V. K. Semina

Sputtering of solids by heavy ions and temperature effects in electronic and lattice subsystems

The results of sputtering coefficient measurements for pure metals, alloys, amorphous alloys, semiconductors, and highly oriented pyrolytic graphite under irradiation by high energy ions are considered. The possible mechanisms of strong sputtering of materials with high defect concentrations are discussed. The three-dimensional thermal spike model (“hot ion track”) with the temperature dependence of thermodynamic parameters (specific heat thermal conductivity) is formulated for single-layer mono-and polycrystals and multilayer systems (materials). The results of a numerical solution to the introduced system of partial differential equations are considered for the lattice and electronic subsystem temperatures around and along the fast heavy ion trajectory as a function of the time t, as well as radial r and longitudinal z coordinates, taking into account possible phase transitions such as melting and evaporation. The results obtained are discussed.

Sputtering of metals by heavy ions in the inelastic energy loss range

Abstract Existing experimental data on the sputtering of coarse-grained metals by swift heavy ions is reviewed. Inelastic energy losses of ions have been noted to influence the sputtering yield of metals, but this effect is negligible. Experiments have shown that the sputtering yield of coarse-grained metals by swift heavy ions increases by a factor 3 at high irradiation fluence, but at the expense of accumulating radiation defects in the crystalline structure of the target. Similar experiments for the design and development of heavy ion accelerators and for the use of swift heavy ions in materials processing for implantation of deep-buried layers are also important.

Thermal processes in multilayer second-generation HTSC under swift heavy-ion irradiation

On the basis of the thermal spike model, the estimations with regard to tapes of the second-generation Ag/YBaCuO/MgO/Hastelloy HTSC under irradiation with Ar, Kr, and Xe ions of an energy of about 1.2 MeV/amu have been carried out. The results have been compared with the available experimental data. In addition, the possibility of processes such as melting, recrystallization, amorphization, and other phase transitions in multilayer structures under ion irradiation has been studied.

Numerical investigation of temperature effects in materials irradiated by high-energy heavy ions in the framework of heat conduction equation for electrons and lattice

A system of equations for electron gas and lattice around and along the trajectory of a heavy uranium ion with an energy of 700 MeV in nickel at constant heat capacity and heat conduction taken at room temperature is solved numerically in an axially symmetric cylindrical coordinate system. On the basis of the lattice temperature obtained as a function of radius around the ion trajectory and depth, a conclusion is made that the ionization energy losses of a uranium ion in nickel are sufficient for melting and evaporating the material from the surface. The maximum radius and depth of the region in which melting and evaporation take place are estimated.

Nickel sputtering by high-energy heavy ions

Recent experimental data on the sputtering of coarse-grained metals by high-energy heavy ions are reviewed. It is pointed out that inelastic energy losses of ions have rather insignificant effect on the sputtering yield of metals. Experimental data on the sputtering of nickel by 86Kr+ ions are presented. The accumulation of radiation defects in the crystal lattice of nickel in the course of irradiation leads to an increase in the metal sputtering yield from the surface of grains, making it comparable with the sputtering yield from the intergranular region. The results of such experiments are important for development of the heavy ion acceleration facilities and for the high-energy heavy-ion doping of deep layers in semiconductors.

The Use of a Thermal Spike Model for Temperature Calculation in Two-Layer Structures along the Projective Track of a High-Energy Heavy Ion

A thermal spike model in a three-dimensional case is used for the calculation of temperatures in a structure consisting of two layers of different materials. The systems of equations for electron gas and lattice temperatures are solved numerically in the axial-symmetric coordinate system at constant values of specific capacities and thermal conductivities for the Ni(2 μm)/W two-layer system. One can conclude on the basis of the obtained results that the phase transitions can take place when there is irradiation of the Ni(2 μm)/W two-layer structure with 209Bi ions with an energy of 710 MeV: melting, in both layers; and evaporation, only in the Ni layer (first layer). The maximum radii and depths where the melting (Ni and W layers) and evaporation (Ni layer) processes occur are calculated.

Effect of 305-MeV krypton ions on the surface of highly oriented pyrolytic graphite

The surface of highly oriented pyrolytic graphite (HOPG) irradiated by 305-MeV krypton ions was studied in a scanning tunneling microscope. It was found that inelastic energy losses of the krypton ions do not significantly affect the sputtering of carbon from the surface of crystalline HOPG grains. Similarly to the case of metals, preferential sputtering takes place in the grain boundaries. The inhomogeneous sputtering of polycrystalline conductors has to be taken into account in interpreting experimental data on the sputtering of such targets by high-energy heavy ions in the range of inelastic energy losses. The results can be also implemented in the technology of ion implantation into deep layers of solids.