ZnO/CuSCN Nano-Heterostructure as a Highly Efficient Field Emitter: a Combined Experimental and Theoretical Investigation.

We report the synthesis of two-dimensional porous ZnO nanosheets, CuSCN nanocoins, and ZnO/CuSCN nano-heterostructure thin films grown on fluorine-doped tin oxide substrates via two simple and low-cost solution chemical routes, i.e., chemical bath deposition and successive ionic layer adsorption and reaction methods. Detail characterizations regarding the structural, optoelectronic, and morphological properties have been carried out, which reveal high-quality and crystalline synthesized materials. Field emission (FE) investigations performed at room temperature with a base pressure of 1 × 10-8 mbar demonstrate superior FE performance of the ZnO/CuSCN nano-heterostructure compared to the isolated porous ZnO nanosheets and CuSCN nanocoins. For instance, the turn-on field required to draw a current density of 10 µA/cm2 is found to be 2.2, 1.1, and 0.7 V/µm for the ZnO, CuSCN, and ZnO/CuSCN nano-heterostructure, respectively. The observed significant improvement in the FE characteristics (ultralow turn-on field of 0.7 V/µm for an emission current density of 10 µA/cm2 and the achieved high current density of 2.2 mA/cm2 at a relatively low applied electric field of 1.8 V/µm) for the ZnO/CuSCN nano-heterostructure is superior to the isolated porous ZnO nanosheets, CuSCN nanocoins, and other reported semiconducting nano-heterostructures. Complementary first-principles density functional theory calculations predict a lower work function for the ZnO/CuSCN nano-heterostructure (4.58 eV), compared to the isolated ZnO (5.24 eV) and CuSCN (4.91 eV), validating the superior FE characteristics of the ZnO/CuSCN nano-heterostructure. The ZnO/CuSCN nanocomposite could provide a promising class of FE cathodes, flat panel displays, microwave tubes, and electron sources.

Enhanced Field Emission Properties of Au/SnSe Nano-heterostructure: A Combined Experimental and Theoretical Investigation.

We report the field emission properties of two-dimensional SnSe nanosheets (NSs) and Au/SnSe nano-heterostructure (NHS) prepared by a simple and economical route of one-pot colloidal and sputtering technique. Field Emission Scanning Electron Microscope (FESEM) analysis reveal surface protrusions and morphology modification of the SnSe NSs by Au deposition. By decorating the SnSe NSs with Au nanoparticles, significant improvement in field emission characteristics were observed. A significant reduction in the turn-on field from 2.25 V/µm for the SnSe NSs to 1.25 V/µm for the Au/SnSe NHS was observed. Emission current density of 300 µA/cm2 has been achieved at an applied field of 4.00 and 1.91 V/µm for SnSe NSs and Au/SnSe NHS, respectively. Analysis of the emission current as a function of time also demonstrated the robustness of the present Au/SnSe NHS. Consistent with the experimental data, our complementary first-principles DFT calculations predict lower work function for the Au/SnSe NHS compared to the SnSe NSs as the primary origin for improved field emission. The present study has evidently provided a rational heterostructure strategy for improving various field emission related applications via surface and electronic modifications of the nanostructures.

Uncovering the origin of enhanced field emission properties of rGO-MnO2 heterostructures: a synergistic experimental and computational investigation.

The unique structural merits of heterostructured nanomaterials including the electronic interaction, interfacial bonding and synergistic effects make them attractive for fabricating highly efficient optoelectronic devices. Herein, we report the synthesis of MnO2 nanorods and a rGO/MnO2 nano-heterostructure using low-cost hydrothermal and modified Hummers' methods, respectively. Detailed characterization and confirmation of the structural and morphological properties are done via X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). Compared to the isolated MnO2 nanorods, the rGO/MnO2 nano-heterostructure exhibits impressive field emission (FE) performance in terms of the low turn-on field of 1.4 V µm-1 for an emission current density of 10 µA cm-2 and a high current density of 600 µA cm-2 at a relatively very low applied electric field of 3.1 V µm-1. The isolated MnO2 nanorods display a high turn-on field of 7.1 for an emission current density of 10 µA cm-2 and a low current density of 221 µA cm-2 at an applied field of 8.1 V µm-1. Besides the superior FE characteristics of the rGO/MnO2 nano-heterostructure, the emission current remains quite stable over the continuous 2 h period of measurement. The improvement of the FE characteristics of the rGO/MnO2 nano-heterostructure can be ascribed to the nanometric features and the lower work function (6.01 and 6.12 eV for the rGO with 8% and 16% oxygen content) compared to the isolated α-MnO2(100) surface (Φ = 7.22 eV) as predicted from complementary first-principles electronic structure calculations based on density functional theory (DFT) methods. These results suggest that an appropriate coupling of rGO with MnO2 nanorods would have a synergistic effect of lowering the electronic work function, resulting in a beneficial tuning of the FE characteristics.

Controlled Ti seed layer assisted growth and field emission properties of Pb(Zr0.52Ti0.48)O3 nanowire arrays.

We report on the directed upright growth of ferroelectric (FE) Pb(Zr0.52Ti0.48)O3 (PZT) nanowire (NW) arrays with large aspect ratios of >60 using a Ti seed layer assisted hydrothermal process over large surface areas on ITO/glass substrates. In a two-step growth process, Ti seed layer of low surface roughness with a thickness of ~500 nm and grain size of ~100 nm was first deposited by radio frequency (RF) sputtering which was subsequently used as substrates for the growth of highly dense, single crystalline PZT NWs by controlled nucleation. The electron emission properties of the PZT NWs were investigated using the as-grown NWs as FE cathodes. A low turn-on field of ~3.4 V/µm was obtained from the NW arrays, which is impressively lower than that from other reported values. The results reported in this work give direction to the development of a facile growth technique for PZT NWs over large surfaces and also are of interest to the generation of high current electron beam from FE NW based cathodes for field emitter applications.

Synthesis and characterization of self-assembled nanofiber-bundles of V2O5: their electrochemical and field emission properties.

High-quality self-assembled V(2)O(5) nanofiber-bundles (NBs) are synthesized by a simple and direct hydrothermal method using a vanadium(v) hydroxylamido complex as a vanadium source in the presence of HNO(3). The possible reaction pathway for the formation of V(2)O(5) NBs is discussed and demonstrated that HNO(3) functions both as an oxidizing and as an acidification agent. V(2)O(5) NBs are single-crystals of an orthorhombic phase that have grown along the [010] direction. A bundle is made of indefinite numbers of homogeneous V(2)O(5) nanofibers where nanofibers have lengths up to several micrometres and widths ranging between 20 and 50 nm. As-prepared V(2)O(5) NBs display a high electrochemical performance in a non-aqueous electrolyte as a cathode material for lithium ion batteries. Field emission properties are also investigated which shows that a low turn-on field of ∼1.84 V µm(-1) is required to draw the emission current density of 10 µA cm(-2).

Enhanced field-emission from SnO2:WO(2.72) nanowire heterostructures.

The field-emission properties of SnO(2):WO(2.72) hierarchical nanowire heterostructure have been investigated. Nanoheterostructure consisting of SnO(2) nanowires as stem and WO(2.72) nanothorns as branches are synthesized in two steps by physical vapor deposition technique. Their field emission properties were recorded. A low turn-on field of ~0.82 V/µm (to draw an emission current density ~10 µA/cm(2)) is achieved along with stable emission for 4 h duration. The emission characteristic shows the SnO(2):WO(2.72) nanoheterostructures are extremely suitable for field-emission applications.

Controlled growth of well-aligned GaS nanohornlike structures and their field emission properties.

Here, we report the synthesis of vertically aligned gallium sulfide (GaS) nanohorn arrays using simple vapor-liquid-solid (VLS) method. The morphologies of GaS nano and microstructures are tuned by controlling the temperature and position of the substrate with respect to the source material. A plausible mechanism for the controlled growth has been proposed. It is important to note that the turn-on field value of GaS nanohorns array is found to be the low turn-on field 4.2 V/µm having current density of 0.1 µA/cm(2). The striking feature of the field emission behavior of the GaS nanohorn arrays is that the average emission current remains nearly constant over long time without any degradation.

Synthesis of single crystalline CdS nanocombs and their application in photo-sensitive field emission switches.

Single crystalline CdS nanocombs were synthesized by a thermal evaporation route. The photo-sensitive field emission current shows a reproducible switching behavior, with a rise in current level of nearly five times the initial preset value of ∼1 µA. An ultra low turn-on field, required to draw an emission current density of ∼0.1 µA cm(-2) (100 nA), is found to be ∼0.26 V µm(-1) (260 V), which is much lower than the reported values for various other CdS nanostructures. Upon illumination with visible light the CdS nanocombs act as a photo field emission switch. At an applied field of ∼0.65 V µm(-1) the current densities are observed to be ∼14.6 µA cm(-2) and ∼26.9 µA cm(-2), without and with light illumination, respectively. The average emission current is seen to be stable over the duration of measurement for two preset values. The high sensitivity and fast response in the visible range indicates that the CdS nanocombs can be used as a photo-sensitive field emitting switch in device applications, and also in pulsed electron beam technology.

Photo-enhanced field emission study of TiO2 nanotubes array.

Aligned TiO(2) nanotubes were synthesized by simple anodization of the Ti foil surface. The as-anodized product is further characterized by SEM, XRD, and PL. The tube inner diameter is found to be ≈ 60-80 nm with the average wall thickness ≈ 30 nm and areal density ≈ 15 × 10(6)/cm(2). FE studies of the aligned TiO(2) nanotubes are carried out at base pressure of ≈ 1 × 10(-8) mbar. The turn-on field observed for an emission current density of ≈ 10 µA/cm(2) is found to be ≈ 1.7V/µm and current density of ≈ 44 µA/cm(2) is obtained at an applied field of ≈ 2.3 V/µm. Photo-enhanced FE study is carried out by shining visible and UV light on the cathode. The aligned TiO(2) nanotubes show sensitivity to both the light sources. The FE current shows fast switching response to the visible light. The increment in the preset current upon UV illumination can be attributed to the band edge excitation of the electrons. The free excitons associated with band gap of the TiO(2) nanotubes array may be responsible for the visible light sensitivity. TiO(2) nanotubes are also grown on the Ti wire and exhibit similar photo-enhanced behavior. The FE and photo-enhanced FE properties demonstrate the applicability of the aligned TiO(2) nanotubes in the FE based micro/nanoelectronic devices.