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  1. Article ; Online: Extraction of local structure differences in silica based on unsupervised learning.

    Lu, Anh Khoa Augustin / Lin, Jianbo / Futamura, Yasunori / Sakurai, Tetsuya / Tamura, Ryo / Miyazaki, Tsuyoshi

    Physical chemistry chemical physics : PCCP

    2024  Volume 26, Issue 15, Page(s) 11657–11666

    Abstract: Silica exhibits a rich phase diagram with numerous stable structures existing at different temperature and pressure conditions, including its glassy form. In large-scale atomistic simulations, due to the small energy difference, several phases may ... ...

    Abstract Silica exhibits a rich phase diagram with numerous stable structures existing at different temperature and pressure conditions, including its glassy form. In large-scale atomistic simulations, due to the small energy difference, several phases may coexist. While, in terms of long-range order, there are clear differences between these phases, their short- or medium-range structural properties are similar for many phases, thus making it difficult to detect the structural differences. In this study, a methodology based on unsupervised learning is proposed to detect the differences in local structures between eight phases of silica, using atomic models prepared by molecular dynamics (MD) simulations. A combination of two-step locality preserving projections (TS-LPP) and locally averaged atomic fingerprints (LAAF) descriptor was employed to find a low-dimensional space in which the differences among all the phases can be detected. From the distance between each structure in the found low-dimensional space, the similarity between the structures can be discussed and subtle local changes in the structures can be detected. Using the obtained low-dimensional space, the β-α transition in quartz at a low temperature was analyzed, as well as the structural evolution during the melt-quench process starting from α-quartz. The proper differentiation and ease of visualization make the present methodology promising for improving the analysis of the structure and properties of glasses, where subtle differences in structure appear due to differences in the temperature and pressure conditions at which they were synthesized.
    Language English
    Publishing date 2024-04-17
    Publishing country England
    Document type Journal Article
    ZDB-ID 1476244-4
    ISSN 1463-9084 ; 1463-9076
    ISSN (online) 1463-9084
    ISSN 1463-9076
    DOI 10.1039/d3cp06298h
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Entropy-driven docosahedral short-range order in simple liquids and glasses.

    Nishio, Kengo / Lu, Anh Khoa Augustin / Miyazaki, Takehide

    Physical review. E

    2019  Volume 99, Issue 2-1, Page(s) 22121

    Abstract: The energetically favored icosahedral structure has been seen as the central figure for describing the local structure of simple liquids and glasses. Although regular icosahedral structures are rarely found, it is accepted that distorted icosahedral ... ...

    Abstract The energetically favored icosahedral structure has been seen as the central figure for describing the local structure of simple liquids and glasses. Although regular icosahedral structures are rarely found, it is accepted that distorted icosahedral structures occur in simple liquids and glasses. However, which local structure dominates and why it is more frequent than the others remain unanswered questions. In this study, by using a recently developed structure descriptor, we show that docosahedral structures are the most favored not only in models of simple liquids and glasses but also in an experimental colloid glass. We also show that the the predominance of docosahedral structures is entropy-driven. Our findings represent a significant milestone towards comprehending mysterious phenomena such as supercooling, glass transition, and crystallization, where local structures play a key role.
    Language English
    Publishing date 2019-03-21
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2844562-4
    ISSN 2470-0053 ; 2470-0045
    ISSN (online) 2470-0053
    ISSN 2470-0045
    DOI 10.1103/PhysRevE.99.022121
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article: On Hydrogenated Bilayer GaN: New Stable Structures along the c-Plane, m-Plane, or a-Plane

    Lu, Anh Khoa Augustin / Yayama, Tomoe / Morishita, Tetsuya / Nakanishi, Takeshi

    Journal of physical chemistry. 2020 July 10, v. 124, no. 31

    2020  

    Abstract: Two-dimensional III–V materials such as GaN have been realized experimentally in recent years. While their pristine two-dimensional structures have been studied in detail in previous works, the effect of the environment, such as hydrogen passivation, ... ...

    Abstract Two-dimensional III–V materials such as GaN have been realized experimentally in recent years. While their pristine two-dimensional structures have been studied in detail in previous works, the effect of the environment, such as hydrogen passivation, remains unclear. In the present work, new stable buckled structures of hydrogenated bilayer GaN are uncovered using first-principles calculations. It is shown that different types of structures are favored, depending on the hydrogen concentration. Interestingly, in several cases, structures along the a- or m-plane are the most stable, instead of the often-studied c-plane, with a significant difference in their properties. First-principles molecular dynamics (FPMD) simulations confirm that these structures are stable at a finite temperature. Therefore, the process used to grow two-dimensional GaN can be adjusted to tailor its atomic structure and properties.
    Keywords hydrogen ; molecular dynamics ; temperature
    Language English
    Dates of publication 2020-0710
    Size p. 16888-16894.
    Publishing place American Chemical Society
    Document type Article
    Note NAL-AP-2-clean
    ISSN 1932-7455
    DOI 10.1021/acs.jpcc.0c01709
    Database NAL-Catalogue (AGRICOLA)

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  4. Article ; Online: Toward an Understanding of the Electric Field-Induced Electrostatic Doping in van der Waals Heterostructures: A First-Principles Study.

    Lu, Anh Khoa Augustin / Houssa, Michel / Radu, Iuliana P / Pourtois, Geoffrey

    ACS applied materials & interfaces

    2017  Volume 9, Issue 8, Page(s) 7725–7734

    Abstract: Since the discovery of graphene, a broad range of two-dimensional (2D) materials has captured the attention of the scientific communities. Materials, such as hexagonal boron nitride (hBN) and the transition metal dichalcogenides (TMDs) family, have shown ...

    Abstract Since the discovery of graphene, a broad range of two-dimensional (2D) materials has captured the attention of the scientific communities. Materials, such as hexagonal boron nitride (hBN) and the transition metal dichalcogenides (TMDs) family, have shown promising semiconducting and insulating properties that are very appealing for the semiconductor industry. Recently, the possibility of taking advantage of the properties of 2D-based heterostructures has been investigated for low-power nanoelectronic applications. In this work, we aim at evaluating the relation between the nature of the materials used in such heterostructures and the amplitude of the layer-to-layer charge transfer induced by an external electric field, as is typically present in nanoelectronic gated devices. A broad range of combinations of TMDs, graphene, and hBN has been investigated using density functional theory. Our results show that the electric field induced charge transfer strongly depends on the nature of the 2D materials used in the van der Waals heterostructures and to a lesser extent on the relative orientation of the materials in the structure. Our findings contribute to the building of the fundamental understanding required to engineer electrostatically the doping of 2D materials and to establish the factors that drive the charge transfer mechanisms in electron tunneling-based devices. These are key ingredients for the development of 2D-based nanoelectronic devices.
    Language English
    Publishing date 2017-03-01
    Publishing country United States
    Document type Journal Article
    ISSN 1944-8252
    ISSN (online) 1944-8252
    DOI 10.1021/acsami.6b14722
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Large-Scale 1T'-Phase Tungsten Disulfide Atomic Layers Grown by Gas-Source Chemical Vapor Deposition.

    Okada, Mitsuhiro / Pu, Jiang / Lin, Yung-Chang / Endo, Takahiko / Okada, Naoya / Chang, Wen-Hsin / Lu, Anh Khoa Augustin / Nakanishi, Takeshi / Shimizu, Tetsuo / Kubo, Toshitaka / Miyata, Yasumitsu / Suenaga, Kazu / Takenobu, Taishi / Yamada, Takatoshi / Irisawa, Toshifumi

    ACS nano

    2022  Volume 16, Issue 8, Page(s) 13069–13081

    Abstract: The control of crystal polymorphism and exploration of metastable, two-dimensional, 1T'-phase, transition-metal dichalcogenides (TMDs) have received considerable research attention. 1T'-phase TMDs are expected to offer various opportunities for the study ...

    Abstract The control of crystal polymorphism and exploration of metastable, two-dimensional, 1T'-phase, transition-metal dichalcogenides (TMDs) have received considerable research attention. 1T'-phase TMDs are expected to offer various opportunities for the study of basic condensed matter physics and for its use in important applications, such as devices with topological states for quantum computing, low-resistance contact for semiconducting TMDs, energy storage devices, and as hydrogen evolution catalysts. However, due to the high energy difference and phase change barrier between 1T' and the more stable 2H-phase, there are few methods that can be used to obtain monolayer 1T'-phase TMDs. Here, we report on the chemical vapor deposition (CVD) growth of 1T'-phase WS
    Language English
    Publishing date 2022-07-18
    Publishing country United States
    Document type Journal Article
    ISSN 1936-086X
    ISSN (online) 1936-086X
    DOI 10.1021/acsnano.2c05699
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Book ; Online: Enhanced ferromagnetism in artificially stretched lattice in quasi two-dimensional Cr2Ge2Te6

    Idzuchi, Hiroshi / Allcca, Andres E Llacsahuanga / Lu, Anh Khoa Augustin / Saito, Mitsuhiro / Houssa, Michel / Meng, Ruishen / Inoue, Kazutoshi / Pan, Xing-Chen / Tanigaki, Katsumi / Ikuhara, Yuichi / Nakanishi, Takeshi / Chen, Yong P

    2023  

    Abstract: In the fundamental understanding of magnetic interactions between atoms in solids, the crystal lattice is one of the key parameters. As the effective tool for controlling the lattice using tensile stress is limited, there are only few demonstrations of ... ...

    Abstract In the fundamental understanding of magnetic interactions between atoms in solids, the crystal lattice is one of the key parameters. As the effective tool for controlling the lattice using tensile stress is limited, there are only few demonstrations of the control in magnetic properties with expanding the lattice structure. Here, we observe that the Curie temperature (Tc) of quasi two-dimensional Cr2Ge2Te6 with NiO overlayer doubles from ~60 K to ~120 K, describe a clear correlation of magnetic properties with lattice expansion, which is characterized by several probes and computational approaches, and address on the mechanisms leading to the increase in Tc via the change in exchange interactions.
    Keywords Condensed Matter - Materials Science
    Publishing date 2023-06-15
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

    Full text online

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  7. Article: Toward an Understanding of the Electric Field-Induced Electrostatic Doping in van der Waals Heterostructures: A First-Principles Study

    Lu, Anh Khoa Augustin / Houssa Michel / Pourtois Geoffrey / Radu Iuliana P

    ACS Applied Materials & Interfaces. 2017 Mar. 01, v. 9, no. 8

    2017  

    Abstract: Since the discovery of graphene, a broad range of two-dimensional (2D) materials has captured the attention of the scientific communities. Materials, such as hexagonal boron nitride (hBN) and the transition metal dichalcogenides (TMDs) family, have shown ...

    Abstract Since the discovery of graphene, a broad range of two-dimensional (2D) materials has captured the attention of the scientific communities. Materials, such as hexagonal boron nitride (hBN) and the transition metal dichalcogenides (TMDs) family, have shown promising semiconducting and insulating properties that are very appealing for the semiconductor industry. Recently, the possibility of taking advantage of the properties of 2D-based heterostructures has been investigated for low-power nanoelectronic applications. In this work, we aim at evaluating the relation between the nature of the materials used in such heterostructures and the amplitude of the layer-to-layer charge transfer induced by an external electric field, as is typically present in nanoelectronic gated devices. A broad range of combinations of TMDs, graphene, and hBN has been investigated using density functional theory. Our results show that the electric field induced charge transfer strongly depends on the nature of the 2D materials used in the van der Waals heterostructures and to a lesser extent on the relative orientation of the materials in the structure. Our findings contribute to the building of the fundamental understanding required to engineer electrostatically the doping of 2D materials and to establish the factors that drive the charge transfer mechanisms in electron tunneling-based devices. These are key ingredients for the development of 2D-based nanoelectronic devices.
    Keywords boron nitride ; electric field ; graphene ; industry ; ingredients ; methodology ; semiconductors ; van der Waals forces
    Language English
    Dates of publication 2017-0301
    Size p. 7725-7734.
    Publishing place American Chemical Society
    Document type Article
    ISSN 1944-8252
    DOI 10.1021%2Facsami.6b14722
    Database NAL-Catalogue (AGRICOLA)

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