Bombarding Effects of Gas Cluster Ion Beams on Sapphire Surfaces; Characteristics of Modified Layers and their Mechanica
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In order to modify the mechanical characteristics of sapphire, ion implantation techniques have been considered [6-8]. Internal stress effects due to implantation can influence the surface hardness. At low ion dose, internal stress can be introduced into the crystalline substrate and the surface hardness increases. With high ion dose, however, the near surface region can be amorphized and the internal stress can be relaxed in the modified surface region. Then the surface hardness decreases. Cluster ions provide equivalently low-energy and high-current ion beams, because each constituent atom in a cluster with sizes of a few thousands has an energy of several eV [9-10]. Impact processes of energetic cluster ions on solid surfaces are quite different from those of monomer ions because of multiple collisions and high-density energy deposition within a local surface region [11-14]. Therefore, gas cluster ion bombardment can modify an outermost surface region effectively. Various kinds of interesting phenomena resulting from the cascade interactions and the extremely high-density energy deposition have been reported [9-16]. In this paper, the effects of cluster ion bombardment upon the characteristics of sapphire surfaces are studied. EXPERIMENT A 200 keV gas cluster implantation system developed at Kyoto University is shown 279 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
Fig. 1 Schematic diagram of 200 keV gas cluster ion accelerator. in Fig.1. It consists of a cluster generator, an electron bombardment ionizer, an ExB massfilter (Wien-filter), an acceleration tube and a target chamber. Adiabatic expansion of highpressure gas through a nozzle is utilized for formation of high-intensity gas cluster beams. Size distributions of Ar and CO 2 cluster ions were analyzed by the ExB mass-filter over a range of source pressures. The size distribution was observed within the region of 90 to 110 in the case of 100 atoms cluster, of 400 to 600 in the case of 500 atoms cluster and of 1000 to 5000 in the case of 3000 atoms cluster at a source pressure of 4 atm. With increasing source pressure, the size distribution shifted to larger sizes and the cluster ion beam intensity increased. Bombarding effects of Ar and CO 2 cluster ions on sapphire were investigated by 80 70
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DOSE [/1013 ionslcm2] Fig.2 RBS channeling spectra from sapphire(0001) and Fig.3 Cluster ion dose dependence of the unirradiated sapphire(0001) irradiated by 150 keV Ar3 number of disordered atoms for various cluster ions at a dose of 1.25x101 cluster sizes. The value were calculated 2 ions/cm . The average cluster size was from the surface peaks of RBS 3000 atoms. channeling spectra.
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AFM, RBS channeling measurements, FT-IR spectr
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