Carbon Nanostructure Embedded Novel Sensor Implementation for Detection of Aromatic Volatile Organic Compounds: An Organized Review

For field-like environmental gas monitoring and noninvasive illness diagnostics, effective sensing materials with exceptional sensing capabilities of sensitive, quick detection of volatile organic compounds (VOCs) are required. Carbon-based nanomaterials (CNMs), like CNTs, graphene, carbon dots (Cdots), and others, have recently drawn a lot of interest for their future application as an elevated-performance sensor for the detection of VOCs. CNMs have a greater potential for developing selective sensors that target VOCs due to their tunable chemical and surface properties. Additionally, the mechanical versatility of CNMs enables the development of novel gas sensors and places them ahead of other sensing materials for wearable applications. An overview of the latest advancements in the study of CNM-based sensors is given in this comprehensive organized review.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Theoretical Study of ZnS Monolayer Adsorption Behavior for CO and HF Gas Molecules

Adsorption of carbon monoxide (CO) and hydrogen fluoride (HF) gas molecules on a ZnS monolayer with weak van der Waals interactions is studied using the DFT + U method. From our calculation, the ZnS monolayer shows chemisorption with CO (E _ads = -0.96 eV) and HF (E _ads = -0.86 eV) gas molecules. Bader charge analysis shows that charge transfer is independent of the binding environment. A higher energy barrier for CO when migrating from one optimal site to another suggests that clustering may be avoided by the introduction of multiple CO molecules upon ZnS, while the diffusion energy barrier (DEB) for HF suggests that binding may occur more easily for HF gas upon the ZnS ML. Adsorption of the considered diatomic molecule also results in a significant variation in effective mass and therefore can be used to enhance the carrier mobility of the ZnS ML. Additionally, the calculation of recovery time shows that desirable sensing and desorption performance for CO and HF gas molecules can be achieved at room temperature (300 K).

MOCVD Growth and Structural Properties of ZnS Nanowires: A Case Study of Polytypism

Controlling the morphology, orientation, and crystal phase of semiconductor nanowires is crucial for their future applications in nanodevices. In this work, zinc sulfide (ZnS) nanowires have been grown by metalorganic chemical vapor deposition (MOCVD), using gold or gold-gallium alloys as catalyst. At first, basic studies on MOCVD growth regimes (mass-transport, zinc- or sulfur- rich conditions) have been carried out for ZnS thin films. Subsequently, the growth of ZnS nanowires was investigated, as a function of key parameters such as substrate temperature, S/Zn ratio, physical state and composition of the catalyst droplet, and supersaturation. A detailed analysis of the structural properties by transmission electron microscopy (TEM) is given. Depending on the growth conditions, a variety of polytypes is observed: zinc-blende (3C), wurtzite (2H) as well as an uncommon 15R crystal phase. It is demonstrated that twinning superlattices, i.e., 3C structures with periodic twin defects, can be achieved by increasing the Ga concentration of the catalyst. These experimental results are discussed in the light of growth mechanisms reported for semiconductor nanowires. Hence, in this work, the control of ZnS nanowire structural properties appears as a case study for the better understanding of polytypism in semiconductor 1D nanostructures.

Simultaneous Detection of CO and NH3 Gases at Room Temperature with an Array of ZnS Chemiresistive Sensors and the Superposition Principle

Simultaneous detection of multiple toxic gases in the air using room temperature gas sensors is significant in low-power environmental monitoring applications. However, the low-temperature resistive gas sensors are sensitive to more than one gas, and thus, an array of gas sensors and high energy-consuming machine learning algorithms are required to predict the concentrations of the individual gases in mixed target gas. Here, we report a computationally less intensive method to predict the composition of the target gases using linear gas sensors. A sensor array consisting of two ZnS resistive gas sensors biased at different voltages in conjunction with the superposition principle is used to predict the concentration of individual gases in the binary mixture of NH₃ and CO present in the air. Further, the effect of humidity on response is mitigated by formulating the sensitivity of the sensors as a function of relative humidity. The proposed algorithm predicted the concentration of the individual gases in mixed gas with a maximum absolute error of ∼15% irrespective of humidity levels, which is practically allowed in most gas sensing applications. As the superposition principle is a low-power consuming technique, the proposed approach can be used in applications where trace levels of gases in mixed targets need to be detected with energy-efficient methods.

Incorporation of Au Nanoparticles on ZnO/ZnS Core Shell Nanostructures for UV Light/Hydrogen Gas Dual Sensing Enhancement

ZnO/ZnS nanocomposite-based nanostructures exhibit dual light and gas sensing capabilities. To further boost the light/dual sensing properties, gold nanoparticles (Au NPs) were incorporated into the core-shell structures. Multiple material characterizations revealed that Au NPs were successfully well spread and decorated on ZnO/ZnS nanostructures. Furthermore, our findings show that the addition of Au NPs could enhance both 365 nm UV light sensing and hydrogen gas sensing in terms of light/gas sensitivity and light/gas response time. We postulate that the optimization of gas/light dual sensing capability may result from the induced electric field and inhabitation of electron-hole recombination. Owing to their compact size, simple fabrication, and stable response, ZnO/ZnS/Au NPs-based light/gas dual sensors are promising for future extreme environmental monitoring.

The Influence of CBD Parameters on the Energy Gap of ZnS Narcissus-Like Nanostructured Thin Films

Recently, the efficient preparation techniques of zinc sulfide (ZnS) nanostructured films have drawn great attention due to their potential applications in optoelectronics. In this study, the low-cost and high-yield chemical bath deposition (CBD) technique was used to deposit ZnS nanostructured thin films. The effect of various deposition parameters such as time, pH, precursor concentration, and temperature on the morphology and energy bandgap (Eg) of the prepared thin films were investigated. The characterization of the prepared thin films revealed the formation of polycrystalline ZnS with Narcissus-like nanostructures. Moreover, the optical characterization showed inverse proportionality between both the transmission and Eg of the nanostructured thin films and the variation of the deposition parameters. A range of different Eg values between 3.92 eV with 20% transmission and 4.06 eV with 80% transmission was obtained. Tuning the Eg values and transmission of the prepared nanostructured films by manipulating the deposition parameters of such an efficient technique could lead to applications in optoelectronics such as solar cells and detectors.

Oriented Growth of In-Oxo Chain Based Metal-Porphyrin Framework Thin Film for High-Sensitive Photodetector

The potential of metal-organic frameworks (MOFs) for applications in optoelectronics results from a unique combination of interesting photophysical properties and straightforward tunability of organic and inorganic units. Here, it is demonstrated that using MOF approach chromophores can be assembled into well-ordered 1D arrays using metal-oxo strands as lead structure, and the resulting porphyrinic rows exhibit unique photophysical properties and allow the realization of highly sensitive photodetectors. A porphyrinic MOF thin film, In-TCPP surface-coordinated MOF thin films with [021] orientation is fabricated using a layer-by-layer method, from In(NO3)3 and TCPP (5,10,15,20-(4-carboxyphenyl)porphyrin). Detailed experimental and theoretical analysis reveals that the assembly yields a structure where In-oxo strands running parallel to the substrate fix the chromophoric linkers to yield 1D arrays of porphyrins. The frontier orbitals of this highly anisotropic arrangement are localized in these columnar arrangements of porphyrins and result in high photoactivity, which is exploited to fabricate a photodetector with record (as compared to other organic materials) responsivity in visible regime of 7.28 × 1014 Jones and short rise/fall times (0.07/0.04 s). This oriented MOF thin film-based high-sensitive photodetector provides a new avenue to use inorganic, stable lead structures to assemble organic semiconductors into regular arrays, thus creating a huge potential for the fabrication of optoelectronic devices.

ZnS Quantum Dot Based Acetone Sensor for Monitoring Health-Hazardous Gases in Indoor/Outdoor Environment

This study reports the ZnS quantum dots (QDs) synthesis by a hot-injection method for acetone gas sensing applications. The prepared ZnS QDs were characterized by X-ray diffraction (XRD) and transmission electron microscopy analysis. The XRD result confirms the successful formation of the wurtzite phase of ZnS, with a size of ~5 nm. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and fast Fourier transform (FFT) images reveal the synthesis of agglomerated ZnS QDs with different sizes, with lattice spacing (0.31 nm) corresponding to (111) lattice plane. The ZnS QDs sensor reveals a high sensitivity (92.4%) and fast response and recovery time (5.5 s and 6.7 s, respectively) for 100 ppm acetone at 175 °C. In addition, the ZnS QDs sensor elucidates high acetone selectivity of 91.1% as compared with other intrusive gases such as ammonia (16.0%), toluene (21.1%), ethanol (26.3%), butanol (11.2%), formaldehyde (9.6%), isopropanol (22.3%), and benzene (18.7%) for 100 ppm acetone concentration at 175 °C. Furthermore, it depicts outstanding stability (89.1%) during thirty days, with five day intervals, for 100 ppm at an operating temperature of 175 °C. In addition, the ZnS QDs acetone sensor elucidates a theoretical detection limit of ~1.2 ppm at 175 °C. Therefore, ZnS QDs can be a promising and quick traceable sensor nanomaterial for acetone sensing applications.

The recent progress of triboelectric nanogenerator-assisted photodetectors

Since 2012, triboelectric nanogenerator (TENG) has attracted significant interest from researchers in the field of energy conversion due to its unique output characteristics of high voltage, pulse and low current. In addition, recent advancements have demonstrated that photodetection platforms based on TENG exhibit great advantages such as being simple, low-cost, portable, with high sensitivity, high response, etc, and are environment friendly. Here, this article provides a comprehensive review on the state-of-the-art photodetectors based on TENG in recent years, and a detailed introduction to the structural design and potential mechanisms. It mainly focuses on self-powered photodetectors (including photodetectors as a load resistance of a TENG and photosensitive materials such as tribo-layer of TENG) and the modulation of photodetectors based on TENG (including utilizing the voltage of TENG as well as triboelectric microplasma). Finally, we put forward some perspectives and outlook, including structure engineering and mechanism guidance, for the future development of simple, high-performance and portable photodetectors based on TENG.

Blown bubble assembly of ultralong 1D bismuth sulfide nanostructures with ordered alignment and shape control

Recently, semiconducting chalcogenide nanostructures have attracted intense attention due to their excellent properties and broad applications, especially metal chalcogenides in the form of A₂(V)B₃(VI). Here we synthesized one-dimensional (1D) bismuth sulfide (Bi₂S₃) nanostructures with a length of more than 100 μm via a one-step hydrothermal method, and found that the reaction temperature and the alkali concentration play vital roles in the morphology of the 1D nanostructures. Since the as-synthesized Bi₂S₃ nanostructures were disordered in powder form, it is necessary to align them with ordered orientation and uniform distribution before further application. A blown bubble method was specifically applied to align these ultralong 1D nanostructures, and the assembly mechanism was also deeply analyzed, including the drift of nanostructures in the bubble film thickness direction, the relationship between (nanowire) NW spacing and array density, and the angle deviation of aligned arrays assembled from different bubble solutions. Interestingly, the initial straight Bi₂S₃ NWs could also be converted into buckled nanosprings (NSs) with regular pitches during the assembly process, and different NS formation stages were observed. A possible deformation mechanism or load bearing model of the wavy NS was proposed and verified, and the Young's modulus of an individual NW was figured out for the first time. After annealing under a N₂ atmosphere, the aligned Bi₂S₃ NWs embedded in the bubble film were exposed, and the clean arrays were fabricated into functional optoelectronic devices such as photodetectors with a high performance.

Ni-Doped ZnS Nanospheres Decorated with Au Nanoparticles for Highly Improved Gas Sensor Performance

Novel Ni-doped wurtzite ZnS nanospheres decorated with Au nanoparticles (Au NPs⁻ZnS NSs) have been successfully fabricated using a simple method involving vacuum evaporation followed by an annealing process. This transition metal-doped gas sensor had high responsivity, extremely fast response and recovery time, and excellent selectivity to formaldehyde at room temperature. The response and recovery time are only 29 s and 2 s, respectively. Since ZnS is transformed into ZnO at a high temperature, superior room temperature-sensing performance can improve the stability and service life of the sensor. The improvement in sensing performance could be attributed to the reduced charge-transfer distance resulting from the creation of a local charge reservoir layer, and the catalytic and spillover effect of Au nanoparticles. The rough and porous spherical structure can also facilitate the detection and diffusion of gases. The as-prepared Au NPs⁻ZnS NSs are considered to be an extremely promising candidate material for gas sensors, and are expected to have other potential applications in the future.

Two-dimensional CsPbBr3/PCBM heterojunctions for sensitive, fast and flexible photodetectors boosted by charge transfer

Inorganic halide perovskites exhibited promising potentials for high-performance wide-band photodetectors (PDs) due to their high light absorption coefficients, long carrier diffusion length and wide light absorption ranges. Here, we report two-dimensional (2D) CsPbBr₃/PCBM heterojunctions for sensitive, fast and flexible PDs, whose performances can be greatly boosted by the charge transfer through the energy-aligned interface. The 2D CsPbBr₃ nanosheets with high crystallinity were fabricated via a simple solution-process at room temperature, and then assembled into flexible heterojunctions films with polymerphenyl-C61-butyric acid methyl ester (PCBM). Significantly, the efficient and fast charge transfer at the heterojunctions interface was evidenced by the obvious photoluminescence quenching and variation of recombination dynamics. Subsequently, such heterojunctions PD exhibited an enhanced responsivity of 10.85 A W^-1 and an ultrahigh detectivity of 3.06 × 10¹³ Jones. In addition, the PD shows a broad linear dynamic range of 73 dB, a fast response speed with rise time of 44 μs and decay time of 390 μs, respectively. Moreover, the PD lying on polyethylene terephthalate substrates exhibited an outstanding mechanical flexibility and a robust electrical stability. These results could provide a new avenue for integration of 2D perovskites and organic functional materials and for high-performance flexible PDs.

Heterostructured ZnS/InP nanowires for rigid/flexible ultraviolet photodetectors with enhanced performance

Heterostructured ZnS/InP nanowires, composed of single-crystalline ZnS nanowires coated with a layer of InP shell, were synthesized via a one-step chemical vapor deposition process. As-grown heterostructured ZnS/InP nanowires exhibited an ultrahigh I_on/I_off ratio of 4.91 × 10³, a high photoconductive gain of 1.10 × 10³, a high detectivity of 1.65 × 10¹³ Jones and high response speed even in the case of very weak ultraviolet light illumination (1.87 μW cm^-2). The values are much higher than those of previously reported bare ZnS nanowires owing to the formation of core/shell heterostructures. Flexible ultraviolet photodetectors were also fabricated with the heterostructured ZnS/InP nanowires, which showed excellent mechanical flexibility, electrical stability and folding endurance besides excellent photoresponse properties. The results elucidated that the heterostructured ZnS/InP nanowires could find good applications in next generation flexible optoelectronic devices.

Fabrication of single Ga-doped ZnS nanowires as high-gain photosensors by focused ion beam deposition

ZnS nanowires were synthesized via a vapor-liquid-solid mechanism and then fabricated into a single-nanowire field-effect transistor by focused ion beam (FIB) deposition. The field-effect electrical properties of the FIB-fabricated ZnS nanowire device, namely conductivity, mobility and hole concentration, were 9.13 Ω^-1 cm^-1, 13.14 cm² V^-1 s^-1and 4.27 × 10¹⁸ cm^-3, respectively. The photoresponse properties of the ZnS nanowires were studied and the current responsivity, current gain, response time and recovery time were 4.97 × 10⁶ A W^-1, 2.43 × 10⁷, 9 s and 24 s, respectively. Temperature-dependent I-V measurements were used to analyze the interfacial barrier height between ZnS and the FIB-deposited Pt electrode. The results show that the interfacial barrier height is as low as 40 meV. The energy-dispersive spectrometer elemental line scan shows the influence of Ga ions on the ZnS nanowire surface on the FIB-deposited Pt contact electrodes. The results of temperature-dependent I-V measurements and the elemental line scan indicate that Ga ions were doped into the ZnS nanowire, reducing the barrier height between the FIB-deposited Pt electrodes and the single ZnS nanowire. The small barrier height results in the FIB-fabricated ZnS nanowire device acting as a high-gain photosensor.

Self-powered ZnS Nanotubes/Ag Nanowires MSM UV Photodetector with High On/Off Ratio and Fast Response Speed

In this study, we design and demonstrate a novel type of self-powered UV photodetectors (PDs) using single-crystalline ZnS nanotubes (NTs) as the photodetecting layer and Ag nanowires (NWs) network as transparent electrodes. The self-powered UV PDs with asymmetric metal-semiconductor-metal (MSM) structure exhibit attractive photovoltaic characteristic at 0 V bias. Device performance analysis reveals that the as-assembled PDs have a high on/off ratio of 19173 and a fast response speed (τ_r = 0.09 s, τ_f = 0.07 s) without any external bias. These values are even higher than that of ZnS nanostructures- and ZnS heterostructure-based PDs at a large bias voltage. Besides, its UV sensivity, responsivity and detectivity at self-powered mode can reach as high as 19172, 2.56 A/W and 1.67 × 10¹⁰ cm Hz^1/2 W^-1, respectively. In addition, the photosensing performance of the self-powered UV PDs is studied in different ambient conditions (e.g., in air and vacuum). Moreover, a physical model based on band energy theory is proposed to explain the origin of the self-driven photoresponse characteristic in our device. The totality of the above study signifies that the present self-powered ZnS NTs-based UV nano-photodetector may have promising application in future self-powered optoelectronic devices and integrated systems.

One-step fabrication of single-crystalline ZnS nanotubes with a novel hollow structure and large surface area for photodetector devices

ZnS nanotubes (NTs) were successfully prepared via a one-step thermal evaporation process without using any templates. The resulting NTs were single crystalline and structurally uniform. Based on experimental analysis, a tube-growth vapor-liquid-solid process was proposed as the growth mechanism of ZnS NTs. A metal-semiconductor-metal full-nanostructured ultraviolet (UV) photodetector with ZnS NTs as the active layer, and Ag nanowires of low resistivity and high transmissivity as electrodes, was fabricated and characterized. The ZnS NT-based device displayed a high I _on/I _off ratio of up to ∼1.56 × 10⁵ with a high response to UV incident light at low operation voltage. This work is a meaningful exploration for preparing other one-dimensional semiconductor NTs, and developing a high-performance and power-saving UV sensor.

Visible-light-driven photocatalytic properties of binary MoS2/ZnS heterostructured nanojunctions synthesized via one-step hydrothermal route

The MoS₂/ZnS binary heterojunctions obtained by a facile one-step hydrothermal route is competent to retrench the forbidden energy gap by creating sulfur vacancies. The tailoring of the lattice parameters of sulfides for interfacial charge transfer through the heterojunctions enhanced photocatalytic activity.

Fabrication of a Functionally Graded Copper-Zinc Sulfide Phosphor

Functionally graded materials (FGMs) are compositionally gradient materials. They can achieve the controlled distribution of the desired characteristics within the same bulk material. We describe a functionally graded (FG) metal-phosphor adapting the concept of the FGM; copper (Cu) is selected as a metal and Cu- and Cl-doped ZnS (ZnS:Cu,Cl) is selected as a phosphor and FG [Cu]-[ZnS:Cu,Cl] is fabricated by a very simple powder process. The FG [Cu]-[ZnS:Cu,Cl] reveals a dual-structured functional material composed of dense Cu and porous ZnS:Cu,Cl, which is completely combined through six graded mediating layers. The photoluminescence (PL) of FG [Cu]-[ZnS:Cu,Cl] is insensitive to temperature change. FG [Cu]-[ZnS:Cu,Cl] also exhibits diode characteristics and photo reactivity for 365 nm -UV light. Our FG metal-phosphor concept can pave the way to simplified manufacturing of low-cost and can be applied to various electronic devices.

Ultraviolet/visible photodetectors with ultrafast, high photosensitivity based on 1D ZnS/CdS heterostructures

One-dimensional (1D) semiconducting heterostructures have been widely studied for optoelectronics applications because of their unique geometry and attractive physical properties. In this study, we successfully synthesized 1D ZnS/CdS heterostructures, which can be used to fabricate high performance ultraviolet/visible photodetectors. Due to the separation of photo-generated electron-hole pairs, the resultant photodetector showed excellent photoresponse properties, including ultrahigh Ion/Ioff ratios (up to 10(5)) and specific detectivity (2.23 × 10(14) Jones), relatively fast response speed (5 ms), good stability and reproducibility. Moreover, the as-fabricated flexible photodetectors showed great mechanical stability under different bending conditions. Our results revealed the possibility of 1D ZnS/CdS heterostructures for application in the detection of UV and visible light. The main advantages of the heterostructures have great potential application for future optoelectronic devices.

Nanostructured Photodetectors: From Ultraviolet to Terahertz

Inspired by nanoscience and nanoengineering, numerous nanostructured materials developed by multidisciplinary approaches exhibit excellent photoelectronic properties ranging from ultraviolet to terahertz frequencies. As a new class of building block, nanoscale elements in terms of quantum dots, nanowires, and nanolayers can be used for fabricating photodetectors with high performance. Moreover, in conjunction with traditional photodetectors, they exhibit appealing performance for practical applications including high density of integration, high sensitivity, fast response, and multifunction. Therefore, with the perspective of photodetectors constructed by diverse low-dimensional nanostructured materials, recent advances in nanoscale photodetectors are discussed here; meanwhile, challenges and promising future directions in this research field are proposed.

An overview on emerging photoelectrochemical self-powered ultraviolet photodetectors

In recent years, as a new member of ultraviolet photodetectors (UV-PDs), photoelectrochemical UV-PDs (PEC UV-PDs) have received great attention. Compared to conventional photoconductors, PEC UV-PDs exhibit a number of merits, including low cost, environmentally friendly nature, being self-powered, and fast response. This tutorial review provides a comprehensive introduction to this research field, covering from the basics of performance evaluation of PEC UV-PDs, the state-of-the-art advances in structural design, electrolyte matching, and electrode fabrication of PEC UV-PDs, to the integration of multiple functions into a PEC UV-PD. In the end, we present our perspectives on the future development of PEC UV-PDs and highlight the key technical challenges in aiming to stimulate further developments in this research field.

Synthesis and enhanced gas sensing properties of Au-nanoparticle decorated CdS nanowires

CdS nanowires (NWs) with an average diameter of 30 nm were synthesized by a solvothermal method and then Au nanoparticles with a size of 10–25 nm were decorated on the surface of the as-synthesized CdS NWs through a simple deposition process.

Gas Sensors Based on Metal Sulfide Zn(1-x)Cd(x)S Nanowires with Excellent Performance

Metal sulfide Zn1-xCdxS nanowires (NWs) covering the entire compositional range prepared by one step solvothermal method were used to fabricate gas sensors. This is the first time for ternary metal sulfide nanostructures to be used in the field of gas sensing. Surprisingly, the sensors based on Zn1-xCdxS nanowires were found to exhibit enhanced response to ethanol compared to those of binary CdS and ZnS NWs. Especially for the sensor based on the Zn1-xCdxS (x = 0.4) NWs, a large sensor response (s = 12.8) and a quick rise time (2 s) and recovery time (1 s) were observed at 206 °C toward 20 ppm ethanol, showing preferred selectivity. A dynamic equilibrium mechanism of oxygen molecules absorption process and carrier intensity change in the NWs was used to explain the higher response of Zn1-xCdxS. The reason for the much quicker response and recovery speed of the Zn1-xCdxS NWs than those of the binary ZnS NWs was also discussed. These results demonstrated that the growth of metal sulfide Zn1-xCdxS nanostructures can be utilized to develop gas sensors with high performance.

High-performance ultraviolet photodetectors based on solution-grown ZnS nanobelts sandwiched between graphene layers

Ultraviolet (UV) light photodetectors constructed from solely inorganic semiconductors still remain unsatisfactory because of their low electrical performances. To overcome this limitation, the hybridization is one of the key approaches that have been recently adopted to enhance the photocurrent. High-performance UV photodetectors showing stable on-off switching and excellent spectral selectivity have been fabricated based on the hybrid structure of solution-grown ZnS nanobelts and CVD-grown graphene. Sandwiched structures and multilayer stacking strategies have been applied to expand effective junction between graphene and photoactive ZnS nanobelts. A multiply sandwich-structured photodetector of graphene/ZnS has shown a photocurrent of 0.115 mA under illumination of 1.2 mWcm(-2) in air at a bias of 1.0 V, which is higher 10(7) times than literature values. The multiple-sandwich structure of UV-light sensors with graphene having high conductivity, flexibility, and impermeability is suggested to be beneficial for the facile fabrication of UV photodetectors with extremely efficient performances.

Porous Au-embedded WO3 Nanowire Structure for Efficient Detection of CH4 and H2S

We developed a facile method to fabricate highly porous Au-embedded WO₃ nanowire structures for efficient sensing of CH₄ and H₂S gases. Highly porous single-wall carbon nanotubes were used as template to fabricate WO₃ nanowire structures with high porosity. Gold nanoparticles were decorated on the tungsten nanowires by dipping in HAuCl₄ solution, followed by oxidation. The surface morphology, structure, and electrical properties of the fabricated WO₃ and Au-embedded WO₃ nanowire structures were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and current–voltage measurements. Formation of a nanowire structure resulted in significant enhancement in sensing response to H₂S and CH₄ gases. Furthermore, Au embedment into the WO₃ nanowire structures remarkably improved the performance of the sensors. The increase in response performance of sensors and adsorption–desorption kinetic processes on the sensing layers were discussed in relation with the role of Au embedment.

Fabrication of spinel one-dimensional architectures by single-spinneret electrospinning for energy storage applications

A facile and general method is developed to fabricate one-dimensional (1D) spinel composite oxides with complex architectures by using a facile single-spinneret electrospinning technique. It is found that precursor polymers and heating rates could control the structures of the products, such as 1D solid, nanotube and tube-in-tubes structures. Especially, the tube-in-tube structures have been successfully fabricated for various mixed metal oxide, including CoMn2O4, NiCo2O4, CoFe2O4, NiMn2O4 and ZnMn2O4. Benefiting from the unique structure features, the tube-in-tube hollow nanostructures possess superior electrochemical performances in asymmetric supercapacitors and Li-O2 batteries.

Flexible ultraviolet photodetectors with broad photoresponse based on branched ZnS-ZnO heterostructure nanofilms

The application of nanofilm networks made of branched ZnS-ZnO nanostructures as a flexible UV photodetector is demonstrated. The fabricated devices show excellent operational characteristics: tunable spectral selectivity, widerange photoresponse, fast response speed, and excellent environmental stability.

Soluble polymer-based, blown bubble assembly of single- and double-layer nanowires with shape control

We present here an efficient blown bubble method for large-scale assembly of semiconducting nanowires, with simultaneous control on the material shape. As-synthesized Te nanowires in powder form are dispersed in a polymethylmethacrylate (PMMA) solution, assembled in a large size bubble blown from the solution, and then transferred (repeatedly) to arbitrary substrates. By this way, we have obtained single-layer (aligned) and double-layer (crossed) Te nanowires as well as buckled Te nanosprings which are converted from initially straight nanowires in situ during bubble blowing. The PMMA bubble film can be removed by direct dissolution in acetone to expose nanostructures with clean surface while maintaining original configuration. After matrix removal, these clean nanowire and nanospring arrays can be fabricated into functional nanoelectronic devices such as photodetectors and gas sensors with high performance.

Photochemistry-based method for the fabrication of SnO(2) monolayer ordered porous films with size-tunable surface pores for direct application in resistive-type gas sensor

A new photochemistry-based method was introduced for fabricating SnO2 monolayer ordered porous films with size-tunable surface pores on ceramic tubes used for gas sensors. The growth of the spherical pore walls was controlled by two times irradiation of the ultraviolet light using polystyrene microsphere two-dimensional colloidal crystal as a template. The surface pore size of the final obtained porous films was well tuned by changing the second irradiation time rather than replacing the template microspheres. The monolayer ordered porous films on the tubes were directly used, for the first time, as gas sensors. The sensitivity of the sensor depended on the surface pore size and was carefully analyzed by ethanol gas detection. The sensor also exhibited short response-recovery time and long-term stability at lower than 300 °C in practical applications. Therefore, this study opens up a kind of construction method for gas sensors, provides a new strategy for controlling the surface pore size of the monolayer ordered porous film, and introduces a new type of sensitivity-controllable gas sensor.

Selective synthesis of Sb2S3 nanoneedles and nanoflowers for high performance rigid and flexible photodetectors

Needle-like and flower-like antimony sulfide nanostructures were synthesized and applied for both rigid and flexible photodetectors. Rigid photodetectors based on both nanostructures have the features of linear photocurrent characteristics, low linear dynamic range and good sensitivity to light intensity. Especially, the rigid Sb2S3 nanoflowers photodetector has high photoresponse characteristics and its response time and decay time were found to be relatively fast as 6 ms and 10 ms respectively. The flexible Sb2S3 nanoflowers photodetector has high flexible, light-weight and adequate bendability with a response time of about 0.09 s and recovery time of 0.27 s. Our results revealed that the rigid and flexible photodetectors based on Sb2S3 nanostructures have great potential in next generation optoelectronic devices.

Fabrication of high-quality ZnTe nanowires toward high-performance rigid/flexible visible-light photodetectors

ZnTe is an important p-type semiconductor with great applications as field-effect transistors and photodetectors. In this paper, individual ZnTe nanowires based field-effect transistors was fabricated, showing evident p-type conductivity with an effect mobility of 11.3 cm(2)/Vs. Single ZnTe nanowire based photodetectors on rigid silicon substrate exhibited high sensitivity and excellent stability to visible incident light with responstivity and quantum efficiency as high as 1.87 × 10(5) A/W and 4.36 × 10(7)% respectively and are stable in a wide temperature range (25-250 °C). The polarization-sensitivity of the ZnTe nanowires was studied for the first time. The results revealed a periodic oscillation with the continuous variation of polarization angles. Besides, flexible photodetectors were also fabricated with the features of excellent flexibility, stability and sensitivity to visible incident light. Our work would enable application opportunities in using ZnTe nanowires for ultrahigh-performance photodetectors in scientific, commercial and industrial applications.

High-performance UV-visible-NIR broad spectral photodetectors based on one-dimensional In₂Te₃ nanostructures

For the first time, high quality In(2)Te(3) nanowires were synthesized via a chemical vapor deposition (CVD) method. The synthesized In(2)Te(3) nanowires are single crystals grown along the [132] direction with a uniform diameter of around 150 nm and an average length of tens of micrometers. Further, two kinds of photodetectors made by 1D In(2)Te(3) nanostructures synthesized by CVD and solvothermal (ST) methods respectively were fabricated. To our best knowledge, this is the first time photoresponse properties of In(2)Te(3) nanowire have been studied. The CVD grown nanowire device shows better performance than the ST device, which demonstrates a fast, reversible, and stable photoresponse and also a broad light detection range from 350 nm to 1090 nm, covering the UV-visible-NIR region. The excellent performance of the In(2)Te(3) nanowire photodetectors will enable significant advancements of the next-generation photodetection and photosensing applications.