Sputtering alloy

If a surface is sputtered at sufficiently low temperature to avoid bulk diffusion, atoms of the species preferentially sputtered can reach the surface by displacement mixing and radiation-induced segregation. This leads to a so-called altered layer, which has a composition different from that of the bulk and a thickness close to the penetration depth of the projectiles. Since surface diffusion has a much lower activation barrier than bulk diffusion, annealing a sputtered alloy surface first leads to a local equilibrium between the surface and the immediate subsurface layers, which still belong to the altered layer. Only after the onset of bulk diffusion is reached, usually around 60 - 70% of the melting temperature, the altered layer equilibrates with the bulk and true equilibrium segregation is observed [45]. For alloys of atoms with different size the existence and dissolution of an altered layer can be studied by STM because of the development of a misfit dislocation network between the altered layer and the bulk [46] (Fig. 7). 

Later on [87, 88] it was observed by STM that ion bombardment of the Pt25Ni7s(l 11) surface leads to the formation of a pattern of shallow ditches (some 0.2-0.5 A deep) that have been attributed to the dislocations generated by the lattice mismatch of the top layers and the bulk ones. The top layers are enriched in Pt by ion bombardment and hence have a different lattice constant. These dislocations in sputtered alloys may provide diffusion pipes for implanted atoms to reach the surface. Diffusion of metal atoms in the surface region at relatively low temperatures has however been proven to be related to the presence of defects, such as the pinholes observed by STM at the Co/Cu( 100) interface [89]... 

Another technique that requires less instrumentation than those discussed above involves the analysis of the sputter deposited film from the alloy. A flat metallic plate is positioned so that it intercepts part of the sputtered flux without being resputtered by the ion beam. The sputter deposited layer should be built up for periods longer than it takes to generate a steady state surface on the sputtered alloy to insure that the sputtered film has reached a composition equal to the bulk alloy and yet be several times thicker than the analysis depth of the surface technique. If the angular distribution of the sputtered flux of A and B is not uniform, then the deposited film composition will differ at different locations. It is often assumed that the sticking coefficient of each element is identical. Of course if one element in the alloy is volatile the method will fail. 

Some of the studies investigated carbon-supported alloys while the others sputtered alloy films or metallurgically prepared bulk alloys. The enhancement of the oxygen reduction rate was ascribed to the several effects and their interplay the inhibition of the OH adsorption on Pt surface by the alloying metal [34], the geometric... 

Most recently, R alloy catalysts that have the so-called structure of a R skin, i.e., with a pure R topmost atomic layer on the surface of the alloys, were reported to be the most aetive catalysts towards the ORR [14—17]. Stamenkovic et al. [14] studied the surface properties of R-M (M = Co, Ni, Fe) polycrystalline alloys prepared by sputtering, aimealing, and leaching, respectively. They found two kinds of surface structure on the alloys, depending on the preparation procedure. The merely sputtered alloys could form R-skeleton outermost layers due to the dissolution of transition metal atoms in acid electrolyte, whereas the aimealed alloys had a R-skin topmost layer containing only R. The eatalytie activity towards the ORR on these two surfaces was much higher than that on a pure polycrystalline R surface, and the Pt-skin surface displayed the highest activity. In particular, the RsNi alloy with the (111) face was 10 times more active than the... 

A transmission electron microscopy (TEM) image of the sputtering film is shown in Fig. 4.5, which indicates that the grain size of sputtering alloy is about 300 nm and the diffraction pattern confirmed that crystal grain has a (hexagonal close packed, HCP) a-phase structure. 

Figure 11.5 Concentration of the topmost atomic layer of Pt25Rh75(lll) measured via LEIS [1] as a function of temperature. The filled symbols show the Pt enrichment during stepwise heating of the sputtered alloy...

Kun] Kunitskiy, Yu.A., Nemirovskiy, A.V., Korzhik, V.N., Variation of the Local Magnetic Parameters in Cast Amorphous and Sputtered Alloys Fe4oNi4oB2o after Mechanical and Heat Treatment , Phys. Met. Metall, 65(2), 78-84 (1988), translatedfiomFiz. Metal Metalloved., 65(2), 295-301, (1988) (Crys. Stracture, Experimental, Magn. Prop., Thermodyn., 14)... 

Ion implantation (qv) has a large (10 K/s) effective quench rate (64). This surface treatment technique allows a wide variety of atomic species to be introduced into the surface. Sputtering and evaporation methods are other very slow approaches to making amorphous films, atom by atom. The processes involve deposition of a vapor onto a cold substrate. The buildup rate (20 p.m/h) is also sensitive to deposition conditions, including the presence of impurity atoms which can faciUtate the formation of an amorphous stmcture. An approach used for metal—metalloid amorphous alloys is chemical deposition and electro deposition. 

R. Behrisch, ed., "Sputtering by Particle Bombardment II Sputtering of Alloys and Compound, Electron and Neutron Sputtering, Surface Topography," in Topics in Applied Physics, Vol. 52, Springer-Vedag, Berlin, 1983. 

In the sputtering process, each surface atomic layer is removed consecutively. If there is no diffusion in the target, the composition of the vapor flux leaving the surface is the same as the composition of the bulk of the material being sputtered, even though the composition of the surface may be different from the bulk. This allows the sputter deposition of alloy compositions, which can not be thermally vaporized as the alloy because of the greatly differing vapor pressures of the alloy constituents. 

Magneto-optic and magnetic disc materials DyCo, TbFeCo, garnets, sputtered magnetic media (CoNiCr alloys and their carbon overcoats). 

Mass spectrum obtained from the NIST Hasteloy Ni-basad standard alloy, using electron-gas SNMSd (Laybold INA-3). The sputtering energy was 1250 V, increasing the sputtered atom flux at the expense of depth resolution. Matrix ion currents ware about 10 cps, yielding background limHed detection at about 2 ppm. 

The analysis of specific elements for which GDMS is particularly well suited compared to other methods (e.g., measurement to ppb levels of S, Se, Te, Pb, Bi, Tl, in high-performance alloys and measurement of U andTh in sputter targets)... 

The results of a GDMS analysis of high-purity TiW are summarized in Table 4. High-purity TiW is very commonly used as the metallization to provide the conducting links in the construction of semiconductor devices. The metallization is commonly deposited by sputtering from a high-purity alloy target onto the sub-... 

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