The interactions between condensed molecules at cryogenic temperatures (15–200 K) have been investigated on the basis of secondary ion mass spectrometry. It is demonstrated that the protonated molecular ions, emitted via the proton transfer reactions, provide us unique information about the reorganization of hydrogen-bonded molecules. From the CH3OH molecules adsorbed on the D2O–ice surface, the D+(CH3OH) ions are sputtered predominantly in the temperature range between 100 and 150 K since most of the CH3OH molecules are bound to the D2O layer via hydrogen bonds. A rapid and almost complete H/D exchange, yielding the D+(CH3OD) species, occurs above 150 K due to the enhanced mobility of the surface D2O molecules. Up to the desorption temperature of 180 K, a considerable amount of methanol exists on the surface without mixing with the heavy-water layer due to hydrophobicity of the methyl group. On the methanol–ice surface, the adsorbed D2O molecules form hydrogen bonds preferentially with the CH3OH molecules and tend to be incorporated in the thin-layer bulk of methanol above 120 K.

Corundum-structured -Ga 2 O 3 epitaxial thin films were grown on c-plane -Al 2 O 3 (sapphire) substrates by a mist chemical vapor deposition method. To reveal the defect structures, the -Ga 2 O 3 film was observed by high-resolution transmission electron microscopy (TEM). We found that the -Ga 2 O 3 thin film was in-plane compressive stressed from the -Al 2 O 3 substrate. Although misfit dislocations were periodically generated at the -Ga 2 O 3 /-Al 2 O 3 interface owing to the large lattice mismatches between -Ga 2 O 3 and -Al 2 O 3 , 3.54% (c-axis) and 4.81% (a-axis), most of the misfit dislocations did not thread through the layer. An extra-half plane was f 2110g consisting only of Ga. Screw dislocations were not confirmed, i.e., the density was under 10 7 cm À2 . The threading dislocation density was 7 Â 10 10 cm À2 .

Atomic and electronic structures of TaB 2 (0001) and HfB 2 (0001) surfaces are investigated with use of the first-principles pseudopotential calculations. Our calculated surface formation energies indicate that the graphitic-boron-terminated TaB 2 (0001) surface is energetically more favorable, whereas the HfB 2 (0001) surface prefers termination with a close-packed Hf layer. These findings are consistent with experimental facts. We have also found the difference in the surface relaxation between them. The first interlayer spacing of the B-terminated TaB 2 surface is expanded by 0.39%. On the other hand, the outermost Hf-terminated HfB 2 surface is contracted by 4.8%.

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The interaction of HCl with the D(2)O-ice surface has been investigated in the temperature range 15-200 K by utilizing time-of-flight secondary ion mass spectroscopy, temperature-programmed desorption, and x-ray photoelectron spectroscopy. The intensities of sputtered H(+)(D(2)O) and Cl(-) ions (the H(+) ions) are increased (decreased) markedly above 40 K due to the hydrogen bond formation between the HCl and D(2)O molecules. The HCl molecules which form ionic hydrates undergo H/D exchange at 110-140 K and a considerable fraction of them dissolves into the bulk above 140 K. The neutral hydrates of HCl should coexist as evidenced by the desorption of HCl above 170 K. They are incorporated completely in the D(2)O layer up to 140 K. The HCl molecules embedded in the thick D(2)O layer dissolve into the bulk, and the ionic hydrate tends to segregate to the surface above 150 K.

Low energy ion beams for surface modification and film deposition AIP Conf. Proc. 576, 911 (2001); 10.1063/1.1395451 Molecular dynamics simulations of low-energy (25-200 eV) argon ion interactions with silicon surfaces: Sputter yields and product formation pathways Capture and loss of valence electrons during low-energy ͑50-500 eV͒ proton scattering from some alkali-halide surfaces such as LiCl, NaCl, and KF have been investigated in comparison with those from the TiO 2 ͑110͒ and Cs-adsorbed Si͑100͒ surfaces. The primary H ϩ ion survives neutralization when scattered from the highly ionized target species existing on the surface. For H Ϫ ion formation, a close atomic encounter with individual target ions is found to be important; the H Ϫ ion is formed more efficiently on the cationic site than on the anionic site despite the fact that the valence electron is spacially localized on the latter. This is because the charge state of scattered hydrogen is determined during a transient chemisorption state and amphoteric hydrogen tends to be coordinated negatively ͑positively͒ on the cationic site ͑the anionic site͒. The final charge state of scattered hydrogen is fixed at a certain bond-breaking distance ͑ϳ5.0 a.u.͒ from the surface where the well-defined atomic orbital of hydrogen evolves. The competing nonlocal resonance tunneling is suppressed at the ionic-compound surfaces due to the existence of a large band gap, so that hydrogen is scattered without losing the memory of such a transient chemisorption state.

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