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Martinez P, Blanchet V, Descamps D, Dory JB, Fourment C, Papagiannouli I, Petit S, Raty JY, Noé P, Gaudin J. Sub-Picosecond Non-Equilibrium States in the Amorphous Phase of GeTe Phase-Change Material Thin Films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2102721. [PMID: 34427368 DOI: 10.1002/adma.202102721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 06/01/2021] [Indexed: 06/13/2023]
Abstract
The sub-picosecond response of amorphous germanium telluride thin film to a femtosecond laser excitation is investigated using frequency-domain interferometry and ab initio molecular dynamics. The time-resolved measurement of the surface dynamics reveals a shrinkage of the film with a dielectric properties' response faster than 300 fs. The systematic ab initio molecular dynamics simulations in non-equilibrium conditions allow the atomic configurations to be retrieved for ionic temperature from 300 to 1100 K and width of the electron distribution from 0.001 to 1.0 eV. Local order of the structures is characterized by in-depth analysis of the angle distribution, phonon modes, and pair distribution function, which evidence a transition toward a new amorphous electronic excited state close in bonding/structure to the liquid state. The results shed a new light on the optically highly excited states in chalcogenide materials involved in both important processes: phase-change materials in memory devices and ovonic threshold switching phenomenon induced by a static field.
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Affiliation(s)
- Paloma Martinez
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
| | - Valérie Blanchet
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
| | - Dominique Descamps
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
| | - Jean-Baptiste Dory
- Université Grenoble Alpes, CEA, LETI, 17 rue des Martyrs, Grenoble Cedex 9, F-38000, France
| | - Claude Fourment
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
- CEA-CESTA, 15 avenue des Sablières, CS 60001, Le Barp CEDEX, F-33116, France
| | - Irène Papagiannouli
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
| | - Stéphane Petit
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
| | - Jean-Yves Raty
- Université Grenoble Alpes, CEA, LETI, 17 rue des Martyrs, Grenoble Cedex 9, F-38000, France
- FRS-FNRS and CESAM, University of Liège, Allée du 6 Août 19, Sart-Tilman, 4000, Belgium
| | - Pierre Noé
- Université Grenoble Alpes, CEA, LETI, 17 rue des Martyrs, Grenoble Cedex 9, F-38000, France
| | - Jérôme Gaudin
- CELIA, Université Bordeaux, CEA, CNRS, UMR 5107, 351 Cours de la Libération, Talence, F-33405, France
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Sans JA, Vilaplana R, da Silva EL, Popescu C, Cuenca-Gotor VP, Andrada-Chacón A, Sánchez-Benitez J, Gomis O, Pereira ALJ, Rodríguez-Hernández P, Muñoz A, Daisenberger D, García-Domene B, Segura A, Errandonea D, Kumar RS, Oeckler O, Urban P, Contreras-García J, Manjón FJ. Characterization and Decomposition of the Natural van der Waals SnSb 2Te 4 under Compression. Inorg Chem 2020; 59:9900-9918. [PMID: 32640163 DOI: 10.1021/acs.inorgchem.0c01086] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
High pressure X-ray diffraction, Raman scattering, and electrical measurements, together with theoretical calculations, which include the analysis of the topological electron density and electronic localization function, evidence the presence of an isostructural phase transition around 2 GPa, a Fermi resonance around 3.5 GPa, and a pressure-induced decomposition of SnSb2Te4 into the high-pressure phases of its parent binary compounds (α-Sb2Te3 and SnTe) above 7 GPa. The internal polyhedral compressibility, the behavior of the Raman-active modes, the electrical behavior, and the nature of its different bonds under compression have been discussed and compared with their parent binary compounds and with related ternary materials. In this context, the Raman spectrum of SnSb2Te4 exhibits vibrational modes that are associated but forbidden in rocksalt-type SnTe; thus showing a novel way to experimentally observe the forbidden vibrational modes of some compounds. Here, some of the bonds are identified with metavalent bonding, which were already observed in their parent binary compounds. The behavior of SnSb2Te4 is framed within the extended orbital radii map of BA2Te4 compounds, so our results pave the way to understand the pressure behavior and stability ranges of other "natural van der Waals" compounds with similar stoichiometry.
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Affiliation(s)
- Juan A Sans
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain
| | - Rosario Vilaplana
- Centro de Tecnologías Físicas, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain
| | - E Lora da Silva
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain
| | | | - Vanesa P Cuenca-Gotor
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain
| | - Adrián Andrada-Chacón
- Departamento de Química-Física, MALTA-Consolider Team, Universidad Complutense de Madrid, Madrid, Spain
| | - Javier Sánchez-Benitez
- Departamento de Química-Física, MALTA-Consolider Team, Universidad Complutense de Madrid, Madrid, Spain
| | - Oscar Gomis
- Centro de Tecnologías Físicas, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain
| | - André L J Pereira
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain.,Grupo de Pesquisa de Materiais Fotonicos e Energia Renovavel - MaFER, Universidade Federal da Grande Dourados, Dourados, MS 79825-070, Brazil
| | - Plácida Rodríguez-Hernández
- Departamento de Física, MALTA-Consolider Team, Instituto de Materiales y Nanotecnología, Universidad de La Laguna, Tenerife, Spain
| | - Alfonso Muñoz
- Departamento de Física, MALTA-Consolider Team, Instituto de Materiales y Nanotecnología, Universidad de La Laguna, Tenerife, Spain
| | | | - Braulio García-Domene
- Departamento de Física Aplicada-ICMUV, MALTA-Consolider Team, Universidad de Valencia, Valencia, Spain
| | - Alfredo Segura
- Departamento de Física Aplicada-ICMUV, MALTA-Consolider Team, Universidad de Valencia, Valencia, Spain
| | - Daniel Errandonea
- Departamento de Física Aplicada-ICMUV, MALTA-Consolider Team, Universidad de Valencia, Valencia, Spain
| | - Ravhi S Kumar
- Department of Physics, University of Illinois at Chicago, Chicago Illinois 60607-7059, United States
| | - Oliver Oeckler
- Institut für Mineralogie, Kristallographie und Materialwissenschaft, Universität Leipzig, Leipzig, Germany
| | - Philipp Urban
- Institut für Mineralogie, Kristallographie und Materialwissenschaft, Universität Leipzig, Leipzig, Germany
| | | | - Francisco J Manjón
- Instituto de Diseño para la Fabricación y Producción Automatizada, MALTA-Consolider Team, Universitat Politècnica de València, Valencia, Spain
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Sukhomlinov SV, Müser MH. A mixed radial, angular, three-body distribution function as a tool for local structure characterization: Application to single-component structures. J Chem Phys 2020; 152:194502. [PMID: 33687244 DOI: 10.1063/5.0007964] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A mixed radial, angular three-body distribution function g3(rBC, θABC) is introduced, which allows the local atomic order to be more easily characterized in a single graph than with conventional correlation functions. It can be defined to be proportional to the probability of finding an atom C at a distance rBC from atom B while making an angle θABC with atoms A and B, under the condition that atom A is the nearest neighbor of B. As such, our correlation function contains, for example, the likelihood of angles formed between the nearest and the next-nearest-neighbor bonds. To demonstrate its use and usefulness, a visual library for many one-component crystals is produced first and then employed to characterize the local order in a diverse body of elemental condensed-matter systems. Case studies include the analysis of a grain boundary, several liquids (argon, copper, and antimony), and polyamorphism in crystalline and amorphous silicon including that obtained in a tribological interface.
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Affiliation(s)
- Sergey V Sukhomlinov
- Department of Materials Science and Engineering, Universität des Saarlandes, Saarbrücken, Germany
| | - Martin H Müser
- Department of Materials Science and Engineering, Universität des Saarlandes, Saarbrücken, Germany
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Ren K, Xia M, Zhu S, Wang G, Xin T, Lv S, Song Z. Crystal-Like Glassy Structure in Sc-Doped BiSbTe Ensuring Excellent Speed and Power Efficiency in Phase Change Memory. ACS APPLIED MATERIALS & INTERFACES 2020; 12:16601-16608. [PMID: 32174106 DOI: 10.1021/acsami.0c00476] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Phase change memory (PCM) is regarded as a promising technology for storage-class memory and neuromorphic computing, owing to the excellent performances in operation speed, data retention, endurance, and controllable crystallization dynamics, whereas the high power consumption of PCM remains to be a short-board characteristic that limits its extensive applications. Here, Sc-doped Bi0.5Sb1.5Te3 has been proposed for high-speed and low-power PCM applications. An operation speed of 6 ns and a threshold current of 0.7 mA have been achieved in 190 nm Sc0.23Bi0.5Sb1.5Te3 PCM, which consumes lower power than GeSbTe and ScSbTe PCM. A good endurance of 5 × 105 has been achieved, which is attributed to the small volume change of 4% during phase change and a good homogeneity phase in the crystalline state. The structure of amorphous Sc0.23Bi0.5Sb1.5Te3 has been characterized by experimental and theoretical methods, showing the existence of a large amount of crystal-like structural factions, which can efficiently minimize the atomic movements required for crystallization and subsequently improve the operation speed and power efficiency. The low diffusivity of Sc and Bi at room temperature and the rapidly increased diffusivity of Bi at elevated temperatures are fundamental for the high data retention of 94 °C and the fast crystallization in Sc0.23Bi0.5Sb1.5Te3. The combination of high atomic mobility and minimized atomic movements during crystallization ensures the high speed and low power consumption of Sc0.23Bi0.5Sb1.5Te3 PCM, which can promote its application to energy-efficient systems, that is, AI chips and wearable electronics.
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Affiliation(s)
- Kun Ren
- College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou, Zhejiang 310018, China
- State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-System and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Mengjiao Xia
- International Laboratory of Quantum Functional Materials of Henan, School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001, China
| | - Shuaishuai Zhu
- ULVAC Research Center Suzhou Company, Ltd, Suzhou 215026, China
| | - Guoxiang Wang
- Research Institute of Advanced Technologies, Laboratory of Infrared Materials and Devices, Ningbo University, Ningbo 315211, Zhejiang, China
| | - Tianjiao Xin
- State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-System and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Shilong Lv
- State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-System and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Zhitang Song
- State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-System and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
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5
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Direct atomic insight into the role of dopants in phase-change materials. Nat Commun 2019; 10:3525. [PMID: 31388013 PMCID: PMC6684653 DOI: 10.1038/s41467-019-11506-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 07/15/2019] [Indexed: 11/09/2022] Open
Abstract
Doping is indispensable to tailor phase-change materials (PCM) in optical and electronic data storage. Very few experimental studies, however, have provided quantitative information on the distribution of dopants on the atomic-scale. Here, we present atom-resolved images of Ag and In dopants in Sb2Te-based (AIST) PCM using electron microscopy and atom-probe tomography. Combing these with DFT calculations and chemical-bonding analysis, we unambiguously determine the dopants’ role upon recrystallization. Composition profiles corroborate the substitution of Sb by In and Ag, and the segregation of excessive Ag into grain boundaries. While In is bonded covalently to neighboring Te, Ag binds ionically. Moreover, In doping accelerates the crystallization and hence operation while Ag doping limits the random diffusion of In atoms and enhances the thermal stability of the amorphous phase. Quantitative imaging on the doping in phase-change materials for data storage remains scarce. Here, the authors combine electron microscopy, atom probe tomography, and simulations to determine the role of indium and silver dopants during recrystallization.
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Ren K, Zhu M, Song W, Lv S, Xia M, Wang Y, Lu Y, Ji Z, Song Z. Electrical switching properties and structural characteristics of GeSe-GeTe films. NANOSCALE 2019; 11:1595-1603. [PMID: 30475356 DOI: 10.1039/c8nr07832g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Germanium chalcogenides, especially GeSe and GeTe alloys, have recently gained popularity because of their Ovonic threshold (volatile) and memory (non-volatile) switching properties, with great potential for electric storage applications. Materials designed in a pseudo-binary way may possess superior properties in their phase transition, e.g. GeTe-Sb2Te3 materials, and bring about revolutionary advances in optical storage. However, to date, the electrical switching behaviors of films of pseudo-binary GeSe-GeTe have not yet been studied, and neither have the structural characteristics. Herein, we present both the thermally and electrically induced switching behaviors of GeSe-GeTe film, as well as the structural evolution due to composition tuning. The crystallization temperature of GeSe-GeTe films increases with GeSe content quite sensitively. An atom-resolved picture of the GeSe-GeTe alloy with a state-of-the-art atomic mapping technology has been presented, where a randomly mixed arrangement of Se and Te atoms is determined unambiguously in Ge50Se13Te34 with a GeTe-like rhombohedral structure. The local structural motifs in GeSe-GeTe, more specifically, sixfold coordinated octahedra with a distinguished degree of Peierls distortion and geometric variety, are essential to understand its electric properties. GeSe-GeTe alloy, Ge50Se13Te34, based memory cells have been fabricated, showing a fast memory switching behavior and excellent retention of 10 years at 208 °C.
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Affiliation(s)
- Kun Ren
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Micro-System and Information Technology, Chinese Academy of Sciences, Shanghai 200050, People's Republic of China.
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7
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Lukyanov A, Lubchenko V. Amorphous chalcogenides as random octahedrally bonded solids: I. Implications for the first sharp diffraction peak, photodarkening, and Boson peak. J Chem Phys 2017; 147:114505. [PMID: 28938820 DOI: 10.1063/1.4990759] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We develop a computationally efficient algorithm for generating high-quality structures for amorphous materials exhibiting distorted octahedral coordination. The computationally costly step of equilibrating the simulated melt is relegated to a much more efficient procedure, viz., generation of a random close-packed structure, which is subsequently used to generate parent structures for octahedrally bonded amorphous solids. The sites of the so-obtained lattice are populated by atoms and vacancies according to the desired stoichiometry while allowing one to control the number of homo-nuclear and hetero-nuclear bonds and, hence, effects of the mixing entropy. The resulting parent structure is geometrically optimized using quantum-chemical force fields; by varying the extent of geometric optimization of the parent structure, one can partially control the degree of octahedrality in local coordination and the strength of secondary bonding. The present methodology is applied to the archetypal chalcogenide alloys AsxSe1-x. We find that local coordination in these alloys interpolates between octahedral and tetrahedral bonding but in a non-obvious way; it exhibits bonding motifs that are not characteristic of either extreme. We consistently recover the first sharp diffraction peak (FSDP) in our structures and argue that the corresponding mid-range order stems from the charge density wave formed by regions housing covalent and weak, secondary interactions. The number of secondary interactions is determined by a delicate interplay between octahedrality and tetrahedrality in the covalent bonding; many of these interactions are homonuclear. The present results are consistent with the experimentally observed dependence of the FSDP on arsenic content, pressure, and temperature and its correlation with photodarkening and the Boson peak. They also suggest that the position of the FSDP can be used to infer the effective particle size relevant for the configurational equilibration in covalently bonded glassy liquids, where the identification of the effective rigid molecular unit is ambiguous.
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Affiliation(s)
- Alexey Lukyanov
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
| | - Vassiliy Lubchenko
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
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8
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Boschker JE, Wang R, Calarco R. GeTe: a simple compound blessed with a plethora of properties. CrystEngComm 2017. [DOI: 10.1039/c7ce01040k] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A selection from the wide range of functional properties present in the binary compound, GeTe, are reviewed is this paper.
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Affiliation(s)
- Jos E. Boschker
- Paul-Drude-Institut für Festkörperelektronik
- 10117 Berlin
- Germany
| | - Ruining Wang
- Paul-Drude-Institut für Festkörperelektronik
- 10117 Berlin
- Germany
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9
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Ordered Peierls distortion prevented at growth onset of GeTe ultra-thin films. Sci Rep 2016; 6:32895. [PMID: 27612303 PMCID: PMC5017194 DOI: 10.1038/srep32895] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 08/03/2016] [Indexed: 11/26/2022] Open
Abstract
Using reflection high-energy electron diffraction (RHEED), the growth onset of molecular beam epitaxy (MBE) deposited germanium telluride (GeTe) film on Si(111)-(√3 × √3)R30°-Sb surfaces is investigated, and a larger than expected in-plane lattice spacing is observed during the deposition of the first two molecular layers. High-resolution transmission electron microscopy (HRTEM) confirms that the growth proceeds via closed layers, and that those are stable after growth. The comparison of the experimental Raman spectra with theoretical calculated ones allows assessing the shift of the phonon modes for a quasi-free-standing ultra-thin GeTe layer with larger in-plane lattice spacing. The manifestation of the latter phenomenon is ascribed to the influence of the interface and the confinement of GeTe within the limited volume of material available at growth onset, either preventing the occurrence of Peierls dimerization or their ordered arrangement to occur normally.
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10
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Levin EM, Kramer MJ. Role of chemically and thermally induced crystal lattice distortion in enhancing the Seebeck coefficient in complex tellurides. CrystEngComm 2016. [DOI: 10.1039/c6ce01405d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Mayo M, Yahel E, Greenberg Y, Makov G. Short range order in liquid pnictides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:505102. [PMID: 24219904 DOI: 10.1088/0953-8984/25/50/505102] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Liquid pnictides have anomalous physical properties and complex radial distribution functions. The quasi-crystalline model of liquid structure is applied to interpret the three-dimensional structure of liquid pnictides. It is shown that all the column V elements can be characterized by a short range order lattice symmetry similar to that of the underlying solid, the A7 structure, which originates from a Peierls distorted simple cubic lattice. The evolution of the liquid structure down the column as well as its temperature and pressure dependence is interpreted by means of the effect of thermodynamic parameters on the Peierls distortion. Surprisingly, it is found that the Peierls effect increases with temperature and the nearest neighbour distances exhibit negative thermal expansion.
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Affiliation(s)
- M Mayo
- Materials Engineering Department, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
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12
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Park SJ, Jang MH, Park SJ, Ahn M, Park DB, Ko DH, Cho MH. Effect of amorphization on the structural stability and reversibility of Ge2Sb2Te5 and oxygen incorporated Ge2Sb2Te5 films. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c2jm31764h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Lencer D, Salinga M, Wuttig M. Design rules for phase-change materials in data storage applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2011; 23:2030-2058. [PMID: 21469218 DOI: 10.1002/adma.201004255] [Citation(s) in RCA: 146] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Indexed: 05/30/2023]
Abstract
Phase-change materials can rapidly and reversibly be switched between an amorphous and a crystalline phase. Since both phases are characterized by very different optical and electrical properties, these materials can be employed for rewritable optical and electrical data storage. Hence, there are considerable efforts to identify suitable materials, and to optimize them with respect to specific applications. Design rules that can explain why the materials identified so far enable phase-change based devices would hence be very beneficial. This article describes materials that have been successfully employed and dicusses common features regarding both typical structures and bonding mechanisms. It is shown that typical structural motifs and electronic properties can be found in the crystalline state that are indicative for resonant bonding, from which the employed contrast originates. The occurence of resonance is linked to the composition, thus providing a design rule for phase-change materials. This understanding helps to unravel characteristic properties such as electrical and thermal conductivity which are discussed in the subsequent section. Then, turning to the transition kinetics between the phases, the current understanding and modeling of the processes of amorphization and crystallization are discussed. Finally, present approaches for improved high-capacity optical discs and fast non-volatile electrical memories, that hold the potential to succeed present-day's Flash memory, are presented.
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Affiliation(s)
- Dominic Lencer
- I. Physikalisches Institut IA, RWTH Aachen University, Germany
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14
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Kolobov AV, Krbal M, Fons P, Tominaga J, Uruga T. Distortion-triggered loss of long-range order in solids with bonding energy hierarchy. Nat Chem 2011; 3:311-6. [PMID: 21430691 DOI: 10.1038/nchem.1007] [Citation(s) in RCA: 168] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Accepted: 02/08/2011] [Indexed: 11/09/2022]
Abstract
An amorphous-to-crystal transition in phase-change materials like Ge-Sb-Te is widely used for data storage. The basic principle is to take advantage of the property contrast between the crystalline and amorphous states to encode information; amorphization is believed to be caused by melting the materials with an intense laser or electrical pulse and subsequently quenching the melt. Here, we demonstrate that distortions in the crystalline phase may trigger a collapse of long-range order, generating the amorphous phase without going through the liquid state. We further show that the principal change in optical properties occurs during the distortion of the still crystalline structure, upsetting yet another commonly held belief that attributes the change in properties to the loss of long-range order. Furthermore, our results suggest a way to lower energy consumption by condensing phase change inducing energy into shorter pulses or through the use of coherent phonon excitation.
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Affiliation(s)
- A V Kolobov
- Nanodevice Innovation Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba 305-8562, Japan.
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15
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Zhugayevych A, Lubchenko V. An intrinsic formation mechanism for midgap electronic states in semiconductor glasses. J Chem Phys 2010; 132:044508. [DOI: 10.1063/1.3298989] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
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16
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Local atomic structure and chemical bonding in liquid Te: An ab initio molecular-dynamics simulation. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.04.113] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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17
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Wuttig M, Yamada N. Phase-change materials for rewriteable data storage. NATURE MATERIALS 2007; 6:824-32. [PMID: 17972937 DOI: 10.1038/nmat2009] [Citation(s) in RCA: 946] [Impact Index Per Article: 55.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.
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Affiliation(s)
- Matthias Wuttig
- Physikalisches Institut, RWTH Aachen University, 52056 Aachen, Germany.
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18
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Raty JY, Schwegler E, Bonev SA. Electronic and structural transitions in dense liquid sodium. Nature 2007; 449:448-51. [PMID: 17898764 DOI: 10.1038/nature06123] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2007] [Accepted: 07/19/2007] [Indexed: 11/09/2022]
Abstract
At ambient conditions, the light alkali metals are free-electron-like crystals with a highly symmetric structure. However, they were found recently to exhibit unexpected complexity under pressure. It was predicted from theory--and later confirmed by experiment--that lithium and sodium undergo a sequence of symmetry-breaking transitions, driven by a Peierls mechanism, at high pressures. Measurements of the sodium melting curve have subsequently revealed an unprecedented (and still unexplained) pressure-induced drop in melting temperature from 1,000 K at 30 GPa down to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behaviour in dense sodium. We show that molten sodium undergoes a series of pressure-induced structural and electronic transitions, analogous to those observed in solid sodium but commencing at much lower pressure in the presence of liquid disorder. As pressure is increased, liquid sodium initially evolves by assuming a more compact local structure. However, a transition to a lower-coordinated liquid takes place at a pressure of around 65 GPa, accompanied by a threefold drop in electrical conductivity. This transition is driven by the opening of a pseudogap, at the Fermi level, in the electronic density of states--an effect that has not hitherto been observed in a liquid metal. The lower-coordinated liquid emerges at high temperatures and above the stability region of a close-packed free-electron-like metal. We predict that similar exotic behaviour is possible in other materials as well.
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Wuttig M, Lüsebrink D, Wamwangi D, Wełnic W, Gillessen M, Dronskowski R. The role of vacancies and local distortions in the design of new phase-change materials. NATURE MATERIALS 2007; 6:122-8. [PMID: 17173032 DOI: 10.1038/nmat1807] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Accepted: 11/13/2006] [Indexed: 05/09/2023]
Abstract
Phase-change materials are of tremendous technological importance ranging from optical data storage to electronic memories. Despite this interest, many fundamental properties of phase-change materials, such as the role of vacancies, remain poorly understood. 'GeSbTe'-based phase-change materials contain vacancy concentrations around 10% in their metastable crystalline structure. By using density-functional theory, the origin of these vacancies has been clarified and we show that the most stable crystalline phases with rocksalt-like structures are characterized by large vacancy concentrations and local distortions. The ease by which vacancies are formed is explained by the need to annihilate energetically unfavourable antibonding Ge-Te and Sb-Te interactions in the highest occupied bands. Understanding how the interplay between vacancies and local distortions lowers the total energy helps to design novel phase-change materials as evidenced by new experimental data.
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Affiliation(s)
- Matthias Wuttig
- I. Physikalisches Institut (IA), RWTH Aachen, 52056 Aachen, Germany.
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