Surface Science Letters最新文献

Growth of Pb on $\text{Ru}\text{(10}\text{1}\text{0)}$ has been investigated at 140 and 300 K by LEED and Auger spectroscopy. The interfacial contact layer evolves through a series of ordered Pb phases “split (2×1)”, c(3×2), c(4×2) - in which the Pb atoms assume their “normal” size. Beyond the monolayer point a c(2×4) phase appears, corresponding to development of compressed quasihexagonal lead overlayer. This phase is followed by a most unusual structure: a (0001)-oriented multilayer film of hexagonally close-packed lead in which the interatomic spacing is much smaller (16%) than that in fcc bulk lead. Furthermore, this spacing ($\text{3.02 ± 0.06}\text{A}\text{̊}$) is ∼ 9% less than that characteristics of the high pressure hcp phase of bulk lead and therefore corresponds to the most dense form of metallic Pb known. The ultra-high density phase was stable at 300 K and was still observable after heating to ∼ 600 K. No transitions to “normal” hcp or fcc structures occurred over the whole coverage range studied - up to 30 monolayers. These ultra-dense Pb films are also unreactive towards oxygen. In contrast to this, normal density, oxidisable, fcc Pb films are formed other fcc substrates, indicating that the structural and electronic properties of the ultra dense Pb films depend critically on the specific structure of the Ru(10$\text{1}$0) substrate.

Oxygen adsorption on Ag(110) and Cu(110) surfaces has been investigated by means of first-principles total-energy, and force calculations for repeated-slab geometries within the local density approximation (LDA). As for the chemisorption structure, the added row model speculated by the obserbed STM images is confirmed to be one of the stable structures, if bucking of the AgOAg added row and some distortions of the substrate structure are allowed. The adsorbed oxygen atom and noble metal atoms in the added row and in the surface first-layer are relaxed toward the configuration of the minimum total energy in terms of steepest descent method. Moreover comparing the optimized geometrics of the added row model of Ag(110)(n × 1)−O (n = 2, 3) and Cu(110)(2 × 1)−O, we obtain an important clue for the mechanism of the difference in the formation modes of the added row on Ag(110) and Cu(110) surfaces.

We report the formation of an Fe oxychloride species at the surface of an O- and Cl-covered Fe polycrystalline surface below 230 K under UHV conditions. Our data show that FeOCl (amu 107) desorbs at 230 K. For FeCl₂ (amu 126) desorption, two desorption peaks are observed at 230 and 620 K in the presence of chemisorbed oxygen. In the absence of oxygen, only one FeCl₂ desorption peak at 620 K is observed. Auger electron spectroscopy and temperature programmed desorption studies reveal that the reaction leading to Fe oxychloride formation involves dissociatively adsorbed O and Cl at the Fe surface. These results indicate that chemisorbed or low coordinate oxygen plays an important and previously unsuspected role in chloride-induced corrosion at ferrous surfaces.

The B/Si(110) system with B coverages below 0.1 ML has been studied by LEED-AES (low energy electron diffraction-Auger electron spectroscopy). The ($\text{10}\text{0}\text{− 2}\text{1}$) reconstruction has been found to form at above 0.07 ML of B. This reconstruction is a particular case of a more general type of superstructures with basic translation vectors, $\text{a}{}_{\mathrm{s}}\text{=(n/2[1}\text{1}\text{10]}$ and $\text{b}{}_{\mathrm{s}}\text{=[1}\text{1}\text{11]}$. Reconstructions of this type are observed for a number of adsorbates (Ge, AL, Sb) on the Si(110) surface. The factor n equals 8, 9 and 14 for Ge/Si(110), Al/Si(110) and Sb/Si(110) reconstructions, respectively. For the B/Si(110) reconstruction n = 10, but ordering along the [$\text{1}$10] direction is not perfect while the periodicity along the [1$\text{1}$1] direction is well-defined. The deposition of 0.05 to 0.15 ML of Al onto the B/Si(110) surface produces a well-ordered structure of the above-described type with n = 12. The deposited Al atoms replace the B atoms reducing the boron surface concentration.