Modification of wetting of copper (Cu) on carbon (C) by plasma treatment and molybdenum (Mo) interlayers C. Eisenmenger-Sittner a, * , C. Schrank a , E. Neubauer b , E. Eiper c , J. Keckes c,d a Vienna University of Technology, Institute of Solid State Physics, E-138, Thin Film Group, Wiedner Hauptstrasse 8-10, A-1040 Vienna, Austria b ARC Seibersdorf Research, Department Materials Research, A-2444 Seibersdorf, Austria c Erich Schmid Institute, Leoben, Austria d Materials Center Leoben, Leoben, Austria Available online 20 January 2006 Abstract Manipulating wetting and adhesion between the chemically immiscible elements Cu and C is of high interest for the production of C-fiber reinforced Cu–C metal matrix composites (MMC’s) which are potential materials for high performance heat sinks. This work presents two approaches to adhesion manipulation: (i) the activation of the C-surface by a treatment in nitrogen (N 2 ) radio frequency (RF) plasma and (ii) the deposition of a Mo-interlayer on the C-surface. Both approaches yield a significant increase in adhesion for Cu-coatings deposited immediately after pre treatment. Heat treatment (30 min, 800 8C, high vacuum furnace) leads to a drastic loss in adhesion for the plasma treated samples while the samples containing the Mo-interlayer retain excellent adhesion values. Results of thermal cycling experiments (RT—500 8C) combined with in situ X-ray diffraction (XRD) measurements show a similar picture. The Cu-coating on the plasma treated sample delaminates after one cycle. The sample with the Mo-interlayer can go through several cycles and is able to sustain thermally induced stresses. The difference in the response of the two sample types to post deposition thermal treatment can be tracked back to the de-wetting behavior of Cu on the different substrates. Void formation is observed at the Cu–C interface in the case of plasma treatment but not for samples with a Mo- interlayer. # 2005 Elsevier B.V. All rights reserved. PACS: 68.08.Bc; 68.35.Np; 68.55.Àa; 81.15.Cd; 81.20.Ev; 07.10.Lw; 61.10.Nz Keywords: Carbon; Copper; Metal matrix composite; Plasma treatment; Molybdenum interlayer; De-wetting 1. Introduction Metal matrix composites (MMC’s) represent a material class with mechanical and thermal properties tuneable by the ratio of the constituents. They find applications in environments where the matching of thermomechanical characteristics is crucial. Carbon-fiber reinforced copper carbon MMC’s are potential materials for heat sinks in high performance electronic components or fusion reactor components. These applications require a reliable joining of the two components, Cu and C. A promising route to produce Cu–C MMC’s is coating short C-fibers (approximately 0.5 mm length, 7–10 mm diameter) with copper and then consolidating the material by unidirec- tional hot pressing [1,2]. Copper may be deposited by electrochemical methods [3–5] or by magnetron sputtering [6,7] which has the advantage of either allowing a plasma- pre-treatment of the C-surface or the deposition of adhesion promoting interlayers. Both, plasma-pre-treatment by a radio frequency nitrogen (RF-N 2 ) discharge as well as the deposition of a 100 nm Mo interlayer on a C surface have a beneficial effect on the adhesion of Cu-coatings in the as-deposited state. If the samples are heat treated there is a drastic adhesion loss in the case of the plasma treated samples while heat treatment increases the adhesion promoting effect of the Mo interlayer [6]. It is the intention of this paper to further investigate the influence of heat treatment on the adhesion of Cu on modified C www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 5343–5346 * Corresponding author. Tel.: +43 1 58801 13774; fax: +43 1 58801 13899. E-mail address: christoph.eisenmenger@ifp.tuwien.ac.at (C. Eisenmenger-Sittner). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.12.038