Principle of Sputtering

Higher pressure, by placing too many argon atoms in the path of the ions and ejected atoms, would not allow these to travel relatively unimpeded by collision. In other words the mean-free path would be too short. 

Reactive Sputtering. Like reactive evaporation reviewed in Secs. 6.2 and 6.3, reactive sputtering is used in the deposition of refractory carbides and nitrides by providing a small partial pressure of hydrocarbons or nitrogen. A problem is target poisoning caused by the reaction of the target with the reactive gas. 

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Chapter 3 also considered those entrapment pumps that remove gas particles by sorption effects such as gettering and implantation. The operating principles of sputter ion pumps were explained (Example 3.26) and some typical calculations performed (Examples 3.27-3.29). Aspects of the use of titanium sublimation pumps were dealt with (Examples 3.30-3.33). 

Figure 14 A schematic diagram demonstrating the principle of sputter coating.

The basic principle of e-beam SNMS as introduced by Lipinsky et al. in 1985 [3.60] is simple (Fig. 3.30) - as in SIMS, the sample is sputtered with a focused keV ion beam. SN post-ionization is accomplished by use of an e-beam accelerated between a filament and an anode. The applied electron energy Fe a 50 20 eV is higher than the range of first ionization potentials (IP) of the elements (4—24 eV, see Fig. 3.31). Typical probabilities of ionization are in the 0.01% range. SD and residual gas suppression is achieved with electrostatic lenses before SN post-ionization and energy filtering, respectively. 

Abstract The principles of coatings to either enhance reflectivity of mirrors or to enhance transmission of glass optics are described. Then the ion assisted deposition and ion beam sputtering techniques are addressed. Performances of these technique-sand their limitations are illustrated with the characteristics of the VIRGO mirrors coated at LMA. The importance of metrology is emphasized. 

The measurements that have been made at Rochester and the experience that has been gathered over the years on the operation of sputter ion sources [38] indicate that an analytical tool of unprecedented sensitivity and accuracy for isotopic ratio determinations can be constructed by coupling SIMS technology with the new accelerator technique. The only difference in principle between the experiments that have been conducted to date and the technique as it would be applied in secondary ion mass spectrometry is that the primary beam of cesium would be focussed to a fine probe of pm dimensions rather than the spot diameters of approximately 1 mm that have been used to date. 

SIMS is by far the most sensitive surface technique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. The principle of SIMS is conceptually simple A primary ion beam (Ar+, 0.5-5 keV) is used to sputter atoms, ions and molecular fragments from the surface which are consequently analyzed with a mass spectrometer. It is as if one scratches some material from the surface and puts it in a mass spectrometer to see what elements are present. However, the theory behind SIMS is far from simple. In particular the formation of ions upon sputtering in or near the surface is hardly understood. The interested reader will find a wealth of information on SIMS in the books by Benninghoven et al. [2J and Vickerman el al. [4], while many applications have been described by Briggs et al. [5]. 

Figure 1. Principles of plasma interaction with material. The Ar ions hit polymer surface and create a collision cascade in the surface layer by which a number of atoms are set in movement. As a result ionization of atoms and molecular bond cleavage take place and some of liberated atoms are ejected (sputtering process) [6].

Despite recent promising strategies, the principle of micro-process engineering is still not widely used in combinatorial catalysis. One drawback certainly is the increasing distance from industrial applications with decreasing dimensions. However, the small structures possess laminar flow conditions that are fully accessible by analytical as well as numerical macroscopic descriptions. This offers the chance to describe thoroughly the fluidic, diffusive and reactive phenomena in catalysis to find intrinsic kinetics on using, for example, non-porous sputtered catalysts. 

The principle of CHARISMA is as follows the sample is ablated with a pulsed Nd YAG laser, focused into a spot of micrometer size. Neutral species drift up while ions are suppressed. Two lasers (Ti Sapphire), tuned to resonantly ionize the element of interest, are bred into the ablated, neutral material. The ions are extracted and accelerated and analyzed with a TOF mass spectrometer where mass separation occurs due to different flight times of species with different mass. The useful yield (detected ions/sputtered atoms) is around 1% in the current set-up. A planned modification is aiming at a useful yield of around 30% which would open up new possibilities for the isotope study of trace elements (e.g. the rare earth elements) in presolar grains. With the new set-up it will also be possible to extend the analyses to sub-micrometer-sized grains, which are much more representative of presolar grains than the currently studied micrometer-sized grains. 

The principles of ion sources which use a primary ion beam for sputtering of solid material on sample surface in a high vacuum ion source of a secondary ion mass spectrometer or a sputtered neutral mass spectrometer are shown in Figure 2.30a and Figure 2.30b, respectively. Whereas in SIMS the positive or negative secondary ions formed after primary ion bombardment are analyzed, in SNMS the secondary sputtered ions are suppressed by a repeUer voltage and the sputtered neutrals which are post-ionized either in an argon plasma ( plasma SNMS ), by electron impact ionization ( e-beam SNMS ) or laser post-ionization are nsed for the surface analysis (for details of the ionization mechanisms see references 122-124). 

The operating principle of SIMS is not unlike other techniques in this section that is, a high-energy (1-30 keV) ion source is directed onto a sample surface. However, the absorption of this energy by the top ca. 50 A of the sample results in the sputtering... 

The principle of the hollow cathode tube, production of a vapor of atoms by cathodic sputtering, has been employed by Gatehouse and Walsh (Gl) for sample vaporization. The sample is introduced into a vacuum chamber and is made the cathode which produces a cloud of activated atoms. The light of a separate hollow cathode tube is passed through this vapor and absorption is measured in a spectrophotometer. 

Ali, Hung and Yongyi (2010) reviewed the application of focused ion beam (FIB) sputtering for micro/nano fabrication. Although less relevant for discussion of bioceramic coatings, treatment of basic principles of FIB, and evaluation of empirical and fundamental models for sputtering yield, material removal rate and surface roughness were presented and compared. Fabrication of various micro- and nanostructures was discussed. 

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