Autoionising state production in N þ ,O þ ,Ne þ and Ar þ scattering on clean and K covered Al(111) surfaces E.A. S anchez a, * , O. Grizzi a , V.A. Esaulov b a Centro At omico Bariloche, Instituto Balseiro, CNEA and CONICET, 8400 San Carlos de Bariloche, R  ıo Negro, Argentina b Laboratoire des Collisions Atomiques et Mol eculaires (Unit e Mixte de Recherche CNRS-Universit e No. 8625), B^ atiment 351, Universit e Paris-Sud, F-91405 Orsay, France Received 12 July 2001; accepted for publication 29 November 2001 Abstract WepresentastudyoftheautoionisingstateproductioninN,O,NeandArioncollisionswithacleanandpotassium covered Al(111) surface in an energy range from 5 to 50 keV. In case of clean Al, we only observe production of 2p 4 nln 0 l 0 ,2s2p 5 nl, 2s2p 6 nl autoionising states for Ne þ projectiles; for N þ ,O þ andAr þ scattering no sign of production ofdoublyexcitedstateswasfound,althoughionbackscatteringisknowntooccur.IncaseofKcoveredsurfaceswein all cases observe production of sputtered excited K atoms in 3p 5 4s 2 autoionising states. For Ar þ the quasi-symmetric collision with K produces excitation of Ar in 3p 4 4s 2 states. For N þ scattering the electron spectra reveal a small structure which we attribute to the formation of metastable N  ( 1 D). K adsorption does not lead to the appearance of any new Ne  related structures. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Aluminum; Electron emission; Ion–solid interactions 1. Introduction Inelastic collisions of rare gas atoms and ions with surfaces have been studied in the past 20 years [1–23]. In particular, the production of autoionisingstatesofNeofthe2p 4 nln 0 l 0 ,2p 3 nln 0 l 0 , and 2s2p 5 nl in collisions with Mg, Al and Si sur- faces has been extensively investigated. Efficient backscattering of ions, a feature of interest in ion scattering spectroscopy (ISS), has been attributed to excitation of these states. Most of these studies were performed on polycrystalline surfaces and in the low keV energy range. Recently we per- formed a study of the electron emission resulting fromautoionisationofNescatteredoffanAl(111) surface in a wider energy range extending from 3 to 50 keV and observed strong excitation of additional states [24]. This work allowed us to obtain additional information about the nature of these states and the dynamics of their forma- tion. Some attempts have been made in the past few years to investigate the collisions of other atoms such as O [25], F and Cl [26] and a search for ev- idence of excitation of similar autoionising states, which could play some role in positive ion back- scattering was made. No sign of production of such doubly excited states was found for energies Surface Science 501 (2002) 132–137 www.elsevier.com/locate/susc * Corresponding author. Tel.: +54-2944-445299/445220; fax: +54-2944-445299. E-mail address: esanchez@cab.cnea.gov.ar (E.A. S anchez). 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0039-6028(01)01923-9