Ruchita T. Khare

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 properties of ZnO nanosheet arrays

Electron emission properties of electrodeposited ZnO nanosheet arrays grown on Indium tin oxide coated glass substrates have been studied. Influence of oxygen vacancies on electronic structures and field emission properties of ZnO nanosheets are investigated using density functional theory. The oxygen vacancies produce unshared d electrons which form an impurity energy state; this causes shifting of Fermi level towards the vacuum, and so the barrier energy for electron extraction reduces. The ZnO nanosheet arrays exhibit a low turn-on field of 2.4 V/μm at 0.1 μA/cm2 and current density of 50.1 μA/cm2 at an applied field of 6.4 V/μm with field enhancement factor, β = 5812 and good field emission current stability. The nanosheet arrays grown by a facile electrodeposition process have great potential as robust high performance vertical structure electron emitters for future flat panel displays and vacuum electronic device applications.

Enhanced field emission of plasma treated multilayer graphene

Electron emission properties of multilayer graphene (MLG) prepared by a facile exfoliation technique have been studied. Effect of CO2 Ar, N2, plasma treatment was studied using Raman spectroscopy and investigated for field emission based application. The CO2 plasma treated multilayer graphene shows an enhanced field emission behavior with a low turn on field of 0.18 V/μm and high emission current density of 1.89 mA/cm2 at an applied field of 0.35 V/μm. Further the plasma treated MLG exhibits excellent current stability at a lower and higher emission current value.

Field emission properties of spinel ZnCo2O4 microflowers

ZnCo2O4 microflowers were synthesized by a simple low temperature hydrothermal route. A single three-dimensional microflower consists of hundreds of self-assembled petals, with a thickness of several nanometers. These microflowers have exceptionally thin edges with a few petal layers. The ZnCo2O4 microflowers appeared to be stable and good field emitters.

Graphene nanoribbons as prospective field emitter

Field emission characteristics of graphene nanoribbons (GNRs) synthesized by unzipping of multiwall carbon nanotubes using a facile hydrothermal route have been investigated at a base pressure of 1 × 10−8 mbar. The values of turn-on field, required to draw an emission current densities of 1 and 10 μA/cm2, are found to be 2.8 and 5.8 V/μm, respectively, and a maximum emission current density of 500 μA/cm2 has been drawn at an applied field of 9.8 V/μm. The emission current stability of the GNRs emitter was studied at preset values of 1 and 10 μA over a period of 3 h, and is found to be excellent. The field emission results demonstrated herein suggest that GNRs based field emitters can open up many opportunities for their potential utilization as large area field emitters in various vacuum micro-nanoelectronic devices such as flexible field emission displays, portable X-ray, and microwave tubes.

Single step hydrothermal approach for devising hierarchical Ag–ZnO heterostructures with significant enhancement in field emission performance

Hierarchical Ag–ZnO heterostructures have been synthesized via a template free single step hydrothermal method. Structural and morphological studies reveal the formation of heterostructures comprised of Ag nanoparticles (∼20 nm) organized on tapered ZnO nanorods under the prevailing experimental conditions. A plausible reaction and growth mechanism has been discussed. Furthermore, the hierarchical creation of ZnO with Ag as a relatively low work function material offers an effective approach to tailor its field emission properties. The field emission studies reveal a remarkable low turn-on field of ∼ 1 V μm−1, corresponding to an emission current density of ∼10 μA cm−2, and an emission current density of ∼400 μA cm−2 has been drawn at an applied field of 2.24 V μm−1. In addition, the Ag–ZnO heterostructures exhibit a good emission current stability at the pre-set value of ∼1 and 4 μA over a duration of 3 h. The enhancement of the field emission characteristics resulting from Ag nanoparticles decorating the tapered ZnO nanorods is discussed on the basis of band structure modifications. The ease of the synthesis route and the remarkable field emission properties offer Ag–ZnO heterostructures as a promising electron source for high current density applications.

Controlled synthesis of aligned Bi2S3 nanowires, sharp apex nanowires and nanobelts with its morphology dependent field emission investigations

Well-aligned ultra-long Bi2S3 nanowire arrays with three kinds of apex morphology – abruptly sharpened apex, thin belt and flat – have been systematically fabricated on tungsten (W) foil by a facile hydrothermal method. The structural and morphological studies reveal formation of distinct tip morphologies, possessing high aspect ratio, single crystalline nature and growth along the orthorhombic [001] axis. A plausible growth mechanism has been proposed on the basis of observed experimental results. The field emission properties of Bi2S3 nanowires and sharp apex Bi2S3 nanowires are investigated. From the field emission studies, the values of the turn-on field, required to draw emission current density of ∼0.1 μA cm−2, are observed to be ∼2.01 and 1.21 V μm−1 for nanowires and sharp apex nanowires, respectively. Furthermore, ultra-long Bi2S3 nanowires are also grown on the W microtip (brush-like) from which very high emission current density ∼11 mA cm−2 has been drawn. These results are helpful for the design, fabrication and optimization of integrated field emitters using 1D nanostructures as cold cathode material.

Enhanced electron field emission from NiCo2O4 nanosheet arrays

Electron emission properties of electrodeposited spinel NiCo2O4 nanosheet arrays grown on Ni foam have been studied. The work function of NiCo2O4 was calculated by density functional theory using the plane-wave basis set and used to estimate the field enhancement factor. The NiCo2O4 nanosheet arrays exhibited a low turn-on field of 1.86 V μm−1 at 1 μA cm−2 and current density of 686 μA cm−2 at 3.2 V μm−1, with field enhancement factor β = 1460 and good field emission current stability. The field emission properties of the NiCo2O4 nanosheet arrays showed enhanced performance compared to chemically prepared NiCo2O4 nanosheets. Hence, the nanosheet arrays have great potential as robust high performance vertical structure electron emitters for future flat panel displays and vacuum electronic device applications.

Glucose sensing and low-threshold field emission from MnCo2O4 nanosheets

Manganese cobalt oxide (MnCo2O4) nanosheets were grown on nickel (Ni) foam by a simple electrodeposition method. The as-synthesized nanosheets were characterized using X-ray diffraction and scanning electron microscopy. The Ni foam supports the growth of MnCo2O4 nanosheets without any aggregation, thereby increasing its catalytic and electronic properties. The electrochemical studies show that MnCo2O4 exhibits excellent electrocatalytic activity towards glucose sensing applications. The MnCo2O4 based glucose sensor shows a good sensitivity value of 8.2 μA μM−1 cm−2, with a response time of 19 s. In addition to this, field emission studies of as-synthesized MnCo2O4 reveal a low turn-on field value of 1.9 V μm−1 and good emission current stability, demonstrating MnCo2O4 nanosheets as a good field emitter material.

Promising field electron emission performance of vertically aligned one dimensional (1D) brookite (β) TiO2 nanorods

We evidence field-electron emission (FE) studies on the large-area array of one-dimensional (1D) brookite (β) TiO2 nanorods. The pure 1D β-TiO2 nanorods of 10 nm width and 760 nm long were synthesized on Si substrate utilizing hot-filament metal vapor deposition technique. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis evidenced the β-TiO2 nanorods to be composed of orthorhombic crystals in brookite (β) phase. X-ray photoemission spectroscopy (XPS) revealed the formation of pure stoichiometric (i.e. 1 : 1.98) 1D TiO2 nanorods. The values of turn-on field, required to draw current density of 10 μA cm−2, was observed 3.9 V μm−1 for pristine 1D β-TiO2 nanorods emitters, which were found significantly lower than doped/undoped 1D TiO2 nanostructures (i.e. nanotubes, nanowires, nanorods) based field emitters. The enhanced FE behavior of the TiO2/Si emitter can be attributed to modulation of electronic properties due to the high aspect ratio of vertically aligned TiO2 nanorods. Furthermore, the orthodox emission situation of pristine TiO2/Si emitters exhibit good emission stability and reveal their potentials as promising FE material.