CdS Nanowires Research Articles

Catalyst- and template-free low-temperature in situ growth of n-type CdS nanowire on p-type CdTe film and p-n heterojunction properties.

CdS is an important semiconductor used in optoelectronic devices. Simple techniques for growing CdS nanostructures are thus essential at a low cost. This study presents a novel method for growing single-crystal n-type CdS nanowires on p-type CdTe films by thermal annealing in an H2S/N2 mixed gas flow, which does not require the help of a catalyst or template. The formation process and growth mechanism of the nanowires are investigated. Well-dispersed whiskerlike CdS nanostructures are obtained at an appropriate annealing temperature and duration. We suggest that the stress-driving mechanism of nanowire formation may contribute to the growth of CdS nanowires, and that the evaporation of Te through the boundaries of the CdS grain seeds plays an important role in the sustainable growth of nanowire. In addition, CdS/CdTe heterojunction device is fabricated on Mo glass. The I-V characteristic of the heterojunction in dark shows typical rectifying diode behavior. The turn-on voltage can be regulated by annealing conditions. Meanwhile, the obvious photovoltaic effect is obtained on the in situ growth heterojunction prepared at low annealing temperature. Hence, this is a new fabricated method for CdTe-based materials in the field of energy conversion.

Insights into photo-activated electrode for boosting electrocatalytic methanol oxidation based on ultrathin MoS2 nanosheets enwrapped CdS nanowires

In this paper, a new and high-performance visible-light-activated electrode is designed in terms of two dimensional (2D) MoS2 nanosheets enwrapped 1D CdS nanowires as photo-activated support for depositing Pt nanoclusters. Compare to traditional ambient electrocatalytic process, the as-prepared photo-activated electrode shows evidently improved electrocatalytic activity and stability of methanol oxidation reaction (MOR) under visible light illumination. The efficient interfacial electron transfer from the excited CdS moieties to the decorated ultrathin MoS2 shell contributes to the synergistic effect of photocatalytic and electrocatalytic process for the boosting of catalytic efficiency.

Shape-Controlled Assembly of Nanowires for Photonic Elements

We fabricated a single U-shaped nanowire (NW) and tangent-coupled straight and U-shaped NWs using a novel technique of shape-controlled deterministic assembly of NWs with nanoscale controllability. To examine the optical properties of these structures, we calculated the transmitted and crossover optical powers of the fundamental guided mode in both the single and coupled CdS NWs by varying the key structural parameters such as the radius of curvature of the U-shaped head and the gap between the NWs. In addition, we experimentally studied active waveguiding in the assembled CdS NWs, which exhibited light coupling to the waveguide mode and direct transmission in the single U-shaped NW. Furthermore, the crossover coupling was measured for the tangent-coupled straight and U-shaped CdS NWs with a gap width of 70 nm. The shape-controlled deterministic assembly technique can open up a new opportunity to demonstrate subwavelength-scale photonic waveguides and couplers in compact nanophotonic integrated circuits.

Light-induced electrochemical performance of 3D- CdS nanonetwork: Effect of annealing

Present investigation focused on the fundamental understanding regarding the tailoring of photovoltaic (PV) device efficiency of 3D-CdS nanonetwork through annealing with the aid of electrochemical studies. The synthesis of CdS nanowires (NWs) have been performed using Cd(OH)2 NWs as intermediate sacrificial templates based on negative free energy of formation. The changes in structure, morphology and optical properties of CdS by annealing have been studied. The enhancement in crystallite size by annealing was correlated to the negative shift of the conduction band position, charge transport and electron life time towards PV performance. These have been performed by studying lattice parameters which in turn correlated to the capacitance, external quantum efficiency and impedance analysis through light-induced electrochemical studies.

Tunable emission and conductivity enhancement by tellurium doping in CdS nanowires for optoelectronic applications

Improvement of the optical and electrical characteristics is essential to get advanced performance from one dimensional (1D) material. Here, we report the first synthesis of a single crystalline Te-doped CdS nanowires (NWs) by a chemical-vapor-deposition (CVD) method. Room temperature photoluminescence (PL) spectra showed that Te concentration plays an important role in tuning emission color from orange to infrared (IR). Decrease in bandgap and PL intensity with increase in Te concentration was observed as compared to undoped CdS NWs. Red and IR emissions were found at 736.5 and 881nm for doping concentration >6.06%. To our best knowledge, IR emission band has been observed for the first time in CdS NWs. Red-shift of LO phonon mode and its overtone in Raman spectra, and lifetime of red and IR emissions are longer than bandgap of host indicating the doping effect of CdS NWs. Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) of the Te-doped CdS NWs further confirms the presence of Te in the CdS NWs. Output characteristics confirm enhanced output current Ids with the increase in doping concentration. A possible growth mechanism was proposed. Doping technique offers to develop high-quality, a very stable, effective, and easily-applicable way to enhance the performance of one dimensional optoelectronic devices and solar cell applications.

Magnetic MoS2 Interface Monolayer on a CdS Nanowire by Cation Exchange

MoS2 atomic layers have recently attracted much interest because of their two-dimensional structure as well as tunable optical, electrical, and mechanical properties for next generation electronic and electro-optical devices. Here we have achieved facile fabrication of MoS2 thin films on CdS nanowires by cation exchange in solution at room temperature and importantly observed their extraordinary magnetic properties. We establish the atomic structure of the MoS2/CdS heterostructure by taking atomic images of the MoS2/CdS interface as well as performing first-principles density functional geometry optimizations and STEM-ADF image simulations. Furthermore, our first principles density functional calculations for the MoS2/CdS heterostructure reveal that the magnetism in the MoS2/CdS heterostructure stems from the ferromagnetic MoS2 monolayer next to the MoS2/CdS interface. The ferromagnetism is attributed to the partial occupation of the Mo dx2-y2/dxy conduction band in the interfacial MoS2 monolayer caused by the mixed covalent-ionic bonding among the MoS2 and CdS monolayers near the MoS2/CdS interface. The present findings of the ferromagnetic MoS2 monolayer with large spin polarization at the MoS2-semiconductor interface suggest a new route for fabrication of the transition metal dichalcogenide-based magnetic semiconductor multilayers for applications in spintronic devices.

In-situ Growth of Ultrathin ZIF-67 Nanosheets on Conductive Ti@TiO2/CdS Substrate for High-efficient Electrochemical Catalysis

Efficient charge transport is a key to the successful design of electrocatalyst. In this work, we report the in-situ growth of ultrathin MOF material (ZIF-67) nanosheets on conductive Ti@TiO2/CdS substrate for high-efficient electrochemical catalysis due to optimized charge transport. The ultrathin ZIF-67 nanosheets were grown on Ti@TiO2/CdS nanowire array substrates resulting unique 3D hierarchical structures, which were investigated as electrocatalyst for the oxygen-evolution reaction (OER) and H2O2 oxidation. The nanowire-supported ZIF-67 nanosheet electrode shows remarkable electrocatalytic activity and excellent stability toward OER and H2O2 oxidation, which can be explained by the rapid electron transport along the 1D Ti@TiO2/CdS nanowire to Ti substrates, large electrochemical active surface area and the rising valence state of Co ions induced by electronegative N atom in imidazole ligands. Compared with other MOFs catalysts, we obtained a very small Tafel slope (42mV/dec) and a small overpotential (0.41V) at 10mAcm−2 for OER. When used for H2O2 detection, the electrode gave a high sensitivity of 1214.3μAmM−1cm−2, a wide linear range of 5μM–14mM and a low detection limit of 1.11μM. This research suggests that the in-situ grown nanostructure of Ti@TiO2/CdS/ZIF-67 hold great promise for advanced electrocatalytic electrode in water oxidation and H2O2 detection.

Bosonic Lasing from Collective Exciton Magnetic Polarons in Diluted Magnetic Nanowires and Nanobelts

Exciton magnetic polarons (EMPs) are self-organized magnetic quasiparticles that can be formed by excitons in diluted magnetic semiconductors (DMSs). The optical response of EMPs in DMS microstructures is not yet well understood because it is affected by many competing factors, including spin-dependent exchange interactions, phonon coupling, and collective and nonlinear effects upon the dopant concentration and structural relaxation. Here, we report on lasing from collective EMP states in Co(II)-doped CdS nanowires (NWs) and nanobelts (NBs) that we interpret in terms of bosonic lasing, the spontaneous emission of radiation by a single quantum state macroscopically populated by bosonic quasiparticles. The lasing threshold coincides with the appearance of ferromagnetic domains, indicating an important role of spin ordering in the formation of coherent collective EMPs. These results pave the way to the realization of a new type of bosonic laser, different from exciton-polariton lasers, where formation of the...

Geometry dependent structural and electronic properties of CdS nanowires: An ab-inito study

Cadmium sulphide nanowires in wurtzite hexagonal and triangular shape have been investigated using density functional theory based ab initio approach. Stability of these nanowires increases with enlarging diameter, evaluated in terms of formation energies. The increase in diameter of these geometric nanowires, reduces the bandgap, however increases the electronic charge carrier mobility. Electron difference density contour analysis reveal almost similar distribution of charges over diametrically large triangular and hexagonal nanowires. These observations further verified for almost same effective mass of negative and positive charge carriers along the length of large diameter nanowires and may be considered for their use in solar cells and Gas/chemical sensors.

Dynamic application of novel electro-optic switchable device modulation by graphene oxide dispersed liquid crystal cell assembling CdS nanowires

In nanotechnology, the novel creation of nanostructures consistently feeds back into efforts to fabricate novel complex hybrid nanomaterials. Two-dimensional graphene oxide dispersed liquid crystalline materials (GDLC) module assembled with CdS nanowires(NW's) have received widespread unprecedented attention due to their exceptional mechanical, electrical, thermal properties. However, making macroscopic graphene oxide (GO) sheets with average diameter 2.1 μm, CdS nanowires (15–20 nm) requires novel technology to fabricate few layered graphene oxide (FGO)-sheets were uniformly distributed as macroscopically ordered structures. Aqueous GDLC-CdS nanowires are continuously twist to obtain macroscopic GO-sheets. Subsequently chemical reduction gave first macroscopic neat graphene sheets with high conductivity and good mechanical performance. Liquid crystal formation is the most viable approach to produce macroscopic, periodic self-assembled materials from oriented graphene sheets. We discovered well-soluble FLG-sheets can exhibit nematic liquid crystallinity into Dimethyl sulfoxide (DMSO), first established isotropic-nematic solid phase diagram demonstrated by optical microscopy textural evidences of switching and relevant spectroscopic characterizations. GO utilizes light absorption and nanoscale heat source to thermally induced phase transition with LC from homogeneous alignment to isotropic phase. Thus, volume contraction occurred over the surface area of the GDLC-nanowires hybrid complex module due to photothermal effect. Thus, an excellent conductor as well as high contrast electro-optic switchable cell also deserves most promising applications. These novel findings shed focus on microscopically assembled graphene-LC based semiconductor nanomaterial's textural phase behavior, which can only be realized as the field moves forward and makes more significant advances.

One-dimensional CdS@MoS2 core-shell nanowires for boosted photocatalytic hydrogen evolution under visible light

The well-defined one-dimensional (1D) CdS@MoS2 (CM) core-shell nanowires are constructed by employing CdS nanowires (CdS NWs) as nanobuilding blocks via a facile hydrothermal strategy. The synergistic interaction, stemming from the large and intimate coaxial interfacial contact between MoS2 thin shell and 1D CdS core, can efficiently retard the charge carrier recombination and the MoS2 as noble-metal-free cocatalyst enriches the active sites for H2 evolution from water. Consequently, in comparison to bare CdS nanowires, the resultant 1D core-shell CM composite exhibits distinctly enhanced visible light activity for the evolution of H2. Notably, the activity of 1D CM with the optimized 2wt% of MoS2 exceeds that of pure CdS and CdS–1wt% Pt composite by a factor of 64 and 4 times, respectively, under identical reaction conditions, while the apparent quantum yield (A.Q.Y.) at 420nm over 1D CM reaches 28.5%. This work provides a simple paradigm for facile and finely controlled synthesis of well-shaped 1D-based composite photocatalysts towards boosted solar energy conversion.

High‐Performance Ferroelectric Polymer Side‐Gated CdS Nanowire Ultraviolet Photodetectors

An efficient ferroelectric‐enhanced side‐gated single CdS nanowire (NW) ultraviolet (UV) photodetector at room temperature is demonstrated. With the ultrahigh electrostatic field from polarization of ferroelectric polymer, the depletion of the intrinsic carriers in the CdS NW channel is achieved, which significantly reduces the dark current and increases the sensitivity of the UV photodetector even after the gate voltage is removed. Meanwhile, the low frequency noise current power of the device reaches as low as 4.6 × 10−28 A2 at a source‐drain voltage Vds = 1 V. The single CdS NW UV photodetector exhibits high photoconductive gain of 8.6 × 105, responsivity of 2.6 × 105 A W−1, and specific detectivity (D*) of 2.3 × 1016 Jones at a low power density of 0.01 mW cm−2 for λ = 375 nm. In addition, the spatially resolved scanning photocurrent mapping across the device shows strong photocurrent signals near the metal contacts. This is promising for the design of a controllable, high‐performance, and low power consumption ultraviolet photodetector.

Statistically Analyzed Photoresponse of Elastically Bent CdS Nanowires Probed by Light-Compatible In Situ High-Resolution TEM.

We demonstrate that high resolution transmission electron microscopy (HRTEM) paired with light illumination of a sample and its electrical probing can be utilized for the in situ study of initiated photocurrents in free-standing nanowires. Morphology, phase and crystallographic information from numerous individual CdS nanowires is obtained simultaneously with photocurrent measurements. Our results indicate that elastically bent CdS nanowires possessing a wurtzite structure show statistically unchanged values of ON/OFF (photocurrent/dark current) ratios. Photocurrent spectroscopy reveals red shifts of several nanometers in the cutoff wavelength after nanowire bending. This results from deformation-induced lattice strain and associated changes in the nanowire band structure, as confirmed by selected area electron diffraction (SAED) analyses and density functional tight binding (DFTB) simulations. The ON/OFF ratio stabilities and photocurrent spectroscopy shift of bent CdS nanowires are important clues for future flexible electronics, optoelectronics, and photovoltaics.

Turning the n-Type CdS to p-Type CdS Nanowires By Surface Charge Transfer Doping

One-dimensional semiconductor nanostructure has been attracted great attention in electronic and optoelectronic applications in recent years. N-type CdS nanowires (NWs) doped with gallium were synthesized via chemical vapor deposition method[ 1 ]. In contrast to have n-type doping for CdS, p-type doping is relatively difficult to achieve due to the strong self-compensation [ 2,3 ]. In this work, we emonstrated the p-type doping of CdS NWs can be achieved by coating ~ 100 nm MoO3 onto CdS surface. Owing to the large work function of MoO3, the electrons in CdS are transfer to MoO3 and CdS exhibits the p-type characteristics, this process is called surface charge transfer doping. The charge transfer process was analyzed by X-ray photoelectron spectroscopy. MoO3-coated CdS NWs were then confirmed to be p-type by the back-gate field-effect transistors (FETs). Fig. 1(a) shows the optical microscopy image of back-gate Ga-doped CdS NW FET device. Fig. 1(b) depicts drain current (Id) versus drain voltage (Vd) at gate voltages (Vg) ranging from -30 V to 30 V at room temperature, it reveals typical n-type behavior. Besides, the transfer characteristic curves (Id-Vg) of Ga-doped CdS NW and MoO3-coated CdS NW devices shown in Fig. 1(c) as black and red curves, respectively. It is obvious that Ga-doped CdS NW reveals p-type characteristic after MoO3 layer coating. Finally, the MoO3-coated CdS/CdS NW junction photovoltaic devices were fabricated and discussed. Reference Cai, Jiajun et al., Phys. Chem. Chem. Phys., 13, 14663-14667, 2011Xie, Chao et al., J. Mater. Chem. C, 3, 6307-6313, 2015Li, Fang-Ze et al., Adv. Energy Mater., 3, 579-583, 2013 Figure 1

Integrating Two CdS-Based Z-Scheme Heterostructures for Realizing Overall Photoelectrochemical Water Splitting

As inspired by the natural photosynthesis, semiconductor nanostructures with Z-scheme charge transfer mechanism have been regarded as the ideal photocatalyst platform for realizing overall water splitting. The Z-scheme charge transfer mechanism involves a two-step photoexcitation process, in which a vectorial charge transfer pathway can be attained to evince strong redox powers for driving efficient photochemical reactions. In this work, two different configurations of CdS-based Z-scheme heterostructures were proposed and integrated to demonstrate photoelectrochemical overall water splitting. The samples were prepared by depositing Au particles on the CdS nanowires arrays, followed by the selective growth of ZnO or Cu2O on the Au surface. For CdS-Au-ZnO, the embedded Au may mediate interfacial charge transfer to effectuate electron concentration on CdS and hole accumulation on ZnO. As to the CdS-Au-Cu2O, an analogous vectorial charge transfer results in electron concentration on Cu2O and hole accumulation on CdS. The two composite structures of CdS-Au-ZnO and CdS-Au-Cu2O can respectively work as photoanode and photocathode in a single photoelectrochemical cell for achieving overall water splitting. The demonstration from this work delivers a novel structural engineering strategy for designing unique yet practical photoelectrochemical systems capable of performing artificial photosynthesis as well as solar fuel generation.As inspired by the natural photosynthesis, semiconductor nanostructures with Z-scheme charge transfer mechanism have been regarded as the ideal photocatalyst platform for realizing overall water splitting. The Z-scheme charge transfer mechanism involves a two-step photoexcitation process, in which a vectorial charge transfer pathway can be attained to evince strong redox powers for driving efficient photochemical reactions. In this work, two different configurations of CdS-based Z-scheme heterostructures were proposed and integrated to demonstrate photoelectrochemical overall water splitting. The samples were prepared by depositing Au particles on the CdS nanowires arrays, followed by the selective growth of ZnO or Cu2O on the Au surface. For CdS-Au-ZnO, the embedded Au may mediate interfacial charge transfer to effectuate electron concentration on CdS and hole accumulation on ZnO. As to the CdS-Au-Cu2O, an analogous vectorial charge transfer results in electron concentration on Cu2O and hole accumulation on CdS. The two composite structures of CdS-Au-ZnO and CdS-Au-Cu2O can respectively work as photoanode and photocathode in a single photoelectrochemical cell for achieving overall water splitting. The demonstration from this work delivers a novel structural engineering strategy for designing unique yet practical photoelectrochemical systems capable of performing artificial photosynthesis as well as solar fuel generation.

Electronic structure and intersubband magnetoabsorption spectra of CdSe/CdS core-shell nanowires

The electronic structures of CdSe/CdS core-shell nanowires are calculated based on the effective-mass theory, and it is found that the hole states in CdSe/CdS core-shell nanowires are strongly mixed, which are very different from the hole states in CdSe or CdS nanowires. In addition, we find the three highest hole states at the Γ point are almost localized in the CdSe core and the energies of the hole states in CdSe/CdS core-shell nanowires can be enhanced greatly when the core radius Rc increases and the total radius R is fixed. The degenerate hole states are split by the magnetic field, and the split energies will increase when |Jh| increases from 1/2 to 7/2, while they are almost not influenced by the change of the core radius Rc. The absorption spectra of CdSe/CdS core-shell nanowires at the Γ point are also studied in the magnetic field when the temperature T is considered, and we find there are only two peaks will arise if the core radius Rc and the temperature T increase. The intensity of each optical absorption can be considerably enhanced by increasing the core radius Rc when the temperature T is fixed, it is due to the increase of their optical transition matrix element. Meanwhile, the intensity of each optical absorption can be decreased when the temperature T increases and the core radius Rc is fixed, and this is because the Fermi-Dirac distribution function of the corresponding hole states will increase as the increase of the temperature T.

Aligned arrays of CdS nanotubes for high-performance fully nanostructured photodetector with higher photosensitivity

We report a novel and simple method to fabricate a high-sensitivity fully nanostructured photodetector by using CdS nanotubes (NTs) aligned arrays as active layer and Ag nanowires (NWs) transparent film as electrodes. The assembly of highly ordered and aligned CdS NTs arrays is obtained by a simple modified contact printing process. A fully nanostructured photodetector is fabricated by transferring the electrodes produced by Ag NWs network on the aligned CdS NTs arrays substrate, such that the aligned CdS NTs arrays as active layer are in contact with Ag NWs network as transparent electrodes. The resulting photodetector exhibits lower dark currents (<5 nA) and a higher photoresponse ratio (Ilight/Idark ≈ 219, 321) than that based on aligned arrays of CdS NWs, and its photosensitivity characteristics are even comparable to those of single nanostructure-based devices. In addition, the comparative studies of aligned NTs-based photodetetor in air and vacuum are investigated. The effects of the oxygen molecules on the photocurrent, dark current, rise time and decay time are investigated in details. This research may pave a way for large-scale fabrication of high performance and low cost nanostructured photodetectors for industrial applications.

Pseudocapacitive behavior of unidirectional CdS nanoforest in 3D architecture through solution chemistry

Two step soft chemical route has been utilized for the fabrication of CdS nanowire electrode in 3D architecture at room temperature (300K). The electrochemical pseudocapacitive behavior of thin film consisting of CdS nanowires has been evaluated by using cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy in an aqueous media. The electrochemical test revealed that CdS nanowire attained a specific capacitance of 181F/g at a scan rate of 5mV/s. An energy density of 1.72Wh/kg and power density of 27.14W/kg has been achieved at 89mA/g current density in 1M Na2SO3 solution.

CdS nanowire-modified 3D graphene foam for high-performance photo-electrochemical anode

A photo-electrochemical photo-anode of CdS-modified graphene foam (GF) was prepared by chemical vapor deposition method. The interconnected 3D scaffold network of the as-prepared CdS-modified GF composite not only facilitates the separation of photo-generated charge carrier, but also provides a direct pathway for charge transport in the conductive network, resulting in the enhanced photo-current response. Experimental results confirm that the deposition of the CdS nanowires (NWs) makes a major contribution to improving the photo-current density of as-prepared CdS NWs/GF photo-anode, which reaches a high value of 55 μA/cm2 with clear light-on and -off. Meanwhile, the PEC reaction leads to the photo-corrosion of CdS NWs/GF photo-anode, resulting in the prominent decrease of photo-current density during the photo-electrochemical reactions. Such a CdS-modified 3D GF photo-anode with impressive photovoltaic properties provides a promising platform for photo-electrochemical applications.

CdS Nanowires with Large Aspect Ratio and Their Composite with CuS and Au Nanoparticles.

We prepared CdS nanowires with small diameter (2.9 nm) and a large aspect ratio (more than 60) via a seed growth method. Wurtzite CdS seeds were firstly obtained via an organic synthesis at 310 degrees C. CdS nanowires with a single-crystal wurtzite structure and grown along the [0001] (c-axis) were further created through controlling the growth process. The injection of precursors plays an important role for getting a large respect ratio. The average size of the seeds is 2.9 nm. The growth along c-axis occurred during the preparation of the nanowires. The diameter of 2.9 nm remained unchanged within short reaction time. The heterostructures of the nanowires were fabricated by depositing CuS and Au nanoparticles (NPs). CuS monomers firstly deposited on the top of the nanowire and then to form a CuS shell on the top. In contrast, Au NPs deposited firstly on the top part of the nanowire. With increasing time or the amount of precursors, small Au NPs on side part of the nanowire was observed. The possible deposition kinetics was discussed. Because of homogeneous and uniform morphology, the heterostructures may be utilizable for applications.