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Introduction
1. Synthesis and patterning of Cd-Free III-V QDs
2. QD-LEDs
3. TMDC based on electronic and optoelectronic devices.
Additional affiliations
November 2007 - June 2012
Publications
Publications (76)
Challenges in the development of a multi-level memory device for multinary arithmetic computers have posed an obstacle to low-power, ultra-high-speed operation. For the effective transfer of a huge amount of data between arithmetic and storage devices, optical communication technology represents a compelling solution. Here, by replicating a floatin...
The 2D–0D hybrid photodetector, with its special structure, high sensitivity, and wavelength tunability, is reported as a promising candidate system for optoelectronic devices. As research on hybrid lead halide perovskite quantum dots (PQDs) has progressed, PQDs with high photoluminescence (PL) quantum yield and excellent absorption properties are...
Atomically thin 2D transition metal dichalcogenides (TMDs) have recently been spotlighted for next‐generation electronic and photoelectric device applications. TMD materials with high carrier mobility have superior electronic properties different from bulk semiconductor materials. 0D quantum dots (QDs) possess the ability to tune their bandgap by c...
While two-dimensional transition metal dichalcogenides (TMDs) are promising building blocks for various optoelectronic applications, limitations remain for multilayered TMD-based photodetectors: an indirect bandgap and a short carrier lifetime by strongly bound excitons. Accordingly, multilayered TMDs with a direct bandgap and an enhanced carrier l...
The probing of fundamental photophysics is a key prerequisite for the construction of diverse optoelectronic devices and circuits. To date, though, photocarrier dynamics in two-dimensional materials remains unclear, plagued primarily by two issues: a large exciton binding energy, and the lack of a suitable system that enables the manipulation of ex...
Heterojunction structures using 2D materials are promising building blocks for electronic and optoelectronic devices. The limitations of conventional silicon photodetectors and energy devices are able to be overcome by exploiting quantum tunneling and adjusting charge balance in 2D p–n and n–n junctions. Enhanced photoresponsivity in 2D heterojunct...
0D-2D hybrid optoelectronic devices have demonstrated high sensitivity and high performance due to high absorption coefficient of 0D materials with a tunable detection range and high carrier transport property of 2D materials. However, the reported 0D-2D hybrid devices employ toxic nanomaterials as sensitizing layers, which can limit the practical...
Semiconductor p–n junctions are building blocks for optoelectronic devices. Recently, p–n junction devices based on 2D transition metal dichalcogenides (TMDCs) have been demonstrated in optoelectronic applications due to their thin thickness, flexibility, high carrier mobility, and high light‐absorption properties. To fabricate 2D semiconductor p–n...
Plenty of chalcogenide families with tremendous potential for functional applications remain unexplored due to the limi-tations of conventional synthesis methods. However, cation exchange reactions in colloidal synthesis offer an alternative way to overcome these limitations and provide a route to synthesize pure phases and morphologies that otherw...
2D van der Waals materials are promising for various electronic and optoelectronic devices because of their thickness‐dependent mobility and tunable bandgap. Recently, heterojunction structures based on 2D van der Waals materials have exhibited their potential for photovoltaic applications as ultrathin p–n diodes. In this study, the photovoltaic ef...
Few-layer black phosphorus has shown great potential for next-generation electronics with tunable band gap and high carrier mobility. For the electronic applications, the thickness modulation of a BP flake is an essential due to its thickness-dependent electronic properties. However, controlling the precise thickness of few-layer BP is a challenge...
Recently, black phosphorus (BP) with direct band gap exhibited excellent potential for optoelectronic applications due to its high charge carrier mobility and low dark current as well as the variable band gap of 0.3 eV to 1.5 eV depending on the number of layers. However, few-layer BP-based phototransistors (photo-FETs) have been limited in sensiti...
Two-dimensional black phosphorus (BP) has attracted much attention recently because of its applicability in high-performance electronic and optoelectronic devices. BP field-effect transistors (FETs) with a tunable bandgap (0.3–1.5 eV) have demonstrated a high on-off current ratio and a high hole mobility with ambipolar behavior in global-gated devi...
Black phosphorus (BP) has drawn enormous attention for both intriguing material characteristics and electronic and optoelectronic applications. In spite of excellent advantages for semiconductor device applications, the performance of BP devices is hampered by the formation of phosphorus oxide on the BP surface under ambient conditions. It is thus...
We report a new family of inorganic ligands, namely, transition metal-based thiometallates, for the surface functionalization of colloidal nanocrystals (NCs). We synthesized Pt-, Fe-, Co-, and Ni-based thiometallates, in which transition metal ions were complexed with polysulfides. These inorganic anions easily exchanged the surface organic ligands...
Synthesis of cadmium (Cd)-free quantum dots (QDs) with tunable emission and high color purity has been a big challenge for the academic and industrial research community. Among various Cd-free QDs, indium phosphide (InP) QDs exhibit reasonably good color purity with emission full width at half-maximum (fwhm) values between 45 and 50 nm for green an...
Recently, metal halide perovskite nanocrystals have demonstrated outstanding properties in various optoelectronic applications. Cesium lead halides (CsPbX3) are the most studied perovskites in nanoscale dimensions. However, halide perovskite nanocrystals with other cations have rarely been reported. It is important to develop new perovskite composi...
In this communication, we present a new synthesis method for the fabrication of hybrid metal-Cu2S (M = Pt, FePt) nanocrystals (HNs). The metal-Cu2S HNs were investigated in photocatalytic hydrogen generation as effective co-catalysts on TiO2. The Pt-Cu2S/TiO2 catalyst showed a higher hydrogen generation rate compared with a pure TiO2 catalyst. This...
2-Dimensional (2D) and 0-dimensional (0D) hybrid nanostructures have been reported as promising new systems for highly-sensitive and wavelength-tunable photodetectors. Although the performance of hybrid photodetectors was enhanced by charge injection from 0D nanocrystals (NCs) to 2D nanosheets (NSs), the response time of hybrid photodetectors is st...
We demonstrate that the presence of a small amount of water as an impurity during the hot-injection synthesis can significantly decrease the emission lines full width at half-maximum (FWHM) and improve the quantum yield (QY) of InP/ZnS quantum dots (QDs). By utilizing the water present in the indium precursor and solvent, we obtained InP/ZnS QDs em...
In this study, the strategy of using an organic-inorganic hybrid planar heterojunction consisting of polymeric semiconductors and inorganic nanocrystals is introduced to realize a high-performance hybrid photodiode (HPD) with low dark current and high detectivity. To prevent undesired charge injection under the reverse bias condition, which is the...
We demonstrate a highly sensitive hybrid photodetector based on graphene-CsPbBr3-xIx perovskite nanocrystals. This hybrid photodetector exhibits a high photo-responsivity of ∼10⁸ A W⁻¹ and detectivity of ∼10¹⁶ jones at an irradiance power of 0.07 μW cm⁻² under 405 nm illumination.
Herein, we describe simple, fast and reproducible halide ion exchange reactions in CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) at room temperature. Through the simple adjustment of the halide ion concentration, the photoluminescence of these NCs can be tuned over the entire visible region (425-655 nm). Photodetector devices based on entirely inorgani...
We report the synthesis of 2D nanosheets of GeS and GeSe by facile solution based approaches. The synthesized nanosheets are single-crystalline in nature with lateral dimensions in micrometers. Band structures calculated from DFT calculations predicted a direct bandgap value of 1.67 and 1.37 eV for GeS and GeSe, respectively. The experimental bandg...
Copper based ternary and quaternary semiconductor nanostructures are of great interest for the fabrication of low cost photovoltaics. Although well-developed syntheses are available for zero dimensional (0D) nanoparticles, colloidal synthesis of two dimensional (2D) nanosheets remains a big challenge. Here we report, for the first time, a simple an...
We report the improvement of a CdSe quantum-dot-sensitized solar cell (QDSSCs) based on surface modification of Cu2S nanoparticle counter-electrode (CE). In this work, we explored a low-cost, easy method to fabricate counter electrodes by direct deposition of colloidal Cu2S NCs on conducting FTO glass using drop casting or spin coating. The colloid...
We demonstrate an approach to enhance the photosensitivity of an organic single-crystal photodetector by combining it with a nanocrystal (NC) array. A systematic study of the dependence of the photodetector performance on illumination wavelength and light power together with the charge carrier mobility reveals that charge separation at the single-c...
Nanostructured Bi1-xSbx alloys constitute a convenient system to study charge transport in a nanostructured narrow-gap semiconductor with promising thermoelectric properties. In this work, we developed the colloidal synthesis of monodisperse sub-10 nm Bi1-xSbx alloy nanocrystals (NCs) with controllable size and compositions. The surface chemistry o...
We report a colloidal synthesis and electrical and magnetotransport properties of multifunctional “magnet-in-the-semiconductor” nanostructures composed of FePt core and CdSe or CdS shell. Thin films of all-inorganic FePt/CdSe and FePt/CdS core–shell nanostructures capped with In2Se42– molecular chalcogenide (MCC) ligands exhibited n-type charge tra...
In this work we synthesized InP and InAs nanocrystals (NCs) capped with different inorganic ligands, including various molecular metal chalcogenide complexes (MCCs) and chalcogenide ions. We found that MCCs and chalcogenide ions can quantitatively displace organic ligands from the surface of III-V NCs and serve as the inorganic capping groups for I...
High-mobility solution-processed all-inorganic solid state nanocrystal (NC) transistors with low operation voltage and near-zero hysteresis are demonstrated using high-capacitance ZrO(x) and hydroxyl-free Cytop gate dielectric materials. The use of inorganic capping ligands (In(2)Se(4)(2-) and S(2-)) allowed us to achieve high electron mobility in...
We report a new platform for design of soluble precursors for CuInSe(2) (CIS), Cu(In(1-x)Ga(x))Se(2) (CIGS), and Cu(2)ZnSn(S,Se)(4) (CZTS) phases for thin-film potovoltaics. To form these complex phases, we used colloidal nanocrystals (NCs) with metal chalcogenide complexes (MCCs) as surface ligands. The MCC ligands both provided colloidal stabilit...
All-inorganic colloidal nanocrystals were synthesized by replacing organic capping ligands on chemically synthesized nanocrystals with metal-free inorganic ions such as S(2-), HS(-), Se(2-), HSe(-), Te(2-), HTe(-), TeS(3)(2-), OH(-) and NH(2)(-). These simple ligands adhered to the NC surface and provided colloidal stability in polar solvents. The...
Flexible, thin-film electronic and optoelectronic devices typically involve a trade-off between performance and fabrication cost. For example, solution-based deposition allows semiconductors to be patterned onto large-area substrates to make solar cells and displays, but the electron mobility in solution-deposited semiconductor layers is much lower...
We developed different strategies toward the synthesis of colloidal nanocrystals stabilized with molecular metal chalcogenide complexes (MCCs). Negatively charged MCCs, such as SnS(4)(4-), Sn(2)S(6)(4-), SnTe(4)(4-), AsS(3)(3-), MoS(4)(2-), can quantitatively replace the organic ligands at the nanocrystal surface and stabilize nanocrystal solutions...
The energy efficiency of heat engines could be improved by the partial recovery of waste heat using thermoelectric (TE) generators. We show the possibility of designing nanostructured TE materials using colloidal inorganic nanocrystals functionalized with molecular antimony telluride complexes belonging to the family of Zintl ions. The unique advan...
We report a synthesis of colloidal nanostructures combining a magnetic material (FePt) with a narrow-gap semiconductor (PbS and PbSe) in form of core-shells or nanodumbbells and explore their optical, magnetic, electrical, and magnetotransport properties. The arrays of "magnet-in-the-semiconductor" nanostructures show semiconductor-type transport p...
The inorganic Nanocrystals (NCs) which have witnessed a tremendous development in the past decade, with novel synthesis strategies discovered for metallic, semiconducting, and magnetic materials has been reported. Significant success has been achieved in the synthesis of NCs of different technologically important semiconductors. Selective adhesion...
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The contact potential between a single ZnO nanowire and Ti/Au contacts was estimated to be ∼30 meV by considering the Arrhenious
plot of the two-probe resistance, the thermionic emission conduction, and the Fowler–Nordheim tunneling model. The net voltages
applied to the contacts were calculated by subtracting the four-probe voltages from the two-p...
We present a comparative study of optical and electronic properties for PbS nanocrystals and Au-PbS core-shell nanostructures. In Au-PbS nanostructures, we observed two nontrivial synergistic effects: (i) extinction enhancement due to coupling of surface plasmon resonance in the Au core to the excitonic states in the semiconducting PbS shell, and (...
We examine the effect of strong three-dimensional quantum confinement on the thermopower and electrical conductivity of PbSe nanocrystal superlattices. We show that for comparable carrier concentrations PbSe nanocrystal superlattices exhibit a substantial thermopower enhancement of several hundred microvolts per Kelvin relative to bulk PbSe. We als...
We have measured the local resistances in the arms and at the junction in a ZnO tetrapod separately by means of ac impedance spectroscopy. The resistance at the junction is found to be even greater than that in the arms although a volume fraction of the junction is negligibly small compared to that of the arms. This result clearly demonstrates that...
Thin films assembled of solution-processed PbSe nanocrystals have a thermopower 2 -- 3 times greater than bulk PbSe. In addition, the thermopower and electrical conductivity both exhibit a size-dependence on nanocrystal size. As the nanocrystal diameter changes from 4 to 9 nm, the thermopower and electrical conductivity change from 850 to 650 muV/K...
A direct calorimetric measurement of the dependence of the surface enthalpy of nanophase ZnO on morphology is reported. Nanoparticles, nanoporous composites, nanorods, and nanotetrapods were prepared with various sizes, and their surface enthalpies were derived from their drop solution enthalpies in molten sodium molybdate. Water adsorption calorim...
A solution-phase synthesis of monodisperse SnTe nanocrystals via the reaction of bis[bis(trimethylsilyl)amino]tin(II) with trioctylphosphine telluride in oleylamine is demonstrated. The obtained SnTe nanocrystals are single-crystalline particles with a cubic rock-salt crystal structure. The size of the SnTe nanocrystals can be precisely tuned in th...
We have recently reported fabrication of ZnO nanobridge devices using a single-step thermal evaporation method. In this fabrication process, we completely eliminated the need of either any metal catalysts or a ZnO seed layer to synthesize the ZnO nanobridges. As initially postulated, the morphology of an anisotropic crystalline substrate alone defi...
Self-assembly of chemically-synthesized nanocrystals can yield complex long-range ordered structures which can be used as model systems for studying transport phenomena in low-dimensional materials [1]. Treatment of close-packed PbSe nanocrystal arrays with hydrazine enhanced exchange coupling between the nanocrystals and improved conductance by mo...
A direct experimental evidence of electron accumulation in the grain boundary of yttria-doped (2.44 and 6.29 mol %) zirconia ceramics with the grain size of about 30 nm is demonstrated. Upon introducing extra electrons into the 2.44 mol % yttria-doped sample by reduction, its specific grain boundary resistivity decreased significantly compared with...
Well-aligned single crystalline ZnO nanobridges have been synthesized selectively across the prefabricated electrodes on silicon substrates by a single-step thermal evaporation method without using any metal catalysts or a predeposited ZnO seed layer that was a prerequisite for such synthesis. The growth region was self-defined by the anisotropic s...
Single crystalline In2O3 nanowires have been synthesized by thermal evaporation of ball-milled In2O3 powders without any catalysis. The diameter and length range of the synthesized In2O3 nanowires are about 25 nm and 20-30 mum, respectively. Their X-ray diffraction pattern is indexed to bcc structure with a lattice constant of a=1.0126 nm. High-res...
Four-probe device of single ZnO nanowire was fabricated by electron beam lithography. Electrical characterizations in a two-probe and a four-probe configuration with a back-gate were carried out to clarify the relative contribution of the contact and the intrinsic part in a ZnO nanowire. I-V characteristic in four-probe measurement showed an ohmic...
Lead oxide nanotubes filled partially with lead were synthesized by a simple thermal evaporation on Si(100) substrates without any catalysts. The inner diameter, wall thickness, and length of the nanotubes were 10–40nm, 5–7nm, and 2–10μm, respectively. Selected area electron diffraction patterns obtained from these nanotubes revealed that the lead...
We report the sonochemical synthesis of mercury telluride (HgTe) nanoparticles and the photocurrents of these nanoparticles and their organic hybrid system. The HgTe nanoparticles were about 5 nm in size and their lattice structure was cubic. Poly(N-vinylcarbazole)(PVK) was added to the HgTe nanoparticles for the formation of an inorganic(HgTe)-org...
Structural and optical properties of as-synthesized, Ga2O3-coated, and Al2O3-coated GaN nanowires are examined in this paper. GaN nanowires were synthesized by thermal evaporation of ball-milled GaN powders in an NH3 atmosphere. The thermal annealing of the as-synthesized GaN nanowires in an argon atmosphere allows their surfaces to be oxidized, le...
The dark current, photocurrent and photoluminescence (PL) of networked GaN nanowires were characterized in this study. GaN nanowires were synthesized from Ni particles dispersed on an alumina substrate, and subsequent Ti deposition was performed on the as-synthesized GaN nanowires to form electrodes. For the networked GaN nanowires, a significant d...
Structural and optoelectronic properties of as-synthesized SnO2 nanowires were examined in this study. The SnO2 nanowires were first synthesized by thermal evaporation of ball-milled SnO2 powders in argon atmosphere without the presence of any catalysts, and their structural properties are then investigated by X-ray diffraction, Raman scattering, s...
Structural and optoelectronic properties of as-synthesized SnO_2 nanowires were examined in this study. The SnO_2 nanowires were first synthesized by thermal evaporation of ball-milled SnO_2 powders in argon atmosphere without the presence of any catalysts, arid their structural properties are then investigated by X-ray diffraction, Raman scatterin...
Structural and optical properties of as-synthesized, Ga_2O_3-coated, and Al_2O_3-coated GaN nanowires are examined in this paper. GaN nanowires were synthesized by thermal evaporation of ball-milled GaN powders in an NH_3 atmosphere. The thermal annealing of the as-synthesized GaN nanowires in an argon atmosphere allows their surfaces to be oxidize...
ZnO nanorods were grown on SiO2/Si substrates by a sol-gel method at low temperatures of around T = 95 °C. The diameters and the lengths of ZnO nanorods increased at high concentrations of zinc nitrate hexahydrate and methenamine solution. Current–voltage characteristics of the ZnO nanorods network followed a typical nonlinear behavior with signifi...
ZnO nanowires were grown between two Au electrodes on an Al2O3-deposited Si wafer. Photoresponse, photoresponse spectrum, and current–voltage (I–V) studies were performed for the investigation into photoconduction mechanism in these nanowires. The photoresponse of the nanowires under the continuous illumination of light with above- or below-gap ene...
Transmuted isotopes doped in neutron-irradiated ZnO thin films were first identified on the basis of nuclear reactions of ZnO with thermal neutrons, and their existence in the ZnO thin films was then confirmed by photoluminescence (PL). ZnO thin films were irradiated by neutron beams at room temperature. The ZnO films consist of eight constituent (...
Photoluminescence, absorption, and photocurrent measurements were made for a hybrid system of 1-thioglycerol-capped HgTe nanoparticles synthesized by colloidal method to investigate the photocurrent mechanism in this hybrid system. Absorption and photoluminescence spectra taken for the capped HgTe nanoparticles reveal strong exciton peaks in the ne...
The GaN, GaP, InP, Si3N4, SiO2/Si, SiC, and ZnO semiconductor nanowires were synthesized by a variety of growth methods, and they were wrapped cylindrically
with amorphous aluminum oxide (Al2O3) shells. The Al2O3 was deposited on these seven different semiconductor nanowires by atomic layer deposition (ALD) at a substrate temperature
of 200°C using...
ZnO nanobelts, nanorods, and nanowires were synthesized at three different substrate temperatures from the thermal evaporation of ball-milled ZnO powders at 1380^{\circ}C. Transmission electron microscopy (TEM) revealed that the ZnO nanobelts are single crystalline with the growth direction perpendicular to the (010) lattice planes, and that the Zn...
Three different ZnO nanomaterials (nanobelts, nanorods, and nanowires) were synthesized at three different substrate temperatures from the thermal evaporation of ball-milled ZnO powders at 1380°C. Transmission electron microscopy revealed that the ZnO nanobelts are single crystalline with the growth direction perpendicular to the lattice planes, an...
Photocurrent mechanism in a hybrid system of 1-thioglycerol and HgTe quantum dots(QDs) was studied for the first time in the intra-red (IR) range. 1-thioglycerol-capped HgTe QDs were prepared using colloidal method in aqueous solution; the synthesis and size of the HgTe QDs were examined by x-ray diffraction, Raman scattering, and high-resolution t...
ZnO nanowires were synthesized at 1380°C from ball-milled ZnO powders by a thermal evaporation procedure with argon carrier gas without any catalysts. Scanning electron microscopy revealed that the typical diameter and length of the ZnO nanowires are in the uniform ranges of 15 to 40 nm and 10 to 70 mum, respectively. Transmission electron microsco...
Ga2O3 nanomaterials were synthesized from mechanically ground GaN powders with thermal annealing; Ga2O3 nanobelts were formed in a nitrogen atmosphere, while Ga2O3 nanoparticles were formed in an oxygen atmosphere. The structural properties of the Ga2O3 nanomaterials were investigated by X-ray diffractometer (XRD) and high-resolution transmission e...
The study presents a new testing and analysis method for brake judder on vehicle. For the identification of the excitation mechanism of a brake judder, it is necessary to measure the dynamic brake disc geometry during braking on vehicle. The non-contact sensor system was used to monitor the brake disc geometry. Brake torque variation (BTV) caused b...
Ga 2 O 3 nanomaterials were synthesized from mechanically ground GaN powders with thermal annealing; Ga 2 O 3 nanobelts were formed in a nitrogen atmosphere, while Ga 2 O 3 nanoparticles were formed in an oxygen atmosphere. The structural properties of the Ga 2 O 3 nanomaterials were investigated by X-ray diffractometer (XRD) and high-resolution tr...
