Thermal Roughening Transition Research Articles

Two Phase-Diagrams of the Thermal Roughening Transition in Anodic Dissolution of Polycrystalline Nickel

Two Phase-Diagrams of the Thermal Roughening Transition in Anodic Dissolution of Polycrystalline Nickel

Indication of thermal roughening in the retrieved mean inner potential across a Σ5 grain boundary in SrTiO3 annealed at different temperatures

We have measured the mean inner potential depth at a Σ5 grain boundary in a SrTiO3 bicrystal by reconstructing the exit-face wave function from an image focal series collected by transmission electron microscopy. We find that, as the annealing temperature increases, the potential depth at the grain boundary exponentially increases. We interpret the temperature dependence of the potential depth as the signature of a grain-boundary thermal roughening transition.

Grain Growth Stagnation Caused by the Grain Boundary Roughening Transition

Molecular dynamics simulations of bicrystals show that grain boundaries undergo a thermal roughening transition, and the grain boundary mobility increases abruptly when the boundary roughens. The roughening transition temperature varies widely from boundary to boundary, ranging from less than 0.4 to more than 0.9 of the melting temperature. Thus, at typical annealing temperatures we expect polycrystals to contain both smooth (slow) and rough (fast) boundaries, with the fraction of each type varying with temperature.

Thermal roughening transition of a dissolved nickel surface

A thermal roughening transition in a polycrystalline nickel surface dissolved anodically by a rectangular pulse current is found. The drastic change in normalized dissolution mass at the transition temperature is shown to be consistent with that in surface roughness such as a smooth or rough surface. The normalized dissolution mass below the transition temperature exponentially decreases with the frequency of the rectangular pulse current and asymptotically approaches a fixed value much less than 1.0. The normalized dissolution mass above the transition temperature is almost equal to 1.0 irrespective of the frequency. The frequency dependence of the normalized dissolution mass is described by an electric circuit model equivalent to an electric double layer.

Kinetic roughening of a Σ5 tilt grain boundary in SrTiO 3

The grain boundary kinetics of a SrTiO 3 bicrystal with a misorientation relationship of 36.8°/[1 0 0] (Σ5) is examined at elevated temperatures by in situ high-resolution transmission electron microscopy. At 973 K, the grain boundary migrates by the propagation of atomic steps with a height of half a unit cell (∼0.2 nm), but at 1173 K, it becomes rough and advances without the requirement of steps. All the temperatures examined are below the thermal roughening transition temperature of the grain boundary. These results give a clear indication of grain boundary kinetic roughening. We suggest that our present results may lead to the development of a unifying framework for previously suggested grain boundary migration mechanisms.

Energetics of Si(001)

A classical thermodynamic description of a surface requires the introduction of a number of energetic parameters related to the surface steps. These parameters are the step free energy, the kink creation energy, and the energetic and entropic interactions between steps. This review will demonstrate how a statistical analysis of scanning tunneling microscopy images of stepped surfaces can provide appropriate values of these fundamental energetic parameters. The Si(001) surface is used as a model system. In order to illustrate the significance of these energetic parameters, two morphological surface phase transitions are discussed, namely, the thermal roughening transition and the orientational phase diagram.

Dynamic roughening: Nucleation and stochastic equations

A crystal surface, which in equilibrium shows a thermal roughening transition, may roughen, under growth conditions, beneath the equilibrium transition temperature. After discussing a simple nucleation approach, this topic is treated from a point of view based on the Chui–Weeks stochastic differential equation. Numerical solutions are presented. Special care has been made in order to get a reliable algorithm and a correct sampling for numerical integration. Scaling properties are also discussed: they appear to be essential to choose good values of the parameters ν, Y, D. A finite size effect in equilibrium, revealed by numerical computations and related to dynamic roughening, is discussed. The ratio D/ ν between the coefficients of the noise and Laplacian terms plays the role of temperature; off equilibrium, the dependence of the growth velocity on the flux and on the strength of the layering potential shows a non-trivial, non-linear behaviour, going over from a Becker–Döring to a Wilson–Frenkel growth mode.

Surface energetics and thermal roughening of Ag(115) studied with STM movies

We present a high-speed scanning tunneling microscope ~STM! study of the energetics and the thermal roughening transition of the Ag~115! surface. Using a statistical analysis of large numbers of STM images we directly determine the kink creation energy and the step interaction energy. From these two energies we predict the roughening temperature after the terrace-ledge-kink model of Villain et al. This prediction is compared with an experimental estimate of the roughening temperature, obtained from STM observations at elevated temperatures. In addition, we derive an interaction energy for two neighboring kinks. @S0163-1829~96!50220-1#

First-order thermal roughening of normal alkane crystals.

In this paper a study of the critical behavior of the thermal-roughening transition occurring at the {110} faces of odd-numbered n-paraffin crystals in n-hexane solution systems is presented. It follows from our measurements that the edge free energy, the order parameter of the roughening phase transition, remains constant when the temperature T is lower than the roughening temperature ${\mathit{T}}_{\mathit{r}}$, and abruptly vanishes at T=${\mathit{T}}_{\mathit{r}}$. (${\mathit{T}}_{\mathit{r}}$=273.260 K.) This critical behavior of the order parameter shows the character of a first-order phase transition, rather than the conventional infinite-order phase transition of the Kosterlitz-Thouless type. An explanation of this observation is suggested in terms of the change of the motional state of solid molecules in the interfacial phase.

Modification of surface structures and roughening phase transition in Pb(110) by impurities

Using high-resolution low-energy electron diffraction, we show that the thermal roughening transition of a clean unreconstructed Pb(110) surface can be altered by impurities in the surface. The flat surface becomes a two-level regular terrace structure (1D) along the close-packed direction above 350 K with terraces modeled by a cut-off geometric distribution. The original Kosterlitz-Thouless roughening transition at 415 K for the clean surface was delayed until 480 K and the transition was irreversible due to the change in the amount of impurities in the surface.

Modification of surface structures and roughening phase transition in Pb(110) by impurities

Using high-resolution low-energy electron diffraction, we show that the thermal roughening transition of a clean unreconstructed Pb(110) surface can be altered by impurities in the surface. The flat surface becomes a two-level regular terrace structure (1D) along the close-packed direction above 350 K with terraces modeled by a cut-off geometric distribution. The original Kosteriitz-Thouless roughening transition at 415 K for the clean surface was delayed until 480 K and the transition was irreversible due to the change in the amount of impurities in the surface.

Growth of rough surfaces

The growth of objects with rough surfaces is a common phenomenon. We describe several models used in the study of the temporal evolution of fluctuating interfaces and then we explain the dynamical scaling in this class of growth models with self-affine surfaces. The recent progress in this field is reviewed. Much emphasis is put on roughness properties and in particular on a possible kinetic roughening transition — a nonequilibrium analog of the thermal roughening transition. Both analytical and numerical results for scaling exponents are summarized and indications of a phase transition in some models are discussed.

Thermal roughening studied by scanning tunneling microscopy

We have used scanning tunneling microscopy to observe the thermal roughening transition at the Ag(115) surface. For this purpose, a scanner and crystal assembly was employed that minimizes the lateral thermal drift of our microscope. Images were taken from room temperature, where the surface was smooth, up to 260 °C, where the surface is in the rough state. The topographs vividly demonstrate how the stepped metal surface goes through its roughening transition by the proliferation of kinks in the step edges. The roughening temperature of Ag(115), TR, is estimated to be 78±20 °C.