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Morrow JD, Ugwumadu C, Drabold DA, Elliott SR, Goodwin AL, Deringer VL. Understanding Defects in Amorphous Silicon with Million-Atom Simulations and Machine Learning. Angew Chem Int Ed Engl 2024; 63:e202403842. [PMID: 38517212 DOI: 10.1002/anie.202403842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Revised: 03/14/2024] [Accepted: 03/18/2024] [Indexed: 03/23/2024]
Abstract
The structure of amorphous silicon (a-Si) is widely thought of as a fourfold-connected random network, and yet it is defective atoms, with fewer or more than four bonds, that make it particularly interesting. Despite many attempts to explain such "dangling-bond" and "floating-bond" defects, respectively, a unified understanding is still missing. Here, we use advanced computational chemistry methods to reveal the complex structural and energetic landscape of defects in a-Si. We study an ultra-large-scale, quantum-accurate structural model containing a million atoms, and thousands of individual defects, allowing reliable defect-related statistics to be obtained. We combine structural descriptors and machine-learned atomic energies to develop a classification of the different types of defects in a-Si. The results suggest a revision of the established floating-bond model by showing that fivefold-bonded atoms in a-Si exhibit a wide range of local environments-analogous to fivefold centers in coordination chemistry. Furthermore, it is shown that fivefold (but not threefold) coordination defects tend to cluster together. Our study provides new insights into one of the most widely studied amorphous solids, and has general implications for understanding defects in disordered materials beyond silicon alone.
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Affiliation(s)
- Joe D Morrow
- Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QR, United Kingdom
| | - Chinonso Ugwumadu
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute (NQPI), Ohio University, Athens, Ohio, 45701, United States
| | - David A Drabold
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute (NQPI), Ohio University, Athens, Ohio, 45701, United States
| | - Stephen R Elliott
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of, Oxford, OX1 3QZ, United Kingdom
| | - Andrew L Goodwin
- Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QR, United Kingdom
| | - Volker L Deringer
- Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QR, United Kingdom
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2
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Sun YT, Ding DW, Lu Z, Li MZ, Liu YH, Wang WH. Observation of an isothermal glass transition in metallic glasses. J Chem Phys 2024; 160:044501. [PMID: 38258930 DOI: 10.1063/5.0188538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Accepted: 12/22/2023] [Indexed: 01/24/2024] Open
Abstract
Glass transition, commonly manifested upon cooling a liquid, is continuous and cooling rate dependent. For decades, the thermodynamic basis in liquid-glass transition has been at the center of debate. Here, long-time isothermal annealing was conducted via molecular dynamics simulations for metallic glasses to explore the connection of physical aging in supercooled liquid and glassy states. An anomalous two-step aging is observed in various metallic glasses, exhibiting features of supercooled liquid dynamics in the first step and glassy dynamics in the second step, respectively. Furthermore, the transition potential energy is independent of initial states, proving that it is intrinsic for a metallic glass at a given temperature. We propose that the observed dynamic transition from supercooled liquid dynamics to glassy dynamics could be glass transition manifested isothermally. On this basis, glass transition is no longer cooling rate dependent, but is shown as a clear phase boundary in the temperature-energy phase diagram. Hence, a modified out-of-equilibrium phase diagram is proposed, providing new insights into the nature of glass transition.
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Affiliation(s)
- Yi-Tao Sun
- Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, China
| | - Da-Wei Ding
- Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Zhen Lu
- Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Mao-Zhi Li
- Department of Physics, Beijing Key Laboratory of Opto-Electronic Functional Materials and Micro-Nano Devices, Renmin University of China, Beijing 100872, China
- Key Laboratory of Quantum State Construction and Manipulation (Ministry of Education), Renmin University of China, Beijing 100872, China
| | - Yan-Hui Liu
- Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wei-Hua Wang
- Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
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3
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Eltareb A, Lopez GE, Giovambattista N. Nuclear quantum effects on the dynamics and glass behavior of a monatomic liquid with two liquid states. J Chem Phys 2022; 156:204502. [DOI: 10.1063/5.0087680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We perform path integral molecular dynamics (PIMD) simulations of a monatomic liquid that exhibits a liquid–liquid phase transition and liquid–liquid critical point. PIMD simulations are performed using different values of Planck’s constant h, allowing us to study the behavior of the liquid as nuclear quantum effects (NQE, i.e., atoms delocalization) are introduced, from the classical liquid ( h = 0) to increasingly quantum liquids ( h > 0). By combining the PIMD simulations with the ring-polymer molecular dynamics method, we also explore the dynamics of the classical and quantum liquids. We find that (i) the glass transition temperature of the low-density liquid (LDL) is anomalous, i.e., [Formula: see text] decreases upon compression. Instead, (ii) the glass transition temperature of the high-density liquid (HDL) is normal, i.e., [Formula: see text] increases upon compression. (iii) NQE shift both [Formula: see text] and [Formula: see text] toward lower temperatures, but NQE are more pronounced on HDL. We also study the glass behavior of the ring-polymer systems associated with the quantum liquids studied (via the path-integral formulation of statistical mechanics). There are two glass states in all the systems studied, low-density amorphous ice (LDA) and high-density amorphous ice (HDA), which are the glass counterparts of LDL and HDL. In all cases, the pressure-induced LDA–HDA transformation is sharp, reminiscent of a first-order phase transition. In the low-quantum regime, the LDA–HDA transformation is reversible, with identical LDA forms before compression and after decompression. However, in the high-quantum regime, the atoms become more delocalized in the final LDA than in the initial LDA, raising questions on the reversibility of the LDA–HDA transformation.
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Affiliation(s)
- Ali Eltareb
- Department of Physics, Brooklyn College of the City University of New York, Brooklyn, New York 11210, USA
- PhD Program in Physics, The Graduate Center of the City University of New York, New York, New York 10016, USA
| | - Gustavo E. Lopez
- Department of Chemistry, Lehman College of the City University of New York, Bronx, New York 10468, USA
- PhD Program in Chemistry, The Graduate Center of the City University of New York, New York, New York 10016, USA
| | - Nicolas Giovambattista
- Department of Physics, Brooklyn College of the City University of New York, Brooklyn, New York 11210, USA
- PhD Program in Physics, The Graduate Center of the City University of New York, New York, New York 10016, USA
- PhD Program in Chemistry, The Graduate Center of the City University of New York, New York, New York 10016, USA
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4
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Abstract
This review article discusses the effects of inorganic content and mechanisms on raw biomass and char during gasification. The impacts of the inherent inorganics and externally added inorganic compounds are summarized based on a literature search from the most recent 40 years. The TGA and larger-scale studies involving K-, Ca-, and Si-related mechanisms are critically reviewed with the aim of understanding the reaction mechanisms and kinetics. Differences between the reaction pathways of inorganic matter, and subsequent effects on the reactivity during gasification, are discussed. The present results illustrate the complexity of ash transformation phenomena, which have a strong impact on the design of gasifiers as well as further operation and process control. The impregnation and mixing of catalytic compounds into raw biomass are emphasized as a potential solution to avoid reactivity-related operational challenges during steam and CO2 gasification. This review clearly identifies a gap in experimental knowledge at the micro and macro levels in the advanced modelling of inorganics transformation with respect to gasification reactivity.
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Goswami Y, Vasisht VV, Frenkel D, Debenedetti PG, Sastry S. Thermodynamics and kinetics of crystallization in deeply supercooled Stillinger-Weber silicon. J Chem Phys 2021; 155:194502. [PMID: 34800966 DOI: 10.1063/5.0069475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We study the kinetics of crystallization in deeply supercooled liquid silicon employing computer simulations and the Stillinger-Weber three-body potential. The free energy barriers to crystallization are computed using umbrella sampling Monte Carlo simulations and from unconstrained molecular dynamics simulations using a mean first passage time formulation. We focus on state points that have been described in earlier work [S. Sastry and C. A. Angell, Nat. Mater. 2, 739 (2003)] as straddling a liquid-liquid phase transition (LLPT) between two metastable liquid states. It was argued subsequently [Ricci et al., Mol. Phys. 117, 3254 (2019)] that the apparent transition is due to the loss of metastability of the liquid state with respect to the crystalline state. The presence of a barrier to crystallization for these state points is therefore of importance to ascertain, which we investigate, with due attention to ambiguities that may arise from the choice of order parameters. We find a well-defined free energy barrier to crystallization and demonstrate that both umbrella sampling and mean first passage time methods yield results that agree quantitatively. Our results thus provide strong evidence against the possibility that the liquids at state points close to the reported LLPT exhibit slow, spontaneous crystallization, but they do not address the existence of a LLPT (or lack thereof). We also compute the free energy barriers to crystallization at other state points over a broad range of temperatures and pressures and discuss the effect of changes in the microscopic structure of the metastable liquid on the free energy barrier heights.
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Affiliation(s)
- Yagyik Goswami
- Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, India
| | - Vishwas V Vasisht
- Indian Institute of Technology Palakkad, Ahalia Integrated Campus, Kozhippara P.O., Palakkad, India
| | - Daan Frenkel
- Department of Chemistry, University of Cambridge, Cambridge, England
| | - Pablo G Debenedetti
- Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Srikanth Sastry
- Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, India
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6
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Wang Y, Ding J, Fan Z, Tian L, Li M, Lu H, Zhang Y, Ma E, Li J, Shan Z. Tension-compression asymmetry in amorphous silicon. NATURE MATERIALS 2021; 20:1371-1377. [PMID: 34059813 DOI: 10.1038/s41563-021-01017-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Accepted: 04/20/2021] [Indexed: 06/12/2023]
Abstract
Hard and brittle materials usually exhibit a much lower strength when loaded in tension than in compression. However, this common-sense behaviour may not be intrinsic to these materials, but arises from their higher flaw sensitivity to tensile loading. Here, we demonstrate a reversed and unusually pronounced tension-compression asymmetry (tensile strength exceeds compressive strength by a large margin) in submicrometre-sized samples of isotropic amorphous silicon. The abnormal asymmetry in the yield strength and anelasticity originates from the reduction in shear modulus and the densification of the shear-activated configuration under compression, altering the magnitude of the activation energy barrier for elementary shear events in amorphous Si. In situ coupled electrical tests corroborate that compressive strains indeed cause increased atomic coordination (metallization) by transforming some local structures from sp3-bonded semiconducting motifs to more metallic-like sites, lending credence to the mechanism we propose. This finding opens up an unexplored regime of intrinsic tension-compression asymmetry in materials.
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Affiliation(s)
- Yuecun Wang
- Center for Advancing Materials Performance from the Nanoscale and Hysitron Applied Research Center in China, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China
| | - Jun Ding
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China
| | - Zhao Fan
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - Lin Tian
- Institute of Materials Physics, University of Göttingen, Niedersachsen, Germany
| | - Meng Li
- Center for Advancing Materials Performance from the Nanoscale and Hysitron Applied Research Center in China, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China
| | - Huanhuan Lu
- Center for Advancing Materials Performance from the Nanoscale and Hysitron Applied Research Center in China, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China
| | - Yongqiang Zhang
- Center for Advancing Materials Performance from the Nanoscale and Hysitron Applied Research Center in China, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China
| | - En Ma
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China.
| | - Ju Li
- Department of Nuclear Science and Engineering, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Zhiwei Shan
- Center for Advancing Materials Performance from the Nanoscale and Hysitron Applied Research Center in China, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China.
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7
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Karim ET, He M, Salhoumi A, Zhigilei LV, Galenko PK. Kinetics of solid-liquid interface motion in molecular dynamics and phase-field models: crystallization of chromium and silicon. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2021; 379:20200320. [PMID: 34275355 DOI: 10.1098/rsta.2020.0320] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/20/2021] [Indexed: 06/13/2023]
Abstract
The results of molecular dynamics (MD) simulations of the crystallization process in one-component materials and solid solution alloys reveal a complex temperature dependence of the velocity of the crystal-liquid interface featuring an increase up to a maximum at 10-30% undercooling below the equilibrium melting temperature followed by a gradual decrease of the velocity at deeper levels of undercooling. At the qualitative level, such non-monotonous behaviour of the crystallization front velocity is consistent with the diffusion-controlled crystallization process described by the Wilson-Frenkel model, where the almost linear increase of the interface velocity in the vicinity of melting temperature is defined by the growth of the thermodynamic driving force for the phase transformation, while the decrease in atomic mobility with further increase of the undercooling drives the velocity through the maximum and into a gradual decrease at lower temperatures. At the quantitative level, however, the diffusional model fails to describe the results of MD simulations in the whole range of temperatures with a single set of parameters for some of the model materials. The limited ability of the existing theoretical models to adequately describe the MD results is illustrated in the present work for two materials, chromium and silicon. It is also demonstrated that the MD results can be well described by the solution following from the hodograph equation, previously found from the kinetic phase-field model (kinetic PFM) in the sharp interface limit. The ability of the hodograph equation to describe the predictions of MD simulation in the whole range of temperatures is related to the introduction of slow (phase field) and fast (gradient flow) variables into the original kinetic PFM from which the hodograph equation is obtained. The slow phase-field variable is responsible for the description of data at small undercoolings and the fast gradient flow variable accounts for local non-equilibrium effects at high undercoolings. The introduction of these two types of variables makes the solution of the hodograph equation sufficiently flexible for a reliable description of all nonlinearities of the kinetic curves predicted in MD simulations of Cr and Si. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.
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Affiliation(s)
- Eaman T Karim
- Department of Innovation and Technology Research, American Dental Association Science and Research Institute, 100 Bureau Drive, Gaithersburg, MD 20899, USA
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904-4745, USA
| | - Miao He
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904-4745, USA
| | - Ahmed Salhoumi
- Faculty of Sciences Ben M'Sik, Department of Physics, Laboratory of Condensed Matter Physics (LPMC), University of Hassan II Casablanca, BP 7955 Casablanca, Morocco
| | - Leonid V Zhigilei
- Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904-4745, USA
| | - Peter K Galenko
- Otto Schott Institute of Materials Research, Physics-Astronomy Faculty, Friedrich Schiller University Jena, 07743 Jena, Germany
- Laboratory of Multi-scale Mathematical Modeling, Department of Theoretical and Mathematical Physics, Ural Federal University, 620000 Ekaterinburg, Russia
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8
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Origins of structural and electronic transitions in disordered silicon. Nature 2021; 589:59-64. [DOI: 10.1038/s41586-020-03072-z] [Citation(s) in RCA: 97] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2019] [Accepted: 11/12/2020] [Indexed: 12/21/2022]
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9
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Affiliation(s)
- Hajime Tanaka
- Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan
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10
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Houska J. Maximum Achievable N Content in Atom-by-Atom Growth of Amorphous Si-C-N. ACS APPLIED MATERIALS & INTERFACES 2020; 12:41666-41673. [PMID: 32830493 DOI: 10.1021/acsami.0c08300] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The maximum achievable N content in atom-by-atom growth of Si-C-N films is examined by combining ab initio molecular dynamics simulations in a wide range of compositions and densities with experimental data. When and only when the simulation algorithm allows the formation and final presence of N2 molecules, the densities leading to the deepest local energy minima are in agreement with the experiment. The main attention is paid to unbonded N2 molecules, with the aim to predict and explain the maximum content of N bonded in the amorphous networks. There are significant differences resulting from different compositions, ranging from no N2 at the lowest energy density of a-Si3N4 (57 atom % of bonded N) to many N2 at the lowest energy density of a-C3N4 (42 atom % of bonded N). The theoretical prediction is in agreement with the experimental results of reactive magnetron sputtering at varied Si+C sputter target compositions and N2 partial pressures. A detailed analysis reveals that while there is a relationship between the N2 formation and the packing factor, which is valid in the whole compositional range investigated, the lowest-energy packing factor depends on the composition. The results are important for the explanation of experimentally reported maximum N contents, design of technologically important amorphous nitrides and pathways of their preparation, prediction of their stability, and identification of what may or may not be achieved in this field.
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Affiliation(s)
- Jiri Houska
- Department of Physics and NTIS - European Centre of Excellence, University of West Bohemia, Univerzitni 8, 30614 Plzen, Czech Republic
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11
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Freitas R, Reed EJ. Uncovering the effects of interface-induced ordering of liquid on crystal growth using machine learning. Nat Commun 2020; 11:3260. [PMID: 32591501 PMCID: PMC7319977 DOI: 10.1038/s41467-020-16892-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 05/26/2020] [Indexed: 11/25/2022] Open
Abstract
The process of crystallization is often understood in terms of the fundamental microstructural elements of the crystallite being formed, such as surface orientation or the presence of defects. Considerably less is known about the role of the liquid structure on the kinetics of crystal growth. Here atomistic simulations and machine learning methods are employed together to demonstrate that the liquid adjacent to solid-liquid interfaces presents significant structural ordering, which effectively reduces the mobility of atoms and slows down the crystallization kinetics. Through detailed studies of silicon and copper we discover that the extent to which liquid mobility is affected by interface-induced ordering (IIO) varies greatly with the degree of ordering and nature of the adjacent interface. Physical mechanisms behind the IIO anisotropy are explained and it is demonstrated that incorporation of this effect on a physically-motivated crystal growth model enables the quantitative prediction of the growth rate temperature dependence. Crystallization is a challenging process to model quantitatively. Here the authors use machine learning and atomistic simulations together to uncover the role of the liquid structure on the process of crystallization and derive a predictive kinetic model of crystal growth.
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Affiliation(s)
- Rodrigo Freitas
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.
| | - Evan J Reed
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
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12
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Maity G, Dubey S, El-Azab A, Singhal R, Ojha S, Kulriya PK, Dhar S, Som T, Kanjilal D, Patel SP. An assessment on crystallization phenomena of Si in Al/a-Si thin films via thermal annealing and ion irradiation. RSC Adv 2020; 10:4414-4426. [PMID: 35495262 PMCID: PMC9049056 DOI: 10.1039/c9ra08836a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Accepted: 01/14/2020] [Indexed: 11/21/2022] Open
Abstract
In the present study, crystallization of amorphous-Si (a-Si) in Al/a-Si bilayer thin films under thermal annealing and ion irradiation has been investigated for future solar energy materials applications. In particular, the effect of thickness ratio (e.g. in Al : a-Si, the ratio of the Al and a-Si layer thickness) and temperature during irradiation on crystallization of the Si films has been explored for the first time. Two sets of samples with thickness ratio 1 : 1 (set-A: 50 nm Al/50 nm a-Si) and thickness ratio 1 : 3 (set-B: 50 nm Al/150 nm a-Si) have been prepared on thermally oxidized Si-substrates. In one experiment, thermal annealing of the as-prepared sample (of both the sets) has been done at different temperatures of 100 °C, 200 °C, 300 °C, 400 °C, and 500 °C. Significant crystallization was found to initiate at 200 °C with the help of thermal annealing, which increased further by increasing the temperature. In another experiment, ion irradiation on both sets of samples has been carried out at 100 °C and 200 °C using 100 MeV Ni7+ ions with fluences of 1 × 1012 ions per cm2, 5 × 1012 ions per cm2, 1 × 1013 ions per cm2, and 5 × 1013 ions per cm2. Significant crystallization of Si was observed at a remarkably low temperature of 100 °C under ion irradiation. The samples irradiated at 100 °C show better crystallization than the samples irradiated at 200 °C. The maximum crystallization of a-Si has been observed at a fluence of 1 × 1012 ions per cm2, which was found to decrease with increasing ion fluence at both temperatures (i.e. 100 °C & 200 °C). The crystallization of a-Si is found to be better for set-B samples as compared to set-A samples at all the fluences and irradiation temperatures. The present work is aimed at developing the understanding of the crystallization process, which may have significant advantages for designing crystalline layers at lower temperature using appropriate masks for irradiation at the desired location. The detailed mechanisms behind all the above observations are discussed in this paper.
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Affiliation(s)
- G Maity
- Department of Pure & Applied Physics, Guru Ghasidas Vishwavidyalaya (A Central University) Bilaspur-495009 India
| | - S Dubey
- Department of Physics, School of Engineering, University of Petroleum & Energy Studies Bidholi Dehradun-248007 India
| | - Anter El-Azab
- Material Science & Engineering, Purdue University West Lafayette IN-47906 USA
| | - R Singhal
- Department of Physics, Malaviya National Institute of Technology Jaipur-302017 India
| | - S Ojha
- Inter University Accelerator Centre Aruna Asaf Ali Marg New Delhi-110067 India
| | - P K Kulriya
- Inter University Accelerator Centre Aruna Asaf Ali Marg New Delhi-110067 India
| | - S Dhar
- Department of Physics, Shiv Nadar University Gautam Buddha Nagar-201314 India
| | - T Som
- Institute of Physics Sachivalaya Marg Bhubaneswar-751005 India
| | - D Kanjilal
- Inter University Accelerator Centre Aruna Asaf Ali Marg New Delhi-110067 India
| | - Shiv P Patel
- Department of Pure & Applied Physics, Guru Ghasidas Vishwavidyalaya (A Central University) Bilaspur-495009 India
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13
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Kim CS, Hobbs RG, Agarwal A, Yang Y, Manfrinato VR, Short MP, Li J, Berggren KK. Focused-helium-ion-beam blow forming of nanostructures: radiation damage and nanofabrication. NANOTECHNOLOGY 2020; 31:045302. [PMID: 31578000 DOI: 10.1088/1361-6528/ab4a65] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Targeted irradiation of nanostructures by a finely focused ion beam provides routes to improved control of material modification and understanding of the physics of interactions between ion beams and nanomaterials. Here, we studied radiation damage in crystalline diamond and silicon nanostructures using a focused helium ion beam, with the former exhibiting extremely long-range ion propagation and large plastic deformation in a process visibly analogous to blow forming. We report the dependence of damage morphology on material, geometry, and irradiation conditions (ion dose, ion energy, ion species, and location). We anticipate that our method and findings will not only improve the understanding of radiation damage in isolated nanostructures, but will also support the design of new engineering materials and devices for current and future applications in nanotechnology.
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Affiliation(s)
- Chung-Soo Kim
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139, United States of America
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14
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Wang Y, Liang B, Xu S, Tian L, Minor AM, Shan Z. Tunable Anelasticity in Amorphous Si Nanowires. NANO LETTERS 2020; 20:449-455. [PMID: 31804092 DOI: 10.1021/acs.nanolett.9b04164] [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
In situ bending tests of amorphous Si nanowires (a-Si NWs) found different elastic behavior depending on whether they were straight or curved to begin with. The axially straight NWs exhibit pure elastic deformation; however, the axially curved NWs exhibit obvious anelastic behavior when they are bent in the direction of original curvature. On the basis of STEM-EELS analysis, we propose that the underlying mechanism for this anelastic behavior is a bond-switching assisted redistribution of the nonuniform density (structure) in the curved NWs under the inhomogeneous stress field. This mechanism was further supported by the fact that the originally straight a-Si NWs also display similar anelasticity with the as-grown curved NWs after focused ion beam irradiation that can cause nonuniform structure distribution. As compared to what has been reported in other 1D materials, the anelasticity of a-Si NWs can be tuned by modifying their morphology, controlling the loading direction, or irradiating them via ion beam. Our findings suggest that a-Si NWs could be a promising material in the nanoscale damping systems, especially the semiconductor nanodevices.
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Affiliation(s)
- Yuecun Wang
- Center for Advancing Materials Performance from the Nanoscale (CAMP-NANO) and Hysitron Applied Research Center in China (HARCC), State Key Laboratory for Mechanical Behavior of Materials , Xi'an Jiaotong University , Xi'an 710049 , P. R. China
| | - Beiming Liang
- Center for Advancing Materials Performance from the Nanoscale (CAMP-NANO) and Hysitron Applied Research Center in China (HARCC), State Key Laboratory for Mechanical Behavior of Materials , Xi'an Jiaotong University , Xi'an 710049 , P. R. China
| | - Shuigang Xu
- Department of Physics , The Hong Kong University of Science and Technology , Hong Kong , P.R. China
| | - Lin Tian
- Center for Advancing Materials Performance from the Nanoscale (CAMP-NANO) and Hysitron Applied Research Center in China (HARCC), State Key Laboratory for Mechanical Behavior of Materials , Xi'an Jiaotong University , Xi'an 710049 , P. R. China
- Institute of Materials Physics , University of Göttingen , Göttingen 37077 , Germany
| | - Andrew M Minor
- Department of Materials Science and Engineering , University of California , Berkeley , California 94720 , United States
- National Center for Electron Microscopy, Molecular Foundry , Lawrence Berkeley National Laboratory , 1 Cyclotron Road , Berkeley , California 94720 , United States
| | - Zhiwei Shan
- Center for Advancing Materials Performance from the Nanoscale (CAMP-NANO) and Hysitron Applied Research Center in China (HARCC), State Key Laboratory for Mechanical Behavior of Materials , Xi'an Jiaotong University , Xi'an 710049 , P. R. China
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15
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Garg V, Chou T, Liu A, De Marco A, Kamaliya B, Qiu S, Mote RG, Fu J. Weaving nanostructures with site-specific ion induced bidirectional bending. NANOSCALE ADVANCES 2019; 1:3067-3077. [PMID: 36133581 PMCID: PMC9418629 DOI: 10.1039/c9na00382g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 06/18/2019] [Indexed: 05/13/2023]
Abstract
Site-specific ion-irradiation is a promising tool fostering strain-engineering of freestanding nanostructures to realize 3D-configurations towards various functionalities. We first develop a novel approach of fabricating freestanding 3D silicon nanostructures by low dose ion-implantation followed by chemical-etching. The fabricated nanostructures can then be deformed bidirectionally by varying the local irradiation of kiloelectronvolt gallium ions. By further tuning the ion-dose and energy, various nanostructure configurations can be realized, thus extending its horizon to new functional 3D-nanostructures. It has been revealed that at higher-energies (∼30 kV), the nanostructures can exhibit two-stage bidirectional-bending in contrast to the bending towards the incident-ions at lower-energies (∼16), implying an effective transfer of kinetic-energy. Computational studies show that the spatial-distribution of implanted-ions, dislocated silicon atoms, has potentially contributed to the local development of stresses. Nanocharacterization confirms the formation of two distinguishable ion-irradiated and un-irradiated regions, while the smoothened morphology of the irradiated-surface suggested that the bending is also coupled with sputtering at higher ion-doses. The bending effects associated with local ion irradiation in contrast to global ion irradiation are presented, with the mechanism elucidated. Finally, weaving of nanostructures is demonstrated through strain-engineering for new nanoscale artefacts such as ultra-long fully-bent nanowires, nano-hooks, and nano-meshes. The aligned growth of bacterial-cells is observed on the fabricated nanowires, and a mesh based "bacterial-trap" for site-specific capture of bacterial cells is demonstrated emphasizing the versatile nature of the current approach.
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Affiliation(s)
- Vivek Garg
- IITB-Monash Research Academy, Indian Institute of Technology Bombay Powai Mumbai 400076 India
- Department of Mechanical Engineering, Indian Institute of Technology Bombay Powai Mumbai 400076 India
- Department of Mechanical and Aerospace Engineering, Monash University Wellington Road Clayton Victoria 3800 Australia
| | - Tsengming Chou
- Laboratory of Multiscale Imaging, Stevens Institute of Technology Hoboken NJ 07030 USA
| | - Amelia Liu
- Monash Centre for Electron Microscopy, Monash University Clayton VIC 3800 Australia
| | - Alex De Marco
- Department of Biochemistry and Molecular Biology, Monash University Clayton VIC 3800 Australia
| | - Bhaveshkumar Kamaliya
- IITB-Monash Research Academy, Indian Institute of Technology Bombay Powai Mumbai 400076 India
- Department of Mechanical and Aerospace Engineering, Monash University Wellington Road Clayton Victoria 3800 Australia
- Department Physics, Indian Institute of Technology Bombay Powai Mumbai 400076 India
| | - Shi Qiu
- Department of Mechanical and Aerospace Engineering, Monash University Wellington Road Clayton Victoria 3800 Australia
| | - Rakesh G Mote
- Department of Mechanical Engineering, Indian Institute of Technology Bombay Powai Mumbai 400076 India
| | - Jing Fu
- Department of Mechanical and Aerospace Engineering, Monash University Wellington Road Clayton Victoria 3800 Australia
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16
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Bernstein N, Bhattarai B, Csányi G, Drabold DA, Elliott SR, Deringer VL. Quantifying Chemical Structure and Machine-Learned Atomic Energies in Amorphous and Liquid Silicon. Angew Chem Int Ed Engl 2019; 58:7057-7061. [PMID: 30835962 PMCID: PMC6563111 DOI: 10.1002/anie.201902625] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Indexed: 11/29/2022]
Abstract
Amorphous materials are being described by increasingly powerful computer simulations, but new approaches are still needed to fully understand their intricate atomic structures. Here, we show how machine-learning-based techniques can give new, quantitative chemical insight into the atomic-scale structure of amorphous silicon (a-Si). We combine a quantitative description of the nearest- and next-nearest-neighbor structure with a quantitative description of local stability. The analysis is applied to an ensemble of a-Si networks in which we tailor the degree of ordering by varying the quench rates down to 1010 K s-1 . Our approach associates coordination defects in a-Si with distinct stability regions and it has also been applied to liquid Si, where it traces a clear-cut transition in local energies during vitrification. The method is straightforward and inexpensive to apply, and therefore expected to have more general significance for developing a quantitative understanding of liquid and amorphous states of matter.
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Affiliation(s)
- Noam Bernstein
- Center for Materials Physics and TechnologyU.S. Naval Research LaboratoryWashingtonDC20375USA
| | - Bishal Bhattarai
- Department of Physics and AstronomyOhio UniversityAthensOH45701USA
| | - Gábor Csányi
- Department of EngineeringUniversity of CambridgeCambridgeCB2 1PZUK
| | - David A. Drabold
- Department of Physics and AstronomyOhio UniversityAthensOH45701USA
| | | | - Volker L. Deringer
- Department of EngineeringUniversity of CambridgeCambridgeCB2 1PZUK
- Department of ChemistryUniversity of CambridgeCambridgeCB2 1EWUK
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17
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Bernstein N, Bhattarai B, Csányi G, Drabold DA, Elliott SR, Deringer VL. Quantifying Chemical Structure and Machine‐Learned Atomic Energies in Amorphous and Liquid Silicon. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201902625] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Noam Bernstein
- Center for Materials Physics and Technology U.S. Naval Research Laboratory Washington DC 20375 USA
| | - Bishal Bhattarai
- Department of Physics and Astronomy Ohio University Athens OH 45701 USA
| | - Gábor Csányi
- Department of Engineering University of Cambridge Cambridge CB2 1PZ UK
| | - David A. Drabold
- Department of Physics and Astronomy Ohio University Athens OH 45701 USA
| | | | - Volker L. Deringer
- Department of Engineering University of Cambridge Cambridge CB2 1PZ UK
- Department of Chemistry University of Cambridge Cambridge CB2 1EW UK
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18
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Hanif I, Camara O, Tunes MA, Harrison RW, Greaves G, Donnelly SE, Hinks JA. Ion-beam-induced bending of semiconductor nanowires. NANOTECHNOLOGY 2018; 29:335701. [PMID: 29781443 DOI: 10.1088/1361-6528/aac659] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The miniaturisation of technology increasingly requires the development of both new structures as well as novel techniques for their manufacture and modification. Semiconductor nanowires (NWs) are a prime example of this and as such have been the subject of intense scientific research for applications ranging from microelectronics to nano-electromechanical devices. Ion irradiation has long been a key processing step for semiconductors and the natural extension of this technique to the modification of semiconductor NWs has led to the discovery of ion beam-induced deformation effects. In this work, transmission electron microscopy with in situ ion bombardment has been used to directly observe the evolution of individual silicon and germanium NWs under irradiation. Silicon NWs were irradiated with either 6 keV neon ions or xenon ions at 5, 7 or 9.5 keV with a flux of 3 × 1013 ions cm-2 s-1. Germanium NWs were irradiated with 30 or 70 keV xenon ions with a flux of 1013 ions cm-2 s-1. These new results are combined with those reported in the literature in a systematic analysis using a custom implementation of the transport of ions in matter Monte Carlo computer code to facilitate a direct comparison with experimental results taking into account the wide range of experimental conditions. Across the various studies this has revealed underlying trends and forms the basis of a critical review of the various mechanisms which have been proposed to explain the deformation of semiconductor NWs under ion irradiation.
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Affiliation(s)
- Imran Hanif
- School of Computing and Engineering, University of Huddersfield, Queensgate, Huddersfield, HD1 3DH, United Kingdom
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19
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Hanif I, Camara O, Tunes MA, Harrison RW, Greaves G, Donnelly SE, Hinks JA. Ion-beam-induced bending of semiconductor nanowires. NANOTECHNOLOGY 2018; 29:335701. [PMID: 29781443 DOI: 10.1002/admi.201800276] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The miniaturisation of technology increasingly requires the development of both new structures as well as novel techniques for their manufacture and modification. Semiconductor nanowires (NWs) are a prime example of this and as such have been the subject of intense scientific research for applications ranging from microelectronics to nano-electromechanical devices. Ion irradiation has long been a key processing step for semiconductors and the natural extension of this technique to the modification of semiconductor NWs has led to the discovery of ion beam-induced deformation effects. In this work, transmission electron microscopy with in situ ion bombardment has been used to directly observe the evolution of individual silicon and germanium NWs under irradiation. Silicon NWs were irradiated with either 6 keV neon ions or xenon ions at 5, 7 or 9.5 keV with a flux of 3 × 1013 ions cm-2 s-1. Germanium NWs were irradiated with 30 or 70 keV xenon ions with a flux of 1013 ions cm-2 s-1. These new results are combined with those reported in the literature in a systematic analysis using a custom implementation of the transport of ions in matter Monte Carlo computer code to facilitate a direct comparison with experimental results taking into account the wide range of experimental conditions. Across the various studies this has revealed underlying trends and forms the basis of a critical review of the various mechanisms which have been proposed to explain the deformation of semiconductor NWs under ion irradiation.
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Affiliation(s)
- Imran Hanif
- School of Computing and Engineering, University of Huddersfield, Queensgate, Huddersfield, HD1 3DH, United Kingdom
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20
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Cubuk ED, Malone BD, Onat B, Waterland A, Kaxiras E. Representations in neural network based empirical potentials. J Chem Phys 2018; 147:024104. [PMID: 28711053 DOI: 10.1063/1.4990503] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Many structural and mechanical properties of crystals, glasses, and biological macromolecules can be modeled from the local interactions between atoms. These interactions ultimately derive from the quantum nature of electrons, which can be prohibitively expensive to simulate. Machine learning has the potential to revolutionize materials modeling due to its ability to efficiently approximate complex functions. For example, neural networks can be trained to reproduce results of density functional theory calculations at a much lower cost. However, how neural networks reach their predictions is not well understood, which has led to them being used as a "black box" tool. This lack of understanding is not desirable especially for applications of neural networks in scientific inquiry. We argue that machine learning models trained on physical systems can be used as more than just approximations since they had to "learn" physical concepts in order to reproduce the labels they were trained on. We use dimensionality reduction techniques to study in detail the representation of silicon atoms at different stages in a neural network, which provides insight into how a neural network learns to model atomic interactions.
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Affiliation(s)
- Ekin D Cubuk
- Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Brad D Malone
- Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Berk Onat
- Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Amos Waterland
- Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Efthimios Kaxiras
- Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
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21
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Liu Q, Qi R, Song S, Yan Z, Huang Q. Controllable conversion of liquid silicon from high-density to low-density towards amorphous silicon nanospheres on a wafer scale. Chem Commun (Camb) 2018; 54:12694-12697. [DOI: 10.1039/c8cc05827j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hydrogen pressure plays a key role in keeping silicon in low-density liquid, benefiting the formation of amorphous silicon spheres.
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Affiliation(s)
- Qiang Liu
- School of Chemical Engineering
- Sichuan University
- Chengdu 610065
- China
| | - Ruifeng Qi
- School of Chemical Engineering
- Sichuan University
- Chengdu 610065
- China
| | - Shuang Song
- College of Architecture & Environment
- Sichuan University
- Chengdu 610065
- China
| | - Zhihui Yan
- School of Chemical Engineering
- Sichuan University
- Chengdu 610065
- China
| | - Qingsong Huang
- School of Chemical Engineering
- Sichuan University
- Chengdu 610065
- China
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22
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Xia W, Song J, Jeong C, Hsu DD, Phelan FR, Douglas JF, Keten S. Energy-Renormalization for Achieving Temperature Transferable Coarse-Graining of Polymer Dynamics. Macromolecules 2017; 50:10.1021/acs.macromol.7b01717. [PMID: 30996475 PMCID: PMC6463524 DOI: 10.1021/acs.macromol.7b01717] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The bottom-up prediction of the properties of polymeric materials based on molecular dynamics simulation is a major challenge in soft matter physics. Coarse-grained (CG) models are often employed to access greater spatiotemporal scales required for many applications, but these models normally experience significantly altered thermodynamics and highly accelerated dynamics due to the reduced number of degrees of freedom upon coarse-graining. While CG models can be calibrated to meet certain properties at particular state points, there is unfortunately no temperature transferable and chemically specific coarse-graining method that allows for modeling of polymer dynamics over a wide temperature range. Here, we pragmatically address this problem by "correcting" for deviations in activation free energies that occur upon coarse-graining the dynamics of a model polymeric material (polystyrene). In particular, we propose a new strategy based on concepts drawn from the Adam-Gibbs (AG) theory of glass formation. Namely we renormalize the cohesive interaction strength and effective interaction length-scale parameters to modify the activation free energy. We show that this energy-renormalization method for CG modeling allows accurate prediction of atomistic dynamics over the Arrhenius regime, the non-Arrhenius regime of glass formation, and even the non-equilibrium glassy regime, thus allowing for the predictive modeling of dynamic properties of polymer over the entire range of glass formation. Our work provides a practical scheme for establishing temperature transferable coarse-grained models for predicting and designing the properties of polymeric materials.
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Affiliation(s)
- Wenjie Xia
- Materials Science & Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
- Department of Civil & Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, United States
- Center for Hierarchical Materials Design, Northwestern University, Evanston, Illinois 60208-3109, United States
| | - Jake Song
- Department of Materials Science & Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, United States
| | - Cheol Jeong
- Materials Science & Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - David D. Hsu
- Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, United States
| | - Frederick R. Phelan
- Materials Science & Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Jack F. Douglas
- Materials Science & Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Sinan Keten
- Department of Civil & Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, United States
- Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3109, United States
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23
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Wingert MC, Kwon S, Cai S, Chen R. Fluid-like Surface Layer and Its Flow Characteristics in Glassy Nanotubes. NANO LETTERS 2016; 16:7545-7550. [PMID: 27798834 DOI: 10.1021/acs.nanolett.6b03377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We show that amorphous silica and Si nanotubes can flow at room temperature under Giga-Pascal order stress when going to the nanometer scale. This creep behavior is unique for the amorphous nanotubes and is absent in crystalline Si nanotubes of similar dimensions. A core-shell model shows that there exists an approximately 1 nm thick viscoelastic "fluid-like" surface layer, which exhibits a room temperature viscosity equivalent to that of bulk glass above 1000 °C.
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Affiliation(s)
- Matthew C Wingert
- Department of Mechanical and Aerospace Engineering, University of California, San Diego , La Jolla, California 92093, United States
| | - Soonshin Kwon
- Department of Mechanical and Aerospace Engineering, University of California, San Diego , La Jolla, California 92093, United States
| | - Shengqiang Cai
- Department of Mechanical and Aerospace Engineering, University of California, San Diego , La Jolla, California 92093, United States
| | - Renkun Chen
- Department of Mechanical and Aerospace Engineering, University of California, San Diego , La Jolla, California 92093, United States
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24
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Beltukov YM, Fusco C, Parshin DA, Tanguy A. Boson peak and Ioffe-Regel criterion in amorphous siliconlike materials: The effect of bond directionality. Phys Rev E 2016; 93:023006. [PMID: 26986404 DOI: 10.1103/physreve.93.023006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Indexed: 06/05/2023]
Abstract
The vibrational properties of model amorphous materials are studied by combining complete analysis of the vibration modes, dynamical structure factor, and energy diffusivity with exact diagonalization of the dynamical matrix and the kernel polynomial method, which allows a study of very large system sizes. Different materials are studied that differ only by the bending rigidity of the interactions in a Stillinger-Weber modelization used to describe amorphous silicon. The local bending rigidity can thus be used as a control parameter, to tune the sound velocity together with local bonds directionality. It is shown that for all the systems studied, the upper limit of the Boson peak corresponds to the Ioffe-Regel criterion for transverse waves, as well as to a minimum of the diffusivity. The Boson peak is followed by a diffusivity's increase supported by longitudinal phonons. The Ioffe-Regel criterion for transverse waves corresponds to a common characteristic mean-free path of 5-7 Å (which is slightly bigger for longitudinal phonons), while the fine structure of the vibrational density of states is shown to be sensitive to the local bending rigidity.
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Affiliation(s)
- Y M Beltukov
- Ioffe Physical Technical Institute, 194021 St Petersburg, Russian Federation and Université Montpellier II, CNRS, Montpellier 34095, France
| | - C Fusco
- Université de Lyon, MATEIS, INSA-Lyon, CNRS UMR5510, F-69621, France and Institut Lumière Matière, UMR 5306 Université Lyon 1-CNRS, F-69622 Villeurbanne Cedex, France
| | - D A Parshin
- Saint Petersburg State Polytechnical University, 195251 Saint Petersburg, Russian Federation
| | - A Tanguy
- Université de Lyon, LaMCoS, INSA-Lyon, CNRS UMR5259, F-69621, France and Institut Lumière Matière, UMR 5306 Université Lyon 1-CNRS, F-69622 Villeurbanne Cedex, France
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25
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Mancini G, Celino M, Iesari F, Di Cicco A. Glass polymorphism in amorphous germanium probed by first-principles computer simulations. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:015401. [PMID: 26642884 DOI: 10.1088/0953-8984/28/1/015401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions.
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Affiliation(s)
- G Mancini
- Physics Division, School of Science and Technology, Università di Camerino, Via Madonna delle Carceri 62032, Camerino (MC), Italy
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26
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Shen B, Wang ZY, Dong F, Guo YR, Zhang RJ, Zheng YX, Wang SY, Wang CZ, Ho KM, Chen LY. Dynamics and Diffusion Mechanism of Low-Density Liquid Silicon. J Phys Chem B 2015; 119:14945-51. [PMID: 26540341 DOI: 10.1021/acs.jpcb.5b09138] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A first-order phase transition from a high-density liquid to a low-density liquid has been proposed to explain the various thermodynamic anomies of water. It also has been proposed that such liquid-liquid phase transition would exist in supercooled silicon. Computer simulation studies show that, across the transition, the diffusivity drops roughly 2 orders of magnitude, and the structures exhibit considerable tetrahedral ordering. The resulting phase is a highly viscous, low-density liquid silicon. Investigations on the atomic diffusion of such a novel form of liquid silicon are of high interest. Here we report such diffusion results from molecular dynamics simulations using the classical Stillinger-Weber (SW) potential of silicon. We show that the atomic diffusion of the low-density liquid is highly correlated with local tetrahedral geometries. We also show that atoms diffuse through hopping processes within short ranges, which gradually accumulate to an overall random motion for long ranges as in normal liquids. There is a close relationship between dynamical heterogeneity and hopping process. We point out that the above diffusion mechanism is closely related to the strong directional bonding nature of the distorted tetrahedral network. Our work offers new insights into the complex behavior of the highly viscous low density liquid silicon, suggesting similar diffusion behaviors in other tetrahedral coordinated liquids that exhibit liquid-liquid phase transition such as carbon and germanium.
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Affiliation(s)
- B Shen
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China.,Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University , Ames, Iowa 50011, United States
| | - Z Y Wang
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China
| | - F Dong
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China
| | - Y R Guo
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China
| | - R J Zhang
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China
| | - Y X Zheng
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China
| | - S Y Wang
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China.,Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University , Ames, Iowa 50011, United States.,Key Laboratory for Information Science of Electromagnetic Waves (MoE) , Shanghai, 200433, China
| | - C Z Wang
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University , Ames, Iowa 50011, United States
| | - K M Ho
- Ames Laboratory, U.S. Department of Energy and Department of Physics and Astronomy, Iowa State University , Ames, Iowa 50011, United States
| | - L Y Chen
- Key Laboratory of Micro and Nano Photonic Structures (MoE) and Department of Optical Science and Engineering, Fudan University , Shanghai, 200433, China
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27
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Zhao G, Yu YJ, Tan XM. Nature of the first-order liquid-liquid phase transition in supercooled silicon. J Chem Phys 2015; 143:054508. [DOI: 10.1063/1.4928194] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- G. Zhao
- School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, People’s Republic of China
| | - Y. J. Yu
- School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, People’s Republic of China
| | - X. M. Tan
- School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, People’s Republic of China
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28
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Johannes A, Noack S, Wesch W, Glaser M, Lugstein A, Ronning C. Anomalous Plastic Deformation and Sputtering of Ion Irradiated Silicon Nanowires. NANO LETTERS 2015; 15:3800-7. [PMID: 25951108 PMCID: PMC4463547 DOI: 10.1021/acs.nanolett.5b00431] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 04/24/2015] [Indexed: 05/27/2023]
Abstract
Silicon nanowires of various diameters were irradiated with 100 keV and 300 keV Ar(+) ions on a rotatable and heatable stage. Irradiation at elevated temperatures above 300 °C retains the geometry of the nanostructure and sputtering can be gauged accurately. The diameter dependence of the sputtering shows a maximum if the ion range matches the nanowire diameter, which is in good agreement with Monte Carlo simulations based on binary collisions. Nanowires irradiated at room temperature, however, amorphize and deform plastically. So far, plastic deformation has not been observed in bulk silicon at such low ion energies. The magnitude and direction of the deformation is independent of the ion-beam direction and cannot be explained with mass-transport in a binary collision cascade but only by collective movement of atoms in the collision cascade with the given boundary conditions of a high surface to volume ratio.
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Affiliation(s)
- Andreas Johannes
- Institute for Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743, Jena, Germany
| | - Stefan Noack
- Institute for Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743, Jena, Germany
| | - Werner Wesch
- Institute for Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743, Jena, Germany
| | - Markus Glaser
- Institute of Solid State Electronics, Vienna
University of Technology, Floragasse 7, 1040, Vienna, Austria
| | - Alois Lugstein
- Institute of Solid State Electronics, Vienna
University of Technology, Floragasse 7, 1040, Vienna, Austria
| | - Carsten Ronning
- Institute for Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743, Jena, Germany
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29
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Lü YJ, Zhang XX, Chen M, Jiang JZ. Exploring the nature of the liquid–liquid transition in silicon: a non-activated transformation. Phys Chem Chem Phys 2015; 17:27167-75. [DOI: 10.1039/c5cp04231c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dynamics of the HDL–LDL transformation in silicon shows that this process is actually a continuous transition.
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Affiliation(s)
- Y. J. Lü
- School of Physics
- Beijing Institute of Technology
- Beijing 100081
- P. R. China
- State Key Laboratory of Silicon Materials
| | - X. X. Zhang
- Department of Engineering Mechanics
- Tsinghua University
- Beijing 100084
- P. R. China
| | - M. Chen
- Department of Engineering Mechanics
- Tsinghua University
- Beijing 100084
- P. R. China
| | - Jian-Zhong Jiang
- State Key Laboratory of Silicon Materials
- Zhejiang University
- Hangzhou 310027
- P. R. China
- International Center for New-Structured Materials (ICNSM)
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Jiang YC, Gao J. Strain-induced photoconductivity in thin films of Co doped amorphous carbon. Sci Rep 2014; 4:6738. [PMID: 25338641 PMCID: PMC4206866 DOI: 10.1038/srep06738] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2014] [Accepted: 10/03/2014] [Indexed: 11/10/2022] Open
Abstract
Traditionally, strain effect was mainly considered in the materials with periodic lattice structure, and was thought to be very weak in amorphous semiconductors. Here, we investigate the effects of strain in films of cobalt-doped amorphous carbon (Co-C) grown on 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT) substrates. The electric transport properties of the Co-C films were effectively modulated by the piezoelectric substrates. Moreover, we observed, for the first time, strain-induced photoconductivity in such an amorphous semiconductor. Without strain, no photoconductivity was observed. When subjected to strain, the Co-C films exhibited significant photoconductivity under illumination by a 532-nm monochromatic light. A strain-modified photoconductivity theory was developed to elucidate the possible mechanism of this remarkable phenomenon. The good agreement between the theoretical and experimental results indicates that strain-induced photoconductivity may derive from modulation of the band structure via the strain effect.
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Affiliation(s)
- Y C Jiang
- Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - J Gao
- Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China
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Zhang K, Li H, Jiang YY. Liquid-liquid phase transition in quasi-two-dimensional supercooled silicon. Phys Chem Chem Phys 2014; 16:18023-8. [PMID: 25050842 DOI: 10.1039/c4cp00694a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Anomalies of the local structural order in quasi-two-dimensional liquid silicon upon cooling are investigated. Results show that the appearance of the left subpeak in pair correlation functions is the signature of the liquid-liquid phase transition (LLPT). The structural origin of the LLPT is the formation of a crystal-like ordered structure with a short-range scale, which in turn forms the local well-organized paracrystalline region. Unlike in the bulk liquid silicon, the stages of the LLPT and liquid-solid phase transition (LSPT) in the quasi-two-dimensional liquid silicon do not overlap. The crystal-like ordered structures formed in the LLPT are precursors which are prepared for the subsequent LSPT. Also observed was a strong interconnection between the local well-organized paracrystalline region and the transition from the typical metal to the semimetal in the two-dimensional silicon. This study will aid in better understanding of the essential phase change in two-dimensional liquid silicon.
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Affiliation(s)
- K Zhang
- National Engineering Research Central for Rare Earth Materials, General Research Institute for Non-Ferrous Metals, GRIREM Advanced Co. Ltd., Beijing 100088, China
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France-Lanord A, Merabia S, Albaret T, Lacroix D, Termentzidis K. Thermal properties of amorphous/crystalline silicon superlattices. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:355801. [PMID: 25105883 DOI: 10.1088/0953-8984/26/35/355801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Thermal transport properties of crystalline/amorphous silicon superlattices using molecular dynamics are investigated. We show that the cross-plane conductivity of the superlattices is very low and close to the conductivity of bulk amorphous silicon even for amorphous layers as thin as ≃ 6 Å. The cross-plane thermal conductivity weakly increases with temperature which is associated with a decrease of the Kapitza resistance with temperature at the crystalline/amorphous interface. This property is further investigated considering the spatial analysis of the phonon density of states in domains close to the interface. Interestingly, the crystalline/amorphous superlattices are shown to display large thermal anisotropy, according to the characteristic sizes of elaborated structures. These last results suggest that the thermal conductivity of crystalline/amorphous superlattices can be phonon engineered, providing new directions for nanostructured thermoelectrics and anisotropic materials in thermal transport.
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Affiliation(s)
- Arthur France-Lanord
- Université de Lorraine, LEMTA, CNRS-UMR7563, Faculté des Sciences et Technologies, BP 70239, 54506 Vandoeuvre-les-Nancy Cedex, France. Materials Design SARL, 92120 Montrouge, France. CEA, DSM-IRAMIS-SPEC, Saclay, 91191 Gif-sur-Yvette Cedex, France
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France-Lanord A, Blandre E, Albaret T, Merabia S, Lacroix D, Termentzidis K. Atomistic amorphous/crystalline interface modelling for superlattices and core/shell nanowires. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:055011. [PMID: 24445610 DOI: 10.1088/0953-8984/26/5/055011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this paper we present a systematic and well controlled procedure for building atomistic amorphous/crystalline interfaces in silicon, dedicated to the molecular dynamics simulations of superlattices and core/shell nanowires. The obtained structures depend on the technique used to generate the amorphous phase and their overall quality is estimated through comparisons with structural information and interfacial energies available from experimental and theoretical results. While most of the related studies focus on a single planar interface, we consider here both the generation of multiple superlattice planar interfaces and core/shell nanowire structures. The proposed method provides periodic homogeneous and reproducible, atomically sharp and defect free interface configurations at low temperature and pressure. We also illustrate how the method may be used to predict the thermal transport properties of composite crystalline/amorphous superlattices.
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Ridgway MC, Bierschenk T, Giulian R, Afra B, Rodriguez MD, Araujo LL, Byrne AP, Kirby N, Pakarinen OH, Djurabekova F, Nordlund K, Schleberger M, Osmani O, Medvedev N, Rethfeld B, Kluth P. Tracks and voids in amorphous Ge induced by swift heavy-ion irradiation. PHYSICAL REVIEW LETTERS 2013; 110:245502. [PMID: 25165936 DOI: 10.1103/physrevlett.110.245502] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2013] [Revised: 05/02/2013] [Indexed: 06/03/2023]
Abstract
Ion tracks formed in amorphous Ge by swift heavy-ion irradiation have been identified with experiment and modeling to yield unambiguous evidence of tracks in an amorphous semiconductor. Their underdense core and overdense shell result from quenched-in radially outward material flow. Following a solid-to-liquid phase transformation, the volume contraction necessary to accommodate the high-density molten phase produces voids, potentially the precursors to porosity, along the ion direction. Their bow-tie shape, reproduced by simulation, results from radially inward resolidification.
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Affiliation(s)
- M C Ridgway
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - T Bierschenk
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - R Giulian
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - B Afra
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - M D Rodriguez
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - L L Araujo
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - A P Byrne
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
| | - N Kirby
- Australian Synchrotron, Clayton 3168, Australia
| | - O H Pakarinen
- Department of Physics and Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland
| | - F Djurabekova
- Department of Physics and Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland
| | - K Nordlund
- Department of Physics and Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland
| | - M Schleberger
- Fakultät für Physik, Universität Duisburg-Essen, 47057 Duisburg, Germany
| | - O Osmani
- Fakultät für Physik, Universität Duisburg-Essen, 47057 Duisburg, Germany and Department of Physics and OPTIMAS Research Center, Technical University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - N Medvedev
- Department of Physics and OPTIMAS Research Center, Technical University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - B Rethfeld
- Department of Physics and OPTIMAS Research Center, Technical University of Kaiserslautern, 67663 Kaiserslautern, Germany
| | - P Kluth
- Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia
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35
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Vasisht VV, Sastry S. Liquid-Liquid Phase Transition in Supercooled Silicon. LIQUID POLYMORPHISM 2013. [DOI: 10.1002/9781118540350.ch18] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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McMillan PF, Greaves GN, Wilson M, Wilding MC, Daisenberger D. Polyamorphism and Liquid-Liquid Phase Transitions in Amorphous Silicon and Supercooled Al 2O 3-Y 2O 3Liquids. LIQUID POLYMORPHISM 2013. [DOI: 10.1002/9781118540350.ch12] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Li W, Fenton JC, Cui A, Wang H, Wang Y, Gu C, McComb DW, Warburton PA. Felling of individual freestanding nanoobjects using focused-ion-beam milling for investigations of structural and transport properties. NANOTECHNOLOGY 2012; 23:105301. [PMID: 22350591 DOI: 10.1088/0957-4484/23/10/105301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report that, to enable studies of their compositional, structural and electrical properties, freestanding individual nanoobjects can be selectively felled in a controllable way by the technique of low-current focused-ion-beam (FIB) milling with the ion beam at a chosen angle of incidence to the nanoobject. To demonstrate the suitability of the technique, we report results for zigzag/straight tungsten nanowires grown vertically on support substrates and then felled for characterization. We also describe a systematic investigation of the effect of the experimental geometry and parameters on the felling process and on the induced wire-bending phenomenon. The method of felling freestanding nanoobjects using FIB is an advantageous new technique enabling investigations of the properties of selected individual nanoobjects.
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Affiliation(s)
- Wuxia Li
- Beijing National Lab of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.
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Garcez KMS, Antonelli A. Pressure effects on the transitions between disordered phases in supercooled liquid silicon. J Chem Phys 2011; 135:204508. [DOI: 10.1063/1.3663387] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Ashtekar S, Scott G, Lyding J, Gruebele M. Direct imaging of two-state dynamics on the amorphous silicon surface. PHYSICAL REVIEW LETTERS 2011; 106:235501. [PMID: 21770518 DOI: 10.1103/physrevlett.106.235501] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2011] [Indexed: 05/31/2023]
Abstract
Amorphous silicon is an important material, amidst a debate whether or not it is a glass. We produce amorphous Si surfaces by ion bombardment and vapor growth, and image discrete Si clusters which hop by two-state dynamics at 295 K. Independent of surface preparation, these clusters have an average diameter of ∼5 atoms. Given prior results for metallic glasses, we suggest that this cluster size is a universal feature. The hopping activation free energy of 0.93±0.15 eV is rather small, in agreement with a previously untested surface glass model. Hydrogenation quenches the two-state dynamics, apparently by increasing surface crystallinity.
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Affiliation(s)
- S Ashtekar
- Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801, USA
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Beye M, Sorgenfrei F, Schlotter WF, Wurth W, Föhlisch A. The liquid-liquid phase transition in silicon revealed by snapshots of valence electrons. Proc Natl Acad Sci U S A 2010; 107:16772-6. [PMID: 20805512 PMCID: PMC2947918 DOI: 10.1073/pnas.1006499107] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The basis for the anomalies of water is still mysterious. Quite generally tetrahedrally coordinated systems, also silicon, show similar thermodynamic behavior but lack--like water--a thorough explanation. Proposed models--controversially discussed--explain the anomalies as a remainder of a first-order phase transition between high and low density liquid phases, buried deeply in the "no man's land"--a part of the supercooled liquid region where rapid crystallization prohibits any experimental access. Other explanations doubt the existence of the phase transition and its first-order nature. Here, we provide experimental evidence for the first-order-phase transition in silicon. With ultrashort optical pulses of femtosecond duration we instantaneously heat the electronic system of silicon while the atomic structure as defined by the much heavier nuclear system remains initially unchanged. Only on a picosecond time scale the energy is transferred into the atomic lattice providing the energy to drive the phase transitions. With femtosecond X-ray pulses from FLASH, the free-electron laser at Hamburg, we follow the evolution of the valence electronic structure during this process. As the relevant phases are easily distinguishable in their electronic structure, we track how silicon melts into the low-density-liquid phase while a second phase transition into the high-density-liquid phase only occurs after the latent heat for the first-order phase transition has been transferred to the atomic structure. Proving the existence of the liquid-liquid phase transition in silicon, the hypothesized liquid-liquid scenario for water is strongly supported.
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Affiliation(s)
- Martin Beye
- Institut für Experimentalphysik, Universität Hamburg and Centre for Free-Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany.
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42
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Borschel C, Niepelt R, Geburt S, Gutsche C, Regolin I, Prost W, Tegude FJ, Stichtenoth D, Schwen D, Ronning C. Alignment of semiconductor nanowires using ion beams. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2009; 5:2576-2580. [PMID: 19714732 DOI: 10.1002/smll.200900562] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Gallium arsenide nanowires are grown on 100 GaAs substrates, adopting the epitaxial relation and thus growing with an angle around 35 degrees off the substrate surface. These straight nanowires are irradiated with different kinds of energetic ions. Depending on the ion species and energy, downwards or upwards bending of the nanowires is observed to increase with ion fluence. In the case of upwards bending, the nanowires can be aligned towards the ion beam direction at high fluences. Defect formation (vacancies and interstitials) within the implantation cascade is identified as the key mechanism for bending. Monte Carlo simulations of the implantation are presented to substantiate the results.
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Affiliation(s)
- Christian Borschel
- Institute for Solid State Physics, University of Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
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Ganesh P, Widom M. Liquid-liquid transition in supercooled silicon determined by first-principles simulation. PHYSICAL REVIEW LETTERS 2009; 102:075701. [PMID: 19257690 DOI: 10.1103/physrevlett.102.075701] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Indexed: 05/27/2023]
Abstract
First-principles molecular dynamics simulations reveal a liquid-liquid phase transition in supercooled elemental silicon. Two phases coexist below Tc approximately 1232 K and above pc approximately -12 kB. The low-density phase is nearly tetracoordinated, with a pseudogap at the Fermi surface, while the high-density phase is more highly coordinated and metallic in nature. The transition is observed through the formation of van der Waals loops in pressure-volume isotherms below Tc.
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Affiliation(s)
- P Ganesh
- Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA
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44
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Jakse N, Pasturel A. Dynamic aspects of the liquid-liquid phase transformation in silicon. J Chem Phys 2008; 129:104503. [DOI: 10.1063/1.2970084] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Glasmacher UA, Lang M, Keppler H, Langenhorst F, Neumann R, Schardt D, Trautmann C, Wagner GA. Phase transitions in solids stimulated by simultaneous exposure to high pressure and relativistic heavy ions. PHYSICAL REVIEW LETTERS 2006; 96:195701. [PMID: 16803109 DOI: 10.1103/physrevlett.96.195701] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2005] [Revised: 03/28/2006] [Indexed: 05/10/2023]
Abstract
In many solids, heavy ions of high kinetic energy (MeV-GeV) produce long cylindrical damage trails with diameters of order 10 nm. Up to now, no information was available how solids cope with the simultaneous exposure to these energetic projectiles and to high pressure. We report the first experiments where relativistic uranium and gold ions from the SIS heavy-ion synchrotron at GSI were injected through several mm of diamond into solid samples pressurized up to 14 GPa in a diamond anvil cell. In synthetic graphite and natural zircon, the combination of pressure and ion beams triggered drastic structural changes not caused by the applied pressure or the ions alone. The modifications comprise long-range amorphization of graphite rather than individual track formation, and in the case of zircon the decomposition into nanocrystals and nucleation of the high-pressure phase reidite.
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Affiliation(s)
- Ulrich A Glasmacher
- Forschungsstelle Archäometrie der Heidelberger Akademie der Wissenschaften am Max-Planck-Institut für Kernphysik, Germany.
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McMillan PF, Wilson M, Daisenberger D, Machon D. A density-driven phase transition between semiconducting and metallic polyamorphs of silicon. NATURE MATERIALS 2005; 4:680-4. [PMID: 16113681 DOI: 10.1038/nmat1458] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Accepted: 06/29/2005] [Indexed: 05/04/2023]
Abstract
Amorphous and crystalline forms of silicon are well-known, tetrahedrally coordinated semiconductors. High-pressure studies have revealed extensive polymorphism among various metallic crystal structures containing atoms in six-, eight- and 12-fold coordination. Melting silicon at ambient or high pressure results in a conducting liquid, in which the average coordination is greater than four (ref. 3). This liquid cannot normally be quenched to a glass, because of rapid crystallization to the diamond-structured semiconductor. Solid amorphous silicon is obtained by synthesis routes such as chemical or physical vapour deposition that result in a tetrahedrally bonded semiconducting state. It has long been speculated that the amorphous solid and the liquid could represent two polymorphic forms of the amorphous state that are linked by density- or entropy-driven transformations. Such polyamorphic transitions are recognized to occur among several different types of liquid and glassy systems. Here we present experimental evidence for the occurrence of a density-driven polyamorphic transition between semiconducting and metallic forms of solid amorphous silicon. The experiments are combined with molecular dynamics simulations that map the behaviour of the amorphous solid on to that of the liquid state.
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Affiliation(s)
- Paul F McMillan
- Department of Chemistry and Materials Chemistry Centre, Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
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