virtual microchannels have great flexibility and controllability. The relationship between the ODEP force and the alternating current (AC) voltage or the AC frequency exerted on the cells was assessed. The experimental results indicated that the ODEP force was increased with the increase of the AC voltage, and it was reduced with the increase of the AC frequency. Moreover, different virtual microchannels were designed to carry out the transportation, aggregation and sorting of yeast cells and rat basophilic leukemia cells (RBL-2H3 cells). This work shows that the virtual microchannels can be flexibly realized by ODEP in liquid environments.
... The independent and precise manipulation of nanostructures is a prerequisite for fully exploiting the potential of nanodevices in various applications [1][2][3][4][5][6], especially for the anisotropic nanostructures, nanowires for example [2][3][4][5], of which the chemical and physical properties are highly dependent to their orientation and position [7,8]. At present, several nanowire manipulation techniques have been investigated based on the magnetic field [9], electric field [10,11], optical field [12,13], and others [14,15], most of which were performed in a liquid environment to prevent the adhesion of nanowires to substrates. Among them, the optical field-based manipulation technique, represented by optical tweezers [16], has attracted widespread attention for its high precision, great flexibility, and versatility, and succeeded in trapping and manipulating various nanowires, such as SnO 2 , Ag, Au, and Si nanowires [12,[17][18][19]. ...
Metal nanowires are promising building blocks for optoelectronic nanodevices, so their independent and precise manipulation is urgently needed. However, the direct optical manipulation methods are severely hampered due to the high absorption and scattering characteristics of the metal nanowires. Here, a microsphere-assisted indirect optical manipulation method is proposed, and precise manipulation of a single Ag nanowire is demonstrated in liquid. The microsphere is actuated to rotate to generate a microvortex by dynamic optical traps. Under the action of shear stress, the Ag nanowire within the microvortex can be controllably rotated and accurately orientated. By manipulating the position of the microsphere using a single optical trap, a precise positioning of the nanowire can be achieved under the action of pushing force. On this basis, the Ag nanowire-based structures were assembled. This indirect optical manipulation avoids the direct interaction between the light and the nanowires, which makes it independent of both the laser (power, wavelength) and the nanowire (material, size, and shape). Hence, the microsphere-assisted manipulation method is simple and general for independent and precise manipulation of a single nanowire, which is of great significance to the fabrication of optoelectronic nanodevices.
... Various methods have been employed to achieve such interconnectivity, including: cold welding, fusion welding, solidstate welding, diffusion bonding, soldering, mechanical bonding, and atomic diffusion. For example, Moreno-Moreno et al. joined two gold nanowires or silver nanowires by a cold-welding technique [2] and Seong et al. achieved fusion welding of two silver nanowires by exploiting their high contact resistance to locally melt the junction by Joule heating [3]. Polymer adhesive coatings have also been employed. ...
Ion beam assisted joining of nanostructured materials is a relatively new field. In particular ion beam technique has been proven to be worthwhile for joining ceramic nanostructures. However, a large scope is still remaining to study heterojunctions between two dissimilar materials as the process of formation of bonds between two dissimilar materials is still to be understood. In this work we pick up a ceramic oxide and carbon based material to study ion beam joining. Specifically, we for the first time show heterojunction formation between hydrogen titanate nanowire (HTNW) and carbon nanotube (CNT) by the low energy ion beam. In order to understand the mechanism, we have invoked density functional theory and three-dimensional ion-solid interaction simulations. Experimental results are supported by predictions of simulations and suggest that the joining is established through ion beam mixing, surface defects and sputter redeposition at the junction points. The current study enlightens how the defects and sputtered out atoms are involved in the joining process. The chemical bonds between HTNW and CNT are formed only when C vacancy and simultaneously non-lattice O and C were produced during irradiation. The effect of joining on electrical conductivity and surface wetting has also been studied experimentally in this work, which is supported by simulations.
... To date, specifically, there have been assorted methods allowing for precisely manipulating and rotating single nano objects based on different physical effects, such as optical [2,3,7], magnetic [8], electrical [9], dielectrophoretic (DEP) [1] and mechanical [5,6,10,11] methods. For acoustic manipulation methods, although it has been demonstrated that the acoustic radiation torque/force can be employed to rotate single micro objects [12][13][14] and particle clusters [15,16], it is still challenging to use the acoustic radiation torque/force to rotate single nanoscale objects owing to the nature that the acoustic radiation torque/force exerted on a nanoscale object is too small. ...
The micromanipulation probe-type (MMP-type) ultrasonic nanomotor (UNM) has proven to be a type of robust and versatile tool for controllable rotary driving, dynamic trapping and high-precision orientation of a single one-dimensional (1D) nano object. The manipulation functions of the MMP-type UNM are implemented in the probe-liquid-substrate (PLS) system, in which a MMP is inserted into a liquid film of nano suspension on a stationary substrate. When the MMP elliptically vibrates parallel to the substrate surface, the acoustic streaming can be engendered to rotate a single silver nanowire (AgNW) at the liquid-substrate interface. Although the experimental results have demonstrated the effectiveness and high performance of the developed UNM, there have been no simulation results and quantitative analysis method to show the details of acoustic streaming field and to perform principle analysis for the MMP-type UNM, which has hindered a deeper understanding of the underlying physical mechanisms as well as optimization for the MMP-type UNM. In this work, to deeply analyze the principle for the developed UNM, we carry out numerical investigations on the thermo-viscous acoustic field and acoustic streaming field in the PLS system of the MMP-type UNM based on the finite element method (FEM). The simulation result shows that the elliptical vibration of the MMP parallel to the substrate surface can induce the reversed acoustic streaming vortex (compared to the MMP’s vibration trajectory direction) at the liquid-substrate interface, which enables controllable rotary driving of a single AgNW. With the simulation results of acoustic streaming fields, we theoretically predict the driving angular velocities of the AgNW at the liquid-substrate interface, and verify that the quantitative simulation results agree well with the reported experimental results. Moreover, the effects of device’s parameters and working conditions such as the distance between the MMP’s tip and substrate surface, the MMP’s length and radius and the liquid film’s thickness on the acoustic streaming field and the angular velocity of the AgNW are analyzed and clarified through both simulation results and experimental verifications, and the effect of the MMP’s material is also predicted via simulations.
... Generalized manipulation of single sub-100 nm particles of matter is an outstanding technological challenge, with applications including functionalized tip fabrication for scanning probe microscopy (SPM) and intracellular sensing and perturbation [1][2][3]. While tools such as transmission electron microscope in-situ manipulation, atomic force microscope attachment, optical tweezers, and application-specific bottom-up nanofabrication efforts have driven scientific progress, none are simultaneously scalable and generalizable to arbitrary nanoparticles (NP) [4][5][6][7]. ...
The controllable handling of an arbitrary single particle of matter with sub-100 nanometer (nm) dimensions is an essential but unsolved scientific challenge. We demonstrate nanoparticle-seeded glancing angle deposition using 10-100 nm diameter nanoparticle seeds (Er2O3, Fe@C, and Fe). The products are nanoparticle-nanowire heterostructures composed of arbitrary nanoscale tips attached to micron-length nanowire handles. Optical micromanipulation of the micron-scale handles enables concurrent manipulation of the attached nanoscale particles of matter.
... Gold nanoparticles were used in this research. Circuits made by this group are easily reconfigurable, and their fabrication does not require the use of polymers and chemicals [5] . Ju et al., developed a protocol for searching the synergistic parameter combinations to push single-wall carbon nanotubes (SWCNTs) to maintain their original shape after manipulation based on AFM as far as possible, without requiring the sample physical properties and the tip-manipulation mechanisms [6] . ...
This article investigates the effect of impact on the dynamic modeling and simulation of cubic and elliptic nanoparticles in the manipulation process based on atomic force microscopy (AFM). First, the dynamic equations prior to the motion are presented. Then, according to these equations, two assumptions are considered for nanoparticles motion. Using the Hertz, JRK, and Jamari theories as well as the approximate impact relation of Hunter, the effects of impact in motion are also taken into consideration. The results indicated that after 3 s and under constant, linear, second-order and sinusoidal forces, the elliptic nanoparticle moves, respectively, less than 0.08 µm, 0.1143 µm, 0.36 µm and 25 nm. In addition, the results of cubic nanoparticles nanomanipulation show that the cubic nanoparticle moves less than 0.08 µm in 3 s under constant force scheme. This type of nanoparticle does not move when acted upon by a linear force along the Z-axis, while it shows a displacement of 0.0117 µm along the Y-axis. After the same 3 s, it moves about 0.37 µm and less than 25 nm under second-order and sinusoidal forces, respectively.
... Metallic nanowires have wide applications in various fields, such as micro-nano electronics, biotechnology, solar cells, sensors, and catalysis [1][2][3][4][5]. Metallic nanowires with small size and high aspect ratio are ideal materials for micro-nano devices, such as Zn, Ag, Ni, Au, and Cu micro-nanometer wires have been widely applied [6][7][8][9][10]. In order to realize the excellent properties of metallic nanowires, research on the mechanical and electrical conductivity of single metallic nanowire are fundamental and necessary. ...
High aspect ratio tungsten nanowires have been prepared by selective dissolution of Nickel-aluminum-tungsten (NiAl−W) alloys which were directionally solidified at growth rates varying from 2 to 25 μm/s with a temperature gradient of 300 K·cm−1. Young’s modulus and electrical resistivity of tungsten nanowires were measured by metallic mask template method. The results show that the tungsten nanowires with uniform diameter and high aspect ratio are well aligned. The length of tungsten nanowires increases with prolongation of etching time, and their length reaches 300 μm at 14 h. Young’s modulus of tungsten nanowires is estimated by Hertz and Sneddon models. The Sneddon model is proper for estimating the Young’s modulus, and the value of calculating Young’s modulus are 260–460 GPa which approach the value of bulk tungsten. The resistivity of tungsten nanowires is measured and fitted with Fuchs−Sondheimer (FS) + Mayadas−Shatzkes (MS) model. The fitting results show that the specific resistivity of W nanowires is a litter bigger than the bulk W, and its value decreases with decreasing diameter.
... AFM tip-based nanomanipulation has been intensively studied in the past decade, helping us to fabricate nanodevices and nanostructures or conduct studies for improving our fundamental understanding of the material physical and chemical properties [11][12][13][14][15][16][17][18][19]. However, the AFM tip cannot perform operations of imaging and manipulation simultaneously. ...
Atomic force microscopy (AFM) based nanomanipulation can align the orientation and position of individual carbon nanotubes accurately. However, the flexible deformation during the tip manipulation modifies the original shape of these nanotubes, which could affect its electrical properties and reduce the accuracy of AFM nanomanipulation. Thus, we developed a protocol for searching the synergistic parameter combinations to push single-wall carbon nanotubes (SWCNTs) to maintain their original shape after manipulation as far as possible, without requiring the sample physical properties and the tip-manipulation mechanisms. In the protocol, from a vast search space of manipulating parameters, the differential evolution (DE) algorithm was used to identify the optimal combinations of three parameters rapidly with the DE algorithm and the feedback of the length ratio of SWCNTs before and after manipulation. After optimizing the scale factor F and crossover probability Cr, the values F = 0.4 and Cr = 0.6 were used, and the ratio could reach 0.95 within 5–7 iterations. A parameter region with a higher length ratio was also studied to supply arbitrary pushing parameter combinations for individual manipulation demand. The optimal pushing parameter combination reduces the manipulation trajectory and the tip abrasion, thereby significantly improving the efficiency of tip manipulation for nanowire materials. The protocol for searching the best parameter combinations used in this study can also be extended to manipulate other one-dimensional nanomaterials.
... While the main result is promising (the clusters can be easily arranged in a series of stripes, the separation of which is controlled by the Au density and concentration), the connection between the Au clusters forming a stripe seems to be prevented by the electrostatic repulsion and the corrugation of the MoS 2 substrate. This problem may be overcome with different 2D materials such as antimonene, the potential of which as a substrate for nanomanipulation has been recently demonstrated by Moreno-Moreno et al. in their AFM experiments on gold nanorods [15]. ...
Single crystal gold clusters (10 nm in size) have been collectively manipulated on mono- and bi-layered MoS 2 islands (up to 20 µm) grown on SiO 2 using AFM. On the monolayer the clusters tend to move in a direction corresponding to the zigzag alignment of the Mo and S atoms, and assemble into long striation patterns parallel to the scan direction. The distance between consecutive stripes is inversely proportional to the cluster concentration and size. A more detailed observation based on SEM shows that within each stripe the clusters remain separated by gaps of few nm in width possibly caused by electrostatic repulsion and/or the roughness of the SiO 2 substrate (∼2 nm). The stripes also proved to be thermally stable, preserving their superstructures up to 823 K. On the bilayer gold clusters are much less prone to move and assemble into stripes. These results suggest that the formation of nanostructures resulting from collective manipulation of metal clusters can be oriented by a properly chosen scan path in a rather straightforward way (as compared to one-by-one displacement of single clusters). The goal of forming µm-long but nm-thin wires with a geometrically defined shape could be easily reached with the use of smoother substrates or TMD materials with lesser charge transfer to metals adsorbed on them.
... Micromachines 2020, 11, 78 2 of 20 acoustic [16,17], electrokinetics [18,19], magnetic [20,21], optical [22,23], thermal [24,25], and atomic force microscope [26,27] approaches. An emerging topic on the manipulation and fabrication of micro/nanoparticles is about how to develop a novel mechanism that can complement what a single technique can offer. ...
Optoelectrokinetics (OEK), a fusion of optics, electrokinetics, and microfluidics, has been demonstrated to offer a series of extraordinary advantages in the manipulation and fabrication of micro/nanomaterials, such as requiring no mask, programmability, flexibility, and rapidness. In this paper, we summarize a variety of differently structured OEK chips, followed by a discussion on how they are fabricated and the ways in which they work. We also review how three differently sized polystyrene beads can be separated simultaneously, how a variety of nanoparticles can be assembled, and how micro/nanomaterials can be fabricated into functional devices. Another focus of our paper is on mask-free fabrication and assembly of hydrogel-based micro/nanostructures and its possible applications in biological fields. We provide a summary of the current challenges facing the OEK technique and its future prospects at the end of this paper.
... For example, metallic NWs (Ag, Au, and Cu) have been considered as electrical interconnects, assembled transparent planar electrodes, and plasmonic propagation media. [1][2][3][4][5][6][7][8] Due to their abundant electrical, photonic, and mechanical properties, semiconductor nanowires, including Si, Ge, metal oxides, and III-V and II-VI compounds, have undergone great progress in the fields of electronics, subwavelength light waveguiding, and sensing (for photoelectric, chemical, and biological purposes). [9][10][11][12][13][14][15][16][17][18][19][20] Furthermore, more integrated devices with multifunctionalities have been investigated from both proof-of-concept and nanosystem integration perspectives. ...
As natural one‐dimensional confined electron transport channels and photon propagation paths, nanowires (NWs) display unmatched properties and huge potential for application in diverse fields. The ability to construct a nanoscale functional system would enable significant advances in the currently desired miniaturized device integration. To date, the basic properties of all types of nanowire crystals, including metallic NWs, as well as group IV‐related, III‐V/II‐VI compounds, and metal oxide NWs, are well understood. Regarding future work, compositional (ie, doping and alloying) and structural (defect and heterostructure) designs to flexibly realize custom‐made functionality are emphasized. Along this line, recent progress is reviewed, including the basic properties (nanowire mechanics, electronics, and photonics) and applications such as photodetectors and chemical/biological sensors. A review of the correlations between the compositional/structural configuration of nanowires and the corresponding functionality is also presented. The future development direction of this field is concluded and highlighted at the end. Nanowires have been investigated as one‐dimensional carriers/photons for confined transport paths, based on which conceptual functional devices are developed over the years, in fields such as mechanics, microelectronics, nanophotonics, optoelectronics, and bioelectronics. Related advanced perspectives and recent progress are reviewed. Toward optimized figure of merit in these applications, rational designs of nanowires via structures and composition route are emphasized.
The impact of Artificial Intelligence (AI) is rapidly expanding, revolutionizing both science and society. It is applied to practically all areas of life, science, and technology, including materials science, which continuously requires novel tools for effective materials characterization. One of the widely used techniques is scanning probe microscopy (SPM). SPM has fundamentally changed materials engineering, biology, and chemistry by providing tools for atomic‐precision surface mapping. Despite its many advantages, it also has some drawbacks, such as long scanning times or the possibility of damaging soft‐surface materials. In this paper, we focus on the potential for supporting SPM‐based measurements, with an emphasis on the application of AI‐based algorithms, especially Machine Learning‐based algorithms, as well as quantum computing (QC). It has been found that AI can be helpful in automating experimental processes in routine operations, algorithmically searching for optimal sample regions, and elucidating structure–property relationships. Thus, it contributes to increasing the efficiency and accuracy of optical nanoscopy scanning probes. Moreover, the combination of AI‐based algorithms and QC may have enormous potential to enhance the practical application of SPM. The limitations of the AI‐QC‐based approach were also discussed. Finally, we outline a research path for improving AI‐QC‐powered SPM.
Research Highlights
Artificial intelligence and quantum computing as support for scanning probe microscopy.
The analysis indicates a research gap in the field of scanning probe microscopy.
The research aims to shed light into ai‐qc‐powered scanning probe microscopy.
The resolution of positioning and the availability of diverse testing environments are pivotal for nanorobotic manipulation (NRM) at small scales. The former involves the measurement of length-related physical quantities, such as velocity based on displacement, forces based on deformation, and electrostatic fields based on range. The latter ensures alignment between rudimentary experiments and actual working conditions. Piezoelectric-ceramic-based manipulators, widely used by NRM inside electron microscopes, are expected to provide sub-nano level positioning resolution. However, practical experiments reveal limitations in achieving this spectacular resolution due to microscopes’ capability in dynamic length sensing. Here, we propose an NRM system with ultrafine positioning resolution for
operando
characterization inside a spherical aberration correction transmission electron microscope (Cs-TEM). The Cs-TEM, with sub-angstrom precision in length sensing, demonstrated the ability to achieve picometer-scale positioning resolution of the lead zirconate titanate (PZT)-based manipulator (204 pm, 171 pm, and 140 pm in X, Y, and Z directions). Moreover, the system's compatibility with in-situ chips and optical fibers allows the integration of multi-physical stimuli, such as electrical, thermal, optical, liquid, and magnetic, into the confined chamber of Cs-TEM. This NRM system establishes a versatile platform for
operando
characterization, facilitating the investigation of performance-mechanism correlations and enabling device-level prototyping.
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.
Gold-metallic nanofibrils were prepared from three different iso-apoferritin (APO) proteins with different Light/Heavy (L/H) subunit ratios (from 0% up to 100% L-subunits). We show that APO protein fibrils have the ability to in situ nucleate and grow gold nanoparticles (AuNPs) simultaneously assembled on opposite strands of the fibrils, forming hybrid inorganic-organic metallic nanowires. The AuNPs are arranged following the pitch of the helical APO protein fiber. The mean size of the AuNPs was similar in the three different APO protein fibrils studied in this work. The AuNPs retained their optical properties in these hybrid systems. Conductivity measurements showed ohmic behavior like that of a continuous metallic structure.
Abstract Metallic nanowires (NWs) exhibit a number of interesting properties, such as high conductivity, flexibility, and cold‐weldability, making them ideal for nanocircuits. They are usually adsorbed on substrates by depositing a colloidal solution of NWs on the surface. However, they remain randomly scattered and solvent residues may contaminate/ degrade the sample. This study presents a method for forming electrical contacts with gold nanowires based on all‐dry deterministic transfer. The process begins with the adsorption of gold nanowires by drop casting the colloidal solution onto a viscoelastic substrate. These wires are transferred to selected locations on the substrate, minimizing manipulation with fabrication times a factor of 2 shorter than direct drop casting deposition, preserving surface and sample conditions, and improving the fabrication of nanocircuits. Atomic force microscopy is used to manipulate the NWs for the final connections, which have contact resistances of a few ohms. To illustrate the technique, three different examples of applicability are presented. This work is expected to be a starting point for expanding the potential of deterministic transfer that is successfully used in 2D materials. For example, to study local electrical transport in heterogeneous samples such as van der Waals heterostructures and twisted layers of 2D materials.
Nanowires (NWs) provide opportunities for building high-performance sensors and devices at micro-/nanoscales. Directional movement and assembly of NWs have attracted extensive attention; however, controllable manipulation remains challenging partly due to the lack of understanding on interfacial interactions between NWs and substrates (or contacting probes). In the present study, lateral bending of Ag NWs was investigated under various bending angles and pushing velocities, and the mechanical performance corresponding to microstructures was clarified based on high-resolution transmission electron microscope (HRTRM) detections. The bending-angle-dependent fractures of Ag NWs were detected by an atomic force microscope (AFM) and a scanning electron microscope (SEM), and the fractures occurred when the bending angle was larger than 80°. Compared with an Ag substrate, Ag NWs exhibited a lower system stiffness according to the nanoindentation with an AFM probe. HRTRM observations indicated that there were grain boundaries inside Ag NWs, which would be contributors to the generation of fractures and cracks on Ag NWs during lateral bending and nanoindentation. This study provides a guide to controllably manipulate NWs and fabricate high-performance micro-/nanodevices.
Atomic force microscopy (AFM) is a unique and extremely versatile surface‐imaging technique that can give information on structural changes and behavior with high resolution. Moreover, it allows to manipulate surface entities like single atoms, single molecules, biomolecules, and viruses, on different inorganic materials. AFM is essential for characterizing biointerfaces and functional materials and supports the development of nanoscale devices. This chapter gives an overview of the versatility of AFM as a powerful, multifunctional tool for characterizing and manipulating material surfaces and biological surface entities. AFM cantilever and cantilever arrays can be converted into “lab‐on‐a‐tip,” and then employed for simultaneously imaging and probing a variety of phenomena such as antigen recognition, flexibility, elasticity or electric current, with a detection sensitivity in the picomolar range. AFM will strongly contribute to the development of novel systems for environmental monitoring, biochemical analysis, and medical applications not limited to but especially powerful for characterizing functionalized ceramics for biotechnological, biomedical, and environmental applications.
Transition metal dichalcogenides (TMDs) have been widely studied as attractive two-dimensional (2D) materials. In particular, specific TMD materials have attracted increasing attention because of their intriguing features as 2D topological insulators (TIs), which have a metallic edge state and bulk band gap. To realize next-generation devices that employ the metallic edge states of 2D TI materials, precise patterning of the edges is essential. In this study, we demonstrate a simple nanopatterning technique for 1 T’-MoTe2, which is known to be a 2D TI material, using atomic force microscopy (AFM)-based scanning probe lithography (SPL). Our AFM-based SPL method entails delicately scratching a few-layer 1 T’-MoTe2 sample while applying an electric field using a conductive AFM tip. The proposed method enables nanoscale lines, holes, and letters to be reliably patterned on the 1 T’-MoTe2 sample. This study results in the development of a clean method that is compatible with existing mass-production facilities to fabricate various TMD materials for realizing next-generation electronic devices and for studying the underlying physics of these materials.
With the introduction of techniques to grow highly functional nanowires of exotic materials and demonstrations of their potential in new applications, techniques for depositing nanowires on functional platforms have been an area of active interest. However, difficulties in handling individual nanowires with high accuracy and reliability have so far been a limiting factor in large‐scale integration of high‐quality nanowires. Here, a technique is demonstrated to transfer single nanowires reliably on virtually any platform, under ambient conditions. Functional nanowires of InP, AlGaAs, and GeTe on various patterned structures such as electrodes, nanophotonic devices, and even ultrathin transmission electron microscopy (TEM) membranes are transferred. It is shown that the versatility of this technique further enables to perform on‐chip nano‐optomechanical measurements of an InP nanowire for the first time via evanescent field coupling. Thus, this technique facilitates effortless integration of single nanowires into applications that were previously seen as cumbersome or even impractical, spanning a wide range from TEM studies to in situ electrical, optical, and mechanical characterization.
Nano-manipulation technology, as a kind of “bottom-up” tool, has exhibited an excellent capacity in the field of measurement and fabrication on the nanoscale. Although variety manipulation methods based on probes and microscopes were proposed and widely used due to locating and imaging with high resolution, the development of non-contacted schemes for these methods is still indispensable to operate small objects without damage. However, optical manipulation, especially near-field trapping, is a perfect candidate for establishing brilliant manipulation systems. This paper reports about simulations on the electric and force fields at the tips of metallic probes irradiated by polarized laser outputted coming from a scanning near-field optical microscope probe. Distributions of electric and force field at the tip of a probe have proven that the polarized laser can induce nanoscale evanescent fields with high intensity, which arouse effective force to move nanoparticles. Moreover, schemes with dual probes are also presented and discussed in this paper. Simulation results indicate that different combinations of metallic probes and polarized lasers will provide diverse near-field and corresponding optical force. With the suitable direction of probes and polarization direction, the dual probe exhibits higher trapping force and wider effective wavelength range than a single probe. So, these results give more novel and promising selections for realizing optical manipulation in experiments, so that distinguished multi-functional manipulation systems can be developed.
In this review article, various methods for the light-induced manipulation of plasmonic nanoobjects are described, and some sample applications of this process are presented. The methods of the photo-induced nanomanipulation analyzed include methods based on: the light-induced isomerization of some compounds attached to the surface of the manipulated object causing formation of electrostatic, host-guest or covalent bonds or other structural changes, the photo-response of a thermo-responsive material attached to the surface of the manipulated nanoparticles, and the photo-catalytic process enhanced by the coupled plasmons in manipulated nanoobjects. Sample applications of the process of the photo-aggregation of plasmonic nanosystems are also presented, including applications in surface-enhanced vibrational spectroscopies, catalysis, chemical analysis, biomedicine, and more. A detailed comparative analysis of the methods that have been applied so far for the light-induced manipulation of nanostructures may be useful for researchers planning to enter this fascinating field. This journal is
Gold nanowires (AuNWs) possess strong potential application in micro- and nanoelectronics as well as in plasmonic waveguides because of their low electrical resistance. However, the synthesis of pure solvent-dispersible AuNWs with full control over their length still remains a challenge. All the previously reported methods produce AuNWs with other impurities such as smaller nanorods, platelets, and spherical particles and are limited to a certain length (typically below 10 μm). This article describes a one-step synthesis of extremely long AuNWs (up to 25 μm) with great control over their dimensions by using pentahedrally twinned gold nanorods (AuNRs) as seed particles. To induce the AuNW growth, the reduction of Au(I) to Au(0) was carried out on the surface of AuNRs at a very low pH by introducing HCl into the growth solution. The slow conversion of Au(I) to Au(0) due to the increase in reduction potential at lower pH promoted the preferential deposition of metallic gold on the more reactive tips of AuNRs compared to their sides, resulting in the formation of AuNWs. In analogy to the "living" polymerization reaction, the length of the AuNWs was proportional to the amount of Au(I) added to the growth solution; thus, the desired length of AuNWs was achieved by controlling the supply of Au(I) ions in the reaction mixture. The AuNWs longer than 6 μm were found to be responsive to microwave radiation. When an aqueous solution of AuNWs was exposed to microwaves, the formation of sharp kinks was observed in several locations of AuNWs without their disintegration into smaller pieces.
A drastic size effect in cold-welded metallic nanowire for surface fasteners was observed in our previous experiment. In this work, a large-scale molecular dynamics (MD) simulation and a finite element (FE) simulation coupled with the nonsingular dislocation theory are combined to probe the true origin of this drastic size effect. Very large diameter (up to 200 nm) is involved in the direct MD simulation, leaving no gap between the simulation and the experiment. It was once believed that the drastic size effect comes from the Van der Waals (vdW) force transmitted through the bonding interface, which does give a mathematically agreeable scaling law. However, based on present simulations, new understanding is established―the drastic size effect is linked to dislocation emission, rather than vdW force. Compared with a single nanowire, the externally induced stress surges near the bonding corner of cold-welded nanocrystals due to the enormous stress concentration. The dislocation emission is hence triggered. It is also revealed that, overwhelmingly, dislocation emission should be energetically favorable in cold-welded nanocrystals. Additionally, MD simulations with polycrystalline nanocrystals reveal that both the random orientation effect and the grain boundary effect are secondary to the enormous stress concentration effect. Under such less ideal situation, dislocation emission still determines the maximum stress.
Atomic force microscope (AFM) based nanomanipulation has been proved to be a possible way to assemble various nanoparticles into complex patterns and devices. To achieve an efficient and full-automatic nanomanipulation, the nanoparticles as well as other features on the substrate must be quickly identified by the computer. This work focuses on an autodetection method for flexible nanowires based on deep learning. The You Only Look Once (YOLO) network is applied to find all movable nanowires in the AFM images. A series of morphology transformation algorithms, including an adaptive threshold edge detection, are applied to refine the skeletons of the nanowires. The bidirectional long short-term memory model with conditional random field layer (BI-LSTM-CRF) is proposed to precisely determine the posture and position of the detected nanowires. Benefiting from these algorithms, our detecting program is able to automatically detect the nanowires of different morphology with nanometer resolution and with over 80% reliability in the testing set. The detecting results are less affected by the image quality, which demonstrates good robustness of this algorithm.
Nanowires and nanotubes composed of layered or nonlayered materials have been fabricated via different techniques, among which Anodic Aluminium Oxide (AAO) template-based electrodeposition technology provides a versatile technique for synthesizing one or two-dimensional nanostructured materials. Herein, Conductive Atomic Force Microscopy (CAFM) has been used to image and characterise the nanorods for nanorods with diameter of 50 nm ±5. Given that only one previous study using CAFM on gold nanorods exists [1], recording the difficulties encountered with this technique will be of wider interest to the scientific community. This work details experiments on electrical response as a function of applied force on the AFM tip and contamination on the top surface on nanorods. We report a novel observation, revealing a hollow shaped conductive pattern of some of our gold nanorods. This is explained with reference to competing growth rates in horizontal and vertical directions inside the pores.
In this article, the collection of studies with regard to the modeling of nanomanipulation based on atomic force microscope (AFM) is discussed. To model the manipulation process, two-dimensional and three-dimensional models in the classical environment and molecular dynamics can be presented. The decisive factor in determining the solution’s type depends on the dimensions and application of manipulation. In general, however, benefiting from multiscale methods offers more realistic results from the inherent characteristics of AFM point of view. In addition, the manipulation process is examined empirically. Different parameters affect the process. Overall, these include the geometric properties of AFM, geometric properties and material of nanoparticles, process execution environment, initial impact of nanoparticles, contact mechanics, and roughness. The geometric parameters of AFM have less importance compared with other factors. The material and geometry of nanoparticles and environmental reaction play their most dominant role in contact and roughness equations as well as intermolecular forces. For instance, for softer nanoparticles, elastoplastic and viscoelastic contact theories are more suited. In contrast, in environments except vacuum and air, roughness models with more developed adhesion terms are better choices. Employing complex contact theories can provide us with permanent deformations, roughness, reduction in force, and critical indentation depth. In addition to the involved parameters in modeling the nanomanipulation process, path planning techniques for obtaining the optimal path and control of the AFM set for its exact execution are other influential notions.
A novel multiscale model is developed to investigate the mechanical performance of gold nanowires surface fasteners. The cold welding of two contacting nanowires of different diameters and overlapping depth was simulated using molecular dynamics simulations. The strength of the welded interface was obtained via tensile simulations performed at temperatures up to 500 K. A Monte Carlo algorithm was developed to determine the bulk properties of the nanofastener by calculating the average number of welded joints per unit area. Our model shows that the nanojoints are formed by solid-state diffusion and intermixing of the interface atoms. The nanojoints strength increases with the increase of the preloading pressure, leading to the fracture of the nanowire outside the welded region. The results further show that the strength of the nanojoint slightly increases with the increase of the nanowires diameter beyond 10 nm. The effective strength of the fastener was found to increase by four orders of magnitude when the nanowire diameter decreased from 200 nm to 3 nm. Increasing the surface density and improving the patterning accuracy of the nanowire arrays are critical in improving the adhesive performance. The results of the multiscale model are in good agreement with previous experimental measurements.
Cocrystallization of a nonconductive boron based-host with aromatic guests generates conductive cocrystals. Carrier mobilities of the cocrystals with either pyrene or tetrathiafulvalene were measured using conducting probe atomic force microscopy. The incorporation of the π-rich aromatic guests results in electrically conductive cocrystals. The cocrystal with tetrathiafulvalene as guest shows approximately 7-times higher charge carrier mobility than the cocrystal with pyrene.
The fabrication of high-performance solid-state silicon quantum-devices requires high resolution patterning with minimal substrate damage. We have fabricated room temperature single-electron transistors (SETs) based on point-contact tunnel junctions using a hybrid lithography tool capable of both high resolution thermal scanning probe lithography and high throughput direct laser writing. The best focal z-position and the offset of the tip- and the laser-writing positions were determined in-situ with the scanning probe. We demonstrate < 100 nm precision in the registration between the high resolution and high throughput lithographies. The SET devices were fabricated on degenerately doped n-type > 1020/cm3 silicon on insulator (SOI) chips using a CMOS compatible geometric oxidation process. The characteristics of the three devices investigated were dominated by the presence of Si nanocrystals or phosphorous atoms embedded within the SiO2, forming quantum dots (QDs). The small size and strong localisation of electrons on the QDs facilitated SET operation even at room temperature. Temperature measurements showed that in the range 300 K > T > ~100 K, the current flow was thermally activated but at < 100 K, it was dominated by tunnelling.
Over the past decades, DNA, the carrier of genetic information, has been used by researchers as a structural template material. Watson‐Crick base pairing enables the formation of complex 2D and 3D structures from DNA through self‐assembly. Various methods have been developed to functionalize these structures for numerous utilities. Metallization of DNA has attracted much attention as a means of forming conductive nanostructures. Nevertheless, most of the metallized DNA wires reported so far suffer from irregularity and lack of end‐to‐end electrical connectivity. An effective technique for formation of thin gold‐coated DNA wires that overcomes these drawbacks is developed and presented here. A conductive atomic force microscopy setup, which is suitable for measuring tens to thousands of nanometer long molecules and wires, is used to characterize these DNA‐based nanowires. The wires reported here are the narrowest gold‐coated DNA wires that display long‐range conductivity. The measurements presented show that the conductivity is limited by defects, and that thicker gold coating reduces the number of defects and increases the conductive length. This preparation method enables the formation of molecular wires with dimensions and uniformity that are much more suitable for DNA‐based molecular electronics. Conductive metallized DNA wires merge advantageous DNA properties, such as its ability to self‐assemble, with high conductivity and stability of the metal coating. In this work, an improved method for uniformly coating DNA with a continuous gold layer is presented, achieving very thin conducting wires. Detailed conductivity measurements show the importance of defects in limiting the conductive length of these wires.
Silver nanowires (Ag NWs) are promising material for building various sensors and devices at nanoscale. However, fast and precise placement of individual Ag NWs is still a challenge today. Atomic force microscopy (AFM) has been widely used to manipulate nanoparticles, yet this technology meets many difficulties when being applied to move Ag NWs as well as other soft one-dimensional (1D) materials, since these samples are easily distorted or even broken due to the frictions and adhesion on the substrate. In this paper, two novel manipulation strategies based on parallel pushing method are presented. This method applies a group of short parallel pushing vectors (PPVs) to the Ag NW along its longitude direction. Identical and proportional vectors are respectively proposed to translate and rotate Ag NWs with straight-line configuration. The rotation strategy is also applied to straighten flexed Ag NWs. Finite element method (FEM) simulation is introduced to analyse the Ag NW's behaviour as well as to optimize the PPVs. Experiments are carried out to confirm the efficiency of the presented strategies. By comprehensive application of the new strategies, four Ag NWs are continuously assembled into a rectangular pattern. This study improves the controllability of the position and configuration of Ag NWs on the flat substrate. It also indicates the practicability of automatic nano-fabrication using common AFMs.
Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 10⁴ S m⁻¹ and good optical transparency in the visible light range, promising in transparent conductive electrode applications.
Summary: Scanning Probe Microscopy (SPM) is already a relevant tool in biological research at the nanoscale. We present “Flatten plus”, a recent and helpful implementation in the well-known WSxM free software package. “Flatten plus” allows reducing low frequency noise in SPM images in a semi-automated way preventing the appearance of typical artifacts associated with such filters.
Availability and implementation: WSxM is a free software implemented in C++ supported on MS Windows, but it can also be run under Mac or Linux using emulators such as Wine or Parallels. WSxM can be downloaded from http://www.wsxmsolutions.com/.
Contact: ignacio.horcas@wsxmsolutions.com.
© The Author (2015). Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
We investigate conductance fluctuations in molecular junctions using a mechanically controllable break junction setup in a liquid environment. In contrast to conventional break junction measurements, time-dependent conductance signals were recorded while reducing the gap size between the two contact electrodes. Only small amplitude fluctuations of the conductance are observed when measuring in pure solvent. Conductance traces recorded in solutions containing alkanedithiols show significantly larger fluctuations which can take the form of random telegraph signals. Such signals emerge in a limited conductance range, which corresponds well to the known molecular conductance of the compounds investigated. These large-amplitude fluctuations are attributed to the formation and thermally driven breaking of bonds between a molecule and a metal electrode and provide a still poorly explored source of information on the dynamics of molecular junctions formation. The lifetimes of the high and low conductance states are found to vary between 0.1 ms and 0.1 s.
Local oxidation of silicon surfaces by atomic force microscopy is a very promising lithographic approach at nanometer scale. Here, we study the reproducibility, voltage dependence, and kinetics when the oxidation is performed by dynamic force microscopy modes. It is demonstrated that during the oxidation, tip and sample are separated by a gap of a few nanometers. The existence of a gap increases considerably the effective tip lifetime for performing lithography. A threshold voltage between the tip and the sample must be applied in order to begin the oxidation. The existence of a threshold voltage is attributed to the formation of a water bridge between tip and sample. It is also found that the oxidation kinetics is independent of the force microscopy mode used (contact or noncontact).
The scanning tunneling microscope is proposed as a method to measure forces as small as 10-18 N. As one application for this concept, we introduce a new type of microscope capable of investigating surfaces of insulators on an atomic scale. The atomic force microscope is a combination of the principles of the scanning tunneling microscope and the stylus profilometer. It incorporates a probe that does not damage the surface. Our preliminary results in air demonstrate a lateral resolution of 30 ÅA and a vertical resolution less than 1 Å.
A method for the fabrication of nanometer size gold wires on insulating surfaces is presented. An oscillating gold-coated atomic force microscope tip is brought into close proximity of a silicon dioxide surface. The application of a negative sample voltage produces the transport of gold atoms from the tip to the surface. The voltage is applied when there is a tip–surface separation of ∼3 nm. The finite tip–surface separation enhances the tip lifetime. It also allows the application of sequences of multiple voltage pulses. Those sequences allow the fabrication of continuous nanowires. The atomic force microscope gold deposition is performed at room temperature and in ambient conditions which makes the method fully compatible with standard lithographic techniques. Electron transport measurements of the wires show a clear metallic behavior. Electrical resistivities of ∼ 3×10−7 Ω m and current densities of up to 5×1011 A m−2 are reported. © 2001 American Institute of Physics.
Contact resistances of multiwalled nanotubes deposited on gold contact fingers are very large. We show that the contact resistances decrease by orders of magnitudes when the contact areas are selectively exposed to the electron beam in a scanning electron microscope. The focused electron beam enables the selection of one particular nanotube for electrical measurement in a four-terminal configuration, even if a loose network of nanotubes is deposited on the gold electrodes. For all measured nanotubes, resistance values lie in a narrow range of 0.35–2.6 kΩ at room temperature. © 1998 American Institute of Physics.
Metallic point contacts and tunnel junctions with a small and adjustable number of conduction channels have been obtained in the last few years using scanning tunneling microscope and break junction techniques. For conventional break junctions, the reported drift of the interelectrode spacing in the tunnel regime is typically of the order of 0.5 pm/min (1 pm=10<sup>-12</sup> m). We have nanofabricated break junctions which display a drift smaller than 0.2 pm/h. The improvement results from the scaling down by two orders of magnitude of the device dimensions. We describe the nanofabrication process, which can be adapted to most metals. We have performed measurements on Al, Cu, and Nb devices. The results illustrate the ability of the technique to explore phenomenalike conductance quantization and two level fluctuations. These new adjustable atomic size contacts and tunnel junctions can be integrated in complex circuits. © 1996 American Institute of Physics.
The use of individual molecules as functional electronic devices was first proposed in the 1970s (ref. 1). Since then, molecular electronics(2,3) has attracted much interest, particularly because it could lead to conceptually new miniaturization strategies in the electronics and computer industry. The realization of single molecule devices has remained challenging, largely owing to difficulties in achieving electrical contact to individual molecules. Recent advances in nanotechnology, however, have resulted in electrical measurements on single molecules(4-7). Here we report the fabrication of a field-effect transistor-a three-terminal switching device-that consists of one semiconductings(8-10) single-wall carbon nanotube(11,12) connected to two metal electrodes. By applying a voltage to a gate electrode, the nanotube can be switched from a conducting to an insulating state. We have previously reported(5) similar behaviour for a metallic single-wall carbon nanotube operated at extremely low temperatures. The present device, in contrast, operates at room temperature, thereby meeting an important requirement for potential practical applications. Electrical measurements on the nanotube transistor indicate that its operation characteristics can be qualitatively described by the semiclassical band-bending models currently used for traditional semiconductor devices. The fabrication of the three-terminal switching device at the level of a single molecule represents an important step towards molecular electronics.
Resolving individual atoms has always been the ultimate goal of surface microscopy. The scanning tunneling microscope images
atomic-scale features on surfaces, but resolving single atoms within an adsorbed molecule remains a great challenge because
the tunneling current is primarily sensitive to the local electron density of states close to the Fermi level. We demonstrate
imaging of molecules with unprecedented atomic resolution by probing the short-range chemical forces with use of noncontact
atomic force microscopy. The key step is functionalizing the microscope’s tip apex with suitable, atomically well-defined
terminations, such as CO molecules. Our experimental findings are corroborated by ab initio density functional theory calculations.
Comparison with theory shows that Pauli repulsion is the source of the atomic resolution, whereas van der Waals and electrostatic
forces only add a diffuse attractive background.
A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional
spontaneously broken symmetry–based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless
quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive
measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom
and demonstrated that topological quantum numbers are completely determined from spin texture–imaging measurements. Applying
this method to Sb and Bi1–xSbx, we identified the origin of its topological order and unusual chiral properties. These results taken together constitute
the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality,
which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall–like
topological phenomena.
This paper shows that the nanostructures deposited at room temperature in scanning tunneling microscopy experiments are produced by mechanical contact between tip and sample. Gold mounds are deposited in gold substrates and it is observed that the current flowing between tip and sample is quantized and the resistance can be as low as 100 Omega.
Attempts to infer DNA electron transfer from fluorescence quenching measurements on DNA strands doped with donor and acceptor molecules have spurred intense debate over the question of whether or not this important biomolecule is able to conduct electrical charges. More recently, first electrical transport measurements on micrometre-long DNA 'ropes', and also on large numbers of DNA molecules in films, have indicated that DNA behaves as a good linear conductor. Here we present measurements of electrical transport through individual 10.4-nm-long, double-stranded poly(G)-poly(C) DNA molecules connected to two metal nanoelectrodes, that indicate, by contrast, large-bandgap semiconducting behaviour. We obtain nonlinear current-voltage curves that exhibit a voltage gap at low applied bias. This is observed in air as well as in vacuum down to cryogenic temperatures. The voltage dependence of the differential conductance exhibits a peak structure, which is suggestive of the charge carrier transport being mediated by the molecular energy bands of DNA.
Carbon nanotubes are a good realization of one-dimensional crystals where basic science and potential nanodevice applications merge. Defects are known to modify the electrical resistance of carbon nanotubes; they can be present in as-grown carbon nanotubes, but controlling their density externally opens a path towards the tuning of the electronic characteristics of the nanotube. In this work, consecutive Ar+ irradiation doses are applied to single-walled nanotubes (SWNTs) producing a uniform density of defects. After each dose, the room-temperature resistance versus SWNT length (R(L)) along the nanotube is measured. Our data show an exponential dependence of R(L) indicating that the system is within the strong Anderson localization regime. Theoretical simulations demonstrate that mainly di-vacancies contribute to the resistance increase induced by irradiation, and that just a 0.03% of di-vacancies produces an increase of three orders of magnitude in the resistance of a SWNT of 400 nm length.
In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
Using remarkably simple experimental techniques it is possible to gently break a metallic contact and thus form conducting nanowires. During the last stages of the pulling a neck-shaped wire connects the two electrodes, the diameter of which is reduced to single atom upon further stretching. For some metals it is even possible to form a chain of individual atoms in this fashion. Although the atomic structure of contacts can be quite complicated, as soon as the weakest point is reduced to just a single atom the complexity is removed. The properties of the contact are then dominantly determined by the nature of this atom. This has allowed for quantitative comparison of theory and experiment for many properties, and atomic contacts have proven to form a rich test-bed for concepts from mesoscopic physics. Properties investigated include multiple Andreev reflection, shot noise, conductance quantization, conductance fluctuations, and dynamical Coulomb blockade. In addition, pronounced quantum effects show up in the mechanical properties of the contacts, as seen in the force and cohesion energy of the nanowires. We review this reseach, which has been performed mainly during the past decade, and we discuss the results in the context of related developments. Comment: Review, 120 pages, 98 figures. In view of the file size figures have been compressed. A higher-resolution version can be found at: http://lions1.leidenuniv.nl/wwwhome/ruitenbe/review/QPASC-hr-ps-v2.zip (5.6MB zip PostScript)
Electrical operation of room-temperature (RT) single dopant atom quantum dot (QD) transistors,
based on phosphorous atoms isolated within nanoscale SiO2 tunnel barriers, is presented. In contrast
to single dopant transistors in silicon, where the QD potential well is shallow and device operation
limited to cryogenic temperature, here, a deep (∼2 eV) potential well allows electron confinement at
RT. Our transistors use ∼10 nm size scale Si/SiO2/Si point-contact tunnel junctions, defined by scanning
probe lithography and geometric oxidation. “Coulomb diamond” charge stability plots are measured
at 290 K, with QD addition energy ∼0.3 eV. Theoretical simulation gives a QD size of similar
order to the phosphorous atom separation ∼2 nm. Extraction of energy states predicts an anharmonic
QD potential, fitted using a Morse oscillator-like potential. The results extend single-atom transistor
operation to RT, enable tunneling spectroscopy of impurity atoms in insulators, and allow the
energy landscape for P atoms in SiO2 to be determined. Published by AIP Publishing.
https://doi.org/10.1063/1.5050773
Using mechanical exfoliation combined with a controlled double step transfer procedure we demonstrate that single layers of antimony can be readily produced. These flakes are not significantly contaminated upon exposure to ambient conditions and they do not react with water. DFT calculations confirm our experimental observations and predict a band gap of 1.2-1.3 eV (ambient conditions) for single layer antimonene, which is smaller than that calculated under vacuum conditions at 0 K. Our work confirms antimonene as a highly stable 2D material with promising relevant applications in optoelectronics.
Templating the electroless reduction of metal ions on DNA is now an established route to the preparation of nanowires and can be particularly useful for the formation of nanowires in the desirable <10 nm size range. However, different preparation conditions produce nanowires of widely different morphologies and conductivities. We describe a method for the synthesis of Cu nanowires in which electroless metal deposition is carried out on DNA ‘template’ molecules in bulk solution. Though analogous to previous surface-based routes, importantly this now produces conductive material. AFM was used to evaluate the size and morphology of the resulting nanowires; a mean nanowire diameter of 7.1nm (standard deviation = 4.7nm) was determined from a statistical analysis of 100 nanowires and the Cu coatings were continuous and smooth. These findings represent a notable improvement in nanowire morphology in comparison to the previous surface-based routes. UV-vis spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to confirm formation of Cu(0) metal takes place during nanowire synthesis, and additional scanning probe microscopy techniques were employed to probe the electrical properties of the nanowires. The nanowires are less conductive [resistivity ~ 2Ωcm] than bulk Cu, but much more conductive than nanowires prepared by the analogous method on surface-bound DNA. Using an extension of our thermodynamic model for DNA-templating, we show that the templating process in bulk solution favours the formation of continuous nanowires compared to templating on surface-bound DNA
Employing the admittance formula for double-barrier junctions [Fu and Dudley, Phys. Rev. Lett. 70, 65 (1993)], we have estimated an ac susceptance (imaginary part of admittance) of Au/1,4-benzenedithiol/Au single-molecule junctions from their current-voltage characteristics. In the MHz regime, we find that the junction susceptance shows a very small ( ∼ 0.1 aF) capacitive component that can be entirely masked by a larger electrode capacitance. Direct ac signal transmission measurements up to 1 GHz reveal no molecular signals and confirm the smallness of the molecular capacitance in the MHz regime.
A simple yet highly reproducible method to fabricate metallic electrodes with nanometer separation is presented. The fabrication is achieved by passing a large electrical current through a gold nanowire defined by electron-beam lithography and shadow evaporation. The current flow causes the electromigration of gold atoms and the eventual breakage of the nanowire. The breaking process yields two stable metallic electrodes separated by ~1 nm with high efficiency. These electrodes are ideally suited for electron-transport studies of chemically synthesized nanostructures, and their utility is demonstrated here by fabricating single-electron transistors based on colloidal cadmium selenide nanocrystals.
We investigated electron-beam lithography with an aberration-corrected scanning transmission electron microscope. We achieved 2 nm isolated feature size and 5 nm half-pitch in hydrogen silsesquioxane resist. We also analyzed the resolution limits of this technique by measuring the point-spread function at 200 keV. Furthermore, we measured the energy loss in the resist using electron-energy-loss spectroscopy.
We examine the influence of surface and grain-boundary scattering on the total electrical resistivity of copper as dimensions are reduced close to the bulk electron mean free path (39 nm). Through resistivity and grain size characterization on copper wires with sizes down to 95×130 nm2 in a temperature range of 4.2 to 293 K, it was found that the influence of surface scattering is less than previously speculated, while grain-boundary scattering is dominant. A reduction of the background scattering length due to small grains accounts for the observed behavior. The reflection coefficient varies as expected from impurity enrichment in the grain boundaries. © 2004 American Institute of Physics.
A new procedure for analysis of random telegraph signals in time domain has been developed and applied to the analysis of voltage fluctuations in the current induced dissipative state in superconducting thin films. The procedure, based entirely on the difference in the statistical properties of discrete Marcovian telegraph fluctuations and Gaussian background noise, ascribes each point of the experimental time record to one of the telegraph states. The average statistical lifetimes and amplitudes of the telegraph signal are then determined in an iterative way by fitting the amplitude histogram of thus obtained record of the redistributed data to the two-Gaussian histogram of the original experimental signal. The procedure allows for analyzing “noisy” random telegraph signals with low ratio between the signal amplitude and the intensity of the background noise that cannot be analyzed by the classical approach. Separation of the time record into two subrecords relative to two telegraph states also enables in-depth analysis of the spectral properties of the background noise observed together with the telegraph fluctuations. © 2000 American Institute of Physics.
The resistivities of thin metal films and wires are highly sensitive to their polycrystalline structure and surface morphology because grain boundaries and surfaces provide additional scattering sites compared to bulk materials. Here, we investigated polycrystalline gold wires of nanometer-scale diameter that were—at some locations—connected through single grain boundaries. A detailed topography of the wires was recorded by atomic force microscopy. A Pt-coated tip in a conducting atomic force microscopy setup served as a mobile electrode to probe the resistance of a wire. Analyzing the topographical cross section and the resistance data allowed us to evaluate the effective specific resistivity of the wire as well as reflection coefficients of single grain boundaries. © 2002 American Institute of Physics.
We have studied electron transport properties of benzenedithiol and benzenedimethanethiol covalently bonded to gold electrodes by repeatedly creating a large number of molecular junctions. For each molecule, conductance histogram shows peaks at integer multiples of a fundamental conductance value, which is used to identify the conductance of a single molecule. The conductance values of a benzenedithiol and benzenedimethanethiol are 0.011 G0 and 0.0006 G0 (G0 = 2e2/h), respectively. The conductance peaks are broad, which reflects variations in the microscopic details of different molecular junctions. We have also studied electrochemical gate effect.
Gold nanorods with aspect ratios of 4.6 ± 1.2, 13 ± 2, and 18 ± 2.5 (all with 16 ± 3 nm short axis) are prepared by a seeding growth approach in the presence of an aqueous miceller template. Citrate-capped 3.5 nm diameter gold particles, prepared by the reduction of HAuCl4 with borohydride, are used as the seed. The aspect ratio of the nanorods is controlled by varying the ratio of seed to metal salt. The long rods are isolated from spherical particles by centrifugation.
We have investigated the possibility of using carbon nanotubes as flexible, mobile electrical probes able to electrically contact nanometre-scaled objects. Configurations with metal electrodes evaporated on top of multi-, few- and single-wall carbon nanotubes have been studied. Scanning probe manipulation was used to create nano-mechanical switches by first cutting the various tubes, and then moving the parts back into electrical contact. We found multiwall tubes to be best suited as mobile probes, mainly due to their insensitivity to mechanical deformation. Finally, we present an example where the scanning probe manipulation technique has been used to electrically connect two carbon nanotubes to a 7 nm gold particle.
The resistivity of tungsten interconnect structures manufactured by a damascene CVD process was studied for a wide range of line widths (40–1000 nm). A significant electrical size effect was observed: The relative increase reaches values up to 65% for a 50 nm line compared to wide lines. The root cause for the size effect is the reduced mobility of the charge carriers as critical dimensions decrease. For the first time the size effect in tungsten nano-interconnects is studied on the basis of a broad experimental data set. It was found for a temperature range down to 6 K that the size effect is independent of temperature. An excellent fit of the resistivity increase using our size effect model has been obtained. Based on SEM and TEM images a line width dependence of the median grain size was found. The median grain size was used to quantify the modeling parameter for scattering at grain boundaries. For grain boundary scattering a reflection coefficient R of 0.25 was found. For the contribution of surface scattering, the specularity parameter p was 0.3. The bulk value of resistivity and the mean free path of charge carriers were 8.7 μΩ cm and 33 nm.
The use of a scanning force microscope with a metallized tip to do selective area oxidation of silicon is demonstrated. Sub‐100 nm lines have been achieved. Removal of the oxide lines with buffered hydrofluoric acid reveals trenches in the silicon consistent with silicon consumption in SiO 2 formation.
We report on a new atomic force microscope (AFM)-based data storage concept called the “Millipede” that has a potentially ultrahigh density, terabit capacity, small form factor, and high data rate. Its potential for ultrahigh storage density has been demonstrated by a new thermomechanical local-probe technique to store and read back data in very thin polymer films. With this new technique, 30–40-nm-sized bit indentations of similar pitch size have been made by a single cantilever/tip in a thin (50-nm) polymethylmethacrylate (PMMA) layer, resulting in a data storage density of 400–500 Gb/in.<sup>2</sup> High data rates are achieved by parallel operation of large two-dimensional (2D) AFM arrays that have been batch-fabricated by silicon surface-micromachining techniques. The very large scale integration (VLSI) of micro/nanomechanical devices (cantilevers/tips) on a single chip leads to the largest and densest 2D array of 32 × 32 (1024) AFM cantilevers with integrated write/read storage functionality ever built. Time-multiplexed electronics control the write/read storage cycles for parallel operation of the Millipede array chip. Initial areal densities of 100–200 Gb/in.<sup>2</sup> have been achieved with the 32 × 32 array chip, which has potential for further improvements. In addition to data storage in polymers or other media, and not excluding magnetics, we envision areas in nanoscale science and technology such as lithography, high-speed/large-scale imaging, molecular and atomic manipulation, and many others in which Millipede may open up new perspectives and opportunities.
More than a decade after the first report of single-molecule conductance, it remains a challenging goal to prove the exact nature of the transport through single molecules, including the number of transport channels and the origin of these channels from a molecular orbital point of view. We demonstrate for the archetypical organic molecule, benzenedithiol (BDT), incorporated into a mechanically controllable break junction at low temperature, how this information can be deduced from studies of the elastic and inelastic current contributions. We are able to tune the molecular conformation and thus the transport properties by displacing the nanogap electrodes. We observe stable contacts with low conductance in the order of 10(-3) conductance quanta as well as with high conductance values above ∼0.5 quanta. Our observations show unambiguously that the conductance of BDT is carried by a single transport channel provided by the same molecular level, which is coupled to the metallic electrodes, through the whole conductance range. This makes BDT particularly interesting for applications as a broad range coherent molecular conductor with tunable conductance.
(Figure Presented) Atomically smooth gold nanowires with high aspect ratios are grown using the seeded growth process. This allows control of the diameter of the nanowires to a high degree of precision. Two and fourprobe nanoscale transport measurements reveal that the nanowires have low resistivity. Only a small increase in resistivity is observed between diameters of 29 nm and 185 nm suggesting that surface scattering is only a small contribution.
The welding of metals at the nanoscale is likely to have an important role in the bottom-up fabrication of electrical and mechanical nanodevices. Existing welding techniques use local heating, requiring precise control of the heating mechanism and introducing the possibility of damage. The welding of metals without heating (or cold welding) has been demonstrated, but only at macroscopic length scales and under large applied pressures. Here, we demonstrate that single-crystalline gold nanowires with diameters between 3 and 10 nm can be cold-welded together within seconds by mechanical contact alone, and under relatively low applied pressures. High-resolution transmission electron microscopy and in situ measurements reveal that the welds are nearly perfect, with the same crystal orientation, strength and electrical conductivity as the rest of the nanowire. The high quality of the welds is attributed to the nanoscale sample dimensions, oriented-attachment mechanisms and mechanically assisted fast surface-atom diffusion. Welds are also demonstrated between gold and silver, and silver and silver, indicating that the technique may be generally applicable.
A study was conducted to demonstrate a method for investigating ultralong graphene nanoribbons (GNR) and their electrical conductivity. The method investigated graphene-flake deposition based on silicone stamps using optical and atomic force microscopy (AFM) to characterize the flakes. It was demonstrated that ultralong GNRs with a minimum width below 20nm were electrically characterized by conductance AFM. It was observed that additional properties emerged in the graphene when it was reduced to a long nanometer-wide ribbon. It was also demonstrated that crystallographic orientation played a key role in determining the electrical properties of GNRs. A more detailed inspection near these ribbons using AFM and scanning electron microscopy revealed that they were composed of narrower nanoribbons whose widths ranged between ≈20-120 nm. The use of AFM allowed to characterize the thickness of these flakes and nanoribbons that were thin as a single monolayer.
High aspect ratio gold nanowires with single crystalline surface have long been a missing piece in the toolbox of plasmonics metal nanostructures. Such wires are now made with a room temperature, surfactant assisted chemical synthesis in acidic aqueous solution. The diameters and lengths of the multiply twinned gold nanowires can be tuned by varying the amount of seed particles and acid in the growth solution. Nanowires with diameters around 35 nm and lengths up to 10 micron were made with a low seed concentration in pH approximately 1 solution.
A direct-write “dip-pen” nanolithography (DPN) has been developed to deliver collections of molecules in a positive printing
mode. An atomic force microscope (AFM) tip is used to write alkanethiols with 30-nanometer linewidth resolution on a gold
thin film in a manner analogous to that of a dip pen. Molecules are delivered from the AFM tip to a solid substrate of interest
via capillary transport, making DPN a potentially useful tool for creating and functionalizing nanoscale devices.
We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions,
metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between
valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in
concentrations up to 1013 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by
applying gate voltage.
We investigate electronic transport in lithographically patterned graphene ribbon structures where the lateral confinement of charge carriers creates an energy gap near the charge neutrality point. Individual graphene layers are contacted with metal electrodes and patterned into ribbons of varying widths and different crystallographic orientations. The temperature dependent conductance measurements show larger energy gaps opening for narrower ribbons. The sizes of these energy gaps are investigated by measuring the conductance in the nonlinear response regime at low temperatures. We find that the energy gap scales inversely with the ribbon width, thus demonstrating the ability to engineer the band gap of graphene nanostructures by lithographic processes.