CRITICAL THICKNESS OF SINGLE-CRYSTAL FCC IRON ON DIAMOND

The growth of (100) diamond/iron/copper multilayer structures has been examined by reflection high energy electron diffraction, extended X-r ay absorption fine structure, and scanning electron microscopy in an e ffort to determine the thickness limit for metastable face-centered-cu bic Fe on (100) diamond. Both copper films deposited on iron layers wi th thicknesses below 1.4 nm and the iron layers themselves were found to be face-centered cubic single crystal, while films grown on iron th at was 2.0 nm and thicker and the iron itself were found to be polycry stalline. This critical thickness range of 1.4-2.0 nm compares well wi th the theoretically calculated value of 1.8 nm. This value was determ ined using the mechanical equilibrium theories (Matthews-Blakeslee and van der Merwe) with a lattice parameter for face-centered cubic iron that was derived by estimating the functional form of the linear therm al expansion coefficient and extrapolating the Poisson's ratio for aus tenitic stainless steel to the temperature of interest. The shear modu lus, and intrinsic stacking fault energy for fcc Fe from similar to 13 50 degrees C down to below room temperature have also been estimated. A more likely room temperature lattice parameter for fcc Fe than is us ually assumed was estimated to be 0.3579 nm. The measured in-plane lat tice parameter of strained fcc Fe on diamond was 3.54 +/- 0.1 Angstrom .