Evidence is presented that π-bonding is present in the surface dimers on clean Si(100)–(2×1) and, as a consequence, that hydrogen atoms preferentially pair on surface dimer atoms even at low coverage. We propose a simple lattice gas model in order to calculate the equilibrium distribution of doubly- and singly-occupied dimers as a function of coverage and temperature, and show that even a very conservative estimate of the enthalpy difference between hydrogen on doubly- and singly-occupied dimers can explain the observed first-order desorption kinetics.

We present atomic force microscopy images of diamond films grown by chemical vapor deposition epitaxially on diamond (100), (110), and (111) substrates. The films were grown from 0.2%–1.6% mixtures of CH4 and C2H2 in H2 in a hot-filament reactor at a total pressure of 25 Torr. The substrate and filament temperatures were held at 810–1000 and 2000–2150 °C, respectively. A (100)-oriented diamond film grown with 0.3% CH4 at a substrate temperature of 810 °C was rough on the μm scale, exhibiting pyramidal features, terraces, and penetration twins, while films grown at higher substrate temperatures and hydrocarbon flow rates were smooth on the nm scale and showed evidence of a (2×1) reconstruction. A (110)-oriented film was very rough on the μm scale but nearly atomically smooth on the 0.5–5 nm scale and exhibited local slopes higher than 40° with no evidence of faceting. A film grown on a diamond (111) substrate underwent spontaneous fracture due to tensile stress and exhibited a roughness of ≊10–50 nm on the ≊100 nm lateral scale in regions far away from any cracks. The implications of the morphological features for diamond growth mechanisms are discussed.

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We present the first atomic force microscopy images of diamond films grown homoepitaxially in a hot filament reactor on ( 100)) ( 1 1 1 ), and ( 110) natural diamond substrates. ( 100) -oriented diamond films grown with 0.3% CH4 at a substrate temperature of 810 "C were rough on the micron scale, exhibiting pyramidal features and penetration twins, while films grown with 1.6% CH, at 1000 "6 were nearly atomically smooth and showed evidence of a (2 x 1) reconstruction. A ( 111 )-oriented film cracked due to tensile stress and was rough on the 50-500 nm scale, while a (llO)-oriented film was rough on the micron scale but nearly atomically smooth on the 0.5-5 nm scale. Implications of the observed morphologies for diamond growth mechanisms are discussed.

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Tunable diode laser spectroscopy offers unique advantages for high resolution infrared reflection absorption spectroscopy (IRRAS) studies of monolayers on single crystal surfes. Its greatest potentials lie in anal'ses of lineshapes less than 1 cm (FWHM), for resolving narrow features on absorption peaks, and for in situ solid-liquid interfacial studies, where high intensity is often required. Other IRRAS techniques introduce instrumental broadening sufficient to create considerable uncertainty in the intrinsic linewidth of very narrow peaks, and can mask sharp features. Using isolated or 0-81 94-0782-8192/$4.0O

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