Mahendra A. More

Enhanced Field‐Emission Behavior of Layered MoS2 Sheets

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.

Remarkably low turn-on field emission in undoped, nitrogen-doped, and boron-doped graphene

Field emission studies have been carried out on undoped as well as N- and B-doped graphene samples prepared by arc-discharge method in a hydrogen atmosphere. These graphene samples exhibit very low turn-on fields. N-doped graphene shows the lowest turn-on field of 0.6 V/μm, corresponding to emission current density of 10 μA/cm2. These characteristics are superior to the other types of nanomaterials reported in the literature. Furthermore, emission currents are stable over the period of more than 3 h for the graphene samples. The observed emission behavior has been explained on the basis of nanometric features of graphene and resonance tunneling phenomenon.

Superior Field Emission Properties of Layered WS2-RGO Nanocomposites

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/cm2 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/cm2 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.

Pulsed Laser-Deposited MoS2 Thin Films on W and Si: Field Emission and Photoresponse Studies

We report field electron emission investigations on pulsed laser-deposited molybdenum disulfide (MoS2) thin films on W-tip and Si substrates. In both cases, under the chosen growth conditions, the dry process of pulsed laser deposition (PLD) is seen to render a dense nanostructured morphology of MoS2, which is important for local electric field enhancement in field emission application. In the case of the MoS2 film on silicon (Si), the turn-on field required to draw an emission current density of 10 μA/cm(2) is found to be 2.8 V/μm. Interestingly, the MoS2 film on a tungsten (W) tip emitter delivers a large emission current density of ∼30 mA/cm(2) at a relatively lower applied voltage of ∼3.8 kV. Thus, the PLD-MoS2 can be utilized for various field emission-based applications. We also report our results of photodiode-like behavior in (n- and p- type) Si/PLD-MoS2 heterostructures. Finally we show that MoS2 films deposited on flexible kapton substrate show a good photoresponse and recovery. Our investigations thus hold great promise for the development of PLD MoS2 films in application domains such as field emitters and heterostructures for novel nanoelectronic devices.

Field emission studies of novel ZnO nanostructures in high and low field regions

A study of the field emission characteristics of novel structures of ZnO, namely marigolds, multipods and microbelts, has been carried out in both the close proximity configuration and the conventional field emission microscope. The use of a conventional field emission microscope overcomes the drawback of arc formation at high field values. The nonlinearity in the Fowler-Nordheim (F-N) plot, a characteristic feature of semiconductors has been observed and explained on the basis of electron emission from both the conduction and the valence bands. The current stability exhibited by these structures is also promising for future device applications.

Ultralow threshold field emission from a single multipod structure of ZnO

The field emission of individual ZnO multipods and a single arm of a multipod structure grown by a vapor deposition were carried out. A current of 1 nA with an ultralow onset voltage of 40 V was observed repeatedly for the single multipod as well as for the arm. The nonlinearity observed in the Fowler–Nordheim plots have been interpreted on the basis of the theory of electron emission from semiconductors and a scheme explaining the field emission behavior in both the high- and low-field regions owing to the very high geometrical factor has been picturized.

Enhanced field emission properties of doped graphene nanosheets with layered SnS2

We report here our experimental investigations on p-doped graphene using tin sulfide (SnS2), which shows enhanced field emission properties. The turn on field required to draw an emission current density of 1 μA/cm2 is significantly low (almost half the value) for the SnS2/reduced graphene oxide (RGO) nanocomposite (2.65 V/μm) compared to pristine SnS2 (4.8 V/μm) nanosheets. The field enhancement factor β (∼3200 for the SnS2 and ∼3700 for SnS2/RGO composite) was calculated from Fowler-Nordheim (F-N) plots, which indicates that the emission is from the nanometric geometry of the emitter. The field emission current versus time plot shows overall good emission stability for the SnS2/RGO emitter. The magnitude of work function of SnS2 and a SnS2/graphene composite has been calculated from first principles density functional theory (DFT) and is found to be 6.89 eV and 5.42 eV, respectively. The DFT calculations clearly reveal that the enhanced field emission properties of SnS2/RGO are due to a substantial lowe...

Cu2O/ZnO hetero-nanobrush: hierarchical assembly, field emission and photocatalytic properties

Zinc oxide (ZnO) nanorods are grown hierarchically on cuprous oxide (Cu2O) nanoneedles to form a Cu2O/ZnO hetero-nanobrush assembly. This increases the overall aspect ratio, which helps to enhance the field emission properties of the system. Also, the charge separation and transport are facilitated because of the multiple p–n junctions formed at p-Cu2O/n-ZnO interfaces and quasi-1-D structures of both the materials, respectively. This helps to significantly enhance the photocatalytic properties. As compared to only Cu2O nanoneedles, the Cu2O/ZnO hetero-nanobrush shows excellent improvement in both field emission and photocatalytic applications.

The Fowler−Nordheim Plot Behavior and Mechanism of Field Electron Emission from ZnO Tetrapod Structures

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.

Field emission studies on well adhered pulsed laser deposited LaB6 on W tip

Lanthanum hexaboride films have been deposited on a tungsten tip by pulsed laser deposition technique. The field emission studies have been performed in the conventional field emission geometry. The Fowler-Nordheim plot obtained from the current-voltage characteristic is found to be linear in accordance with the quantum mechanical tunneling phenomenon. A current density of 1.2×104A∕cm2 is drawn from the deposited tip. The field enhancement factor is calculated to be 5537cm−1, indicating that the field emission is from nanoscale protrusions present on emitter surface. The emission current-time plots show the very good stability of the emitter.