Synthesis, structure, and multiply enhanced field-emission properties of branched ZnS nanotube-in nanowire core-shell heterostructures

Single-Walled ZnSe Nanotubes for High-Performance Photodetectors: A Computational Prediction

Low-dimensional nanomaterials show great potential for developing semiconducting materials due to their distinct electronic, optical, and mechanical properties. In this study, we constructed various one-dimensional ZnSe nanotubes and investigated their transport and photoresponse properties by using the density functional theory (DFT) and non-equilibrium Green's function (NEGF) method. Under bias regulation, one-dimensional tetragonal ZnSe nanotube curled along the diagonal can reach a current of 111.3 μA at a bias of 4.0 eV. It is worth noting that for all considered photon energies, the photocurrent exhibits a cosine dependence on the polarization angle, which is consistent with the photogalvanic effect. The results show that our constructed ZnSe nanotubes have potential for applications in electronic and optoelectronic devices.

Amphi-Luminescent MoS2 nanostructure for photocatalytic splitting of water and removal of Methylene Blue

Chemical dyes used in the textile industries are one of the major pollutants in water. Methylene blue (MB) is a commonly seen dye that creates hazardous health problems. In this article the photocatalytic degradation of MB by the nanocatalyst MoS2 (Nano-MoS2) and carbon dot (C Dots) incorporated MoS2 (Nano-CD-MoS2) is reported. The photocatalytic degradation of MB is analyzed based on the electron-hole recombination rate of the catalyst. Photoluminescence emission exhibited by the catalyst is used as a key indicator to probe the electron-hole recombination rate. Nano-MoS2 was synthesized hydrothermally at 180 0C for 8 h from ammonium tetra thiomolybdate (ATTM). C Dot was prepared following a green root from ash guard extract which later mixed with Nano-MoS2 and kept in an autoclave at a temperature 140 °C for 4 h to get Nano-CD-MoS2. The photoluminescence (PL) and photocatalytic behavior of Nano-MoS2 and Nano-CD-MoS2 and their application for water splitting and water purification are reported. The incorporation of graphene and artificial C Dot into MoS2 nanostructures are reported to increase the conductivity and active edge sites of MoS2 that enhances the photocatalytic action. Since green C Dots are eco-friendly and easily synthesizable than artificial C Dots, as a novel study, this article investigated the influence of green C Dots on the PL and photocatalytic performance of nanosized MoS2. Nano-MoS2 and Nano-CD-MoS2 exhibited both upconversion and downconversion PL; accordingly the nanostructures were termed as amphi-luminescent. The amphi-luminescence property widens the photon absorption range and hence enhances the catalytic degradation of dyes. Nano-MoS2 which exhibited lesser intensity of amphi-luminescence emission compared to Nano-CD-MoS2 showed better results in degradation of MB. C Dots may bind with the valence band electrons of MoS2, resulting in the reduction of dangling bonds. Dangling bonds can trap photo-induced excitons to hinder the rate of electron-hole recombination. So, fast electron-hole recombination occurs in Nano-CD-MoS2 than Nano-MoS2. Fast electron-hole recombination supports radiative electron-hole recombination while suppresses the non-radiative energy transfer of electrons and causes high PL intensity. However, according to the energy level diagram, Nano-MoS2 with minimal electron-hole recombination rate is more favorable for O2/O2-,.OH/ OH- and.OH/H2O reactions that facilitate MB degradation. Photocatalytic activity of catalysts were confirmed by measuring the photocurrent from a simple custom-made two-electrode water photolysis cell where the nanocatalysts were dispersed in electrolyte. Lead and steel rods were used as electrodes. Multimeter was used to measure current. Nano-MoS2 exhibited better performance with a maximum photocurrent of 141 µA. Influence of green C Dots in energy levels, PL and photocatalysis of MoS2 and mechanisms of PL and degradation of MB are thoroughly investigated in this article.

Controllable Fabrication of Zn2+ Self-Doped TiO2 Tubular Nanocomposite for Highly Efficient Water Treatment

Tailoring high-efficiency photocatalytic composites for various implementations is a major research topic. 1D TNTs-based nanomaterials show promise as a photocatalyst for the remediation of organic pigments in an aqueous solution. Despite this, TiO2 (TNTs) is only photoactive in the UV range due to its inherent restriction on absorption of light in the UV range. Herein, we provide a facile recipe to tailor the optical characteristics and photocatalytic activity of TNTs by incorporating Zn (II) ionic species via an ion-exchange approach in an aqueous solution. The inclusion of Zn (II) ions into the TNTs framework expands its absorption of light toward the visible light range, therefore TiO2 nanotubes shows the visible-light photo-performance. Activity performance on photocatalytic decontamination of RhB at ambient temperature demonstrates that Zn-TNTs offer considerable boosted catalytic performance compared with untreated tubular TiO2 during the illumination of visible light. RhB (10 mg L−1) degradation of around 95% was achieved at 120 min. Radical scavenger experiment demonstrated that when electron (e−) or holes (h+) scavengers are introduced to the photodegradation process, the assessment of decontamination efficacy decreased by 45% and 76%, respectively. This demonstrates a more efficient engagement of the photoexcited electrons over photogenerated holes in the photodegradation mechanism. Furthermore, there seems to be no significant decrease in the activity of the Zn-TNTs after five consecutive runs. As a result, the fabricated Zn-TNTs composite has a high economic potential in the energy and environmental domains.

In situ synthesis of hierarchically-assembled three-dimensional ZnS nanostructures and 3D printed visualization

Nanomaterials have gained enormous interest in improving the performance of energy harvest systems, biomedical devices, and high-strength composites. Many studies were performed fabricating more elaborate and heterogeneous nanostructures then the structures were characterized using TEM tomographic images, upgrading the fabrication technique. Despite the effort, intricate fabrication process, agglomeration characteristic, and non-uniform output were still limited to presenting the 3D panoramic views straightforwardly. Here we suggested in situ synthesis method to prepare complex and hierarchically-assembled nanostructures that consisted of ZnS nanowire core and nanoparticles under Ag₂S catalyst. We demonstrated that the vaporized Zn and S were solidified in different shapes of nanostructures with the temperatures solely. To our knowledge, this is the first demonstration of synthesizing heterogeneous nanostructures, consisting of a nanowire from the vapor-liquid-solid and then nanoparticles from the vapor-solid grown mechanism by in situ temperature control. The obtained hierarchically-assembled ZnS nanostructures were characterized by various TEM technologies, verifying the crystal growth mechanism. Lastly, electron tomography and 3D printing enabled the nanoscale structures to visualize with centimeter scales. The 3D printing from randomly fabricated nanomaterials is rarely performed to date. The collaborating work could offer a better opportunity to fabricate advanced and sophisticated nanostructures.

High-Performance Field Emitters Based on SiC Nanowires with Designed Electron Emission Sites

Making field emitters with both low turn-on field (E_to) and high current emission stability is one of the keys to push forward their practical applications. In the present work, we report the exploration of high-performance field emitters with designed sharp corners around SiC nanowires for fundamentally enhanced electron emission sites. The sharp corners with tailored densities are rationally created based on a facile etching technique. Accordingly, the emission sites and nanowires are integrated into a single-crystalline configuration without interfaces, which could offer the emitters with a robust structure to avoid the structural damage induced by the generated Joule heat and electrostatic forces over long-term field emission (FE) operation. Consequently, the E_to of the as-fabricated SiC field emitter is low down to 0.52 V/μm, which is comparable to the state-of-the-art one ever reported. Moreover, they have high electron emission stability with a current fluctuation of just 2% over 10 h, representing their promising applications in FE-based electronic units.

An interlinked computational–experimental investigation into SnS nanoflakes for field emission applications

Layered binary semiconductor materials have attracted significant interest as field emitters due to their low work function, mechanical stability, and high thermal and electrical conductivity.

Antiblocking Heterostructure to Accelerate Kinetic Process for Na-Ion Storage

Heterostructures are attracting increasing attention in the field of sodium-ion batteries. However, it is still unclear whether any two monophase components can be used to construct a high-performance heterostructure for sodium-ion batteries, as well as the kind of heterostructures that can boost electrochemical performances. In this study, based on classical semiconductor theories on antiblocking and blocking interfaces, attempts are made to answer the abovementioned queries. For this purpose, NiTe₂ -ZnTe antiblocking and CoTe₂ -ZnTe blocking heterostructures are synthesized through a bimetal-hexamine framework-derived strategy. The NiTe₂ -ZnTe antiblocking heterostructure exhibits excellent high-rate and cycling performances, while the CoTe₂ -ZnTe blocking heterostructure performs poorly, even compared to their monophase components. Further, kinetic measurements and theoretical calculation confirm that antiblocking heterointerfaces can boost Na-ion diffusion efficiency and decrease the diffusion barrier, which can be attributed to the highly conductive antiblocking heterointerfaces generated due to electron transfer from NiTe₂ to ZnTe. Therefore, this study provides a new perspective to design heterostructures more efficiently, with significantly better Na-ion storage performance.

Heterostructure Manipulation via in Situ Localized Phase Transformation for High-Rate and Highly Durable Lithium Ion Storage

Recently, heterostructures have attracted much attention in widespread research fields. By tailoring the physicochemical properties of the two components, creating heterostructures endows composites with diverse functions due to the synergistic effects and interfacial interaction. Here, a simple in situ localized phase transformation method is proposed to transform the transition-metal oxide electrode materials into heterostructures. Taking molybdenum oxide as an example, quasi-core-shell MoO₃@MoO₂ heterostructures were successfully fabricated, which were uniformly anchored on reduced graphene oxide (rGO) for high-rate and highly durable lithium ion storage. The in situ introduction of the MoO₂ shell not only effectively enhances the electronic conductivity but also creates MoO₃@MoO₂ heterojunctions with abundant oxygen vacancies, which induces an inbuilt driving force at the interface, enhancing ion/electron transfer. In operando synchrotron X-ray powder diffraction has confirmed the excellent phase reversibility of the MoO₂ shell during charge/discharge cycling, which contributes to the excellent cycling stability of the MoO₃@MoO₂/rGO electrode (1208.9 mAh g^-1 remaining at 5 A g^-1 after 2000 cycles). This simple in situ heterostructure fabrication method provides a facile way to optimize electrode materials for high-performance lithium ion batteries and possibly other energy storage devices.

Branched CdO/ZnO Core/Shell Heterogeneous Structure and Its Enhanced Photoelectrocatalytic Performance

Branched nanostructures of semiconductors based on one-dimensional heterostructures have many promising applications in optoelectronics, supercapacitors, photocatalysts, etc. Here, we report a novel branched core/shell CdO/ZnO hetero-nanostructure that resembles a Crimson bottlebrush (Callistemon Citrinus) but with intriguing hexagonal symmetry. The nanomaterials were fabricated via an improved one-step chemical vapor deposition method and consist of a CdO wire as the core and ZnO as the shell. With cadmium acting as a catalyst, ZnO nanowires grow as perpendicular branches from the CdO/ZnO one-dimensional core/shell structure. The nanostructures were characterized with X-ray diffraction scanning and transmission electron microscopy. A homogeneous epitaxial growth mechanism has been postulated for the formation of the nanostructure. The materials show a broad and strong absorption ranging from visible to ultraviolet and a better photoelectrocatalytic properties in comparison to pure ZnO or CdO. Our synthetic strategy may open up a new way for controlled preparation of one-dimensional nanomaterials with core/shell heterostructure, which could find potential applications in solar cells and opto-electrochemical water-splitting devices.

Direct Patterning of Zinc Sulfide on a Sub-10 Nanometer Scale via Electron Beam Lithography

Nanostructures of metal sulfides are conventionally prepared via chemical techniques and patterned using self-assembly. This poses a considerable amount of challenge when arbitrary shapes and sizes of nanostructures are desired to be placed at precise locations. Here, we describe an alternative approach of nanoscale patterning of zinc sulfide (ZnS) directly using a spin-coatable and electron beam sensitive zinc butylxanthate resist without the lift-off or etching step. Time-resolved electron beam damage studies using micro-Raman and micro-FTIR spectroscopies suggest that exposure to a beam of electrons leads to quick disappearance of xanthate moieties most likely via the Chugaev elimination, and further increase of electron dose results in the appearance of ZnS, thereby making the exposed resist insoluble in organic solvents. Formation of ZnS nanocrystals was confirmed by high-resolution transmission electron microscopy and selected area electron diffraction. This property was exploited for the fabrication of ZnS lines as small as 6 nm and also enabled patterning of 10 nm dots with pitches as close as 22 nm. The ZnS patterns fabricated by this technique showed defect-induced photoluminescence related to sub-band-gap optical transitions. This method offers an easy way to generate an ensemble of functional ZnS nanostructures that can be arbitrarily patterned and placed in a precise way. Such an approach may enable programmable design of functional chalcogenide nanostructures.

Superior B-Doped SiC Nanowire Flexible Field Emitters: Ultra-Low Turn-On Fields and Robust Stabilities against Harsh Environments

Low turn-on fields together with boosted stabilities are recognized as two key factors for pushing forward the implementations of the field emitters in electronic units. In current work, we explored superior flexible field emitters based on single-crystalline 3C-SiC nanowires, which had numbers of sharp edges, as well as corners surrounding the wire body and B dopants. The as-constructed field emitters behaved exceptional field emission (FE) behaviors with ultralow turn-on fields (E_to) of 0.94-0.68 V/μm and current emission fluctuations of ±1.0-3.4%, when subjected to harsh working conditions under different bending cycles, various bending configurations, as well as elevated temperature environments. The sharp edges together with the edges were able to significantly increase the electron emission sites, and the incorporated B dopants could bring a more localized state close to the Fermi level, which rendered the SiC nanowire emitters with low E_to, large field enhancement factor as well as robust current emission stabilities. Current B-doped SiC nanowires could meet all essential requirements for an ideal flexible emitters, which exhibit their promising prospect to be applied in flexible electronic units.

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.

Fluorescence sensing of amine vapours based on ZnS-supramolecular organogel hybrid films

A selective fluorescent ZnS-supramolecular organogel hybrid film was constructed for sensing volatile organic monoamines and diamines vapour by adopting supramolecular gel films as substrates.

ZnO-(Cu/Ag)TCNQ heterostructure network over flexible platform for enhanced cold cathode application

Multistage field emitters consisting of organic/inorganic hybrid nanostructures with branched geometry are designed via a two-step protocol: a simple wet chemical method followed by a vapor-solid-phase technique. (Cu/Ag)TCNQ (copper/silver-7,7,8,8-tetracyanoquinodimethane) nanowires (NWs) were grown hierarchically on zinc oxide (ZnO) nanorods (NRs) to form ZnO-(Cu/Ag)TCNQ heterostructure assemblies. By monitoring the metallic Cu and Ag coating thickness on ZnO NRs, precise control over the morphology and orientations of the secondary organic NWs is achieved. In-depth analysis of electron field emission (FE) behavior of the ZnO-(Cu/Ag)TCNQ-based hierarchy suggests highest emission performance with low turn-on as well as threshold fields of 1.15 and 3.75 V μm(-1) respectively from the morphology-optimized hierarchy. Beneficial orientation of the branched organic NWs ensures sequential electric field enhancement in the consecutive stem and branches whereas its low work function eases electron emission; these aspects combined together render an overall enhancement in the emission behavior of the hybrid system. As compared to individual building units, the heterostructures show improved field electron emission. Additionally, successful construction of this novel hybrid over a fabric platform displays great potential in opening up new pathways in the highly-anticipated field of flexible electronics.

Effect of isovalent dopants on photodegradation ability of ZnS nanoparticles

Isovalent (Mn, Cd, Cu, Co)-doped-ZnS nanoparticles having size vary in between 2 to 5nm are synthesized by co-precipitation route. Their photocatalytic activity for decoloration of Cango Red and Malachite Green dyes is tested in visible radiation under natural conditions. Structural and morphological features of the samples are investigated by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and UVVis spectrometer. Single phase zinc blende structure of as-synthesized undoped and doped-ZnS is confirmed by XRD and revealed by Rietveld fitting. SEM and TEM images show ultrafine nanoparticles having size in the range of 2 to 5nm. UV-Vis absorption spectra exhibit blue shift in absorption edge of undoped and doped ZnS as compared to bulk counterpart. The photocatalytic activity as a function of dopant concentration and irradiation time is systematically studied. The rate of de-coloration of dyes is detected by UVVis absorption spectroscopy and organic dye mineralization is confirmed by table of carbon (TOC) study. The photocatalytic activity of Mn-doped ZnS is highest amongst all dopants; however Co as a dopant is found to reduce photocatalytic activity than pure ZnS.

Hierachical Ni@Fe2O3 superparticles through epitaxial growth of γ-Fe2O3 nanorods on in situ formed Ni nanoplates

One endeavour of nanochemistry is the bottom-up synthesis of functional mesoscale structures from basic building blocks. We report a one-pot wet chemical synthesis of Ni@γ-Fe2O3 superparticles containing Ni cores densely covered with highly oriented γ-Fe2O3 (maghemite) nanorods (NRs) by controlled reduction/decomposition of nickel acetate (Ni(ac)2) and Fe(CO)5. Automated diffraction tomography (ADT) of the Ni-Fe2O3 interface in combination with Mössbauer spectroscopy showed that selective and oriented growth of the γ-Fe2O3 nanorods on the Ni core is facilitated through the formation of a Fe0.05Ni0.95 alloy and the appearance of superstructure features that may reduce strain at the Ni-Fe2O3 interface. The common orientation of the maghemite nanorods on the Ni core of the superparticles leads to a greatly enhanced magnetization. After functionalization with a catechol-functional polyethylene glycol (C-PEG) ligand the Ni@γ-Fe2O3 superparticles were dispersible in water.

High Performance Field Emitters

The field electron emission performance of bulk, 1D, and 2D nanomaterials is here empirically compared in the largest metal-analysis of its type. No clear trends are noted between the turn-on electric field and maximum current density as a function of emitter work function, while a more pronounced correlation with the emitters dimensionality is noted. The turn-on field is found to be twice as large for bulk materials compared to 1D and 2D materials, empirically confirming the wider communities view that high aspect ratios, and highly perturbed surface morphologies allow for enhanced field electron emitters.

Hierarchical hexagonal boron nitride nanowall–diamond nanorod heterostructures with enhanced optoelectronic performance

Covering diamond nanorod with hexagonal boron nitride nanowalls is an effective approach for the fabrication of hierarchical heterostructured field emission devices that open new prospects in flat panel displays and high brightness electron sources.

Extremely Stable Current Emission of P-Doped SiC Flexible Field Emitters

Novel P-doped SiC flexible field emitters are developed on carbon fabric substrates, having both low E_to of 1.03-0.73 Vμm^-1 up to high temperatures of 673 K, and extremely high current emission stability when subjected to different bending states, bending circle times as well as high temperatures (current emission fluctuations are typically in the range ±2.1%-3.4%).

Facile synthesis of ZnPc nanoflakes for cold cathode emission

Field emission characteristics of well resolved ZnPc nanoflakes through hydrothermal method and simulation via finite element method.

The hydrothermal evolution of the phase and shape of ZnS nanostructures and their gas-sensing properties

The evolution of the phase of ZnS was achieved by adjusting the hydrothermal holding time or the dosage of the surfactant.

2D Hybrid Nanostructure of Reduced Graphene Oxide-CdS Nanosheet for Enhanced Photocatalysis

Graphene-based hybrid nanostructures have recently emerged as a new class of functional materials for light-energy conversion and storage. Here, we have synthesized reduced graphene oxide (RGO)-semiconductor composites to improve the efficiency of photocatalysis. Zero-dimensional CdS nanoparticles (0D), one-dimensional CdS nanorods (1D), and two-dimensional CdS nanosheets (2D) are grafted on the RGO sheet (2D) by a surface modification method using 4-aminothiophenol (4-ATP). Structural analysis confirms the attachment of CdS nanocrystals with RGO, and the strong electronic interaction is found in the case of a CdS nanosheet and RGO, which has an influence on photocatalytic properties. The degradation of dye under visible light varies with changing the dimension of nanocrystals, and the catalytic activity of the CdS NS/RGO composite is ∼4 times higher than that of CdS nanoparticle/RGO and 3.4 times higher than that of CdS nanorod/RGO composite samples. The catalytic activity of the CdS nanosheet/RGO composite is also found to be ∼2.5 times than that of pure CdS nanosheet samples. The unique 2D-2D nanoarchitecture would be effective to harvest photons from solar light and transport electrons to reaction sites with respect to other 0D-2D and 1D-2D hybrid systems. This observation can be extended to other graphene-based inorganic semiconductor composites, which can provide a valuable opportunity to explore novel hybrid materials with superior visible-light-induced catalytic activity.

Precise Determination of the Crystallographic Orientations in Single ZnS Nanowires by Second-Harmonic Generation Microscopy

We report on the systematical study of the second-harmonic generation (SHG) in single zinc sulfide nanowires (ZnS NWs). The high-quality ZnS NWs with round cross-section were fabricated by chemical vapor deposition method. The transmission electron microscopy images show that the actual growth axis has a deviation angle of 0°∼20° with the preferential growth direction [120], which leads to the various polarization-dependent SHG response patterns in different individual ZnS NWs. The SHG response is quite sensitive to the orientations of c axis as well as the (100) and (010) crystal-axis of ZnS NWs; thus, all the three crystal-axis orientations of ZnS NWs are precisely determined by the SHG method. A high SHG conversion efficiency of 7 × 10(-6) is obtained in single ZnS NWs, which shows potential applications in nanoscale ultraviolet light source, nonlinear optical microscopy, and nanophotonic devices.

Hierarchical cupric oxide nanostructures on copper substrate for cold cathode emission: an experimental venture with theoretical correlation

In this paper we report a facile route for the synthesis of controlled CuO nanoarchitectures directly grown on a copper substrate by a one-step simple chemical route with varying concentration of non-ionic surfactant PEG-6K. The phase purity and degree of crystallinity of the as-developed nanostructures were systemically investigated by X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy (HRTEM). A detailed analysis by field emission scanning electron microscopy confirmed the uniformity of the prepared nanostructures on the substrates. These architectures displayed substantial improvement of field emission properties with respect to other structures of CuO reported so far. A particular nanostructure (needle) among them showed a down shift of the turn-on field to 2.2 V μm(-1) coupled with a good enhancement factor (β) ∼516, which are deemed as sufficient for electron emission based applications such as field emission displays and vacuum nanoelectronic devices. The origin of this efficient field emission from CuO nanoarchitectures, were probed computationally by investigating the local electric field distribution through finite element based simulation method using the ANSYS Maxwell simulation package.

Enhanced electron field emission properties from hybrid nanostructures of graphene/Si tip array

High efficiency with excellently stable electron field emitters based on monolayer graphene coated on well-aligned Si tip (graphene/SiT) arrays fabricated by a simple transfer method is demonstrated.

A facile solution-based approach to a photocatalytic active branched one-dimensional TiO2 array

Branched one-dimensional TiO₂ array with enhanced photocatalytic activity was fabricated via a facile solution-based strategy.

Spontaneous hyper-branching in ZnO nanostructures: morphology dependent electron emission and light detection

The structure and intrinsic defect-induced electron field emission and photodetection are monitored in ZnO nanoforms with assorted morphology prepared in ambient conditions via a facile wet chemical approach.

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.

Vapor-liquid-solid growth of one-dimensional tin sulfide (SnS) nanostructures with promising field emission behavior

Single-crystalline ultralong tin sulfide (SnS) nanowires has been grown by a thermal evaporation technique under optimized conditions on gold-coated silicon substrates, and for the first time, field emission investigations on the SnS nanowires at the base pressure of 1 × 10(-8) mbar are reported. It has been revealed that the surface morphology of the as-synthesized SnS nanostructures is significantly influenced by the deposition temperature and duration. Structural and morphological analyses of as-synthesized SnS nanostructures have been carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). To understand the optical and electronic properties of as-synthesized SnS nanowires, ultraviolet-visible (UV-vis), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) studies were carried out. The SEM and TEM measurements reveal the formation of ultralong SnS nanowires, with an average diameter of 80 nm. A plausible explanation on the vapor-solid-liquid (VLS) growth mechanism based on the experimental results and reported literature has been presented. Furthermore, the field emission characteristics of the SnS nanowires are found to be superior to the other metal chalcogenide nanostructures. The synthesized SnS nanowire emitter delivers a high current density of ∼2.5 mA/cm(2) at an applied electric field of ∼4.55 V/μm. The emission current stability over a period of 6 h is observed to be good. The observed results demonstrate the potential of the SnS nanowire emitter as an electron source for practical applications in vacuum nano/microelectronic devices.

Effect of solvent and environmental conditions on the structural and optical properties of CdS nanoparticles

Different crystal structures, and tuning of absorption and emission of CdS nanoparticles have been obtained by changing the type of solvent and environmental conditions.

Efficient electrostatic self-assembly of one-dimensional CdS-Au nanocomposites with enhanced photoactivity, not the surface plasmon resonance effect

A series of CdS nanowire-Au nanocomposites (CdS NW-Au NCs) with different weight addition ratios of Au nanoparticles (NPs) are successfully synthesized by using a simple and efficient electrostatic self-assembly method at room temperature for utilizing the natural surface charge properties of the CdS NWs and Au NPs. These natural surface charge properties are dependent on the synthesis approaches. The probe reactions for photocatalytic selective reduction of nitroaromatic compounds in the aqueous phase under visible light irradiation are utilized to evaluate the photoactivity of this series of as-prepared CdS NW-Au NCs. The CdS NW-Au NCs exhibit significantly enhanced photoactivity as compared to the CdS nanowires (CdS NWs). The addition of Au NPs into the CdS NW domain enables efficient enhancement of the lifetime and transfer of photogenerated charge carriers from CdS NWs under visible light irradiation. However, the addition of excess amounts of Au NPs not only influences the penetration of light but the Au NPs also become the recombination centers, and result in decreased photoactivity. The optimal proportion of the Au NPs is proved to be 1 wt%, which indicates the synergistic effect between the CdS NWs and Au NPs. In addition, the surface plasmon resonance (SPR) effect of Au NPs is proved to not play an efficient role in the reaction and the possible photocatalytic reaction mechanism is proposed. It is hoped that this work could aid in the fabrication of 1-D semiconductor-metal nanocomposites by using such a simple and efficient electrostatic self-assembly strategy. In addition, it is also expected to enrich and supplement their application as visible light photocatalysts toward selective organic transformations through our investigation.

Anodic formation of anatase TiO2 nanotubes with rod-formed walls for photocatalysis and field emitters

Anatase TiO(2) nanotube arrays with rod-formed walls have been fabricated using a one-step anodic oxidation method for the first time. XRD, Raman spectroscopy, SEM, and HRTEM analysis were used for the structural characterization of the synthesized nanostructures. Their photocatalytic and field emission (FE) properties were also systematically investigated, and the experimental results indicated that the crystallization of the starting polycrystalline nanostructures turned into a better anatase phase after the annealed process. The photocatalytic properties showed that the nanostructures with optimized crystallization demonstrated faster degradation rate than the as-prepared polycrystalline counterparts, which would be caused by the improved crystallinity. Furthermore, the dependence of the FE properties on the distances between the anodes and the samples was investigated and the results revealed that the annealed samples have higher field enhancement factor β compared to the as-prepared nanostructures. The formation mechanism of this novel rod-formed TiO(2) nanotubes is also briefly discussed.

Controlled growth of SnO₂@Fe₂O₃ double-sided nanocombs as anodes for lithium-ion batteries

A novel heterostructure is developed by grafting 1D SnO(2) nanorods onto both sides of pre-grown 2D Fe(2)O(3) nanoflakes, forming a comb-like rather than tree-like branched nanostructure. The SnO(2) nanorod branches are determined to grow along the [001] direction on the (±001) planes of Fe(2)O(3) nanoflakes. The resulting SnO(2)@Fe(2)O(3) nanocombs show stabilized cycling performance and improved volumetric energy density compared to pristine Fe(2)O(3) nanoflakes presumably due to the integration of SnO(2) branches as well as the 3D hierarchical structural features.

One-step solvothermal synthesis of Fe3O4@C core-shell nanoparticles with tunable sizes

We report the synthesis of Fe3O4@C core-shell nanoparticles (FCNPs) by using a facile one-step solvothermal method. The FCNPs consisted of Fe3O4 particles as the cores and amorphous uniform carbon shells. The content of Fe3O4 is up to 81.6 wt%. These core-shell nanoparticles are aggregated by primary nanocrystals with a size of 10-12 nm. The FCNPs possess a hollow interior, high magnetization, excellent absorption properties and abundant surface hydroxyl groups. A possible growth mechanism of the FCNPs is proposed. The role of glucose in regulating the grain size and morphology of the particles is discussed. The absorption properties of the FCNPs towards Cr(VI) in aqueous solution is investigated. We demonstrate that the FCNPs can effectively remove more than 90 wt% of Cr(VI) from aqueous solution.

Dense and vertically-aligned centimetre-long ZnS nanowire arrays: ionic liquid assisted synthesis and their field emission properties

Based on the self-ordering behavior of ionic liquids on solid surface, a gold ion containing ionic liquid was employed to obtain a uniform pattern of gold nanoparticles on Si substrate. Using this catalytic pattern, super-dense, centimetre long, well-crystallized and vertically-aligned ZnS nanowire arrays were then generated. It was found that the densely-packed gold nanoparticles played a key role in the nanowire alignment. Furthermore, the field-emission measurements show that the present ultralong ZnS nanowires arrays possess a low turn-on field of 3.69 V μm(-1) and a high field-enhancement factor of 1215.4, indicating they are valuable field emitters.

Tuning the optical property and photocatalytic performance of titanate nanotube toward selective oxidation of alcohols under ambient conditions

Titanate nanotube (TNT) represents one class of novel one-dimensional semiconducting nanomaterials that can be used as photocatalyst for given applications. However, TNT is only UV-light photoactive because of its intrinsic limitation of light absorption in the UV region. Here, we report a facile approach to tune the optical property and photocatalytic performance of TNT by doping various metal ions (Cu(2+), Co(2+), Ni(2+), Fe(2+), and Mn(2+)) via an ion-exchange method in an aqueous phase. The optical properties of TNT can be finely tuned by incorporating different kinds of metal ions into its tubular framework. In particular, the incorporation of metal ions into the matrix of TNT is able to extend its light absorption to the visible-light region, thus making TNT have the visible-light photoactivity. Activity testing on photocatalytic selective oxidation of a variety of benzylic and allylic alcohols under mild conditions demonstrates that these metal-ion-doped TNTs exhibit markedly enhanced catalytic performance as compared to the undoped TNTs under both the irradiation of UV light and visible light. Such an enhancement of photocatalytic activity with regard to metal-ion-doped TNT is primarily attributed to the prolonged lifetime of photogenerated electron-hole pairs in comparison with that of undoped TNT. Our current research work demonstrates the tunable optical property of TNT by doping metal ions and, more significantly, opens promising prospects of one-dimensional nanotubular TNT or TNT-based materials as visible-light-driven photocatalyst in the area of selective transformation using molecular oxygen as benign oxidant under ambient conditions.

Luminescence and Morphological Kinetics of Functionalized ZnS Colloidal Nanocrystals

This paper reports functionalized zinc sulphide (ZnS) semiconductor nanocrystals (quantum dots, approx., 2.5 nm) which are an important building block in self-assembled nanostructures. ZnS is functionalized by organic stabilizer Thio glycolic acid (TGA). The samples have been synthesized by colloidal technique at relatively low temperature (below 100°C) at an atmospheric pressure of 10−3 torr. Manganese (Mn) doping ions have been incorporated (doped) in ZnS host lattice and observed its effect on growth morphology and optical properties of ZnS colloidal nanocrystals. By XRD, SEM, TEM, and PL, the obtained cubic phase nanosized TGA-capped ZnS materials were characterized. The morphology of ZnS obtained at different temperatures are analyzed by SEM. The crystallite size of the ZnS nanoparticles was estimated from the X-ray diffraction pattern by using Scherrer’s formula (approximately 2.5 nm) which is confirmed by TEM. The estimated bandgap value of ZnS NC’s by ()2 versus plot was 4.89 eV. Gaussian fitting curve in photoluminescence (PL) spectra indicated room temperature emission wavelength range from 300 to 500 nm in undoped and Mn-doped ZnS, with different emission peak intensities, and suggested the wide band emission colours in visible and near UV region which has wider applications in optical devices.

Controlled fabrication of core-shell TiO2/C and TiC/C nanofibers on Ti foils and their field-emission properties

Core-shell TiO(2)/C and TiC/C nanofibers are fabricated in situ on Ti and Al ion-implanted Ti substrates by a thermochemical reaction in acetone and the growth mechanism is described. Implantation of Al into Ti leads to in situ growth of TiC/C in lieu of TiO(2)/C nanofibers. This is because Al has a higher affinity to oxygen than Ti and Ti reacts preferentially with C to form TiC. The Ti foil serves as both the Ti source and substrate for the core-shell TiO(2)/C and TiC/C NFs to ensure strong bonding and small contact resistance between the Ti substrate and the core-shell field emitters. The core-shell TiC/C and TiO(2)/C nanofibers have similar morphology and structure, but the TiC/C nanofibers possess better field emission properties with a turn on field (E(to)) of 2.2 V/μm compared to an E(to) of 3.2 V/μm measured from the TiO(2)/C nanofibers. The enhanced field-emission property of the TiC/C nanofibers is attributed to the high electrical and thermal conductivity of the TiC inner core, which provides a more effective electron transfer pathway between the cathode and C shell emitters.