Padmakar G. Chavan

High current density, low threshold field emission from functionalized carbon nanotube bucky paper

Field emission studies of bucky paper of multiwalled carbon nanotubes (MWNTs), prepared after microwave (MW) assisted acid functionalization are reported along with a comparison with that of “as-grown” sample. MW treated bucky papers reveal an interesting linear field emission behavior in Fowler–Nordheim plot. The field emission currents at preset value are found to be remarkably stable over a period of more than 3 h sustaining current densities of 4.9 mA/cm2 and 8.5 mA/cm2 for “as-grown” and functionalized sample, respectively. The enhancement in the field emission due to functionalization has been discussed in terms of tip opening and defect induced charge transport caused by intershell and intertubular interaction.

Self-catalytic growth and field-emission properties of Ga2O3 nanowires

Ga2O3 nanowires with very narrow width (~30 nm) were fabricated from precursor gallium metal via a self-catalytic vapour–liquid–solid method using sol–gel derived Ga2O3 thin films as substrates. The morphological evolution of Ga2O3 nanostructures has been analysed by scanning electron microscopy and transmission electron microscopy. The field-emission (FE) properties of Ga2O3 nanowires are recorded and the turn-on field is found to be 1.88 V µm−1. It is shown from the I–t plot that the emission current remains nearly constant over 2 h at the pre-set current value of 1 µA. The average emission current at the stabilized value is seen to be fairly constant suggesting that the Ga2O3 nanowires are potentially important for applications in FE based devices.

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.

Enhancement in the field emission behavior of graphene in N 2 /O 2 high vacuum ambience

Herein we report, pressure dependent field emission (FE) behaviour of a few-layer graphene emitter. Gas dependent FE properties have been investigated in ultra high vacuum (UHV), as well as in N₂ and O₂ ambience at base pressure ~ 1×10^-6 torr. Interestingly, the graphene emitter when operated in N₂/O₂ ambience exhibits lower turn-on field and higher emission current density, as compared to the UHV conditions. The emission current stability investigated at preset value of ~1μA over the period of more than 2 hrs is found better in the N₂ ambience and is characterized by fewer fluctuations, in contrast to the behaviour in the O₂ ambience. The observed enhanced electron emission behavior in N₂/O₂ ambience is attributed to modulation of the work function of graphene emitter.

2D Porous ZnO Nanosheets: One Pot Synthesis with Low Turn-on Field

Low turn-on field of 2.3 V/µm was found for the emission current density of 10 µA/cm2 from 2D porous ZnO nanosheets. High current density of 0.76 mA/cm2 was drawn at an applied field of 4.1 V/µm. The observed low turn-on field of porous ZnO nanosheets has been found to be superior to the other ZnO nanostructures reported in the literature. Also, the emission current stability over a period of 3 hr is found to be better. The field emission current density-applied field (J-E) and current-time (I-t) measurements were carried out in all metal field emission microscope by using ‘close proximity’ (also termed as ‘planar diode’). The porous ZnO nanosheets were synthesized by Chemical Bath Deposition (CBD) method at room temperature followed by annealing at 200 oC. The annealed ZnO nanosheets were subjected to structural and morphological analysis prior to the field emission studies. The XRD spectrum of the as-synthesized product reveals formation of crystalline hexagonal phase of ZnO. Simple synthesis route with superior field emission properties indicate the possible use of porous ZnO nanosheets for micro/nanoelectronic devices.

TiO2 nanotubes decorated by silver nanocubes: Extraction of high field emission current density

Silver (Ag) nanocubes with average size of 69 nm were decorated on TiO2 nanotubes by using UV-switchable reducing agent. The field emission current density versus applied field (J-E) and emission current versus time (I-t) characteristics were measured in a planer diode configuration at the base pressure of 1 × 10−8 mbar. Turn-on field defined for the emission current density of 10 µA/cm2 has been found to be 4.1 V/μm and upon the application of high applied electric field of 7.4 V/μm, maximum current density of 1.1 mA/cm2 has been achieved. I-t measurement has been studied at the preset of 1 µA emission current for the duration of 3 hr. Overall nature of emission current has been seen to be stable for duration of measurement. Superior field emission behavior in terms of maximum current density and emission stability makes the present emitter more suitable for micro/nano-electronics device applications.

Photo-enhanced field emission studies of tapered CdS nanobelts

Field emission and photo-enhanced field emission characteristics of single crystalline tapered CdS nanobelts have been investigated. The turn-on field for the emission current density of ~ 0.1 μA/cm2 is found to be ~ 2.1 V/μm, which is much lower than reported values for various CdS nanostructures. The photo-enhanced field emission current shows a reproducible photo-switching behavior with rise in current level nearly four times that of its initial preset value (~ 1 μA) which is found to be very remarkable. Possible mechanism of photo-enhanced field emission is discussed.

Photo-assisted field emission and current noise analysis from single submicron CdS wire

A single crystalline CdS submicron wire has been synthesized by simple thermal evaporation route. A non-linear and linear F-N plots have been observed for the single submicron CdS wire and multiple nanowires, respectively. The observed non-linearity can be attributed to the band structure of CdS. We believe that at low electric field electron emission is believed to be from the conduction band and at high field values, the field emission is a contribution from both the conduction as well as the valence band. Single submicron CdS wire is seen to exhibit photo assisted field emission behavior upon visible light illumination. The photo-enhanced field emission current is found to switch rapidly between the preset to five times the preset value. The field emission current noise analysis has also been investigated using a Fast Fourier Transform analyzer. The current-time traces show step like fluctuations, with 1/fα type of power spectrum. The observed fluctuations in the field emission current are attributed to the various processes at the emitter surface and intrinsic band structure of CdS.

Spectral analysis of current fluctuations in CdS nanocombs and nanowires array

The field emission studies and, in particular, spectral analysis of field emission current from CdS nanocombs and nanowires array have been carried out at a base pressure of ~1×10-8 mbar. The CdS nanocombs and nanowires array are found to exhibit step like fluctuations in the field emission current. The power spectra for nanocombs and nanowires array show slope values ~2 and ~1.8, respectively, implying that the field emission current fluctuations occur due to the generation-recombination of charge carriers at surface states.

Field emission and photo-enhanced field emission investigations of CdS nanowires array

The CdS nanowires array were grown by thermal evaporation technique on Au patterned silicon substrate. The SEM and TEM are used to analyze surface morphology as well as crystallinity of the as-synthesized CdS nanowires film. The field emission properties of CdS nanowires array were investigated in a parallel plate diode configuration. A high current density of ∼ 68 µA/cm2 has been drawn at the applied electric field of ∼ 5.2 V/μm. The field emission current-time stability measurements depict that the emission current is stable over the period of measurement (3h). The photo-enhanced field emission study shows the photo-switching behavior with rise in the current level to ∼ 3μA for the preset value of ∼ 1μA repetitively.