Stress-Dependent Contact Potential in Copper

We have measured the compressionally induced change in contact potential for the (100) face of a single crystal of copper. For a change in stress of about 34 atm we observed a negative contact-potential change which is interpreted as a decrease in work function. This change is (-2.0 ±{} 1.2) {μ}V/atm, which gives an equivalent gravitationally induced field of (-1.8 ±{} 1.0) {μ}V/m. The crystal face was cleaned by Ar⁺ bombardment and measurements made at 2×{}10^-8 Torr. Some experiments on polycrystalline copper in different environments are also reported. A simple calculation based on the Gordy equation as interpreted by Steiner and Gyftopoulos gives, for a stress applied along the [001] cube axis, an increase of the work function with stress of 4.3 {μ}V/atm for the (100) face but a decrease of 3.8 {μ}V/atm for the (110) face.