Auger Neutralization of Slow Protons at Solid Surfaces

Abstract

Auger neutralization of slow protons ( s a few keV) scattered from solid surfaces is considered.The neutralization probability per unit time P(s) is calculated as a function of the proton distance 8 from the surface to P ( s ) = A{e-zxs + (Bs + C) e-(xfao')s + (Ds2 + Es + F) e-zaols}, where a, is the Bohr radius and A, B, C, D, E, F, and x proper constants depending on the target. A t large distances from the surface, the second and third terms of P(s) can be neglected. As the proton approaches the surface, however, P(s) deviates from the simple exponential dependence of s. The neutral fraction QO is also calculated. From the obtained rpo, it is shown that Auger neutralization is important, at least in the low energy region.Es wird Augerneutralisation von langsamen Protonen ( s einige keV) betrachtet, die von Festkorperoberfliichen gestreut werden. Die Neutralisierungswahrscheinlichkeit pro Einheitszeit P(s) wird als Funktion des Protonenabstands s von der Oberflache zu P(s) = A{e-Zxs + (Bs + C) X x e-(x+ac')s + (Dsa + Es + F) e-zao's} berechnet, wobei a, der Bohrsche Radius und A, B, C, D, E, F und x geeignete Konstanten sind, die vom Target abhangen. Bei groBen Entfernungen von der Oberfliiche konnen die zweiten und dritten Terme von P(s) vernachliissigt werden. Wenn das Proton jedoch die Oberfliiche erreicht, weicht P(s) von der einfachen exponentiellen Abhiingigkeit von s ab. Der neutrale Anteil wird ebenfalls berechnet. Aus dem erhaltenen rpo wird gezeigt, da8 die Augerneutralisation wesentlich ist, mindestens im Bereich niederer Energien.

Theory of Auger neutralization and deexcitation of slow ions at metal surfaces

“…These are complex quantum-mechanical scattering calculations, where many approximations are required. Horiguchi et al 27 and Hentschke et al 28 computed Auger rates for a proton-metal system using analytical wave functions for the metal electrons ͑those of a step potential͒. They simplified the eight dimensional k-space integration by taking the contribution of electrons at the Fermi level normal to the surface.…”

“…5 In an analogous way, the theoretical work can also be divided into calculations concerning electron emission, [21][22][23][24][25][26] or neutralization rates. [27][28][29][30][31][32][33][34][35] Propst 21 calculated the Auger matrix elements using a WKB approach for the wave function of the captured electron tunneling through the ionsurface barrier. His work qualitatively reproduces the experimental spectra by Hagstrum.…”

Auger Neutralization of Fast Ions at Surfaces

“…Throughout this paper we use the notation of Horiguchi et a]. [5]. All calculations are performed in atomic units.…”

“…It is therefore of interest to develop a theory of Auger neutralization in which the velocity-dependent effects are included. I n order to get some rough idea of the relevant magnitudes we have applied simple approximations following the treatment of Horiguchi et al [ 5 ] . We will consider cases, where the incident ion moves with constant relocity u parallel to the surface a t constant distance s and where one electron is captured into a 2p-state of He+.…”

On the Charge Distribution of Ions after Auger Neutralisation at Surfaces

“…In two earlier papers [l, 21 we have calculated Auger neutralisation rates at surfaces by developing the model by Horiguchi et al [12]. We considered the case where ions move parallel to a metal surface with velocity u and constant distance s and where one conduction electron is captured in a 2p orbital of the ion.…”