Highly site-specific H2 adsorption on vicinal Si(001) surfaces

Experimental and theoretical results for the dissociative adsorption of H_2 on vicinal Si(001) surfaces are presented. Using optical second-harmonic generation, sticking probabilities at the step sites are found to exceed those on the terraces by up to six orders of magnitude. Density functional theory calculations indicate the presence of direct adsorption pathways for monohydride formation but with a dramatically lowered barrier for step adsorption due to an efficient rehybridization of dangling orbitals.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Lett. (1998). Other related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

The structure-sensitive adsorption of H₂O and H₂S on flat and stepped Si(001) surfaces

The adsorption of H20 at 350 K and of H2S between 90 and 550 K has been investigated by photoelectron spectroscopy on a spherical lens shaped Si sample with (001) in its center. In this paper, the vicinal orientations in the [110] and the [100] zone are compared up to a deviation of 14° from (001). On (001), H2O at 350 K and H2S at 150 K are adsorbed with a constant sticking probability near unity until saturation which occurs sharply at a coverage of 12 monolayer. This implies a kinetics with mobile precursors. The adsorbed species are OH + H and SH + H, respectively. The same kinetics and species are observed on stepped surfaces up to a deviation of about 9° from (001). The saturation coverage decreases slightly with increasing step density. This is in full agreement with a step structure with a rebonded row of adatoms which reduce the density of dangling bonds. The step related sites turn thus out to be as reactive as the dimers on (001). At 90 K, H2S adsorption shows the same kinetics. However, the adsorbate at the steps is different, probably molecular. Beyond about 9° from (001), the saturation coverage drops more steeply and the spectra for water adsorption change their shape. This indicates a change from purely stepped structures to structures with admixture of other facets. At 550 K, H2S adsorption is still fast, but no mobile precursor kinetics is observable. The adsorbate is fully dissociated.Never forget to use the Div - Table style generator and the online HTML editor to compose perfect articles for your website

Complete valence-band structure of Ge determined by photoemission

The valence-band structure along the high-symmetry directions ΓL, ΓX, and ΓKX was studied with synchrotron radiation for a wide photon energy range (10–106 eV). A cylindrically shaped Ge crystal with [11¯0] axis was used, which allowed us to record the spectra in normal emission for different orientations. The data were analyzed by applying the model of direct transition into free-electron final-state bands. Due to the wide photon energy range, a complete band scheme along the three directions including critical points was obtained. The data are compared with theoretical results and other measurements. The bands along the ΓKX direction are reported for the first time to our knowledge. Applying the wide photon energy range, the inner potential V0=-8.8 eV was determined self-consistently using the method suggested by Middelmann et al. [Phys. Rev. B 34, 957 (1986)]

Adsorption and dissociation of NO on germanium

A cylindrically-shaped Ge crystal with the orientations (001), (113), (111), (110) and all intermediates between them on its surface was used to study the adsorption of NO by Auger and photoelectron spectroscopy applying laboratory sources (He I, Mg Ka) and synchrotron radiation. A strong orientation dependence of the adsorbed amount is observed. Between 60 K and 130 K, coadsorption of NO and O with a maximum at (001) is observed. No or only very little atomic N is found. Upon warming up to above 200 K, NO desorbs and only atomic O remains. Exposure at 300 K, however, yields fully dissociative adsorption of both atomic N and O. The orientation dependence of this reaction indicates a strong influence of atomic steps. The atomic N is quite tightly bound and desorps thermally at higher temperatures than oxygen

Emotion talk during mother-child reminiscing and book sharing and children’s socioemotional competence: Evidence from Costa Rica and Germany

This paper examined cross-cultural differences in emotion talk during reminiscing and book sharing and its link with children’s social problem-solving skills. Twenty-six Costa Rican mothers, representing the cultural model of autonomy-relatedness, and 26 German mothers, representing the cultural model of autonomy, discussed a negative past event and read a book with their four-year-old children. Children’s social problem-solving skills were also assessed. Results indicated that cultural contexts did not differ in complexity of emotion talk but Costa Rican dyads talked overall more about emotions than German dyads. Costa Rican dyads marked others as the agents of emotions more often than German dyads, but groups did not differ in the frequency of emotions referring to the child as the agent. Across cultural contexts, mother-child dyads provided significantly more emotional attributions than emotion explanations during book sharing, but not during reminiscing. Emotion talk was related to children’s social problem-solving skills for the Costa Rican group, but not for the German group. The higher the amount of emotion talk in Costa Rican dyads during reminiscing, the lower the child’s social problem-solving skills. Results are discussed in light of the culture-specific nature of emotion socialization and its relation to children’s socioemotional development.Universidad de Costa Rica/[723-B7-219]/UCR/Costa RicaKompetenzzentrum frühe Bildung/[]/KFB/AlemaniaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Sociales::Instituto de Investigaciones Psicológicas (IIP