High-Performance Field-Emission Properties of Boron Nitride Nanotube Field Emitters

Boron nitride nanotubes (BNNTs) have attracted considerable attention as a field emission material because of their high mechanical strength, high negative electron affinity, and high oxidation resistance. Nevertheless, the obtained field-emission properties of BNNTs have indicated poor emission performance, which is a very high turn-on electric field with a low emission current. We fabricated BNNT field emitters and investigated their field-emission properties. The field-emission properties of the BNNT field emitters were considerably enhanced compared to those of other BN nanomaterial-based field emitters. The turn-on and the threshold electric fields of the BNNT field emitter were 3.1 and 5.4 V/μm at the gap distance of 750 μm, respectively. Both the turn-on and the threshold electric fields of the BNNT field emitters were decreased by increasing the gap distance between the emitter tip and the anode electrode. Degradation of the emission current during field emission operation for 20 h showed no significant difference according to the gap distance. Emission current fluctuation of the BNNT field emitters showed that the smaller gap was more unstable than the larger gap. The enhanced emission properties are mainly attributed to the small diameter, high-quality, and straight structure of BNNTs as well as the stable network formation of the BNNT film with good mechanical and electrical contact between the BNNTs and the cathode electrode. The remarkable emission performance of the BNNT field emitters might have promising applications for various field-emission devices.

Fabrication of a silica/titania hollow nanorod and its electroresponsive activity

In this study, a 1D oriented hollow SiO₂/TiO₂ (HST) rod-like material was successfully fabricated via a sequential combination of sol–gel use, TiO₂ incorporation, and a sonication-mediated etching and redeposition method.

Fabrication of periodic arrays of needle-like Si nanowires on (001)Si and their enhanced field emission characteristics

We report here the fabrication and field emission properties of highly-ordered, vertically-aligned tapered Si nanostructure arrays on (001)Si.

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.

Passivated Single-Crystalline CH3NH3PbI3 Nanowire Photodetector with High Detectivity and Polarization Sensitivity

Photodetectors convert light signals into current or voltage outputs and are widely used for imaging, sensing, and spectroscopy. Perovskite-based photodetectors have shown high sensitivity and fast response due to the unprecedented low recombination loss in this solution processed semiconductor. Among various types of CH₃NH₃PbI₃ morphology (film, single crystal, nanowire), single-crystalline CH₃NH₃PbI₃ nanowires are particularly interesting for photodetection because of their reduced grain boundary, morphological anisotropy, and excellent mechanical flexibility. The concomitant disadvantage associated with the CH₃NH₃PbI₃ nanowire photodetectors is their large surface area, which catalyzes carrier recombination and material decomposition, thus significantly degrading device performance and stability. Here we solved this key problem by introducing oleic acid soaking to passivate surface defects of CH₃NH₃PbI₃ nanowires, which leads to a device with much improved stability and unprecedented sensitivity (measured detectivity of 2 × 10¹³ Jones). By taking advantage of their one-dimensional geometry, we also showcased, for the first time, the linear dichroic photodetection of our CH₃NH₃PbI₃ nanowire photodetector.

Effects of ZnO Quantum Dots Decoration on the Field Emission Behavior of Graphene

ZnO quantum dots (QDs) have been decorated on graphene deposited on patterned Ag electrodes as a field emission cathode by a solution process. Effects of ZnO QDs on the field emission behavior of graphene are studied by experiment and first-principles calculations. The results indicate that the attachment of ZnO QDs with a C atom leads to the enhancement of electron emission from graphene, which is mainly attributed to the reduction of the work function and ionization potential, and the increase of the Fermi level of graphene after the decoration. A change in the local density distribution and the density of states near the Fermi level may also account for this behavior. Our study may help to develop new field emission composites and expand ZnO QDs in applications for electron emission devices as well.

The ultra-rapid synthesis of 2D graphitic carbon nitride nanosheets via direct microwave heating for field emission

The 2D g-C3N4 nanosheets were ultra-rapidly prepared via a direct microwave heating approach. The as-synthesized g-C3N4 possessed a large surface area, few stacking layers, a large aspect ratio and an enlarged bandgap. As a consequence, the excellent field emission properties of 2D g-C3N4 nanosheets were exhibited with extremely low turn-on fields.

Characterization of the fullerene end-functionalized ZnO nanotube: A computational study

The electronic and field emission properties of the fullerene end-functionalized zinc oxide nanotube (ZnONT) are investigated by density functional theory (DFT) to search for novel field emitter nano material. The interaction energies of ZnONT/fullerenes complexes gradually increase, with increasing the nanotube lengths which indicate that ZnONTs with higher lengths could improve the stability of the complexes. The band gaps of connected construction of fullerene molecules with ZnONTs gradually reduced by increasing the tube length, but were not sensitive to the tubes diameter. It is found that the ionization potentials of ZnONT/fullerenes complexes mainly decrease compared to that of pristine nanotube in the presence of 0, 0.002, 0.004[Formula: see text]a.u. electric field. The reduction of the ionization potential means the enhancement of the field emission properties of ZnONT/fullerenes complexes compared with simple ZnONT and fullerene molecules. The calculations show that the combination of ZnONT with fullerene molecules indeed improves the field emission by controlling the tube size and electric field strength.

SiC Nanowires with Tunable Hydrophobicity/Hydrophilicity and Their Application as Nanofluids

In this paper, several methods including HF, NaOH, TEOS, and PVP treatment were adopted to modify the wettability of silicon carbide (SiC) nanowires switching from hydrophobic to hydrophilic. The phase and microstructure investigated by XRD, FT-IR, XPS, TGA, SEM, and TEM demonstrated SiC nanowires switching from hydrophobic to hydrophilic due to the surface-tethered hydrophilic layer as well as increasing interspace between nanowires. Besides this, SiC nanowires with hydrophilicity may effectively improve the thermal conductivity of a fluid. The thermal conductivity of aqueous SiC nanowires after TEOS treatment with just 0.3 vol % was remarkably improved up to ca. 13.0%.

Photoinduced Hydrodefluorination Mechanisms of Perfluorooctanoic Acid by the SiC/Graphene Catalyst

Cleavage of the strong carbon-fluorine bonds is critical for elimination of perfluorooctanoic acid (PFOA) from the environment. In this work, we investigated the decomposition of PFOA with the SiC/graphene catalyst under UV light irradiation. The decomposition rate constant (k) with SiC/graphene was 0.096 h(-1), 2.2 times higher than that with commercial nano-TiO2. Surface fluorination on SiC/graphene was analyzed by X-ray photoelectron spectroscopy (XPS), revealing the conversions of Si-H bonds into Si-F bonds. A different route was found to generate the reactive Si-H bonds on SiC/graphene, substituting for silylium (R3Si(+)) to activate C-F bonds. During the activation process, photogenerated electrons on SiC transfer rapidly to perfluoroalkyl groups by the medium of graphene, further reducing the electron cloud density of C-F bonds to promote the activation. The hydrogen-containing hydrodefluorination intermediates including (CF3(CF2)2CFH, CF3(CF2)3CH2, CF3(CF2)4CH2, and CF3(CF2)4CFHCOOH) were detected to verify the hydrodefluorination process. The photoinduced hydrodefluorination mechanisms of PFOA can be consequently inferred as follows: (1) fluorine atoms in perfluoroalkyl groups were replaced by hydrogen atoms due to the nucleophilic substitution reaction via the Si-H/C-F redistribution, and (2) generation of CH2 carbene from the hydrogen-containing perfluoroalkyl groups and the C-C bonds scission by the Photo-Kolbe decarboxylation reaction under UV light excitation. This photoinduced hydrodefluorination provides insight into the photocatalytic decomposition of perfluorocarboxylic acids (PFCAs) in an aqueous environment.

Adopting Novel Strategies in Achieving High-Performance Single-Layer Network Structured ZnO Nanorods Thin Film Transistors

High-performance, solution-processed transparent and flexible zinc oxide (ZnO) nanorods (NRs)-based single layer network structured thin film transistors (TFTs) were developed on polyethylene terephthalate (PET) substrate at 100 °C. Keeping the process-temperature under 100 °C, we have improved the device performance by introducing three low temperature-based techniques; regrowing ZnO to fill the void spaces in a single layer network of ZnO NRs, passivating the back channel with polymer, and adopting ZrO2 as the high-k dielectric. Notably, high-k amorphous ZrO2 was synthesized and deposited using a novel method at an unprecedented temperature of 100 °C. Using these methods, the TFTs exhibited a high mobility of 1.77 cm(2)/V·s. An insignificant reduction of 2.18% in mobility value after 3000 cycles of dynamic bending at a radius of curvature of 20 mm indicated the robust mechanical nature of the flexible ZnO NRs SLNS TFTs.

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.

Water Activated Graphene Oxide Transfer Using Wax Printed Membranes for Fast Patterning of a Touch Sensitive Device

We demonstrate a graphene oxide printing technology using wax printed membranes for the fast patterning and water activation transfer using pressure based mechanisms. The wax printed membranes have 50 μm resolution, longtime stability and infinite shaping capability. The use of these membranes complemented with the vacuum filtration of graphene oxide provides the control over the thickness. Our demonstration provides a solvent free methodology for printing graphene oxide devices in all shapes and all substrates using the roll-to-roll automatized mechanism present in the wax printing machine. Graphene oxide was transferred over a wide variety of substrates as textile or PET in between others. Finally, we developed a touch switch sensing device integrated in a LED electronic circuit.

Effect of different oxide thickness on the bending Young's modulus of SiO2@SiC nanowires

The surface or sheath effect on core-shell nanowires plays an important role in the nanomechanical test. In the past few years, SiC nanowires have been synthesized using various methods with an uneven and uncontrollable amorphous silicon dioxide sheath. The bending Young’s modulus of the SiC nanowires has scarcely been measured, and the effect of the oxide sheath has not been taken into account. In this paper, SiO₂-coated SiC (SiO₂@SiC) nanowires were synthesized using the chemical vapor deposition method, followed by thermal reduction. Scanning electron microscopy and transmission electron microscopy show that the SiO₂@SiC nanowires in this paper have diameters ranging from 130 ~ 150 nm, with the average thickness of SiO₂ layer approximately 14 nm. After different processing times with 1 mol/L NaOH, approximately 5 nm, 9 nm, 14 nm silicon dioxide layers were obtained. The results of the three-point-bending test show that the modulus of SiO₂@SiC nanowires is found to clearly decrease with the increase in oxide thickness and the influence of the oxide sheath should not be ignored when the layer thickness is above 5 nm. Young’s modulus of the SiO₂@SiC nanowires calculated in this study by the core-shell structure model is in good agreement with the theoretical value.

RGO enveloped vertically aligned Co3O4 nanowires on carbon fabric: a highly efficient prototype for flexible field emitter arrays

RGO enveloped Co₃O₄ nanowires on flexible carbon fabric exhibit a splendid field emission performance with remarkably enhanced current density.

Aligned 2D CuSCN nanosheets: a high performance field emitter

Aligned 2D CuSCN nanosheets were grown by a simple, low cost and room temperature SILAR technique. The field emission properties of aligned 2D CuSCN nanosheets were studied in detail.

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.

ZnO quantum dots decorated on optimized carbon nanotube intramolecular junctions exhibit superior field emission properties

Sensitive optical and superior field emission properties can be attained through the use of ZnO selective quantum well heterostructures grown on carbon nanotubes to fabricate carbon-zinc-oxide (CZO) nanotubes.

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%).

Metamaterials and imaging

Resolution of the conventional lens is limited to half the wavelength of the light source by diffraction. In the conventional optical system, evanescent waves, which carry sub-diffraction spatial information, has exponentially decaying amplitude and therefore cannot reach to the image plane. New optical materials called metamaterials have provided new ways to overcome diffraction limit in imaging by controlling the evanescent waves. Such extraordinary electromagnetic properties can be achieved and controlled through arranging nanoscale building blocks appropriately. Here, we review metamaterial-based lenses which offer the new types of imaging components and functions. Perfect lens, superlenses, hyperlenses, metalenses, flat lenses based on metasurfaces, and non-optical lenses including acoustic hyperlens are described. Not all of them offer sub-diffraction imaging, but they provide new imaging mechanisms by controlling and manipulating the path of light. The underlying physics, design principles, recent advances, major limitations and challenges for the practical applications are discussed in this review.

Optimizing Field Emission Properties of the Hybrid Structures of Graphene Stretched on Patterned and Size-controllable SiNWs

Graphene is one of the ideal nanomaterials to be paired with silicon, and their complementary properties can be exploited in field emission (FE) devices. We reported an efficient way to produce and adjust the dimension of uniform protrusions within graphene. First, a multistep template replication process was utilized to fabricate highly periodic and well-aligned silicon nanowires (SiNWs) of different diameters (400, 500 and 600 nm). Then, large-scale and uniform graphene, fabricated by chemical vapor deposition (CVD), was transferred onto these size-controlled SiNWs to obtain the nanoscale and uniform undulations. As compared to the nanowires alone, the hybrid structures lead to higher FE performance due to electron conductivity enhancement, high-density emmison protrusions and band bending. These hybrid SiNWs/graphene structures could provide a promising class of field emission cathodes.

Controlled Synthesis of Ultrathin Sb2Se3 Nanowires and Application for Flexible Photodetectors

A new solvothermal approach is introduced to synthesize ultrathin Sb₂Se₃ nanowires with diameters ranging from 10 to 20 nm and with length up to 30 μm. The Sb₂Se₃ nanowire-based photodetectors are firstly fabricated on polyethylene terephthalate and printing paper substrates, which exhibit excellent response to visible light with fast response time (0.18 and 0.22 s), high flexibility, and durability.

High-temperature stable field emission of B-doped SiC nanoneedle arrays

Current emission stability is one of the key issues for field emitters for them to be practically applied as electron sources. In the present work, large-scale and well-aligned B-doped SiC nanoneedle arrays have been grown on 6H-SiC wafer substrates via pyrolysis of polymeric precursors. The measured field emission (FE) characteristics suggest that the turn-on fields of the as-synthesized SiC nanoneedle arrays are reduced from 1.92 to 0.98 V μm(-1) with temperature increasing from room temperature (RT) to 500 °C, suggesting their excellent FE performances. The slightly changed current fluctuations (only ∼1.3%) between RT and 200 °C confirm that the present SiC nanoarrays with B dopants could be highly stable field emitters to be used in service under harsh conditions of high temperatures.

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.

Self-assembly of functional molecules into 1D crystalline nanostructures

Self-assembled functional nanoarchitectures are employed as important nanoscale building blocks for advanced materials and smart miniature devices to fulfill the increasing needs of high materials usage efficiency, low energy consumption, and high-performance devices. One-dimensional (1D) crystalline nanostructures, especially molecule-composed crystalline nanostructures, attract significant attention due to their fascinating infusion structure and functionality which enables the easy tailoring of organic molecules with excellent carrier mobility and crystal stability. In this review, we discuss the recent progress of 1D crystalline self-assembled nanostructures of functional molecules, which include both a small molecule-derived and a polymer-based crystalline nanostructure. The basic principles of the molecular structure design and the process engineering of 1D crystalline nanostructures are also discussed. The molecular building blocks, self-assembly structures, and their applications in optical, electrical, and photoelectrical devices are overviewed and we give a brief outlook on crucial issues that need to be addressed in future research endeavors.

Large-scale growth of well-aligned SiC tower-like nanowire arrays and their field emission properties

Fabrication of well-aligned one-dimensional (1D) nanostrucutres is critically important and highly desired since it is the key step to realize the patterned arrays to be used as the display units. In the present work, we report the large-scale and well-aligned growth of n-type SiC nanowire arrays on the 6H-SiC wafer substrates via pyrolysis of polymeric precursors assisted by Au catalysts. The obtained n-type SiC nanowires are highly qualified with sharp tips and numerous sharp corners around the wire bodies, which bring the emitters excellent field emission (FE) performance with low turn-on fields (1.50 V/μm), low threshold fields (2.65 V/μm), and good current emission stabilities (fluctuation <3.8%). The work abilities of the n-type SiC tower-like nanowire arrays under high-temperature harsh environments have been investigated, suggesting that the resultant field emitters could be well serviced up to 500 °C. The temperature-enhanced FE behaviors could be attributed to the reduction of the work function induced by the rise of temperatures and the incorporated N dopants. It is believed that the present well-aligned n-type SiC tower-like nanowire arrays could meet nearly all stringent requirements for an ideal FE emitter with excellent FE properties, making their applications very promising in displays and other electronic nanodevices.

Nitrogen content and morphology dependent field emission properties of nitrogen-doped SiC nanowires and density functional calculations

N-Doped SiC NWs with varying N content have been synthesized via a one-step CVR, and they exhibit excellent FE properties.

Hierarchical CdS nanostructure by Lawesson's reagent and its enhanced photocatalytic hydrogen production

Lawesson's reagent (LR) has been effectively exploited for the synthesis of hierarchical architectures of cadmium sulphide (CdS) nanostructures for the first time.

Fabrication of V2O5 super long nanobelts: optical, in situ electrical and field emission properties

A low turn-on field of 1.4 V μm⁻¹, carrier concentrations of N_d = 1.48 × 10¹⁸ cm⁻³ and electron mobility of 1.26 cm² V⁻¹ s⁻¹ were obtained for V₂O₅ super long nanobelts.

Solution-phase hierarchical self-organization of ultralong Se nanowires into diverse macroarchitectures and their enhanced field emission

A variety of self-organized superstructures of ultralong Se nanowires and their superior field emission characteristics are demonstrated in this contribution.

Rational Design of WO3 Nanostructures as the Anode Materials for Lithium-Ion Batteries with Enhanced Electrochemical Performance

A facile, one-step hydrothermal method was employed to synthesize two kinds of WO₃ nanostructures. By using different kinds of sylvine, tungsten trioxide (WO₃) with different morphologies of microflowers and nanowires was obtained, respectively. The discharge capacities for microflowers and nanowires are 107 and 146 mAh g^-1 after 180 cycles, and their corresponding capacity retentions after the first cycle are 72 and 85 %, respectively. Even at a high current density of 1,600 mAh g^-1, the discharge capacities of WO₃ microflowers and nanowires are as high as 433 and 557 mAh g^-1 after 40 cycles, in which the current densities were increased stepwise. It is worth mentioned that the rate capability of the nanowires is superior to that of the microflowers. However, the cycle performance of the microflowers is better than nanowires, revealing that the morphology and structure of the as-synthesized WO₃ products can exert great influence on the electrochemical performances.

Synthesis and field emission studies of tower-like GaN nanowires

Tower-like GaN nanowires were successfully fabricated on Au-coated Si substrates by chemical vapor deposition. The tower-like nanowire consisted of a nanowire at the center and microcrystal layers stacked one by one around the nanowire. The tower-like nanowires grew along the [0001] direction, and the exposed surfaces of the microcrystal layers are [Formula: see text] and [Formula: see text] facets. The growth mechanism of the tower-like GaN nanowires was proposed. The field emission property of tower-like GaN nanowires was tested. Due to the sharp tips, nearly vertical alignment and rough surfaces caused by the microcrystal layers, the tower-like GaN nanowires show excellent performance in field emission with a turn-on field of 2.44 V/μm which is lower than those of other GaN one-dimensional (1D) nanomaterials.

PACS

81.15.Gh; 68.37.Lp; 68.37.Vj.

Band gap tunable Zn2SnO4 nanocubes through thermal effect and their outstanding ultraviolet light photoresponse

This work presents a method for synthesis of high-yield, uniform and band gap tunable Zn₂SnO₄ nanocubes. These nanocubes can be further self-assembled into a series of novel nanofilms with tunable optical band gaps from 3.54 to 3.18 eV by simply increasing the heat treatment temperature. The Zn₂SnO₄ nanocube-nanofilm based device has been successfully fabricated and presents obviously higher photocurrent, larger photocurrent to dark current ratio than the previously reported individual nanostructure-based UV-light photodetectors, and could be used in high performance photodetectors, solar cells, and electrode materials for Li-ion battery.

Uncoupled surface spin induced exchange bias in α-MnO2 nanowires

We have studied the microstructure, surface states, valence fluctuations, magnetic properties, and exchange bias effect in MnO2 nanowires. High purity α-MnO2 rectangular nanowires were synthesized by a facile hydrothermal method with microwave-assisted procedures. The microstructure analysis indicates that the nanowires grow in the [0 0 1] direction with the (2 1 0) plane as the surface. Mn(3+) and Mn(2+) ions are not found in the system by X-ray photoelectron spectroscopy. The effective magnetic moment of the manganese ions fits in with the theoretical and experimental values of Mn(4+) very well. The uncoupled spins in 3d(3) orbitals of the Mn(4+) ions in MnO6 octahedra on the rough surface are responsible for the net magnetic moment. Spin glass behavior is observed through magnetic measurements. Furthermore, the exchange bias effect is observed for the first time in pure α-MnO2 phase due to the coupling of the surface spin glass with the antiferromagnetic α-MnO2 matrix. These α-MnO2 nanowires, with a spin-glass-like behavior and with an exchange bias effect excited by the uncoupled surface spins, should therefore inspire further study concerning the origin, theory, and applicability of surface structure induced magnetism in nanostructures.

Field electron emission of layered Bi₂Se₃ nanosheets with atom-thick sharp edges

Field electron emission properties of solution processed few-layer Bi₂Se₃ nanosheets are studied for the first time, which exhibit a low turn-on field of 2.3 V μm(-1), a high field enhancement factor of up to 6860 and good field emission stability. This performance is better than that of the as reported layered MoS₂f sheets and is comparable to that of single layer graphene films. The efficient field emission behaviours are found to be not only attributed to their lower work function but also related to their numerous sharp edges or protrusion decorated structure based on our simulation results. Besides, the contribution of possible two-dimensional electron gas surface states of atom-thick layered Bi₂Se₃ nanosheets is discussed in this paper. We anticipate that these solution processed layered Bi₂Se₃ nanosheets have great potential as robust high-performance vertical structure electron emitters for future light weight and highly flexible vacuum micro/nano-electronic device applications.

Shape dependent synthesis and field emission induced rectification in single ZnS nanocrystals

We report on the synthesis of shape controlled ZnS nanocrystals designed into nanodots, nanorods, and nanowires retaining the same diameter and crystallographic phase. We used UHV scanning tunneling microscopy and spectroscopy to study rectification behavior from single nanocrystals. The nanorod and nanowire show large tunneling current at the negative bias in comparison to the positive bias demonstrating current rectification, while the nanodot shows symmetric current-voltage behavior. We proposed a tunneling mechanism where direct tunneling is followed by resonant tunneling mechanism through ZnS nanocrystal at lower applied bias voltages. Stimulation of field emission in Fowler-Nordheim tunneling regime at higher negative bias voltages enables the rectification behavior from the ZnS nanorod or nanowire. Absence of rectification from the ZnS nanodot is associated with spherical shape where the field emission becomes less significant. Realizing functional electronic component from such shape dependent single ZnS nanocrystal may provide a means in realizing nanocrystal based miniaturized devices.

Reliability enhancement of germanium nanowires using graphene as a protective layer: aspect of thermal stability

We synthesized thermally stable graphene-covered Ge (Ge@G) nanowires and applied them in field emission devices. Vertically aligned Ge@G nanowires were prepared by sequential growth of the Ge nanowires and graphene shells in a single chamber. As a result of the thermal treatment experiments, Ge@G nanowires were much more stable than pure Ge nanowires, maintaining their shape at high temperatures up to 850 °C. In addition, field emission devices based on the Ge@G nanowires clearly exhibited enhanced thermal reliability. Moreover, field emission characteristics yielded the highest field enhancement factor (∼2298) yet reported for this type of device, and also had low turn-on voltage. Our proposed approach for the application of graphene as a protective layer for a semiconductor nanowire is an efficient way to enhance the thermal reliability of nanomaterials.

Luminance behavior of Ce3+ doped ZnS nanostructures

We report the synthesis and characterization of undoped and various levels of Ce(3+) doped ZnS nanocrystal. The structure and size of the products were studied by X-ray diffraction (XRD). The existence of functional groups was identified by Fourier transform infrared spectrometry (FT-IR). The UV-Visible measurements reveal that the synthesized products are blue shifted when compared with bulk phase of ZnS as a result of quantum confinement effect. The PL studies show an enhancement in the intensity of emission band in the UV region on increased Ce(3+) doping. The morphology of the products was evaluated by Field emission scanning electron microscope (FESEM) and High resolution transmission electron microscopy (FESEM). The presence of Ce(3+) was confirmed by Energy dispersive spectral analysis (EDS). The thermal stability of pure and doped products was analyzed by thermo gravimetric and differential thermal analysis (TG-DTA).

Electron field emission enhancement of vertically aligned ultrananocrystalline diamond-coated ZnO core-shell heterostructured nanorods

Enhanced electron field emission (EFE) behavior of a core-shell heterostructure, where ZnO nanorods (ZNRs) form the core and ultrananocrystalline diamond needles (UNCDNs) form the shell, is reported. EFE properties of ZNR-UNCDN core-shell heterostructures show a high emission current density of 5.5 mA cm(-2) at an applied field of 4.25 V μm(-1) , and a low turn-on field of 2.08 V μm(-1) compared to the 1.67 mA cm(-2) emission current density (at an applied field of 28.7 V μm(-1) ) and 16.6 V μm(-1) turn-on field for bare ZNRs. Such an enhancement in the field emission originates from the unique materials combination, resulting in good electron transport from ZNRs to UNCDNs and efficient field emission of electrons from the UNCDNs. The potential application of these materials is demonstrated by the plasma illumination measurements that lowering the threshold voltage by 160 V confirms the role of ZNR-UNCDN core-shell heterostructures in the enhancement of electron emission.

Tungsten oxide nanorods: an efficient nanoplatform for tumor CT imaging and photothermal therapy

We report here a facile thermal decomposition approach to creating tungsten oxide nanorods (WO_2.9 NRs) with a length of 13.1 ± 3.6 nm and a diameter of 4.4 ± 1.5 nm for tumor theranostic applications. The formed WO_2.9 NRs were modified with methoxypoly(ethylene glycol) (PEG) carboxyl acid via ligand exchange to have good water dispersability and biocompatibility. With the high photothermal conversion efficiency irradiated by a 980 nm laser and the better X-ray attenuation property than clinically used computed tomography (CT) contrast agent Iohexol, the formed PEGylated WO_2.9 NRs are able to inhibit the growth of the model cancer cells in vitro and the corresponding tumor model in vivo, and enable effective CT imaging of the tumor model in vivo. Our “killing two birds with one stone” strategy could be extended for fabricating other nanoplatforms for efficient tumor theranostic applications.

Tunable field emission properties of well-aligned silicon nanowires with controlled aspect ratio and proximity

The FE properties were influenced by dimensionality and surface geometry structures, and improved with the increase of proximity.

Controlled growth of SiC flexible field emitters with clear and sharp tips

We report the controlled growth of 3C-SiC flexible field emitters with clear and sharp tips based on the VLS mechanism.