Facet Planes Research Articles

Strain-Induced Asymmetric Line Segregation at Faceted Si Grain Boundaries

The unique combination of atomic-scale composition measurements, employing atom probe tomography, atomic structure determination with picometer resolution by aberration-corrected scanning transmission electron microscopy, and atomistic simulations reveals site-specific linear segregation features at grain boundary facet junctions. More specific, an asymmetric line segregation along one particular type of facet junction core, instead of a homogeneous decoration of the facet planes, is observed. Molecular-statics calculations show that this segregation pattern is a consequence of the interplay between the asymmetric core structure and its corresponding local strain state. Our results contrast with the classical view of a homogeneous decoration of the facet planes and evidence a complex segregation patterning.

Effect of synthesis method on structural properties and soot oxidation activity of gadolinium-doped ceria

EDTA–citrate complex and solvothermal methods were adopted for the synthesis of gadolinium-doped ceria (GDC) (Ce0.9Gd0.1O2) solid solution, and the obtained GDC sample is tested for soot oxidation activity. Based on XRD results, it was evident that the reactive facet planes of {100} and {110} were highly intense [intensity ratio (%) of (200)/(100) (34.2%) and (220)/(111) (51.2%)] for GDC prepared by the EDTA–citrate method in comparison with the solvothermal method, and this highly intense reactive facet plane correlates to the lower energy for oxygen vacancy formation. Apart from the smaller crystallite size (10 nm) the GDC sample prepared by the EDTA–citrate method displayed lower band gap energy (2.99 eV), higher ratio of reducibility (45.45%) and lower binding energy (528.8 eV) for surface-adsorbed oxygen. The GDC obtained by EDTA–citrate method displayed a better soot oxidation activity (T50 = 468 °C) than compared to the GDC obtained by solvothermal method (T50 = 500 °C). The obtained results significantly show that the synthesis method plays a crucial role in controlling the structural properties and in enhancing the soot oxidation activity.

Sublimation Growth and Characterization of Erbium Nitride Crystals

Erbium nitride (ErN) is a rare earth nitride notable for its magnetic and optical properties. Here we report on its growth on a non-native substrate, tungsten foil, via physical vapor transport, and its characterization. The source material was erbrium metal that was converted to ErN by heating in nitrogen. Subsequently, it was sublimed to form the ErN crystals. The operating conditions were 1620–1770 °C and 150–330 Torr in pure nitrogen. The growth rate increased exponentially with temperature with an activation energy of 508 kJ/mol, and inversely with pressure. X-ray diffraction revealed that the ErN preferentially adopted a (100) orientation, the same as the dominant orientation of the tungsten sheet. The lattice constant was 4.853 A. The crystal shapes and sizes were dependent on the temperature, as revealed by SEM and optical microscopy. The ErN crystals were highly faceted, bound by (100) and (111) crystal planes. The ErN compound deviated from stoichiometry: the Er:N atomic ratio ranged from 1:1.15...

Design optimization and tolerance analysis of a spot-size converter for the taper-assisted vertical integration platform in InP.

We report on the design optimization and tolerance analysis of a multistep lateral-taper spot-size converter based on indium phosphide (InP), performed using the Monte Carlo method. Being a natural fit to (and a key building block of) the regrowth-free taper-assisted vertical integration platform, such a spot-size converter enables efficient and displacement-tolerant fiber coupling to InP-based photonic integrated circuits at a wavelength of 1.31μm. An exemplary four-step lateral-taper design featuring 0.35dB coupling loss at optimal alignment of a standard single-mode fiber; ≥7 μm 1dB displacement tolerance in any direction in a facet plane; and great stability against manufacturing variances is demonstrated.

3D mapping of discontinuity traces using fusion of point cloud and image data

A new methodology is presented for 3-D automated mapping of joints that are exposed primarily as traces in a rock face as opposed to planar facets. The method identifies 3-D points in a photogrammetry or a LiDAR derived point cloud that corresponds to the traces of the joints as observed in image data. First, the 2-D trace texture is extracted from image data using a hybrid global and local threshold method and integrating a series of image-processing algorithms. Second, data matching links the pixel locations corresponding to the identified traces in an image to the 3-D coordinates in the point cloud. This matching is accomplished by a coordinate transformation between the image coordinates and point cloud coordinates. Finally, a 3-D discontinuity trace map is acquired by analysing the 3-D spatial features of the traces. A case study of a rock slope along a highway is presented using the proposed method. The results demonstrate that the fusion of image data and point cloud data improves the mapping of discontinuities that primarily appear as traces in outcrops versus that achieved by existing methods that rely only on point cloud data.

Electron affinity and surface states of GaN m -plane facets: Implication for electronic self-passivation

The electron affinity and surface states are of utmost importance for designing the potential landscape within (heterojunction) nanowires and hence for tuning conductivity and carrier lifetimes. Therefore, we determined for stoichiometric nonpolar $\mathrm{GaN}(10\overline{1}0)$ $m$-plane facets, i.e., the dominating sidewalls of GaN nanowires, the electron affinity to $4.06\ifmmode\pm\else\textpm\fi{}0.07\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ and the energy of the empty Ga-derived surface state in the band gap to $0.99\ifmmode\pm\else\textpm\fi{}0.08\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ below the conduction band minimum using scanning tunneling spectroscopy. These values imply that the potential landscape within GaN nanowires is defined by a surface state-induced Fermi-level pinning, creating an upward band bending at the sidewall facets, which provides an electronic passivation.

Faceting for direction-dependent spectral deconvolution

The new generation of radio interferometers is characterized by high sensitivity, wide fields of view and large fractional bandwidth. To synthesize the deepest images enabled by the high dynamic range of these instruments requires us to take into account the direction-dependent Jones matrices, while estimating the spectral properties of the sky in the imaging and deconvolution algorithms. In this paper we discuss and implement a wideband wide-field spectral deconvolution framework (ddfacet) based on image plane faceting, that takes into account generic direction-dependent effects. Specifically, we present a wide-field co-planar faceting scheme, and discuss the various effects that need to be taken into account to solve for the deconvolution problem (image plane normalization, position-dependent Point Spread Function, etc). We discuss two wideband spectral deconvolution algorithms based on hybrid matching pursuit and sub-space optimisation respectively. A few interesting technical features incorporated in our imager are discussed, including baseline dependent averaging, which has the effect of improving computing efficiency. The version of ddfacet presented here can account for any externally defined Jones matrices and/or beam patterns.

Correlating Scatter in Fatigue Life with Fracture Mechanisms in Forged Ti-6242Si Alloy

Unlike the quasi-static mechanical properties, such as strength and ductility, fatigue life can vary significantly (by an order of magnitude or more) for nominally identical material and test conditions in many materials, including Ti-alloys. This makes life prediction and management more challenging for components that are subjected to cyclic loading in service. The differences in fracture mechanisms can cause the scatter in fatigue life. In this study, the fatigue fracture mechanisms were investigated in a forged near-α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si, which had been tested under a condition that resulted in life variations by more than an order of magnitude. The crack-initiation and small crack growth processes, including their contributions to fatigue life variability, were elucidated via quantitative characterization of fatigue fracture surfaces. Combining the results from quantitative tilt fractography and electron backscatter diffraction, crystallography of crack-initiating and neighboring facets on the fracture surface was determined. Cracks initiated on the surface for both the shortest and the longest life specimens. The facet plane in the crack-initiating grain was aligned with the basal plane of a primary α grain for both the specimens. The facet planes in grains neighboring the crack-initiating grain were also closely aligned with the basal plane for the shortest life specimen, whereas the facet planes in the neighboring grains were significantly misoriented from the basal plane for the longest life specimen. The difference in the extent of cracking along the basal plane can explain the difference in fatigue life of specimens at the opposite ends of scatter band.

Thermal Transport is Influenced by Nanoparticle Morphology: A Molecular Dynamics Study

Molecular dynamics simulations were performed to model the interfacial thermal conductance (G) from bare gold nanoparticles (icosahedral, cuboctahedral, and spherical) to a hexane solvent. The computed conductance was found to depend not only on particle shape, but also on the size of the nanoparticles, particularly for nanospheres. These results are compared with conductance out of the planar facets: (111), (100), and (110); all commonly exhibited in small patches on the spherical particles. Undercoordination of the surface atoms and the vibrational density of states in the icosahedra explain some of these observations. The exposed surfaces of icosahedral particles are dominated by (111) facets with 9-coordinated gold atoms. Cuboctahedral particles are dominated by the (100) and (111) facets with 8- and 9-coordinated surface atoms, respectively. The nanospheres approach a constant surface density of 6–9 coordinated sites at large particle sizes, and these surface atoms play a large role in the conductanc...

Towards Realizing Cybermanufacturing Kiosks: Quality Assurance Challenges and Opportunities

This paper presents the cyberphysical system (CPS) challenges associated with realizing manufacturing-as-a-service paradigm, capable of creating custom functional, freeform structures. While earlier efforts have addressed the product design, resource allocation, and asset management challenges in custom manufacturing, those pertaining to quality and performance assurance have not received much attention thus far. For low volume custom manufacturing, the intelligence comprising all the steps involved in the production process and its continuous monitoring should reside in the real-time service, rather than requiring an upfront costly design process for each product. In this paper, we first outline the technical challenges associated with autonomous monitoring and control of tool motion and process parameters of a laser kirigami (origami with cuts) process to create custom freeform components, with planar facets, from peel-off sensors embedded on sheet precursors. In the sequel, we present an implementation of image-based monitoring, particularly for the estimation of the dihedral angle between the facets being bent during the laser kirigami process. As the sheet is formed, the sensors embedded on the sheets serve as a swarm of mobile sensors whose instantaneous location and orientation are discerned using optimally placed cameras to estimate the process state. This allows the tuning of process parameters, specifically the laser intensity and transverse feed rate to mitigate quality issues. The results from the current experimental investigations of the laser kirigami process suggest that the process state can be estimated to error rates of less than 2% at 10 frames per second, which is orders of magnitude faster than that achievable using the present stereo digital image correlation technologies.

Interdependence Between Tool Misalignment and Cutting Forces in Ultraprecise Single Point Inverted Cutting

Ultraprecise single point inverted cutting (USPIC) is a microfabrication technique that has been recently developed for the generation of micro-optical microstructures with sharp concave geometries. Among the multiple challenges encountered during the micromachining process, tool alignment represents one of the critical factors affecting the overall accuracy of the microstructure that in turn affects its optical functionality. Since none of the presently available tool alignment techniques was found to perform well in the particular context of the diamond insert used in USPIC, an in-depth analysis of its mechanics was used in this study to provide insight on the interdependence between cutting tool misalignment and cutting forces. For this purpose, an experimental setup was devised to record the 3D cutting forces generated during the fabrication of two representative concave geometries delimited by planar facets. The first test geometry represents an instance of an isolated right triangular prism (RTP) whose quality and optical functionality will be significantly affected by diamond insert misalignment, particularly due to the undesirable contact to occur between the secondary/lateral cutting edges of the tool and the optically nonfunctional RTP facets. By contrast, the second test geometry had both lateral facets removed, such that the cutting conditions obtained in this case could be regarded as similar with that of the classical orthogonal cutting setup. Direct comparisons of the cutting force profiles obtained for the two cutting scenarios enable unequivocal identifications of tool misalignment direction and magnitude, such that targeted corrective actions could be performed to address the issue.

Integrated Lloyd's mirror on planar waveguide facet as a spectrometer.

A low-cost and simple Fourier transform spectrometer based on the Lloyd's mirror configuration is proposed in order to have a very stable interferogram. A planar waveguide coupled to a fiber injection is used to spatially disperse the optical beam. A second beam superposed to the previous one is obtained by a total reflection of the incident beam on a vertical glass face integrated in the chip by dicing with a specific circular precision saw. The interferogram at the waveguide output is imaged on a near-infrared camera with an objective lens. The contrast and the fringe period are thus dependent on the type and the fiber position and can be optimized to the pixel size and the length of the camera. Spectral resolution close to λ/Δλ=80 is reached with a camera with 320 pixels of 25μm width in a wavelength range from O to L bands.

Compatible, energy conserving, bounds preserving remap of hydrodynamic fields for an extended ALE scheme

From the very origins of numerical hydrodynamics in the Lagrangian work of von Neumann and Richtmyer [83], the issue of total energy conservation as well as entropy production has been problematic. Because of well known problems with mesh deformation, Lagrangian schemes have evolved into Arbitrary Lagrangian–Eulerian (ALE) methods [39] that combine the best properties of Lagrangian and Eulerian methods. Energy issues have persisted for this class of methods. We believe that fundamental issues of energy conservation and entropy production in ALE require further examination.The context of the paper is an ALE scheme that is extended in the sense that it permits cyclic or periodic remap of data between grids of the same or differing connectivity. The principal design goals for a remap method then consist of total energy conservation, bounded internal energy, and compatibility of kinetic energy and momentum. We also have secondary objectives of limiting velocity and stress in a non-directional manner, keeping primitive variables monotone, and providing a higher than second order reconstruction of remapped variables.In particular, the new contributions fall into three categories associated with: energy conservation and entropy production, reconstruction and bounds preservation of scalar and tensor fields, and conservative remap of nonlinear fields. The paper presents a derivation of the methods, details of implementation, and numerical results for a number of test problems. The methods requires volume integration of polynomial functions in polytopal cells with planar facets, and the requisite expressions are derived for arbitrary order.

Atomic scale study of surface orientations and energies of Ti2O3 crystals

For nanostructured particles, the faceting planes and their terminating chemical species are two critical factors that govern their chemical behavior. The surface atomistic structure and termination of Ti2O3 crystals were analyzed using atomic-scale aberration-corrected scanning transmission electron microscopy (STEM) combined with density functional theory (DFT) calculations. STEM imaging reveals that the Ti2O3 crystals are most often faceted along (001), (012), (−114), and (1–20) planes. The DFT calculation indicates that the (012) surface with TiO-termination has the lowest cleavage energy and correspondingly the lowest surface energy, indicating that (012) will be the most stable and prevalent surfaces in Ti2O3 nanocrystals. These observations provide insights for exploring the interfacial process involving Ti2O3 nanoparticles.

Morphological and morphometric features of cuboid bone

Abstract Background and aims : Morphological and morphometric data of cuboid is of significance in creating 3D model of midfoot alignment and in understanding pathologies and instabilities in the region. There is minimal data on biometric values of cuboid. The objective of the study was to evaluate morphological variations in calcaneal articulating facet and metatarsal articulating facet. The other objective was to report morphometric data of cuboid. Methodology: This descriptive study was conducted in the department of Anatomy, using 24 dry cuboid bones. Each bone was observed for pattern of articular surfaces. Articular surface of each bone was photographed and categorized. Presence of navicular facet was noted. Results: Pattern of calcaneal articular facet was classified into four types: IA – concavo-convex facet with posteromedial projection and overall oval or reniform shaped; 1B – concavo-convex facet without posteromedial projection and rectangular shaped; 2A – plane facet with posteromedial projection and oval or reniform shaped; 2B – plane facet without posteromedial projection and rectangular shaped. Type I was the most common. Pattern of metatarsal articulating facet was classified into three groups: Concave – the edges of metatarsal articulating facet projected anteriorly making a depression for articulation of 4th and 5th metatarsal bones; Plane – articulating facet is flat; Convex – the articulating surface slopes posteriorly. Concave pattern was most common. Mean medial length of cuboid was 33.9 [°3.3] mm, lateral length was 17.9[ °1.6]mm, height was 22[°1.5] mm, length index was 188.8, area of calcaneal articular facet was 124.9 [°10.9] mm2, area of metatarsal articulating facet was 91.9[°5.7]mm2, depth of peroneal groove was 1.83 [°1.3]mm. Conclusion: Morphological characterization of articular surfaces of cuboid, especially the calcaneal facet helps to understand the degree of movement at calcaneocuboid joint and also joint pathologies.

Isoradial meshes: Covering elastic gridshells with planar facets

Abstract Elastic gridshells are structures made of flat two-way grids which are deformed elastically before they are braced and which afterwards mechanically behave like continuous shells. Gridshells present some advantages in terms of manufacturing, lightness and time of assembly. Their covering remains however a technical issue. The present article proposes hence an alternative method to cover them by planar quadrilateral facets, which could also be used as natural bracing if connected properly. It relies on the duality between a certain family of circular meshes with a unique radius and some Tchebycheff nets. The approach is versatile and allows for the design of a large variety of shapes from two curves in space. Real time numerical tools are developed for open and closed curves as well as a strategy for umbilical points. The relaxation of the Tchebycheff net shows finally that an equilibrium configuration can be found in the vicinity of the planar quadrilateral mesh (PQ-Mesh) which confirm the practical feasibility of elastic gridshells covered with planar facets.

Fine structure of excitons in InAs quantum dots on GaAs(110) planar layers and nanowire facets

We investigate the optical properties of InAs quantum dots grown by molecular beam epitaxy on GaAs(110) using Bi as a surfactant. The quantum dots are synthesized on planar GaAs(110) substrates as well as on the {110} sidewall facets of GaAs nanowires. At 10 K, neutral excitons confined in these quantum dots give rise to photoluminescence lines between 1.1 and 1.4 eV. Magneto-photoluminescence spectroscopy reveals that for small quantum dots emitting between 1.3 and 1.4 eV, the electron-hole coherence length in and perpendicular to the (110) plane is on the order of 5 and 2 nm, respectively. The quantum dot photoluminescence is linearly polarized, and both binding and antibinding biexcitons are observed, two findings that we associate with the strain in the (110) plane This strain leads to piezoelectric fields and to a strong mixing between heavy and light hole states, and offers the possibility to tune the degree of linear polarization of the exciton photoluminescence as well as the sign of the binding energy of biexcitons.

Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation

Rare earth rich magnesium alloys are used in aerospace and automotive fields because of their high specific strength and good castability. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating are necessary, when they have to be used in humid or corrosive environments. The present study was aimed at evaluating the effect of plasma electrolytic oxidation (PEO) and different surface roughness (Ra ≈ 0.8 μm and Ra ≈ 0.3 μm) on the rotating bending fatigue of an innovative Mg alloy, with a high content of Nd (up to 3.1 wt %) and Gd (up to 1.7 wt %). Fatigue tests revealed a 15% decrease in the fatigue strength of the PEO-treated alloy (fatigue strength = 88 MPa) with respect to the bare alloy (fatigue strength = 103 MPa). The reduction of fatigue strength was mainly due to the residual tensile stresses induced by the PEO treatment. The effect of surface roughness on the bare alloy was, instead, negligible. The mechanisms of crack initiation were similar in the untreated and PEO-treated alloy, with crack nucleation sites located in correspondence to large facets of the cleavage planes.

Marionette Meshes: Modelling free-form architecture with planar facets

We introduce an intuitive method, called Marionette, for the modelling of free-form architecture with planar facets. The method takes inspiration from descriptive geometry and allows to design complex shapes with one projection and the control of elevation curves. The proposed framework achieves exact facet planarity in real time and considerably enriches previous geometrically constrained methods for free-form architecture. A discussion on the design of quadrilateral meshes with a fixed horizontal projection is first proposed, and the method is then extended to various projections and patterns. The method used is a discrete solution of a continuous problem. This relation between smooth and continuous problem is discussed and shows how to combine the marionette method with modelling tools for smooth surfaces, like non-uniform rational basis spline or T-splines. The result is a versatile tool for shape modelling, suited to engineering problems related to free-form architecture.

A Review of Subsurface Crack Initiation Models in High-Cycle Fatigue for Titanium Alloys

The characterization of subsurface fatigue crack initiate sites of near α and α-β types titanium alloys and their cracking models proposed were reviewed. The crack initiation sites consisted of facets mostly on near basal plane of α grain, although the crystallographic orientation and surface topography of the facets presented a subtle difference. The crack initiation mechanisms were a quasi-cleavage accompanying high normal stress on the plane, a combination of basal slip and normal stress across the basal plane, and a pure slip on facet plane inclined near 45 degree to loading axis.