Growth of Sn whiskers after low temperature implantation of 20 keV He or H

Single crystalline whiskers have been observed to form on thin films (- 100 nm) of Sn following implantation of 20 keV H or He at temperatures below 150 K. Rapid warming prevented the formation of whiskers, indicating that the growth occurs predominantly during the warming, and not during implantation. Samples that had been warmed rapidly did show whisker growth only after several days in air at room temperature. The adhesion of the films to the substrate is remarkably enhanced by the irradiation, as measured by scratch tests. Thicker films produced progressively few whiskers, and none were observed on implanted foils, or films of In, Bi, Zn, or Pb. Possible origins of the driving force for whisker growth are discussed. Whiskers grew on Sn films on all of the substrates that were tested: quartz, sapphire, glass, Si, Cu, stainless steel and NaCl.