B. Sundaravel

Structural and electronic properties of nitrogen ion implanted ultra nanocrystalline diamond surfaces

Enhanced electron field emission (EFE) properties have been observed for nitrogen implanted ultra-nanocrystalline diamond (UNCD) films grown by microwave plasma enhanced CVD. X-ray photoelectron spectroscopy (XPS) measurements show that sp2 fraction and C-N bonding increase upon N-implantation and annealing. Significant difference in current-voltage (I-V) curves at the grain and grain boundary has been observed from scanning tunneling spectroscopic (STS) measurement. From the variation of normalized conductance (dI/dV)/(I/V) versus V, bandgap is measured to be 4.8 eV at the grain and 3.8 eV at the grain boundary for as prepared UNCD. Upon nitrogen implantation and annealing, the bandgap decreases for both grain and grain boundary and density of states are introduced in the bandgap. Current imaging tunneling spectroscopy (CITS) imaging shows that the grain boundaries have higher conductivity than the grains and are the prominent electron emitters. The enhancement in EFE properties upon nitrogen implantatio...

Engineering the Interface Characteristics of Ultrananocrystalline Diamond Films Grown on Au-Coated Si Substrates

Enhanced electron field emission (EFE) properties have been observed for ultrananocrystalline diamond (UNCD) films grown on Au-coated Si (UNCD/Au-Si) substrates. The EFE properties of UNCD/Au-Si could be turned on at a low field of 8.9 V/μm, attaining EFE current density of 4.5 mA/cm(2) at an applied field of 10.5 V/μm, which is superior to that of UNCD films grown on Si (UNCD/Si) substrates with the same chemical vapor deposition process. Moreover, a significant difference in current-voltage curves from scanning tunneling spectroscopic measurements at the grain and the grain boundary has been observed. From the variation of normalized conductance (dI/dV)/(I/V) versus V, bandgap of UNCD/Au-Si is measured to be 2.8 eV at the grain and nearly metallic at the grain boundary. Current imaging tunneling spectroscopy measurements show that the grain boundaries have higher electron field emission capacity than the grains. The diffusion of Au into the interface layer that results in the induction of graphite and converts the metal-to-Si interface from Schottky to Ohmic contact is believed to be the authentic factors, resulting in marvelous EFE properties of UNCD/Au-Si.

XPS and SIMS analysis of gold silicide grown on a bromine passivated Si(111) substrate

Abstract When a thin film of Au (∼100 nm) deposited under high vacuum conditions on a chemically prepared Br-passivated Si(111) substrate was annealed around 363°C, epitaxial layer-plus-island mode growth of gold silicide was observed along with some unreacted gold in stringy patterns. This unreacted gold was removed by etching the sample in aqua regia. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) measurements were carried out on these samples. SIMS results reveal that the height of the islands is about 1.2 μm and the silicide/Si interface is abrupt. XPS measurements were made after sputtering the sample surface at constant intervals of time. Si 2 p , Au 4 f , C 1 s and O 1 s photoelectrons were detected. XPS spectra of Si 2 p are resolved into three peaks corresponding to bulk Si, Si in silicide and Si in oxide. The Au 4 f 7/2 peak in the silicide is shifted by 1–1.2 eV towards higher binding energy compared to metallic Au. The shift of Si 2 p towards the higher binding energy in the silicide is understood from the higher electronegativity of Au, while the shift of Au 4 f 7/2 peak towards higher binding energy is known to be due to d-electron depletion to form an sd hybrid. The XPS peak intensity profile with sputtering time indicates that the thin uniform layer (∼5.5 nm) of gold silicide is sandwiched between a thin (∼2.8 nm) SiO 2 layer and the Si(111) substrate.

Structural and Electrical Properties of Conducting Diamond Nanowires

Conducting diamond nanowires (DNWs) films have been synthesized by N₂-based microwave plasma enhanced chemical vapor deposition. The incorporation of nitrogen into DNWs films is examined by C 1s X-ray photoemission spectroscopy and morphology of DNWs is discerned using field-emission scanning electron microscopy and transmission electron microscopy (TEM). The electron diffraction pattern, the visible-Raman spectroscopy, and the near-edge X-ray absorption fine structure spectroscopy display the coexistence of sp³ diamond and sp² graphitic phases in DNWs films. In addition, the microstructure investigation, carried out by high-resolution TEM with Fourier transformed pattern, indicates diamond grains and graphitic grain boundaries on surface of DNWs. The same result is confirmed by scanning tunneling microscopy and scanning tunneling spectroscopy (STS). Furthermore, the STS spectra of current-voltage curves discover a high tunneling current at the position near the graphitic grain boundaries. These highly conducting regimes of grain boundaries form effective electron paths and its transport mechanism is explained by the three-dimensional (3D) Motts variable range hopping in a wide temperature from 300 to 20 K. Interestingly, this specific feature of high conducting grain boundaries of DNWs demonstrates a high efficiency in field emission and pave a way to the next generation of high-definition flat panel displays or plasma devices.

Gold ion implantation induced high conductivity and enhanced electron field emission properties in ultrananocrystalline diamond films

We report high conductivity of 185 (Ω cm)−1 and superior electron field emission (EFE) properties, viz. low turn-on field of 4.88 V/μm with high EFE current density of 6.52 mA/cm2 at an applied field of 8.0 V/μm in ultrananocrystalline diamond (UNCD) films due to gold ion implantation. Transmission electron microscopy examinations reveal the presence of Au nanoparticles in films, which result in the induction of nanographitic phases in grain boundaries, forming conduction channels for electron transport. Highly conducting Au ion implanted UNCD films overwhelms that of nitrogen doped ones and will create a remarkable impact to diamond-based electronics.

Epitaxial growth of silver on Br-passivated Si(111) substrates under high vacuum

Abstract Ag thin films (∼125 nm) were deposited on Br-passivated vicinal (4° miscut) Si(111) surfaces at room temperature under high vacuum conditions. The films have been characterized by Rutherford backscattering spectrometry (RBS) and channeling, X-ray diffraction and transmission electron microscopy and diffraction measurements. The [111] axis of the Ag epilayer is tilted from the substrate [111] orientation by 0.4° towards the substrate surface normal. The films are grainy with a mosaic spread of 0.74°. The crystal quality of the Ag layer improves and the mosaic spread decreases to 0.37° upon annealing in high vacuum at higher temperatures (400 and 500°C) as observed from RBS/channeling and high resolution X-ray diffraction measurements. The tilt angle of the Ag[111] axis and the layer strain also decrease to some extent upon annealing at 500°C.

Raman scattering studies of cobalt nanoclusters formed during high energy implantation of cobalt ions in a silica matrix

Nanoscale cobalt clusters are synthesized in a silica glass matrix through implantation of high energy cobalt ions. Surface acoustic symmetrical vibrational modes of cobalt nanoclusters are detected using Raman spectroscopy. Mode intensity is found to depend strongly on excitation wavelengths. X-ray diffraction studies reveal face-centered-cubic phase of cobalt nanoclusters in postannealed samples. Postannealing in vacuum has led to significant growth of the cobalt nanoclusters in the matrix.

Enhanced Electron Field Emission Properties of Conducting Ultrananocrystalline Diamond Films after Cu and Au Ion Implantation

The effects of Cu and Au ion implantation on the structural and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. High electrical conductivity of 186 (Ω•cm)(-1) and enhanced EFE properties with low turn-on field of 4.5 V/μm and high EFE current density of 6.70 mA/cm(2) have been detected for Au-ion implanted UNCD (Au-UNCD) films that are superior to those of Cu-ion implanted UNCD (Cu-UNCD) ones. Transmission electron microscopic investigations revealed that Au-ion implantation induced a larger proportion of nanographitic phases at the grain boundaries for the Au-UNCD films in addition to the formation of uniformly distributed spherically shaped Au nanoparticles. In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged in the row-like pattern were formed, and only a smaller proportion of nanographite phases along the grain boundaries was induced. From current imaging tunneling spectroscopy and local current-voltage curves of scanning tunneling spectroscopic measurements, it is observed that the electrons are dominantly emitted from the grain boundaries. Consequently, the presence of nanosized Au particles and the induction of abundant nanographitic phases in the grain boundaries of Au-UNCD films are believed to be the authentic factors, ensuing in high electrical conductivity and outstanding EFE properties of the films.

Self-assembled gold silicide wires on bromine-passivated Si(110) surfaces

Thin Au films (∼45 nm) deposited by thermal evaporation under high vacuum on bromine-passivated Si(110) substrates, upon annealing showed the formation of long gold silicide wire-like islands on top of a thin uniform layer of gold silicide in a self-assembled Stranski–Krastanov growth process. Optical micrographs showed long, straight and narrow islands with aspect ratios as large as 200:1. Scanning electron microscopy images revealed the presence of facets. The islands are aligned along the [110] direction on the Si(110) surface. Rutherford backscattering spectrometry measurements with an ion microbeam identified the islands to possess varying thickness across a single island as one would expect for islands having facets and also showed the uniform silicide layer over the Si substrate to be very thin (∼1.5 nm). The observed alignment of the gold silicide islands on the Si(110) surface has been explained in terms of the lattice mismatch between gold–silicide and silicon and invoking the theory of shape t...

Ion dechanneling studies of defects in an ion-beam-synthesized epilayer sandwich system: Si(111)/CoSi2/Si

Rutherford backscattering and channeling studies have been performed on an ion-beam-synthesized heteroepitaxial Si(111)/CoSi 2 (68 nm)/Si(88 nm) sample. The dependence of dechanneling probability on the incident ion energy has been determined to characterize the defects at the buried interfaces and in the epilayers. While the defects at the bulk Si/CoSi 2 interface have been identified to be misfit dislocations, the scattering behavior from the top Si/CoSi 2 interface and the Si epilayer appears to be that of stacking faults. The incident ion energy dependence of the direct backscattering yield confirms these results.