Direct force measurements at the smooth gold/mica interface

We have developed a technique for accessing a very smooth gold surface (4 Angstrom root-mean-square roughness) with nominal area greater than 100 mu m(2). It is a simple, controlled, and chemically noninvasive procedure of separating the smooth gold/mica interface carried out in the surface forces apparatus. Taking advantage of cold welding between surfaces of thin gold films and using carefully chosen quantities of compression, we have been able to isolate a region of the smooth gold/mica interface from forces other than those of adhesion. This allows measurement of the pull-off force required to separate smooth gold from mica (F-p/R = 1800 mN/m); this represents a significant end point to data of previous studies addressing the impact of roughness on adhesion. Roughening of the gold surface during the separation process acts to reduce the pull-off forces required on subsequent separations.