Deformation enhanced photoemission from oriented aluminum single crystal surfaces

Plastic-deformation-enhanced UV photoemission from oriented single crystal surfaces of aluminum has been studied. Clean single crystals of aluminum oriented in [111] direction were flexurally fatigued under UHV conditions and for the first time photoelectron energy distribution curves were obtained as a function of fatigue life using the Hel (21.2 eV) and the HeII (40.8 eV) photon lines. The integrated photocurrent was measured as a function of fatigue life using the photon lines from helium and argon sources. A progressive decrease in work function was observed as the specimen was subjected to increasing number of fatigue cycles. At a strain amplitude of ±0.2%, a drop of 0.2 eV in the work function occurred after 3000 fatigue cycles. Further, significant changes in aluminum valence band emission as a result of fatigue have been observed along with the formation of slip-steps on the surface of the aluminum specimen as seen under the scanning electron microscope. This alteration in the surface microgeometry caused by fatigue is believed to be responsible for the observed changes in the work function and the electronic band structure. The change in the total integrated photoyield caused by fatigue is thus determined by work function and valence band changes.