High-Pressure Synthesis of Dirac Materials: Layered van der Waals Bonded BeN4 Polymorph

High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for synthesis of a Dirac material BeN4. A triclinic phase of beryllium tetranitride tr-BeN4 was synthesized from elements at ∼85 GPa. Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN4 layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated π systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN4 layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN4 layer, i.e., beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions. © 2021 American Physical Society.Parts of this research were carried out at the Extreme Conditions Beamline (P02.2) at DESY, a member of Helmholtz Association (HGF). Portions of this work were performed on beamline ID15 at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13) and at HPCAT (sector 16) of the Advanced Photon Source (APS), Argonne National Laboratory. Research was sponsored by the Army Research Office and was accomplished under the Cooperative Agreement No. W911NF-19-2-0172. N. D. and L. D. thank the Deutsche Forschungsgemeinschaft (DFG Projects No. DU 954-11/1, No. DU 393-9/2, and No. DU 393-13/1) and the Federal Ministry of Education and Research, Germany (BMBF, Grant No. No. 05K19WC1) for financial support. D. L. thanks the Alexander von Humboldt Foundation for financial support. Theoretical analysis of chemical bonding was supported by the Russian Science Foundation (Project No. 18-12-00492). Calculations of the phonon dispersion relations were supported by the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST MISIS (No. K2-2020-026) implemented by governmental decree No. 211. Support from the Knut and Alice Wallenberg Foundation (Wallenberg Scholar Grant No. KAW-2018.0194), the Swedish Government Strategic Research Areas in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971) and SeRC, the Swedish Research Council (VR) Grant No. 2019-05600 and Vinnova VINN Excellence Center Functional Nanoscale Materials (FunMat-2) Grant No. 2016–05156 is gratefully acknowledged. The computations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) partially funded by the Swedish Research Council through Grant Agreement No. 2016-07213. The work of M. I. K. was supported by the JTC-FLAGERA Project GRANSPORT. GeoSoilEnviroCARS is supported by the National Science Foundation–Earth Sciences (EAR–1634415) and Department of Energy-Geosciences (DE-FG02-94ER14466). HPCAT operations are supported by DOE-NNSA’s Office of Experimental Sciences. Advanced Photon Source is U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357

High-performance Bragg gratings in chalcogenide rib waveguides written with a modified Sagnac interferometer

This paper was published in Journal of the Optical Society of America B-Optical Physics and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=josab-23-7-1323. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Mehrdad Shokooh-Saremi, Vahid G. Ta'eed, Neil J. Baker, Ian C. M. Littler, David J. Moss, Benjamin J. Eggleton, Yinlan Ruan, and Barry Luther-Davie

Étude mécanique d’un changement de phase allotropique à l’échelle mésoscopique

Nous proposons deux types de modélisations adaptées au calcul de changements de phase allotropiques. Seules les conséquences induites par la variation de volume sont prises en compte, de façon identique à ce que l’on trouve dans les modèles de Greenwood et Johnson. Dans les années 80, Leblond proposa un modèle basé sur la croissance d’une sphère de phase dure dans une matrice plus molle afin de déterminer les lois d’évolutions élasto-plastiques. Dans une première partie, nous proposons d’étendre le modèle de Leblond en prenant également en compte la croissance de la phase molle dans une matrice de phase dure, ce qui correspond à la fin de transformation dans le processus de refroidissement. La seconde partie est consacrée à une modélisation plus fine où l’on représente explicitement le front de transformation par fonctions de niveau. Les équations de propagation du front sont résolues par éléments finis et la simulation mécanique utilise la méthode des éléments finis étendus afin d’éviter les coûteux remaillages

Refractive Index Measurements Of Planar Chalcogenide Thin Film

We report on the measurements of the refractive index of As-S-Se chalcogenide glasses near 1.55 μm. The measurements were made on annealed and non-annealed samples of thermally evaporated thin films. The data for two different series of glasses are presented: the compositions As 40S60-xSex and the compositions As xS(100-x)/2Se(100-x)/2 where the ratio of sulfur to selenium is kept constant (1:1). It has been found that replacing sulfur by selenium in the first series increases the refractive index from 2.4 to 2.8 and increasing the arsenic content in the second series increases the refractive index. In all cases, it has been found that annealing the samples increase the refractive index. The accuracy in the refractive index measurement is ±0.2%. © 2003 Elsevier B.V. All rights reserved

Refractive Index Measurements Of Planar Chalcogenide Waveguide

We report results from a systematic study of the linear refractive index of thin films made of As - S - Se glasses which are part of the chalcogenide family. We have studied eight different compositions. The refractive index are measured by the mean of a grating coupling experiment. The measurements are performed around 1.5/μm for both annealed and non-annealed glasses. We observe that annealing the samples increases their refractive index. We also note that the increase of Selenium concentration increases the refractive index and the decrease of Arsenic concentration decreases-the refractive index

Multiscale Topography Analysis of Waterjet Pocketing of Silica Glass Surfaces

International audienceGlass workpieces are mainly planar and obtained by diamond cutting however if free-form surfaces are required, manufacturing process is usually based on shaping grinding wheels. Multi-axis waterjet cutting, an other means of obtaining planar workpieces, could also be used to machine complex shapes with appropriate manufacturing strategies. Water jet pocketing could also be achieved but it brings challenging issues since the high pressure jet composed of water and abrasive particles must be contained inside the machined pocket. Water jet glass machining optimization requires understanding of numerous parameters such as interaction between the jet and the brittle material behavior or the identification of the jet himself. We focus our investigation on bottom pocket surfaces to study these parameters. Pocket bottom surfaces are characterized by multi-scale defects: shape defects influenced by the tool path and the manufacturing strategy, macro-craters at waviness scale due to the jet interactions, micro-craters at roughness scale due to particles impacts, sub-surface damages (SSD) at micro- roughness scale. This paper focuses on the study of macro and micro craters. We propose a decomposition of the multi-scale defects using modal filtering. Residual topography will then be analyzed to characterize the surface damages

The impact of team-based primary care on health care services utilization and costs: Quebec's family medicine groups

We investigate the effects on health care costs and utilization of team-based primary care delivery: Quebec's Family Medicine Groups (FMGs). FMGs include extended hours, patient enrolment and multidisciplinary teams, but they maintain the same remuneration scheme (fee-for-service) as outsid