S. M. Ivanov

Sputtering of amorphous metallic alloys

The sputtering process of a multicomponent alloy depends significantly on its structural state and the phase condition and on the temperature attained during the irradiation process since in multicomponent materials, the mass transfer processes can occur at relatively low temperatures (e0.2 Tmp) due to the radiation-induced segregation of impurities, the radiation-stimulated diffusion, and the diffusion associated with the selective (preferential) nature of sputtering. A study of the sputtering process of amorphous metallic alloys is extremely important from the physical standpoint owing to the absence of different types of segregation and excess phases (i.e., the regions differing significantly with respect to atomic structure and chemical composition) in this case. Besides this, amorphous alloys always form single-phase systems that do not exhibit crystalline anisotropy and do not contain lattice defects such as dislocations, grain boundaries, blocks, and stacking faults. All these facts make amorphous metallic alloys exceptional experimental objects for studying the specific features of the selective sputtering process of the components of the alloys, the regularities in the angular and the energy distributions of the sputtered particles, and the effect of the chemical composition on the total (complete) coefficient of sputtering of the alloys. A study of the physics of sputtering of amorphous metallic alloys has at least two aspects related to the practical problems of materials science in the first wall of thermonuclear reactors. Firstly, during the interaction of plasma with the wall, amorphous layers can form, in particular, during disruption of plasma at the walls of the vacuum chamber where the energy of plasma is liberated for a short time (~i0 -~ sec) leading to the fusion and evaporation of the material. Steels and the Fe-CrNi alloys are frequently treated as promising materials for the first wall. Secondly, the experimental data concerning the radiation-induced surface erosion of the amorphous metallic alloys during bombardment with He + ions [i] and the first experiments on the sputtering process indicate their higher radiation resistance (as compared to the analogous crystalline alloys) and, therefore, they form promising structural materials for thermonuclear reactors.

Surface topography with blistering of radiation and nonradiation origin

1. M. Ya. Grudskii et al., in: Secondary Electron Emission [in Russian], V. G. Khlopin Radium Institute, Leningrad (1977), pp. 24, 80. 2. V .V . Smirnov and A. V. Malyshenkov, in: Applied Nuclear Spectroscopy [in Russian], Vol. 3, Atomizdat , Moscow (1972), p. 166. 3. P. Ebert and A. Lanson, IEEE Trans. Nucl. Sci., NS-13, No. 2, 735 (1966). 4. V .V. Smirnov and A. V. Malyshenkov, At. Energ., 32, No. 1, 54 (1972).

Sputtering of an Ni-P alloy in the amorphous and crystalline states

Amorphous metallic alloys have unusual properties and interesting applications. Measurements have been made [i] on the effects of irradiation on amorphous alloys. In fusion-reactor materials, there are at least two aspects of the damage caused by hydrogen and helium ion bombardment. Firstly, to select the material for the first wall, one needs to compare the erosion occurring for amorphous and crystalline alloys having the same compositions. Secondly, the plasma may tend to amorphize the material.

Distinctive features of sputtering of Fe−Cr−Ni alloys containing heavy-element alloying constituents

The properties of steel can be controlled over a wide range through the introduction of alloying constituents. In particular, the addition of molybdenum to steel helps make it more heat~resistant and, hence, more promising as a material for the first wall in a hightemperature thermonuclear reactor. However, the entry of heavy-element impurities into a plasma leads to an increase in radiation losses and at a concentration of 0.6% Mo and 0.2% W the radiated power becomes comparable with the energy released by s-particles in the fusion reaction [i]. In view of this, the use of steels that contain several percent molybdenum and tungsten as the material for the first wall of a thermonuclear reactor seems, at first glance, to be inadmissible since during bombardment of a multicomponent alloy with accelerated ions or atoms the flux of sputtered particles should have the same composition as the sputtered target. A process of selective sputtering inevitably causes a change in the composition of the surface layers of multicomponent materials irradiated, if their constituents are characterized by different sputtering rates or different mass numbers. A number of studies [2, 3] have discovered that the processes of selective sputtering and radiationinduced segregation of admixtures in alloys are superimposed and as a result the constituents are redistributed considerably near the surface in comparison with their initial content.

A study of the phenomena of selective sputtering and radiation-induced segregation of impurities in the aluminum alloys containing scandium

In continuation with the studies on the specific features of the sputtering process of the AMG aluminum alloys containing 0.5% Sc, the authors determined the composition of the sputtered particles during bombardment with 10-keV H/sup +/ ions at 200 C using an ILU-2 ion accelerator. In order to study the distribution of elements in the ion bombarded alloy, the Auger electron analysis of the bombarded targets was carried out after layer-by-layer etching with 2-keV Ar/sup +/ ions. The mass of the targets was determined before and after bombardment by weighing them. The results obtained by using the Rutherford back scattering method indicate that the process of selective sputtering of the alloy is superimposed by other phenomena leading to a change in the initial chemical composition of the surface layer.