ML Of Atoms Research Articles

Morphology of the rutile (110) surface after low sputter dose and annealing

The kinetics of diffusion-mediated smoothing of a ${\mathrm{TiO}}_{2}$ rutile (110) surface is studied over atomic length scales, by using a spot profile analysis of low-energy electron-diffraction data to characterize the morphology of the surface during thermal annealing. After the random removal of less than 1 ML of atoms by sputtering with an argon ion beam, the interface width and the distribution of terrace heights were found to stay nearly constant during annealing at 800 K, with terraces at just two heights making up \ensuremath{\approx}90% of the surface area over lateral distances of \ensuremath{\approx}400 \AA{}. Meanwhile, the coarsening of this nearly two-dimensional island structure is characterized by the growth of the average terrace width l from 20 to 60 \AA{} with annealing time, following $l\ensuremath{\sim}{t}^{\ensuremath{\beta}}$ with exponent $\ensuremath{\beta}=0.24\ifmmode\pm\else\textpm\fi{}0.04.$ In addition, the stability of an 8% occupation of a third terrace height indicates negligible diffusion flux between layers during annealing. These results are compared with existing models for the microscopic dynamics involved.

Au onW(001):Change in structure and orientation

Ultraviolet photoemission spectroscopy (UPS) measurements during the deposition of Au on form$\mathrm{W}(001)$ at 150 K show that over 30 ML of Au have to be deposited before the electronic structure of the deposit stabilizes. This large film thickness before a stationary growth situation is reached is a result of the large misfit between various orientations of Au with the $\mathrm{W}(001)$ surface. The orientation at characteristic thicknesses is analyzed with a combination of reflection high-energy electron diffraction, x-ray photoelectron diffraction (XPD), and UPS. The first 3.5 ML form a pseudomorphic body-centered-tetragonal layer that is thermally stable at least up to 900 K. The surface layer of the pseudomorphic triple layer shows a hexagonal reconstruction and consists of 1.5 ML of atoms. After this initial range, the film continues to grow in the bcc (001) orientation up to 10 ML at both 150 and 300 K. Beyond this coverage the orientation changes and a fcc (001)-oriented film is observed for coverages above 23 ML. At 150 K, a (111) orientation appears between 10 and 23 ML, which can be obtained in a pure and perfect form by annealing at 600 K. The transition to fcc (001) shifts to higher coverages with increasing deposition rate.