Growth Rate Anisotropy Research Articles

The effect of growth orientation on the morphology, composition, and growth rate of mercury cadmium telluride layers grown by metalorganic vapor phase epitaxy

We have measured the growth rate dependence of CdTe and HgTe layers in the growth surface direction. The growth mechanism of HgTe and CdTe were concluded to be heterogeneous, surface kinetic limited. The morphology of CdTe and mercury cadmium telluride interdiffusion multilayer process layers is found to be strongly effected by the large anisotropy of the CdTe growth rate. The best morphologies were found to be on surfaces having directions of maximum CdTe growth rates, with respect to surfaces of other crystallographic directions. A model for hillocks formation is given, based on the CdTe growth rate anisotropy. The different nature of twins stacking faults in (111)A and (111)B layers is explained by the different morphologies of these layers.

Simulation of Y-Ba-Cu-0 Epitaxial Growth and Microstructure Formation

ABSTRACTThe results of systematic computer simulations of the deposition and growth of Y-Ba-Cu-0 thin films is reported. The deposition process is modeled by means of a three-step Monte Carlo simulation incorporating one sorption deposition mode and two modes of film annealing addressing surface and bulk diffusion. The simulation is used to investigate the evolution of surface morphology and film microstructure, growth rate anisotropy, and the dependence of film texture on deposition parameters. Characteristic defects and surface morphologies observed by simulation are found to be in good agreement with those observed experimentally. It is observed that surface kinetics can dominate the evolution of film microstructure.

Toughness and Fatigue Crack Growth Rate of Textured Metals

The influence of anisotropy of crystallographic origin on both fracture toughness and the rate of stage‐II ductile fatigue crack growth in textured metals is discussed in terms of a plane‐strain small geometry change solution for plastic non‐hardening materials (a Prandtl‐type slip‐line field solution accounting for anisotropy). Results corresponding to FCC or BCC metals sliding, respectively, on {111} 〈110〉 or {110} 〈111〉 systems are presented. Remarkable effects of both texture toughening and fatigue crack growth rate anisotropy are predicted. Stronger effects are anticipated in more anisotropic metals (HCP).

Preferred Mineral Orientations Related to Magmatic Flow in Ophiolite Layered Gabbros

Detailed study of Shape Preferred Orientations (SPOs) and Lattice Preferred Orientations (LPOs) of olivine, clinopyroxene, and plagioclase have been carried out for samples of compositionally layered gabbro from the lower crustal section of the Oman ophiolite. These gabbros have a strong magmatic foliation and magmatic lineation which are oblique with respect to the compositional layering. The results of SPO analysis indicate that the rock fabric is due to a laminar viscous magmatic flow within the ophiolite magma chamber. LPO fabrics correspond to SPO fabrics proving that mineral shape anisometry corresponds to anisotropic growth rates controlled by crystal structure. Magmatic flow has been induced by a deformation including an important component of non-coaxial strain, as indicated by the monoclinic symmetry of the SPO fabric. It is proposed that the monoclinic symmetry may be used to determine shear sense during magmatic flow. Due to non-coaxial deformation in the magmatic state, the magmatic foliation would tend towards parallelism with compositional layering. The obliquity between magmatic foliation and compositional layering may thus provide a field criterion for magmatic shear sense determination.

Interaction between dislocations and cellular front of crystallization: (0001)SiO 2 face

The interaction between dislocations and a groove on the cellular growth front has been analyzed. It is shown that under certain conditions the dislocation outcrop at the groove bottom may be energetically advantageous. As a result, dislocations in the grown crystal should be located in the boundaries between neighboring cells. The criteria for dislocation capture by the groove are formulated. These criteria essentially depend on the crystallographic anisotropy in the dislocation energy and growth rate. The general theory is applied to the analysis of the dislocation structure formed by the pinacoidal quartz face growing from hydrothermal solutions. With this aim the anisotropy in growth rate in measured on concave spherical surfaces. The dislocation energy and its anisotropy for the [21̄1̄0], [21̄1̄1], [21̄1̄1̄], and [0001] Burgers vectors was calculated with the use of elastic constants at 350°C. The effects caused by dislocation piling along the boundaries and the corresponding experimental data are analyzed.

Model for molecular-beam-epitaxy growth over nonplanar surfaces

A model for molecular-beam-epitaxy growth is proposed to describe the morphology formed on a nonplanar, profiled surface that may consist of multifaceted crystal structures. Anisotropy of growth rate is introduced as a main factor for explaining the observed growth morphology. We show that on the nonplanar surface, the migration of adatoms modifies the growth rate at each point of the growing surface and thus affects the formation of the morphology within the range of migration length. The model can successfully describe the growth behavior including the development of sharp facet edges, since it is formulated in terms of a difference (rather than differential) equation which does not require the continuity of surface slope. The morphology simulated on the basis of this model agrees to experimental results of GaAs growth.

Study of the growth mechanism in the ADP‐type anion‐doped crystals

AbstractA simultaneous simulation of the growth process in the A(K)DP‐type anion‐doped crystal and growing of this crystal from aqueous solution under controlled conditions has made it possible to analyse the mechanism of impurity influence on the growth rate of various crystal faces. The anisotropy of the face growth rate and the capture coefficient of various impurities by the faces have been determined by the difference in dissolution heats and in sizes of replacing ions. The increase in energy change, when the ion in a solution enters a crystal, causes an increase in the growth rate and the capture of impurities by the face with the largest change. Breaking of one of the joined faces and increased growth of another one resulted in forming of the new faces, i.e. in changing crystal morphology.

Grain growth and re-orientation of phyllosilicate minerals during the development of slaty cleavage in the South Kitakami Mountains, northeast Japan

Using X-ray diffraction analysis, the mutual relations among illite crystallinity, degree of preferred orientation of chlorite, grain size change of chlorite and illite during metamorphism and development of slaty cleavage have been investigated for argillaceous rocks in the South Kitakami Mountains, northeast Japan. The metamorphic grade of IC (illite crystallinity index) = 0.29 is a critical one, beyond which the homogenization of chlorite composition, coarsening of chlorite and illite grains and degree of preferred orientation of chlorite are abruptly advanced. Grain coarsening is also promoted by the development of slaty cleavage, especially in the range of coarser grain size. The oriented growth by the effects of both the anisotropy of intrinsic growth rate of mineral grains and that of the environment in which grains grow, is considered to bring about the preferred orientation of chlorite and illite.

On the growth of two dimensional crystals. I. Fluctuations and the relation of step free energies to morphology

Some fundamental aspects of crystallization of two dimensional (2D) crystals are examined, including an analysis of the fluctuations in step positions, computer simulation results for the step density and growth rates, and analysis for predicting crystal shapes. A discussion is given of whether nucleation can occur on the 1D surface of a 2D crystal. During the course of the paper it is shown that a more appropriate description, for any infinite 1D surface, is of a step density related to the equilibrium value and a growth rate which is proportional to the density and speed of these steps. The speed depends essentially linearly on the net thermodynamic driving force for crystallization. (This description is not appropriate for a 2D surface since the equilibrium step density can then be zero.) Nevertheless, one can define a criterion, depending both on the density of steps and on the extent of the fluctuations in step positions, for a regime of growth with some similarities to nucleation (1D nucleation). Kinetic (nucleation) theories for polymer crystallization, using a rate equation approach, have implicitly assumed the conditions for 1D nucleation to hold. Even when the conditions do not hold, the results of this rate equation approach are in reasonable agreement with the simulation results (though a rather curious discrepancy of a factor of 21/2 occurs since the rate equation approach omits a growth mediated approach to equilibrium). The agreement in general trend is shown to be the fortuitous consequence, in the rate equation approach, of neglecting both the enhancement of step annihilations caused by fluctuations and the creation of pairs of steps at cavities. If the latter effect is neglected but not the former, anomalous results can be obtained which violate thermodynamic principles. Growth rate results from simulation are obtained as a function of the obliquity of the growth face with respect to the principal directions in the lattice. These growth rate anisotropy data are used to predict the shapes of crystal outlines. Comparisons between these results and experimental observations on shapes of polymer crystals are made, and a preliminary account is given of how the step free energy per length of step decreases with increasing temperature. In general, the total step free energies tend to decrease as the crystal thickness increases for polyethylene.

Integrated optical bent waveguide with grown 45° mirror by selective liquid-phase epitaxy of GaAs

An integrated optical bent waveguide with as-grown 45° mirror is fabricated using nearly atomically smooth facets only. These facets are grown by single-step selective liquid-phase epitaxy of GaAs. The mirror orientation is automatically adjusted to the optimum angles since the waveguide on {100} substrate uses only the as-grown {111} and {100} crystal planes as waveguide walls and 45° mirrors. The technique for the mirror location control is described taking into consideration the growth rate anisotropy.

Silicon Selective Epitaxial Growth over Thick SiO2 Islands

Silicon selective epitaxial overgrowth from a seed area to thick SiO2 islands top surface using chemical vapor deposition method was studied. A single crystal silicon layer on SiO2 islands without stacking faults was obtained on {100} and {110} oriented wafers. Lateral to vertical growth ratio is influenced by the substrate orientation and the striped pattern sidewall orientation. Facet planes appearing at a lateral growth front are caused by the growth rate anisotropy.

Effect of a Liquid Phase on the Morphology of Grain Growth in Alumina

In this investigation we have studied how the presence of a liquid phase affects the grain morphology and grain growth kinetics in Al2O3 at 1800°C using the growth of both matrix grains and large spherical single‐crystal seeds growing into the matrix. The growth rates of the matrix grains were found to decrease in the following order: undoped Al2O3, AI2O3 with anorthite, AI2O3 with anorthite and MgO, and Al2O3 with MgO. Except for the samples doped with MgO alone, the matrix grains were faceted and appeared tabular in polished sections. In samples containing anorthite both with and without MgO, the single‐crystal seeds exhibit basal facets with continuous liquid films and slow growth in the 〈0001〉 relative to all other crystallographic directions. When only MgO is added, the growth of the single‐crystal seeds was not isotropic; however, no faceting was observed. We discuss how anisotropic growth rates caused by the anorthite additions can stimulate discontinuous grain growth in Al2O3.

Nucleation and growth of titanium silicide studied by i n s i t u annealing in a transmission electron microscope

We have studied the crystallization of sputter-deposited amorphous Ti-Si alloy thin films of different compositions. A versatile means of discriminating between phenomena occurring in the nucleation and subsequent growth stages was offered by in situ annealing in a transmission electron microscope. Nucleation of TiSi2 with the ZrSi2 structure was observed for all alloys studied (Ti:Si=1:2 to Ti:Si=1:3). The activation energy for nucleation was independent of composition. TiSi2 crystallites appeared to possess a rather high density of stacking faults, predominantly concentrated in the center of the crystallites. The character of these stacking faults was analyzed. The growth of TiSi2 was anisotropic in amorphous alloys up to a composition of Ti:Si=1:2.5; more silicon-rich alloys yielded isotropic growth. The anisotropy in growth rate, and the resulting morphology of the crystallites were related to the crystal structure. The crystallization of the amorphous alloy with the composition Ti:Si=1:2 proceeded via a polymorphous phase transformation. The Si-rich alloys crystallized through eutectic decomposition. This was clearly evidenced by a difference in the activation enthalpy for growth. Since the activation enthalpy for growth differed from the activation energy for nucleation, an influence of the heating rate on the microstructure of the completely crystallized alloy could be predicted. This, in turn, might affect the resistivity, roughness and transformation temperature to the C54 TiSi2 equilibrium phase.

On the interaction between order and a moving interface: Dynamical disordering and anisotropic growth rates

The way in which the velocity of a propagating interface determines the degree of surface disorder and the anisotropy of such interfacial velocities due to a crystalline lattice are examined using steady state solutions of the time dependent Landau–Ginzburg or Cahn–Hilliard equations. In the case of an interface described by two weakly coupled order parameters a divergence of the thickness of the surface disorder at a critical interfacial velocity is described. It is demonstrated that even for two surfaces with the same surface tension the growth rates may differ significantly due to a geometric factor arising from the underlying crystal lattice.

Anisotropic lateral growth in GaAs MOCVD layers on (001) substrates

For metalorganic chemical vapor deposition, a fast lateral growth rate is observed for the first time on (001) GaAs having round mesas. The lateral growth rate is greater than the vertical growth rate by a factor of 3–5. The lateral growth rates have anisotropy with respect to the crystallographic directions on the (001) surfaces. The fastest growth direction is the [110] and the slowest one is the [ 1 10]. The [110] and [ 1 10] growth rates were found to be strongly dependent on growth conditions, though the vertical one is independent. The [110] growth rate decreases with decreasing As pressure, while the [ 1 10] remains constant. As growth temperature increases, both the [110] and the [ 1 10] growth rates decrease. A simple model for the lateral growth mechanism is proposed from the consideration of atomic arrangements and the number of dangling bonds at [110] and [ 1 10] step sites. According to the model, the lateral growth rate is proportional to the number of bonds available for binding Ga atoms at step sites. The model can explain well the anisotropy in the lateral growth rate and its dependence on the growth conditions.

Crack propagation property and fracture surface of anisotropic rolled steel in fatigue. Examinations based on CT specimens.

Pulsating tensile fatigue tests were carried out, using CT specimens cut out in three different directions from a rolled steel having inclusions with a remarkable directionality, in spite of having slightly laminated structures. The crack growth rate in each directional specimen was measured by an optical microscope and the fracture surface was observed by a scanning electron microscope. The main results obtained are as follows. (1) the crack growth resistance is lowest in the case of SL specimens whose cracks propagate along the inclusions with directionality, but anisotropy of the crack growth rate is small in comparison with that of the fatigue limit. (2) The anisotropy of the crack propagation is clearly recognized also by observing the fracture surface in fatigue. (3) The effect of material strength on the crack growth rate is remarkable when the stress intensity factor range ΔK is large, while it is slight when ΔK is small.

Morphology of AgO Crystallites Deposited from Alkaline Solutions under Potential Step and Stimulated Pulse Potentiostatic Conditions

Different morphologies of deposits on substrates were obtained by varying the potential program of the crystallization process. The nucleation and growth of under the potential step conditions produced deposits in the form of spherical particles. After lowering the deposition potential, the growth rate anisotropy could be visualized. The strong anisotropy of the crystal growth rate was reflected by the formation of needles, blocks, pillars, and plates when the nucleation process was initiated by a potential pulse and the growth continued at very low overvoltage. Influence of the morphology of the basal layer on the nucleation and growth of has also been found. The deposits with different morphologies were obtained by changing the deposition potential and thickness of the deposit. The current‐time transients for nucleation and growth of the phase indicate an increasing amount of the oxides formed, as the number of charging‐discharging cycles increases. Increases in the surface roughness and in the number of available growth sites result in the increase in the oxidation charge used for crystallization of phase. Variation of the nucleation and growth transients for the deposition is correlated with scanning electron microscope observations.

The influence of anisotropy on the liquid-solid phase transitions in pure metals I. The case of Cd and Zn

Experiments reported in the literature indicate that γ sl is orientation dependent for Bi, Cd and Zn. On this evidence the reversible work which must be expanded for the homogeneous formation of a facetted nucleus in the bulk of the liquid or in its surface is calculated. Facetted nuclei are always favoured and nucleation in the surface requires imperfect wetting of the solid by its own melt and is encouraged by anisotropic growth rates and certain ranges of values of the anisotropy of interfacial energy. Surface nuclei can be pseudo-equiaxed or have the shape of thin disks which can be retained during growth. Experiments on the solidification of Cd and Zn droplets support the latter conclusion. The maximum possible anisotropy of interfacial energy, expressed as the angular deviation, from the basal orientation, of the planes bounding the nucleus is predictedto be approximately equal to 56° for Cd and Zn. This value is in the range of reported results and leads to γ {0.01}−L ⩾ 0.165 N m −1 and 0.214 N m -1 for the two metals, respectively. The former value is in excellent agreement with published data. It is concluded that the nuclei of Cd and Zn will be thin disks of basal orientation. They will grow towards thin floating rafts by simultaneous spreading and thickening.

Anisotropic growth in the olivine-spinel transformation of Mg 2GeO 4 under nonhydrostatic stress

The olivine-spinel phase transformation in Mg 2GeO 4 does not occur by a martensitic mechanism. The evidence, from samples transformed in a Griggs-type solid medium deformation apparatus, are: 1. (1) lack of microstructural features in the olivine phase which can be specifically associated with a martensitic mechanism 2. (2) the orientation relationship between the two phases that is predicted by the martensitic mechanism does not occur nor is there any apparent consistency of relative orientations 3. (3) application of a differential stress to the transforming sample resulted in an anisotropic growth rate for the spinel phase indicating that growth was externally controlled rather than crystallographically controlled. Anisotropic growth of the spinel phase results in elongation of the residual olivine phase grains in the plane normal to the direction of maximum principal compressive stress. A velocity ratio of 1.7 −0.7 +5.4 has been determined for the growth rate of the spinel from measurements on residual olivine grains. The interphase grain boundary in samples transformed under stress has cusp-shaped fingers of spinel with a blunt end separated by thin spikes of olivine. Samples transformed isostatically do not exhibit this feature providing further confirmation of anisotropic growth of the spinel. The preferred growth of the spinel is consistent with a theory of phase transformation under nonhydrostatic stress. The predicted spinel finger shape based on this theory is generally consistent with observed shapes except for the blunt end. The discrepancy may be due to surface energy which has not been considered here, or to local deviations of the applied macroscopic stress.

CVD silicon structures formed by amorphous and crystalline growth

Amorphous and crystalline growth of silicon by chemical vapour deposition (CVD) via silane in hydrogen at atmospheric pressure is investigated as a function of temperature (560–900°C) and deposition rate (0.003–2 μm/min) by in situ optical reflectivity and emissivity techniques, and after growth by X-ray diffraction and microscopy. The structure of the amorphous grown films is to a large extent governed by solid-state transformations (a-Si:H → a-Si; a-Si → c-Si) during and after deposition in the temperature range studied. If solid-state crystallization occurs, the resulting amorphous and crystalline regions can be shown by bevelling the sample. Different crystallization modes (unidirectional, three-dimensional) are related to different crystallographic texture and grain size of the resulting material. For the case that the crystallization process obeys a particular Avrami kinetics ( A, 3) the remaining overall amorphous layer thickness is calculated as a function of the time of growth. The internal and external structure of films formed by crystalline growth is related to growth rate anisotropy. The growth rate and the temperature at the transition between crystalline and amorphous growth are mutually related by the solid-state crystallization kinetics ( E act = 5.4 eV).