Incipient amorphous-to-crystalline transition in Ge

Extended x-ray-absorption fine-structure (EXAFS) measurements were made on three samples of germanium films that were sputtered on substrates at temperatures of 175°C, intermediate between 175 and 250°C, and 325°C. Analysis of the second coordination shell of these samples gives clear evidence of incipient heterogeneous crystallization from an amorphous matrix. Although x-ray diffraction and optical-absorption measurements indicated that the low- and intermediate-Ts samples were amorphous, EXAFS indicated that the intermediate-Ts sample was heterogeneous, 20% of which consisted of microcrystallites approximately 10 in size embedded in an amorphous matrix. The fact that EXAFS can distinguish between microcrystalline and amorphous states gives the most direct experimental evidence to date that the amorphous state is a continuous random network.