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A novel carbon-enclosed chemical vapor deposition (CE-CVD) to grow high quality monolayer graphene on Cu substrate at a low temperature of 500 °C was demonstrated. The quality of the grown graphene was investigated by Raman spectra, and the detailed growth mechanism of high quality graphene by the CE-CVD process was investigated in detail. In addition to growth of high quality monolayer graphene, a transparent hybrid few-layer graphene/CuNi mesh electrode directly synthesized by the CE-CVD process on a conventional glass substrate at the temperature of 500 °C was demonstrated, showing excellent electrical properties (∼5 Ω/□ @ 93.5% transparency) and ready to be used for optical applications without further transfer process. The few-layer graphene/CuNi mesh electrode shows no electrical degradation even after 2 h annealing in pure oxygen at an elevated temperature of ∼300 °C. Furthermore, the few-layer graphene/CuNi mesh electrode delivers an excellent corrosion resistance in highly corrosive solutions suc...

Two-dimensional layered semiconductors present a promising material platform for band-to-band-tunneling devices given their homogeneous band edge steepness due to their atomically flat thickness. Here, we experimentally demonstrate interlayer band-to-band tunneling in vertical MoS2/WSe2 van der Waals (vdW) heterostructures using a dual-gate device architecture. The electric potential and carrier concentration of MoS2 and WSe2 layers are independently controlled by the two symmetric gates. The same device can be gate modulated to behave as either an Esaki diode with negative differential resistance, a backward diode with large reverse bias tunneling current, or a forward rectifying diode with low reverse bias current. Notably, a high gate coupling efficiency of ∼80% is obtained for tuning the interlayer band alignments, arising from weak electrostatic screening by the atomically thin layers. This work presents an advance in the fundamental understanding of the interlayer coupling and electron tunneling in semiconductor vdW heterostructures with important implications toward the design of atomically thin tunnel transistors.

We herein report a gas-solid transformation mechanism for the surfactant-free synthesis of Te NWs at room temperature by electrolysis of bulk Bi2Te3 using H2Te gas. Te NWs, with an average diameter below 20 nm, grow along the [001] direction due to the unique spiral chains in the crystal structure and show an enhanced Raman scattering effect, a broad absorption band over the range of 350-750 nm and an emission band over the range of 400-700 nm in the photoluminescence spectrum. In terms of device applications, we demonstrate how Te NWs can be directly applied as a p-type dopant source in order to shift the Dirac point in ambipolar field effect graphene transistors. Finally, the favorable capacitive properties of Te NWs are established as supercapacitor electrodes with negligible internal resistance and excellent electrochemical reversibility and a specific capacitance of 24 F g(-1).

A facile wet soaking process by immersing a CIGS thin film in a mixed aqueous solution, containing gallium trichloride and thioacetamide at 80 °C for a few tens of seconds, was proposed to reduce the existence of defects in the CIGS absorption layer which can be confirmed by the temperature dependence of the open-circuit voltage (Voc). The depth profiles of X-ray photoelectron spectroscopy (XPS) results indicate that the gallium (Ga) concentration increases during the short wet soaking time, resulting in a widening of the band gap near the surface region. The enhanced carrier lifetime attributed to the Ga-induced defect reduction during thermal treatment of device fabrication was evaluated by time-resolved photoluminescence (TRPL) spectroscopy. With wet and light soaking processes, Voc, short circuit current (Jsc) and fill factor (F.F.) can be increased, yielding a significant enhancement in cell efficiency from ∼1% to ∼6.4%. We believe that this fast, simple and effective method can further stimulate the development of CBD-Zn(O,S)/post-selenization CIGS solar cells toward commercialized thin film photovoltaics.

A prominent anodic material of silicon ultranano-particles (SiUPs, size < 10 nm) using recycled Si wafer fractures as raw materials and further improvement called top-down dispersion for high-capacitive Li-ion batteries has been addressed originally in this work. Economic benefits and outstanding electrochemical properties, including shorter Li-ion diffusive paths and low-strained effects as a result of the unique ultra-nanometric structure, enable such SiUPs to possess superior advantages for scalable manufacturing procedures as compared to other nanometric Si powders and become the priority of starting materials for Si-based anodes potentially. Meanwhile, an advanced top-down dispersive process has been optimized systematically to prevent severe particle aggregation to ameliorate the electrochemical performance of SiUP electrodes. In addition to avoiding pre-aggregation, this top-down dispersion brings in adequate buffer spaces, constructed by dispersive media (graphite flakes) and well-dispersive ultrasmall SiUP nanoclusters (size < 100 nm), alleviating drastic volume variation and local stress during cycling. These improved SiUP electrodes maintained 1200 mA h g−1 specific capacity over 300 cycles at a high current density of 0.8 A g−1, coupled with ca. 98.5% reversibility. On the basis of these advantages, including low cost, facile manufacture and high performance, this original method provides a pathway to achieve commercial high-capacitive Si–C composite anodes for Li-ion batteries.

Directing the morphological evolution of one-dimensional materials in order to tune their properties for a variety of practical applications in optical sensing and solar cells is an ongoing effort. Here, we establish a systematic method for exerting control over the morphology of nanowires (NWs) grown via a vapour–solid–solid (VSS) process from different metal catalysts. We use germanium, a technologically important material, to demonstrate how catalysts influence the axial growth rate of a crystalline core against the lateral vapour deposition of an amorphous shell which in turn deforms the NWs into straight, tapered or spiral geometries due to interfacial stress. Finite element method (FEM) and molecular dynamic (MD) simulations are further utilized to confirm the proposed mechanism of deformation in crystalline–amorphous core–shell NWs.

HfO2/porous nickel silicide (NiSi) hierarchical structures fabricated by metal-assisted chemical etching (MACE) followed by a silicidation process and deposition of HfO2 by atomic layer deposition (ALD) have been. The as-formed porous structures are systematically investigated using etching solutions of various HF/H2O2 ratios and the manipulation of electrical double-layer (EDL) overlapping, leading to electrical charge-induced selective ion penetration in HfO2/porous NiSi hierarchical structures. Its desalination ability was examined, in which the ionic concentration of saline water can be reduced by 21% when a bias of 2 V was applied. In addition, the mechanical property of the as-formed porous NiSi membrane was estimated to have a flexural strength of 124.04 MPa. These porous NiSi membranes can be continuously operated for 18 h without loss of its deionization ability.

Phase-engineered type-II metal-selenide heterostructures are demonstrated by directly selenizing indium-tin oxide to form multimetal selenides in a single step. The utilization of a plasma system to assist the selenization facilitates a low-temperature process, which results in large-area films with high uniformity. Compared to single-metal-selenide-based photodetectors, the multimetal-selenide photodetectors exhibit obviously improved performance, which can be attributed to the Schottky contact at the interface for tuning the carrier transport, as well as the type-II heterostructure that is beneficial for the separation of the electron-hole pairs. The multimetal-selenide photodetectors exhibit a response to light over a broad spectrum from UV to visible light with a high responsivity of 0.8 A W-1 and an on/off current ratio of up to 102 . Interestingly, all-transparent photodetectors are successfully produced in this work. Moreover, the possibility of fabricating devices on flexible substrates is also demonstrated with sustainable performance, high strain tolerance, and high durability during bending tests.

A p-a-SiC:H window layer was used in amorphous Si thin film solar cells to boost the conversion efficiency in an indoor lighting of 500 lx. The p-a-SiC:H window layer/p-a-Si:H buffer layer scheme moderates the abrupt band bending across the p/i interface for the enhancement of VOC, JSC and FF in the solar spectra of short wavelengths. The optimized thickness of i-a-Si:H absorber layer is 400 nm to achieve the conversion efficiency of ~9.58% in an AM1.5 G solar spectrum. However, the optimized thickness of the absorber layer can be changed from 400 to 600 nm in the indoor lighting of 500 lx, exhibiting the maximum output power of 25.56 μW/cm2. Furthermore, various durability tests with excellent performance were investigated, which are significantly beneficial to harvest the indoor lights for applications in the self-powered internet of thing (IoT).

Integration of strain engineering of two-dimensional (2D) materials in order to enhance device performance is still a challenge. Here, we successfully demonstrated the thermally strained band gap engineering of transition-metal dichalcogenide bilayers by different thermal expansion coefficients between 2D materials and patterned sapphire structures, where MoS2 bilayers were chosen as the demonstrated materials. In particular, a blue shift in the band gap of the MoS2 bilayers can be tunable, displaying an extraordinary capability to drive electrons toward the electrode under the smaller driven bias, and the results were confirmed by simulation. A model to explain the thermal strain in the MoS2 bilayers during the synthesis was proposed, which enables us to precisely predict the band gap-shifted behaviors on patterned sapphire structures with different angles. Furthermore, photodetectors with enhancement of 286% and 897% based on the strained MoS2 on cone- and pyramid-patterned sapphire substrates were demo...

Core-shell NWs offer an innovative approach to achieve nanoscale metal-insulator-metal (MIM) heterostructures along the wire radial direction, realizing three-dimensional geometry architecture rather than planar type thin film devices. This work demonstrated the tunable resistive switching characteristics of ITO/HfO

Development of manufacture trend for TFTs technologies has focused on improving electrical properties of films with the cost reduction to achieve commercialization. To achieve this goal, high-performance sub-50 nm TFTs-based MOSFETs with ON-current (Ion)/subthreshold swing (S.S.) of 181 µA/µm/107 mV/dec and 188 µA/µm/98 mV/dec for NMOSFETs and PMOSFETs in a monolithic 3D circuit were demonstrated by a low power with low thermal budget process. In addition, a stackable static random access memory (SRAM) integrated with TFTs-based MOSFET with static noise margins (SNM) equals to 390 mV at VDD = 1.0 V was demonstrated. Overall processes include a low thermal budget via ultra-flat and ultra-thin poly-Si channels by solid state laser crystallization process, chemical-mechanical polishing (CMP) planarization, plasma-enhanced atomic layer deposition (ALD) gate stacking layers and infrared laser activation with a low thermal budget. Detailed material and electrical properties were investigated. The advanced 3D architecture with closely spaced inter-layer dielectrics (ILD) enables high-performance stackable MOSFETs and SRAM for power-saving IoT/mobile products at a low cost or flexible substrate.

Ink-printing method emerges as a viable way for manufacturing large-scale flexible Cu(In,Ga)Se

Multigas sensors on a chip with chemical-sensitive nanoscale silicon transistors., There is great interest in developing a low-power gas sensing technology that can sensitively and selectively quantify the chemical composition of a target atmosphere. Nanomaterials have emerged as extremely promising candidates for this technology due to their inherent low-dimensional nature and high surface-to-volume ratio. Among these, nanoscale silicon is of great interest because pristine silicon is largely inert on its own in the context of gas sensing, unless functionalized with an appropriate gas-sensitive material. We report a chemical-sensitive field-effect transistor (CS-FET) platform based on 3.5-nm-thin silicon channel transistors. Using industry-compatible processing techniques, the conventional electrically active gate stack is replaced by an ultrathin chemical-sensitive layer that is electrically nonconducting and coupled to the 3.5-nm-thin silicon channel. We demonstrate a low-power, sensitive, and selective multiplexed gas sensing technology using this platform by detecting H2S, H2, and NO2 at room temperature for environment, health, and safety in the oil and gas industry, offering significant advantages over existing technology. Moreover, the system described here can be readily integrated with mobile electronics for distributed sensor networks in environmental pollution mapping and personal air-quality monitors.

Using thermal strain concept, we can tune the bandgap of bilayer MoS 2 through the two different thermal expansion coefficients of sapphire. Also, we propose a simple model to explain and precisely predict the bandgap-shifted behavior.

We have successfully demonstrated that the femtosecond laser annealing treatment can give rise to significant improvements in both crystalline structure and defects reduction for the nonvacuum ink-printing CIGS thin films without introducing melting effect.

Modified stacking sequence of precursors and pre-annealing process on Se vapor at low temperature were applied to Cu(In,Ga)Se 2 (CIGS) solar. The remarkable improvement of efficiency (5.53–10.10% and further 11.04%) and open circuit voltage (0.41 V–0.53 V and further 0.56 V) comes from a compact, smooth microstructure, and modified depth profile of Ga with suitable thickness of CuGa multi-stacking layers in the top of precursors as well as surface bandgap enhancement via pre-annealing process without Se vapor followed by a specific non-toxic hydrogen-assisted solid Se vapor selenization process. The effects of microstructural, compositional and electrical characteristics of Ga distribution including accumulation and interdiffusion were examined in detail. Finally, a large-area (40×30 cm 2 ) CIGS solar cell efficiency with improved open circuit voltage ( V OC ) and fill factor (FF) of 36% and 14% has been demonstrated, yielding a promising efficiency of ~11.04%.

Work function engineering, a precise tuning of the work function, is essential to achieve devices with the best performance. In this study, we demonstrate a simple technique to deposit graphene on insulators with in situ controlled boron doping to tune the work function. At a temperature higher than 1000 °C, the boron atoms substitute carbon sites in the graphene lattice with neighboring carbon atoms, leading to the graphene with a p-type doping behavior. Interestingly, the involvement of boron vapor into the system can effectively accelerate the reaction between nickel vapor and methane, achieving a fast graphene deposition. The changes in surface potential and work function at different doping levels were verified by Kelvin probe force microscopy, for which the work function at different doping levels was shifted between 20 and 180 meV. Finally, the transport mechanism followed by the Mott variable-range hopping model was found due to the strong disorder nature of the system with localized charge-carrie...

Gelatin is a natural protein, which works well as the gate dielectric for pentacene/N,N-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) ambipolar organic field-effect transistors (OFETs) in air ambient and in vacuum. An aqueous solution process was used to form the gelatin gate dielectric film on poly(ethylene terephthalate) (PET) by spin-coating and subsequent casting. Pentacene morphology and interface roughness are two major factors affecting the electron and hole field-effect mobility (μFE) values of pentacene/PTCDI-C8 ambipolar OFETs in vacuum and in air ambient. In contrast, water absorption in gelatin has higher contribution to the electron and hole μFE values in air ambient. The ambipolar performance of pentacene/PTCDI-C8 ambipolar OFETs depends on their layer sequence. For example, when PTCDI-C8 is deposited onto pentacene, i.e. in the structure of PTCDI-C8/pentacene, unbalanced ambipolar characteristics appear. In contrast, better ambipolar performance occurs in the structure of pentacene/PTCDI-C8. The optimum ambipolar characteristics with electron μFE of 0.85 cm2 V−1 s−1 and hole μFE of 0.95 cm2 V−1 s−1 occurs at the condition of pentacene (40 nm)/PTCDI-C8 (40 nm). Surprisingly, water absorption plays a crucial role in ambipolar performance. The device performance changes tremendously in pentacene/PTCDI-C8 ambipolar OFETs due to the removal of water out of gelatin in vacuum. The optimum ambipolar characteristics with electron μFE of 0.008 cm2 V−1 s−1 and hole μFE of 0.007 cm2 V−1 s−1 occurs at the condition of pentacene (65 nm)/PTCDI-C8 (40 nm). The roles of layer sequence, relative layer thickness, and water absorption are proposed to explain the ambipolar performance.

Silicate glass irradiated by γ-rays was investigated in this study using spectroscopic analyses which included ultraviolet–visible (UV–Vis) absorption, electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR). The phenomenon of coloration on γ-ray-irradiated silicate glass was analyzed and the effect of annealing on the silicate coloration was also investigated. The results revealed that the coloration originates from the creation of hole-centers ( HC ) caused by radiation. The shade of the coloration highly correlates to the amount of these HC -related defects but can be reversed by thermal annealing. The variation in coloration is an effective predictive factor in understanding radiation damage on silicate glass. Therefore, this study is relevant in the development of radiation detectors using silicate material as well as in the permanent disposal of high-level nuclear waste in glass form.

Dense nanoscale twins were introduced into Cu films and nanowires through bombardment with high-energy Ar+ ions at low temperatures. Both the twin boundary density and indentation hardness of the ion-irradiated Cu films increased with decreases in the bombardment temperature. The improved mechanical strength in the ion-irradiated Cu films is attributed to twin boundary–dislocation and dislocation–dislocation interactions. The strengthened region is several hundreds of nanometers beneath the surface of the bombarded nanowires and thin strips. A mechanism based on irradiation-induced thermal spike cascades is proposed to explain the influence of the energy of the Ar+ ions and bombardment temperature on nanoscale twinning in crystalline Cu. This study provides a route to developing advanced interconnection technology for micro- and nanoelectronic devices.

We have successfully demonstrated a great advantage of plasmonic Au nanoparticles for efficient enhancement of Cu(In,Ga)Se2(CIGS) flexible photovoltaic devices. The incorporation of Au NPs can eliminate obstacles in the way of developing ink-printing CIGS flexible thin film photovoltaics (TFPV), such as poor absorption at wavelengths in the high intensity region of solar spectrum, and that occurs significantly at large incident angle of solar irradiation. The enhancement of external quantum efficiency and photocurrent have been systematically analyzed via the calculated electromagnetic field distribution. Finally, the major benefits of the localized surface plasmon resonances (LSPR) in visible wavelength have been investigated by ultrabroadband pump-probe spectroscopy, providing a solid evidence on the strong absorption and reduction of surface recombination that increases electron-hole generation and improves the carrier transportation in the vicinity of pn-juction.

We report a versatile method based on low vacuum annealing of cellulose acetate on nickel (Ni) surface for rapid fabrication of graphene and carbon nanotube (CNT)-graphene hybrid films with tunable properties. Uniform films mainly composed of tri-layer graphene can be achieved via a surface precipitation of dissociated carbon at 800 °C for 30 seconds under vacuum conditions of ∼0.6 Pa. The surface precipitation process is further found to be efficient for joining the precipitated graphene with pre-coated CNTs on the Ni surface, consequently, generating the hybrid films. As expected, the hybrid films exhibit substantial opto-electrical and field electron emission properties superior to their individual counterparts. The finding suggests a promising route to hybridize the graphene with diverse nanomaterials for constructing novel hybrid materials with improved performances.

One-step facile methodology to create nanotip arrays on chalcopyrite materials (such as CuInS2, Cu(In,Ga)S2, CuInSe2, and Cu(In,Ga)Se2) via a low energy ion beam bombardment process has been demonstrated. The mechanism of formation for nanotip arrays has been proposed by sputtering yields of metals and reduction of metals induced by the ion beam bombardment process. The optical reflectance of these chalcopyrite nanotip arrays has been characterized by UV–vis spectrophotometer and the efficient light-trapping effect has been observed. Large scale (∼4′′) and high density (1010 tips/cm2) of chalcopyrite nanotip arrays have been obtained by using low ion energy (< 1 kV), short processing duration (< 30 min), and template-free. Besides, orientation and length of these chalcopyrite nanotip arrays are controllable. Our results can be the guide for other nanostructured materials fabrication by ion sputtering and are available for industrial production as well.

The major ampullate (MA) silk collected from giant wood spiders Nephila pilipes consists of 12% glutamic acid (Glu) and 4% tyrosine (Tyr) acidic amino residues. The MA silk may act as a natural polyelectrolyte for organic field-effect transistors (OFETs). Pentacene and F16CuPc OFETs were fabricated with the MA silk thin film as the gate dielectric. The MA silk thin film with surface roughness of 4 nm and surface energy of 36.1 mJ/m2 was formed on glass using a hexafluoroisopropanol (HFIP) organic process. The MA silk gate dielectric in pentacene OFETs may improve the field-effect mobility (μFE,sat) value in the saturation regime from 0.11 in vacuum to 4.3 cm2 V−1 s−1 in air ambient at ca. 70% RH. The corresponding threshold voltage (VTH) value reduced from −6 V in vacuum to −0.5 V in air ambient. Similar to other polyelectrolytes, the changes of μFE,sat and VTH may be explained by the generation of electric double layers (EDLs) in the MA silk thin film in air ambient due to water absorption.

Gelatin is a natural protein, which works well as the gate dielectric for N,N-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) organic field-effect transistors (OFETs). An aqueous solution process was applied to form the gelatin gate dielectric on poly(ethylene terephthalate) (PET) by spin-coating and subsequent casting. The field-effect mobility in the saturation regime (μFE,sat) and the threshold voltage (VT) values of a typical 40 nm PTCDI-C8 OFET are (0.22 cm2 V−1 s−1, 55 V) in vacuum and (0.74 cm2 V−1 s−1, 2.6 V) in air ambient. The maximum voltage shift in hysteresis is also reduced from 10 V to 2 V when the operation environment for PTCDI-C8 OFETs is changed from vacuum to air ambient. Nevertheless, a slight reduction of electron mobility was found when the device was stressed in the air ambient. The change in the device performance has been attributed to the charged ions generation owing to water absorption in gelatin in air ambient.

A nontoxic hydrogen-assisted solid Se vapor selenization process (HASVS) technique to achieve a large-area (40 × 30 cm2) Cu(In,Ga)Se2 (CIGS) solar panel with enhanced efficiencies from 7.1 to 10.8% (12.0% for active area) was demonstrated. The remarkable improvement of efficiency and fill factor comes from improved open circuit voltage (Voc) and reduced dark current due to (1) decreased interface recombination raised from the formation of a widened buried homojunction with n-type CdCu participation and (2) enhanced separation of electron and hole carriers resulting from the accumulation of Na atoms on the surface of the CIGS film. The effects of microstructural, compositional, and electrical characteristics with hydrogen-assisted Se vapor selenization, including interdiffusion of atoms and formation of buried homojunction, were examined in detail. This methodology can be also applied to CIS (CuInSe2) thin film solar cells with enhanced efficiencies from 5.3% to 8.5% (9.4% for active area) and provides a f...

We demonstrated that hierarchical structures combining different scales (i.e., pyramids from 1.5 to 7.5 μm in width on grooves from 40 to 50 μm in diameter) exhibit excellent broadband and omnidirectional light-trapping characteristics. These microscaled hierarchical structures could not only improve light absorption but prevent poor electrical properties typically observed from nanostructures (e.g., ultra-high-density surface defects and nonconformal deposition of following layers, causing low open-circuit voltages and fill factors). The microscaled hierarchical Si heterojunction solar cells fabricated with hydrogenated amorphous Si layers on as-cut Czochralski n-type substrates show a high short-circuit current density of 36.4 mA/cm(2), an open-circuit voltage of 607 mV, and a conversion efficiency of 15.2% due to excellent antireflection and light-scattering characteristics without sacrificing minority carrier lifetimes. Compared to cells with grooved structures, hierarchical heterojunction solar cells exhibit a daily power density enhancement (69%) much higher than the power density enhancement at normal angle of incidence (49%), demonstrating omnidirectional photovoltaic characteristics of hierarchical structures. Such a concept of hierarchical structures simultaneously improving light absorption and photocarrier collection efficiency opens avenues for developing large-area and cost-effective solar energy devices in the industry.

Tunable surface morphology in III-V semiconductor nanomembranes provides opportunities to modulate electronic structures and light interactions of semiconductors. Here, we introduce a vacuum-induced wrinkling method for the formation of ordered wrinkles in InGaAs nanomembranes (thickness, 42 nm) on PDMS microwell arrays as a strategy for deterministic and multidirectional wrinkle engineering of semiconductor nanomembranes. In this approach, a vacuum-induced pressure difference between the outer and inner sides of the microwell patterns covered with nanomembranes leads to bulging of the nanomembranes at the predefined microwells, which, in turn, results in stretch-induced wrinkle formation of the nanomembranes between the microwells. The direction and geometry of the nanomembrane wrinkles are well controlled by varying the PDMS modulus, depth, and shape of microwells, and the temperature during the transfer printing of nanomembrane onto heterogeneous substrates. The wrinkling method shown here can be applied to other semiconductor nanomembranes and may create an important platform to realize unconventional electronic devices with tunable electronic properties.

The influence of organically capped nucleation on morphogenesis of zinc oxide (ZnO) as a technologically important iono-covalent material has been extensively investigated. However, the effect of lipid–lipid interactions on selective adsorption and the mechanism of growth is largely unknown. Here, we demonstrate a novel route toward synthesis of various ZnO nanostructures using zinc stearate, a metal soap, rather than the commonly utilised polar-soluble salts. Study of a variety of amphiphilic ligands suggests that during decomposition, secondary carboxylic acids substitute primary aliphatic tails in the precursor. In this regard, saturated and unsaturated fatty acids appear to influence the rate of progression quite differently. On the other hand, in the early stages of growth, amine adsorbates are inhibited by lipophilic tails of carboxylic acids, leading to a multi-step growth. The subsequent self-assembly of these nanorods into bundles is accompanied by recrystallisation of their stems and formation of planar defects which promote random secondary nucleation.

Nanolizing of thermoelectric materials is one approach to reduce the thermal conductivity and hence enhance the figure of merit. Bismuth telluride (Bi2Te3)-based materials have excellent figure of merit at room temperature. For device applications, precise control and rapid fabrication for the nanostructure of thermoelectric materials are essential issues. In the present study, we demonstrate a one-step electrolysis process to directly form Bi2Te3 nanosheet arrays (NSAs) on the surface of bulk Bi2Te3 with controllable spacing distance and depth by tuning the applied bias and duration. The single sheet of NSAs reveals that the average thickness and electrical resistivity of single crystalline Bi2Te3 in composition are 399.8 nm and 137.34 μΩ m, respectively. The formation mechanism of NSAs has been proposed. A 1.12% efficiency of quantum dot-sensitized solar cells with Bi2Te3 NSAs for counter electrode has been demonstrated, indicating that Bi2Te3 NSAs from top-down processing with a high ratio of surface area to volume are a promising candidate for possible applications such as thermoelectrics, dye-sensitized solar cells (DSSCs), and lithium-ion batteries.

Manipulated bias control of a selector to a memristor was demonstrated in Zn-doped amorphous SiOx (SZO) films, within which ZnOx/Zn nanoclusters were segregated. For the selector, namely diode-like (pre-forming) switching, the threshold voltage varied from 9 to 2.7 V, with a resistance ratio of ∼104, by tuning the concentration of ZnOx/Zn nanoclusters. Stable bipolar resistive switching was achieved by current-controlled RESET and voltage-controlled SET processes. The working mechanism of the selector was explained by a transport mechanism which involved the “generalized trap-assisted tunnelling” of electrons resulting from doping with ZnOx/Zn nanoclusters. The dual-switching-mode of SZO provides a promising application for 3D cross-bar RRAM.

Densely nanotwinned Cu nanowire (NW) arrays with an identical diameter of ∼55 nm were fabricated by pulse electrochemical deposition at low temperature using anodic aluminum oxide as a template. Different growth orientations of nanotwinned Cu nanowire arrays were investigated. The endurance of the electrical current density before breakdown of the nanotwinned Cu NWs can reach up to 2.4 × 10(8) A cm(-2). The formation of highly dense nanotwins is attributed to relaxation of coalescence induced stress and twin fault stacking when Cu NWs grow by two-dimensional kinetics. A mechanism based on the twinning structure effect on the electromigration was proposed to explain the improved electrical endurance of Cu. The result demonstrates that the formation of nanotwins into Cu NWs can effectively suppress the void growth, leading to extended life time for use in electronic devices.

Enhanced field emission properties of Sn-doped In2O3 (ITO) nanowires (NWs) after the formation of a heterostructure core–shell configuration, namely ZnO nanoparticle-decorated HfO2/Sn-doped ITO NWs, by the atomic layer deposition (ALD) process were reported and investigated in detail. Island growth of a ZnO layer on the ITO NWs, with a low density, after the ALD process was observed while for the growth of the ZnO layer on the HfO2/ITO core–shell NWs, a ZnO layer with very tiny nanoparticles (NPs) can be achieved along the axial direction throughout the whole nanowire. A turn-on field of ∼10.8 eV with a field enhancement factor (β) of 409 can be found for the ITO NWs while the turn-on field decreases from 10.8 to 6 V μm−1 with an increase in the field enhancement factor (β) from 409 to 753 after the ZnO nanoparticle growth on the ITO NW. By combining the two materials utilizing surface modification engineering, a highly dense ZnO NP decorated on HfO2/ITO core–shell NWs can be achieved, resulting in a significant reduction of the turn-on field to 3.7 V μm−1 with an excellent field enhancement factor of 1677. The findings provide an effective way of improving the field emission properties for nanodevice applications.

III–V semiconductor nanowire (NW) materials possess a combination of fascinating properties, including their tunable direct bandgap, high carrier mobility, excellent mechanical flexibility, and extraordinarily large surface-to-volume ratio, making them superior candidates for next generation electronics, photonics, and sensors, even possibly on flexible substrates. Understanding the synthesis, property manipulation, and device integration of these III–V NW materials is therefore crucial for their practical implementations. In this review, we present a comprehensive overview of the recent development in III–V NWs with the focus on their cost-effective synthesis, corresponding property control, and the relevant low-operating-power device applications. We will first introduce the synthesis methods and growth mechanisms of III–V NWs, emphasizing the low-cost solid-source chemical vapor deposition (SSCVD) technique, and then discuss the physical properties of III–V NWs with special attention on their dependences on several typical factors including the choice of catalysts, NW diameters, surface roughness, and surface decorations. After that, we present several different examples in the area of high-performance photovoltaics and low-power electronic circuit prototypes to further demonstrate the potential applications of these NW materials. Towards the end, we also make some remarks on the progress made and challenges remaining in the III–V NW research field.

One-dimensional polycrystallineTa2O5nanostructures are synthesized by the annealing of theSiO2nanowires at 950°C in a reductive Ta vapor ambiance. The formation mechanism ofTa2O5nanostructures is discussed and illustrated in detail. The nucleation and grain growth ofTa2O5crystals were investigated during the formation of theSiO2/Ta2O5core-shelled structures. The diffusion-controlled growth is suggested to be the rate-determining step for the diffusion of the Ta atoms through the ash layer to react with O atoms and substitute Si atoms.

Recent advances in the development of quantum dots (QDs) have offered new possibilities for the exploration of sensors, bio imaging, batteries, electrochemical water splitting and optoelectronic applications because of their intriguing optical, electrical, catalytic and electrochemical properties. Among QDs, atomically thin two-dimensional quantum dots (2D QDs) derived from graphene sheets, transition metal dichalcogenide (TMD) layers and phosphorene have been of considerable interest for the past few years. There have been several intensive studies of carbon QDs, but TMD QDs and heterostructures based on 2D QDs are rapidly advancing. Herein, the synthesis and properties of 2D QDs, particularly carbon and TMD QDs, are reviewed for the recent progress in their application toward electrochemical water splitting, photocatalytic wastewater treatment, supercapacitors, batteries and photodetectors. Moreover, the assembly of such 2D QDs to achieve industrial-scale production and boost their performance in widespread applications is emphasized.

A highly efficient nitrogen-doped carbon nanotubes (N-CNTs) electrocatalyst derived from nitrogen-doped carbon dots (N-Cdots) and metal-organic frameworks (MOFs) for oxygen reduction reaction (ORR) was demonstrated successfully for the first time. The N-Cdots with plenty of hydroxyl and amine groups can favor the formation of N-CNTs through the catalytic decomposition of MOFs in a lower temperature. On the other hand, the N-Cdots serve as inducers of the graphitic structure and supply extra nitrogen, extending a potential electrocatalytic activity of N-CNTs. Results show that the N-CNTs provided an excellent ORR electrocatalytic performance, yielding a positive onset potential of 0.88 V vs. RHE and a high kinetic current density of up to 5.58 mA cm−2 at 0.2 V. In addition, the slope of N-CNTs being ∼81 mV/dec can be found to be much lower than that of the Pt/C catalyst (∼132 mV/dec). These superior performances are attributed to defects in the graphitic crystal structure and the synergistic coupling effects of N-Cdots and N-CNTs. In addition, a slight loss in activity for the N-CNTs catalyst can be found whereas the Pt/C catalyst decreases nearly 45% of its initial activity, which exhibit highly catalytic durability and tolerance to methanol in an alkaline media.

2D materials have attracted much attention because of frontier electronic materials due to its superior electronic transport properties and mechanical flexibility in the future, making it a potential material for high performance and wearable electronics. Graphene is a typical 2D materials with high carrier mobility; however, it still cannot be applied in transistor due to the lack of bandgap. A new type of 2D semiconducting materials called transition metal dichalcogenides (TMDCs), which are layered structure with the strong in-plane bonding and weak out-of-plane interactions similar to graphite, have been intensively studied. Recent studies have predicted exceptional physical properties upon reduced dimensionality attracting lots of attention due to the versatile physical chemical behaviors. Nevertheless, the synthesis and the study of the fundamental physical properties of TMDs are still in early stages. The lack of a large-area and reliable synthesis method restrict exploring all the potential applications of the TMDs. Chemical vapor deposition (CVD) is a traditional approach for the growth of TMDs; nevertheless, the high growth temperature is a major drawback for its to be applied in flexible electronics. In this talk, an inductively coupled plasma (ICP) was used to synthesize Transition Metal Dichalcogenides (TMDs) through a plasma-assisted selenization process of metal oxide (MOx) at a low temperature, as low as 250 °C. Compared to other CVD processes the use of ICP facilitates the decomposition of the precursors at lower temperatures; therefore, the temperature required for the formation of TMDs can be drastically reduced. WSe2 was chosen as a model material system due to its technological importance as a p-type inorganic semiconductor with an excellent hole mobility. Large-area synthesis of WSe2 on polyimide (30 x 40 cm2) flexible substrates and 8-inch silicon wafers with good uniformity was demonstrated at the formation temperature of 250 °C as confirmed by Raman and X-ray Photoelectron (XPS) spectroscopy. Furthermore, by controlling different H2/N2 ratios, hybrid WOx/WSe2 films can be formed at the formation temperature of 250 ºC as shown by TEM and confirmed by XPS. The applications including (1) water splitting, (2) gas sensors and (3) photodetectors will be reported.

Ultrathin 2D molybdenum disulfide (MoS2 ), which is the flagship of 2D transition-metal dichalcogenide nanomaterials, has drawn much attention in the last few years. 2D MoS2 has been banked as an alternative to platinum for highly active hydrogen evolution reaction because of its low cost, high surface-to-volume ratio, and abundant active sites. However, when MoS2 is used directly as a photocatalyst, contrary to public expectation, it still performs poorly due to lateral size, high recombination ratio of excitons, and low optical cross section. Besides, simply compositing MoS2 as a cocatalyst with other semiconductors cannot satisfy the practical application, which stimulates the pursual of a comprehensive insight into recent advances in synthesis, properties, and enhanced hydrogen production of MoS2 . Therefore, in this Review, emphasis is given to synthetic methods, phase transitions, tunable optical properties, and interfacial engineering of 2D MoS2 . Abundant ways of band edge tuning, structural modification, and phase transition are addressed, which can generate the neoteric photocatalytic systems. Finally, the main challenges and opportunities with respect to MoS2 being a cocatalyst and coherent light-matter interaction of MoS2 in photocatalytic systems are proposed.

In this work, we present a novel pH sensor using efficient laterally coupled structure enabled by Complementary Metal-Oxide Semiconductor (CMOS) Fin Field-Effect Transistor (FinFET) processes. This new sensor features adjustable sensitivity, wide sensing range, multi-pad sensing capability and compatibility to advanced CMOS technologies. With a self-balanced readout scheme and proposed corresponding circuit, the proposed sensor is found to be easily embedded into integrated circuits (ICs) and expanded into sensors array. To ensure the robustness of this new device, the transient response and noise analysis are performed. In addition, an embedded calibration operation scheme is implemented to prevent the proposed sensing device from the background offset from process variation, providing reliable and stable sensing results.

Molybdenum disulfide (MoS2)-based phototransistors are attractive for optical electronics in a large-scale size, such as transparent touch screens. However, most of the work done over the past decade has been on an opaque SiO2/Si wafer with a small size (micrometer to millimeter). In this work, a large-scale multilayer MoS2-based phototransistor has been fabricated on a transparent freestanding gallium nitride (GaN) wafer using a scalable chemical vapor deposition method. Due to the near lattice match and small thermal expansion mismatch between GaN and MoS2, the as-grown multilayer MoS2-on-GaN film shows high material quality in terms of low full width at half-maximum (∼5.16 cm−1) for the E2g1 Raman mode and a high absorption coefficient (∼106 cm−1) in the wavelength range of 405–638 nm. Under a wavelength of 405 nm at an incident power of 2 mW and applied voltage of 9 V, the fabricated MoS2-on-GaN phototransistor achieved a maximum responsivity of 17.2 A/W, a photocurrent gain of 53.6, and an external quantum efficiency of 5289%, with specific detectivity (∼1010–1012 Jones) and low noise equivalent power (10−12–10−14 W/Hz1/2) in the visible range of 405–638 nm. A typical response time of 0.1–4 s in the ambient air has also been recorded for the demonstrated MoS2-on-GaN phototransistor. Our work paves a technologic stepping stone for MoS2-based phototransistors for multifunctional transparent and touch-based optoelectronics in the future.

A facile approach for the synthesis of Au- and Pt-decorated CuInS2 nanocrystals (CIS NCs) as sensitizer materials on the top of MoS2 bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS2 bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20-40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS2 bilayers-based photodetectors. Remarkably, by using Pt- or Au-decorated CIS NCs, the photocurrent enhancement of MoS2 photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS2 -based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.