Positrons in surface physics

Abstract

Within the last decade powerful methods have been developed to study surfaces using bright low-energy positron beams. These novel analysis tools exploit the unique properties of positron interaction with surfaces, which comprise the absence of exchange interaction, repulsive crystal potential and positron trapping in delocalized surface states at low energies. By applying reflection highenergy positron diffraction (RHEPD) one can benefit from the phenomenon of total reflection below a critical angle that is not present in electron surface diffraction. Therefore, RHEPD allows the determination of the atom positions of (reconstructed) surfaces with outstanding accuracy. The main advantages of positron annihilation induced Auger-electron spectroscopy (PAES) are the missing secondary electron background in the energy region of Auger-transitions and its topmost layer sensitivity for elemental analysis. In order to enable the investigation of the electron polarization at surfaces low-energy spin-polarized positrons are used to probe the outermost electrons of the surface. Furthermore, in fundamental research the preparation of well defined surfaces tailored for the production of bound leptonic systems plays an outstanding role. In this report, it is envisaged to cover both, the fundamental aspects of positron surface interaction and the present status of surface studies using modern positron beam techniques.

Experimental progress in positronium laser physics

“…Some examples include new measurements of the Ps ground state hyperfine interval that may solve the long-standing discrepancy between theory and experiment [81], the resolution of the (perhaps related) positronium "lifetime puzzle" [82,83], advances in positron scattering from atoms and molecules [84][85][86], antihydrogen research [87][88][89][90], positron beam [91][92][93] and trap [66,69] development, materials science [65,94], and surface physics [95] (including positron diffraction [96,97] and positron induced Auger emission [98,99]). These areas, and others, will not be discussed here.…”

Ion-Beam-Induced Defects in CMOS Technology: Methods of Study

“…Also, positrons can be used in diffraction experiments having the advantage that interaction with solids can be easier modeled due to the sign of the scattering potential (the scattering potential between the positron and the atomic nucleus is repulsive) and the total reflection, which is only present in the positron diffraction [18,19]. The interaction of an energetic positron with the solid may differ from that of electrons of the same energy.…”

Comparison of azimuthal plots for reflection high-energy positron diffraction (RHEPD) and reflection high-energy electron diffraction (RHEED) for Si(111) surface

“…It appears that there are many potential possibilities for the use of RHEPD in surface crystallography (Hugenschmidt, 2016). However, current knowledge of this technique itself is still limited.…”