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-$T_s$ samples were amorphous, EXAFS indicated that the intermediate-$T_s$ sample was heterogeneous, 20% of which consisted of microcrystallites approximately 10 Å 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.