Change In Growth Direction Research Articles

Nanostructured Al2O3-YAG-ZrO2 ternary eutectic components prepared by laser engineered net shaping

The present work proposed a novel 3D printing approach for fabricating ternary eutectic ceramics (Al2O3-YAG-ZrO2, or AYZ in short) using laser engineered net shaping (LENS) technique. Highly dense (≥98%) thin wall components with refined eutectic microstructures were successfully fabricated. The as-fabricated ceramic eutectics mainly consist of cellular eutectics with three phases interpenetrated. In each deposited layer, the solidified microstructure changes from planar to cellular along building direction. The evolution of characteristic dimension of microstructure can be well interpreted using Jackson-Hunt relationship. Irregular interpenetrating to regular fibrous eutectic structure transition occurs at boundary region of LENSed specimens, primarily due to much higher solidification rate. The texture of <0001>Al2O3//<001>YAG//<001>ZrO2 is recognized at the interior region of LENSed eutectic part along building direction, but gradually tilts from central to edge due to change of cellular growth direction. The LENSed AYZ samples exhibit almost isotropic property, and have mechanical performances comparable to those fabricated using conventional direction solidification methods.

Evaluation of interfacial structure of [111] and [001] oriented epitaxial NiO layers on GaAs substrate by non-destructive techniques

The interface at NiO and GaAs heterojunction is found to have claudetite phase of As2O3 with monoclinic structure, which increases with oxygen (O2) partial pressure. It is determined that rough interface, caused by recrystallization of GaAs surface along [111] direction, is not the main governing factor for the observed change in growth direction for NiO epitaxial layer from [111] to [001] direction with increase in O2 partial pressure. The out-of-plane and in-plane epitaxial relationships of [111] oriented NiO layer with respect to substrate are [111]NiO || [001]GaAs, [-1-12]NiO || [-1-10]GaAs and [-110]NiO || [-110]GaAs. The interfacial structure of NiO/GaAs heterojunction thus determined can have implications into the characteristics of optoelectronic devices based on this heterojunction.

An evolutionarily conserved NIMA-related kinase directs rhizoid tip growth in the basal land plant Marchantia polymorpha.

Tip growth is driven by turgor pressure and mediated by the polarized accumulation of cellular materials. How a single polarized growth site is established and maintained is unclear. Here, we analyzed the function of NIMA-related protein kinase 1 (MpNEK1) in the liverwort Marchantia polymorpha In the wild type, rhizoid cells differentiate from the ventral epidermis and elongate through tip growth to form hair-like protrusions. In Mpnek1 knockout mutants, rhizoids underwent frequent changes in growth direction, resulting in a twisted and/or spiral morphology. The functional MpNEK1-Citrine protein fusion localized to microtubule foci in the apical growing region of rhizoids. Mpnek1 knockouts exhibited increases in both microtubule density and bundling in the apical dome of rhizoids. Treatment with the microtubule-stabilizing drug taxol phenocopied the Mpnek1 knockout. These results suggest that MpNEK1 directs tip growth in rhizoids through microtubule organization. Furthermore, MpNEK1 expression rescued ectopic outgrowth of epidermal cells in the Arabidopsis thaliana nek6 mutant, strongly supporting an evolutionarily conserved NEK-dependent mechanism of directional growth. It is possible that such a mechanism contributed to the evolution of the early rooting system in land plants.

Root cap-mediated evaluation of soil resistance towards graviresponding roots of maize (Zea mays L.) and the relevance of ethylene

Besides biological and chemical impacts, mechanical resistance represents an important obstacle that growing roots face. Graviresponding roots must assess the mechanical resistance of the substrate and take decisions on whether they change growth direction and grow around obstacles or tolerate growth conditions impaired to varying degrees. To test the significance of the root cap, we measured pressure and growth behaviour of single intact, as well as decapped, roots encountering diverse mechanical obstacles. We examined ethylene emission in intact roots as well as roots without a root cap, thereby lacking the capacity to deviate. Roots of fixed seedlings were grown vertically onto diverse mechanical obstacles. Developing pressure profiles of vertically growing roots encountering horizontal mechanical obstacles were measured employing electronic milligram scales, with and without root caps in given local environmental conditions. The evolution of root-borne ethylene was measured in intact roots and roots without the root cap. In contrast to decapped roots, intact roots develop a tentative, short-lasting pressure profile, the resolution of which is characterized by a definite change of growth direction. Similarly, pressure profiles and strengths of roots facing gradually differing surface resistances differ significantly between the two. This correlates in the short term with root cap-dependent ethylene emission which is lacking in roots without caps. The way gravistimulated and graviresponding roots cope with exogenous stimuli depends on whether and how they adapt to these impacts. With respect to mechanical hindrances, roots without caps do not seem to be able to evaluate soil strengths in order to respond adequately. On encountering resistance, roots with intact caps emit ethylene, which is not observed in decapped roots. It therefore appears that it is the root cap which specifically orchestrates the resistance needed to overcome mechanical resistance by specifically inducing ethylene.

Nanostructured Al &lt;sub&gt;2&lt;/sub&gt;O &lt;sub&gt;3&lt;/sub&gt;-YAG-ZrO &lt;sub&gt;2&lt;/sub&gt; Ternary Eutectic Components Prepared by Laser Engineered Net Shaping

The present work proposed a novel 3D printing approach for fabricating ternary eutectic ceramics (Al2O3-YAG-ZrO2, or AYZ in short) using laser engineered net shaping (LENS) technique. Highly dense (≥ 98%) thin wall components with refined eutectic microstructures were successfully fabricated. The as-fabricated ceramic eutectics mainly consist of cellular eutectics with three phases interpenetrated. In each deposited layer, the solidified microstructure changes from planar to cellular along building direction. The evolution of characteristic dimension of microstructure can be well interpreted using Jackson-Hunt relationship. Irregular interpenetrating to regular fibrous eutectic structure transition occurs at boundary region of LENSed specimens, primarily due to much higher solidification rate. The texture of Al2O3 // YAG // ZrO2 is recognized at the interior region of LENSed eutectic part along building direction, but gradually tilts from central to edge due to change of cellular growth direction. The LENSed AYZ samples exhibit almost isotropic property, and have mechanical performances comparable to those fabricated using conventional direction solidification methods.

Solution processed ZnO homogeneous quasisuperlattice materials

Heterogeneous multilayered oxide channel materials have enabled low temperature, high mobility thin film transistor technology by solution processing. The authors report the growth and characterization of solution-based, highly uniform and c-axis orientated zinc oxide (ZnO) single and multilayered thin films. Quasisuperlattice (QSL) metal oxide thin films are deposited by spin-coating and the structural, morphological, optical, electronic, and crystallographic properties are investigated. In this work, the authors show that uniform, coherent multilayers of ZnO can be produced from liquid precursors using an iterative coating-drying technique that shows epitaxial-like growth on SiO2, at a maximum temperature of 300 °C in air. As QSL films are grown with a greater number of constituent layers, the crystal growth direction changes from m-plane to c-plane, confirmed by x-ray and electron diffraction. The film surface is smooth for all QSLs with root mean square roughness &amp;lt;0.14 nm. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) of electronic defects in the QSL structure show a dependence of defect emission on the QSL thickness, and PL mapping demonstrates that the defect signature is consistent across the QSL film in each case. XPS and valence-band analysis shown a remarkably consistent surface composition and electronic structure during the annealing process developed here.

Patterned semiconductor structures modulate neuronal outgrowth: Implication for the development of a neurobionic interface

Auditory implants stimulate the neurons by broad electrical fields, which leads to a low number of spectral channels. A reduction in the distance between the electrode and the neuronal structures might lead to better electrical transduction. The use of microstructured semiconductors offers a large number of contacts, which could attract neurons and stimulate them individually. To investigate the interaction between neurons and semiconductors, differentiated neuronal precursor cells were cultured on silicon wafers. Different structures were added on the wafers by electron beam lithography, and deep reactive ion etching in different depths (2 and 7 µm). Grooved surfaces guided the neurons and resulted in straight oriented axons, but neuronal outgrowth was impaired by the 7 µm grooves. Within the 7 µm structures, the neuronal cell body was totally encased and the nuclei were deformed from a round to an elliptical shape. On both square and cylindrical structures neuronal bridging could be detected in different forms, either between the tops of the structures or between the bottom and the top. Furthermore, neuronal bridges were established on the lateral part of the structures, and change in direction of neuronal growth was induced by the structure. Finally, it could be shown that neuronal growth cones were particularly attracted by the top of the cylinders, which might allow for the stimulation of neurons via this structure. In conclusion, study results indicate that structured semiconductors can modulate neuronal growth and its direction, offering a novel method for the development of new implants with improved neuronal stimulation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 65-72, 2018.

Zigzag configurations of hafnium carbide nanowires synthesised by chemical vapour deposition below the eutectic temperature

Hafnium carbide nanowires were synthesised by a Ni-catalysed vacuum chemical vapour deposition method below the eutectic temperature of the Ni–C–Hf alloy. The zigzag growth behaviour of the hafnium carbide nanowires resulting from metastable growth was investigated by transmission electron microscopy in order to understand the sub-eutectic growth. Three typical zigzag configurations at joint angles of ∼125°, 45°, and 90° can be observed from the synthesised nanowires, where the structure with an angle of ∼125° is the most common, formed via a change in the growth direction from [ 2 ¯ 1 1 ¯ ] to [ 01 1 ¯ ] , or vice versa. The 45° zigzag structure is the second most common and is formed by alternating the axial direction three times between 〈011〉 and 〈001〉. The number of the zigzag structures with a 90° angle is the most rare among the three types and is formed by the change in growth direction between two energy-equal directions, from [ 1 ¯ 1 ¯ 0 ] to [ 1 1 ¯ 0 ] . Although alternating the growth direction brings about the zigzag geometry, the zigzag structured hafnium carbide nanowires have a single-crystal structure. In addition, the surface energies of the crystal planes play an important role in the growth of the hafnium carbide zigzag nanowires.

Mobergellans from the early Cambrian of Greenland and Labrador: new morphological details and implications for the functional morphology of mobergellans

AbstractNew morphological features of the mobergellan Discinella micans (Billings, 1871) from the lower Cambrian (Stage 4) of Northeast Greenland and southern Labrador are described. The new features include: (1) the morphology of the larval shell, which is shown to be cap-shaped, subcircular, and with impressions of the internal muscle attachment scars; (2) a range of unusual shell deformations (changes in growth direction resulting in thickened shells, partial detachment of shell laminae and subsequent regrowth, internal projections of shell material increasing the depth of the shell by up to 150%, disturbances and irregular fusion of muscle scars). In addition, we provide new details about the variability in number and shape of the anteriormost internal muscle scars, which often fuse and may vary in number from one to three (resulting in nine to 11 scars in total). Together the new observations provide additional strength for the hypothesis that mobergellan shells represent opercula of an as yet unknown tubular organism.

Facile Green Synthesis of WO3·H2O Nanoplates and WO3 Nanowires with Enhanced Photoelectrochemical Performance

The synthesis of nanostructured materials with controlled shape without using a capping agent and/or a hazardous chemical is one of the major existing challenges. Herein, we report a facile precipitation method to synthesize stacked orthorhombic tungsten trioxide hydrate (WO3·H2O) nanoplates by simply mixing WCl6 (0.025 M) in ethanol at room temperature for 1 h. On subsequent solvothermal treatment of WO3·H2O nanoplates at 200 °C in ethanol, formation of monoclinic tungsten trioxide (WO3) nanowires of <20 nm diameter is demonstrated. The morphology evolution of WO3 nanowires from WO3·H2O nanoplates and change in growth direction through dissolution and recrystallization process is further confirmed by varying the solvothermal duration and temperature. The as-synthesized WO3·H2O nanoplates and WO3 nanowires are used as photoanodes for the hydrogen generation through photoelectrochemical (PEC) water splitting in a neutral pH. The photocurrent density of WO3 nanowires is found ∼21 times higher than that of W...

Thermal conductivity of yttria-stabilized zirconia thin films with a zigzag microstructure

Yttria-stabilized zirconia (YSZ) is the most common material used as a thermal barrier in several engineering applications. In order to improve the insulator potential of these thin films, an oblique-angle deposition approach was used to grow YSZ with tilted columnar structures. Initially, the period (n) was defined as the repetition unit composed of two layers each with different columnar growth directions, and then, n was increased (n = 1, 2, 10, 30, and 50), keeping constant the total thickness (∼3.50 μm). The influence of (n) on the structure, roughness, grain size, microstructure, and thermal conductivity (κ) of thin films deposited was determined by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy, and hot-plate technique, respectively. For all the samples, XRD patterns indicate the presence of the characteristic 8YSZ tetragonal phase peaks. Through AFM analysis, it was established that the roughness of the films deposited decreases from (4.0 ± 0.6) to (2.0 ± 0.6) nm when n is increased. Cross-sectional images recorded by SEM corroborate the formation of marked interfaces when growth direction changes occur, allowing to identify a multilayer system with a “zigzag” microstructure and an evolution towards more refined and isolated columns. Moreover, the SEM images reveal that for n = 10, 30, 50, and 70, the growth direction of the column is perpendicular to the substrate plane, losing its tilted form and the “zigzag” behavior becomes intra-columnar, reaching nanometer scale. Finally, analyses by hot-plate technique for different n repetition units showed that the thermal conductivity of YSZ films decreases from 0.151 W/m K to 0.064 W/m K, establishing the direct influence of the “zigzag” microstructure on the κ value. This study shows the potential of growing YSZ thin films by oblique-angle deposition as an effective method to improving the thermal insulator potential of this material.

Influence of substrate temperature on morphology and behavior under cyclic thermal load of gas flow sputtered zirconia coatings

The aim of this work is to gain an understanding of the influence of substrate temperature during deposition on the resulting microstructure and crystallographic properties of gas flow sputtered (GFS) partially yttria stabilized zirconia coatings (PSZ).PSZ coatings were deposited on a FeCrAl-Alloy substrate, varying the substrate temperature between 500°C and 800°C. Regardless of the substrate temperature, all coatings were columnar, but varied in their morphology. Four different groups of sub-microstructures, each defined by a substrate temperature range, were identified based on morphology and X-ray diffraction (XRD) pattern.The two low-temperature groups exhibit a novel microstructure characterized by three dense ridges at intervals of 120° converging at the column center. Supported by these ridges small stacked plates lead to a featherlike porosity. The XRD pattern revealed a monoclinic fraction, besides the tetragonal and/or cubic one, and a 〈111〉 growth direction. Higher temperatures diminish the monoclinic fraction until it vanishes at 800°C accompanied by a change in growth direction to 〈100〉.Thermal cycling experiments were conducted between 1050°C and 100°C. Macroscopic spallation occurred for one group while the other samples were intact after the end of the experiment at 1300cycles. Microscopic delaminations were found between a pure alumina scale and a mixed oxide zone, consisting of zirconia particles embedded into an alumina matrix. A hypothesis was proposed explaining the observed failure mode.

Influence of withdrawing speed on the porous structures of Gasar ingots fabricated by Bridgman method

The pore straightness of Gasar ingots was investigated through experiments and numerical simulation. The pore growth direction changes from diverging to convergent as the withdrawing speed increases, and straight pores are obtained when the solid/liquid interfaces are almost planar. The optimum withdrawing speed to obtain straight pores increases as the sample size decreases. Under optimum conditions, the average pore diameter of the small ingot is smaller than that of the large ingot, while the penetrative porosity of the large ingot is superior. The shape of the solid/liquid interfaces at the bottom of the ingot can be improved effectively by modifying the structure of the mold. Bridgman method is applicable for the fabrication of Gasar ingots with large size and high quality, and suitable sample size should be considered for different structural requirements.

Mechanism of competitive grain growth in a curvilinear channel of crystal-sorter during the orientational solidification of nickel-based heat-resistant alloy

Using numerical simulation in the ProCAST program complex, the conditions of the solidification of heat-resistant nickel alloy in curvilinear channels of a ceramic mold have been investigated. It has been shown that, in practically important cases, the vector of the temperature gradient is oriented along the axis of the curvilinear channel. In a spiral crystal selector, a cyclic change in the preferred direction of growth occurs because of the cyclic change in the direction of the vector of the temperature gradient. The fact that the vector of the temperature gradient is almost always directed along the axis of the curvilinear channel makes it possible to govern the orientation of the vector of the temperature gradient in space and, therefore, to obtain a grain with the preferred crystallographic orientation. Based on the results of this investigation, a method of the grain selection with a desired azimuthal orientation is proposed.

Understanding misfit strain releasing mechanisms via molecular dynamics simulations of CdTe growth on {112}zinc-blende CdS

Molecular dynamics simulations have been used to analyse microstructures of CdTe films grown on {112} surfaces of zinc-blende CdS. Interestingly, CdTe films grow in ⟨331⟩ orientations as opposed to ⟨112⟩ epitaxial orientations. At the CdTe-{331}/CdS-{112} interface, however, there exists an axis that is parallel to the ⟨110⟩ orientation of both CdS and CdTe. It is the direction orthogonal to this ⟨110⟩ that becomes different, being ⟨116⟩ for CdTe and ⟨111⟩ for CdS, respectively. Missing CdTe-{110} planes are found along the ⟨110⟩ axis, suggesting that the misfit strain is released by the conventional misfit dislocation mechanism along this axis. In the orthogonal axis, the misfit strain is found to be more effectively released by the new grain orientation mechanism. Our finding is supported by literature experimental observations of the change of growth direction when Cd0.96Zn0.04Te films are deposited on GaAs. Analyses of energetics clearly demonstrate the cause for the formation of the new orientation, and the insights gained from our studies can help understand the grain structures experimentally observed in lattice mismatched systems.

Influence of Growth Rate and Magnetic Field on Microstructure and Properties of Directionally Solidified Ag-Cu Eutectic Alloy.

We report the influence of growth rate and external magnetic field on the eutectic lamellar spacing and properties of directionally-solidified Ag-Cu eutectic alloys. The results indicated that the relationship between the lamellar spacing of directionally-solidified Ag-Cu alloys and the growth rate matched the prediction of the Jackson-Hunt model, and the constant was 5.8 µm3/s. The increasing external magnetic field during solidification tilted the growth direction of the lamellar eutectics, and coarsened the eutectic lamellar spacing. These decreased the microhardness and strength of Ag-Cu alloys, but increased their electrical conductivity. The competitive strengthening contributions between the refinement of the eutectic lamellar spacing and the change in growth direction of the eutectics resulted in higher strength in the as-rolled sample with a 0.8 T magnetic field than with other samples, which was confirmed from higher relieved deformation energy using differential scanning calorimetry.

Morphology Control of Zinc Oxide Nanostructure on Single Layer Graphene.

Various morphologies of zinc oxide (ZnO) nanostructures on single layer graphene were synthesized by electrodeposition method. The current density was utilized to control the morphology of the ZnO. The Scanning Electron Microscope (SEM) was used to examine the surface morphology of the samples. SEM analysis shows morphology changes to nanorod, flower, and flakes with increase in the current density from 0.1, 0.2, and 0.3 mA/cm(-1) respectively. The XRD, XPS, and Raman spectroscopy were adopted to characterize the ZnO nanostructure and to understand the formation of various morphologies. The Raman result clearly shows extra modes due to for flakes structure caused by c-axis orientation along the substrate direction. Further, XPS data also supports formation of ZnO without any other intermediate compound such as Zn(OH)2. The formation of various morphologies was correlated to the formation different ratio of Zn2+ and OH- ions and the change in growth direction due to various current densities.

Growth strategies of the tabulate coral Favosites bohemicus on unstable, soft substrates: An example from the Hamar Laghdad (Lower Devonian, Anti-Atlas, Morocco)

Coralla of the tabulate coral Favosites bohemicus coming from the famous Kess-Kess mud mound locality of the Hamar Laghdad (SE Morocco) area have been studied with respect to their growth patterns and colony development. The Emsian Kess-Kess mounds developed in a relatively deep-water, low-energy environment, below fair-weather wave-base. After the mound growth ceased, the slopes of the mounds were covered by soft, muddy sediment and colonised by tabulate corals. The morphological characteristics of F. bohemicus coralla analysed in the present study document various responses of the coral colonies to sediment creeping on the steeply inclined slopes. The coralla are massive and display a strong variability in shape and size; most of the specimens are, however, of spherical and sub-spherical shape. The striking feature of the majority of the colonies is that they are either deflected and tilted in one direction, or display indications of being continuously overturned, both features reflecting changes in growth direction of the corals. The tilted and curved direction of growth was likely caused by the slow creeping of the sediment, along with which the colonies were being slowly moved down the slope. The most important factor that controlled the intensity of the mass movements was presumably the slope inclination, which varied among both different mounds and different slopes of individual mounds. Since corals affected differently by mass movements of variable strength attained various sizes and shapes, morphological analyses of F. bohemicus provide clues on the sediment characteristics, as well as type and frequency of mass movements in the cover of the Kess-Kess mud mounds, enabling valuable insights into the initial stages of their burial.

Equivalent Activities of Repulsive Axon Guidance Receptors.

A prevailing concept that has emerged in the axon guidance field is the importance of repulsion as a guidance mechanism for steering axons to their appropriate targets. Given the number and variety of different repulsive receptors, it is generally thought that there are differences in the signals that they transduce. However, this has never been tested directly. We have used the advanced genetics of Drosophila to compare directly the outputs of different repulsive receptors. Surprisingly, we found no qualitative differences in receptor-mediated repulsion, suggesting that, despite their highly diverged domain structure, each receptor couples to a common repulsive pathway. We went on to show that this common pathway involves Trio, a guanine nucleotide exchange factor known to promote cytoskeletal remodeling.

Surgical treatment of adolescent internal condylar resorption (AICR) with articular disc repositioning and orthognathic surgery in the growing patient--a pilot study.

BackgroundThe aim of this study was to better understand how surgical repositioning and stabilization of anteriorly displaced articular discs using the Mitek mini-anchor technique affects condylar growth in growing patients with adolescent internal condylar resorption (AICR).MethodsTwenty-two adolescent patients diagnosed with AICR and anterior temporomandibular disc displacement were compared to untreated control subjects without AICR matched for age, sex, and Angle classification. Pre-surgical (T1 and T2) and post-surgical (T3 and T4) mandibular tracings were superimposed on natural stable structures to evaluate the horizontal, vertical, and total changes in the position of condylion.ResultsThe treated group showed an overall decrease in condylar height pre-surgically and statistically significant changes in condylar growth direction between the pre- and post-surgical observation periods. Pre-surgically, the treated group showed significantly more posterior condylar growth than the control group; they also showed inferior condylar growth, while the controls showed superior growth. Controls and patients in the treated group showed no significant differences in condylar growth post-surgically.ConclusionsAdolescent patients diagnosed with AICR and anterior disc displacement treated with mandibular ramus and maxillary osteotomies, along with Mitek anchors to reposition internally deranged discs, showed post-surgical normalization of condylar growth.