Texture (chemistry)

In physical chemistry and materials science, texture is the distribution of crystallographic orientations of a polycrystalline sample (it is also part of the geological fabric). A sample in which these orientations are fully random is said to have no distinct texture. If the crystallographic orientations are not random, but have some preferred orientation, then the sample has a weak, moderate or strong texture. The degree is dependent on the percentage of crystals having the preferred orientation. Texture is seen in almost all engineered materials, and can have a great influence on materials properties. The texture forms in materials during thermo-mechanical processes, for example during production processes e.g. rolling. Consequently, the rolling process is often followed by a heat treatment to reduce the amount of unwanted texture. Controlling the production process in combination with the characterization of texture and the material's microstructure help to determine the materials

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CH-633: Advanced Solid State and Surface Characterization

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Competition on Counter Measures to 2-D Facial Spoofing Attacks

André Anjos, Murali Mohan Chakka, Sébastien Marcel, Zhiwei Zhang

Spoofing identities using photographs is one of the most common techniques to attack 2-D face recognition systems. There seems to exist no comparative studies of different techniques using the same protocols and data. The motivation behind this competition is to compare the performance of different state-of-the-art algorithms on the same database using a unique evaluation method. Six different teams from universities around the world have participated in the contest. Use of one or multiple techniques from motion, texture analysis and liveness detection appears to be the common trend in this competition. Most of the algorithms are able to clearly separate spoof attempts from real accesses. The results suggest the investigation of more complex attacks.

2011

Biaxial texture development in aluminum nitride layers during off-axis sputter deposition

Paul Muralt

Polycrystalline aluminum nitride (AlN) layers were deposited by pulsed-dc reactive magnetron sputtering from a variable deposition angle alpha = 0 degrees-84 degrees in 5 mTorr pure N-2 at room temperature. X-ray diffraction pole figure analyses show that layers deposited from a normal angle (alpha=0 degrees) exhibit fiber texture, with a random in-plane grain orientation and the c-axis tilted by 42 degrees +/- 2 degrees off the substrate normal, yielding wurtzite AlN grains with the {10 (1) over bar2} plane approximately parallel (+/-2 degrees) to the substrate surface. However, as alpha is increased to 45 degrees, two preferred in-plane grain orientations emerge, with populations I and II having the c-axis tilted toward and away from the deposition flux, by 53 degrees +/- 2 degrees and 47 degrees +/- 1 degrees off the substrate normal, respectively. Increasing alpha further to 65 degrees and 84 degrees, results in the development of a single population II with a 43 degrees +/- 1 degrees tilt. This developing biaxial texture is attributed to a competitive growth mode under conditions where the adatom mobility is sufficient to cause intergrain mass transport, but insufficient for the thermodynamically favored low energy {0001} planes to align parallel to the layer surface. Consequently, AlN nuclei are initially randomly oriented and form a kinetically determined crystal habit exposing {0001} and {11 (2) over bar0} facets. The expected direction of its highest growth rate is 49 degrees +/- 5 degrees tilted relative to the c-axis, in good agreement with the 42 degrees-53 degrees measured tilt. The in-plane preferred orientation for alpha > 0 degrees is well explained by the orientation dependence in the cross section of the asymmetric pyramidal nuclei to capture directional deposition flux. The observed tilt is ideal for shear mode electromechanical coupling, which is maximized at 48 degrees. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4732129]

American Vacuum Society2012

van der Waals Epitaxy of Earth-Abundant Zn3P2 on Graphene for Photovoltaics

Cyril Cayron, Simon Robert Escobar Steinvall, Anna Fontcuberta i Morral, Nicolas Philippe Laurent Humblot, Shreyas Sanjay Joglekar, Jean-Baptiste Leran, Roland Logé, Rajrupa Paul, Elias Zsolt Stutz, Mahdi Zamani

Earth-abundant semiconducting materials are a potential solution for large-scale deployment of solar cells at a lower cost. Zinc phosphide (Zn3P2) is one such Earth-abundant material with optoelectronic properties suitable for photovoltaics. Herein, we report the van der Waals epitaxy of tetragonal Zn3P2 (α-Zn3P2) on graphene using molecular beam epitaxy. The growth on graphene progresses by the formation of Zn3P2 triangular flakes, which merge to form a thin film with a strong (101) crystallographic texture. Photoluminescence from the Zn3P2 thin films is consistent with previously reported Zn3P2. This work demonstrates that the need for a lattice-matched substrate can be circumvented by the use of graphene as a substrate. Moreover, the synthesis of highquality Zn3P2 flakes and films on graphene brings new material choices for low-cost photovoltaic applications.

2020