Field emission studies are reported for the first time on layered MoS2 sheets at the base pressure of ∼1 × 10−8 mbar. The turn‐on field required to draw a field emission current density of 10 μA/cm2 ...is found to be 3.5 V/μm for MoS2 sheets. The turn‐on values are found to be significantly lower than the reported MoS2 nanoflowers, graphene, and carbon nanotube‐based field emitters due to the high field enhancement factor (∼1138) associated with nanometric sharp edges of MoS2 sheet emitter surface. The emission current–time plots show good stability over a period of 3 h. Owing to the low turn‐on field and planar (sheetlike) structure, the MoS2 could be utilized for future vacuum microelectronics/nanoelectronic and flat panel display applications.
Field emission studies of few‐layer MoS2 sheets show that the turn‐on field required to draw a current density of 10 μA/cm2 is 3.5 V/μm. The turn‐on value is comparable with MoS2 nanoflower‐, graphene‐, and carbon nanotube‐based field emitters. The low turn‐on field value is due to the high field‐enhancement factor (∼1138) associated with the nanometric sharp edges of the MoS2 sheets. It is possible to orient the layered MoS2 sheets for achieving a higher field enhancement factor, resulting in a high current density obtainable at the lower field.
We report here the field emission studies of a layered WS2-RGO composite at the base pressure of ~1 × 10(-8) mbar. The turn on field required to draw a field emission current density of 1 μA/cm(2) is ...found to be 3.5, 2.3 and 2 V/μm for WS2, RGO and the WS2-RGO composite respectively. The enhanced field emission behavior observed for the WS2-RGO nanocomposite is attributed to a high field enhancement factor of 2978, which is associated with the surface protrusions of the single-to-few layer thick sheets of the nanocomposite. The highest current density of ~800 μA/cm(2) is drawn at an applied field of 4.1 V/μm from a few layers of the WS2-RGO nanocomposite. Furthermore, first-principles density functional calculations suggest that the enhanced field emission may also be due to an overalp of the electronic structures of WS2 and RGO, where graphene-like states are dumped in the region of the WS2 fundamental gap.
We report first‐principles DFT calculations of the single‐layer VS2 work function, the experimental synthesis of flower‐like few‐layer‐thick VS2 nanosheets by a simple one‐step hydrothermal method, ...and the investigation of their field emission properties. The turn‐on field required to draw emission current densities of 1 and 10 μA/cm2 were 4 and 5.01 V/μm, respectively. The observed turn‐on field values are attributed to the high field enhancement factor (ca. 2500), which is due to presence of sharp protrusions in the VS2 nanosheets. Furthermore, the field‐emission current stability of the VS2 emitter shows stable behavior over a period of 12 h. Further, DFT calculations show that the work function (f) of the single‐layer VS2 emitter is 6.01 eV.
We report first‐principles DFT calculations of the single‐layer VS2 work function, the experimental synthesis of flower‐like few‐layer‐thick VS2 nanosheets by a simple hydrothermal method, and its field emission properties.
Field emission measurements of current−voltage characteristics are reported for tetrapod structures of ZnO. The nonlinear Fowler−Nordheim (FN) plot is analyzed according to a model of calculation ...based on saturation of conduction band current and predominance of valence band current at high-field values. The simulated FN plot exhibits similar features to those observed experimentally. The model of calculation suggests that the slope variation of the FN plot, in the high-field and low-field regions, does not depend on the magnitude of saturation. Instead, it is a characteristic of the energy band structure and voltage-to-barrier-field conversion factor of the emitting material.
We report a novel method for producing aligned ZnO nanorods (ANR) on self-grown ZnO template in a single step process involving growth of ZnO by vapor transport, followed by quenching of growing ZnO ...flux in liquid nitrogen. In the present study Zn powder turns into ZnO sheet under oxygen flow at ∼900
°C and bottom surface of the sheet acts as template for the growth of ANR. It is revealed from XRD and EDAX analysis that the bottom of the sheet is Zn rich region and acts as self catalyst for the growth of ANR. The grown nanorods have length up to several tens of micrometers with diameters ranging from ∼100 to 150
nm. Microstructural analysis of ANR indicates the fractal like configuration. The field emission properties have been investigated for ANR with fractal geometry using the ANR on self-grown ZnO template as a cathode directly. The turn-on electric field required to draw current density of ∼1.0
μA/cm
2 has been found to be ∼0.98
V/μm. The field enhancement factor based on Fowler–Nordheim (F–N) plot was found to be ∼7815 for ANR. The fractal geometry of ANR has been shown to be advantageous for achieving improved field emission features. The present investigations of synthesis involving formation of ANR over self-grown ZnO template, together with fractal configuration of the as-synthesized ANR, are first of their type.
Sn–ZnO nanoneedles were grown by cathodic electrodeposition and an annealing process on Zn wire as a substrate. Scanning electron microscope studies showed the formation of ZnO nanoneedles. From the ...field emission studies, the field required to draw an emission current density of ~15.2mA/cm2 was observed at an applied field of ~0.14V/μm. In addition, field emission behavior of specimen grown on wire substrate demonstrates the applicability of Sn–ZnO as an electron current source with small optical size and switching device. The observed results suggest the suitability of this synthesis route for fabrication of pointed emitter.
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•Sn–ZnO nanoneedles have been synthesized on wire substrate.•Electrodeposition method and annealing process was used for growth of nanoneedles.•Field emission measurement of nanoneedles grown on wire substrate is found to be superior.•The results suggest the suitability of synthesis route for fabricating of pointed emitter.
A simple method of vapor deposition for the shape selective synthesis of ZnO structures, namely, multipods, submicron wires, and spheres, has been successfully demonstrated. A plausible growth ...mechanism based on the studies of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) is proposed. Our studies suggest that the growth of a multipod structure is governed by the screw dislocation propagation while the vapor−liquid−solid (VLS) mechanism is responsible for the formation of submicron wires and spheres. Moreover, the flow rate of the carrier gas plays a crucial role in governing the morphology. Further, these structures exhibit an enhanced field emission behavior. The nonlinearity in the Fowler−Nordheim (F−N) plot, a characteristic feature of electron emission from semiconductors, is explained by considering the contributions from both the conduction and the valence bands of ZnO.
Sn-doped ZnO nanowire films have been successfully synthesized by electrodeposition on zinc foil followed by annealing in air at 400 °C for 4 h. The XRD patterns of the annealed specimens exhibit a ...set of well-defined diffraction peaks indexed to the wurtzite phase of ZnO. The surface morphology of the as-synthesized films showed a network of densely packed flakes/sheets on the substrate. However, upon annealing, the formation of ZnO nanowires, processing length in the range of several micrometers and diameter less than 150 nm, on the entire substrate is observed. The relative atomic percentage of Sn, estimated from the energy dispersive spectra, was found to be 0.5 and 2.0 in the ZnO films deposited for 10 and 40 min durations, respectively. From the field emission studies, the values of the turn-on field and threshold field, required to draw emission current density of 10 and 100 μA/cm2, are observed to be 0.68 and 1.1 V/μm for 0.5% Sn-doped ZnO and 1.72 and 2.25 V/μm for 2.0% Sn-doped ZnO, respectively. The field emission current stability investigated for a duration of 6 h at the preset value of 100 μA is found to be excellent. A prominent photoenhancement in the field emission current upon visible light illumination of the Sn-doped ZnO nanowires films has been observed. This enhancement has been attributed to the photoconductivity of the Sn-doped ZnO.
Sn doped ZnO films were obtained by cathodic electrodeposition on Zn foil. The X-ray diffraction analysis revealed formation of the wurtzite phase of ZnO only. The scanning electron microscopic ...images showed formation of randomly oriented ZnO nanowires having diameter less than 150
nm and lengths of several micrometers. The relative atomic percentage of Sn, estimated from the energy-dispersive spectra, was found to be 0.5 and 2.0 in the post-annealed ZnO films deposited for 10 and 40
min durations, respectively. The field emission characteristics of the Sn doped ZnO nanowires are found to be appreciable in terms of the threshold field and emission current stability.
We demonstrate the synthesis of large-scale high-quality single-crystalline γ-Mo2N fibers using α-MoO3 fibers as precursors by temperature-programmed reactions with NH3. The formation mechanism is ...discussed, and the morphology, structure, composition, and chemical states of the prepared fibers were characterized by X-ray diffraction pattern, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction pattern, and X-ray photoelectron spectroscopy studies. The normal field emission properties of the product were investigated, and the turn-on field of 0.6 V/μm is reported for the first time. The Fowler−Nordheim (F-N) plot obtained from the current density-applied field (J-E) characteristic is almost found to be linear, and the I-t plot shows that the emission current remains nearly constant over 2 h. The γ-Mo2N fibers exhibit an enhanced performance as compared to other nitrides. Therefore, our field emission results show that the γ-Mo2N fibers might be potential field emitters in the future devices.
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