-
[show abstract]
[hide abstract]
ABSTRACT: The lateral growth of an isolated nucleated facet is studied using a simple two-dimensional step model. An effective Hamiltonian that causes a planar surface to phase separate into facets and step bunches is proposed. The motions of the steps are determined by the relaxational dynamics of the effective Hamiltonian with and without a local conservation requirement. An even simpler mean-field-like model is used to illustrate the mechanism of the experimentally observed constant-velocity facet tip propagation. Numerical calculations using thermodynamic and transport coefficients previously measured give good agreement with experiments under the local conservation requirement.
Phys. Rev. B. 03/1997; 55(12).
-
[show abstract]
[hide abstract]
ABSTRACT: Theoretical and experimental studies of the rate of decay of metastable structures are compared quantitatively. The effect of decay mechanism, size, and periodicity of the structure on the rate of decay is evaluated within both a coarse‐grained step‐based model and a continuum model. For high‐amplitude structures, the decay scales with size (N) and time as (t/N<sup>α</sup>)<sup>-β</sup>. The exponents α and β depend on the mass transport mechanism. The size scaling is α=4 for locally conserved diffusive flux and α=2 for locally nonconserved flux. The time scaling exponent is β=1/5 for diffusive limited mass transport and β=1/4 for step attachment limited mass transport. Experiments were performed on metastable structures of controlled sizes 3–5 nm in height, prepared by direct current heating on Si(111). Quantitative agreement with theoretical predictions of both scaling (α=4.3±0.5, β=0.2-0.3) and absolute rate of decay were obtained. © 1996 American Vacuum Society
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1996; · 1.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The step morphology of clean Si surfaces has been studied under conditions of thermal etching in the temperature range 950 – 1250°C. Kinetic-bunching of steps is caused by direct current in the step-down direction around 950°C. By comparing the rate of thermal decay of these structures with and without direct current, the electromigration force causing this step bunching is estimated to be due to an effective charge of less than or approximately 0.01 electron units. Around 1150°C, step-bunching is caused by direct current in the step-up direction. By analysis of the patterns of step structure, the effective charge of the driving force is found to be approximately -0.1 electron units. Oxygen-induced etching of Si(001) and Si(111) has been studied in the temperature range of 700 – 900 °C, and at a pressure of 5 × 10−7 torr, conditions under which the surface is etched by the desorption of SiO. On Si(001), the original narrow distribution of double-layer height steps is preserved during the oxygen-etching process. On Si(111), the original narrow distribution of mixed single- and triple-layer height steps changes dramatically during oxygen-etching, leaving wide terraces of flat (111) surface separated by regions of high step density. At low etching temperatures (700°C), the steps remain straight within the step bunches and retain their distinct character as single- and triple-height steps. However, following higher temperature etching, the steps begin to merge into facets in the vicinity of defect structures. Following etching at the highest temperatures studied (815 and 830°C), the pinning action of the defect structures becomes apparent, and the pinned step-bunches become identifiable as (113) facets.
MRS Proceedings. 12/1995; 466.
-
[show abstract]
[hide abstract]
ABSTRACT: Low‐energy electron diffraction (LEED) has been used to study the influence of steps and of temperature variation on the formation of ordered islands of CO on the (001) surface of ruthenium. The clean surface was found to have steps two atoms (one hcp unit cell) high separated by terraces with an average width between 135 and 270 Å. Widths of the beam profiles for the CO overlayer were measured as a function of coverage at 100 and 310 K. The coverage dependence requires that there be increasing numbers of islands per terrace at decreasing coverages. The temperature dependence of the overlayer was measured also. The frequency of the frustrated translational motion of the CO admolecules parallel to the surface is estimated to be 45 cm−1. At fractional (ϑ) coverages up to 1/6, the ordered islands of CO disorder substantially below the desorption temperature. At ϑ = 1/3, disordering is much less marked. The disordering behavior depends strongly on the distribution of sizes of islands in the overlayer. The correct distribution was determined and used to calculate the island sizes as a function of coverage. The mean number of CO molecules per island is 1000 at ϑ = 1/6, 500 at ϑ = 0.14, and 300 at ϑ = 0.12.
The Journal of Chemical Physics 01/1982; 76(2):1150-1161. · 3.33 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A Monte Carlo simulation has been carried out to describe two‐dimensional order–disorder phenomena. The model contains (attractive) first, (repulsive) second, and (attractive) third neighbor pairwise interactions. The special case of oxygen chemisorption on a tungsten (110) surface, on which an ordered p (2×1) overlayer is formed at low surface temperatures, is considered explicitly. From the measured order–disorder transition temperatures at both quarter‐ and half‐monolayer surface coverages, (nonunique) values of the three pairwise interaction energies have been determined. These pairwise interaction energies have been used to determine the variation in the total interaction energy, the heat capacity and the entropy with surface temperature.
The Journal of Chemical Physics 05/1978; 68(10):4688-4693. · 3.33 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Overlayer structures of CO on Ru(001) have been studied at low temperatures (100-300 K) using LEED. A model which involves repulsive CO-CO interactions and relative homogeneity of the Ru surface with respect to adsorption energy has been proposed to explain the experimental observations.
Surface Science.
-
[show abstract]
[hide abstract]
ABSTRACT: We report quantitative measurement of terrace size as a function of annealing time for step bunching induced by direct current heating in the step-down direction for the temperatures 945°C and 1245°C. This result is shown to be inconsistent with simple models of step bunching in which there is a temperature-independent electromigration force on diffusing surface atoms. Deposition of Si atoms onto the surface held at 945°C with current running in the step-down direction slows the step bunching. By estimating the parameters governing step flow from experimental observations, this result is shown to be inconsistent with simple models of step bunching incorporating an electromigration force as the source of diffusional anisotropy. The evolution of step bunching was monitored by measuring the growth of the terrace sizes revealing a functional form of tα, with α∼0.5.
Surface Science.
-
[show abstract]
[hide abstract]
ABSTRACT: In an attempt to determine the influence of the presence of adjacent islands on LEED beam profiles, an excluded area model has been proposed to describe the relative positions of ordered islands on a crystal surface. On the basis of this model, overlayers of different island density have been created on a finite lattice using a simple computer algorithm. The LEED from these overlayers has been calculated kinematically. Although the placement of the islands is not random, this does not perturb the LEED beam profile observably. Therefore, the kinematically diffracted intensity depends solely on the distribution of island sizes. Using this result, the intensity and half-width as functions of coverage have been calculated for one model of island growth.
Surface Science.
-
[show abstract]
[hide abstract]
ABSTRACT: Instabilities in step structure induced by direct-current heating have been measured using STM on Si(111) surfaces with an equilibrium step separation of approximately 1500 Å. The two-dimensional structure of kinetically formed step bunches and associated “crossing arrays” of single-height steps shows qualitatively good agreement with predictions of a generalized theory of step-flow instability. Quantitative analysis of the structures is consistent with the theory. The result provides the first experimental determination of an effective anisotropy ratio governing kinetic step bunching. The measured value of this anisotropy ratio is 0.20 ± 0.03.
Surface Science.
-
[show abstract]
[hide abstract]
ABSTRACT: The rate of thermal decay of a metastable sawtooth morphology on Si(111) is greatly accelerated by the application of a bulk direct current in the “uphill” direction. STM measurements of the rate are compared with a mesoscopic theory of surface mass transport incorporating an effective surface electromigration force on the diffusing species. Quantitative agreement with the experimental observations is obtained for an effective charge ≤ 0.01 electron charge at 900°C.
Surface Science.
