This article looks at the development of vacuum from its known origins in 500 BC to an important field of modern science with numerous applications in industry and, more recently, in medicine. The author describes his personal experience in vacuum research and vacuum community activity. The main achievements of his team and colleagues are highlighted in this paper.

Iron-disilicide films were sputter deposited on Si(100) wafers to 300–400 nm, at substrate temperatures ranging from room temperature to 700 °C. As-deposited films were amorphous at deposition temperatures up to 200 °C, and crystalline β-FeSi2at 300–700 °C. Amorphous films were heat-treated after deposition at 300–700 °C. They remained amorphous up to 400 °C, and transformed to crystalline β-FeSi2at 500–700 °C. Optical absorption measurements showed that the band gap of all films is direct in nature, ranging from 0.88 to 0.93 eV. The deposition temperature was seen to affect the crystallinity of the as-deposited films and to vary their optical properties significantly. The photoabsorption coefficient, measured at 1 eV, increased from 5.6 ×104cm-1for amorphous films to 1.2 ×105cm-1for the samples deposited at 700 °C. The films crystallized by heat-treatment had a markedly different and irregular structure, resulting in their lower optical absorption.

Objectives. Nickel chromium is widely used as a restorative material in dentistry but its bio-compatibility is of concern as there are reports of patients suffering adverse effects caused by exposure to nickel-based restorations. The aim of this work was to quantify the amount of nickel released into solution from commercially available nickel-based alloys with varying compositions and to identify the potential use of thin films in further understanding the role of chromium in reducing nickel release.Methods. Six commercially available nickel-based alloys were cast using the lost wax technique. Nickel chromium thin films were deposited onto silicon substrates by ion beam assisted physical vapor deposition. Both types of alloys were immersed into solution representative of saliva at pH 5 for 7 days. The amount of nickel released into solution was quantified by graphite-furnace atomic absorption spectrophotometry.Results. The amount of nickel released from commercially available cast alloys did not correspond to the amount of nickel within the alloy. The total amount of chromium and molybdenum within the alloys proved to be of greater influence. Increasing the amount of chromium in the thin film alloys reduced the amount of nickel released but this was not linear.Significance. Differences in the composition of commercial cast alloys highlighted the importance of other elements within the alloy on reducing the amount of nickel released. The use of thin film alloys can be useful in further understanding how the composition of an alloy can affect the amount of nickel released. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

The ease of removal of differently sized and shaped bacteria from substrata with defined surface topographies and features was investigated. Surfaces with defined surface topography (smooth or with randomly spaced surface features (pits) of 0.5 microm diameter), chemistry (titanium oxide), and wettability (89-93 degrees) were produced. Atomic force microscopy (AFM) was used to determine the ease of bacterial removal from substrata; gram negative Pseudomonas aeruginosa (rods 1 microm width x 3 microm length) and gram positive Staphylococcus aureus (1 microm diameter coccus). The AFM tip was scanned across the retained cells under liquid (contact mode). Over time, using a continuous perpendicular tip force, approximately one third of the cells were removed from the surface following lateral movement of the AFM tip across the surface. When the perpendicular tip force was increased S. aureus were removed more easily from smooth surfaces. In contrast P. aeruginosa cells were removed more easily from the 0.5 microm featured surfaces. The shape of the cell with respect to the shape of the substratum features influences the ease of removal of the cell from the surface: on smooth surfaces the cocci had a smaller cell:surface contact area, whereas the rods had a larger cell:surface contact area. Conversely on featured surfaces the cocci had a larger cell:surface contact area, whereas rods that lay across features had a smaller cell:surface contact area. Using engineered surfaces with defined properties, it has been shown that manipulation of a single parameter (surface roughness) had an effect on the strength of microbial retention.

Surfaces were produced with defined topographical features and surface chemistry. Silicon wafers, and wafers with attached nucleopore filters and quantifoils were coated with titanium using ion beam sputtering technology. Irregularly spaced, but regularly featured surface pits, sizes 0.2 and 0.5 microm, and regularly spaced pits with regular features (1 and 2 microm) diameter were produced. The smallest surface feature that could be successfully produced using this system was of diameter 0.2 microm. Ra, the average absolute deviation of the roughness irregularities from the mean line over one sampling length, Rz, the difference in height between the average of the five highest peaks, and the five lowest valleys along the assessment length of the profile and surface area values increased with surface feature size, with Ra values of 0.04-0.217 microm. There was no significant difference between the contact angles observed for smooth titanium surfaces with 0.2 and 0.5 microm features. However, a significant difference in contact angle was observed between the 1 and 2 microm featured surfaces (p<0.005). Substrata were used in microbial retention assays, using a range of unrelated, differently sized microorganisms. Staphylococcus aureus (cells 0.5-1 microm diameter) were retained in the highest numbers. S. aureus was well retained in the 0.5 microm sized pits and began to accumulate within larger surface features. Rod shaped Pseudomonas aeruginosa (1 microm x 3 microm) were preferentially retained, often end on, within the 1 microm surface features. Some daughter cells of Candida albicans blastospores were retained in 2 microm pits. For S. aureus and P. aeruginosa, the greatest numbers of cells were retained in the largest (2 microm) surface features. The number of C. albicans was similar across all the surfaces. The use of defined surfaces in microbial retention assays may lead to a better understanding of the interaction occurring between cells and surface features.

A study of the stability of amorphous FeSi2 films and their transition to a crystalline phase as a function of deposition or annealing temperature is presented. Stoichiometric FeSi2 films, 300–400nm thick, were deposited on (100) Si substrates by co-sputtering of Fe and Si. It was found that the films grow in an amorphous form for the substrate temperature ranging from room temperature to 200°C, while from 300–700°C, they grow in form of a crystalline β-FeSi2 phase. In a postdeposition 30min heat treatments, the layers retain the amorphous structure up to 400°C, transforming to the crystalline β phase at 500–700°C. The results are discussed in the frame of the existing models, and compared to those found in the literature. It is shown that in as-deposited films, the growth is controlled by surface diffusion, the crystalline layers growing in a columnar structure strongly correlated to the Si substrate. Postdeposition treatments induce a random crystallization controlled by bulk diffusion, the resulting structure not being influenced by the substrate. The results of this work contribute to a better understanding of the processes involved in a transition of amorphous FeSi2 films to a crystalline phase, and provide a basis to determine the processing parameters in potential applications of this promising semiconducting material.

The dissolution of metal during the passivation of Fe-Cr alloys has been studied in situ as a function of alloy composition in order to investigate the critical Cr content required for corrosion protection. This is achieved using synchrotron X-ray fluorescence microprobe analysis on a sputter-deposited Fe-Cr thin film with a continuous lateral variation in composition. The technique can resolve the dissolution of less than one layer of atoms during electrochemical treatment of the graded alloy surface. The results show that there is a sharp change in behavior in the region of 17-18% Cr. Above 18% Cr, almost no metal dissolution occurs during passive film development, while below this composition there is continual dissolution. This result is consistent with the gelation model of passivation that uses an approach based on percolation theory. (C) 2001 The Electrochemical Society.

This chapter discusses the development and applications of physical vapor deposition (PVD). PVD is the general name given to coating processes where the transport of material to the substrate is affected by a physical driving mechanism. Such mechanisms include evaporation, sputtering, ion-plating, and ion-assisted sputtering. The coated samples can usually be maintained at a temperature between ambient and 100°C during the deposition and the working pressure is below 10−2 Pa. In this process, materials are vaporized, by heating, using direct resistance-heating, radiation, eddy current heating, electron-beam heating, or running an arc discharge. One advantage of the technique is that the evaporation can be carried out in an ultra-high vacuum (UHV) chamber, so that contamination of the substrate, by residual gases, is minimal. For best purity, an electron-beam heating system should be used, as the material can then be evaporated from the center of the crucible, in which it is held and the reactions, with the crucible walls, are minimized. It is found that the additional energy provided to the condensing atoms during ion-assisted deposition can produce similar growth zone regimes but at lower substrate temperature, since this transferred energy provides the adatoms with the ability to move further across the surface and to the adjacent sites in the bulk.

When film deposition is accompanied by bombardment by low energy (less than a few 100 eV) particles, the resulting film nucleation, growth, stress content, adhesion, density, composition, morphology, and crystal structure may be significantly altered. Current methods for providing the energy-assisted conditions for film growth are described. Recent selected results are given demonstrating all the above features together with a discussion of the fundamental reasons for the improved film quality. Selected applications of the novel materials that can now be created on various substrates to improve friction, wear, corrosion resistance, and optical qualities are presented. The review concludes with an outline of future trends.