ULTRAHIGH-VACUUM SCANNING ELECTRON-MICROSCOPY CHARACTERIZATION OF THE GROWTH OF FE ON CAF2/SI(111) - SELECTIVE NUCLEATION ON ELECTRON-BEAM MODIFIED SURFACES

The initial stages of Fe island growth on electron-beam modified and unmodified CaF2/Si(111) surfaces were studied with a nanometer lateral spatial resolution ultrahigh-vacuum scanning electron microscope. Fe coverages between 7 and 8 ML (deposition rates from 0.12 to 0.19 ML/min, 1 ML=7.7×1014 atom/cm2) grown on room temperature through 300 °C CaF2/Si(111) relaxed and unrelaxed substrates produced a relatively uniform distribution of islands that cover 23% of the substrate with an island density of 7.4×1012 island/cm 2. Chemical or defect dominated Fe growth on the CaF 2/Si(111) substrates is indicated by the temperature independence of the Fe island distributions for 20 °C≤T≤300 °C. Substrate temperatures near 400 °C yielded mottled surfaces and an altered island distribution relative to those formed during growth at temperatures between 20 and 300 °C. Parallel step edges separated by 25-75 nm were observed for unrelaxed films of CaF2 on Si(111), while relaxed CaF2 films exhibited a saw-toothed step pattern. Fe coverages of θ=21.4 ML produced a percolation network of connected islands rather than a continuous film covering the CaF2 substrate. The production of nanometer-sized surface structures was evaluated for electron-beam modified growth of Fe on CaF2/Si(111) substrates. Pregrowth (100 keV, 8.2-140 pA) electron irradiation doses as low as 1.14 C/cm2 altered the Fe film morphology on the selectively irradiated regions. Areas dosed with electron irradiation prior to Fe growth were more stable to the damaging effects of post-growth electron irradiation as compared to regions that had not been exposed.