Positrons in Surface Physics

Secondary electron emission from gold caused by the impacts of positrons and electrons at keV or less energy is investigated by means of a Monte Carlo simulation of elastic and inelastic collision processes of the projectiles and cascade electrons inside the solid. The cross-section for the elastic collision of each particle with an atom in the solid is calculated using the partial wave expansion technique, whereas the cross-section for the inelastic collision or for the electron excitation is calculated from the Ashley’s optical-data model. Because of less large-angle elastic scattering of the positron, the calculated backscattering coefficient is smaller for the positron than the electron. At low impact energies (

Comparative study of secondary electron emission from solids under positron and electron impacts

Surface physics with slow positron beams

This work deals with the mechanisms of electronic transitions induced by low-energy positrons. For isolated atomic systems we discuss the role of successive binary collisions, the so-called Thomas mechanisms, between the positron, the excited electron and the atomic core. Furthermore, we consider transfer processes in which one of the charged particles is trapped in a low-lying continuum state of one of the reaction participants. In the second part of the paper, we investigate the various pathways for the secondary-electron emission from metallic surfaces following the bombardment by low-energy positrons. From a formal analysis it is shown that the probability rate for the production of an electron–positron pair is connected to the interacting electron–positron two-particle Green operator. The scattering of the interacting positron–electron subsystem from the crystal potential is treated and it is pointed out that a diffraction of the electron–positron pair as a whole might take place leading to characteristic diffraction pattern. The analysis is substantiated by numerical studies for the secondary electron emission from Cu(0 0 1) and Fe(1 1 0) (BCC) samples.

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Mechanisms of electronic excitations by low-energy positrons: From finite to extended electronic systems

Positron annihilation induced Auger-electron spectroscopy (PAES) has several advantages over conventional Auger-electron spectroscopy such as extremely high surface sensitivity and outstanding signal-to-noise ratio at the Auger-transition energy In order to benefit from these prominent features a low-energy positron beam of high intensity is required for surface sensitive PAES studies In addition, an electron energy analyzer is required, which efficiently detects the Auger electrons with acceptable energy resolution For this reason a novel time-of-flight (TOF) spectrometer has been developed at the intense positron source NEPOMUC that allows PAES studies within short measurement time This TOF-PAES setup combines a trochoidal filter and a flight tube in a Faraday cage in order to achieve an improved energy resolution of about 1eV at high electron energies up to E≈1000eV The electron flight time is the time between the annihilation radiation at the sample and when the electron hits a microchannel plate

Novel time-of-flight spectrometer for the analysis of positron annihilation induced Auger electrons

Energy spectra of electrons and positrons emitted from surfaces as a result of low energy positron bombardment

The Study of Secondary Electrons and Redistributed Primaries (Electrons and Positrons) from Ge(100) Surface Utilizing the Electron and the Positron Beams

S. Starnes

Papers

Energy spectra of electrons and positrons emitted from surfaces as a result of low energy positron bombardment

The Study of Secondary Electrons and Redistributed Primaries (Electrons and Positrons) from Ge(100) Surface Utilizing the Electron and the Positron Beams

Studies of the Auger spectrum from the (100) surface of GaAs using positron annihilation induced Auger electron spectroscopy

Studies of the Auger spectrum from the Si(111) surface using positron annihilation induced Auger electron spectroscopy