Ion assisted deposition

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 most widely deposition technique is the ion assisted deposition (lAD). A material in a melting-pot is vaporized by heating either with an electron beam, or by Joule effect, or with a laser beam, or with microwaves, or whatever else. The vapor flow condensates on the substrate. In the same time, an ion... 

Figure 19. Schematic view of the ion assisted deposition technique. As the vapor condenses on the substrate, ions hammer the coating in formation to compress it.

Ion assisted deposition (IAD), 14 441-442 Ion-beam amorphization, 14 447 Ion-beam-assisted deposition (IBAD),... 

Figure 15.24 shows the fabrication process of the optical filter on a fluorinated polyimide substrate. First, the low-thermal-expansion-coefficient PMDA/TFDB poly(amic acid) solution was spin-coated onto a Si substrate and baked. Then alternate TiO2 and SiO2 layers were formed on the polyimide film by ion-assisted deposition. The multilayered polyimide film was diced and peeled off from the Si substrate. In this way, thin optical filters on a fluorinated polyimide substrate are easily fabricated. 

In ion assisted deposition, there are two methods one is decomposition of hydrocarbon oil using energetic ions and the other is evaporation of graphite with eoncurrent bombardment of the growing film with energetic ions. With these methods, diamond like films with reasonably good properties can be deposited over large areas (1 m ) at low temperatures (< 140°C). 

The fundamental processes involved in the nucleation of diamond like films during the ion beam deposition processes, the critical role of the impinging ion energy and the differences in the basic mechanisms of depositing carbon ions versus the use of argon ions (in the case of ion assisted deposition) are still not well understood. In the following sections some of the established concepts are reviewed and discussed. 

A new material consisting of sp -carbon which is characterized by a special electron diffraction pattern and DOVS distribution has been developed. This material is obtained by ion-assisted deposition from pulsed carbon plasmas. 

Babaev, V. Guseva, M. Ion assisted deposition. In Carbyne and Carbynoid Structures, Evsyukov S. and Kavan L., Eds., Kluwer Academic Publishers, 2000. 

Many films deposited on heated substrates (250-350°C) possess packing densities larger than 0.9, so that the changes in refractive index on exposure to the atmosphere are very small and can often be neglected. The effect is even improved with films produced by ion-assisted deposition techniques, such as sputtering and ion plating. 

We have shown that ion-assisted deposited on rubber and silicon thin metal films include not only metal atoms but also carbon, oxygen, hydrogen and silicon (from Si substrate), and sulphure, calcium, and zinc (from rubber). The coatings on rubber are characterized by semi-ellipsoids surface topography and increased roughness. The coatings on silicon are uniform with smooth surface. 

Thus, during the process of ion-assisted deposition, the bombardment with gas ions of several dozens of keV plays a dual role. The ionized gas media between the ion source and substrate creates a flow of ionized atoms that facilitate the formation of nitride (carbide and oxide) phase on entering the film. A direct bombardment of the film with gas ions creates conditions for the formation of a nanocrystaUine structure. 

Interestingly, a similar nucleation effect as found for the ion impact seems to exist in the case of the substrate temperature. As has been found by several authors [34,36] a minimum substrate temperature of 150°C is necessary in order to nucleate cubic BN in ion-assisted deposition. However, very recently Feldermann et al. [71] have found for mass selected ion beam deposition that switching off the substrate heating after cBN nucleation and allowing the substrate to cool down to room temperature, does not interrupt cBN growth. 

P. J. Martin et al. Properties of thin films of tantalum oxide deposited by ion-assisted deposition. Thin Solid Films 1994, 238, 183-184. 

Surface polymerization by ion-assisted deposition Glass transition temperature Transmission electron microscopy Tetrahydrofuran... 

An alternative process to PT thin film has been developed using direct surface polymerization. It was proved that PT thin film was formed via surface polymerization by ion-assisted deposition (SPIAD), in which 55-200 eV thiophene ions and R-terthiophene neutrals are codeposited on surfaces [339-342]. This PT film displayed unique optical properties in its photoluminescence (PL) and ultraviolet-visible (UV-vis) absorption compared with the film prepared by direct thiophene ion deposition only. This method was clearly applicable to a wide range of different ions and neutral species. However, vaporized and ionized reagent species could not be applied by SPIAD. 

Oelting S, Martini D, Bonnet D (1992) Ion assisted deposition of Si films for solar cells. In 11th European photovoltaic solar energy conference and exhibition, Montreux, 1992. Harwood Academic Publisher, Chur, pp 491-494... 

Recently, an evaporation deposition technique was employed for preparation of thin films, because it can maintain deposition conditions in a vacuum in the course of deposition. Therefore high-quality thin films can be obtained. Physical vapor deposition techniques include mainly vacuum evaporation, sputtering deposition ion-assisted deposition, molecular beam epitaxy (MBE), and ICB deposition. Table 1 shows characteristics of these deposition methods. 

Temperature control of the fiber during coating is another parameter that must be monitored. Research has shown that the refractive indices of a cold -coated film are usually less than that of a hot film, even with the use of ion-assisted deposition. In many cases they are also nonuniform. If the fibers have epoxy or plastic jackets, as is usually the case, they cannot be exposed to high temperatures. The temperature controller of the coating system is usually programmed to a temperature between 35 °C and 90 °C however, the heat from the electron-beam gun or ion gun will raise the... 

Martin, P.J., Netterfield, R.P. (1986). Properties of indium tin oxide films prepared by ion-assisted deposition. Thin Solid Films, Vol. 137, pp. 207-214. 

Seok-Kyun Song. (1999). Characteristics of SnOx films deposited by reactive ion-assisted deposition. Phys. Rev., Vol. 60, pp. 11137-11148. 

Netterfield RP, Martin PJ (1986) Nucleation and growth smdies of gold films prepared by evaporation and ion-assisted deposition. Appl Surf Sci 25 265-278... 

Ion plating (Ch. 9), which is sometimes called ion-assisted deposition (lAD) or ion vapor deposition (IVD), utihzes concurrent or periodic bombardment of the depositing film by atomic-sized energetic particles to modify and control the properties of the depositing film. 

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