Grain (céréale)

vignette|redresse|Grains de blé. vignette|redresse|Grains de maïs. vignette|redresse|Structure schématique d'un grain de blé (coupe longitudinale). Le grain est le fruit, ou la semence, des céréales (famille des Gramineae). Sur le plan botanique, c'est un caryopse, fruit sec indéhiscent contenant une seule graine dont le tégument est soudé aux tissus du péricarpe. Ce terme est dans le langage courant un quasi-synonyme de céréale, il est cependant parfois utilisé pour désigner les graines de légumes secs (famille des Leguminosae)lien web|langue =fr|url = =GRAIN subst. masc.|site = CNRTL - Lexicographie|consulté le =2022/04/23.. Parfois, « grain » et « graine » sont considérés comme des synonymes, l'un et l'autre pouvant servir de semences pour multiplier les plantes. Toutefois, outre le fait que sur le plan botanique, le grain n'est pas une graine, il y une nuance indiquée par le dictionnaire de Trévoux : le semis de

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Highly efficient, stable and hysteresis-less planar perovskite solar cell based on chemical bath treated Zn2SnO4 electron transport layer

Seckin Akin, Michael Graetzel, Ulf Anders Hagfeldt, Marco Alejandro Ruiz Preciado, Faranak Sadegh, Mohammad Mahdi Tavakoli, Wolfgang Richard Tress, Zaiwei Wang

The electron transport layer (ETL) is a key constituent in perovskite solar cells (PSCs). It should provide efficient and selective electron extraction, low resistivity and high stability. Here, zinc stannate (Zn2SnO4, ZSO) is employed as an ETL in planar PSCs. A surface treatment of a compact ZSO layer is introduced based on chemical bath deposition (CBD). CBD results in a dense and uniform surface morphology that promotes the formation of a perovskite film with better surface coverage and enlarged grains, which lead to reduced recombination losses. Such improvements effectively increase the charge extraction at ETL/perovskite interface and reduce trapassisted recombination, which results in a remarkable photovoltaic performance, low hysteresis index, and good reproducibility. The efficiency of PSCs based on CBD-modified ZSO ETL has been dramatically increased from 19.3% to 21.3% with a notable increase in open circuit voltage of 60 mV compared to bare ZSO-based devices. This value is among the highest for ZSO-based PSCs. More importantly, the CBD-treated PSCs exhibited good stability, retaining more than 90% of its initial efficiency over 1000 h under continuous illumination at maximum power point. These results demonstrate that CBD can significantly improve the performance and stability of ZSO-based planar PSCs, a crucial requirement for commercialization.

ELSEVIER2020

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Zinc blende-wurtzite polytypism in nanocrystalline ZnO films

Arthur Brian Aebersold, Duncan Alexander, Christophe Ballif, Lorenzo Fanni, Cécile Hébert, Aïcha Hessler-Wyser, Sylvain Nicolay

ZnO is commonly observed and assumed to crystallize fully in a wurtzite structure. Indeed, While polytypism between a wurtzite and a zinc blende phase is often seen in some II-VI compounds, it has only rarely been observed in ZnO. Here, by means of automated crystal orientation mapping and high resolution imaging in transmission electron microscopy, we identify nanometer-sized regions of zinc blende forming during the growth of compact nanocrystalline metal organic chemical vapor deposited ZnO films. We analyze a c-fiber-textured wurtzite ZnO film, where the columnar grain growth, typical for polycrystalline films, is interrupted by the formation of these zinc blende regions. These regions in turn provide surfaces for the heteroepitaxial renucleation of newly oriented wurtzite grains. In contrast to the columnar grains, which grow fastest along their c-axis, these new grains are identified to grow fastest along their basal plane. By means of convergent beam electron diffraction, we show that this difference in fast growth direction relates to the polarity of exposed facets. A growth model is proposed, showing how this polytypism affects the microstructure evolution of the film in ways that were not predicted by existing film growth models. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Elsevier2017

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Increasing Polycrystalline Zinc Oxide Grain Size by Control of Film Preferential Orientation

Arthur Brian Aebersold, Duncan Alexander, Christophe Ballif, Lorenzo Fanni, Cécile Hébert, Aïcha Hessler-Wyser, Monica Morales Masis, Sylvain Nicolay

We investigate the structural evolution of polycrystalline zinc oxide films grown by low pressure metal-organic chemical vapor deposition. The goal is to achieve larger grains-leading to higher charge carrier mobility from lower grain boundary density-by controlling the grain orientation during growth. The results are 2-fold. First we describe how the combination of deposition temperature and gas flow influences the nucleation and film thickening stages: low temperature and high gas flow favor a high nucleation density and the development of c-textured films, whereas high temperature and low gas flow lead to a lower nucleation density and a-textured films. Second we demonstrate how a fine control of the film preferential orientation at the different growth stages allows the fabrication of films with grains that are 25% larger, hence improving the carrier mobility with respect to the reference film.

American Chemical Society2015

Chargement

ENV-525: Physics and hydrology of snow

This course covers principles of snow physics, snow hydrology, snow-atmosphere interaction and snow modeling. It transmits sound understanding of physical processes within the snow and at its interfaces with the atmosphere and the ground, including field, laboratory, and modeling techniques.

MSE-422: Advanced metallurgy

This course covers the metallurgy, processing and properties of modern high-performance metals and alloys (e.g. advanced steels, Ni-base, Ti-base, High Entropy Alloys etc.). In addition, the principles of computational alloy design as well as approaches for a sustainable metallurgy will be addressed

MSE-302: Phase transformations

Ce cours est une introduction aux transformations de phases liquide-solide et solide-solide. Il aborde les aspects thermodynamiques et cristallographiques. Il traite principalement des matériaux métalliques, et établira des ponts vers les céramiques et la minéralogie.

Céréale

Blé

vignette|Épi de blé.« Blé » est un terme générique qui désigne plusieurs céréales appartenant au genre Triticum. Ce sont des plantes annuelles de la famille des graminées, cultivées dans de très nombr

Maïs

Le maïs (Zea mays L., ou Zea mays subsp. mays (autonyme)), appelé blé d’Inde au Canada, est une plante herbacée tropicale annuelle de la famille des Poacées (graminées), largement cultivée comme cér