Deepak Varshney

Free standing graphene-diamond hybrid films and their electron emission properties

Free standing graphene-diamond hybrid films have been fabricated using saturated hydrocarbon polymers as seeding material by hot filament chemical vapor deposition technique. The films are characterized with x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). The XRD shows the characteristic diffraction peaks of both diamond and graphene. The Raman spectrum shows the characteristic band of diamond at 1332 cm−1 and D, G, and 2D bands of graphene at 1349, 1592, and 2687 cm−1, respectively. Both SEM and TEM depict the presence of diamond and graphene in the films. The EELS recorded in the carbon K-edge region also shows the signature peaks of diamond and graphene. The free standing hybrid films exhibit a remarkably low turn-on field of about 2.4 V/μm and a high emission current density of 0.1 mA/cm2. Furthermore, emission currents are stable over the period of 7 days. The superior field emission...

Ultrananocrystalline Diamond-Decorated Silicon Nanowire Field Emitters

Silicon nanowires (SiNWs) were uniformly decorated with ultrananocrystalline diamond (UNCD) by a novel route using paraffin wax as the seeding source, which is more efficient in the creation of diamond nuclei than traditional methods. These one-dimensional ultrananocrystalline diamond-decorated SiNWs (UNCD/SiNWs) exhibit uniform diameters ranging from 100 to 200 nm with a bulbous catalytic tip of ∼250 nm in diameter and an UNCD grain size of ∼5 nm. UNCD/SiNW nanostructures demonstrated enhanced electron field emission (EFE) properties with a turn-on field of about 3.7 V/μm. Current densities around 2 mA/cm(2) were achieved at 25 V/μm, which is significantly enhanced as compared to bare SiNWs.

Low frequency dielectric response of mechanosynthesized (Pb0.9Ba0.1 ) (Fe0.50Nb0.50)O3 nanoceramics

The nanocrystalline (40nm) samples of Pb(Fe0.50Nb0.50)O3 (PFN) and Pb0.90Ba0.1(Fe0.5Nb0.5)O3 (PBFN) were synthesized by mechanosynthesis and mixed oxide methods. Preliminary structural analysis of these samples showed that tetragonal PFN can be distorted to orthorhombic structure on 10% Ba substitution in it. One of the relaxor characteristics (i.e., diffuse phase transition with low frequency dielectric dispersion) was observed in PBFN with a decrease in the transition temperature from 380K (PFN) to 170K. The suggested relaxor behavior in a new PFN composition is possibly due to compositional fluctuations at the nanolevel.

Single-step route to diamond-nanotube composite

Candle wax was used as a precursor for the production of a diamond-nanotube composite in a single step. The composite films were fabricated by sulfur-assisted hot-filament chemical vapor deposition technique. The morphology of the composite films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectra of the films show characteristic diamond band at 1,332 cm−1, D-band around 1,342 cm−1, and graphitic G-band around 1,582 cm−1. The electron energy-loss spectroscopy recorded at the carbon K-edge region shows signature features of diamond and carbon nanotube in the fabricated material. The ability to synthesize diamond-nanotube composites at relatively low temperatures by a single-step process opens up new possibilities for the fabrication of nanoelectronic devices.

Electron emission from diamond films seeded using kitchen-wrap polyethylene

Diamond has many potential electronic applications, but the diamond seeding methods are generally harsh on the substrates rendering them unsuitable for integration in electronics. We report a non-abrasive, scalable and economic process of diamond film seeding using kitchen-wrap polyethylene employing hot filament chemical vapour reaction of H2S/CH4/H2 gas mixtures on Cu substrates. The fabricated diamond films were characterized with scanning electron microscopy, transmission electron microscopy and Raman spectroscopy, which confirm that the deposited film consists of a microcrystalline diamond of size in the range 0.5?1.0??m. The synthesized diamond films exhibit a turn-on field of about 8.5?V??m?1 and long-term stability. Diamond film synthesis using polyethylene will enable the integration of diamond heat sinks into high-power and high-temperature electronic devices.

Fabrication and field emission study of novel rod-shaped diamond-like carbon nanostructures

Novel sp(3) rich diamond-like carbon nanorod films were fabricated by a hot filament chemical vapour deposition technique. The results are indicative of a bottom-up synthesis process, which results in a hierarchical structure that consists of microscale papillae comprising numerous nanorods. The papillae have diameters ranging from 2 to 4 microm and the nanorods have diameters in the 35-45 nm range. A growth mechanism based on the vapour-liquid-solid mechanism is proposed that accounts for the morphological aspects at the microscale and nanoscale. Investigation of field emission properties of fabricated nanorods reveals a low turn-on field of about 4.9 V microm( - 1) at 1 nA and a high field-enhancement factor.

New route to the fabrication of nanocrystalline diamond films

Nanocrystalline diamond (NCD) thin films offer applications in various fields, but the existing synthetic approaches are cumbersome and destructive. A major breakthrough has been achieved by our group in the direction of a non-destructive, scalable, and economic process of NCD thin-film fabrication. Here, we report a cheap precursor for the growth of nanocrystalline diamond in the form of paraffin wax. We show that NCD thin films can be fabricated on a copper support by using simple, commonplace paraffin wax under reaction conditions of Hot Filament Chemical Vapor Deposition (HFCVD). Surprisingly, even the presence of any catalyst or seeding that has been conventionally used in the state-of-the-art is not required. The structure of the obtained films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectroscopy and electron energy-loss spectroscopy recorded at the carbon K-edge region confirm the presence of nanocrystalline diamond. The process is a significant step towards cost-effective and non-cumbersome fabrication of nanocrystalline diamond thin films for commercial production.

Genesis of diamond nanotubes from carbon nanotubes

We synthesized sp3-rich crystalline tubular structures, referred to as diamond nanotubes (DNTs), by hot-filament chemical vapor deposition and characterized them using SEM, TEM, EELS, and Raman spectroscopy. The images and spectra indicate the formation of DNTs with internal diameter of about 7–10 nm and external diameter of about 20–30 nm. During the fabrication process, CNTs form first and give way to the synthesis of DNTs. The DNTs show good field emission properties and enhanced temporal stability as compared to CNTs.