Paul Maguire

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.

Synthesis of surfactant-free electrostatically stabilized gold nanoparticles by plasma-induced liquid chemistry

Plasma-induced non-equilibrium liquid chemistry is used to synthesize gold nanoparticles (AuNPs) without using any reducing or capping agents. The morphology and optical properties of the synthesized AuNPs are characterized by transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy. Plasma processing parameters affect the particle shape and size and the rate of the AuNP synthesis process. Particles of different shapes (e.g. spherical, triangular, hexagonal, pentagonal, etc) are synthesized in aqueous solutions. In particular, the size of the AuNPs can be tuned from 5 nm to several hundred nanometres by varying the initial gold precursor (HAuCl4) concentration from 2.5 μM to 1 mM. In order to reveal details of the basic plasma-liquid interactions that lead to AuNP synthesis, we have measured the solution pH, conductivity and hydrogen peroxide (H2O2) concentration of the liquid after plasma processing, and conclude that H2O2 plays the role of the reducing agent which converts Au(+3) ions to Au(0) atoms, leading to nucleation growth of the AuNPs.

A study of microstructure and nanomechanical properties of silicon incorporated DLC films deposited on silicon substrates

Silicon incorporation into DLC films prepared by plasma enhanced chemical vapour deposition (PECVD) was studied by a combination of surface analysis methods and nanomechanical measurements; namely XPS, Raman spectroscopy and nanoindentation. Addition of silicon into the films leads to an increase in the sp(3) contribution, as measured from XPS analysis, and a decrease in the Raman band intensity ratio I-G/I-G. These changes are consistent with an evolving C-C bond network. The mechanical properties were first studied as a function of film thickness and indentation depth to assess the effect of substrate proximity. Silicon incorporation produces films with lower hardness and Youngs modulus. It is suggested that, for such a PECVD process, the weakening of the mechanical properties is caused by the increased hydrogen content in the doped films, as shown by the increased Raman background slope, These tendencies are attributable to the development of polymer-like chains, which weakens the inter-molecular structure ofthe films

Properties of diamond like carbon thin film coatings on stainless steel medical guidewires

An investigation of plasma enhanced chemical vapour deposition of diamond like carbon deposited on medical grade stainless steel guidewires is presented and contrasted with existing guidewire coating techniques. Raman spectroscopy and atomic force microscopy studies indicate that this novel coating of guidewires, exhibits diamond like characteristics which possess a form of bulk microstructure reflecting the desired low coefficient of friction, high bulk hardness and good substrate bonding properties that are required for medical guidewires.

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

Breakdown, scaling and volt-ampere characteristics of low current micro-discharges

We give preliminary results on the breakdown and low current limit of volt‐ampere characteristics of simple parallel plate non-equilibrium dc discharges at standard (centimetre size) and micro-discharge conditions. Experiments with micro-discharges are reported attempting to establish the maintenance of E/N, pd and j/p 2 scalings at small dimensions down to 20 µm. It was found that it may not be possible to obtain properly the left-hand side of the Paschen curve. The possible causes are numerous but we believe that it is possible that long path prevention techniques do not work at high pressures. Nevertheless, the standard scaling laws seem to be maintained down to these dimensions which are consistent with simulations that predict violation of scaling below 10 µm. Volt‐ampere characteristics are also presented and compared with those of the standard size discharges.

Properties of ZnS thin films prepared by 248‐nm pulsed laser deposition

Pulsed laser deposition (PLD) from a hot pressed manganese doped ZnS target using a KrF laser, has produced a high rate deposition method for growing luminescent thin films. Good stoichiometric quality and typical luminescent crystal structures have been observed with a predominant hexagonal phase and little evidence of the cubic phase. The luminescent characteristics were determined by cathodoluminescence and photoluminescence excitation and stable electroluminescence was observed under pulsed dc conditions with a minimum brightness of 150 cd/m2. PLD film characteristics are compared with those observed in radio‐frequency sputtered samples.

Crystalline Si nanoparticles below crystallization threshold: Effects of collisional heating in non-thermal atmospheric-pressure microplasmas

Nucleation and growth of highly crystalline silicon nanoparticles in atmospheric-pressure low-temperature microplasmas at gas temperatures well below the Si crystallization threshold and within a short (100 μs) period of time are demonstrated and explained. The modeling reveals that collision-enhanced ion fluxes can effectively increase the heat flux on the nanoparticle surface and this heating is controlled by the ion density. It is shown that nanoparticles can be heated to temperatures above the crystallization threshold. These combined experimental and theoretical results confirm the effective heating and structure control of Si nanoparticles at atmospheric pressure and low gas temperatures.

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.