Abstracts Category : Other

Structural and Magnetic Properties of Cobalt Implanted Diamond-like Carbon Films Synthesized by Ion Beam Methods

by Gupta Prasanth Sridhar

Novel methods to synthesize and modify the structure, composition, magnetic behavior and electrical conductivity of thin films are of tremendous importance for fabrication of nano-devices. This research focuses on the application of ion beam methods to produce diamond-like carbon thin films and incorporate magnetic nanostructures within them for potential spintronic applications. Diamond-like carbon films were synthesized by ion beam deposition and were implanted with magnetic ions at low energy to induce magnetic order in near-surface region of the thin film. This research work focuses on the exotic ion-solid interactions that occur between the energetic ions and the base matrix and their subsequent effects on the structure, atomic distribution and magnetic behavior of the implanted films. The results are of significant interest to both, ion beam community and spintronics industry. Diamond-like carbon (DLC) is an amorphous carbon material that contains significant fraction of its carbon bonded in sp hybridization. DLC films were produced by high energy ion beam deposition, specifically by both, direct ion beam deposition and mass selective ion beam deposition. Raman spectroscopy revealed that DLC films deposited by molecular ion beams CH with 5 keV deposition energy has 30 - 50 % of its carbon bonded in sp hybridization. The sp content was observed to decrease with increase in deposition energy. The hydrogen content in the deposited films was measured to be 25 - 30 at.% by resonant nuclear reaction analysis. The selection of deposition energy and ion species was observed to have strong influence on the thin film properties. Cobalt was chosen as the preferred magnetic ion for doping diamond-like carbon thin films. Co was implanted at low energy (30 keV) and at room temperature. The implantation fluence (incident ions per unit area) was varied from 0.8-20 x10 atoms.cm. The implantation current density was limited to 5 A.cm to prevent any bulk heating effects. Monte-Carlo simulations suggest the implantation profile to be single Gaussian with a projected range of 37nm. High resolution Rutherford backscattering spectrometry (HR-RBS) however showed that the Co distribution varied from a unimodal distribution at low fluences (< 1:5 x 10 atoms.cm) to an asymmetric bimodal distribution at high fluence (7 x 10 atoms.cm). Furthermore, a steady state condition was reached at an implantation fluence of (12 x 10 atoms.cm) which is not expected from the simulations. Cross-sectional TEM imaging and corresponding fast Fourier transform analysis reveals that the implanted Co atoms precipitate into cobalt carbide nanoparticles. At high fluences, the nanoparticles accumulate at two regions : (i) in the immediate near-surface region (nanoparticles as large as 5 nm) (ii) at the projected range of implanted ions (large density of ~ 2 nm nanoparticles) in agreement with the measured Co distribution.The bimodal distribution along with the nanoparticle formation can only be explained by the occurrence ofAdvisors/Committee Members: Markwitz, Andreas, Williams, Grant.