CdSe Nanowires Research Articles

Tracking Cation Exchange in Individual Nanowires via Transistor Characterization.

Cation exchange is a versatile method for modifying the material composition and properties of nanostructures. However, control of the degree of exchange and material properties is difficult at the single-particle level. Successive cation exchange from CdSe to Ag2Se has been utilized here on the same individual nanowires to monitor the change of electronic properties in field-effect transistor devices. The transistors were fabricated by direct synthesis of CdSe nanowires on prepatterned substrates followed by optical lithography. The devices were then subjected to cation exchange by submerging them in an exchange solution containing silver nitrate. By removal of the devices from solution and probing the electrical transport properties at different times, the change in electronic properties of individual nanowires could be monitored throughout the entire exchange reaction from CdSe to Ag2Se. Transistor characterization revealed that the electrical conductivity can be tuned by up to 8 orders of magnitude and the charge-carrier mobility by 7 orders of magnitude. While analysis of the material composition by energy dispersive X-ray spectroscopy confirmed successful cation exchange from CdSe to Ag2Se, X-ray fluorescence spectroscopy proved that cation exchange also took place below the contacts. The method presented here demonstrates an efficient way to tune the material composition and access the resulting properties nondestructively at the single-particle level. This approach can be readily applied to many other material systems and can be used to study the electrical properties of nanostructures as a function of material composition or to optimize nanostructure-based devices after fabrication.

Modification of the Properties of CdSe Nanowires by Argon Ion Implantation

Modification of the Properties of CdSe Nanowires by Argon Ion Implantation

Pressure Impact on Lattice Thermal Conductivity and Its Related Parameters in CdSe Bulk, Nanowires, and Thin Film

The hydrostatic pressure effect on lattice thermal conductivity (LTC) in CdSe bulk, nanowires, and thin films was calculated. Values of LTC obtained through Callaway with that of Clapeyron equations are used to correlate those of the experimentally measured curves. Frequency‐dependent relaxation time approximation of phonon‐scattering processes was considered, which scattering due to boundary, imperfections, dislocations, electron, and other phonons via Umklapp and normal processes were used and clarified their effects. The impact of pressure on LTC is clarified according to both sample boundary dislocation concentrations. The influence of pressure is described, along with how the size dependence of the melting temperature, Debye temperature, and phonon group velocity of CdSe nanocrystals is affected. These parameters decrease as pressure increases.

Controlled Assembly of CdSe Nanoplatelet Thin Films and Nanowires.

We assemble semiconductor CdSe nanoplatelets (NPs) at the air/liquid interface into 2D monolayers several micrometers wide, distinctly displaying nematic order. We show that this configuration is the most favorable energetically and that the edge-to-edge distance between neighboring NPs can be tuned by ligand exchange without disrupting film topology and nanoparticle orientation. We explore the rich assembly phase space by using depletion interactions to direct the formation of 1D nanowires from stacks of NPs. The improved control and understanding of the assembly of semiconductor NPs offers opportunities for the development of cheaper optoelectronic devices that rely on 1D or 2D charge delocalization throughout the assembled monolayers and nanowires.

Drift velocity saturation in field-effect transistors based on single CdSe nanowires.

Field-effect transistors (FETs) based on semiconductor nanowires (NWs) have been extensively investigated and used for constructing novel nanoelectronic and optoelectronic devices in the past two decades. High electric field transport characteristics in FETs are of significance in both physics and applications. However, some specific physics phenomena at high electric field, such as drift velocity saturation, have rarely been reported in semiconductor NW FETs. In this work, the high electric field transport characteristics in FETs based on CdSe NWs were investigated. In the output characteristic curves, the current saturation phenomenon at high electric field caused by drift velocity saturation was observed. Typical values of saturation drift velocity and low electric field mobility in CdSe NW FETs were obtained. The low electric field mobility is in the range of 265.2 to 388.0 cm2 V-1 s-1. The saturation drift velocity is in the range of 5.1 × 105 to 7.0 × 105 cm s-1 and decreases monotonically with the increase of charge density, indicating that the electron-phonon scattering mechanism dominates at high electric field. Saturation drift velocity is an important figure-of-merit which characterizes the high electric field transport performance in FETs. As far as we know, this is the first experimental report on saturation drift velocity in CdSe NW FETs, which may provide valuable guidance for the design of nanoelectronic and optoelectronic devices based on CdSe NWs in the future.

Jitter-calibrated second-order correlation measurement for pulsed excitation with low repetition rate

Second-order correlation [g2(τ)] measurement has been utilized to characterize a nanolaser with high spontaneous emission coupling factor. Pulse excitation with low repetition rate is usually preferred for nanolasers due to its heat accumulation or photobleaching induced problem; however, introducing pulse-to-pulse timing jitter issue hinders the g2(τ) measurement from functioning. Here, a jitter-calibrated method is proposed by adding an extra reference time channel so that the g2(τ) can be calculated accurately. To verify the validity of this calibration method, the lasing threshold of a CdSe nanowire excited by a pulsed laser with a repetition rate of 1 kHz is studied. The descent of g2(0) to 1 coincides with the kink in light-in vs light-out curve, which confirms the effectiveness of this method.

Photonic Nanolaser with Extreme Optical Field Confinement.

We proposed a photonic approach to a lasing mode supported by low-loss oscillation of polarized bound electrons in an active nano-slit-waveguide cavity, which circumvents the confinement-loss trade-off of nanoplasmonics, and offers an optical confinement down to sub-1-nm level with a peak-to-background ratio of ∼30 dB. Experimentally, the extremely confined lasing field is realized as the dominant peak of a TE_{0}-like lasing mode around 720-nm wavelength, in 1-nm-level width slit-waveguide cavities in coupled CdSe nanowire pairs. The measured lasing characteristics agree well with the theoretical calculations. Our results may pave a way towards new regions for nanolasers and light-matter interaction.

Strongly enhanced propagation and non-reciprocal properties of CdSe nanowire based on hybrid nanostructures at communication wavelength of 1550 nm

We theoretically investigate the propagation and non-reciprocal properties of cadmium selenide (CdSe) nanowire (NW), and achieve strongly field enhancement at communication wavelength of 1550 nm when combined with the hybrid nanostructure. By varying the parameters of the nanostructure, i.e., MgF2 and Ag substrates, together with grooves, relations between these properties and the parameters are illustrated in details. Particularly, with an optimal design, the propagation performance of the NW is highly improved. Moreover, by breaking the symmetry of the system, the non-reciprocal property without time modulations is obtained with high contrast employing the further optimal design. These novel results are significant to related applications such as photonic integrated circuit and optical communications.

PbS nanoparticles anchored 1D- CdSe nanowires: Core-shell design towards energy storage supercapacitor application

Simple, binder free, low-cost chemical route has been employed to design CdSe@PbS core-shell surface architecture in thin film form towards electrochemical supercapacitor application. Horizontal chemical bath deposition (H-CBD) was used to grow one-dimensional (1D) Cd(OH)2 nanowires (NWs) template followed by ion exchange to get 1D CdSe NWs. Further, PbS nanoparticles were encapsulated on the surface of CdSe nanowires by using successive ionic layer adsorption and reaction (SILAR) method. Structural, compositional, and morphological studies have been used to confirm and investigate obtain surface architecture. Interestingly, design CdSe@PbS core-shell surface architecture not only offer maximum active sites but also provide smooth and fast electron transfer path exhibiting significant electrochemical performance with a specific capacity of 82 mAh g-1 and improved long-term stability. Additionally, symmetric electrochemical supercapacitor device of CdSe@PbS exhibits noticeable energy density of 16.14 Wh kg-1 at the power density of 288 W/kg.

Tuning the thermal conductivity of wurtzite CdSe nanowires: effects of size, strain, torsion and temperature

ABSTRACT The thermal transport of wurtzite CdSe nanowires (NWs) is studied by means of nonequilibrium molecular dynamics simulations. It is found that the length, diameter and strain can tune the thermal conductivity of CdSe NWs effectively, while the thermal conductivity exhibits insensitivity to torsion. The results indicate that the thermal conductivity of the CdSe NWs varies with the diameter approximately in the range of 13.8–17.7 W·m−1·K−1. The underlying mechanism is discussed by calculating the phonon power spectral density. The results show that the thermal transport is dominated by the centre atoms of NW, and high-frequency phonons contribute a lot to the thermal transport. Moreover, both tensile strain and compression strain can effectively suppress the thermal transport of CdSe NWs. The minimum thermal conductivity for the tensile strain and compression strain are 9.65 and 2.89 W·m−1·K−1, which are about 35% and 81% less than that of the unstrained structure.

Investigation on synthesis, structural and nonlinear optical responses of cadmium selenide coated with gold nanoparticles induced by femtosecond laser excitation

Nonlinear optical signal enhancement cannot be achieved by using semiconductor materials alone. Here, we show that the recently discovered nonlinear optical behavior of plasmonic nanoparticles and hybrid nanowires enables an enhanced nonlinear optical response. A synthesis, characterization, and nonlinear optical response of synthesized hybrid nanowires structures were studied. The growth of gold nanoparticles (Au NPs) onto cadmium selenide nanowires CdSe NWs with different concentrations of gold nanoparticles coating prepared via an impregnation technique. Au nanoparticles in the CdSe/Au nanowires were uniformly dispersed on the CdSe nanowire surface. The surface morphologies and the propagation manner of hybrid nanostructures were used for transmission electron microscopy (TEM) to study the optical properties of pure and hybrid nanostructures. Dark-field scattering microscopy was used to characterize single CdSe NW and confirm the coating of hybrid CdSe/Au nanowires and characterize the concentration effect of gold nanoparticles. The dark-field scattering spectrum (DFSS) reference to the surface plasmon resonance of nearer Au NPs was observed at ca. 800 nm. By making a comparison between a single cadmium selenide with and without gold nanoparticles coating, hybrid CdSe/Au nanowires exhibit sufficient quality to produce second-harmonic generation stimulated with a pulsed, linearly polarized pump-light from a femtosecond Ti-sapphire laser. The estimated improvement of the second-harmonic generation signal is about ~ 1.8 times, ~ 5.5 times, ~ 6.9 times for low, moderate and full coating of gold nanoparticles, which was mainly due to the high quality of synthesis techniques and good dispersion of gold nanoparticles on CdSe nanowires

Fe-Ion-Catalyzed Synthesis of CdSe/Cu Core/Shell Nanowires.

CdSe/Cu core/shell nanowires (NWs) are successfully synthesized by a wet chemical method for the first time. By utilizing the solution-liquid-solid (SLS) mechanism, CdSe NWs are fabricated by Bi seeds, which act as catalysts. In the subsequent radial overcoating of the Cu shell on the CdSe NWs, Fe ions have been proven to be an indispensable and efficient catalyzer. The thickness of the Cu shell could be well controlled in the range of 3 to 6 nm by varying the growth temperature (from 300 to 360 °C). Our synthetic strategy pioneers a new possibility for the controlled synthesis of semiconductor-metal heterostructure NWs (especially for II-VI semiconductors), such as CdS/Cu, ZnS/Au, and ZnO/Ag, which had broad application prospects in photoconductors, thin-film transistors, and light-emitting diodes. Theoretically, electrons flow from a higher Fermi-level material to the bottom Fermi-level at the metal-semiconductor heterojunction interface, which aligns the Fermi level and establishes the Schottky barrier. It leads to excess negative charges in metals and excess positive charges in semiconductors. Therefore, those effective electron traps reduce the probability of photogenerated electron-hole pair recombination efficiently, which has been widely applied in solar cells, sensors, photocatalysis, and energy storage. The breakthrough and innovation of this synthesis method have opened up a new synthetic route with a mild reaction environment, low energy consumption, and convenience.

Determination of the Wurtzite and Zincblende Fractions in II–VI Semiconductor Nanowires

We present a detailed powder X-ray diffraction (p-XRD) and transmission electron microscopy (TEM) study to explore the structural properties of CdS, CdSe, and CdTe semiconductor nanowires (NWs) gro...

Uncertainty Analysis of the Thermal Bridge Method

Thermal bridge method is widely used in thermal conductance measurements of one-dimensional nanostructures. The studies used by thermal bridge method advances our understanding of one-dimensional nanoscale thermal transport. And many efforts have been made to boost the reliability of the thermal bridge method and improve the measurement sensitivity. In this paper, uncertainty analysis is performed on the thermal bridge measurements of a CNT and a CdSe nanowire. Both the Taylor series method and the Monte Carlo method are used to figure out the propagation of the errors in the direct measurements. Our results show that the uncertainty of the thermal conductance decreases as the thermal conductance of the measured sample decreases, which can be attributed to the increase in the temperature drop on the measured sample. This finding indicates that we can reduce the measurement uncertainty by increasing the measured length of the sample or increasing the Joule heating generated on the heat source.

Atomistic investigation on the mechanical properties and failure behavior of zinc-blende cadmium selenide (CdSe) nanowire

Understanding the mechanical properties of cadmium selenium (CdSe) nanowire has received intense research interest due to its versatile application in semiconductor industries. We investigated the tensile mechanical properties and fracture mechanism of zinc-blende CdSe nanowire (NW) through molecular dynamics simulations by considering the effects of temperature variation, NW size, different loading directions, vacancy defects, and strain rates. We found that both ultimate tensile strength (UTS) and Young’s modulus (YM) linearly decrease with increasing temperature but increase with nanowire cross-sectional area. The [111] -directed CdSe NW shows the largest UTS, YM, and fracture toughness whereas, the lowest values are obtained for [100] direction. The largest failure strain is exhibited by [110] direction. The UTS is found more sensitive in the presence of Cd vacancy, while the YM is more sensitive to the removal of Se atoms. We noticed that at 100 K, the [100] -directed CdSe NW fails along {111} cleavage plane, however, at 600 K, both {111} and {100} cleavage planes activate and cause fracture at a lower strain value. Finally, both the fracture strength and strain increase with the increment in strain rates. The mechanical properties and fracture characteristics of the CdSe NW elucidated in this study will be a guide to design and fabricate CdSe-based optoelectronic and electronic devices.

Structural properties of cadmium selenide nanowires prepared by chemical bath deposition for the electrical and photosensitive characteristics of the p-Si/CdSe heterojunction

Cadmium selenide (n-CdSe) thin films were grown on a silicon substrate with a polished surface and applied to the Schottky type device structure. The n-CdSe thin films produced depended on various deposition times at 70°C by the use of the chemical bath deposition technique. XRD results show that the fabricated thin films consist of both cubic and hexagonal crystal systems. The morphology of CdSe was formed in nanograins and nanowire structures with respect to deposition times of 6 and 10 h, respectively. In addition to structural analysis of CdSe thin films, CdSe nanowires were used as an interfacial layer in a metal–semiconductor device to investigate its effects on the electrical and photosensitive characteristics of the device. As well as under forward bias current–voltage (I − V) conditions, the space charge limited current conduction behaviors were identified at low voltages. The results showed that the film produced at 10 h has a better performance compared to that produced at 6 h in terms of increased electric current.

Diameter Dependent Electronic, Optical and Transport Properties of CdSe Nanowire: Ab-Initio Study

We report the Density functional theory (DFT) based investigations of diameter dependent electronic and optical properties of CdSe nanowire (CdSe-NW) in its wurtzite phase. The DFT calculations are based on generalized gradient approximation, Perdew Burke and Ernzerhof (PBE) type parameterization and localized double-$$\zeta $$ polarized (DZP) orbital basis set. The cohesive energy, electronic band structure, Young’s modulus and effective mass have been calculated for different diameter 5.56, 14.00, and 22.60 A CdSe nanowires. Larger diameter shows bandgap lowering and higher zero bias conductance in comparison to its small diameter counterparts. Interfrontier orbital analysis for diametrically large nanowire reveals dispersion of canonical orbital across the cross-section of nanowire, hence supporting high charge carrier mobility. Computation of dielectric function for the Optical properties analysis, confirms the broad band absorption and low reflectivity of these nanowires in photonic field. Transport properties of CdSe nanowire have been analysed in terms of transmission spectra and current-voltage characteristic.

Efficient Second Harmonic Generation in a Hybrid Plasmonic Waveguide by Mode Interactions.

Developing highly efficient nanoscale coherent light sources is essential for advances in technological applications such as integrated photonic circuits, bioimaging, and sensing. An on-chip wavelength convertor based on second harmonic generation (SHG) would be a crucial step toward this goal, but the light-conversion efficiency would be low for small device dimensions. Here we demonstrate strongly enhanced SHG with a high conversion efficiency of 4 × 10-5 W-1 from a hybrid plasmonic waveguide consisting of a CdSe nanowire coupled with a Au film. The strong spatial overlap of the waveguide mode with the nonlinear material and momentum conservation between the incident and reflected modes are the key factors resulting in such high efficiency. The SHG emission angles vary linearly with excitation wavelength, indicating a nonlinear steering of coherent light emission at the subwavelength scale. Our work is promising for the realization of efficient and tunable nonlinear coherent sources and opens new approaches for efficient integrated nonlinear nanophotonic devices.

Fluorescence spectra of colloidal self-assembled CdSe nano-wire on substrate of porous Al2O3/Au nanoparticles**Project supported by the National Natural Science Foundation of China (Grant Nos. 61741505 and 61865002), the Guizhou Provincial Science and Technology Support Plan, China (Grant No QKHZ [2017]2887), the Guiding Local Science and Technology Development Plan of the Central Government of China (Grant No. QKZYD [2017]4004), the Guizhou

We present a self-assembly method to prepare array nano-wires of colloidal CdSe quantum dots on a substrate of porous Al2O3 film modified by gold nanoparticles. The photoluminescence (PL) spectra of nanowires are in situ measured by using a scanning near-field optical microscopy (SNOM) probe tip with 100-nm aperture on the scanning near-field optical microscope. The results show that the binding sites from the edge of porous Al2O3 nanopores are combined with the carboxyl of CdSe quantum dots’ surface to form an array of CdSe nanowires in the process of losing background solvent because of the gold nanoparticles filling the nano-holes of porous Al2O3 film. Compared with the area of non-self-assembled nano-wire, the fluorescence on the Al2O3/Au/CdSe interface is significantly enhanced in the self-assembly nano-wire regions due to the electron transfer conductor effect of the gold nanoparticles’ surface. In addition, its full width at half maximum (FWHM) is also obviously widened. The method of enhancing fluorescence and energy transfer can widely be applied to photodetector, photocatalysis, optical display, optical sensing, and biomedical imaging, and so on.

Improving the Photoresponse Properties of CdSe Quantum Wires by Alignment and Ligand Exchange.

Semiconductor nanowires are the ideal building blocks to construct various thin-film electronic and optoelectronic devices, the performance of which is largely determined by their ensemble geometry and surface chemistry in addition to the chemical composition. Here, we report the large-scale and oriented assembly of CdSe nanowires on the basis of a light-induced assembly approach under an external electric field. To further increase the electrical conductivity of nanowire films, the original surface-capping organic ligands are exchanged with small ionic species through a solid-state ligand-exchange process. The resulting surface-modified CdSe nanowire films exhibit markedly enhanced photoresponse properties including high on/off ratios and fast response. This work establishes a simple yet scalable method to fabricate aligned nanowire films with a desired surface chemistry, which can be broadly used in various electronic and optoelectronic devices.