One-dimensional CdS nanostructures: a promising candidate for optoelectronics

Highly Repeatable and Recoverable Phototransistors Based on Multifunctional Channels of Photoactive CdS, Fast Charge Transporting ZnO, and Chemically Durable Al2O3 Layers

Highly repeatable and recoverable phototransistors were explored using a "multifunctional channels" structure with multistacked chalcogenide and oxide semiconductors. These devices were made of (i) photoactive CdS (with a visible band gap), (ii) fast charge transporting ZnO (with a high field-effect mobility), and (iii) a protection layer of Al2O3 (with high chemical durability). The CdS TFT without the Al2O3 protection layer did not show a transfer curve due to the chemical damage that occurred on the ZnO layer during the chemical bath deposition (CBD) process used for CdS deposition. Alternatively, compared to CdS phototransistors with long recovery time and high hysteresis (ΔVth = 19.5 V), our "multi-functional channels" phototransistors showed an extremely low hysteresis loop (ΔVth = 0.5V) and superior photosensitivity with repeatable high photoresponsivity (52.9 A/W at 400 nm). These improvements are likely caused by the physical isolation of the sensing region and charge transport region by the insertion of the ultrathin Al2O3 layer. This approach successfully addresses some of the existing problems in CdS phototransistors, such as the high gate-interface trap site density and high absorption of molecular oxygen, which originate from the polycrystalline CdS.

Interface induce growth of intermediate layer for bandgap engineering insights into photoelectrochemical water splitting

A model of interface induction for interlayer growing is proposed for bandgap engineering insights into photocatalysis. In the interface of CdS/ZnS core/shell nanorods, a lamellar solid solution intermediate with uniform thickness and high crystallinity was formed under interface induction process. Merged the novel charge carrier transfer layer, the photocurrent of the core/shell/shell nanorod (css-NR) array was significantly improved to 14.0 mA cm⁻² at 0.0 V vs. SCE, nearly 8 times higher than that of the perfect CdS counterpart and incident photon to electron conversion efficiency (IPCE) values above 50% under AM 1.5G irradiation. In addition, this array photoelectrode showed excellent photocatalytic stability over 6000 s. These results suggest that the CdS/Zn_1−xCd_xS/ZnS css-NR array photoelectrode provides a scalable charge carrier transfer channel, as well as durability, and therefore is promising to be a large-area nanostructured CdS-based photoanodes in photoelectrochemical (PEC) water splitting system.

CdS nanorods/organic hybrid LED array and the piezo-phototronic effect of the device for pressure mapping

As widely applied in light-emitting diodes and optical devices, CdS has attracted the attention of many researchers due to its nonlinear properties and piezo-electronic effect. Here, we demonstrate a LED array composed of

PEDOT

PSS and CdS nanorods and research the piezo-photonic effect of the array device. The emission intensity of the device depends on the electron-hole recombination at the interface of the p-n junction which can be adjusted using the piezo-phototronic effect and can be used to map the pressure applied on the surface of the device with spatial resolution as high as 1.5 μm. A flexible LED device array has been prepared using a CdS nanorod array on a Au/Cr/kapton substrate. This device may be used in the field of strain mapping using its high pressure spatial-resolution and flexibility.

High Efficiency Photoelectrocatalytic Methanol Oxidation on CdS Quantum Dots Sensitized Pt Electrode

A cadmium sulfide quantum dots sensitized Pt (Pt-CdS) composite was synthesized using a solvothermal method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. The catalytic properties of the as-prepared electrode for methanol oxidation were evaluated by cyclic voltammetry (CV), chronoamperometry, electrochemical impedance spectrum (EIS) and photocurrent responses. The as-prepared Pt-CdS electrode displayed a significant enhancement in the electrocatalytic activity and stability for methanol oxidation in the presence of visible light irradiation. The synergistic effect of both the electro- and photocatalytic reaction contributes to this enhanced catalytic performance. Our result suggests a new paradigm to construct photoelectrocatalysts with high performance and good stability for direct methanol fuel cells with the assistance of visible-light illumination.

Photonic Applications of Metal-Dielectric Heterostructured Nanomaterials

Metal materials, supporting plasmon modes on their surface, can confine the optical field at deep subwavelength scale, which is desired for photonic integration. However, their intrinsic high Ohmic losses make it impossible to construct the whole circuit solely with the metal materials. Integrating the plasmonic components with dielectric materials may offer a solution to this dilemma. With outstanding active optical performance, these dielectric components not only can greatly reduce the optical losses of the entire circuits but also offer an efficient way to launch the surface plasmon polaritons through the evanescent field coupling or the direct exciton-plasmon conversion. Furthermore, the cooperative interaction between metal and dielectric materials would bring vast novel optical phenomena and functional photonic devices. In this review, the synergistic effects among metal and dielectric materials in various heterostructures as well as their related applications are highlighted. Comprehensive understanding on their synergistic interactions would offer useful guidance for the design and fabrication of the ultracompact novel optical devices.

Strain Driven Spectral Broadening of Pb Ion Exchanged CdS Nanowires

Broad visible photodetectors based on individual Pb ion exchanged CdS nanowires are reported. They are prepared via an ion exchange reaction initiated on the surface of CdS nanowires with a further diffusion of ionic reactants. The broadening of the response spectrum is relative to electronic band structure transition caused by the tensile strain in the lattice.

Hierarchical CdS Nanowires Based Rigid and Flexible Photodetectors with Ultrahigh Sensitivity

Hierarchical CdS nanowires were synthesized via a facile vapor transport method, which were used to fabricate both rigid and flexible visible-light photodetectors. Studies found that the rigid photodetectors on SiO2/Si substrate showed ultrahigh photo-dark current ratio up to 1.96 × 10(4), several orders of magnitude higher than previously reported CdS nanostructures, as well as high specific detectivity (4.27 × 10(12) Jones), fast response speed and excellent environmental stability. Highly flexible photodetectors were also fabricated on polyimide substrate, which exhibited comparable photoresponse performance as the rigid one. In addition, the as-prepared flexible devices displayed excellent mechanical flexibility, electrical stability and folding endurance. The results indicate that the hierarchical CdS nanowires may be good candidates for nanoscale optoelectronic devices such as high-efficiency photoswitches and highly photosensitive detectors.

Resonance modulated amplified emission from CdSSe nanoribbons

We present evidence of amplified emission mediated by surface plasmon polaritons (SPPs) from a CdS0.2Se0.8 nanoribbon (NR) supported on a gold-coated silicon substrate. Room temperature amplified emission is observed from the nanoribbon above excitation irradiances ~ 25 W/cm(2) when it is supported on the gold coated silicon substrate. The nanoribbon is shown to act as a resonator cavity, leading to amplification of discrete wavelengths in the emission spectrum. Evidence for the formation of SPP waves between the gold-coated substrate and the nanoribbon is shown, and the resulting wavenumber increase allows for the matching of theoretical resonance wavelengths with those observed experimentally.

Colloidal 2D-0D Lateral Nanoheterostructures: A Case Study of Site-Selective Growth of CdS Nanodots onto Bi₂Se₃ Nanosheets

Two-dimensional (2D) nanoheterostructure (2D NHS) with nanoparticles grown on 2D nanomaterial substrates could potentially enable many novel functionalities. Controlled site-selective growth of nanoparticles on either the lateral or the basal directions of 2D nanomaterial substrates is desirable but extremely challenging. Herein, we demonstrate the rational control of lateral- and basal-selective attachment of CdS nanoparticles onto 2D Bi2Se3 nanosheets through solution phase reactions. The combination of experimental and theoretical efforts elucidate that site-relevant interfacial bonding and kinetic control of molecular precursors play vital roles for site selectivity. Furthermore, the electronic structures revealed from density functional theory calculations explain the superior performance of the lateral 2D NHSs compared to their basal counterpart in prototype photoelectrochemical cells. The present study will inspire the construction of other site-selective 2D NHSs with well-defined structure and unique properties.

MoO3 Nanodots Decorated CdS Nanoribbons for High-Performance, Homojunction Photovoltaic Devices on Flexible Substrates

The p-n homojunctions are essential components for high-efficiency optoelectronic devices. However, the lack of p-type doping in CdS nanostructures hampers the fabrication of efficient photovoltaic (PV) devices from homojunctions. Here we report a facile solution-processed method to achieve efficient p-type doping in CdS nanoribbons (NRs) via a surface charge transfer mechanism by using spin-coated MoO3 nanodots (NDs). The NDs-decorated CdS NRs exhibited a hole concentration as high as 8.5 × 10(19) cm(-3), with the p-type conductivity tunable in a wide range of 7 orders of magnitude. The surface charge transfer mechanism was characterized in detail by X-ray photoelectron spectroscopy, Kelvin probe force microscopy, and first-principle calculations. CdS NR-homojunction PV devices fabricated on a flexible substrate exhibited a power conversion efficiency of 5.48%, which was significantly better than most of the CdS nanostructure-based heterojunction devices, presumably due to minimal junction defects. Devices made by connecting cells in series or in parallel exhibited enhanced power output, demonstrating the promising potential of the homojunction PV devices for device integration. Given the high efficiency of the surface charge transfer doping and the solution-processing capability of the method, our work opens up unique opportunities for high-performance, low-cost optoelectronic devices based on CdS homojunctions.

In situ fabrication and optoelectronic analysis of axial CdS/p-Si nanowire heterojunctions in a high-resolution transmission electron microscope

A high-precision technique was utilized to construct and characterize axial nanowire heterojunctions inside a high-resolution transmission electron microscope (HRTEM). By an in-tandem technique using an ultra-sharp tungsten probe as the nanomanipulator and an optical fiber as the optical waveguide the nanoscale CdS/p-Si axial nanowire junctions were fabricated, and in situ photocurrents from them were successfully measured. Compared to a single constituting nanowire, the CdS/p-Si axial nanowire junctions possess a photocurrent saturation effect, which protects them from damage under high voltages. Furthermore, a set of experiments reveals the clear relationship between the saturation photocurrent values and the incident light intensities. The applied technique is expected to be valuable for bottom-up nanodevice fabrications, and the regarded photocurrent saturation feature may solve the Joule heating-induced failure problem in nanowire optoelectronic devices caused by a fluctuating bias.

Engineering interfacial photo-induced charge transfer based on nanobamboo array architecture for efficient solar-to-chemical energy conversion

Engineering interfacial photo-induced charge transfer for highly synergistic photocatalysis is successfully realized based on nanobamboo array architecture. Programmable assemblies of various components and heterogeneous interfaces, and, in turn, engineering of the energy band structure along the charge transport pathways, play a critical role in generating excellent synergistic effects of multiple components for promoting photocatalytic efficiency.

Influence of Buffer Agent Concentration on the Optical Properties from CdS Nanocrystals on Silicon Nanoporous Pillar Array

The chemical bath deposition (CBD) method is very crucial to the reaction rate. Generally, the rate can be controlled through tuning buffer agent concentration. CdS nanocrystals on the silicon nanoporous pillar array (CdS/Si-NPA) have been prepared through the CBD method. By varying the buffer agent concentration, the reaction rates can be tuned. The diffraction peaks of hexagonal CdS and Cd can be observed due to the reduction of Cd2+caused by the silicon nanoporous pillar array. The average size of CdS nanocrystals is decreased with the increasing buffer agent concentration and the optical band gaps from CdS nanocrystals are increased. From the photoluminescence of CdS/Si-NPA, it can be observed that the blue emissions are independent of the buffer agent concentration and the green emissions show blue shift with the increasing buffer agent concentration.

Small molecular amine mediated synthesis of hydrophilic CdS nanorods and their photoelectrochemical water splitting performance

Small molecular amine was selected as the activation agent for elemental sulfur and as a mediator for the formation of hydrophilic CdS nanocrystals with high quality, which exhibit efficient photoelectrochemical properties for water splitting.

Compositionally controlled band gap and photoluminescence of ZnSSe nanofibers by electrospinning

A simple, non-toxic, low-priced, and reproducible manipulation, which meets the standards of green chemistry, is introduced for the synthesis of ZnS_xSe_1−x nanofibers. ZnS_xSe_1−x nanofibers have been prepared in the entire composition range from ZnSe to ZnS by using a low-cost wet-chemical method.

Anion-assisted one-pot synthesis of 1D magnetic α- and β-MnO2 nanostructures for recyclable water treatment application

The as-prepared MnO₂, especially β-MnO₂, exhibits superior degradation ability compared to the conventional adsorbents.

Large scale fabrication of well-aligned CdS/p-Si shell/core nanowire arrays for photodetectors using solution methods

The large scale preparation of CdS/p-Si shell/core nanowires having good rectifying characteristics and photo-sensitivity using a facile preparation method.

Photosensing performance of branched CdS/ZnO heterostructures as revealed by in situ TEM and photodetector tests

CdS/ZnO branched heterostructures have been successfully synthesized by combining thermal vapour deposition and a hydrothermal method. Drastic optoelectronic performance enhancement of such heterostructures was revealed, compared to plain CdS nanobelts, as documented by comparative in situ optoelectronic studies on corresponding individual nanostructures using an originally designed laser-compatible transmission electron microscopy (TEM) technique. Furthermore, flexible thin-film based photodetectors based on standard CdS nanobelts and newly prepared CdS/ZnO heterostructures were fabricated on PET substrates, and comparative photocurrent and photo-responsivity measurements thoroughly verified the in situ TEM results. The CdS/ZnO branched heterostructures were found to have better performance than standard CdS nanobelts for optoelectronic applications with respect to the photocurrent to dark current ratio and responsivity.

Programmable photo-electrochemical hydrogen evolution based on multi-segmented CdS-Au nanorod arrays

Programmable photocatalysts for hydrogen evolution have been fabricated based on multi-segmented CdS-Au nanorod arrays, which exhibited high-efficiency and programmability in hydrogen evolution as the photoanodes in the photoelectrochemical cell. Multiple different components each possess unique physical and chemical properties that provide these cascade nanostructures with multiformity, programmability, and adaptability. These advantages allow these nanostructures as promising candidates for high efficient harvesting and conversion of solar energy.

CdS nanoscale photodetectors

CdS nanostructures have received much attention in recent years as building blocks for optoelectronic devices due to their unique physical and chemical properties. This progress report provides an overview of recent research about rational design of CdS nanoscale photodetectors. Three kinds of photodetectors according to the metal-semiconductor contact types are discussed in detail: Ohmic contact, Schottky contact, and field enhanced transistor configuration. The focus is on the tuning of optical and electrical properties CdS nanostructures by element doping, composition and bandgap engineering, and heterojunction integration, along with thus modified device performances generated during these tuning processes. Latest concepts of photodetector design such as flexible, self-powered, plasmonic, and piezophototronic photodetectors with novel properties are introduced to demonstrate the future directions of such an exciting research field.

Controlled synthesis of kinked ultrathin ZnS nanorods/nanowires triggered by chloride ions: a case study

Colloidal synthesis of kinked ultrathin ZnS nanorods/nanowires with mixed phases using tiny Ag2S nanocrystals as catalysts is reported. It is found that chloride ions can induce the controlled morphology transition from straight to kinking. The synthetic parameters modulating the growth of kinked ZnS nanorods/nanowires are systematically investigated. Chloride ions introduced in the reaction can generate more proportion of wurtzite phase by slowing the nucleation and growth rates during the growth of one-dimensional (1D) ZnS nanorods/nanowires. The formation of kinked morphology is responsible for the increased domains of mixed stacking and twinning in single 1D nanostructures. The present recipe on controlled synthesis of 1D kinked nanorods/nanowires provides a model of crystal growth control, and these unique 1D nanostructures may also offer new opportunities to fabricate nanodevices with special functions.

Starfish-like Au–CdS hybrids for the highly efficient photocatalytic degradation of organic dyes

A novel starfish-like Au–CdS heterostructures are constructed by a simple self-assembling method with centered Au nanoparticles, and exhibit highly efficient visible light photodegradation of organic dyes.