UNCORRECTED PROOF MASPEC 12771 1–9 International Journal of Mass Spectrometry xxx (2004) xxx–xxx Temperature dependence of secondary ion emission from tantalum produced by atomic and polyatomic gold projectiles 3 4 S.F. Belykh a,∗ , I.V. Veryovkin b , V.V. Palitsin c , A.V. Samartsev d , A. Adriaens e , F. Adams a 5 6 a Department of Chemistry, University of Antwerp (UIA), Universiteitsplein 1, B-2610 Antwerp (Wilrijk), Belgium 7 b Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA 8 c Department of Physics, Warwick University, CVI 7AL Coventry, UK 9 d Institute of Experimental Physics, University of Duisburg—Essen, D-45117 Essen, Germany 10 e Department of Analytical Chemistry, Gent University B-9000 Ghent, Belgium 11 Received 12 December 2003; accepted 28 June 2004 12 Abstract 13 Temperature dependencies have been measured within a wide range of target temperatures of 300 K ≤ T ≤ 2400 K for secondary ion yields of Ta n + , Ta n O m + , Ta n Nb + and Ta n Au + (n = 1–14, m = 1–3) under the bombardment of tantalum target with 12 keV atomic Au - and 18 keV polyatomic Au 3 - projectiles. It is demonstrated that yields of Ta n + (n = 2–14) and Ta n Nb + ions increase with temperature for T ≤ 1700 K and then tend to become temperature independent. On the contrary, the yields of Ta n O m + and Ta n Au + ions slightly increase with temperature reaching their maxima in the range of 1000 K ≤ T ≤ 1500 K and then sharply decrease to zero at T ≈ 1700 and 2100 K, respectively. These trends are interpreted to indicate the redistribution of the sputtered flux between these different emission channels while sputtering conditions change with the target temperature. Oxygen presence on the surface at lower temperatures limits the yield of Ta n + clusters and stimulates that of Ta n O m + . Removing oxygen from the surface enhances the yield of Ta n + clusters and the disappearance of Ta n O m + . After clean surfaces are established in the range of 1700 K ≤ T ≤ 2400K, the yield of the Ta n + and Ta n Nb + cluster ions becomes constant thus indicating that their ionization probability does not depend on the target temperature in this range. Some differences in the temperature dependencies obtained under the atomic and polyatomic ion bombardment are observed and interpreted as the indication of different efficiencies of the sputtering process since polyatomic projectiles sputter more material than atomic ones. This, in addition to better surface cleaning, enhances yields of cluster ions. For atomic ions Ta + , an additional emission channel, thermal evaporation/surface ionization, is identified at target temperatures T > 2300 K. No evaporated cluster ions are observed. 14 15 16 17 18 19 20 21 22 23 24 25 26 27 © 2004 Published by Elsevier B.V. 28 PACS: 79.20.Rf; 34.50.Dy; 68.49.Sf 29 Keywords: Secondary atomic and cluster ion emission; Atomic and polyatomic ion bombardment; Temperature dependence; Non-additive sputtering 30 31 1. Introduction 32 It is well known that the bombardment of solids by keV 33 atomic or polyatomic projectiles generates emission of atoms 34 and clusters or molecules in neutral and charged states. This 35 phenomenon called ion sputtering occurs due to linear or non- 36 ∗ Corresponding author. Tel.: +32 3 820 23 63; fax: +32 3 820 23 76. E-mail address: belikh@uia.ua.ac.be (S.F. Belykh). linear collision cascades developing in sub-surface regions 37 of solids [1]. While emission mechanisms for neutral atoms 38 and atomic ions produced by atomic projectiles are now well 39 understood [2], the processes of cluster emission [3–6] and 40 charged state formation [7,8] of the emitted clusters remain a 41 subject of ongoing discussions. Yields of both neutral clusters 42 and cluster ions depend on the interaction characteristics in 43 a given “projectile–solid” system defined by the relationship 44 between chemical and physical properties of the projectile 45 1 1387-3806/$ – see front matter © 2004 Published by Elsevier B.V. 2 doi:10.1016/j.ijms.2004.06.010