Polymorphic crystalline wetting layers on crystal surfaces

2021 ◽  
Author(s):  
Xipeng Wang ◽  
Bo Li ◽  
Mengmeng Li ◽  
Yilong Han
Keyword(s):  
Crystal Surface ◽  
Surface Phenomena ◽  
Surface Wetting ◽  
Crystal Surfaces ◽  
Crystalline Layer ◽  
Coherent Interface ◽  
Wetting Layers ◽  
Double Surface ◽  
Surface Crystal ◽  
Surface Layer Thickness

Abstract Analogous to surface premelting, we propose that a crystal surface can undergo a pre-solid-solid transition, i.e. developing a thin polymorphic crystalline layer before reaching the solid-solid transition temperature if two crystals can form a low-energy coherent interface. We confirm this in simulations and colloid experiments at single-particle resolution. The power-law increase of surface layer thickness is analogous to premelting. Different kinetics and reversibilities of surface-crystal growth are observed in various systems. Surface crystals exist not only under thermal equilibrium, but also during melting, crystallization, and grain coarsening. Furthermore, the premelting and pre-solid-solid transition can coexist, resulting double surface wetting layers. We hypothesize that such surface phenomena exist in atomic and molecular crystals, which provide a novel way to tune material properties.

scholarly journals Coverage dependent adsorption sites in the K/Cu(100) system: A crystal truncation rod analysis

1993 ◽  
Vol 208 (1) ◽  
Author(s):  
H. L. Meyerheim ◽  
I. K. Robinson ◽  
V. Jahns ◽  
P. J. Eng ◽  
W. Moritz
Keyword(s):  
Crystal Surface ◽  
High Coverage ◽  
Adsorption Sites ◽  
System A ◽  
Crystal Truncation Rod ◽  
Surface Crystal

AbstractThe analysis of the intensity along the diffraction rods normal to the crystal surface (crystal truncation rods) has been used to analyse the adsorption sites of potassium atoms adsorbed atAt high coverage (

scholarly journals Limitations of LEED-Structure Determination of Reconstructed Crystal Surfaces

1982 ◽  
Vol 37 (10) ◽  
pp. 1103-1118 ◽  
Author(s):  
H. Jagodzinski
Keyword(s):  
Structure Determination ◽  
Crystal Surface ◽  
Dimensional Space ◽  
Point Group ◽  
Two Dimensional ◽  
Crystal Surfaces ◽  
Difficult Situation ◽  
3 Dimensional ◽  
Lattice Constants

Although a strictly ordered reconstructed crystal surface may have the two-dimensional symmetry prescribed by the bulk (two-dimensional subsymmetry of the 3-dimensional space group), it belongs more frequently to a subgroup. In the LEED-pattern a lower symmetry of the translation group can easily be detected on account of the superstructure reflections observed. In this case anti-phase domains can hardly be avoided. An even more difficult situation arises if the symmetry of the point group is violated, although the symmetry of the diffraction pattern is not altered at the end of the reconstruction. Twin domains without changes of lattice constants have to be taken into account.Dynamical scattering of anti-phase domains is calculated by applying the "Cluster embedded chain"-method for various distributions of domains. It is shown that the incoherent superposition of scattering amplitudes, normally applied in LEED-calculations may lead to serious errors in structure determination. This effect is even more pronounced for twin domains. As an example we discuss the reconstruction of the (001)-surface of Si and Ge, and show that the wellknown (2 X 1)-structure is an averaged structure only, consisting of anti-phase domains with the (4 x 2)-structure. It may be concluded therefrom that none of the present model structures of this reconstruction agrees with this experimental observation.

Vacancy Mediated Diffusion at Surface-Confined Atomic Intermixing

2010 ◽  
Vol 159 ◽  
pp. 121-124 ◽  
Author(s):  
Michail Michailov
Keyword(s):  
Strain Energy ◽  
Crystal Surface ◽  
Adsorbed Layer ◽  
Surface Pattern ◽  
Spontaneous Generation ◽  
Crystal Surfaces ◽  
Adsorbed Atoms ◽  
Atomic Exchange ◽  
Surface Domains ◽  
Experimental Findings

The present study deals with diffusion behavior of adsorbed atoms on stepped crystal surfaces. In volume-immiscible systems, two-dimensional (2D) atomic intermixing at epitaxial interface could be completely blocked on step-free surface domains. This is a result of high diffusion barrier for direct atomic exchange between adsorbed layer and substrate. In that case, diffusion takes place exclusively across the steps of atomic terraces. In such systems, dynamic competition between energy gain by mixing and substrate strain energy results in diffusion scenario where adsorbed atoms form alloyed stripes in the vicinity of terrace edges. At high temperatures, the stripe width increases and finally completely destroys the terraces. This process leads to formation of alloyed 2D atomic islands on top of pure substrate layer. The atomistic Monte Carlo simulations reveal vacancy-mediated mechanism of diffusion inside atomic terraces as a result of spontaneous generation of vacancies at high temperature. Being in agreement with recent experimental findings, the observed surface-confined alloying opens up a way various surface pattern to be configured at different atomic levels on the crystal surface.

RESONANCE SCATTERING OF HIGH ENERGY ELECTRONS BY A CRYSTAL SURFACE

1996 ◽  
Vol 10 (02) ◽  
pp. 133-168 ◽  
Author(s):  
S.L. DUDAREV ◽  
M.J. WHELAN
Keyword(s):  
Crystal Surface ◽  
Theoretical Models ◽  
Resonance Scattering ◽  
High Energy ◽  
Crystal Surfaces ◽  
Molecular Beam Epitaxial ◽  
Semiconductor Crystals ◽  
High Energy Electrons ◽  
Reflection Electron Microscopy ◽  
Molecular Beam Epitaxial Growth

In this review we summarize the results of recent experimental and theoretical studies of the phenomenon known as resonance scattering of high-energy electrons from crystal surfaces. Resonance scattering is responsible for the appearance of bright features observed in reflection high-energy electron diffraction (RHEED) patterns and has found numerous applications in reflection electron microscopy and in RHEED studies of dynamics of molecular beam epitaxial growth of semiconductor crystals. The origin of the effect remained obscure for more than sixty years following the discovery of resonance scattering by Kikuchi and Nakagawa in 1933. Below we review theoretical models of the phenomenon which have been developed recently and which have provided the basis for understanding of the mechanism of resonance scattering. We conclude the review with a list of presently unsolved problems which, as we hope, can stimulate future progress in the theory of RHEED.

scholarly journals Effects of Systemic Fluoride and in vitro Fluoride Treatment on Enamel Crystals

2006 ◽  
Vol 85 (11) ◽  
pp. 1042-1045 ◽  
Author(s):  
H. Chen ◽  
A. Czajka-Jakubowska ◽  
N.J. Spencer ◽  
J.F. Mansfield ◽  
C. Robinson ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Crystal Surface ◽  
Direct Action ◽  
Crystal Surfaces ◽  
Surface Restructuring ◽  
Fluoride Treatment ◽  
Enamel Crystal ◽  
Dose Dependent

Systemically administered fluoride at a concentration of 75 ppm increases the surface roughness of developing enamel crystals in rats, which may be significant in advancing our understanding of the biological mechanism of fluorosis. Thus, the aim of this study was to investigate whether the increased surface roughness may be a result of surface restructuring by the direct action of fluoride at the crystal surface. We examined the fluoride dose-dependent roughening of enamel crystal surfaces in vivo, in the rat, and whether this roughening could be mimicked by the in vitro treatment of rat enamel crystals with neutral pH fluoride solutions. Our results showed that enamel crystal surface roughness increased after treatment with increasing fluoride ion concentrations, whether applied in vitro or administered systemically. This suggests a mechanism, alongside others, for the increased surface roughness of crystals in fluorotic enamel.

Approximate Models for Lateral Growth on Ice Crystal Surfaces during Vapor Depositional Growth

2020 ◽  
Author(s):  
Jerry Y. Harrington ◽  
Gwenore F. Pokrifka
Keyword(s):  
Crystal Surface ◽  
Supercooled Water ◽  
Lateral Growth ◽  
Ice Crystal ◽  
Constant Mass ◽  
Growth Mechanisms ◽  
Empirical Theory ◽  
Crystal Surfaces ◽  
Maximum Dimension ◽  
Deposition Coefficient

AbstractMeasurements show that after facets form on frozen water droplets, those facets grow laterally across the crystal surface leading to an increase in volume and surface area with only a small increase in maximum dimension. This lateral growth of the facets is distinctly different from that predicted by the capacitance model and by the theory of faceted growth. In this paper we develop two approximate theories of lateral growth, one that is empirical and one that uses explicit growth mechanisms. We show that both theories can reproduce the overall features of lateral growth on a frozen, supercooled water droplet. Both theories predict that the area-average deposition coefficient should decrease in time as the particle grows, and this result may help explain the divergence of some prior measurements of the deposition coefficient. The theories may also explain the approximately constant mass growth rates that have recently been found in some measurements. We also show that the empirical theory can reproduce the lateral growth that occurs when a previously sublimated crystal is regrown, as may happen during the recycling of crystals in cold clouds.

X-Ray Diffraction Contrast from Impurity Precipitates in CdS Single Crystals

1966 ◽  
Vol 10 ◽  
pp. 153-158 ◽  
Author(s):  
Jun-ichi Chikawa
Keyword(s):  
Strain Field ◽  
Crystal Surface ◽  
Bragg Angle ◽  
X Rays ◽  
Bragg Condition ◽  
X Ray Diffraction ◽  
Crystal Surfaces ◽  
X Ray ◽  
Impurity Doped ◽  
Free Plane

AbstractImpurity-doped crystals CdS(GaGl3) have been studied by X-ray topography. Some large precipitates are formed close to the crystal surfaces by annealing at 300°C. In the symmetrical Laue case, the precipitates show circular images (30-60 μ in diameter) due to the radial strains around the precipitates which consist of two semicircles separated by a contrast-free plane parallel to the reflecting plane. The observations indicate that the strain field between the crystal surface and precipitate is not responsible for the contrast, and that the images are formed by X-rays which are deviated from the Bragg condition for the perfect region and satisfy the Bragg condition in the strain field on the inside of the precipitate. One of the semicircles is formed by the incident X-rays with larger glancing angles than the Bragg angle and the other with smaller ones. It is concluded that this contrast is due to the strain around a convex lens shaped precipitate.

scholarly journals Interface Dynamics and Far-From-Equilibrium Phase Transitions in Multilayer Epitaxial Growth and Erosion on Crystal Surfaces: Continuum Theory Insights

2011 ◽  
Vol 1 (4) ◽  
pp. 297-371 ◽  
Author(s):  
Leonardo Golubović ◽  
Artem Levandovsky ◽  
Dorel Moldovan
Keyword(s):  
Phase Transitions ◽  
Epitaxial Growth ◽  
Crystal Surface ◽  
Equilibrium Phase ◽  
Continuum Theory ◽  
Mass Conservation ◽  
Crystal Surfaces ◽  
Theoretical Predictions ◽  
Far From Equilibrium ◽  
Interface Structures

AbstractWe review recent theoretical progress in the physical understanding of far-from-equilibrium phenomena seen experimentally in epitaxial growth and erosion on crystal surfaces. The formation and dynamics of various interface structures (pyramids, ripples, etc.), and also kinetic phase transitions observed between these structures, can all be understood within a simple continuum model based on the mass conservation law and respecting the symmetries of the growing crystal surface. In particular, theoretical predictions and experimental results are compared for (001), (110) and (111) crystal surfaces.

The rates of evaporation from different faces of rhombic sulphur

1952 ◽  
Vol 210 (1102) ◽  
pp. 291-309 ◽  
Keyword(s):  
Growth Form ◽  
Crystal Surface ◽  
Characteristic Temperature ◽  
Crystal Surfaces ◽  
Face To Face ◽  
Temperature Coefficients ◽  
Monoclinic Lattice ◽  
Different Temperatures ◽  
The Face ◽  
Rate Of Evaporation

The evaporation pressures of four faces of rhombic sulphur have been measured by a method which is a modification of the effusion technique for the measurement of vapour pressures of solids. The results in the temperature range 20 to 40° C show that each face has a characteristic, reproducible evaporation pressure, irrespective of the conditions under which the crystal was grown; that this evaporation pressure varies from face to face of the crystal; and that the activation energy for evaporation also varies, increasing with the reticular density of the face. From a consideration of the processes occurring at the crystal surface during evaporation, it was concluded that the condensation coefficients of the four faces are different, and that they have characteristic temperature coefficients. This was supported by some data on the growth form of crystals grown from solution at different temperatures, and it was concluded that it is possible that these four faces, with widely differing rates of evaporation, are all equilibrium faces of the crystal. Discontinuities were found to occur in the curves of log P against l/ T for two of the four faces above 40° C. It was suggested that these are due to the onset of rotation on the crystal surfaces at the temperatures concerned, and that for each face a transition occurs at the temperature at which its condensation coefficient reaches unity. The mechanism of evaporation proposed assumes that an evaporating surface always has an inexhaustible supply of molecular terraces and that the rate of evaporation is controlled by the rate of formation of ‘kinks’ on the edge of such a step. Two faces of the crystal were investigated at temperatures above 90° C. Transitions were found to occur in each case at a temperature below that of the transformation of the rhombic into the monoclinic lattice. This was interpreted as a formation of monoclinic crystallites on the rhombic surface.

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