Particle-solid Interactions Research Articles

Peculiar effects induced by statistical processes related to fast particle-matter interactions in dilute and dense media

Traditional reasoning on statistical effects in energy loss and multiple scattering phenomena in random media are based on the concepts of binary interactions, full independence of successive events and finite variance of random energy transfers or angular deflections in single encounters. These assumptions imply Poissonian statistics and a rapid convergence of the corresponding distributions towards the Gausssian with r.m.s.∼( depth) 1 2 ; moreover they may hold rigorously in dilute media only. We shall examine various effects which may appear when the above constraints are relinquished. Thus, density effects in condensed media and the recently evidenced yield enhancement in 180° RBS are due to a breakdown of full independence; the yield enhancement for thick targets near narrow resonances termed the Lewis effect is due to strictly non-Gaussian behaviour of small energy losses. As for infinite variances, they play a major role in multiple scattering or in electron energy loss processes leading to a complete breakdown of the usual ( depth) 1 2 rule of distribution broadening. The key-role of the theory of infinitely divisible and of stable probability densities in particle-solid interaction theory will be discussed.

Ion induced optical emission for surface and depth profile analysis

Low-energy ion bombardment of solid surfaces results in the emission of infrared, visible, and ultraviolet radiation produced by inelastic ion-solid collision processes. The emitted optical radiation provides important insight into low-energy particle-solid interactions and provides the basis for an analysis technique which can be used for surface and depth profile analysis with high sensitivity. The different kinds of collision induced optical radiation emitted as a result of low-energy particle-solid collisions are reviewed. Line radiation arising from excited states of sputtered atoms or molecules is shown to provide the basis for surface and depth profile analysis. The spectral characteristics of this type of radiation are discussed and applications of the ion induced optical emission technique are presented. These applications include measurements of ion implant profiles, detection sensitivities for submonolayer quantities of impurities on elemental surfaces, and the detection of elemental impurities on complex organic substrates.

2–6 Aug: Particle-solid interactions, Proctor Academy, Andover, New Hampshire. Chairman, James W. Mayer inorganic chemistry, New Hampton School, New Hampton, New Hampshire. Chairman, Leonard V. Interrante glass melting, Plymouth State College, Plymouthm New Hampshire. Chairman, S.M. Ohlberg

2–6 Aug: Particle-solid interactions, Proctor Academy, Andover, New Hampshire. Chairman, James W. Mayer inorganic chemistry, New Hampton School, New Hampton, New Hampshire. Chairman, Leonard V. Interrante glass melting, Plymouth State College, Plymouthm New Hampshire. Chairman, S.M. Ohlberg

The beam-foil interaction process

A specific case of the particle-solid interaction that has become known as the beam-foil interaction will be discussed with emphasis on problems related to the beam-foil technique. The nature of the interaction is studied from both a fundamental and a “practical” point of view. Investigations of fundamental processes clarify the role of foil and beam parameters on energy loss, scattering, charge exchange, sputtering yields, and excited state formation. A practical look at a real foil involves problems of foil preparation, changes in foil character, and breakage during experiments. Some non-linear effects such as heating, and foil thickening occur which can affect normalization procedures when the foil is used in beam-foil experiments.

1968 15–19 July Particle solid interactions

1968 15–19 July Particle solid interactions

On the total force of elastic scattering — neutral particles and perfect crystal

Quantum and classical-mechanical microscopic theories are developed for the total force on a cold solid plane surface resulting from the elastic scattering of an incident uniform cold beam of particles. The solid is a semi-infinite perfect dielectric crystal. The particles are neutral noninteracting mass points. The particle-solid interaction potential is that of physical adsorption normal to the surface, with a small sinusoidal perturbation along the surface to represent crystal nuclei. With vanishing perturbation the scattering becomes purely specular. For conceptual simplicity the two-dimensional problem is treated with a square-well interaction potential. Particle energy and incidence effects are studied. The quantum-mechanical forces are shown to be specular at very high energies (particle deBroglie wave length λ → 0), and in a domain of low energies (λ > d). Between these limits some points are computed for helium incident on LiF to show a domain of “strong diffraction” or significantly nonspecular tangential forces. The quantum theory is shown to be essential in this domain and below where the classical theory fails.