V. I. Shulga

Ejection of fast recoils under ion bombardment of crystals

Abstract Ejection of surface recoils produced by Cu crystal irradiation with 1–40 keV Ar ions has been studied using computer simulation in terms of the atomic chain model. The case where a parallel ion beam bombards a nonvibrating chain at 25° to the chain axis is considered here as example. Only high energy (> 0.2 keV) backsputtered and also backscattered particles are analyzed. It has been found that the main contribution to the flux of backsputtered particles is from the primary and secondary knock-on atoms. The atoms may be ejected in a given direction by various ways whose number is a function of the initial ion energy and ejection angle. The angular and energy distributions of these atoms are pronouncedly anisotropic due, in particular, to the shadowing and focusing effects in scattering of ions and recoils by the chain atoms. The possibility for the particles to be doubly focussed is noted. The results obtained in terms of the two- atomic model are also considered here.

Transparency oscillations of a silicon single crystal in passing from axial to planar channelling

Abstract The transparency coefficient, T, of thin (2.5μ) Si single crystals relative to a well collimated 8.16 MeV He ion beam has been measured as a function of angle or between the beam direction and the [110] axis of crystals rotated in the (110) plane. Curve T(α) has been found to display minima at α = 0.15°, 0.34° and 0.5°. Computer simulation of experimental conditions has shown that the first minimum is a result of competition of two processes: increase of the radius of ring-shaped angular distribution with increasing a and ion capture in the (110) planar channel. The remaining two minima are due to particle dechannelling from channel (110) resulting from resonance enhancement of transverse particle oscillations in the channel. Similar calculations have been carried out for the transition from axial [110] to planar (001) channelling. It has been shown that in this case the difference in the conditions resonance result in spatial separation of the ion beams that have passed through channels (001) wi...

Ion beam focusing by the atomic chains of a crystal lattice

Abstract Studied in the present work is the focusing of parallel ion beam by a pair of close packed atomic chains of a crystal. The focal length of this system has been calculated to the approximation of continuous potential of chain in the general form and also for a number of specific potential of ion-atom interaction. Ar ion beam focusing by a 〈110〉 Cu chain pair has been discussed in details. For this case, the focal length has been calculated as a function ion energy using the method of computer simulation of ion trajectories in the chain field. The calculations were made on the basis of the Born-Mayer potential with various constants. A pronounced dependence of focal length on the constant in this potential has been found.

Experimental and computer study of ion scattering from single crystals

Abstract The spatial distribution of reflected particles was experimentally studied in the case of oblique incidence of 4.5 keV Ar ions on a (001) Cu face along the (110) and (100) planes. The distribution in ejection angles of the reflected particles was found to have several peaks and minima. To explain the results of these reflection experiments a computer study was performed. The shape of the calculated spatial distribution curves appears to be very sensitive to variations of the constants in the interaction potentials. Some features of the spatial distribution of the reflected ions have been shown to be connected to the motion of ions in surface semichannels. The spatial distribution of the neutral component of scattered and sputtered particles was also studied in the experiments. A predominant yield of the sputtered particles was observed not only in the low-index but also in high-index directions.

TWO-atomic scattering of ions in their reflection from single crystals

Abstract The classical elastic scattering of parallel and divergent ion beams during their passage between two free atoms is studied. The problems are solved analytically for the momentum approximation and numerically by the computer simulation of ion trajectories. The expressions for the differential cross-sections of two-atomic scattering and the two-atomic focusing energy Ef have been obtained for the inverse power and Born–Mayer potentials. The regularities of two-and one-atom scattering are compared. It has been shown that the characteristics of two-and one-atom scattering are very different in the ion energy range E ≲ Ef . The ion beam scattering by crystal surface semichannel is discussed. It has been shown that, in this case, the ions may be consecutively focused by two atomic pairs.

About the parameters of the Ar Ion-Cu atom potentials

Abstract The experimental semichannel focusing energy is used to find and approbate the parameters in the Born—Mayer and Thomas-Fermi potentials for the Ar-Cu pair.

The experimental determination of the impact parameter dependence of inelastic energy loss of channeled ions

Abstract Using the channeling technique, the impact parameter dependence of inelastic energy loss of fast He and N ions in Si has been measured.

Peculiarities of particle ejection in scattering and sputtering of single crystals

Abstract This paper deals with experimental and computer studies of sputtering : nd scattering of ions with energies of several keV from Cu and InSb single crystals. A substantial importance of the ejected particle channelling for the formation of some peaks in the patterns of spatial distribution of scattered ions and sputtered atoms has been shown.

Angular distribution of atoms sputtered from silicon by 1–10 keV Ar ions

The angular distribution of atoms sputtered from silicon under 1–10u200akeV Ar ion bombardment (normal incidence) has been studied experimentally and using computer simulation. It has been found that the angular distribution is overcosine in the whole energy range studied. This is connected with a high contribution of secondary knock-on atoms to the sputter flux (cascade sputtering). The simulated angular distributions are shown to be quite sensitive to the variation of the interatomic potential. The results obtained are compared with data from the literature.

The nature and distribution of radiation-induced defects in silicon along the range of protons and alpha particles

Abstract The variation in the resistivity of the n-type silicon along the range of protons and α-particles with an energy of 6.3 MeV/nucleon has been studied experimentally over a wide interval of irradiation doses. The initial rate of removal of majority carriers as a function of the distance from the surface of a sample has been determined. The spatial distribution of radiation-induced defects, resulting from elastic collisions between the incident particles and the silicon atoms and the subsequent cascade multiplication, has been calculated by a computer simulation technique. The nature of radiation-induced defects in silicon, which are stable at room temperature, has been examined on the basis of the data obtained, in various segments of the range of heavy charged particles. Both the point defects, containing impurity atoms of oxygen or phosphorus, and the defects proper, which contain no impurity atoms, have been shown to form in the cases under consideration. The relation of electrically active defe...