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Fe, Co, and Ag particles grown on various CaF2 substrates have been studied using ultrahigh vacuum scanning electron microscopy with nanometer resolution. Fe and Co show a very high nucleation density which is remarkably independent of deposition temperature in the range 20<T<300 °C, on both bulk CaF2(111), and on thin CaF2(111) films grown on Si(111). This feature is characteristic of nucleation at defect sites with a high trapping energy. An atomistic nucleation model has been extended to cover this case. The comparison with experiment requires adsorption, pair binding, and defect trapping energies all to be around 1 eV. The trapping sites occupy 1% of the surface, and are thought to be chemical (F-vacancy, oxide, or hydroxide) in nature. In contrast, the growth of Ag on the same substrates shows a more usual nucleation and growth pattern, though the growth of Ag on Fe islands shows interesting features which are discussed. A self-similar coalescence model is tested using the data obtained. The agreement is excellent for Ag, while Co and Fe show the expected deviations due to limited surface diffusion around the islands.

Iron grown on room-temperature CaF2/Si(111) substrates form two-dimensional arrays of nanometer-sized superparamagnetic islands. Deposition of Ag on the Fe/CaF2/Si(111) produced a superparamagnetic response where the effective moment was proportional to the number of Fe islands covered by an average-sized Ag island. The nonmagnetic Ag overlayer mediates a long-range exchange between neighboring Fe islands within an individual Ag island. Monte Carlo methods are used to examine ordering in two dimensions and to set minimum interisland coupling strengths.

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/cm2. Chemical or defect dominated Fe growth on the CaF2/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.

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