On undercut of Cr/Au, see:

Rapid sacrificial layer etching for the fabrication of nanochannels
with integrated metal electrodes
Wouter Sparreboom, Jan C. T. Eijkel, Johan Bomer and Albert van den Berg
Lab Chip, 2008, 8, 402–407
DOI: 10.1039/b716382g

It discusses the electrochemistry you're interested in in the context
of a Cr-Au sacrificially etched nanochannel etched by a Ce containing
etchant.

- Kevin

Kevin P Nichols, Ph.D.

Postdoctoral Scholar
Ismagilov Group
Department of Chemistry
Gordon Center CIS E305
University of Chicago
929 East 57th Street
Chicago, IL 60637

E: kpnichols@uchicago.edu
T: 773-834-8474
F: 773-834-3544

On Tue, Aug 10, 2010 at 3:21 PM, Robert MacDonald
 wrote:
> Does anyone out there know of any good academic papers on the chemistry of
> undercut at a Cr-Au interface? This is a classic problem with this
> metalization scheme. I have seen lateral etch ratios in this material system
> in excess of 1000:1. I wonder that it isn't a matter of the electrochemisty
> of the Cr-Au system. I have not been able to find any papers which study
> this issue, but I'm sure they are out there. If anyone knows of a good
> source I'd appreciate it.
>
> Rob MacDonald
> Shearwater Scientific