1
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Tao J, Liu T. s valence electrons in cations of metal oxides serving as descriptors for electron and hole polarons. Phys Chem Chem Phys 2024; 26:14705-14712. [PMID: 38716579 DOI: 10.1039/d4cp00195h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/23/2024]
Abstract
In some metal oxides, an excess electron can give rise to the formation of a small polaron localized on a single site. However, there are still some metal oxides that exhibit the formation of a large polaron. The underlying mechanism behind this phenomenon remains unclear. In this study, we investigate polaron formation in metal oxides favorable for polaron formation using different functionals and through a review of the literature. Our findings indicate that the s valence electrons in cations could serve as a descriptor to classify the polarons in materials. In metal oxides with cations having ns (n ⩾ 5) valence electrons, excess charges trend to localize on several sites or form a two-dimensional shape, and even a large polaron, as these s electrons are delocalized in nature and have a large effect on p or d state polarons. The delocalized nature of ns (n ⩽ 4) valence electrons in cations is relatively small and does not affect the localization condition of p or d state polarons. Therefore, the excess charges in these metal oxides with ns (n ⩽ 4) valence electrons prefer to form a small polaron localizing on a single site. This work unveils the impact of the s valence in cations on polaron formation and provides a fundamental understanding of various types of polarons in metal oxides.
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Affiliation(s)
- Junyan Tao
- National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Henan University, Kaifeng, 475004, China.
| | - Taifeng Liu
- National & Local Joint Engineering Research Center for Applied Technology of Hybrid Nanomaterials, Henan University, Kaifeng, 475004, China.
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2
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Lee J, Yang K, Kwon JY, Kim JE, Han DI, Lee DH, Yoon JH, Park MH. Role of oxygen vacancies in ferroelectric or resistive switching hafnium oxide. NANO CONVERGENCE 2023; 10:55. [PMID: 38038784 PMCID: PMC10692067 DOI: 10.1186/s40580-023-00403-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 11/08/2023] [Indexed: 12/02/2023]
Abstract
HfO2 shows promise for emerging ferroelectric and resistive switching (RS) memory devices owing to its excellent electrical properties and compatibility with complementary metal oxide semiconductor technology based on mature fabrication processes such as atomic layer deposition. Oxygen vacancy (Vo), which is the most frequently observed intrinsic defect in HfO2-based films, determines the physical/electrical properties and device performance. Vo influences the polymorphism and the resulting ferroelectric properties of HfO2. Moreover, the switching speed and endurance of ferroelectric memories are strongly correlated to the Vo concentration and redistribution. They also strongly influence the device-to-device and cycle-to-cycle variability of integrated circuits based on ferroelectric memories. The concentration, migration, and agglomeration of Vo form the main mechanism behind the RS behavior observed in HfO2, suggesting that the device performance and reliability in terms of the operating voltage, switching speed, on/off ratio, analog conductance modulation, endurance, and retention are sensitive to Vo. Therefore, the mechanism of Vo formation and its effects on the chemical, physical, and electrical properties in ferroelectric and RS HfO2 should be understood. This study comprehensively reviews the literature on Vo in HfO2 from the formation and influencing mechanism to material properties and device performance. This review contributes to the synergetic advances of current knowledge and technology in emerging HfO2-based semiconductor devices.
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Affiliation(s)
- Jaewook Lee
- Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, College of Engineering, Seoul National University, Gwanak-Ro 1, Gwanak-Gu, Seoul, 08826, Republic of Korea
| | - Kun Yang
- Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, College of Engineering, Seoul National University, Gwanak-Ro 1, Gwanak-Gu, Seoul, 08826, Republic of Korea
| | - Ju Young Kwon
- Electronic Materials Research Center, Korea Institute of Science and Technology (KIST), Seoul, 02791, Republic of Korea
| | - Ji Eun Kim
- Electronic Materials Research Center, Korea Institute of Science and Technology (KIST), Seoul, 02791, Republic of Korea
| | - Dong In Han
- Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, College of Engineering, Seoul National University, Gwanak-Ro 1, Gwanak-Gu, Seoul, 08826, Republic of Korea
| | - Dong Hyun Lee
- Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, College of Engineering, Seoul National University, Gwanak-Ro 1, Gwanak-Gu, Seoul, 08826, Republic of Korea
| | - Jung Ho Yoon
- Electronic Materials Research Center, Korea Institute of Science and Technology (KIST), Seoul, 02791, Republic of Korea.
| | - Min Hyuk Park
- Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, College of Engineering, Seoul National University, Gwanak-Ro 1, Gwanak-Gu, Seoul, 08826, Republic of Korea.
- Research Institute of Advanced Materials, Seoul National University, Gwanak-Ro 1, Gwanak-Gu, Seoul, 08826, Republic of Korea.
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Wang X, Ganose AM, Kavanagh SR, Walsh A. Band versus Polaron: Charge Transport in Antimony Chalcogenides. ACS ENERGY LETTERS 2022; 7:2954-2960. [PMID: 36120662 PMCID: PMC9469203 DOI: 10.1021/acsenergylett.2c01464] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 08/09/2022] [Indexed: 06/15/2023]
Abstract
Antimony sulfide (Sb2S3) and selenide (Sb2Se3) are emerging earth-abundant absorbers for photovoltaic applications. Solar cell performance depends strongly on charge-carrier transport properties, but these remain poorly understood in Sb2X3 (X = S, Se). Here we report band-like transport in Sb2X3, determined by investigating the electron-lattice interaction and theoretical limits of carrier mobility using first-principles density functional theory and Boltzmann transport calculations. We demonstrate that transport in Sb2X3 is governed by large polarons with moderate Fröhlich coupling constants (α ≈ 2), large polaron radii (extending over several unit cells), and high carrier mobility (an isotropic average of >10 cm2 V-1 s-1 for both electrons and holes). The room-temperature mobility is intrinsically limited by scattering from polar phonon modes and is further reduced in highly defective samples. Our study confirms that the performance of Sb2X3 solar cells is not limited by intrinsic self-trapping.
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Affiliation(s)
- Xinwei Wang
- Department
of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.
| | - Alex M. Ganose
- Department
of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.
| | - Seán R. Kavanagh
- Department
of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.
- Thomas
Young Centre and Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
| | - Aron Walsh
- Department
of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.
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Sebti Y, Chauveau T, Chalal M, Lalatonne Y, Lefebvre C, Motte L. Assessment of the Morphological, Optical, and Photoluminescence Properties of HfO 2 Nanoparticles Synthesized by a Sol-Gel Method Assisted by Microwave Irradiation. Inorg Chem 2022; 61:6508-6518. [PMID: 35438982 DOI: 10.1021/acs.inorgchem.2c00277] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this work, we optimized the synthesis of HfO2 nanoparticles (NPs) with a nonaqueous sol-gel method assisted by microwave heating, with a direct surfactant-free extraction and stabilization in water. To tune the structural, morphological, and photophysical properties, we explored the influence of reaction time, heating temperature, and type and concentration of a salt precursor. The controlled size, shape, crystallinity associated with high stability, a good yield of production, and stabilization in water without any surfactant modification of these HfO2 NPs open possibilities for future optoelectronic and biomedical applications. The investigation of their optical properties, revealed a high absorption in the UV range and the presence of a large band gap, originating in transparency at visible wavelengths. Under UV excitation, photoluminescence (PL) shows three emission bands centered at 305, 381, and 522 nm and are assigned to the vibronic transition of an excited OH•* radical or to a self-trapped exciton, to threefold oxygen vacancies VO3 with recombination to the valence band, and to defect level, respectively. The presence of oxygen vacancies associated with PL properties is particularly attractive for optoelectronic, photocatalysis, scintillator, and UV photosensor applications. Finally, by changing the nature of the hafnium precursor salt, using hafnium ethoxide or hafnium acetylacetonate, low-crystallized and aggregated NPs were obtained, which requires further investigation.
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Affiliation(s)
- Yasmine Sebti
- Université Sorbonne Paris Nord and Université Paris Cité, INSERM, LVTS, F-75018 Paris, France
| | - Thierry Chauveau
- Université Sorbonne Paris Nord, CNRS, LSPM, F-93430 Villetaneuse, France
| | - Mohand Chalal
- Université Sorbonne Paris Nord, CNRS, CSPBAT, F-93017 Bobigny, France
| | - Yoann Lalatonne
- Université Sorbonne Paris Nord and Université Paris Cité, INSERM, LVTS, F-75018 Paris, France.,Service de Biophysique et Médecine Nucléaire, AP-HP, Hôpital Avicenne, F-93009 Bobigny, France
| | | | - Laurence Motte
- Université Sorbonne Paris Nord and Université Paris Cité, INSERM, LVTS, F-75018 Paris, France
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Pham TD, Deskins NA. Efficient Method for Modeling Polarons Using Electronic Structure Methods. J Chem Theory Comput 2020; 16:5264-5278. [DOI: 10.1021/acs.jctc.0c00374] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Thang Duc Pham
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - N. Aaron Deskins
- Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
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Strand J, Chulkov SK, Watkins MB, Shluger AL. First principles calculations of optical properties for oxygen vacancies in binary metal oxides. J Chem Phys 2019; 150:044702. [DOI: 10.1063/1.5078682] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Jack Strand
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Sergey K. Chulkov
- School of Mathematics and Physics, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, United Kingdom
| | - Matthew B. Watkins
- School of Mathematics and Physics, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, United Kingdom
| | - Alexander L. Shluger
- Department of Physics and Astronomy and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
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7
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Glasbrenner M, Vogler S, Ochsenfeld C. Linear and sublinear scaling computation of the electronic g-tensor at the density functional theory level. J Chem Phys 2019; 150:024104. [DOI: 10.1063/1.5066266] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Michael Glasbrenner
- Chair of Theoretical Chemistry and Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry, University of Munich (LMU), Butenandtstr. 7, 81377 Munich, Germany
| | - Sigurd Vogler
- Chair of Theoretical Chemistry and Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry, University of Munich (LMU), Butenandtstr. 7, 81377 Munich, Germany
| | - Christian Ochsenfeld
- Chair of Theoretical Chemistry and Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry, University of Munich (LMU), Butenandtstr. 7, 81377 Munich, Germany
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8
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Papernov S, Brunsman MD, Oliver JB, Hoffman BN, Kozlov AA, Demos SG, Shvydky A, Cavalcante FHM, Yang L, Menoni CS, Roshanzadeh B, Boyd STP, Emmert LA, Rudolph W. Optical properties of oxygen vacancies in HfO 2 thin films studied by absorption and luminescence spectroscopy. OPTICS EXPRESS 2018; 26:17608-17623. [PMID: 30119572 DOI: 10.1364/oe.26.017608] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 05/10/2018] [Indexed: 05/24/2023]
Abstract
Hafnium oxide thin films with varying oxygen content were investigated with the goal of finding the optical signature of oxygen vacancies in the film structure. It was found that a reduction of oxygen content in the film leads to changes in both, structural and optical characteristics. Optical absorption spectroscopy, using nanoKelvin calorimetry, revealed an enhanced absorption in the near-ultraviolet (near-UV) and visible wavelength ranges for films with reduced oxygen content, which was attributed to mid-gap electronic states of oxygen vacancies. Absorption in the near-infrared was found to originate from structural defects other than oxygen vacancy. Luminescence generated by continuous-wave 355-nm laser excitation in e-beam films showed significant changes in the spectral profile with oxygen reduction and new band formation linked to oxygen vacancies. The luminescence from oxygen-vacancy states was found to have microsecond-scale lifetimes when compared with nanosecond-scale lifetimes of luminescence attributed to other structural film defects. Laser-damage testing using ultraviolet nanosecond and infrared femtosecond pulses showed a reduction of the damage threshold with increasing number of oxygen vacancies in hafnium oxide films.
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Strand J, Kaviani M, Gao D, El-Sayed AM, Afanas'ev VV, Shluger AL. Intrinsic charge trapping in amorphous oxide films: status and challenges. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:233001. [PMID: 29692368 DOI: 10.1088/1361-648x/aac005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states stemming from the disorder of amorphous metal oxide networks. We start from presenting the results for amorphous (a) HfO2, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties. Exhaustive photo-depopulation spectroscopy measurements and theoretical calculations using density functional theory shed light on the atomic nature of electronic gap states responsible for deep electron trapping observed in a-HfO2. We review theoretical methods used for creating models of amorphous structures and electronic structure calculations of amorphous oxides and outline some of the challenges in modeling defects in amorphous materials. We then discuss theoretical models of electron polarons and bi-polarons in a-HfO2 and demonstrate that these intrinsic states originate from low-coordinated ions and elongated metal-oxygen bonds in the amorphous oxide network. Similarly, holes can be captured at under-coordinated O sites. We then discuss electron and hole trapping in other amorphous oxides, such as a-SiO2, a-Al2O3, a-TiO2. We propose that the presence of low-coordinated ions in amorphous oxides with electron states of significant p and d character near the conduction band minimum can lead to electron trapping and that deep hole trapping should be common to all amorphous oxides. Finally, we demonstrate that bi-electron trapping in a-HfO2 and a-SiO2 weakens Hf(Si)-O bonds and significantly reduces barriers for forming Frenkel defects, neutral O vacancies and O2- ions in these materials. These results should be useful for better understanding of electronic properties and structural evolution of thin amorphous films under carrier injection conditions.
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Affiliation(s)
- Jack Strand
- Department of Physics, University College London, Gower Street, London WC1E 6BT, United Kingdom
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10
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Strand J, Kaviani M, Afanas'ev VV, Lisoni JG, Shluger AL. Intrinsic electron trapping in amorphous oxide. NANOTECHNOLOGY 2018; 29:125703. [PMID: 29332843 DOI: 10.1088/1361-6528/aaa77a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We demonstrate that electron trapping at intrinsic precursor sites is endemic in non-glass-forming amorphous oxide films. The energy distributions of trapped electron states in ultra-pure prototype amorphous (a)-HfO2 insulator obtained from exhaustive photo-depopulation experiments demonstrate electron states in the energy range of 2-3 eV below the oxide conduction band. These energy distributions are compared to the results of density functional calculations of a-HfO2 models of realistic density. The experimental results can be explained by the presence of intrinsic charge trapping sites formed by under-coordinated Hf cations and elongated Hf-O bonds in a-HfO2. These charge trapping states can capture up to two electrons, forming polarons and bi-polarons. The corresponding trapping sites are different from the dangling-bond type defects responsible for trapping in glass-forming oxides, such as SiO2, in that the traps are formed without bonds being broken. Furthermore, introduction of hydrogen causes formation of somewhat energetically deeper electron traps when a proton is immobilized next to the trapped electron bi-polaron. The proposed novel mechanism of intrinsic charge trapping in a-HfO2 represents a new paradigm for charge trapping in a broad class of non-glass-forming amorphous insulators.
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Affiliation(s)
- Jack Strand
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
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11
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Xu DP, Yu LJ, Chen XD, Chen L, Sun QQ, Zhu H, Lu HL, Zhou P, Ding SJ, Zhang DW. In Situ Analysis of Oxygen Vacancies and Band Alignment in HfO 2/TiN Structure for CMOS Applications. NANOSCALE RESEARCH LETTERS 2017; 12:311. [PMID: 28454477 PMCID: PMC5407434 DOI: 10.1186/s11671-017-2068-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 04/10/2017] [Indexed: 06/07/2023]
Abstract
The density of oxygen vacancies characterization in high-k/metal gate is significant for semiconductor device fabrication. In this work, a new approach was demonstrated to detect the density of oxygen vacancies by in situ x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurement. Moreover, the band alignment of the structure with optical band gap measured by spectroscopic ellipsometry (SE) and valence band offset by UPS were reported. The specific areal density of oxygen vacancies in high-k dielectric of HfO2/TiN was obtained by fitting the experiment data to be 8.202 × 1010cm- 2. This study would provide an effective approach to characterize the oxygen vacancies based defects which cause threshold voltage shifts and enormous gate leakage in modern MOSFET devices.
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Affiliation(s)
- Da-Peng Xu
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Lin-Jie Yu
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Xu-Dong Chen
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Lin Chen
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Qing-Qing Sun
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Hao Zhu
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Hong-Liang Lu
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Peng Zhou
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - Shi-Jin Ding
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
| | - David Wei Zhang
- State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China
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Dicks OA, Shluger AL. Theoretical modeling of charge trapping in crystalline and amorphous Al 2O 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:314005. [PMID: 28585524 DOI: 10.1088/1361-648x/aa7767] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The characteristics of intrinsic electron and hole trapping in crystalline and amorphous Al2O3 have been studied using density functional theory (DFT). Special attention was paid to enforcing the piece-wise linearity of the total energy with respect to electron number through the use of a range separated, hybrid functional PBE0-TC-LRC (Guidon et al 2009 J. Chem. Theory Comput. 5 3010) in order to accurately model the behaviour of localized states. The tuned functional is shown to reproduce the geometric and electronic structures of the perfect crystal as well as the spectroscopic characteristics of MgAl hole centre in corundum α-Al2O3. An ensemble of ten amorphous Al2O3 structures was generated using classical molecular dynamics and a melt and quench method and their structural characteristics compared with the experimental data. The electronic structure of amorphous systems was characterized using the inverse participation ratio method. Electrons and holes were then introduced into both crystalline and amorphous alumina structures and their properties calculated. Holes are shown to trap spontaneously in both crystalline and amorphous alumina. In the crystalline phase they localize on single O ion with the trapping energy of 0.38 eV. In amorphous phase, holes localize on two nearest neighbour oxygen sites with an average trapping energy of 1.26 eV, with hole trapping sites separated on average by about 8.0 Å. No electron trapping is observed in the material. Our results suggest that trapping of positive charge can be much more severe and stable in amorphous alumina rather than in crystalline samples.
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Affiliation(s)
- Oliver A Dicks
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
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13
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Physical and optical properties of HfO 2 NPs – Synthesis and characterization in finding its feasibility in opto-electronic devices. ADV POWDER TECHNOL 2017. [DOI: 10.1016/j.apt.2017.03.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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15
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Schober C, Reuter K, Oberhofer H. Critical analysis of fragment-orbital DFT schemes for the calculation of electronic coupling values. J Chem Phys 2016; 144:054103. [PMID: 26851904 DOI: 10.1063/1.4940920] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a critical analysis of the popular fragment-orbital density-functional theory (FO-DFT) scheme for the calculation of electronic coupling values. We discuss the characteristics of different possible formulations or "flavors" of the scheme which differ by the number of electrons in the calculation of the fragments and the construction of the Hamiltonian. In addition to two previously described variants based on neutral fragments, we present a third version taking a different route to the approximate diabatic state by explicitly considering charged fragments. In applying these FO-DFT flavors to the two molecular test sets HAB7 (electron transfer) and HAB11 (hole transfer), we find that our new scheme gives improved electronic couplings for HAB7 (-6.2% decrease in mean relative signed error) and greatly improved electronic couplings for HAB11 (-15.3% decrease in mean relative signed error). A systematic investigation of the influence of exact exchange on the electronic coupling values shows that the use of hybrid functionals in FO-DFT calculations improves the electronic couplings, giving values close to or even better than more sophisticated constrained DFT calculations. Comparing the accuracy and computational cost of each variant, we devise simple rules to choose the best possible flavor depending on the task. For accuracy, our new scheme with charged-fragment calculations performs best, while numerically more efficient at reasonable accuracy is the variant with neutral fragments.
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Affiliation(s)
- Christoph Schober
- Chair for Theoretical Chemistry, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
| | - Karsten Reuter
- Chair for Theoretical Chemistry, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
| | - Harald Oberhofer
- Chair for Theoretical Chemistry, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
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16
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Neukirch AJ, Nie W, Blancon JC, Appavoo K, Tsai H, Sfeir MY, Katan C, Pedesseau L, Even J, Crochet JJ, Gupta G, Mohite AD, Tretiak S. Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials. NANO LETTERS 2016; 16:3809-16. [PMID: 27224519 DOI: 10.1021/acs.nanolett.6b01218] [Citation(s) in RCA: 107] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. Despite the remarkable progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. High on the list of unexplained phenomena are very modest mobilities despite low charge carrier effective masses. Moreover, experiments elucidate unique degradation of photocurrent affecting stable operation of perovskite solar cells. These puzzles suggest that, while ionic hybrid perovskite devices may have efficiencies on par with conventional Si and GaAs devices, they exhibit more complicated charge transport phenomena. Here we report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using both periodic boundary conditions and isolated structures. Using the hybrid density functional theory, we found that volumetric strain in a CsPbI3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI3 (MA = CH3NH3) cluster, both volumetric strain and MA reorientation effects lead to larger binding energies at around 600 and 1300 meV for holes and electrons, respectively. Such large reorganization energies suggest appearance of small polarons in organometallic perovskite materials. The fact that both volumetric lattice strain and MA molecular rotational degrees of freedom can cooperate to create and stabilize polarons indicates that in order to mitigate this problem, formamidinium (FA = HC(NH2)2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.
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Affiliation(s)
- Amanda J Neukirch
- Theoretical Physics and Chemistry of Materials, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Wanyi Nie
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Jean-Christophe Blancon
- Physical Chemistry and Applied Spectroscopy Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Kannatassen Appavoo
- Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States
| | - Hsinhan Tsai
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Matthew Y Sfeir
- Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States
| | - Claudine Katan
- Institut des Sciences Chimiques de Rennes, ISCR, CNRS , Université de Rennes 1, 35042 Rennes, France
| | - Laurent Pedesseau
- Fonctions Optiques pour les Technologies de l'Information, FOTON UMR 6082, CNRS, INSA de Rennes , 35708 Rennes, France
| | - Jacky Even
- Fonctions Optiques pour les Technologies de l'Information, FOTON UMR 6082, CNRS, INSA de Rennes , 35708 Rennes, France
| | - Jared J Crochet
- Physical Chemistry and Applied Spectroscopy Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Gautam Gupta
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Aditya D Mohite
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Sergei Tretiak
- Theoretical Physics and Chemistry of Materials, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
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Zeler J, Zych E. On the thermoluminescence properties and mechanism of LuPO4:Eu sintered materials. RSC Adv 2016. [DOI: 10.1039/c6ra18804d] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Thermoluminescence (TL) of X-rayed LuPO4:Eu sintered materials was investigated as a function of the processing parameters and Eu concentration.
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Affiliation(s)
- J. Zeler
- Faculty of Chemistry
- University of Wroclaw
- 50-383 Wroclaw
- Poland
| | - E. Zych
- Faculty of Chemistry
- University of Wroclaw
- 50-383 Wroclaw
- Poland
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18
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Bradley SR, Bersuker G, Shluger AL. Modelling of oxygen vacancy aggregates in monoclinic HfO2: can they contribute to conductive filament formation? JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:415401. [PMID: 26414778 DOI: 10.1088/0953-8984/27/41/415401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Formation of metal rich conductive filaments and their rearrangements determine the switching characteristics in HfO2 based resistive random access memory (RRAM) devices. The initiation of a filament formation process may occur either via aggregation of pre-existing vacancies randomly distributed in the oxide or via generation of new oxygen vacancies close to the pre-existing ones. We evaluate the feasibility of vacancy aggregation processes by calculating the structures and binding energies of oxygen vacancy aggregates consisting of 2, 3 and 4 vacancies in bulk monoclinic (m)-HfO2 using density functional theory (DFT). We demonstrate that formation of neutral oxygen vacancy aggregates is accompanied by small energy gain, which depends on the size and shape of the aggregate. In the most strongly bound configurations, vacancies are unscreened by Hf cations and form voids within the crystal, with the larger aggregates having larger binding energy per vacancy (-0.11 to -0.18 eV). The negatively charged di-vacancy was found to have similar binding energies to the neutral one, while the positively charged di-vacancy was found to be unstable. Thus aggregation process of either neutral or negatively charged oxygen vacancies is energetically feasible.
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Affiliation(s)
- Samuel R Bradley
- Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
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19
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Du MH. Density Functional Calculations of Native Defects in CH3NH3PbI3: Effects of Spin-Orbit Coupling and Self-Interaction Error. J Phys Chem Lett 2015; 6:1461-6. [PMID: 26263152 DOI: 10.1021/acs.jpclett.5b00199] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Native point defects play an important role in carrier transport properties of CH3NH3PbI3. However, the nature of many important defects remains controversial due partly to the conflicting results reported by recent density functional theory (DFT) calculations. In this Letter, we show that self-interaction error and the neglect of spin-orbit coupling (SOC) in many previous DFT calculations resulted in incorrect positions of valence and conduction band edges, although their difference, which is the band gap, is in good agreement with the experimental value. This problem has led to incorrect predictions of defect-level positions. Hybrid density functional calculations, which partially correct the self-interaction error and include the SOC, show that, among native point defects (including vacancies, interstitials, and antisites), only the iodine vacancy and its complexes induce deep electron and hole trapping levels inside of the band gap, acting as nonradiative recombination centers.
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20
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Kweon KE, Hwang GS, Kim J, Kim S, Kim S. Electron small polarons and their transport in bismuth vanadate: a first principles study. Phys Chem Chem Phys 2015; 17:256-60. [DOI: 10.1039/c4cp03666b] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Hybrid density functional calculations demonstrate small polaron formation in electron-doped BiVO4, and predict the polaron hopping barrier to increase with lattice constant and also the possible concentration-dependence of electron mobility.
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Affiliation(s)
- Kyoung E. Kweon
- Department of Chemical Engineering
- University of Texas at Austin
- Austin
- USA
| | - Gyeong S. Hwang
- Department of Chemical Engineering
- University of Texas at Austin
- Austin
- USA
| | - Jinhan Kim
- CAS Center
- Samsung Advanced Institute of Technology (SAIT)
- Yongin 449-712
- South Korea
| | - Sungjin Kim
- CAS Center
- Samsung Advanced Institute of Technology (SAIT)
- Yongin 449-712
- South Korea
| | - SeongMin Kim
- CAS Center
- Samsung Advanced Institute of Technology (SAIT)
- Yongin 449-712
- South Korea
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21
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Ramo DM, Bristowe PD. The effect of defects and disorder on the electronic properties of ZnIr2O4. J Chem Phys 2014; 141:084704. [DOI: 10.1063/1.4893556] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- David Muñoz Ramo
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Paul D. Bristowe
- Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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22
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23
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Wang Z, Yu H, Su H. The transport properties of oxygen vacancy-related polaron-like bound state in HfOx. Sci Rep 2013; 3:3246. [PMID: 24317593 PMCID: PMC3856482 DOI: 10.1038/srep03246] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Accepted: 11/01/2013] [Indexed: 11/09/2022] Open
Abstract
The oxygen vacancy-related polaron-like bound state migration in HfOx accounting for the observed transport properties in the high resistance state of resistive switching is investigated by the density functional theory with hybrid functional. The barrier of hopping among the threefold oxygen vacancies is strongly dependent on the direction of motion. Especially, the lowest barrier along the <001> direction is 90 meV, in agreement with the experimental value measured from 135 K to room temperature. This hopping mainly invokes the z-directional motion of hafnium and threefold oxygen atoms in the vicinity of the oxygen vacancy resulted from the synergized combination of coupled phonon modes. In the presence of surface, the lowest barrier of hopping between the surface oxygen vacancies is 360 meV along the <101> direction, where the significant surface perpendicular motion of hafnium and twofold oxygen atoms surrounding the oxygen vacancy is identified to facilitate this type of polaron-like bound state migration. Thus, the migration on the surfaces could be more important at the high temperature.
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Affiliation(s)
| | - HongYu Yu
- South University of Science and Technology of China, China 518055
| | - Haibin Su
- Nanyang Technological University, Singapore 639798
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24
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Blumberger J, McKenna KP. Constrained density functional theory applied to electron tunnelling between defects in MgO. Phys Chem Chem Phys 2013; 15:2184-96. [DOI: 10.1039/c2cp42537h] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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25
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Edwards AH, Campbell KA, Pineda AC. Self-trapping of single and paired electrons in Ge2Se3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:195801. [PMID: 22498509 DOI: 10.1088/0953-8984/24/19/195801] [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 the theoretical prediction of single and paired electron self-trapping in Ge(2)Se(3). In finite atomic cluster, density functional calculations, we show that excess single electrons in Ge(2)Se(3) are strongly localized around single germanium dimers. We also find that two electrons prefer to trap around the same germanium dimer, rupturing a neighboring Ge-Se bond. Localization is less robust in periodic, density functional calculations. While paired electron self-trapping is present, as shown by wavefunction localization around a distorted Ge-Ge dimer, single-electron trapping is not. This discrepancy appears to depend only on the boundary conditions and not on the exchange-correlation potential or basis set. For single- and paired-electron trapping, we report the adiabatic barriers to motion and we estimate hopping rates and freeze-in temperatures. For the single trapped electron, we also predict the (73)Ge and (77)Se hyperfine coupling constants.
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Affiliation(s)
- A H Edwards
- Air Force Research Laboratory, AFRL/RVSE, Kirtland AFB, NM 87117-5776, USA.
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26
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McKenna KP, Wolf MJ, Shluger AL, Lany S, Zunger A. Two-dimensional polaronic behavior in the binary oxides m-HfO2 and m-ZrO2. PHYSICAL REVIEW LETTERS 2012; 108:116403. [PMID: 22540495 DOI: 10.1103/physrevlett.108.116403] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Indexed: 05/31/2023]
Abstract
We demonstrate that the three-dimensional (3D) binary monoclinic oxides HfO2 and ZrO2 exhibit quasi-2D polaron localization and conductivity, which results from a small difference in the coordination of two oxygen sublattices in these materials. The transition between a 2D large polaron into a zero-dimensional small polaron state requires overcoming a small energetic barrier. These results demonstrate how a small asymmetry in the lattice structure can determine the qualitative character of polaron localization and significantly broaden the realm of quasi-2D polaron systems.
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Affiliation(s)
- Keith P McKenna
- Department of Physics, University of York, Heslington, York, United Kingdom.
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27
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Ramana CV, Noor-A-Alam M, Gengler JJ, Jones JG. Growth, structure, and thermal conductivity of yttria-stabilized hafnia thin films. ACS APPLIED MATERIALS & INTERFACES 2012; 4:200-204. [PMID: 22148322 DOI: 10.1021/am2012596] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Yttria-stabilized hafnia (YSH) films of 90 nm thickness have been produced using sputter-deposition by varying the growth temperature (T(s)) from room-temperature (RT) to 400 °C. The effect of T(s) on the structure, morphology, and thermal conductivity of YSH films has been investigated. Structural studies indicate that YSH films crystallize in the cubic phase. The lattice constant decreases from 5.15 to 5.10 Å with increasing T(s). The average grain size (L) increases with increasing T(s); L-T(s) relationship indicates the thermally activated process of the crystallization of YSH films. The analyses indicate a critical temperature to promote nanocrystalline, cubic YSH films is 300 °C, which is higher compare to that of pure monoclinic HfO(2) films. Compared to pure nanocrystalline hafnia, the addition of yttria lowers the effective thermal conductivity. The effect of grain size on thermal conductivity is also explored.
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Affiliation(s)
- C V Ramana
- Department of Mechanical Engineering, University of Texas at El Paso, El Paso, Texas 79968, USA.
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28
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Sai N, Barbara PF, Leung K. Hole localization in molecular crystals from hybrid density functional theory. PHYSICAL REVIEW LETTERS 2011; 106:226403. [PMID: 21702620 DOI: 10.1103/physrevlett.106.226403] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Indexed: 05/13/2023]
Abstract
We use first-principles computational methods to examine hole trapping in organic molecular crystals. We present a computational scheme based on the tuning of the fraction of exact exchange in hybrid density functional theory to eliminate the many-electron self-interaction error. With small organic molecules, we show that this scheme gives accurate descriptions of ionization and dimer dissociation. We demonstrate that the excess hole in perfect molecular crystals forms self-trapped molecular polarons. The predicted absolute ionization potentials of both localized and delocalized holes are consistent with experimental values.
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Affiliation(s)
- Na Sai
- Center for Nano and Molecular Science and Technology, The University of Texas at Austin, Austin, Texas 78712, USA
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29
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McKenna KP, Shluger AL. Electron and hole trapping in polycrystalline metal oxide materials. Proc Math Phys Eng Sci 2011. [DOI: 10.1098/rspa.2010.0518] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Electron and hole trapping by grain boundaries and dislocations in polycrystalline materials is important for wide ranging technological applications such as solar cells, microelectronics, photo-catalysts and rechargeable batteries. In this article, we first give an overview of the computational and methodological challenges involved in modelling such effects. This is followed by a discussion of two recent studies we have made on electron/hole trapping in wide gap insulators. The results suggest that such effects can be important for many applications which we discuss. These computationally demanding calculations have made extensive use of both the HPCx and HECToR services.
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Affiliation(s)
- Keith P. McKenna
- World Premier International Research Center, Advanced Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Alexander L. Shluger
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
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30
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Ispas A, Bund A, Vrublevsky I. Investigations on current transients in porous alumina films during re-anodizing using the electrochemical quartz crystal microbalance. J Solid State Electrochem 2010. [DOI: 10.1007/s10008-010-1043-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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