Kinds Of Facets Research Articles

Development of Monodisperse Mesoporous Microballs Composed of Decahedral Anatase Nanocrystals

Mesoporous monodisperse microballs of amorphous titania were prepared from solution of absolute ethanol, tetrabutyl titanate (TBOT) and potassium chloride via a sub-zero sol–gel route. The as-obtained microballs were used as the precursor in an alcohothermal (ethanol with a small amount of water) process to synthesize monodisperse mesoporous microballs built of decahedral anatase nanocrystals. FE-SEM observation and XRD analysis have confirmed that the formed decahedral anatase-rich powder retained the original spherical morphology of the precursor. Importantly, a hierarchical structure composed of faceted anatase has been achieved under “green” conditions, i.e., fluorine-free. Additionally, the hysteresis loops (BET results) have confirmed the existence of mesopores. Interestingly, faceted microballs show noticeable photocatalytic activity under UV/vis irradiation for hydrogen generation without any co-catalyst use, reaching almost forty times higher activity than that by famous commercial titania photocatalyst—P25. It has been proposed that enhanced photocatalytic performance is caused by mesoporous structure and co-existence of two kinds of facets, i.e., {001} and {101}, and thus hindered charge carriers’ recombination.

Formula omitted] twin boundary showing very large deviation from the theoretical one in deformed magnesium alloy

Structure of 101¯1 twin boundary in an AZ31 magnesium alloy has been characterized by means of transmission electron microscopy (TEM) and high-resolution TEM. It is found that actual twin boundary entirely departs from theoretical twinning plane in 101¯1 twin system. Furthermore, it is shown that six kinds of facets, including 101¯1 coherent twin boundaries, {0002}‖101¯1¯ basal-pyramidal (BPy), 1¯011¯‖{0002} pyramidal-basal (PyB), 1¯010‖101¯3 prismatic-third pyramidal (P3Py), basal-prismatic (BP/PB) boundaries and 101¯2 coherent twin boundaries, can coexist in one 101¯1 twin system. Based on these structure features, the underling mechanisms responsible for large deviation phenomenon are discussed, with focus on BPy, PyB, P3Py boundaries and strain accommodation.

Facet-Selective Deposition of Metal Nanoparticles on Decahedral-Shaped Anatase Titania Photocatalyst Particles

It has been reported that faceted titanium(IV) oxide (titania) particles, e.g., decahedral-shaped anatase titania particles (DAPs) exposing two {001} and eight {101} facets, show high-level photocatalytic activity, presumably because photogenerated electrons and positive holes migrate to {101} and {001} facets, respectively, to result in charge separation.1,2 This speculation seemed to be based on scanning electron microscopic and/or transmission electron microscopic observations in which most metal and metal-oxide particles deposited on DAPs, through photocatalytic reduction and oxidation of precursors, were seen on {101} and {001} facets, respectively.1,2 However, these studies may include some problems, e.g., (1) there are no statements on the number of metal/metal-oxide particles deposited on the two kind of facets, only showing a single or few microscopic images. (2) there is a possibility that deposited metal particles were desorbed and adsorbed again on the {101} or {001} facets. In this study, metal particles were deposited on DAPs using two methods, observed by scanning electron spectroscopy (SEM) and facet-dependent deposition was quantitatively and precisely measured. DAPs were prepared by a gas-phase reaction of titanium(IV) chloride (TiCl4) with oxygen.3 Gold or platinum particles were deposited on the DAPs through (1) photocatalytic reduction of hexachloroplatinic acid (H2PtCl6) or tetrachloroauric acid (HAuCl4) or (2) mixing a gold or platinum colloid with DAPs suspensions in the dark or under mercury-lamp irradiation. The metal deposited DAPs was washed with water, then the suspension was dried by freeze drying under vacuum for 24 h. The images of the metal particles deposited on the DAPs were observed by SEM, and then the numbers of the metal particles on two kinds of facets were counted for more than 100 DAP particles. Figure 1 shows an SEM image of the platinum colloid-deposited DAPs prepared under mercury-lamp irradiation. A ratio of deposition density (s) was calculated as a measure of facet-selective metal deposition using the following equation: s = p {001} / (p {101}×R ave), (1) where p {001} and p {101} are the number of the metal particles on each facets, and R ave is the average area ratio of {001} and {101} facets (Table 1). If s is smaller than 1, it means that metal particles tend to be deposited preferentially on the {101} facet, and vice versa. In the case of the photocatalytic metal deposition from H2PtCl6 or HAuCl4, s was smaller than 1, as was reported previously. On the other hand, in the case of mixing of a gold or platinum colloid both under irradiation and in the dark, s was also smaller than 1, even though prepared without photocatalytic reaction, i.e., mixing of a metal colloid in the dark exhibited {101}-facet selectivity. These results suggest the difference in ability of metal-particle adsorption between {101} and {001} facets. Therefore, it cannot be excluded the mechanism in which {101}-preferred photocatalytic deposition of metal particles proceeds through facet-selective adsorption of once-deposited metal particles on DAPs. Figure 1

Erosion Triangular Facets as Markers of Order in an Open Dissipative System

The complexity and non-linearity of the morphogenetic system which is responsible for shaping the Earth’s surface have been widely recognised by many authors who have documented the fractal nature of erosion. In this paper, two peculiar kinds of landforms are compared to point out ordered structures, i.e. triangular facets that arise in different geomorphic systems, due to the principle of morphologic convergence. Occurrence of triangular facets has been documented in mountainous areas in relation to base level changes and hydrographical network evolution; similarly shaped landforms are present even in recent tectonic uplift areas along faults. The spatial distribution of the two kinds of facets has been investigated in two river basins located in Liguria (northern Italy) and in a mountainous area in Oman. The results of this analysis document the different spatial features of the two kinds of facets.

Fractographical Investigation on High-Cycle Fatigue Behavior of Direct Aging GH4169 Superalloy

The present work is aimed at the fatigue crack initiation behavior of the direct aging superalloy GH4169 at 650 °C. Un-notched specimens were tested under high-cycle fatigue loading with the two stress ratios of R = 0.1 and 0.5. Fracture surfaces were examined using field emission scanning electron microscopy (FESEM). Special attention is paid to the crack initiation sites. Two microstructure features in the fatigue crack initiation regions have been observed. One is obviously the feature of the Ti (C,N)-inclusions, and the other is some kinds of facets. The analysis on the facets was carried out by using energy dispersive spectra (EDS). It was found that the elements at the facets are similar to the matrix. However, some inclusions, Nb (C,N), have been found in the subsurface facets in a few specimens. Sometimes, fatigue lives of the specimens for the crack initiating from the inclusions are longer than those of cracks from the facets, depending on the size of inclusions and the depth from sample surface. Crack initiation for most of the specimens occurs at inclusions, and therefore inclusion is a primary source of crack initiation for this alloy.

GaN tubes with coaxial non‐ and semipolar GaInN quantum wells

AbstractWe present the position‐controlled growth of GaN nanotubes with coaxial GaInN quantum wells by using ZnO nanowires grown on top of GaN pyramids as templates. High resolution scanning transmission electron microscopy allows us to perform a detailed structural analysis of individual tubes. In particular, we report about structural properties like indium incorporation, thickness, and homogeneity of quantum wells realized on nonpolar m‐plane side facets or on semipolar tips. Additionally, high resolution spatially and spectrally resolved cathodoluminescence spectroscopy performed at low temperature enables us to clearly identify the quantum well luminescence contributions for different kinds of facets on a single tube. The luminescence of the quantum wells deposited at variable temperatures shows a clear spectral shift in the cathodoluminescence signal, yielding an activation energy for the indium desorption from the m‐plane side facets of about 1.6 eV. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Facets of Empowerment in Solution-Focused Brief Therapy for Lower-Status Married Women in Taiwan: An Exploratory Study

Empowerment is an essential component of therapy. Since SFBT is an empowerment approach, it is vital to explore what kinds of facets of empowerment are generated from SFBT sessions. Nine low-status married women in Taiwan participated as clients in this study. The researcher coded and compared the rates of 20 facets of empowerment from 32 verbatim counseling transcripts of clients' statements. The study uncovered two main findings: (a) the assertive, self-discovering, goal-directed, competent, and interdependent facets were the highest rated facets of empowerment in all the SFBT sessions; and (b) between “1 Session Group” and “4–10 Sessions Group,” significant differences emerged regarding 7 facets of empowerment and these two groups. A comparison between SFBT and feminist approach and discussion about cultural factors were presented. Finally, a case example demonstrates how SFBT sessions can generate high levels of specific facets of empowerment.

Effect of crystallographic orientation of microchannel on low-angle incidence microchannel epitaxy on (0 0 1) GaAs substrate

Low-angle incidence microchannel epitaxy (LAIMCE) is a technique to obtain a lateral overgrowth using molecular beam epitaxy. In order to produce a wide and flat lateral overgrowth of GaAs, the effect of the crystallographic orientation of microchannel on GaAs LIMCE was investigated. The cross-sectional shape of GaAs LAIMCE was studied by scanning electron microscope and found to largely change by the choice of microchannel orientation. For example, the layer grown from a microchannel with the orientation of −10° off from [0 1 0] showed a trapezoidal shape, while the layer grown from a microchannel with that of +10° off from [0 1 0] had an inverted-triangular shape with a sharp peak on the growth front. The layer grown from that of +20° off from [0 1¯ 1] had a vertical side. Detailed observation of the layers revealed that several kinds of facets, such as (1 0 1), (1 1¯ 2)B, (1 1 n¯), (3 1 0), formed on the side and shaped the layers. As adatoms on the surface diffuse from these facets to the top of the layers, the lateral growth would be suppressed. Therefore, it is important to control the growth condition not to form facets on the side, at least to suppress the formation of the facets with strong nature of inter-surface diffusion of adatoms form side to top.

TEM study of the structural dependence of the epitaxial passive oxide films on crystal facets in polyhedral nanoparticles of chromium

Nanocubes and partially truncated rhombic dodecahedral nanoparticles of Cr have been studied by electron diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. It is found that the nanoparticles of Cr are enclosed by the epitaxial passive oxide films. The oxide films on 100% truncated nanocubes of Cr with only one kind of facets, {1 0 0} facets, are face-centered cubic (fcc) structured Cr 2O 3 with a lattice constant of 0.407 nm. There are two kinds of oxide films in partially truncated nanoparticles of Cr with two kinds of crystallographic facets, {1 0 0} and {1 1 0}. The same fcc Cr 2O 3 is found on the {1 0 0} facets while the rhombohedral α-Cr 2O 3 is found on the {1 1 0} facets. This is similar to the two kinds of oxides, fcc and rhombohedral Fe 2O 3, which have also been observed in polyhedral nanoparticles of Fe. These passive Cr 2O 3, found in nanoparticles of Cr which have remained unchanged in water for four years, may have important implications for protective oxide films involving Cr.

Coupled catalytic oscillators: Beyond the mass-action law.

We present Monte Carlo simulations of the reaction kinetics corresponding to two coupled catalytic oscillators in the case when oscillations result from the interplay between the reaction steps and adsorbate-induced surface restructuring. The model used is aimed to mimic oscillations on a single nm catalyst particle with two kinds of facets or on two catalyst particles on a support. Specifically, we treat the NO reduction by H(2) on a composite catalyst containing two catalytically active Pt(100) parts connected by an inactive link. The catalyst is represented by a rectangular fragment of a square lattice. The left- and right-hand parts of the lattice mimic Pt(100). With an appropriate choice of the model parameters, these sublattices play a role of catalytic oscillators. The central catalytically inactive sublattice is considered to be able only to adsorb NO reversibly and can be viewed as a Pt(111) facet or a support. The interplay of the reactions running on the catalytically active areas occurs via NO diffusion over the boundaries between the sublattices. Using this model, we show that the coupling of the catalytically active sublattices may synchronize nearly harmonic oscillations observed on these sublattices and also may result in the appearance of aperiodic partly synchronized oscillations. The spatio-temporal patterns corresponding to these regimes are nontrivial. In particular, the model predicts that, due to phase separation, the reaction may be accompanied by the formation of narrow NO-covered zones on the left and right sublattices near the boundaries between these sublattices and the central sublattice. Such patterns cannot be obtained by using the conventional mean-field reaction-diffusion equations based on the mass-action law. The experimental opportunities to observe the predicted phenomena are briefly discussed. (c) 2001 American Institute of Physics.

Geometric and electronic structure of molecular beam epitaxy-prepared GaAs (112) and (113) surfaces

The surface structure and the electronic properties of the high-index molecular beam epitaxy (MBE)-prepared GaAs surfaces (112)A and B as well as (113)A and B were investigated in situ by low-energy electron diffraction and surface core level spectroscopy. Under MBE conditions, both (112) surfaces are unstable. The (112)A surface consists of five kinds of facets with the orientations {110}, {124} and (111). The ( 1 1 2 ) B surface forms four types of facets with the orientations ( 1 1 1 ), ( 1 1 3 ) and { 1 1 0 }. The surface core-level shift analysis on GaAs(112)A yields surface components for the As 3d peak (− 0.31 eV) as well as for the Ga 3d peak (+ 0.28 eV). On GaAs(113)A both the (8 × 1) superstructure and the core-level analysis support a structure model proposed recently by Wassermeier et al. (Phys. Rev. B, 57. (1995) 14721). After MBE preparation, the ( 1 1 3 )B surface forms facets with the orientations ( 1 1 0) and ( 1 1 1).

Preparation and some properties of chemically vapour-deposited Si3N4-TiN composite

Chemically vapour-deposited (CVD) Si3N4-TiN composite (a plate with the maximum thickness of 1.9 mm) has been prepared on a graphite substrate using a mixture of SiCl4, TiCl4, NH3 and H2 gases. The CVD was carried out at deposition temperatures,T dep, in the range of 1050 to 1450 ° C, total gas pressures,P tot, from 1.33 to 10.7 kPa and gas flow rates of 136 (SiCl4), 18 (TiCl4), 120 (NH3) and 2720 (H2) cm3 min−1. The deposits thus obtained appeared black. The Ti content in the composites ranged from 2.1 to 24.8 wt % and was found in the form of Tin. The structure of the Si3N4 matrices varied from amorphous (initially) to theα- andβ-type, with increasingT dep. Most of theα- andβ-type deposits had a preferred orientation (001) parallel to the deposition surface. While the deposition surface of the amorphous deposits showed a pebble structure, the surfaces of theα- andβ-type deposits were composed of various kinds of facets. The heat-treating experiment suggested thatβ-Si3N4 obtained in the present work was formed directly via a vapour phase, and not from crystallization of amorphous Si3N4 or from transformation ofα-Si3N4.