Surface:plasma interactions in GaAs subjected to capacitively coupled RF plasmas

Surface compositional changes in GaAs due to RF plasmas of different gases have been investigated by XPS and etch rates were measured using AFM. Angular Resolved XPS (ARXPS) was also employed for depth analysis of the composition of the surface layers. An important role in this study was determination of oxide thickness using XPS data. The study of surface - plasma interaction was undertaken by correlating results of surface analysis with plasma diagnosis. Different experiments were designed to accurately measure the BEs associated with the Ga 3d, Ga 2P3/2 and LMM peaks using XPS analysis and propose identification in terms of the oxides of GaAs. Along with GaAs wafers, some reference compounds such as metallic Ga and Ga2O3 powder were used. A separate study aiming the identification of the GaAs surface oxides formed on the GaAs surface during and after plasma processing was undertaken. Surface compositional changes after plasma treatment, prior to surface analysis are considered, with particular reference to the oxides formed in the air on the activated surface. Samples exposed to ambient air for different periods of time and also to pure oxygen were analysed. Models of surface processes were proposed for explanation of the stoichiometry changes observed with the inert and reactive plasmas used. In order to help with the understanding of the mechanisms responsible for surface effects during plasma treatment, computer simulation using SRIM code was also undertaken. Based on simulation and experimental results, models of surface phenomena are proposed. Discussion of the experimental and simulated results is made in accordance with current theories and published results of different authors. The experimental errors introduced by impurities and also by data acquisition and processing are also evaluated.

Meta-analytic model comparisons of surface- and deep-level relational diversity effects on social integration and individual effectiveness

While diversity might give an organization a competitive advantage, individuals have a tendency to prefer homogenous group settings. Prior research suggests that group members who are dissimilar (vs. similar) to their peers in terms of a given diversity attribute (e.g. demographics, attitudes, values or traits) feel less attached to their work group, experience less satisfying and more conflicted relationships with their colleagues, and consequently are less effective. However, prior empirical findings tend to be weak and inconsistent, and it remains unclear when, how and to what extent such differences affect group members’ social integration (i.e. attachment with their work group, satisfaction and conflicted relationships with their peers) and effectiveness. To address these issues the current study conducted a meta-analysis and integrated the empirical results of 129 studies. For demographic diversity attributes (such as gender, ethnicity, race, nationality, age, functional background, and tenure) the findings support the idea that demographic dissimilarity undermines individual member performance via lower levels of social integration. These negative effects were more pronounced in pseudo teams – i.e. work groups in which group members pursue individual goals, work on individual tasks, and are rewarded for their individual performance. These negative effects were however non-existent in real teams - i.e. work groups in which groups members pursue group goals, work on interdependent tasks, and are rewarded (at least partially) based on their work group’s performance. In contrast, for underlying psychological diversity attributes (such as attitudes, personality, and values), the relationship between dissimilarity and social integration was more negative in real teams than in pseudo teams, which in return translated into even lower individual performance. At the same time however, differences in underlying psychological attributes had an even stronger positive effect on dissimilar group member’s individual performance, when the negative effects of social integration were controlled for. This implies that managers should implement real work groups to overcome the negative effects of group member’s demographic dissimilarity. To harness the positive effects of group members’ dissimilarity on underlying psychological attributes, they need to make sure that dissimilar group members become socially integrated.

Protein deposition at polymer surfaces:the bulk and surface structure-property effects of hydrogels

The primary objective of this research has been to investigate the interfacial phenomenon of protein adsorption in relation to the bulk and surface structure-property effect s of hydrogel polymers. In order to achieve this it was first necessary to characterise the bulk and surface properties of the hydrogels, with regard to the structural chemistry of their component monomers. The bulk properties of the hydrogels were established using equilibrium water content measurements, together with water-binding studies by differential scanning calorimetry (D.S.C.). Hamilton and captive air bubble-contact angle techniques were employed to characterise the hydrogel-water interface and from which by a mathematical derivation, the interfacial free energy (ðsw) and the surface free energy components (ð psv, ðdsv, ðsv) were obtained. From the adsorption studies using the radio labelled iodinated (125I) proteins of human serum albumin (H.S.A.) and human fibrinogen (H.Fb.), it was Found that multi-layered adsorption was occurring and that the rate and type of this adsorption was dependent on the physico-chemical behaviour of the adsorbing protein (and its bulk concentration in solution), together with the surface energetics of the adsorbent polymer. A potential method for the invitro evaluation of a material's 'biocompatibility' was also investigated, based on an empirically observed relationship between the adsorption of albumin and fibrinogen and the 'biocompatibility' of polymeric materials. Furthermore, some consideration was also given to the biocompatibility problem of proteinaceous deposit formation on hydrophilic soft' contact lenses and in addition a number of potential continual wear contact lens formulations now undergoing clinical trials,were characterised by the above techniques.

Charge effects on the hindered transport of macromolecules across the endothelial surface glycocalyx layer

A fluid mechanical and electrostatic model for the transport of solute molecules across the vascular endothelial surface glycocalyx layer (EGL) was developed to study the charge effect on the diffusive and convective transport of the solutes. The solute was assumed to be a spherical particle with a constant surface charge density, and the EGL was represented as an array of periodically arranged circular cylinders of like charge, with a constant surface charge density. By combining the fluid mechanical analyses for the flow around a solute suspended in an electrolyte solution and the electrostatic analyses for the free energy of the interaction between the solute and cylinders based on a mean field theory, we estimated the transport coefficients of the solute across the EGL. Both of diffusive and convective transports are reduced compared to those for an uncharged system, due to the stronger exclusion of the solute that results from the repulsive electrostatic interaction. The model prediction for the reflection coefficient for serum albumin agreed well with experimental observations if the charge density in the EGL is ranged from approximately -10 to -30 mEq/l.

Surface- and deep-level dissimilarity effects on social integration and individual effectiveness related outcomes in work groups:a meta-analytic integration

Prior research linking demographic (e.g., age, ethnicity/race, gender, and tenure) and underlying psychological (e.g., personality, attitudes, and values) dissimilarity variables to individual group member's work-related outcomes produced mixed and contradictory results. To account for these findings, this study develops a contingency framework and tests it using meta-analytic and structural equation modelling techniques. In line with this framework, results showed different effects of surface-level (i.e., demographic) dissimilarity and deep-level (i.e., underlying psychological) dissimilarity on social integration, and ultimately on individual effectiveness related outcomes (i.e., turnover, task, and contextual performance). Specifically, surface-level dissimilarity had a negative effect on social integration under low but not under high team interdependence. In return, social integration fully mediated the negative relationship between surface-level dissimilarity and individual effectiveness related outcomes under low interdependence. In contrast, deep-level dissimilarity had a negative effect on social integration, which was stronger under high and weaker under low team interdependence. Contrary to our predictions, social integration did not mediate the negative relationship between deep-level dissimilarity and individual effectiveness related outcomes but suppressed positive direct effects of deep-level dissimilarity on individual effectiveness related outcomes. Possible explanations for these counterintuitive findings are discussed. © 2011 The British Psychological Society.

Surface roughness after excimer laser ablation using a PMMA model:profilometry and effects on vision

PURPOSE: To show that the limited quality of surfaces produced by one model of excimer laser systems can degrade visual performance with a polymethylmethacrylate (PMMA) model. METHODS: A range of lenses of different powers was ablated in PMMA sheets using five DOS-based Nidek EC-5000 laser systems (Nidek Technologies, Gamagori, Japan) from different clinics. Surface quality was objectively assessed using profilometry. Contrast sensitivity and visual acuity were measured through the lenses when their powers were neutralized with suitable spectacle trial lenses. RESULTS: Average surface roughness was found to increase with lens power, roughness values being higher for negative lenses than for positive lenses. Losses in visual contrast sensitivity and acuity measured in two subjects were found to follow a similar pattern. Findings are similar to those previously published with other excimer laser systems. CONCLUSIONS: Levels of surface roughness produced by some laser systems may be sufficient to degrade visual performance under some circumstances.