Ionic bombardment

Control of fiber friction is essential to the processing of fibers, and it is sometimes desirable to modify fiber surfaces for particular end-uses. Most fiber friction modifications are accomplished by coating the fibers with lubricants or finishes. In most cases, these are temporary treatments that are removed in final processing steps before sale of the finished good. In some cases, a more permanent treatment is desired, and chemical reactions are performed to attach different species to the fiber surface, e.g. siliconized slick finishes or rubber adhesion promoters. Polyester s lack of chemical bonding sites can be modified by surface treatments that generate free radicals, such as with corrosive chemicals (e.g. acrylic acid) or by ionic bombardment with plasma treatments. The broken molecular bonds produce more polar sites, thus providing increased surface wettability and reactivity. 

A plant for this purpose comprises a vacuum chamber with ancillary equipment. The articles to be plated are mounted on a water-cooled cathode and, following evacuation of the chamber and filling with argon to a pressure of 0.002 Torr, direct current from a supply in the range 2000 to 5000 V is applied—to give a glow discharge in the area of the cathode. The article or articles mounted there thus are cleaned by ionic bombardment. Next, the evaporation source is excited, and the atoms of source material are deposited on the work pieces. 

Regime "A" V - 0. The discharge is driven in the "pure" MW mode, an abundant source of active species in the gas phase. These diffuse to the polymer surface with which they react mostly by attachment. In this case ionic bombardment is very limited and low in energy because the insulating surface rapidly adopts a floating potential (usually a few volts positive with respect to ground). 

A Method Based on Ionic Bombardment. In this procedure, the specimen is placed in a discharge tube, made into a cathode, and is then bombarded with mercury ions. The ionized gas, drawn from the metal by the high potential between the electrodes, is collected and subsequently analyzed by conventional procedures. 

Surface damage Very low with e-beam x-ray damage is possible Ionic bombardment damage... 

The surface anisotropy, which is necessary to induce a certain direction of liquid crystal alignment, can be produced in many different ways, such as rubbing, oblique evaporation, oblique ionic bombardment, surface bombardment... 

Menth et al (1971) have produced a change of the slope of Part B of AS2S3 by doping with noble metals. Olley and Yoffe (1971) observed a similar effect induced by ionic bombardment in a-As2Se3. 

Radical polymerization routes have been suggested by several investigations. The formation of radicals has been proposed to arise from the ionic bombardment of adsorbed species at surfaces, which then react with gas-phase radicals formed by electron impact. Using a pressure-pulsed audio... 

As a conclusion of this section, let us characterise briefly the electronic structure investigations of one more group of materials whose properties are greatly dependent on surface effects. These are thin films made from refractory carbides and nitrides. These films find applications in microelectronics, optics and as coatings for cutting tools and other complicated multilayered materials. Such films can be produced by different methods, such as thermal deposition or laser evaporation, (Morchan, 1982), molecular-beam epitaxy and cathode sputtering (Herman, 1982 Cho, 1983), plasma condensation in vacuum with ionic bombardment of the substrate surface (Dorodnov and Potrosov, 1981), chemical vapour-phase deposition (Anikeev, 1977 Anikin, Anikeev and Zolotaryova, 1979), etc. 

Such studies were focused, as a rule, on the energy changes of the atomic core levels and on the changes in structure of the valence state spectra of condensates when their composition alters during the deposition or under some treatment of the film (ionic bombardment, oxidation, etc.). It has been found by Kuznetsov (1990) that the formation of Ti-N and Ti-Al-N films is accompanied by charge transfer from the metal to the nonmetal atoms. The charge transfer is enhanced when the N content of the films increases. Analysis of the XES of the valence bands of Ti-Al-N films (Fig.. 8.11) leads to qualitative conclusions on the nature of chemical bonding in the condensate, where interatomic bonds are due to the overlap of Tid-Tid and Tid-Als,p-N2p states. Here, the intensity of emission from the hybridised p-d states decreases sharply as the film is depleted of N. 

PVD through ionic bombardment (cathodic or sputtering ) [33,34] Pressures lower than 10 Torr are used, with a Ti cathode, sputtered with an inert or reactive gas (Ar or O2, respectively). 

Plasma enhanced chemical vapor deposition (PECVD) This system uses plasma for systems in which the thermal activation is insufficient for heterogeneous chemical reaction. Plasma activates the chemical reaction on the target surface using ionic bombardment. 

To optimize the surface modification effect of free radicals and ionic bombardment, high-energy, enhanced discharge devices are particularly effective in optimizing surface modification effects. Critical air and gas plasma device design and operational features should include the following ... 

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