A. A. Ogwu

Platelet adhesion on silicon modified hydrogenated amorphous carbon films

We have investigated the effect of changes in microstructure, surface energy, surface charge condition and electronic conduction on the interaction of human platelets with silicon modified hydrogenated amorphous carbon films (a-C:H:Si or Si-DLC). Results based on Raman spectroscopy, Scanning electron microscopy, X-ray photo-electron spectroscopy, surface energy measurements, electrical resistivity, contact potential difference, and thermal annealing indicates a correlation between some of the measured values and the interaction of the films with human blood platelets. Statistical analysis of platelet aggregation on the films using the Students t-test indicated differences between platelet aggregation on the modified films compared to the as-deposited film at a p-value of <0.05.

Characterisation of thermally annealed diamond like carbon (DLC) and silicon modified DLC films by Raman spectroscopy

Raman spectroscopy has been used to investigate the structural changes in thermally annealed diamond like carbon (a-C:H) and silicon modified diamond like carbon (a-C:H:Si) films prepared by plasma enhanced chemical vapour deposition (PECVD) using a 514.53 nm argon ion laser excitation. The changes in the Raman spectra of the films has been used to monitor structural modifications with increasing annealing temperature. The present investigation indicates that the rate of these structural modifications is dependent on both the annealing temperature and the negative self-bias voltage applied during the film deposition process for a fixed annealing time

Surface engineered surgical tools and medical devices

Surface engineered surgical tools and medical devices / , Surface engineered surgical tools and medical devices / , کتابخانه دیجیتال جندی شاپور اهواز

The influence of biological fluids on crack spacing distribution in Si-DLC films on steel substrates

An experimental investigation of the effect of exposure to biological fluids on the adhesion of silicon modified DLC films to steel substrates (304 stainless and mild steel) was conducted. The substrate straining test was used for the adhesion measurement. A statistical procedure, which is faster and more reliable than the ab initio computer simulation of crack spacing distribution adopted by previous authors in the literature was used to treat the crack spacing data. We observed a change in the crack spacing distribution from the Weibull for the as-prepared films to Lognormal for the films immersed in biological fluids. A reduction in the interfacial adhesion values was also observed for the films soaked in biological fluids compared to the as-prepared films. The proposed approach can be used when the crack spacing matches other statistical distributions.

The effect of the substrate bias on the Raman spectra and thermal stability of diamond-like carbon (DLC) and silicon-modified DLC films prepared by plasma-enhanced chemical vapour deposition (PECVD)

An investigation of the dependence of the thermal stability of DLC (a-C:H) and silicon-modified DLC (a-C:H:Si) films on film-deposition conditions has been conducted. An interpretation based on plasma chemistry, x-ray photoelectron spectroscopy, confocal Raman spectroscopy and substrate-bias-voltage changes is proposed to explain the thermally induced structural modifications in the films between 200 and 600 °C. Our recent finding is expected to be beneficial to those designing thermal annealing schedules for reducing or eliminating residual stresses in the films.

Complementary analysis techniques for the morphological study of ultrathin amorphous carbon films

This article presents experimental results for morphological assessment of sub-50-nm thick hydrogenated amorphous carbon (a-C:H) overcoats. The films were grown by rf plasma enhanced chemical vapor deposition using Ar/C2H2 gas mixture onto heterogeneous (Al2O3–TiC) ceramic substrates. They were analyzed using complementary information from scanning electron microscopy, energy dispersive x-ray analysis and atomic force microscopy. We found that the bias deposition voltage and the nature of the substrate (Al2O3 or TiC regions) adversely affect both growth rate and microstructure. Argon inclusion in the C2H2 plasma during the first stage of growth is responsible for the observed effects. These results suggest that the amorphous carbon layer is denser on the TiC than on the Al2O3 region.

The insulating properties of a-C : H on silicon and metal substrates

Amorphous carbon has many important applications. In electronic terms, its use as a dielectric is receiving greater attention. This is particularly important for applications in magnetic head devices as a reader gap insulation layer. Results are presented for resistivity and breakdown fields for hydrogenated amorphous carbon on silicon, undopedand doped with nitrogen, using an atomic flux sourer. Current-voltage characteristics were analysed using a numerical algorithm to determine trap densities. The results indicated that such films can meet the breakdown specifications, on silicon, and that nitrogen doping improves their characteristics. Thickness trends indicate improvements are likely as gaps are scaled. The density of states determination indicated that high breakdown was correlated, in the undoped case, with high DOS but this was not so for the doped films. The DOS was found to increase as the thickness decreased. On substrates other than silicon,the films were observed to have increased roughness, poorer adhesion and a more polymer-like quality. These changes were reflected in a reduction in the observed breakdown field

Electrical characteristics of nitrogen incorporated hydrogenated amorphous carbon

Nitrogen incorporation into hydrogenated amorphous carbon (a-C:H) films has recently attracted a wide range of interest due to its contribution in reducing film stress and improving field emission properties. In this work we characterize the electrical properties of nitrogen containing a-C:H films. The a-C:H films were prepared by plasma enhanced chemical vapor deposition in an acetylene (C2H2) environment with a range of bias voltages. Nitrogen incorporation was achieved by exposing the films to an atomic nitrogen flux from a rf plasma with up to 40% dissociation and atomic nitrogen fluxes of up to 0.85×1018 atoms s−1. Raman results indicate that the doping process is accompanied by some structural changes seen by the G-band peak shifts. X-ray photoelectron spectroscopy spectra suggest that the dopant levels exceed those previously reported. Capacitance probe and I–V techniques showed a decrease in contact potential difference and density of states for doped films, indicating a rise in the Fermi level.

Naniondentation and scratch resistance testing on magnetic tape heads coated with ultra-thin amorphous carbon layers

We present results on nanoindentation and scratch testing on magnetic recording tape heads coated with sub-20 nm amorphous carbon layers, prepared by filtered cathodic deposition and plasma enhanced chemical vapour deposition. The hardness values of the coated devices are higher than that of the sputtered Al2O3 substrate. The coatings do not reduce friction but improve the scratch resistance of the tape heads. Hardness, which shows some correlation with scratch resistance is a contributing factor, especially at high load where it reduces plastic ploughing of the substrate. For low scratching load, the wear seems to be influenced by the adhesive properties of the film/substrate interface. Smoother surfaces and smaller tip radius should improve the accuracy of the results. This could provide better insight into the failure mechanism of these ultra-thin overcoats.

A reactive magnetron sputtering route for attaining a controlled core-rim phase partitioning in Cu2O/CuO thin films with resistive switching potential

The achievement of a reproducible and controlled deposition of partitioned Cu2O/CuO thin films by techniques compatible with ULSI processing like reactive magnetron sputtering has been reported as an outstanding challenge in the literature. This phase partitioning underlies their performance as reversible resistive memory switching devices in advanced microelectronic applications of the future. They are currently fabricated by thermal oxidation and chemical methods. We have used a combination of an understanding from plasma chemistry, thermo-kinetics of ions, and rf power variation during deposition to successfully identify a processing window for preparing partitioned Cu2O/CuO films. The production of a core rich Cu2O and surface rich Cu2O/CuO mixture necessary for oxygen migration during resistive switching is confirmed by XRD peaks, Fourier transform infra red Cu (I)-O vibrational modes, XPS Cu 2P3/2 and O 1S peak fitting, and a comparison of satellite peak ratios in Cu 2P3/2 fitted peaks. We are prop...