http://w0.rz-berlin.mpg.de/hjfdb/pdf/260e.pdf

Metal deposits on well-ordered oxide films

Microscopic view of epitaxial metal growth: nucleation and aggregation

Morphological evolution during epitaxial thin film growth: Formation of 2D islands and 3D mounds

Self-organization of nanostructures in semiconductor heteroepitaxy

Estimating surface diffusion coefficients

The diffuse scattering of conduction electrons at a rough surface has a considerable contribution to the resistivity of thin films, which is well known as the classical size effect We have separated this contribution from other scattering mechanisms such as the phonon and bulk defect scattering by the following procedure: Silver was deposited at low temperatures (\ensuremath{\approxeq}130 K) onto a well-annealed relatively thick silver base layer (\ensuremath{\approxeq}24 nm), which has been deposited onto a Si(111)-7\ifmmode\times\else\texttimes\fi{}7 substrate During deposition the resistivity of the thin film was measured in situ, and afterwards the surface roughness was determined quantitatively with profile analysis of low-energy electron diffraction An increase of both resistivity and surface roughness was observed Such an increase of the measured resistivity must be due to the increase of surface roughness because there was no change in temperature or concentration of bulk defects With the measured surface roughness we are able to evaluate the additional resistivity without any free parameters The experiment reveals excellent agreement with the theoretical predictions

Surface roughness and conductivity of thin Ag films.

The influence of temperature on the morphology of both the homogeneous and the inhomogeneous Cu(311) surfaces is investigated by high-resolution low-energy electron diffraction. Analyzing the spot profile of the diffracted electron beam under various scattering conditions provides information about both the surface roughness and inhomogeneities as a function of temperature. From the reversible spot broadening under the out-of-phase condition, it is concluded that atomic steps may be created reversibly on the Cu(311) surface by increasing the temperature. The critical temperature, at which the surface goes from the smooth, low-temperature phase into the rough, high-temperature phase, is obtained from the vanishing of the central spike of the (00) spot at ${\mathit{T}}_{\mathit{R}}$=750 K. On the basis of a detailed analysis of the spot profile, we find that the height-height correlation of the Cu(311) surface cannot be described by the logarithmic behavior predicted for Kosterlitz-Thouless roughening. Instead of this behavior, in the low-temperature phase the height-height correlation saturates exponentially as the lateral distance goes to infinity, while it is characterized by a linear divergence for the high-temperature phase. Sulfur segregated at the surface has two effects: Large areas of the Cu(311) surface become amorphous and the step-atom density increases. The surface is still rough at room temperature even with small amounts of sulfur. With increasing sulfur coverage, the roughness due to inhomogeneities overwhelms the thermally induced surface roughness.

Thermal roughness of the homogeneous and inhomogeneous Cu(311) surface studied by high-resolution low-energy electron diffraction.

The surface morphology after deposition of Ag on Ag(111) at low temperatures (130–200 K) has been studied in detail with SPA-LEED (Spot-Profile Analysis of Low-Energy Electron Diffraction). The surface roughness Δ and the mean terrace size Γ have been quantitatively determined under various conditions. At 130 K the surface roughness Δ increases with coverage θ exactly according to the relationΔ =θ1/2, which indicates that the inter-layer diffusion can be neglected at 130 K. Although the mean terrace length decreases with increasing coverage θ (following an approximate power law ofГ ℍΘ−2/3) for all studied coverages, it is much larger than expected for a pure random or Poisson-growth mode without any diffusion of the adatoms. Therefore, Ag grows on Ag(111) at this temperature without interlayer diffusion but with intra-layer diffusion. The intralayer diffusion barrierEd has been determined by measuring the temperature dependence of the two-dimensional island density according to the nucleation theory (supposing a critical nucleus size of one). The obtained valueEc=0.18 eV agrees with the theoretical calculations and previous measurements. Furthermore, from comparing measured and Monte-Carlo-simulated (MC) surface roughness Δ at different deposition temperatures we obtain ΔE=0.05 eV as a lower limit for the additional barrier at steps.

SPA-LEED studies of growth of Ag on Ag(111) at low temperatures

Characterizing the roughness of epitaxial films by diffraction techniques with respect to the step density and the rms roughness is well established. For self-affine surfaces the morphology of growing films, however, is often characterized by the correlation length $\ensuremath{\xi}$ of the height-height correlation and the roughness exponent $\ensuremath{\alpha}$ governing the behavior at small lateral distances. Recently, it has been emphasized that for unstable growth conditions, characteristic lengths (average pyramid sizes) appear that produce an oscillating character of the height-height correlation. Here we investigate the influence of both kinds of correlations on the diffraction spots. The oscillating correlation causes a splitting of the diffuse shoulder into satellites. The satellite position and half-width show characteristic oscillations depending on the scattering condition. From the latter one can determine the roughness exponent $\ensuremath{\alpha}$. The correlation length $\ensuremath{\xi}$ and the characteristic length can be evaluated from the satellite half-width and position at the out-of-phase scattering condition taking into account the rms height $w$. This model has been applied to the statistical growth of Ag adlayers on Ag(111) at low temperatures where the satellites of the diffuse shoulder point to the formation of pyramids. From the phase dependence we obtain the roughness exponent $\ensuremath{\alpha}=$$\frac{1}{2}$. The step density and the correlation length $\ensuremath{\xi}$ increase with increasing coverage while no coarsening of the pyramid sizes is observed.

E. Z. Luo

Papers

Surface roughness and conductivity of thin Ag films.

Thermal roughness of the homogeneous and inhomogeneous Cu(311) surface studied by high-resolution low-energy electron diffraction.

SPA-LEED studies of growth of Ag on Ag(111) at low temperatures

Diffraction characterization of rough films formed under stable and unstable growth conditions

Epitaxial growth and thermal behaviour of Pb overlayers on Cu(311) studied by high-resolution low-energy electron diffraction