| AVS 59th Annual International Symposium and Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS-ThA |
| Session: | Applications of Large Cluster Ion Beams - Part 2 (2:00-3:20 pm)/ Surface Analysis using Synchrotron Techniques (3:40-5:40 pm) |
| Presenter: | P. Rajput, ESRF, France |
| Authors: | P. Rajput, ESRF, France A. Gupta, UGC-DAE Consortium for Scientific Research, India C. Meneghini, Universita di“Roma Tre”, Italy G. Sharma, UGC-DAE Consortium for Scientific Research, India J. Zegenhagen, ESRF, France |
| Correspondent: | Click to Email |
Metallic alloys are important in our daily life and in industry, but unfortunately highly susceptible to corrosion in wet environment. De-alloying is a particular type of corrosion, attacking alloys which are composed of metals of different “nobility”. When coming into contact with an electrolyte, the less noble metal may go into solution, typically causing crack formation and subsequent material failure upon stress. Potential controlled corrosion of a well ordered Cu3Au crystal in sulfuric acid had been investigated in situ [1] showing that, far below the critical potential Ec, at which the alloy is massively dissolved, Cu goes into solution, leaving a ≈ 1 nm thick film of small, Au-rich clusters. Just below Ec, the surface is eventually covered with about 10-20 nm large gold islands with a thickness of 2-3 nm. The Au-rich surface protects the bulk of the alloy against further corrosion (unless Ec is exceeded).
We used, hard x-ray photoelectron spectroscopy (HAXPES), x-ray standing waves (XSW) and depth-selective x-ray absorption fine structure (XAFS) to investigate the very early stages of the corrosion of a more ‘realistic’, disordered CuAu binary alloy. Ultra-thin CuxAu films (2.5 nm, x≈3) were deposited on a Ru/B4C multilayer to produce the XSW field. The XSW study provides detailed information about the concentration profile of Cu and Au upon de-alloying. HAXPES provides the binding energies (oxidation states) of Au and Cu and XAFS reveals the local atomic structure around Cu and Au.
The pristine CuxAu film appeared partially oxidized (CuO and Cu2O). After dealloying at 245 mV for 2 min in 0.1 M H2SO4, the partial Cu dissolution leads to the formation of a Au-rich film with CuAu3-like composition. Quantitative XRF analysis showed that, surprisingly, even below Ec de-alloying leads to the loss of some Au as well.
[1] F. U. Renner, A. Stierle, H. Dosch, T. L. Lee, D. M. Kolb, J. Zegenhagen, Nature 439, 707 (2006).