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      Disorder and compositional dependences in Urbach-Martienssen tails in amorphous (GeTe) x(Sb 2Te 3) 1−x alloys

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      Scientific Reports
      Nature Publishing Group UK

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          Abstract

          This work focuses on the compositional dependences in parameters that govern the optical properties of (GeTe) x(Sb 2Te 3) 1−x amorphous alloys in the wide spectral range from above the phonons and to the inter-band electronic transitions. We studied the absorption edge fluctuations that are linked to the variations of the bandgap E g , the width of Urbach-Martienssen tails E U , the Tauc parameter B 1/2 , and average halfwidth < FWHM> of Raman bands in amorphous (GeTe) x(Sb 2Te 3) 1−x alloys at various temperatures. Obtained results reveal the compositional trends in the influence of the disordering on the absorption processes in studied alloys.

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          Phase-change materials for rewriteable data storage.

          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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            Reversible Electrical Switching Phenomena in Disordered Structures

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              Resonant bonding in crystalline phase-change materials.

              The identification of materials suitable for non-volatile phase-change memory applications is driven by the need to find materials with tailored properties for different technological applications and the desire to understand the scientific basis for their unique properties. Here, we report the observation of a distinctive and characteristic feature of phase-change materials. Measurements of the dielectric function in the energy range from 0.025 to 3 eV reveal that the optical dielectric constant is 70-200% larger for the crystalline than the amorphous phases. This difference is attributed to a significant change in bonding between the two phases. The optical dielectric constant of the amorphous phases is that expected of a covalent semiconductor, whereas that of the crystalline phases is strongly enhanced by resonant bonding effects. The quantification of these is enabled by measurements of the electronic polarizability. As this bonding in the crystalline state is a unique fingerprint for phase-change materials, a simple scheme to identify and characterize potential phase-change materials emerges.
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                Author and article information

                Contributors
                k.shportko@ukr.net
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                15 April 2019
                15 April 2019
                2019
                : 9
                : 6030
                Affiliations
                GRID grid.466789.2, V.E. Lashkaryov Institute of Semiconductor Physics of NAS of Ukraine, ; Kyiv, Ukraine
                Article
                42634
                10.1038/s41598-019-42634-8
                6465366
                30988383
                85c7486d-b7d8-46da-b715-0b77cf2a99d2
                © The Author(s) 2019

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 20 September 2018
                : 5 April 2019
                Funding
                Funded by: DAAD, SFB 917 &amp;#x2018;Resistively Switching Chalcogenides for Future Electronics - Structure, Kinetics and Device Scalability&amp;#x2019;.
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