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Xiao T, Nagaoka Y, Wang X, Jiang T, LaMontagne D, Zhang Q, Cao C, Diao X, Qiu J, Lu Y, Wang Z, Cao YC. Nanocrystals with metastable high-pressure phases under ambient conditions. Science 2022; 377:870-874. [PMID: 35981022 DOI: 10.1126/science.abq7684] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The ambient metastability of the rock-salt phase in well-defined model systems comprising nanospheres or nanorods of cadmium selenide, cadmium sulfide, or both was investigated as a function of composition, initial crystal phase, particle structure, shape, surface functionalization, and ordering level of their assemblies. Our experiments show that these nanocrystal systems exhibit ligand-tailorable reversibility in the rock salt-to-zinc blende solid-phase transformation. Interparticle sintering was used to engineer kinetic barriers in the phase transformation to produce ambient-pressure metastable rock-salt structures in a controllable manner. Interconnected nanocrystal networks were identified as an essential structure that hosted metastable high-energy phases at ambient conditions. These findings suggest general rules for transformation-barrier engineering that are useful in the rational design of next-generation materials.
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Affiliation(s)
- Tianyuan Xiao
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Yasutaka Nagaoka
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Xirui Wang
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Tian Jiang
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Derek LaMontagne
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Qiang Zhang
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Can Cao
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Xizheng Diao
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Jiahua Qiu
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Yiruo Lu
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Zhongwu Wang
- Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 14853, USA
| | - Y Charles Cao
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
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2
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Beimborn JC, Walther LR, Wilson KD, Weber JM. Size-Dependent Pressure-Response of the Photoluminescence of CsPbBr 3 Nanocrystals. J Phys Chem Lett 2020; 11:1975-1980. [PMID: 32066242 DOI: 10.1021/acs.jpclett.0c00174] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We report the size-dependent pressure response for CsPbBr3 perovskite nanocrystals in the size range 5.7-10.9 nm using photoluminescence spectroscopy in a diamond anvil cell. As the nanocrystal size decreases below ca. 7.5 nm, we observe a decrease in the transition pressure at which there is a change in the mode of deformation concomitant with an isostructural phase transition. We hypothesize that surface fluctuations regarding the tilt and distortion of surface PbBr6 octahedra facilitate the change in the mode of deformation and phase transition at lower pressures for smaller nanocrystals.
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Affiliation(s)
- J Curtis Beimborn
- JILA and the Department of Chemistry, University of Colorado, Boulder, Colorado 80309-0440, United States
| | - Luke R Walther
- JILA and the Department of Chemistry, University of Colorado, Boulder, Colorado 80309-0440, United States
| | - Kenneth D Wilson
- JILA and the Department of Chemistry, University of Colorado, Boulder, Colorado 80309-0440, United States
| | - J Mathias Weber
- JILA and the Department of Chemistry, University of Colorado, Boulder, Colorado 80309-0440, United States
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3
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Cook JB, Lin TC, Kim HS, Siordia A, Dunn BS, Tolbert SH. Suppression of Electrochemically Driven Phase Transitions in Nanostructured MoS 2 Pseudocapacitors Probed Using Operando X-ray Diffraction. ACS NANO 2019; 13:1223-1231. [PMID: 30604614 DOI: 10.1021/acsnano.8b06381] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Pseudocapacitors with nondiffusion-limited charge storage mechanisms allow for fast kinetics that exceed conventional battery materials. It has been demonstrated that nanostructuring conventional battery materials can induce pseudocapacitive behavior. In our previous study, we found that assemblies of metallic 1T MoS2 nanocrystals show faster charge storage compared to the bulk material. Quantitative electrochemistry demonstrated that the current response is capacitive. In this work, we perform a series of operando X-ray diffraction studies upon electrochemical cycling to show that the high capacitive response of metallic 1T MoS2 nanocrystals is due to suppression of the standard first-order phase transition. In bulk MoS2, a phase transition between 1T and triclinic phases (Li xMoS2) is observed during lithiation and delithiation in both the galvanostatic traces (as distinctive plateaus) and the X-ray diffraction patterns with the appearance of the additional peaks. MoS2 nanocrystal assemblies, on the other hand, show none of these features. We hypothesize that the reduced MoS2 crystallite size suppresses the first-order phase transition and gives rise to solid solution-like behavior, potentially due to the unfavorable formation of nucleation sites in confined spaces. Overall, we find that nanostructuring MoS2 suppresses the 1T-triclinic phase transition and shortens Li-ion diffusion path lengths, allowing MoS2 nanocrystal assemblies to behave as nearly ideal pseudocapacitors.
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Affiliation(s)
- John B Cook
- Department of Chemistry and Biochemistry , University of California Los Angeles , Los Angeles , California 90095 , United States
| | - Terri C Lin
- Department of Chemistry and Biochemistry , University of California Los Angeles , Los Angeles , California 90095 , United States
| | - Hyung-Seok Kim
- Department of Materials Science and Engineering , University of California Los Angeles , Los Angeles , California 90095 , United States
| | - Andrew Siordia
- Department of Materials Science and Engineering , University of California Los Angeles , Los Angeles , California 90095 , United States
| | - Bruce S Dunn
- Department of Materials Science and Engineering , University of California Los Angeles , Los Angeles , California 90095 , United States
| | - Sarah H Tolbert
- Department of Chemistry and Biochemistry , University of California Los Angeles , Los Angeles , California 90095 , United States
- Department of Materials Science and Engineering , University of California Los Angeles , Los Angeles , California 90095 , United States
- The California NanoSystems Institute , University of California Los Angeles , Los Angeles , California 90095 , United States
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4
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Williamson CB, Nevers DR, Nelson A, Hadar I, Banin U, Hanrath T, Robinson RD. Chemically reversible isomerization of inorganic clusters. Science 2019; 363:731-735. [PMID: 30765565 DOI: 10.1126/science.aau9464] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 09/17/2018] [Accepted: 01/16/2019] [Indexed: 01/05/2023]
Abstract
Structural transformations in molecules and solids have generally been studied in isolation, whereas intermediate systems have eluded characterization. We show that a pair of cadmium sulfide (CdS) cluster isomers provides an advantageous experimental platform to study isomerization in well-defined, atomically precise systems. The clusters coherently interconvert over an ~1-electron volt energy barrier with a 140-milli-electron volt shift in their excitonic energy gaps. There is a diffusionless, displacive reconfiguration of the inorganic core (solid-solid transformation) with first order (isomerization-like) transformation kinetics. Driven by a distortion of the ligand-binding motifs, the presence of hydroxyl species changes the surface energy via physisorption, which determines "phase" stability in this system. This reaction possesses essential characteristics of both solid-solid transformations and molecular isomerizations and bridges these disparate length scales.
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Affiliation(s)
- Curtis B Williamson
- Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Douglas R Nevers
- Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA
| | - Andrew Nelson
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA
| | - Ido Hadar
- Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel
| | - Uri Banin
- Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel.
| | - Tobias Hanrath
- Robert F. Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, USA.
| | - Richard D Robinson
- Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA.
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5
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Liu C, Zheng L, Song Q, Xue Z, Huang C, Liu L, Qiao X, Li X, Liu K, Wang T. A Metastable Crystalline Phase in Two-Dimensional Metallic Oxide Nanoplates. Angew Chem Int Ed Engl 2019; 58:2055-2059. [PMID: 30569617 DOI: 10.1002/anie.201812911] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Indexed: 11/10/2022]
Abstract
A simple method was adopted in which ultrathin cerium oxide nanoplates (<1.4 nm) were synthesized to increase the surface atomic content, allowing transformation from a face-centered cubic (fcc) phase to a body-centered tetragonal (bct) phase. Three types of cerium oxide nanoparticles of different thicknesses (1.2 nm ultrathin nanoplates, 2.2 nm nanoplates, and 5.4 nm nanocubes) were examined using transmission electron microscopy and X-ray diffraction. The metastable bct phase was observed only in ultrathin nanoplates. Thermodynamic energy analysis confirmed that the surface energy of the ultrathin nanoplates is the cause of the remarkable stabilization of the metastable bct phase. The mechanism of surface energy regulation can be expanded to other metallic oxides, thus providing a new means for manipulating and stabilizing novel materials under ambient conditions that otherwise would not be recovered.
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Affiliation(s)
- Cong Liu
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Lirong Zheng
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing, 100049, China
| | - Qian Song
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Zhenjie Xue
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Chuanhui Huang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China
| | - Lu Liu
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China
| | - Xuezhi Qiao
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xiao Li
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Keyan Liu
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Tie Wang
- Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences(CAS), Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
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6
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Liu C, Zheng L, Song Q, Xue Z, Huang C, Liu L, Qiao X, Li X, Liu K, Wang T. A Metastable Crystalline Phase in Two-Dimensional Metallic Oxide Nanoplates. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201812911] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Cong Liu
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
| | - Lirong Zheng
- Beijing Synchrotron Radiation Facility; Institute of High Energy Physics; Chinese Academy of Sciences (CAS); Beijing 100049 China
| | - Qian Song
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
| | - Zhenjie Xue
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
| | - Chuanhui Huang
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
| | - Lu Liu
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
| | - Xuezhi Qiao
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
| | - Xiao Li
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
| | - Keyan Liu
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
| | - Tie Wang
- Beijing National Laboratory for Molecular Sciences; Key Laboratory of Analytical Chemistry for Living Biosystems; Institute of Chemistry; Chinese Academy of Sciences(CAS); Beijing 100190 China
- University of Chinese Academy of Sciences; Beijing 100049 China
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7
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Salvadó MA, Franco R, Pertierra P, Ouahrani T, Recio JM. Hysteresis and bonding reconstruction in the pressure-induced B3-B1 phase transition of 3C-SiC. Phys Chem Chem Phys 2017; 19:22887-22894. [PMID: 28812745 DOI: 10.1039/c7cp03732e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The determination of kinetic factors affecting phase metastability is crucial for the design of materials out of the ambient conditions. At a given temperature, the kinetic barrier associated with the reconstruction of the bonding network of a pressure-induced phase transition can be only overcome at pressures where the available vibrational energy of the system is equal or higher than the corresponding activation energy. Our work demonstrates that these pressures provide boundaries to hysteresis cycles that can be evaluated following a three-step computational strategy: (i) total energy electronic structure calculations, (ii) determination of vibrational contributions by means of a simple Debye model, and (iii) description of the energetic profile along the transition path in the framework of the martensitic approximation. In the 3C-SiC polytype, our results reveal that the high pressure rock-salt (B1) structure can not be quenched on release of pressure unless temperature is close to 0 K. The B1 phase transforms back to the low-pressure zinc blende (B3) polymorph at 300 K if pressure is below 30 GPa, in very good agreement with experimental observations. These results are supported by a full characterization of the B3-B1 energetic transition profile in terms of the chemical changes of the bonding network topologically analysed with the electron localization function.
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Affiliation(s)
- Miguel A Salvadó
- MALTA Team and Departamento de Química Física y Analítica, Universidad de Oviedo, E-33006 Oviedo, Spain.
| | - R Franco
- MALTA Team and Departamento de Química Física y Analítica, Universidad de Oviedo, E-33006 Oviedo, Spain.
| | - Pilar Pertierra
- MALTA Team and Departamento de Química Física y Analítica, Universidad de Oviedo, E-33006 Oviedo, Spain.
| | - T Ouahrani
- École Supérieure des Sciences Appliquées, B.P. 230, 13000 Tlemcen, Algeria
| | - J M Recio
- MALTA Team and Departamento de Química Física y Analítica, Universidad de Oviedo, E-33006 Oviedo, Spain.
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8
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Corsini NRC, Zhang Y, Little WR, Karatutlu A, Ersoy O, Haynes PD, Molteni C, Hine NDM, Hernandez I, Gonzalez J, Rodriguez F, Brazhkin VV, Sapelkin A. Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles. NANO LETTERS 2015; 15:7334-7340. [PMID: 26457875 DOI: 10.1021/acs.nanolett.5b02627] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.
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Affiliation(s)
- Niccolo R C Corsini
- Department of Physics, Blackett Laboratory, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom
| | - Yuanpeng Zhang
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
| | - William R Little
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
| | - Ali Karatutlu
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
- Electrical and Electronics Engineering, Yildirim Campus, Bursa Orhangazi University , 16245 Yildirim, Bursa, Turkey
| | - Osman Ersoy
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
| | - Peter D Haynes
- Department of Physics, Blackett Laboratory, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom
| | - Carla Molteni
- Department of Physics, King's College London , Strand, London WC2R 2LS, United Kingdom
| | - Nicholas D M Hine
- TCM Group, Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
- Department of Physics, University of Warwick , Coventry CV4 7AL, United Kingdom
| | - Ignacio Hernandez
- Malta Consolider Team, Departmento CITIMAC, Universidad de Cantabria , Avenida Los Castros s/n, 39005 Santander, Spain
| | - Jesus Gonzalez
- Malta Consolider Team, Departmento CITIMAC, Universidad de Cantabria , Avenida Los Castros s/n, 39005 Santander, Spain
| | - Fernando Rodriguez
- Malta Consolider Team, Departmento CITIMAC, Universidad de Cantabria , Avenida Los Castros s/n, 39005 Santander, Spain
| | - Vadim V Brazhkin
- High Pressure Physics Institute, RAS , 142190 Troitsk, Moscow Region, Russia
| | - Andrei Sapelkin
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
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9
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Guo Y, Sun D, Ouyang B, Raja A, Song J, Heinz TF, Brus LE. Probing the Dynamics of the Metallic-to-Semiconducting Structural Phase Transformation in MoS2 Crystals. NANO LETTERS 2015; 15:5081-5088. [PMID: 26134736 DOI: 10.1021/acs.nanolett.5b01196] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have investigated the phase transformation of bulk MoS2 crystals from the metastable metallic 1T/1T' phase to the thermodynamically stable semiconducting 2H phase. The metastable 1T/1T' material was prepared by Li intercalation and deintercalation. The thermally driven kinetics of the phase transformation were studied with in situ Raman and optical reflection spectroscopies and yield an activation energy of 400 ± 60 meV (38 ± 6 kJ/mol). We calculate the expected minimum energy pathways for these transformations using DFT methods. The experimental activation energy corresponds approximately to the theoretical barrier for a single formula unit, suggesting that nucleation of the phase transformation is quite local. We also report that femtosecond laser writing converts 1T/1T' to 2H in a single laser pass. The mechanisms for the phase transformation are discussed.
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Affiliation(s)
- Yinsheng Guo
- †Department of Chemistry and ‡Department of Physics, Columbia University, New York, New York 10027, United States
| | | | - Bin Ouyang
- §Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5, Canada
| | - Archana Raja
- †Department of Chemistry and ‡Department of Physics, Columbia University, New York, New York 10027, United States
| | - Jun Song
- §Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5, Canada
| | | | - Louis E Brus
- †Department of Chemistry and ‡Department of Physics, Columbia University, New York, New York 10027, United States
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10
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Nirmal M, Brus LE. Semiconductor Nanocrystals: Exciton Quantum Mechanics, Single Nanocrsytal Luminescence, and Metastable High Pressure Phases. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-452-17] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractWe review three areas where significant progress has recently occurred in our understanding of semiconductor nanocrystals. The first two involve luminescence properties of single and ensembles of Cadmium Selenide (CdSe) nanocrystallites (Quantum Dots) between 10 and 50 Å in radius. The size, magnetic field, and temporal dependence of emission from ensembles of nanocrystallites at cryogenic temperatures uncovers the fundamental mechanism of radiative recombination in these nanocrystals. Effective mass models that take into account the electron-hole exchange interaction can quantitatively account for observed luminescence Stokes shifts. Furthermore, the magnetic field dependence of luminescence lifetimes and longitudinal-optical (LO) phonon ratios demonstrate that the exciton ground state in these nanocrystals is optically passive (“dark exciton”) with spin projection ±2. Picosecond time resolved measurements probe exciton relaxation into this level. Recent results on the spectroscopy of single CdSe nanocrystals at room temperature are also presented. Remarkably, emission from a single CdSe nanocrystal under C.W illumination is observed to turn on and off discretely (fluorescence intermittency) on a ∼0.5s timescale. The excitation intensity dependence, and the influence of a passivating high band gap shell of Zinc Sulfide (ZnS) encapsulating the CdSe nanocrystal on the on/off times, suggest that this phenomenon is caused by photoionization. Finally, the third area originates in diamond anvil studies of the solid-solid phase transitions of nanocrystals under pressure. These studies show that a single nucleation event occurs per nanocrystal, and that as a consequence the nanocrystals change shape. The kinetic activation barrier increases with increasing size. Under suitable conditions nanocrystals in dense, six-coordinate high pressure phases may be metastable at STP.
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11
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Alivisatos AP. Scaling law for structural metastability in semiconductor nanocrystals. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/bbpc.19971011104] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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12
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Grünwald M, Dellago C. Nucleation and growth in structural transformations of nanocrystals. NANO LETTERS 2009; 9:2099-2102. [PMID: 19435382 DOI: 10.1021/nl900609d] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Using transition path sampling computer simulations, we reveal the nucleation mechanism of a pressure-induced structural transformation in CdSe nanocrystals. Consistent with experiments, the thermodynamic transition pressure of the transformation increases with decreasing crystal size. Through transition state analysis, we identify the critical nuclei and characterize them by calculating activation enthalpies and volumes. Our simulations reproduce the trends with crystal size observed in experiments. This result supports the observed transformation mechanism, which consists of nucleation on the crystal surface and growth by sliding of parallel crystal planes.
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Affiliation(s)
- Michael Grünwald
- Faculty of Physics and Center for Computational Materials Science, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria.
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13
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Valentini P, Gerberich WW, Dumitrică T. Phase-transition plasticity response in uniaxially compressed silicon nanospheres. PHYSICAL REVIEW LETTERS 2007; 99:175701. [PMID: 17995346 DOI: 10.1103/physrevlett.99.175701] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2007] [Indexed: 05/25/2023]
Abstract
We present a microscopic description for the response of crystalline Si nanospheres up to 10 nm in radius for various uniaxial compression levels. The behavior at low compressions closely resembles the Hertzian predictions. At higher compressions the creation of a new beta-tin phase in the particle core leads to (i) volumetric changes (ii) an increase in elastic moduli, and (iii) significant hardening. Further, (iv) a reversible character of the transformation is obtained with molecular dynamics simulations. The agreement of (i)-(iv) with recent experimental findings challenges the current exclusive view of a dislocation plasticity response in somewhat larger nanoparticles. The phase-transition path should dominate in ultrasmall structures, where dislocation activity is prohibited.
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Affiliation(s)
- P Valentini
- Department of Mechanical Engineering, Institute of Technology, University of Minnesota, Minneapolis, Minnesota 55455, USA
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14
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Cao H, Wang G, Zhang S, Zhang X, Rabinovich D. Growth and Optical Properties of Wurtzite-Type CdS Nanocrystals. Inorg Chem 2006; 45:5103-8. [PMID: 16780332 DOI: 10.1021/ic060440c] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper reports wurtzite-type CdS nanostructures synthesized via a hydrothermal reaction route using dithiol glycol as the sulfur source. The reaction time was found to play an important role in the shape of the CdS nanocrystals: from dots to wires via an oriented attachment mechanism. This work has enabled us to generate nanostructures with controllable geometric shapes and structures and thus optical properties. The CdS nanostructures show a hexagonal wurtzite phase confirmed by X-ray diffraction and show no evidence for a mixed phase of cubic symmetry. The Raman peak position of the characteristic first-order longitudinal optical phonon mode does not change greatly, and the corresponding full width at half-maximum is found to decrease with the CdS shape, changing from nanoparticles to nanowires because of crystalline quality improvement. The photoluminescence measurements indicate tunable optical properties just through a change in the shape of the CdS nanocrystals; i.e., CdS nanoparticles show a band-edge emission at approximately 426 nm in wavelength, while the CdS nanowires show a band-edge emission at approximately 426 nm as well as a weaker trap-state green emission at approximately 530 nm in wavelength. These samples provide an opportunity for the study of the evolution of crystal growth and optical properties, with the shape of the nanocrystals varying from nearly spherical particles to wires.
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Affiliation(s)
- Huaqiang Cao
- Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
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15
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Herhold AB, King HE, Sirota EB. A vanishing nucleation barrier for the n-alkane rotator-to-crystal transformation. J Chem Phys 2002. [DOI: 10.1063/1.1470197] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Jacobs K, Zaziski D, Scher EC, Herhold AB, Paul Alivisatos A. Activation volumes for solid-solid transformations in nanocrystals. Science 2001; 293:1803-6. [PMID: 11546866 DOI: 10.1126/science.1063581] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The transition between four- and six-coordinate structures in CdSe nanocrystals displays simple transition kinetics as compared with the extended solid, and we determined activation volumes from the pressure dependence of the relaxation times. Our measurements indicate that the transformation takes place by a nucleation mechanism and place strong constraints on the type of microscopic motions that lead to the transformation. The type of analysis presented here is difficult for extended solids, which transform by complicated kinetics and involve ill-defined domain volumes. Solids patterned on the nanoscale may prove to be powerful models for the general study of structural transitions in small systems, as well as in extended solids.
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Affiliation(s)
- K Jacobs
- Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
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Wickham JN, Herhold AB, Alivisatos AP. Shape change as an indicator of mechanism in the high-pressure structural transformations of CdSe nanocrystals. PHYSICAL REVIEW LETTERS 2000; 84:923-926. [PMID: 11017406 DOI: 10.1103/physrevlett.84.923] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/1999] [Indexed: 05/23/2023]
Abstract
X-ray diffraction was used to monitor the structure of 45 A diameter CdSe nanocrystals as they transformed repeatedly between fourfold and sixfold coordinated crystal structures. Simulations of the diffraction patterns reveal that a shape change occurs as the crystals transform. They also show that stacking faults are generated in the transition from the high- to the low-pressure phase. The shape change and stacking fault generation place significant constraints on the possible microscopic mechanism of the phase transition.
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Affiliation(s)
- JN Wickham
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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Rockenberger J, Tröger L, Rogach AL, Tischer M, Grundmann M, Eychmüller A, Weller H. The contribution of particle core and surface to strain, disorder and vibrations in thiolcapped CdTe nanocrystals. J Chem Phys 1998. [DOI: 10.1063/1.476216] [Citation(s) in RCA: 137] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Chen CC, Herhold AB, Johnson CS, Alivisatos AP. Size Dependence of Structural Metastability in Semiconductor Nanocrystals. Science 1997; 276:398-401. [PMID: 9103194 DOI: 10.1126/science.276.5311.398] [Citation(s) in RCA: 485] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The kinetics of a first-order, solid-solid phase transition were investigated in the prototypical nanocrystal system CdSe as a function of crystallite size. In contrast to extended solids, nanocrystals convert from one structure to another by single nucleation events, and the transformations obey simple unimolecular kinetics. Barrier heights were observed to increase with increasing nanocrystal size, although they also depend on the nature of the nanocrystal surface. These results are analogous to magnetic phase transitions in nanocrystals and suggest general rules that may be of use in the discovery of new metastable phases.
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Affiliation(s)
- CC Chen
- Department of Chemistry, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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Affiliation(s)
- Louis Brus
- The author is in the Department of Chemistry, Columbia University, New York, NY 10027, USA
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