B.K. Gan

Effect Of Intrinsic Stress On Preferred Orientation In Aln Thin Films

We examine the effect of ion impact energy on the intrinsic stress and microstructure of aluminum nitride thin films deposited using a filtered cathodic arc. The dependence of intrinsic stress on ion impact energy is studied over the range from 0 to 350 V using dc bias and up to several kV for a fraction of the ions using pulse bias. For dc bias, the stress reaches a maximum at 200 V and decreases with further increase in ion bias. The preferred orientation of the crystallites was studied by cross-section transmission electron microscopy and diffraction. We found that there is a preference for the c crystallographic axis to lie in the plane of the film under high intrinsic stress conditions (4 GPa), whereas a c-axis orientation perpendicular to the plane of the film was observed for low intrinsic stress (0.25 GPa). We carried out calculations of the expected distribution of intensity in cross-sectional electron diffraction patterns to predict the effect of rotation freedom of crystallites with the c axis pinned. The calculated patterns agreed well with experiment.We examine the effect of ion impact energy on the intrinsic stress and microstructure of aluminum nitride thin films deposited using a filtered cathodic arc. The dependence of intrinsic stress on ion impact energy is studied over the range from 0 to 350 V using dc bias and up to several kV for a fraction of the ions using pulse bias. For dc bias, the stress reaches a maximum at 200 V and decreases with further increase in ion bias. The preferred orientation of the crystallites was studied by cross-section transmission electron microscopy and diffraction. We found that there is a preference for the c crystallographic axis to lie in the plane of the film under high intrinsic stress conditions (4 GPa), whereas a c-axis orientation perpendicular to the plane of the film was observed for low intrinsic stress (0.25 GPa). We carried out calculations of the expected distribution of intensity in cross-sectional electron diffraction patterns to predict the effect of rotation freedom of crystallites with the c axis ...

Stress relief and texture formation in aluminium nitride by plasma immersion ion implantation

The effect on the intrinsic stress in AlN films of applying pulsed bias during cathodic arc deposition has been studied. We find that the stress depends only on the pulse voltage–pulse frequency product, V f. The form of the dependence is well fitted by an exponential function whose parameters can be interpreted physically. The preferred orientation changes progressively with V f, from hexagonal crystallites having their direction in the plane of the film at low V f, to hexagonal crystallites having their direction normal to the plane of the film at high V f. The in-plane orientation may be consistent with energy minimization in a biaxial stress field whereas the normal orientation is consistent with the alignment of a channelling direction with the ion beam.

Correlation between stress and hardness in pulsed cathodic arc deposited titanium/vanadium nitride alloys

We use a dual source pulsed cathodic arc with centre triggering to produce alloys in the series Ti1−xVxN with accurately controlled composition. We show that the composition x = 0.23 produces the highest indentation hardness and hence the highest yield stress. This composition also shows the highest stress levels, which we explain in terms of its reduced flow during deposition. The microstructure of the alloys shows that they are homogeneously mixed with the rocksalt structure. At the highest vanadium contents a (200) preferred orientation develops. This work shows that the composition Ti0.77V0.23N has a substantially higher hardness than TiN and may have an application as a high performance alloy.

Optimizing the triggering mode for stable operation of a pulsed cathodic arc deposition system

In order to deposit fine structures such as nanoscale multilayers using a pulsed cathodic arc, it is necessary to ensure that the deposition per pulse is stable over a large number of pulses. We compare the deposition rate using centre and edge triggering in a pulsed cathodic arc system by determining the rate of change of thickness of a growing film. Three arc currents were used and the results indicated that the centre triggering configuration provides a constant deposition rate when compared to edge triggering. It was also observed that the highest arc current in the centre mode showed the most uniform deposition rate. The erosion profile of the cathodes for the two different triggering types were examined and used to explain the differences in terms of uniformity of erosion. We also measured the discharge voltage and found that there was an increase with increasing arc current.

Relationship Between Microstructure, Stress and Hardness in Multilayer Coatings.

The need to synthesize advanced materials which exhibit superior mechanical properties has increased over the past decade with the insurgence of machining and bio-medical devices into the global market. These applications including silicon-based semiconductor devices, Micro-ElectroMechanical Systems (MEMS), tool steel coatings and artificial organs require materials with a variety of properties including enhanced surface hardness and wear resistance, and reduced crack propagation and delamination. Significant advances in Physical Vapor Deposition (PVD), mainly Pulsed Filtered Cathodic Arc, have allowed accurate control of thin film properties enabling specifically tailored coatings to be engineered.

Functional attachment of horse radish peroxidase to plasma-treated surfaces

Controlling the interaction of surfaces with macromolecules, such as proteins and antibodies, is the key to producing biocompatible prosthetic devices, biosensors and diagnostic arrays. The development of technologies to control these interactions will result in the early detection of disease and have the potential to dramatically reduce costs associated with clinical treatment. For example, tethering functional anti-bodies to a surface in a patterned array allows the selection of specific proteins from a microlitre serum sample, immediately identifying diseases, well before the symptoms are manifested. Unfortunately, simple physical absorption of proteins onto most surfaces results in changes in their structure and loss of function. The use of ions from plasmas allows flexibility in surface modification by accessing a variety of ion energies and activated chemical species. In this paper we describe plasma based techniques which are being developed to modify the chemistry and morphology of surfaces in order to optimise their interaction with biomolecules. Early results of plasma processes to activate surfaces for non specific attachment of proteins by hydrophilic /hydrophobic interactions are presented, with particular attention to the time stability of such treatments, which is of special interest.

Enhancement of hrp binding on plasmatreated ultra-high molecular weight polyethylene

Summary form only given. Immunoassay technique is one of the actively researched areas since reliable, low cost and sensitive diagnostic immunoassay systems are required for public health care. The enzyme-linked immunosorbent assay (ELISA) is common technique to detect diseases such as HIV or hepatitis virus. The aim of the present work is to modify the surface of ultra-high molecular weight polyethylene (UHMWPE) by plasma immersion ion implantation to increase the number of the specific active enzyme binding sites on the polymer surface. The specimens are incubated in horseradish peroxidase (HRP) overnight and washed by 10 mM PO4 buffer six times. The quantity of HRP can be changed by adding TMB (HRPs substrate) on the polyethylene surface. The optical densities of the treated and untreated samples are monitored and compared. Our results show more active HRP on the plasma-treated PE. In addition, our tests show highly stable and reproductive results and demonstrate that plasma immersion ion implantation is a viable technique