On the optimization of the PIXE technique for thickness uniformity control of ultra-thin chromium layers deposited onto large surface quartz substrate K. Zahraman a , B. Nsouli a, * , M. Roumie ´ a , J.P. Thomas b , S. Danel c a IBA Laboratory, Lebanese Atomic Energy Commission, National Council for Scientiﬁc Research, P.O. Box 11, 8281 Beirut, Lebanon b Institut de Physique Nucle ´aire de Lyon, Universite ´ Claude Bernard Lyon 1, 43 Bd. 11 Novembre 1918, 69622 Villeurbanne Cedex, France c LETI, Commissariat a ` l’Energie Atomique, Grenoble, France Available online 3 May 2006 Abstract Chromium is a good candidate for obtaining conductive ultra-thin layers on insulator substrates such as quartz. The resistivity of such layers is highly related to the quality of the deposited chromium ﬁlm. In order to optimize the deposition process, there is a need for rapid and accurate monitoring of such ﬁlms (ﬁlm thickness, thickness uniformity over a big surface, etc.). In this paper, we demonstrate the ability of the LE-PIXE technique, using proton energies <1 MeV, for the monitoring of the thickness and the thickness uniformity of ultra-thin (0.5 nm < t < 20 nm) chromium layers deposited onto quartz substrates. The acquisition time needed to obtain results with less than 3–4% precision was 5 min for the thinnest layers. The validation for the use of the LE-PIXE technique was checked by means of conventional RBS technique. Ó 2006 Elsevier B.V. All rights reserved. PACS: 41.75.Ak; 29.30.Kv; 32.30.Rj Keywords: PIXE; LE-PIXE; RBS; Chromium; Thin layers 1. Introduction Chromium is a good candidate to obtain ultra-thin con- ductive layers on insulator substrates like quartz. Besides the interesting mechanical properties of the Cr/quartz interface which are due to the good wetability of Cr on quartz, the conductivity of such systems becomes measur- able from thickness values as low as 0.2 nm [1]. The resis- tivity of such systems is highly connected to the quality of the deposited chromium ﬁlm (thickness, thickness uni- formity, interface properties, etc.). In order to optimize the deposition parameters of such ﬁlms, a rapid, accurate and sensitive monitoring of their thickness and thickness uniformities over a relatively big surface (100 cm 2 ) is needed. RBS is the mostly used technique for thin ﬁlm thickness determination and for ﬁlm/substrate interface characteriza- tion. A chromium thin ﬁlm deposited onto a quartz sub- strate is a favorable case to perform RBS measurements with a high sensitivity. However, the accurate thickness determination of ultra-thin layers (<1 nm) needs relatively large acquisition time which is a limiting factor when the number of samples is big. In the same way, and in the case of no signiﬁcant sample surface roughness, the low energy PIXE (LE-PIXE) is now recognized as a powerful tool, being a commonly used method for ultra-thin ﬁlm and sur- face characterization [2–4]. In fact, when the proton energy decreases, the bremsstrahlung decreases much more than the cross-section for inner shell ionization. Consequently, the LE-PIXE, using protons with energy <1.5 MeV, could 0168-583X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.03.028 * Corresponding author. Tel.: +961 1 450812; fax: +961 1 450810. E-mail address: bnsouli@cnrs.edu.lb (B. Nsouli). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 249 (2006) 447–450 NIM B Beam Interactions with Materials & Atoms