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Maßmeyer O, Günkel R, Glowatzki J, Klement P, Ojaghi Dogahe B, Kachel SR, Gruber F, Müller M, Fey M, Schörmann J, Belz J, Beyer A, Gottfried JM, Chatterjee S, Volz K. Synthesis of 2D Gallium Sulfide with Ultraviolet Emission by MOCVD. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024:e2402155. [PMID: 38795001 DOI: 10.1002/smll.202402155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 04/18/2024] [Indexed: 05/27/2024]
Abstract
Two-dimensional (2D) materials exhibit the potential to transform semiconductor technology. Their rich compositional and stacking varieties allow tailoring materials' properties toward device applications. Monolayer to multilayer gallium sulfide (GaS) with its ultraviolet band gap, which can be tuned by varying the layer number, holds promise for solar-blind photodiodes and light-emitting diodes as applications. However, achieving commercial viability requires wafer-scale integration, contrasting with established, limited methods such as mechanical exfoliation. Here the one-step synthesis of 2D GaS is introduced via metal-organic chemical vapor deposition on sapphire substrates. The pulsed-mode deposition of industry-standard precursors promotes 2D growth by inhibiting the vapor phase and on-surface pre-reactions. The interface chemistry with the growth of a Ga adlayer that results in an epitaxial relationship is revealed. Probing structure and composition validate thin-film quality and 2D nature with the possibility to control the thickness by the number of GaS pulses. The results highlight the adaptability of established growth facilities for producing atomically thin to multilayered 2D semiconductor materials, paving the way for practical applications.
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Affiliation(s)
- Oliver Maßmeyer
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - Robin Günkel
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - Johannes Glowatzki
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - Philip Klement
- Institute of Experimental Physics I and Center for Materials Research, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, D-35392, Giessen, Germany
| | - Badrosadat Ojaghi Dogahe
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - Stefan Renato Kachel
- Material Sciences Center and Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany
| | - Felix Gruber
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - Marius Müller
- Institute of Experimental Physics I and Center for Materials Research, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, D-35392, Giessen, Germany
| | - Melanie Fey
- Institute of Experimental Physics I and Center for Materials Research, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, D-35392, Giessen, Germany
| | - Jörg Schörmann
- Institute of Experimental Physics I and Center for Materials Research, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, D-35392, Giessen, Germany
| | - Jürgen Belz
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - Andreas Beyer
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
| | - J Michael Gottfried
- Material Sciences Center and Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany
| | - Sangam Chatterjee
- Institute of Experimental Physics I and Center for Materials Research, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, D-35392, Giessen, Germany
| | - Kerstin Volz
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Hans-Meerwein-Straße 6, 35043, Marburg, Germany
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2
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Lee H, Heo E, Yoon H. Physically Exfoliating 2D Materials: A Versatile Combination of Different Materials into a Layered Structure. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:18678-18695. [PMID: 38095583 DOI: 10.1021/acs.langmuir.3c02418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2023]
Abstract
Improving the properties of the existing two-dimensional (2D) materials is a major concern for many researchers today. Synergistic coupling of single-phase 2D material species with secondary functional materials has resulted in 2D nanohybrids with significantly enhanced properties beyond the sum of their individual components. In particular, nanohybrids created by alternatingly integrating different material species in the confined 2D nanometer regime have the potential to meet the needs of a wide variety of applications, particularly the many important energy-related applications that are of interest. However, scaling up production of 2D nanohybrids is still challenging, which is a major barrier to their practical application. Delamination and exfoliation by physical means separate the weakly bound 2D nanosheets into kinetically stable single- or few-layers. Herein, we provide a concise overview of recent achievements in the physical exfoliation-based fabrication of 2D nanohybrids featuring controlled heterolayered structures. Several strategies to efficiently produce heterolayered 2D nanohybrids in large quantities are described, such as (i) coexfoliation of different 2D species, (ii) aqueous-phase synthesis, and (iii) gas-phase synthesis. The versatility of the 2D nanohybrids was also illustrated by remarkable research examples, especially in energy-related applications.
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Affiliation(s)
- Haney Lee
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, South Korea
| | - Eunseo Heo
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, South Korea
| | - Hyeonseok Yoon
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, South Korea
- School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, South Korea
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3
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Sari B, Zeltmann SE, Zhao C, Pelz PM, Javey A, Minor AM, Ophus C, Scott MC. Analysis of Strain and Defects in Tellurium-WSe 2 Moiré Heterostructures Using Scanning Nanodiffraction. ACS NANO 2023; 17:22326-22333. [PMID: 37956410 PMCID: PMC10690779 DOI: 10.1021/acsnano.3c04283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2023] [Revised: 11/02/2023] [Accepted: 11/03/2023] [Indexed: 11/15/2023]
Abstract
In recent years, there has been an increasing focus on 2D nongraphene materials that range from insulators to semiconductors to metals. As a single-elemental van der Waals semiconductor, tellurium (Te) has captivating anisotropic physical properties. Recent work demonstrated growth of ultrathin Te on WSe2 with the atomic chains of Te aligned with the armchair directions of the substrate using physical vapor deposition (PVD). In this system, a moiré superlattice is formed where micrometer-scale Te flakes sit on top of the continuous WSe2 film. Here, we determined the precise orientation of the Te flakes with respect to the substrate and detailed structure of the resulting moiré lattice by combining electron microscopy with image simulations. We directly visualized the moiré lattice using center of mass-differential phase contrast (CoM-DPC). We also investigated the local strain within the Te/WSe2 layered materials using scanning nanodiffraction techniques. There is a significant tensile strain at the edges of flakes along the direction perpendicular to the Te chain direction, which is an indication of the preferred orientation for the growth of Te on WSe2. In addition, we observed local strain relaxation regions within the Te film, specifically attributed to misfit dislocations, which we characterize as having a screw-like nature. The detailed structural analysis gives insight into the growth mechanisms and strain relaxation in this moiré heterostructure.
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Affiliation(s)
- Bengisu Sari
- Department
of Materials Science and Engineering, University
of California Berkeley, Berkeley, California 94720, United States
- The
National Center for Electron Microscopy, Molecular Foundry, Berkeley, California 94720, United States
- Materials
Science Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720-8099, United States
| | - Steven E. Zeltmann
- Department
of Materials Science and Engineering, University
of California Berkeley, Berkeley, California 94720, United States
| | - Chunsong Zhao
- Department
of Materials Science and Engineering, University
of California Berkeley, Berkeley, California 94720, United States
- Materials
Science Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720-8099, United States
- Department
of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, California 94720, United States
| | - Philipp M. Pelz
- Institute
of Micro- and Nanostructure Research, Center for Nanoanalysis and
Electron Microscopy, Interdisciplinary Center for Nanostructured Films, Friedrich-Alexander-Universitat Erlangen-Nurnberg, Erlangen 91058, Germany
| | - Ali Javey
- Materials
Science Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720-8099, United States
- Department
of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, California 94720, United States
| | - Andrew M. Minor
- Department
of Materials Science and Engineering, University
of California Berkeley, Berkeley, California 94720, United States
- The
National Center for Electron Microscopy, Molecular Foundry, Berkeley, California 94720, United States
| | - Colin Ophus
- The
National Center for Electron Microscopy, Molecular Foundry, Berkeley, California 94720, United States
| | - Mary C. Scott
- Department
of Materials Science and Engineering, University
of California Berkeley, Berkeley, California 94720, United States
- The
National Center for Electron Microscopy, Molecular Foundry, Berkeley, California 94720, United States
- Materials
Science Division, Lawrence Berkeley National
Laboratory, Berkeley, California 94720-8099, United States
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4
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Zhang H, Ahmadi M, Ginanjar WW, Blake GR, Kooi BJ. Effects of Intermixing in Sb 2Te 3/Ge 1+xTe Multilayers on the Thermoelectric Power Factor. ACS APPLIED MATERIALS & INTERFACES 2023; 15:22672-22683. [PMID: 37122126 PMCID: PMC10176324 DOI: 10.1021/acsami.3c00869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Over the past few decades, telluride-based chalcogenide multilayers, such as PbSeTe/PbTe, Bi2Te3/Sb2Te3, and Bi2Te3/Bi2Se3, were shown to be promising high-performance thermoelectric films. However, the stability of performance in operating environments, in particular, influenced by intermixing of the sublayers, has been studied rarely. In the present work, the nanostructure, thermal stability, and thermoelectric power factor of Sb2Te3/Ge1+xTe multilayers prepared by pulsed laser deposition are investigated by transmission electron microscopy and Seebeck coefficient/electrical conductivity measurements performed during thermal cycling. Highly textured Sb2Te3 films show p-type semiconducting behavior with superior power factor, while Ge1+xTe films exhibit n-type semiconducting behavior. The elemental mappings indicate that the as-deposited multilayers have well-defined layered structures. Upon heating to 210 °C, these layer structures are unstable against intermixing of sublayers; nanostructural changes occur on initial heating, even though the highest temperature is close to the deposition temperature. Furthermore, the diffusion is more extensive at domain boundaries leading to locally inclined structures there. The Sb2Te3 sublayers gradually dissolve into Ge1+xTe. This dissolution depends markedly on the relative Ge1+xTe film thickness. Rather, full dissolution occurs rapidly at 210 °C when the Ge1+xTe sublayer is substantially thicker than that of Sb2Te3, whereas the dissolution is very limited when the Ge1+xTe sublayer is substantially thinner. The resulting variations of the nanostructure influence the Seebeck coefficient and electrical conductivity and thus the power factor in a systematic manner. Our results shed light on a previously unreported correlation of the power factor with the nanostructural evolution of unstable telluride multilayers.
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Affiliation(s)
- Heng Zhang
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Majid Ahmadi
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Wastu Wisesa Ginanjar
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Graeme R Blake
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Bart J Kooi
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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5
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Meng Y, Li X, Kang X, Li W, Wang W, Lai Z, Wang W, Quan Q, Bu X, Yip S, Xie P, Chen D, Li D, Wang F, Yeung CF, Lan C, Liu C, Shen L, Lu Y, Chen F, Wong CY, Ho JC. Van der Waals nanomesh electronics on arbitrary surfaces. Nat Commun 2023; 14:2431. [PMID: 37105992 PMCID: PMC10140039 DOI: 10.1038/s41467-023-38090-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 04/14/2023] [Indexed: 04/29/2023] Open
Abstract
Chemical bonds, including covalent and ionic bonds, endow semiconductors with stable electronic configurations but also impose constraints on their synthesis and lattice-mismatched heteroepitaxy. Here, the unique multi-scale van der Waals (vdWs) interactions are explored in one-dimensional tellurium (Te) systems to overcome these restrictions, enabled by the vdWs bonds between Te atomic chains and the spontaneous misfit relaxation at quasi-vdWs interfaces. Wafer-scale Te vdWs nanomeshes composed of self-welding Te nanowires are laterally vapor grown on arbitrary surfaces at a low temperature of 100 °C, bringing greater integration freedoms for enhanced device functionality and broad applicability. The prepared Te vdWs nanomeshes can be patterned at the microscale and exhibit high field-effect hole mobility of 145 cm2/Vs, ultrafast photoresponse below 3 μs in paper-based infrared photodetectors, as well as controllable electronic structure in mixed-dimensional heterojunctions. All these device metrics of Te vdWs nanomesh electronics are promising to meet emerging technological demands.
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Affiliation(s)
- You Meng
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
- State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Xiaocui Li
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
- Department of Mechanical Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Xiaolin Kang
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Wanpeng Li
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Wei Wang
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
- State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Zhengxun Lai
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Weijun Wang
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Quan Quan
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Xiuming Bu
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - SenPo Yip
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, 816-8580, Japan
| | - Pengshan Xie
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Dong Chen
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Dengji Li
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Fei Wang
- State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, 130021, China.
| | - Chi-Fung Yeung
- Department of Chemistry, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Changyong Lan
- School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu, 610054, P. R. China
| | - Chuntai Liu
- Key Laboratory of Advanced Materials Processing & Mold (Zhengzhou University), Ministry of Education, Zhengzhou, 450002, P.R. China
| | - Lifan Shen
- College of Microelectronics and Key Laboratory of Optoelectronics Technology, Faculty of Information Technology, Beijing University of Technology, Beijing, 100124, P.R. China
| | - Yang Lu
- Department of Mechanical Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Furong Chen
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR
| | - Chun-Yuen Wong
- State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR.
- Department of Chemistry, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR.
| | - Johnny C Ho
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR.
- State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon, 999077, Hong Kong SAR.
- Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, 816-8580, Japan.
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Kim D, Kim Y, Oh JS, Lee C, Lim H, Yang CW, Sim E, Cho MH. Conversion between Metavalent and Covalent Bond in Metastable Superlattices Composed of 2D and 3D Sublayers. ACS NANO 2022; 16:20758-20769. [PMID: 36469438 DOI: 10.1021/acsnano.2c07811] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Reversible conversion over multimillion times in bond types between metavalent and covalent bonds becomes one of the most promising bases for universal memory. As the conversions have been found in metastable states, an extended category of crystal structures from stable states via redistribution of vacancies, research on kinetic behavior of the vacancies is highly in demand. However, it remains lacking due to difficulties with experimental analysis. Herein, the direct observation of the evolution of chemical states of vacancies clarifies the behavior by combining analysis on charge density distribution, electrical conductivity, and crystal structures. Site-switching of vacancies of Sb2Te3 gradually occurs with diverged energy barriers owing to their own activation code: the accumulation of vacancies triggers spontaneous gliding along atomic planes to relieve electrostatic repulsion. Studies on the behavior can be further applied to multiphase superlattices composed of Sb2Te3 (2D) and GeTe (3D) sublayers, which represent superior memory performances, but their operating mechanisms were still under debate due to their complexity. The site-switching is favorable (suppressed) when Te-Te bonds are formed as physisorption (chemisorption) over the interface between Sb2Te3 (2D) and GeTe (3D) sublayers driven by configurational entropic gain (electrostatic enthalpic loss). Depending on the type of interfaces between sublayers, phases of the superlattices are classified into metastable and stable states, where the conversion could only be achieved in the metastable state. From this comprehensive understanding on the operating mechanism via kinetic behaviors of vacancies and the metastability, further studies toward vacancy engineering are expected in versatile materials.
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Affiliation(s)
- Dasol Kim
- Department of Physics, Yonsei University, 03722 Seoul, Republic of Korea
- I. Institute of Physics, Physics of Novel Materials, RWTH Aachen University, 52056 Aachen, Germany
| | - Youngsam Kim
- Department of Chemistry, Yonsei University, 03722 Seoul, Republic of Korea
| | - Jin-Su Oh
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, 16419 Suwon, Republic of Korea
| | - Changwoo Lee
- Department of Physics, Yonsei University, 03722 Seoul, Republic of Korea
| | - Hyeonwook Lim
- Department of Physics, Yonsei University, 03722 Seoul, Republic of Korea
| | - Cheol-Woong Yang
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, 16419 Suwon, Republic of Korea
| | - Eunji Sim
- Department of Chemistry, Yonsei University, 03722 Seoul, Republic of Korea
| | - Mann-Ho Cho
- Department of Physics, Yonsei University, 03722 Seoul, Republic of Korea
- Department of System Semiconductor Engineering, Yonsei University, 03722 Seoul, Republic of Korea
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7
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Zhang Y, Si W, Jia Y, Yu P, Yu R, Zhu J. Controlling Strain Relaxation by Interface Design in Highly Lattice-Mismatched Heterostructure. NANO LETTERS 2021; 21:6867-6874. [PMID: 34382816 DOI: 10.1021/acs.nanolett.1c01938] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Strain engineering plays an important role in tuning the microstructure and properties of heterostructures. The key to implement the strain modulation to heterostructures is controlling the strain relaxation, which is generally realized by varying the thickness of thin films or changing substrates. Here, we show that interface polarity can tailor the behavior of strain relaxation in a hexagonal manganite film, whose strain state can be tuned to different extents. Using scanning transmission electron microscopy, a reconstructed atomic layer with elongated interlayer spacing and minor in-plane rotation is observed at the interface, suggesting that the bond hierarchy at interface transits from three-dimension to two-dimension, which accounts for the strain-free heteroepitaxy. Utilizing interface polarity to control the strain relaxation highlights a conceptually opt route to optimize the strain engineering and the realization of strain-free heteroepitaxy in such highly lattice-mismatched heterostructure also provides possibility to transform more bulklike functional oxides to low dimensionality.
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Affiliation(s)
- Yang Zhang
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Key Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, P.R. China
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P.R. China
- Ji Hua Laboratory, Foshan 528299, P.R. China
| | - Wenlong Si
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Key Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, P.R. China
| | - Yanli Jia
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P.R. China
| | - Pu Yu
- State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P.R. China
| | - Rong Yu
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Key Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, P.R. China
| | - Jing Zhu
- National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Key Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, P.R. China
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