INVESTIGATION OF POTASSIUM IMPLANTED

TRANSITION METAL TUNGSTEN ANALYZED BY DENSITY

FUNCTIONAL THEORY METHOD

A. Souissi*, A. Jorio, I. Zorkani

Laboratoire de Physique de Solide, Département de Physique

Faculté des Sciences, B.P.1796, Atlas-Fes, Morocco

* Corresponding author. E-mail : sou_ab@hotmail.com

Received : 20 November 2001; revised version accepted 01 February 2002

Abstract

Ion implantation of potassium has been demonstrated as a valuable new tool to improve the enhancement of the photoelectric emission of pure metal of tungsten in the aim to perform the photocathode electron emission rate. The investigation by density functional theory in the frame work of LSD performed by nolocal density approximation using the functional PW91, allows us to understand and explain the lowering of the work function under 4,5 eV. The results of binding energy calculations are presented to elucidate the prediction of geometry optimization of K/W clusters. K valence electrons originating from the atomic 4s states are polarized toward the W surface leading to an increase of electronic charge in the K/W interface region. The K-induced changes in the charge density are essentially localized outside the surface W atoms. In addition the semi-core K(3p) electrons are markedly counter polarized. The net results of these multiple dipoles is a lowering of the work function upon K atoms adsorbed on W Surface improving the enhancement of the electron emission rate of the surface elaborated.

Keywords : Tungsten; Potassium; Density Functional Theory and Work function.

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