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Ali J.,Jamia Millia Islamia University | Kumar A.,Jamia Millia Islamia University | Husain S.,Jamia Millia Islamia University | Kumari M.,Solid State Physical Laboratory | And 2 more authors.
Current Nanoscience | Year: 2011

Carbon nanotubes are synthesized by Low Pressure Chemical Vapor Deposition (LPCVD) system using NH3: C2H2:H2 gas mixtures on iron coated silicon substrate. The iron catalyst was coated on silicon using RF-sputtering method. The growth temperature was kept at 600oC and growth time was 10 mins. The carbon nanotubes are found to have diameters ranging from 50 to 80 nm and length of up to a few tens of microns. Raman spectra indicate that the CNTs are highly graphitized and several peaks are also found at low frequency range from 100 cm-1 to 500 cm-1, which are assigned to the radial breathing mode (RBM) which is the characteristic of single wall carbon nanotubes. Therefore, this sample also contains single walled carbon nanotubes also. The carbon nanotubes showed a turn-on field of 2.63 V/m and the maximum current density of 2 mA/cm2. The field enhancement factor was calculated to be 3.941 X 103 for as grown carbon nanotubes. The carbon nanotubes grown at this lower temperature show good field emission and are suitable for device applications. © 2011 Bentham Science Publishers Ltd.

Chhoker S.,Indian Institute of Technology Delhi | Vinayak S.,Solid State Physical Laboratory | Shukla A.K.,Indian Institute of Technology Delhi | Vankar V.D.,Indian Institute of Technology Delhi
Journal of Experimental Nanoscience | Year: 2011

Current research on the carbon-based nanotechnology needs progressive methodsto control the shape, location and size of the nanostructures. Here, we reportsignificant progress by synthesising the density controlled carbon nanostructures(CNSs) using acetylene and hydrogen in microwave plasma enhanced chemicalvapour deposition system. Thin films of Ni-Cr (80: 20, 60: 40 and 50: 50) sputteredover silicon (1 0 0) were used as catalysts. Scanning electron microscopy images ofplasma annealed Ni-Cr coated silicon substrates show distributed nanoparticles ofvarying compositions over plasma annealed substrates. Morphologically andstructurally different CNS were obtained when plasma annealed substrates wereexposed to carbon vapours present in plasma. Transmission electron microscopyimages suggested that the length and tip of CNS were in the range 50-100nm and4-6 nm, respectively. High resolution transmission electron microscopy images ofthe samples confirmed the presence of graphite (0 0 2) and nickel (2 0 0) planes inCNS. The field emission studies and Kelvin probe measurements of CNS grownover 80: 20 Ni-Cr substrate show turn-on field and corresponding work functionas 1.4V μm -1 and 4.4 eV, respectively. Preliminary results show that thesenanostructures could act as stable field emitters. © 2011 Taylor & Francis.

Kumar A.,Indian Institute of Technology Delhi | Vinayak S.,Solid State Physical Laboratory | Singh R.,Indian Institute of Technology Delhi
Journal of Nano- and Electronic Physics | Year: 2011

In the present work, the I-V characteristics of Ni/GaN Schottky diodes have been studied. The Schottky diodes, having different sizes using Ni/Au and ohmic contacts using Ti/Al/Ni/Au were made on n-GaN. The GaN was epitaxially grown on c-plane sapphire by metal organic chemical vapor deposition (MOCVD) technique and had a thickness of about 3.7 μm. The calculated ideality factor and barrier height from current-voltage (I-V) characteristics (at 300 K) for two GaN Schottky diodes were close to ~1.3 and ~ 0.8 eV respectively. A high reverse leakage current in the order of 10 -4A/cm 2 (at - 1 V) was observed in both diodes. A careful analysis of forward bias I-V characteristics showed very high series resistance and calculation for ideality factor indicated presence of other current transport mechanism apart from thermionic model at room temperature. © 2011 SumDU.

Kumar A.,Indian Institute of Technology Delhi | Kumar M.,Indian Institute of Technology Delhi | Kaur R.,National Institute of Technology Kurukshetra | Vinayak S.,Solid State Physical Laboratory | Singh R.,Indian Institute of Technology Delhi
Applied Physics Letters | Year: 2014

Wet chemical passivation of n-GaN surface using Ru based solution has been reported. X-ray photoelectron spectroscopy characterization of the GaN surface revealed removal of surface oxides by the introduction of Ru complex species. Ni/n-GaN Schottky barrier diodes were fabricated on passivated GaN and a remarkable improvement in Schottky barrier height from 0.76eV to 0.92eV was observed. © 2014 AIP Publishing LLC.

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