Supporting information. Wear resistance of Cu-Ag multilayers: A microscopic study

Transcription

1 Supporting information Wear resistance of Cu-Ag multilayers: A microscopic study R Madhavan*, P Bellon and RS Averback Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA *Corresponding author: rkmadhav@illinois.edu [S1]

2 Figure S1: SEM image of cono-spherical diamond stylus used for the micro-wear tests. Inset is an image taken at lower magnification. The tip surface and the spherical fit are indicated by solid lines. Figure S2: Variation of indentation hardness as a function of, (a) applied normal load and (b) penetration depth, of Cu/Ag multilayers and solid solution. The hardness values, in all the multilayers and solid solution, are within the deviation of 10% from the mean value with respect to the increasing load and penetration depth. For uniformity, the hardness measurements before and after wear tests were taken at 1500 µn for all multilayers and solid solution samples. [S2]

3 Figure S3: One dimensional scratch testing on Cu 90 Ag 10 multilayers. (a) AFM image of a representative track after 25 scratch cycles under 200µN normal load, (b) depth profile across the track shown as line AB in (a). Figure S4: Microstructure of as-deposited 60nm Cu/10nm Ag multilayer. (a) Bright-field TEM image, (b) corresponding selected area diffraction pattern. Diffraction pattern shows distinct {111} rings of Cu and Ag. The diffracted intensities are equally distributed suggesting the presence of near-random texture in as-grown film. [S3]

4 Figure S5: Wear rate obtained as a function of applied load (a), and number of incremental wear cycles (b). Figure S6: Ratio of h f (depth of residual impression) and h max (penetration depth at maximum load, i.e µn) for indents made on as-deposited films and within wear pattern. Data shown for solid solution and all multilayers. [S4]

5 Figure S7: (a) Representative AFM image of a wear pattern having impressions of hardness indents within the pattern. (b) Depth profile across the indent diagonals shown for 30/5 and 120/20 multilayers as representative cases. Multilayers show slight pile-up around the edges of the indent. Hardness values calculated from the projected contact area of residual indents, indicate that the changes in hardness measurements due to pile-up is about 7-10%. Figure S8: Nano-beam diffraction pattern taken from the sub-surface region beneath the worn surface of solid solution (Corresponding bright field TEM image is shown in Fig. 6a). The pattern confirms that the surface layer below the wear surface remains a single-phase solid solution of Ag in Cu. [S5]

6 Figure S9: EDS spectrum from the chemically mixed region of 12nm(Cu)/2nm(Ag) multilayer, obtained by spot analysis (Corresponding Z-contrast TEM image is shown in Fig. 6b). Quantitative information of the spot confirms that the surface layer is a homogenously mixed solid solution of Cu and Ag, having a composition close to the nominal composition of the multilayer. Figure S10: Montage of Z-contrast TEM images from the cross-section of wear track from the 100nm Cu/10nm Ag/ 750nm Cu multilayer, after 5 wear cycles. The silver layer below the sliding surface becomes very rough and wavy. The RMS value of interface roughness is estimated to be around 18 nm. Sliding direction of the tip is into the plane of paper. [S6]

7 Figure S11: (a) Cross section Z-contrast TEM image from 100nmCu/10nmAg/750nmCu multilayer after 5 wear cycles. (b) EDS line scan showing composition variation across the silver layer along the line shown in (a). The composition mapping shows localized mixing of Cu and Ag near the interface, which influences the wear rate. Figure S12: Bright field TEM images from cross-sections of worn region after 5 wear cycles. (a) Pure copper film, (b) 100nm Cu/10nm Ag/800nm Cu multilayered film. The images show the extent of plastic deformation below the surface during wear, as clearly evident from the dislocation contrast features. [S7]