Pyramidal Faces Research Articles

Crystal Growth of Defect-Free Single-Crystalline Fibers in Super-High Supersaturation Solution.

By controlling the supersaturation and choosing high-quality seeds, we successfully suppress the prismatic growth of the tetragonal potassium dihydrogen phosphate (KDP) SCFs, realize the rapid growth along the [001] direction, and obtain SCFs less than 10 μm in width with lengths of centimeters. The experimental results show that there exist critical supersaturation points, 22.40% and 41.41% at 25 °C, for initiating the growth of KDP SCF on its pyramidal and prismatic faces, respectively, which are quite different from those of the bulk crystals. We use the mechanism of 2D nucleation on smooth faces to explain the peculiar phenomena, assuming that there is no 2D or 3D defect on the surfaces of the seed fiber crystal. The assumption is supported by AFM observation of the surface micromorphology of the SCFs. Our solution growth technique developed can be used to grow ultrafine SCFs unable to be achieved by existing melt growth techniques.

Assessment of sustainability on structure-optical properties of prismatic face ADP crystal at dynamic shocked conditions

In the present research article, we have performed an extensive experimental investigation on the structural and linear optical properties of the prismatic face ammonium dihydrogen phosphate (ADP) crystals under the impact of shock waves of various counts such that the crystals have been analyzed by X-ray diffraction, Raman spectroscopic, Ultra-violet Visible spectroscopic and optical microscopic techniques. XRD and Raman results clearly show that the shocked ADP crystals have undergone significant changes such as lattice deformations, lattice disorders giving rise to the structural disorders and significant reduction in optical transmittance with respect to the number of shock pulses. Optical microscopic images also authenticate the formation of defective surface morphology at shocked conditions. Furthermore, we have made the comparison of the optical transmission of the prismatic face with the previously published pyramidal face ADP crystal with respect to the number of shock pulses.

Step Evolution and Growth Rate on {101} Faces of Potassium Dihydrogen Phosphate Crystals Grown at High Supersaturation

AbstractThe surface micromorphology of the {101} faces of potassium dihydrogen phosphate (KDP) crystals grown at different supersaturation conditions is systematically compared using atomic force microscopy. The height and width of the crystals during different growth steps are measured. The pyramidal face growth rate of KDP crystals is tested by a laser polarization interference system. The X‐ray rocking curve is used to measure the structural perfection of the {101} face of the KDP crystals. The results show that the growth rate of the {101} face increases with the supersaturation degree, and the rate is faster than that of the {100} face at a low supersaturation degree. Step bunching first increases and then decreases upon increasing the supersaturation, and the step height reaches a maximum value of about 6.0–6.9 nm at σ = 0.08 and 0.09. The crystal structural perfection is the worst under these conditions. It should be noted that 2D nuclei form on the surface terraces when the supersaturation is about 0.07. Dendrite‐like steps may be formed due to the development of these 2D nuclei. This work provides a reference for further researching the step evolution law of other crystalline materials.

A Contemporary Look at the Polyhedral Shape Instability of Crystals Growing under Conditions of Diffusion‐Limited Supply of Building Material

AbstractThis paper intends to shed fresh light on the polyhedral shape (in)stability of crystals growing under conditions of uneven diffusion supply of building material. A simplified theoretical consideration of the phenomenon is presented; the whole crystal is regarded as material consumer (but not merely a separate face on it). Accounted is for the fact that different amounts of building material are supplied by diffusion to the diverse types of crystal faces. Besides, critical sizes of crystal faces over which they lose the ability to grow macroscopically flat (because shallow cavities are formed on them) are calculated not only for the basal faces of Zn crystals growing from highly diluted own vapors mixed in inert (in respect to this metal) gases, such as H2 and Ar, but also for the pyramidal crystal faces. So, a logical explanation is given of the long‐standing problem: why the measured critical sizes of Zn single crystals grown in inert atmospheres are much smaller than the theoretically calculated critical sizes? Finally, the widths of the macroscopically flat rims surrounding the cavities on basal faces of Zn and Cd crystals (growing under conditions of uneven diffusion supply of building material) are determined in a simplified way.

Study on the formation mechanism of asymmetric growth hillocks on pyramidal faces of KDP crystals

Growth hillocks on the pyramidal faces of KDP crystals were investigated using an atomic force microscope (AFM) and first-principles analysis techniques.

Exploring the direction of dislocation line in pyramid section of KDP crystal using 3D confocal microscope

By the process of etching and polishing, the dislocation-related etch pits were clearly created on the pyramidal faces for as-grown KDP crystals by rapid growth technique. Through a combination of 3D confocal microscope and optical microscope, the direction of dislocation lines were studied in pyramid section, and the corresponding morphologies of etch pits were also observed in detail. The results show that the dislocation lines are mainly located in the {0 1 0} faces, and the dislocation-related etch pits may be caused by screw dislocations. Moreover, the research indicates that the morphologies of dislocation-related etch pits are somewhat related to the direction of dislocation lines. For the inclined sectors of Iʹ and IIʹ on etch pits, the slope ratio of Iʹ/IIʹ decreases with the increases of β as an angle between the direction of dislocation line and the normal of {101} face. Therefore, the information of dislocation in crystal, especially the orientation of dislocation line, can be inferred by the spatial size characteristics of dislocation-related etch pits.

Surface microstructures developed on polished quartz crystals embedded in wet quartz sand compacted under hydrothermal conditions

Intergranular pressure solution plays a key role as a deformation mechanism during diagenesis and in fault sealing and healing. Here, we present microstructural observations following experiments conducted on quartz aggregates under conditions known to favor pressure solution. We conducted two long term experiments in which a quartz crystal with polished faces of known crystallographic orientation was embedded in a matrix of randomly oriented quartz sand grains. For about two months an effective axial stress of 15 MPa was applied in one experiment, and an effective confining pressure of 28 MPa in the second. Loading occurred at 350 °C in the presence of a silica-saturated aqueous solution. In the first experiment, quartz sand grains in contact with polished quartz prism (overline10{1 }0) faces became ubiquitously truncated against these faces, without indenting or pitting them. By contrast, numerous sand-grain-shaped pits formed in polished pyramidal (17overline{6 }3) and (overline{4 }134) crystal faces in the second experiment. In addition, four-leaved and (in some cases) three-leafed clover-shaped zones of precipitation formed on these prism faces, in a consistent orientation and pattern around individual pits. The microstructures observed in both experiments were interpreted as evidence for the operation of intergranular pressure solution. The dependence of the observed indentation/truncation microstructures on crystal face orientation can be explained by crystallographic control of stress-induced quartz dissolution kinetics, in line with previously published experimental and petrographic data, or possibly by an effect of contact orientation on the stress-induced driving force for pressure solution. This should be investigated in future experiments, providing data and microstructures which enable further mechanism-based analysis of deformation by pressure solution and the effect of crystallographic control on its kinetics in quartz-rich sands and sandstones.

Modelling picosecond and nanosecond laser ablation for prediction of induced damage on textured SiNx/Si surfaces of Si solar cells

AbstractThis study investigated the laser‐induced damage arising from 266 and 532 nm laser ablation of SiNx films on alkaline textured Si surfaces with nanosecond and picosecond pulse durations using a combination of optical‐thermal simulations and measurements of carrier recombination current density. Simulations predict that the melting depth is limited to within 150 nm of the SiNx/Si surface after 266 nm ps laser irradiation due to the greater absorption in both the SiNx and Si resulting in more direct ablation, while temperatures exceeding the melting temperature of Si are predicted to extend up to 1000 nm into the Si substrate with 532 nm ps pulses leading primarily to spallation. Ablation of the SiNx by 266 nm ps irradiation is predicted to be more homogeneous on smaller sized pyramids due to the increased absorption of double‐bounce reflected light on the pyramid faces. This finding has implications for applications requiring uniform ablation of dielectrics on textured Si surfaces. Ablation of SiNx by the longer wavelength 532 nm ps pulses also increases carrier recombination compared to that incurred with 266 nm ps pulses due to the increased melting depth. Longer ns pulses result in less steep temperature gradients and, for 266 nm pulses, an increased melting depth compared to ps pulses. Consequently, shorter ps UV pulses are preferred for SiNx ablation on Si surfaces due to their reduced laser damage penetration, whereas the less steep temperature gradients resulting from ns 532 nm pulses are beneficial for laser doping to form selective emitters.

Building Block Symmetry Relegation Induces Mesopore and Abundant Open-Metal Sites in Metal–Organic Frameworks for Cancer Therapy

Building Block Symmetry Relegation Induces Mesopore and Abundant Open-Metal Sites in Metal–Organic Frameworks for Cancer Therapy

Study on the morphology of dislocation-related etch pits on pyramidal faces of KDP crystals

The dislocation related etch pits on pyramidal faces of KDP crystals were created by an improved wet etching method and investigated using an optical microscope and 3D confocal microscope.

Phase stability analysis of shocked ammonium dihydrogen phosphate by X-ray and Raman scattering studies

Abstract Impact of shock waves on non-linear optical materials bring about a lot of unknown behaviors of materials and such kinds of shock wave recovery experiments are highly required for the better understanding of material-property relationship. In the present context, we have performed experiments on the impact of structural properties of ammonium dihydrogen phosphate (ADP) samples under shock wave loaded conditions and the results of the test samples have been evaluated by X-ray diffraction (XRD), Raman spectroscopy, diffused reflectance spectroscopy (DRS) and field emission scanning electron microscopic (FESEM) technique. Interestingly, prismatic face of ADP shows loss of degree of crystallinity whereas pyramidal face shows enhancement of crystalline nature with respect to number of shock pulses due to shock wave induced dynamic re-crystallization. Hence, the present problem is worthy enough to unearth and understand the anisotropic nature of the ADP crystal and their structural modifications at shock wave loaded conditions.

Efficient and compact face descriptor for driver drowsiness detection

Current advances in driver drowsiness detection consist of a variety of innovative technologies generally based on driver state monitoring systems. Extracting effective and relevant features to characterize drowsy symptoms in images and videos is still an open topic. In this work, we introduce a face monitoring system based on a compact face texture descriptor able to cover the most discriminant drowsy features. The compactness has been achieved by both a multi-scale pyramidal face representation that capture the main characteristics of local and global information, and the feature selection process applied on the raw extracted features. The proposed framework is rolled out in four phases: (i) face detection and alignment; (ii) Pyramid-Multi Level (PML) face representation; (iii) face description using a multi-level multi scale feature extraction; and (vi) feature subset selection and classification. Experiments conducted on the public dataset NTH Drowsy Driver Detection (NTHUDDD) show the effectiveness of the proposed face descriptor and the associated selection schemes. The results show that the proposed method compares favorably with several approaches including those based on deep Convolutional Neural Networks.

Features of Dynamic Deformation of an Elastoviscoplastic Material in the Vicinity of a Moving Crack Tip

Some features of the behavior of ideal tips of transverse shear and tear cracks (“shear-tear” crack tips) propagating together with the shear wave fronts are investigated. It is shown that in the quasi-static approximation, the ideally plastic behavior of the material near the tear crack has a spatial character and has characteristic planes oriented at an angle of 45 degrees to the directions of the principal stresses. This makes it possible to interpret the flow of material at the tip of a tear crack as sliding along the faces of regular polygonal pyramids with bases in the tear plane. The leading edge of a “shear-tear” crack, on which both tear and transverse shear occur, in the process of propagation degenerates either into the tip of a tear crack or into the tip of a transverse shear crack. This is due to the fact that the shear or tear of a smaller magnitude reaches its limiting value earlier (stops) and then the tip of the remaining type of crack propagates.

Exploring differences in primary students\u2019 geometry learning outcomes in two technology-enhanced environments: dynamic geometry and 3D printing

BackgroundThis paper compares the effects of two classroom-based technology-enhanced teaching interventions, conducted in two schools in sixth (age 11–12) grade. In one school, the intervention involves the use of a class set of 3D Printing Pens, and in another school the use of dynamic geometry environments, for inquiry-based learning of the relations among the number of vertices, edges, and faces of prisms and pyramids. An instrument was designed as guided by the van Hiele model of geometric thinking and administered to the two groups in the form of pretests, posttests, and delayed posttests to assess students’ prior knowledge before the intervention started, the learning outcomes obtained immediately after intervention, and the retention of knowledge after the interventions had been completed for a sustained period of time. The purpose of this study is to explore differences in geometry learning outcomes in two technology-enhanced environments, one that involves dynamic, visual representations of geometry and another that involves embodied actions of constructing physical 3D solids.ResultsThe results show that students using dynamic geometry improved at a higher rate than those using 3D Pens. On the other hand, students with the aid of 3D Pens demonstrated better retention of the properties of 3D solids than their dynamic geometry counterparts. Namely, the posttest results show that the dynamic geometry environment (DGE) group generally outperformed the 3D Pen group across categories. The observed outperformance by the DGE group on “advanced” implies that the DGE technology had a stronger effect on higher levels of geometric learning. However, the results from the ANCOVA suggest that the retention effect was more significant with 3D Pens.ConclusionsThis study has established evidence that the DGE instructions produced strong but relatively temporary geometry learning outcomes, while 3D Pen instructions can help solidify that knowledge. The results of this study further shed light on the effect of visual and sensory-motor experiences on school mathematics learning and corroborate previous work showing that the effects of gesture are particularly good at promoting long-lasting learning.

Strong Mesoscopic Prismatic Face Growth Suppression in High-Speed Unidirectional Growth of KDP Single Crystals

We show strong mesoscopic prismatic face growth arrest that coexists with high-speed pyramidal face growth in single-crystalline KDP crystals with large aspect ratios. To explain this unique growth...

Modifications of Textured Silicon Surface Morphology and Its Effect on Poly-Si/SiO x Contact Passivation for Silicon Solar Cells

High-efficiency crystalline silicon ( c -Si) solar cells require textured surfaces for efficient light trapping. However, passivation of a textured pyramidal surface to reduce carrier recombination is challenging due to the presence of sharp tips, edges, and valleys. Using electrical and surface microscopies combined with lifetime measurements, we report on the effect of HF:HNO3 etching on the pyramidal textured Si surface morphology, and on poly -Si/SiO x contact performance. Preferential rounding of either the valleys between pyramids, or the pyramid tips is obtained depending on the HF:HNO3 solution temperature. Both these morphologies make the pyramid shape irregular, with the pyramid faces no longer being predominantly a Si(111) surface. Our atomic force microscopy measurements further show that the nanoscale roughness over the pyramid face also reduces after HF:HNO3 etching. Thus, etching affects the microscopic pyramidal shape, the dominant crystallographic orientation, and the nanoscale roughness of the surface. We speculate that these three surface effects result in the improvement of surface passivation via poly -Si/SiO x contacts. However, this improved passivation is accompanied by increased reflectance of the HF:HNO3-etched textured surface. Finally, our electron-beam-induced current measurements reveal thickness nonuniformities in the thermally grown SiO x layer on the HF:HNO3-etched textured Si surface: SiO x is thicker near the pyramid tips, edges, and faces as compared with near the valleys between pyramids. This nonuniformity in the SiO x layer may explain the poorer passivation obtained on a KOH-textured and HF:HNO3-etched textured surface as compared with a planar surface.

3C-SiC Growth on Inverted Silicon Pyramids Patterned Substrate.

This work reports on the properties of cubic silicon carbide (3C-SiC) grown epitaxially on a patterned silicon substrate composed of squared inverted silicon pyramids (ISP). This compliant substrate prevents stacking faults, usually found at the SiC/Si interface, from reaching the surface. We investigated the effect of the size of the inverted pyramid on the epilayer quality. We noted that anti-phase boundaries (APBs) develop between adjacent faces of the pyramid and that the SiC/Si interfaces have the same polarity on both pyramid faces. The structure of the heterointerface was investigated. Moreover, due to the emergence of APB at the vertex of the pyramid, voids buried on the epilayer form. We demonstrated that careful control of the growth parameters allows modification of the height of the void and the density of APBs, improving SiC epitaxy quality.

Effect of Crystallographic Orientation and Nanoscale Surface Morphology on Poly-Si/SiOx Contacts for Silicon Solar Cells.

High-efficiency crystalline silicon (Si) solar cells require textured surfaces for efficient light trapping. However, passivation of a textured surface to reduce carrier recombination is difficult. Here, we relate the electrical properties of cells fabricated on a KOH-etched, random pyramidal-textured Si surface to the nanostructure of the passivated contact and the textured surface morphology. The effects of both microscopic pyramidal morphology and nanoscale surface roughness on passivated contacts consisting of polycrystalline Si (poly-Si) deposited on top of an ultrathin, 1.5-2.2 nm, SiOx layer are investigated. Using atomic force microscopy, we show a pyramid face, which is predominantly a Si(111) plane to be significantly rougher than a polished Si(111) surface. This roughness results in a nonuniform SiOx layer as determined by transmission electron microscopy of a poly-Si/SiOx contact. Our device measurements also show an overall more resistive and hence a thicker SiOx layer over the pyramidal surface as compared to a polished Si(111) surface, which we relate to increased surfaceroughness. Using electron-beam-induced current measurements of poly-Si/SiOx contacts, we further show that the SiOx layer near the pyramid valleys is preferentially more conducting and hence likely thinner than over pyramid tips, edges, and faces. Hence, both the microscopic pyramidal morphology and nanoscale roughness lead to a nonuniform SiOx layer, thus leading to poor poly-Si/SiOx contact passivation. Finally, we report >21% efficient and ≥80% fill-factor front/back poly-Si/SiOx solar cells on both single-side and double-side textured wafers without the use of transparent conductive oxide layers, and show that the poorer contact passivation on a textured surface is limited to boron-doped poly-Si/SiOx contacts.

Low Faces of Restricted Degree in 3-Polytopes

The degree of a vertex or face in a 3-polytope is the number of incident edges. A k-face is one of degree k, a k−-face has degree at most k. The height of a face is the maximum degree of its incident vertices; and the height of a 3-polytope, h, is the minimum height of its faces. A face is pyramidal if it is either a 4-face incident with three 3-vertices or a 3-face incident with two vertices of degree at most 4. If pyramidal faces are allowed, then h can be arbitrarily large; and so we assume the absence of pyramidal faces in what follows. In 1940, Lebesgue proved that each quadrangulated 3-polytope has a face f with h(f) ≤ 11. In 1995, this bound was lowered by Avgustinovich and Borodin to 10. Recently, we improved it to the sharp bound 8. For plane triangulation without 4-vertices, Borodin (1992), confirming the Kotzig conjecture of 1979, proved that h ≤ 20, which bound is sharp. Later, Borodin proved that h ≤ 20 for all triangulated 3-polytopes. In 1996, Horňak and Jendrol’ proved for arbitrarily polytopes that h ≤ 23. Recently, we obtained the sharp bounds h ≤ 10 for triangle-free polytopes and h ≤ 20 for arbitrary polytopes. Later, Borodin, Bykov, and Ivanova refined the latter result by proving that any polytope has a 10−-face of height at most 20, where 10 and 20 are sharp. Also, we proved that any polytope has a 5−-face of height at most 30, where 30 is sharp and improves the upper bound of 39 obtained by Horňak and Jendrol’ (1996). In this paper we prove that every polytope has a 6−-face of height at most 22, where 6 and 22 are best possible. Since there is a construction in which every face of degree from 6 to 9 has height 22, we now know everything concerning the maximum heights of restricted-degree faces in 3-polytopes.

Crystal-plane-dependent effects of antifreeze glycoprotein impurity for ice growth dynamics.

An impurity effect on ice crystal growth in supercooled water is an important subject in relation to ice crystal formation in various conditions in the Earth's cryosphere regions. In this review, we consider antifreeze glycoprotein molecules as an impurity. These molecules are well known as functional molecules for controlling ice crystal growth by their adsorption on growing ice/water interfaces. Experiments on free growth of ice crystals in supercooled water containing an antifreeze protein were conducted on the ground and in the International Space Station, and the normal growth rates for the main crystallographic faces of ice, namely, basal and prismatic faces, were precisely measured as functions of growth conditions and time. The crystal-plane-dependent functions of AFGP molecules for ice crystal growth were clearly shown. Based on the magnitude relationship for normal growth rates among basal, prismatic and pyramidal faces, we explain the formation of a dodecahedral external shape of an ice crystal in relation to the key principle governing the growth of polyhedral crystals. Finally, we emphasize that the crystal-plane dependence of the function of antifreeze proteins on ice crystal growth relates to the freezing prevention of living organisms in sub-zero temperature conditions. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.