Michi-hiko Mannami

MONOLAYER ANALYSIS IN RUTHERFORD BACKSCATTERING SPECTROSCOPY

Energy spectra of 300‐keV He ions backscattered from single‐crystal surfaces are measured with a 90° magnetic spectrometer at grazing exit angles. The ions scattered from successive atomic layers can be resolved as separated peaks in the energy spectra. It is shown that both high energy resolution and the grazing angle technique are essential to the monolayer analysis.

A new method to detect surface steps by specularly reflected fast ions

Abstract With the use of a computer programme for the simulation of trajectories of MeV light ions at glancing-angle of incidence on a crystal surface, scattering phenomena of He ions at the (001) surfaces of SnTe crystals were calculated. It is found that the yield and angular distribution of scattered ions from the surface depend sensitively on the step density on the surface. A new method to detect the surface step density by measuring the ion yield at glancing-angle of incidence of MeV ions on the crystal surface is proposed.

Specular reflection of fast ions at a single crystal surface

Abstract The interaction of fast ions with a solid surface is studied by the specular reflection of MeV H+ and He+ ions from clean (001) surfaces of SnTe single crystals. Oscillatory structure is observed in the energy spectra of the reflected He ions. This indicates that a part of the incident ions penetrate inside the crystal and travel for a few wavelengths of oscillatory motion in the (001) planar channel before reappearing at the surface. The position dependent stopping power is obtained to be proportional to E − 1 2 exp (−0.15x/a TF ) , where x is the distance from the surface. A large difference is observed in the charge state distribution between the specular reflection and the transmission through a self-supporting foil. This is attributed to the fact that the specularly reflected ions interact exclusively with the valence electrons. It is found that the velocity of convoy electrons emitted at the glancing-angle incidence of He ions is faster than that of the incident ions. This may be due to the acceleration of convoy electrons by the dynamical image potential induced by ions near the surface.

Convoy Electrons Emitted at Glancing Angle Incidence of MeV Light Ions on the Clean (001) Surfaces of SnTe Crystals

Convoy electrons emitted at glancing angle incidence of MeV protons and He + ions on a clean (001) surface of SnTe are observed. It is found that the most probable velocities of convoy electrons are slower than those of the ions at proton incidence, whereas they are faster at He + incidence. A qualitative model is proposed to explain the experimental observations, in which the acceleration of convoy electrons by the wake-like induced charge on the solid surface at glancing angle incidence of swift ions is taken into account.

Layer-by-layer growth of GaAs studied by glancing angle scattering of fast ions

Angular distribution of scattered ions at glancing angle incidence of 3 keV He ions on a (001) surface of GaAs is studied during its molecular beam epitaxial growth. We report observation of intensity oscillations of the scattered ions from the growing surface. The period of the oscillations corresponds to the growth time of one monomolecular layer. The oscillations of the intensity is due to the oscillatory change in surface step density during layer‐by‐layer growth of the surface. This observation is in agreement with the intensity oscillations of reflection high‐energy electron diffraction (RHEED) from epitaxially growing surface of GaAs.

Position-dependent stopping powers of the (100) surfaces of NaCl-type crystals for MeV light ions

Abstract Energy losses of MeV H and He ions after interaction of clean surfaces of several NaCl-type crystals at glancing-angle of incidence are investigated. From the most probable energy losses of ions reflected from the surface atomic plane, position-dependent stopping powers of the (100) surfaces of NaCl, KCl, KBr, SnTe, PbSe and PbTe for MeV H and He ions are determined. The results are explained by a sum of the stopping caused by dynamic response of valence electrons to fast ions in vacuum and that due to single ion-electron collisions.

Surface channeling of MeV He+ ions on a SnTe single crystal

The scattering of 0.7 MeV He+ ions at a (001) surface of a SnTe single crystal is investigated under the condition of surface channeling. The observed azimuthal angle dependence of the scattered ion yield shows anormal peaks due to [100] and [110] surface channeling. The comparison of the observed results with computer simulations shows that the anormal peak is ascribed to the penetration of ions inside the crystal via surface steps.

RBS WITH MONOLAYER RESOLUTION

Abstract A 90° sector magnetic spectrometer ( δE E ∼ 0.1% ) is utilized for high-resolution Rutherford backscattering spectroscopy (HRBS). The ions scattered from successive atomic layers can be resolved as separated peaks in the energy spectrum at grazing exit angles. It is shown that both high-energy resolution and the grazing angle technique are essential to the monolayer resolution. Results of some applications of HRBS are presented.

Glancing-angle scattering of fast ions at solid surfaces

Abstract The interaction of fast ions with solid surface is investigated by small angle scattering of MeV H + , He + and hydrogen molecular ions at grazing incidence on a clean (001) surface of SnTe single crystal. The secondary electrons with energies less than 25 eV shows an increase of the yield when the surface axial channelling occurs, while that of scattered ions shows a dip. This disappearance of the dip cannot be interpreted simply as due to the long dwell time of ions in the thin surface layer caused by surface channelling. The observed energy losses of the specularly reflected ions are 2 to 3 times as large as those calculated with the formula derived by Lucas. Anomalies in the charge state distributions of reflected ions are observed at specular reflection of incident ions at the surface. Further studies to elucidate the physical processes taking place at the surface are needed for the interpretation of these results.

Angular distribution measurements of sputtered Au atoms with quartz oscillator microbalances

Abstract Angular distributions of Au atoms sputtered from a polycrystalline Au plate by irradiation of 35–65 keV Ar + ions were measured with the use of quartz oscillator microbalances as the collectors of sputtered atoms. The distributions were symmetrical with respect to the surface normal of the target plate even when the target was tilted up to 80°. It was also shown that the distributions can be fairly well approximated by a normal distribution with standard deviations 32° ± 4°.