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Brodu A, Ballottin MV, Buhot J, van Harten EJ, Dupont D, La Porta A, Prins PT, Tessier MD, Versteegh MAM, Zwiller V, Bals S, Hens Z, Rabouw FT, Christianen PCM, de Mello Donega C, Vanmaekelbergh D. Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots. ACS PHOTONICS 2018; 5:3353-3362. [PMID: 30175158 PMCID: PMC6115013 DOI: 10.1021/acsphotonics.8b00615] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Indexed: 05/05/2023]
Abstract
Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size-tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = ±2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = ±1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.
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Affiliation(s)
- Annalisa Brodu
- Debye Institute
for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
| | - Mariana V. Ballottin
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The
Netherlands
| | - Jonathan Buhot
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The
Netherlands
| | - Elleke J. van Harten
- Debye Institute
for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
| | - Dorian Dupont
- Physics and Chemistry of Nanostructures, Ghent University, 9000 Ghent, Belgium
| | - Andrea La Porta
- Electron
Microscopy for Materials Research, EMAT, University of Antwerp, 2020 Antwerp, Belgium
| | - P. Tim Prins
- Debye Institute
for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
| | - Mickael D. Tessier
- Physics and Chemistry of Nanostructures, Ghent University, 9000 Ghent, Belgium
| | - Marijn A. M. Versteegh
- Department
of Applied Physics, Royal Institute of Technology
(KTH), 106 91 Stockholm, Sweden
| | - Val Zwiller
- Department
of Applied Physics, Royal Institute of Technology
(KTH), 106 91 Stockholm, Sweden
| | - Sara Bals
- Electron
Microscopy for Materials Research, EMAT, University of Antwerp, 2020 Antwerp, Belgium
| | - Zeger Hens
- Physics and Chemistry of Nanostructures, Ghent University, 9000 Ghent, Belgium
| | - Freddy T. Rabouw
- Debye Institute
for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
| | - Peter C. M. Christianen
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The
Netherlands
| | - Celso de Mello Donega
- Debye Institute
for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
| | - Daniel Vanmaekelbergh
- Debye Institute
for Nanomaterials Science, Utrecht University, 3584 CC Utrecht, The Netherlands
- E-mail:
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Norouzzadeh P, Myles CW, Vashaee D. Prediction of a large number of electron pockets near the band edges in type-VIII clathrate Si46 and its physical properties from first principles. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:475502. [PMID: 24172765 DOI: 10.1088/0953-8984/25/47/475502] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The material design of type-VIII clathrate Si46 is presented based on first principles. The structural, electronic, elastic, vibrational, and thermodynamic properties of this hypothetical material are presented. Our results predict that type-VIII clathrate Si46 is an indirect semiconductor with a bandgap of 1.24 eV. The band structure revealed an interestingly large number of electron pockets near both conduction and valance band edges. Such a large density of states near the band edges, which is higher than that of the best thermoelectric materials discovered so far, can result in a large thermoelectric power factor (>0.004 W m(-1) K(-2)) making it a promising candidate for thermoelectric applications. The elastic properties as well as the vibrational modes and the phonon state densities of this material were also calculated. Our calculations predict that the heat capacity at constant volume (isochoric) of this clathrate increases smoothly with temperature and approaches the Dulong-Petit value near room temperature. The electronic band structure shows a large number of valleys closely packed around the valance band edge, which is rare among the known semiconducting materials. These valleys can contribute to transport at high temperature resulting in a possibly high performance (ZT > 1.5) p-type thermoelectric material.
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Affiliation(s)
- Payam Norouzzadeh
- Helmerich Advanced Technology Research Center, Oklahoma State University, Tulsa, OK 74106, USA
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Della Gaspera E, Tucker R, Star K, Lan EH, Ju YS, Dunn B. Copper-based conductive composites with tailored thermal expansion. ACS APPLIED MATERIALS & INTERFACES 2013; 5:10966-10974. [PMID: 24175870 DOI: 10.1021/am403227c] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We have devised a moderate temperature hot-pressing route for preparing metal-matrix composites which possess tunable thermal expansion coefficients in combination with high electrical and thermal conductivities. The composites are based on incorporating ZrW2O8, a material with a negative coefficient of thermal expansion (CTE), within a continuous copper matrix. The ZrW2O8 enables us to tune the CTE in a predictable manner, while the copper phase is responsible for the electrical and thermal conductivity properties. An important consideration in the processing of these materials is to avoid the decomposition of the ZrW2O8 phase. This is accomplished by using relatively mild hot-pressing conditions of 500 °C for 1 h at 40 MPa. To ensure that these conditions enable sintering of the copper, we developed a synthesis route for the preparation of Cu nanoparticles (NPs) based on the reduction of a common copper salt in aqueous solution in the presence of a size control agent. Upon hot pressing these nanoparticles at 500 °C, we are able to achieve 92-93% of the theoretical density of copper. The resulting materials exhibit a CTE which can be tuned between the value of pure copper (16.5 ppm/°C) and less than 1 ppm/°C. Thus, by adjusting the relative amount of the two components, the properties of the composite can be designed so that a material with high electrical conductivity and a CTE that matches the relatively low CTE values of semiconductor or thermoelectric materials can be achieved. This unique combination of electrical and thermal properties enables these Cu-based metal-matrix composites to be used as electrical contacts to a variety of semiconductor and thermoelectric devices which offer stable operation under thermal cycling conditions.
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Affiliation(s)
- Enrico Della Gaspera
- Department of Materials Science and Engineering, University of California Los Angeles , 420 Westwood Plaza, Los Angeles, California 90095-1595, United States
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Soullard J, Santamaria R, Boyer D. Thermodynamic States of Nanoclusters at Low Pressure and Low Temperature: The Case of 13 H2. J Phys Chem A 2011; 115:9790-800. [DOI: 10.1021/jp204372k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jacques Soullard
- Departamento de Estado Sólido, Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, México, D.F., México
| | - Ruben Santamaria
- Departamento de Física Teórica, Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, México, D.F., México
| | - Denis Boyer
- Departamento de Sistemas Complejos, Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, México, D.F., México
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Abstract
ABSTRACTThermal expansion is important for predicting residual stresses in epitaxial films, composites and electronic devices as well as for providing information relevant to an understanding of interatomic potentials and the equation of state of materials. Model calculations have many assumptions, both inherent and implicit, and have difficulty accurately representing thermal expansion at high temperatures and pressures. We utilize a semi-empirical quasi-harmonic model to evaluate available data for β-silicon carbide, gallium phosphide and indium phosphide. The model allows prediction of the thermal properties of these semiconductors from near 0 K to the vicinity of their melting points. The approach, consisting of a simplified frequency spectrum with several Einstein terms, provides a convenient mathematical method where a minimum of empirical parameters represent the thermal property.
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