Influence of adsorbates on electron emission from amorphous carbon under electron and swift heavy ion bombardment

¹ PHILIPS GmbH, Philips Research Laboratories, Nano-Materials and Devices D303, Weisshausstrasse 2, 52066 Aachen, Germany
² Centre Interdisciplinaire de Recherche Ions Lasers CIRIL (UMR 6637 CEA-CNRS-ISMRA), rue Claude Bloch, BP 5133, 14070 Caen Cedex 05, France
³ Department of Electrical and Computer Engineering, Aristotelian University, GR-54006 Thessaloniki, Greece

Corresponding author: michel.caron@philips.com

Received: 20 February 2002
Revised: 18 July 2002
Accepted: 29 August 2002
Published online: 19 November 2002

Abstract

Secondary Electron Emission (SEE) yield measurements have been used to investigate the desorption of nitrogen adsorbates from amorphous carbon (a-C) surfaces due to swift heavy ion impact. The fluence dependence of ion induced electron emission obeys an exponential decay law when the coverage rate is in the sub-mono-layer range. This reveals the relative contribution of the both emitting zones, the “clean” one (having the SEE properties of carbon) and the covered one (with a higher SEE coefficient) to the total measured yield. The mechanism for the SEE enhancement effect is connected to the surface termination. Nitrogen adsorbates are believed to provide surface states which generate a downwards energy band bending, which on relative scale pushes up the Fermi level towards the conduction band minimum, reducing the work function and increasing the SEE yield subsequently. A shoulder observed on the rising edge of the peak of the true SE peak is ascribe to the fraction of hydrogenated termination of a-C which exhibits a lower electron affinity.