Spiral Growth Steps Research Articles

Copper Pentagonal Micropyramids Grown by Mechanically Activated Electrodeposition

Abstract The formation of copper pentagonal micropyramids (PMPs) with high (multiatomic) spiral growth steps, which are grown by electrocrystallization with mechanical activation of the cathode, is studied experimentally. A new spiral-layer growth mechanism for the formation of such PMP is proposed. It is shown that PMPs grow on flat pentagonal microcrystals (PMCs) formed initially and containing fivefold twins with one of the twin boundaries being inclined by the angle of 35°16’ to the {110}-type substrate crystallographic plane. Such crystal geometry causes an inclined growth step on the PMC surface. The preferential deposition of metal atoms on this step leads to the spiral-layer PMC growth and the formation of PMPs with a structure inherited from the PMCs.

Analysis of the Spiral Step Structure and the Initial Solution Growth Behavior of SiC by Real-Time Observation of the Growth Interface

Microscopic real-time observation of the solution growth interface of SiC using Fe–Si solvent at 1673 K was successfully performed to understand the interface morphology at the initial stage of solution growth. The growth interface was composed of a number of domains with step–terrace structures originating from either spiral growth of 4H-SiC or two-dimensional island growth of other polytypes. The validity of the measurements of the step structures by bright-field and interference images was confirmed by ex-situ atomic force microscopy. In addition, the encounter between a spiral growth domain and steps from another spiral growth domain was observed, and it was found that a certain step height is needed to stop spiral growth by covering the spiral center.

Elementary steps at the surface of ice crystals visualized by advanced optical microscopy

Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional islands on ice crystal surfaces. When the steps of neighboring two-dimensional islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical two-dimensional nucleation theory does not support the appearance of multilayered two-dimensional islands. Hence, we concluded that two-dimensional islands with elementary height (0.37 and 0.39 nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face.

Critical Role of Screw Dislocation in the Growth of Co(OH)2 Nanowires as Intermediates for Co3O4 Nanowire Growth

In our prior studies, we reported the growth of Co3O4 nanowire arrays via the ammonia-evaporation-induced growth in solution and their promising applications in a Li-ion battery and oxygen evolution. Although we had identified that the growth of Co3O4 nanowire went through the β-Co(OH)2 intermediate, the growth mechanism of Co(OH)2 nanowire was still elusive. The problem seemed to be rooted in its layered brucite crystal structure, which was not previously known to grow one-dimensionally (1D) perpendicular to the layers. In this paper, we present our recent discovery that axial screw dislocation is responsible for such longitudinal growth. Through bright-field transmission electron microscope (TEM) characterizations, the screw dislocation was directly observed as a dark-contrasted line along Co(OH)2 nanowires. Emergent spiral growth steps provide active sites for immediate adsorption of incoming molecules, resulting in a fast spiral advance rate along the c-axis of the brucite crystal. This study shows a new example of the screw-dislocation driven growth of 1D nanostructures.

Bulk Growth and Characterization of Semiorganic Nonlinear Optical l-Alanine Cadmium Chloride Single Crystal by Modified Sankaranarayanan−Ramasamy Method

An optically transparent bulk nonlinear optical active single crystal of l-alanine cadmium chloride was grown up to a dimension of 100 mm length and 15 mm diameter with the aid of a modified uniaxial Sankaranarayanan−Ramasamy crystal growth method along the (101) plane. The crystal was subjected to X-ray diffraction analysis to confirm that the crystal belongs to the monoclinic system. The incorporation of cadmium and chlorine in the crystal lattice was confirmed using energy dispersive X-ray analysis (EDAX). The spiral growth-steps of the crystal along the (101) plane were observed using scanning electron microscopy. The Vickers microhardness test establishes improvement of hardness along the growth axis. Prevalence of space charge polarization was enunciated by dielectric measurements along the (101) plane for different temperatures 308, 328, 348 and 368 K.

In Situ Observation of Dislocations in Protein Crystals during Growth by Advanced Optical Microscopy

We attempted to visualize defects in a tetragonal lysozyme crystal in situ by laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM). Birefringence microscopy (BM) and phase-contrast microscopy (PCM) were also employed for the in situ observations. LCM-DIM enabled us to observe the {1 1 0} surfaces of the crystals and visualize the strain fields around the dislocations normal to a light beam with sufficient contrast during growth for the first time. Relatively large inclusions (60 to 300 μm) inside the crystal could also be visualized during growth, with the use of BM and PCM. We found that the dislocations appeared in bundles and were probably generated at the periphery of the relatively large inclusions inside the crystal. The existence of the dislocations was confirmed by etching experiments, in which we observed two kinds of etch pits: those with a point bottom and those with a flat bottom; the former corresponded to the dislocations inside the crystal and the latter corresponded to microdefects. Two different critical undersaturations existed above which the point-bottomed and flat-bottomed etch pits started to appear. The critical undersaturation for the point-bottomed etch pits was definitely less than that for the flat-bottomed ones. In the central region of the spiral growth hillock were many point-bottomed etch pits corresponding to the dislocations but not contributing to the formation of spiral growth steps. Although the point-bottomed etch pits were formed in only the central region of the spiral growth hillock, the flat-bottomed ones were randomly formed all over the {1 1 0} surfaces.

Surface growth mechanisms and structural faulting in the growth of large single and spherulitic titanosilicate ETS-4 crystals

Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to 〈110〉, 〈010〉 and 〈001〉 directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on {100} and {001} surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on {100} surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred.

Characterization of dislocations in protein crystals by means of synchrotron double-crystal topography

Hen egg-white lysozyme (HEWL) crystals have been studied by means of double-crystal synchrotron topography. The crystals reveal a number of features that are quite well known in hydrothermally grown inorganic crystals: dislocations, growth bands and growth sector boundaries. Dislocations in the 〈110〉 sectors have been characterized as edge dislocations with Burgers vector parallel to thecaxis. They are distinguishable only under weak beam conditions. The presence of edge dislocations shown in this paper is consistent with the spiral growth steps previously reported. This spiral growth on protein crystals has been observed many times by surface techniques.

Synchrotron white-beam topographic studies of 2H–SiC crystals

Synchrotron white beam X-ray topography (SWBXT) has been used to characterize 2H–silicon carbide crystals grown by the chemical reduction of methyltrichlorosilane at 1400°C. The crystals studied had the form of tapered needles around 1 mm long with hexagonal cross-sections 0.4 mm in diameter. SWBXT images recorded from two different crystals showed their excellent quality, as evidenced by the presence of Pendellösung fringes. Topographs recorded with various diffraction vectors revealed no evidence of the axial screw dislocations reported in 2H–SiC by Setaka and Ejiri, based on their observations of spiral growth steps. Neither were there any dislocations with Burgers vectors lying in the crystals’ basal planes. The absence of axial screw dislocations indicates that the growth was not screw dislocation assisted, but occurred by diffusion-controlled growth; and some other influence such as thermodynamics, initial nucleation, and/or impurity assisted growth, was responsible for the isolation of the 2H polytype.

Bulk and surface structure of epitaxial YBa 2Cu 3O 7−δ thin films grown on Mg 2TiO 4 (001) substrate layers Part II. Orientation and surface structure

Thin films of YBa 2Cu 3O 7−δ (YBCO) have been grown on Mg 2TiO 4 substrate layers by pulsed laser deposition. The substrate temperature T s has been varied between 600 and 800°C in order to optimize the YBCO film growth. All samples were characterized by means of X-ray diffraction, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM). We have found an optimum T s in the range of 675–700°C where the YBCO thin films show perfect (001) orientation. SEM and STM reveal that the (001) oriented YBCO films have very flat surfaces. STM shows a large number of spiral growth hills and steps of unit cell height. These films exhibit a superconducting transition temperature T c (onset) at 88.5 K and a zero resistance at 86.5 K. Films grown at lower substrate temperatures show no (001) orientation, but (100) and (110)/(103) orientations. At higher T s additional (100) oriented grains occur.

In-situ investigation on growth and dissolution of crystals in aqueous solution

In-situ observation methods to investigate the physics involved in growth and dissolution processes of crystals in aqueous solution at ordinary temperature and pressure are described. The methods visualize insitu the phenomena relating to clustering of nanometer sized embryonic particles, the mass transport from bulk solution and from a crystal, the concentration gradient in the diffusion boundary layer and its distribution around a crystal, and spiral growth steps with height of one nanometer. The techniques measure at the nanometer scale the growth and dissolution rates of individual spiral growth hillocks and etch pits whose dislocation characters are identified in-situ.

Some unusual growth habits of single crystal YBa 2Cu 3O 7-δ

Observations have been made of a 001 surface of single crystal platelets of YBa 2Cu 3O 7-δ grown from a CuO BaCuO 2-(123) flux. In many of the crystals double spiral growth steps are clearly visible with rotations of the same sign. Only rarely have opposite sign spirals been found and there is a complete absence of single spirals. The interlacing of the growth steps shows some features we suggest may be associated with the superlattice ordering of this orthorhombic structure.

In Situ observation of mono-molecular growth steps on crystals growing in aqueous solution. I

It is demonstrated that by combining optical phase contrast microscopy with a conventional TV system, mono-molecular spiral growth steps on crystals can be observed during the growth in aqueous solution. The image of the mono-molecular growth steps is stored either in a video tape recorder or through an A/D converter into the floppy disk in a computer. The minimal step height on CdI 2 crystals measured by the in situ interferometry described in a forthcoming paper is about 1.4 nm, which satisfactorily agrees with the mono-molecular growth step height derived from the crystal structure. This observation method has a great advantage in understanding the growth mechanisms of crystals in more direct way when the growth rate measurement is coupled.

直鎖状分子性物質の蒸着膜表面における結晶成長のステップ・モルホロジー

The surface morphologies of vacuum-deposited stearic acid films have been observed by replica electron microscopy. The crystal structure examined was monoclinic. Lateral and adhesive growth modes were observed under the following conditions; the deposition rate : 45 nm/min and 1.8 nm/min, the substrate temperature : -50°C, -20°C and 25°C, and the film thickness : about 320 nm. Spiral growth steps and closed loops revealed on the surfaces grown with the lateral growth mode. A “fan-shaped growth hillock” showed the most peculiar step morphology, which consists of a circular step segment with one side and of a trancated polygonal one with the other side along the symmetric a-axis. These fan-shaped growth hillocks were observed only on the vapor-grown surfaces.

軟体動物石灰化組織の鉱物化に関する研究-V

1) The investigations on the mechanism of layer formation in several marine bivalves were carried out with radioautographic stripping films. 2) The distribution and concentration of labeled calcium may indicate the mode of layer formation. 3) The circular deposition of labeled calcium on the inner shell surface appeared to be essentially similar to the selective fixation of calcium in the organic matrix and among various layers. 4) The mechanism of formation of the spiral steps and growth hills must be theorized on possible ideas independent of the position of development of embryos of mineral crystals which seems to be determined in certain specific fragments of the conchiolin protein. 5) The mechanism of development of growth hills in the nacre and the calcitostracum seemes to be respectively understood on essentially different ideas. That is, the mechanism of formation of spiral growth steps in the nacre can be consistently explained by the theory of screw dislocation, while the growth hills in the calcitostracum by the theory of dendritic growth.

Formation of platelike colloidal gold

Gold laminar single crystals produced by reductions of auric chloride in acid solution were investigated. A series of different organic reductants and various experimental conditions were used in studying their effects as well as the general growth mechanism. Detailed studies of the auric chloride-salicylic acid system were made, and the results are in excellent agreement on those parts reported by Suito and Uyeda. The size of the small hole observed at the center of the plates is found of the order of 1000 A. whether with or without spiral growth steps. Analysis of the results on the growth for the first 24 hours coupled with electron microscopic observations indicate that the laminar plate formation is a result of aggregation and rearrangement of the primary produced particles of smaller size. Growth of platinum and palladium platelike particles also has been studied and observation presented.

On the Growth of Sapphire Microcrystals

Thermodynamical considerations on the vapor-phase growth of whisker and platelet crystals of α-Al2O3 by the oxidation of aluminum lead to the conclusion that the vapor-phase mass transport is probably due to the suboxide Al2O and not AlO as previously suggested. Electron microscope observations confirm the optical evidence that spiral growth steps do not occur on the (0001) surfaces of Al2O3 crystals grown in this way.

The fine structure of polytetrafluoroethylene

AbstractElectron micrographs of highly crystalline PTFE crystallized by slow cooling from temperatures not far above the melting point show well‐marked bands, often with striations perpendicular to the bands; optical evidence shows that the chain molecules are parallel to the striations. The structure is in marked contrast to the spherulitic structure of most polymers; it appears that in PTFE the molecules are straight and parallel for much greater distances than in other polymers, and it is suggested that the width of the bands is a measure of molecular length. The unusual structure is attributed to the unusual stiffness of the fluorocarbon chain; the molecules in the liquid are straighter and less tangled than in other polymer melts. Heating to 500°C., followed by slow cooling, gives a modified structure approaching the spherulitic type found in other polymers; it is suggested that this is due to increased molecular tangling in the melt at higher temperatures. One type of polymer shows bands of remarkably uniform thickness, suggesting unexpected uniformity of molecular length. PTFE wax made by thermal or radiation degradation of the high polymer shows well‐defined spiral growth steps due to dislocations; the step heights suggest an unexpected uniformity of molecular length.

Observations of Spiral Growth Steps in Ethylene Polymer

THE role of dislocations in crystal growth has been discussed by N. F. Mott1, and later, evidence was given by Griffin2 to support the mechanism suggested by Frank3. Since that time there has been striking examples of this type of growth, described by Dawson and Vand4, and Forty5 along with Verma6, to mention a few.

On the Spiral Growth of Graphite Crystals

Layer growth patters, concentric hexagonal and circular loops, have been observed on the artificial graphite prepared by heat-treatment of carbon black seast 116. Some electron microscope and diffraction data are given. And it is concluded that these patterns are taken as the spiral growth steps, in accordance with the prediction of Frank's theory, expected when some screw dislocation rows emerge on the crystal faces.From the view point of dislocation theory a brief discussion is tried on certain features of graphite. The numerical values of radii of the critical nuclei are calculated 80-270Aring; as well as the supersaturation of vapour pressure 2.5-8%. The step heights in spirals have been estimated to be 150-250A, which may suggest that scores of initial dislocation with unit strength are crowded in the core. of each crystal.A new concepts, termed as “turbinal layer structure”, is proposed to explain the characteristic structure of those crystals which produce circular growth patterns in micrograph and sporty Debye-Scherrer rings, accompanied by ellipses in diffraction diagram.