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Cecchi S, Momand J, Dragoni D, Abou El Kheir O, Fagiani F, Kriegner D, Rinaldi C, Arciprete F, Holý V, Kooi BJ, Bernasconi M, Calarco R. Thick Does the Trick: Genesis of Ferroelectricity in 2D GeTe-Rich (GeTe) m (Sb 2 Te 3 ) n Lamellae. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2304785. [PMID: 37988708 PMCID: PMC10767439 DOI: 10.1002/advs.202304785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 09/28/2023] [Indexed: 11/23/2023]
Abstract
The possibility to engineer (GeTe)m (Sb2 Te3 )n phase-change materials to co-host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe)m (Sb2 Te3 )n with GeTe-rich composition is presented. These layered films feature a tunable distribution of (GeTe)m (Sb2 Te3 )1 blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe)m (Sb2 Te3 )1 lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe)m slab sandwiched in GeTe-rich blocks. That is, the net ferroelectric polarization is confined almost in-plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase-change and ferroelectric switching properties, paving the way for the conception of innovative device architectures.
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Affiliation(s)
- Stefano Cecchi
- Department of Materials ScienceUniversity of Milano‐Bicoccavia R. Cozzi 5520125MilanoItaly
- Paul‐Drude‐Institut für FestkörperelektronikLeibniz‐Institut im Forschungsverbund Berlin e.V.Hausvogteiplatz 5‐710117BerlinGermany
| | - Jamo Momand
- Zernike Institute for Advanced MaterialsUniversity of GroningenNijenborgh 49747 AGGroningenThe Netherlands
| | - Daniele Dragoni
- Department of Materials ScienceUniversity of Milano‐Bicoccavia R. Cozzi 5520125MilanoItaly
| | - Omar Abou El Kheir
- Department of Materials ScienceUniversity of Milano‐Bicoccavia R. Cozzi 5520125MilanoItaly
| | - Federico Fagiani
- Dipartimento di FisicaPolitecnico di MilanoP.zza Leonardo da Vinci 3220133MilanoItaly
| | - Dominik Kriegner
- Institute of Solid State and Materials PhysicsTechnische Universität DresdenHelmholtzstr. 1001069DresdenGermany
- Institute of PhysicsCzech Academy of SciencesCukrovarnická 10/11216200Praha 6Czech Republic
| | - Christian Rinaldi
- Dipartimento di FisicaPolitecnico di MilanoP.zza Leonardo da Vinci 3220133MilanoItaly
| | - Fabrizio Arciprete
- Dipartimento di FisicaUniversità di Roma “Tor Vergata”Via della Ricerca Scientifica 100133RomeItaly
| | - Vaclav Holý
- Department of Condensed Matter PhysicsFaculty of Mathematics and PhysicsCharles University, Ke Karlovu 512116PrahaCzech Republic
- Institute of Condensed Matter PhysicsFaculty of ScienceMasaryk UniversityKotlářská 2611 37BrnoCzech Republic
| | - Bart J. Kooi
- Zernike Institute for Advanced MaterialsUniversity of GroningenNijenborgh 49747 AGGroningenThe Netherlands
| | - Marco Bernasconi
- Department of Materials ScienceUniversity of Milano‐Bicoccavia R. Cozzi 5520125MilanoItaly
| | - Raffaella Calarco
- Paul‐Drude‐Institut für FestkörperelektronikLeibniz‐Institut im Forschungsverbund Berlin e.V.Hausvogteiplatz 5‐710117BerlinGermany
- CNR Institute for Microelectronics and Microsystems–IMMConsiglio Nazionale delle RicercheVia del Fosso del Cavaliere 10000133RomaItaly
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Reflective Terahertz Metasurfaces Based on Non-Volatile Phase Change Material for Switchable Manipulation. PHOTONICS 2022. [DOI: 10.3390/photonics9080508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Recently, metasurfaces have been investigated and exploited for various applications in the THz regime, including modulators and detectors. However, the responsive properties of the metasurface in THz stay fixed once the fabrication process is complete. This limitation can be modified when integrating the phase change material (PCM), whose states are switchable between crystalline and amorphous, into the metasurface structure. This characteristic of the PCM is appealing in achieving dynamic and customizable functionality. In this work, the reflective metasurface structure is designed as a hexagonal unit deposited on a polyimide substrate. The non-volatile PCM chosen for the numerical study is germanium antimony tellurium (GST). Our proposed phase change metasurface provides two resonant frequencies located at 1.72 and 2.70 THz, respectively; one of them shows a high contrast of reflectivity at almost 80%. The effects of geometrical parameters, incident angles, and polarization modes on the properties of the proposed structure are explored. Finally, the performances of the structure are evaluated in terms of the insertion loss and extinction ratio.
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Sakda N, Ghosh S, Chitaree R, Rahman BMA. Performance optimization of a metasurface incorporating non-volatile phase change material. OPTICS EXPRESS 2022; 30:12982-12994. [PMID: 35472922 DOI: 10.1364/oe.453612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 03/24/2022] [Indexed: 06/14/2023]
Abstract
Optical metasurface is a combination of manufactured periodic patterns of many artificial nanostructured unit cells, which can provide unique and attractive optical and electrical properties. Additionally, the function of the metasurface can be altered by adjusting the metasurface's size and configuration to satisfy a particular required property. However, once it is fabricated, such specific property is fixed and cannot be changed. Here, phase change material (PCM) can play an important role due to its two distinct states during the phase transition, referred to as amorphous and crystalline states, which exhibit significantly different refractive indices, particularly in the infrared wavelength. Therefore, a combination of metasurface with a phase change material may be attractive for achieving agile and tunable functions. In this paper, we numerically investigate an array of silicon cylinders with a thin PCM layer at their centers. The GST and GSST are the most well-known PCMs and were chosen for this study due to their non-volatile properties. This structure produces two resonant modes, magnetic dipole and electric dipole, at two different resonating wavelengths. We have numerically simulated the effect of cylinder's height and diameter on the reflecting profile, including the effect of thickness of the phase change material. Additionally, it is shown here that a superior performance can be achieved towards reduced insertion loss, enhanced extinction ratio, and increased figure of merit when a GST layer is replaced by a GSST layer.
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Lotnyk A, Behrens M, Rauschenbach B. Phase change thin films for non-volatile memory applications. NANOSCALE ADVANCES 2019; 1:3836-3857. [PMID: 36132100 PMCID: PMC9419560 DOI: 10.1039/c9na00366e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 09/17/2019] [Indexed: 06/10/2023]
Abstract
The rapid development of Internet of Things devices requires real time processing of a huge amount of digital data, creating a new demand for computing technology. Phase change memory technology based on chalcogenide phase change materials meets many requirements of the emerging memory applications since it is fast, scalable and non-volatile. In addition, phase change memory offers multilevel data storage and can be applied both in neuro-inspired and all-photonic in-memory computing. Furthermore, phase change alloys represent an outstanding class of functional materials having a tremendous variety of industrially relevant characteristics and exceptional material properties. Many efforts have been devoted to understanding these properties with the particular aim to design universal memory. This paper reviews materials science aspects of chalcogenide-based phase change thin films relevant for non-volatile memory applications. Particular emphasis is put on local structure, control of disorder and its impact on material properties, order-disorder transitions and interfacial transformations.
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Affiliation(s)
- A Lotnyk
- Leibniz Institute of Surface Engineering (IOM) Permoserstr. 15 04318 Leipzig Germany
| | - M Behrens
- Leibniz Institute of Surface Engineering (IOM) Permoserstr. 15 04318 Leipzig Germany
| | - B Rauschenbach
- Leibniz Institute of Surface Engineering (IOM) Permoserstr. 15 04318 Leipzig Germany
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Lotnyk A, Dankwort T, Hilmi I, Kienle L, Rauschenbach B. In situ observations of the reversible vacancy ordering process in van der Waals-bonded Ge-Sb-Te thin films and GeTe-Sb 2Te 3 superlattices. NANOSCALE 2019. [PMID: 31135011 DOI: 10.1016/j.scriptamat.2019.03.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Chalcogenide-based thin films are employed in data storage and memory technology whereas van der Waals-bonded layered chalcogenide heterostructures are considered to be a main contender for memory devices with low power consumption. The reduction of switching energy is due to the lowering of entropic losses governed by the restricted motion of atoms in one dimension within the crystalline states. The investigations of switching mechanisms in such superlattices have recently attracted much attention and the proposed models are still under debate. This is partially due to the lack of direct observation of atomic scale processes, which might occur in these chalcogenide systems. This work reports direct, nanoscale observations of the order-disorder processes in van der Waals bonded Ge-Sb-Te thin films and GeTe-Sb2Te3-based superlattices using in situ experiments inside an aberration-corrected transmission electron microscope. The findings reveal a reversible self-assembled reconfiguration of the structural order in these materials. This process is associated with the ordering of randomly distributed vacancies within the studied materials into ordered vacancy layers and with readjustment of the lattice plane distances within the newly formed layered structures, indicating the high flexibility of these layered chalcogenide-based systems. Thus, the ordering process results in the formation of vacancy-bonded building blocks intercalated within van der Waals-bonded units. Moreover, vacancy-bonded building blocks can be reconfigured to the initial structure under the influence of an electron beam, while in situ exposure of the recovered layers to a targeted electron beam leads to the reverse process. Overall, the outcomes provide new insights into local structure and switching mechanism in chalcogenide superlattices.
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Affiliation(s)
- Andriy Lotnyk
- Leibniz Institute of Surface Engineering (IOM), Permoserstr. 15, 04318, Leipzig, Germany.
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Direct atomic identification of cation migration induced gradual cubic-to-hexagonal phase transition in Ge2Sb2Te5. Commun Chem 2019. [DOI: 10.1038/s42004-019-0114-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Singh J, Singh G, Kaura A, Tripathi S. Effect of gradual ordering of Ge/Sb atoms on chemical bonding: A proposed mechanism for the formation of crystalline Ge2Sb2Te5. J SOLID STATE CHEM 2018. [DOI: 10.1016/j.jssc.2018.01.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Momand J, Wang R, Boschker JE, Verheijen MA, Calarco R, Kooi BJ. Dynamic reconfiguration of van der Waals gaps within GeTe-Sb 2Te 3 based superlattices. NANOSCALE 2017. [PMID: 28621784 DOI: 10.1039/c7nr01684k] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Phase-change materials based on GeSbTe show unique switchable optoelectronic properties and are an important contender for next-generation non-volatile memories. Moreover, they recently received considerable scientific interest, because it is found that a vacancy ordering process is responsible for both an electronic metal-insulator transition and a structural cubic-to-trigonal transition. GeTe-Sb2Te3 based superlattices, or specifically their interfaces, provide an interesting platform for the study of GeSbTe alloys. In this work such superlattices have been grown with molecular beam epitaxy and they have been characterized extensively with transmission electron microscopy and X-ray diffraction. It is shown that the van der Waals gaps in these superlattices, which result from vacancy ordering, are mobile and reconfigure through the film using bi-layer defects and Ge diffusion upon annealing. Moreover, it is shown that for an average composition that is close to GeSb2Te4 a large portion of 9-layered van der Waals systems is formed, suggesting that still a substantial amount of random vacancies must be present within the trigonal GeSbTe layers. Overall these results illuminate the structural organization of van der Waals gaps commonly encountered in GeSbTe alloys, which are intimately related to their electronic properties and the metal-insulator transition.
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Affiliation(s)
- Jamo Momand
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
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Mio AM, Privitera SMS, Bragaglia V, Arciprete F, Cecchi S, Litrico G, Persch C, Calarco R, Rimini E. Role of interfaces on the stability and electrical properties of Ge 2Sb 2Te 5 crystalline structures. Sci Rep 2017; 7:2616. [PMID: 28572581 PMCID: PMC5453988 DOI: 10.1038/s41598-017-02710-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 04/18/2017] [Indexed: 12/04/2022] Open
Abstract
GeSbTe-based materials exhibit multiple crystalline phases, from disordered rocksalt, to rocksalt with ordered vacancy layers, and to the stable trigonal phase. In this paper we investigate the role of the interfaces on the structural and electrical properties of Ge2Sb2Te5. We find that the site of nucleation of the metastable rocksalt phase is crucial in determining the evolution towards vacancy ordering and the stable phase. By properly choosing the substrate and the capping layers, nucleation sites engineering can be obtained, thus promoting or preventing the vacancy ordering in the rocksalt structure or the conversion into the trigonal phase. The vacancy ordering occurs at lower annealing temperatures (170 °C) for films deposited in the amorphous phase on silicon (111), compared to the case of SiO2 substrate (200 °C), or in presence of a capping layer (330 °C). The mechanisms governing the nucleation have been explained in terms of interfacial energies. Resistance variations of about one order of magnitude have been measured upon transition from the disordered to the ordered rocksalt structure and then to the trigonal phase. The possibility to control the formation of the crystalline phases characterized by marked resistivity contrast is of fundamental relevance for the development of multilevel phase change data storage.
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Affiliation(s)
- A M Mio
- Institute for Microelectronics and Microsystems (IMM), Consiglio Nazionale delle Ricerche (CNR), VIII Strada 5, 95121, Catania, Italy.,I. Physikalisches Institut (IA), RWTH Aachen University, Sommerfeldstraße 14, 52074, Aachen, Germany
| | - S M S Privitera
- Institute for Microelectronics and Microsystems (IMM), Consiglio Nazionale delle Ricerche (CNR), VIII Strada 5, 95121, Catania, Italy.
| | - V Bragaglia
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117, Berlin, Germany
| | - F Arciprete
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117, Berlin, Germany.,Dipartimento di Fisica, Università di Roma "Tor Vergata", Via della Ricerca Scientifica 1, I-00133, Rome, Italy
| | - S Cecchi
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117, Berlin, Germany
| | - G Litrico
- Institute for Microelectronics and Microsystems (IMM), Consiglio Nazionale delle Ricerche (CNR), VIII Strada 5, 95121, Catania, Italy
| | - C Persch
- I. Physikalisches Institut (IA), RWTH Aachen University, Sommerfeldstraße 14, 52074, Aachen, Germany
| | - R Calarco
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117, Berlin, Germany
| | - E Rimini
- Institute for Microelectronics and Microsystems (IMM), Consiglio Nazionale delle Ricerche (CNR), VIII Strada 5, 95121, Catania, Italy
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10
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Zallo E, Cecchi S, Boschker JE, Mio AM, Arciprete F, Privitera S, Calarco R. Modulation of van der Waals and classical epitaxy induced by strain at the Si step edges in GeSbTe alloys. Sci Rep 2017; 7:1466. [PMID: 28469258 PMCID: PMC5431103 DOI: 10.1038/s41598-017-01502-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 03/29/2017] [Indexed: 11/09/2022] Open
Abstract
The present work displays a route to design strain gradients at the interface between substrate and van der Waals bonded materials. The latter are expected to grow decoupled from the substrates and fully relaxed and thus, by definition, incompatible with conventional strain engineering. By the usage of passivated vicinal surfaces we are able to insert strain at step edges of layered chalcogenides, as demonstrated by the tilt of the epilayer in the growth direction with respect of the substrate orientation. The interplay between classical and van der Waals epitaxy can be modulated with an accurate choice of the substrate miscut. High quality crystalline GexSb2Te3+x with almost Ge1Sb2Te4 composition and improved degree of ordering of the vacancy layers is thus obtained by epitaxial growth of layers on 3-4° stepped Si substrates. These results highlight that it is possible to build and control strain in van der Waals systems, therefore opening up new prospects for the functionalization of epilayers by directly employing vicinal substrates.
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Affiliation(s)
- Eugenio Zallo
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117, Berlin, Germany.
| | - Stefano Cecchi
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117, Berlin, Germany
| | - Jos E Boschker
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117, Berlin, Germany
| | - Antonio M Mio
- Institute for Microelectronics and Microsystems (IMM), Consiglio Nazionale delle Ricerche (CNR), VIII Strada 5, I-95121, Catania, Italy
| | - Fabrizio Arciprete
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117, Berlin, Germany.,Dipartimento di Fisica, Università di Roma "Tor Vergata", Via della Ricerca Scientifica 1, I-00133, Rome, Italy
| | - Stefania Privitera
- Institute for Microelectronics and Microsystems (IMM), Consiglio Nazionale delle Ricerche (CNR), VIII Strada 5, I-95121, Catania, Italy
| | - Raffaella Calarco
- Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117, Berlin, Germany
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