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Madden E, Zwijnenburg MA. The effect of particle size on the optical and electronic properties of hydrogenated silicon nanoparticles. Phys Chem Chem Phys 2024; 26:11695-11707. [PMID: 38563473 DOI: 10.1039/d4cp00119b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
We use a combination of many-body perturbation theory and time-dependent density functional theory to study the optical and electronic properties of hydrogen terminated silicon nanoparticles. We predict that the lowest excited states of these silicon nanoparticles are excitonic in character and that the corresponding excitons are completely delocalised over the volume of the particle. The size of the excitons is predicted to increase proportionally with the particle size. Conversely, we predict that the fundamental gap, the optical gap, and the exciton binding energy increase with decreasing particle size. The exciton binding energy is predicted to counter-act the variation in the fundamental gap and hence to reduce the variation of the optical gap with particle size. The variation in the exciton binding energy itself is probably caused by a reduction in the dielectric screening with decreasing particle size. The intensity of the excited state corresponding to the optical gap and other low energy excitations are predicted to increase with decreasing particle size. We explain this increase in terms of the 'band structure' becoming smeared out in reciprocal space with decreasing particle size, increasing the 'overlap' between the occupied and unoccupied quasiparticle states and thus, the oscillator strength. Fourier transforms of the lowest excitons show that they inherit the periodicity of the frontier quasiparticle states. This, combined with the delocalisation of the exciton and the large exciton binding energy, means that the excitons in silicon nanoparticles combine aspects of Wannier-Mott, delocalisation and effect of periodicity of the underlying structure, and Frenkel, large exciton binding energy, excitons.
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Affiliation(s)
- Eimear Madden
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
| | - Martijn A Zwijnenburg
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
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2
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Sharma M, Panigrahi J, Komarala VK. Nanocrystalline silicon thin film growth and application for silicon heterojunction solar cells: a short review. NANOSCALE ADVANCES 2021; 3:3373-3383. [PMID: 36133724 PMCID: PMC9417196 DOI: 10.1039/d0na00791a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Accepted: 04/18/2021] [Indexed: 05/14/2023]
Abstract
Doped nanocrystalline silicon (nc-Si:H) thin films offer improved carrier transport characteristics and reduced parasitic absorption compared to amorphous silicon (a-Si:H) films for silicon heterojunction (SHJ) solar cell application. In this article, we review the growth conditions of nc-Si:H thin films as the carrier-selective layers for SHJ solar cells. Surface and growth zone models are analysed at different stages of incubation, nucleation, and growth of the silicon nanocrystallites within the hydrogenated amorphous silicon matrix. The recent developments in the implementation of nc-Si:H films and oxygen-alloyed nc-SiO x :H films for SHJ cells are highlighted. Furthermore, hydrogen and carbon dioxide plasma treatments are emphasised as the critical process modification steps for augmenting the nc-Si:H films' optoelectronic properties to enhance the SHJ device performance with better carrier-selective interfaces.
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Affiliation(s)
- Mansi Sharma
- Centre for Energy Studies, Indian Institute of Technology Delhi New Delhi-110016 India
| | - Jagannath Panigrahi
- Centre for Energy Studies, Indian Institute of Technology Delhi New Delhi-110016 India
| | - Vamsi K Komarala
- Centre for Energy Studies, Indian Institute of Technology Delhi New Delhi-110016 India
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3
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Huang CC, Tang Y, van der Laan M, van de Groep J, Koenderink AF, Dohnalová K. Band-Gap Tunability in Partially Amorphous Silicon Nanoparticles Using Single-Dot Correlative Microscopy. ACS APPLIED NANO MATERIALS 2021; 4:288-296. [PMID: 33521589 PMCID: PMC7836094 DOI: 10.1021/acsanm.0c02395] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 12/04/2020] [Indexed: 06/12/2023]
Abstract
Silicon nanoparticles (Si-NPs) represent one of many types of nanomaterials, where the origin of emission is difficult to assess due to a complex interplay between the core and surface chemistry. Band-gap tunability in Si-NPs is predicted to span from the infrared to the ultraviolet spectral range, which is rarely observed in practice. In this work, we directly assess the size dependence of the optical band gap using a single-dot correlative microscopy tool, where the size of the individual NPs is measured using atomic force microscopy (AFM) and the optical band gap is evaluated from single-dot photoluminescence measured on the very same NPs. We analyze 2-8 nm alkyl-capped Si-NPs prepared by a sol-gel method, followed by annealing at 1300 °C. Surprisingly, we find that the optical band gap is given by the amorphous shell, as evidenced by the convergence of the optical band gap size dependence toward the amorphous Si band gap of ∼1.56 eV. We propose that the structural disorder might be the reason behind the often reported limited emission tunability from various Si-NPs in the literature. We believe that our message points toward a pressing need for development and broader use of such direct correlative single-dot microscopy methods to avoid possible misinterpretations that could arise from attempts to recover size-band gap relation from ensemble methods, as practiced nowadays.
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Affiliation(s)
- Chia-Ching Huang
- Institute
of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Yingying Tang
- Institute
of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Marco van der Laan
- Institute
of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Jorik van de Groep
- Institute
of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - A. Femius Koenderink
- Institute
of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Kateřina Dohnalová
- Institute
of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
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4
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Neitzel J, Chelikowsky JR. B-P codopant effects on Raman spectra of Si nanocrystals using real space pseudopotentials. Chem Phys Lett 2019. [DOI: 10.1016/j.cplett.2019.136739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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5
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Yang J, Gao Y. A dipole-dipole interaction tuning the photoluminescence of silicon quantum dots in a water vapor environment. NANOSCALE 2019; 11:1790-1797. [PMID: 30631872 DOI: 10.1039/c8nr09090d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The optical properties of silicon quantum dots (Si QDs) depend on the working conditions, which are critical for their application in optoelectronic devices and fluorescent tags. However, how a humid environment, most common in daily life, influences the photoluminescence (PL) of Si QDs has not been fully understood yet. Herein, we applied time-dependent density functional calculations to show that the adsorption of water molecules would exhibit distinct effects on the PL spectra of Si QDs as a function of size. In particular, the PL of Si QDs presents dual band emission with the adsorption of the cyclic water trimer (H2O)3 under common humid conditions, completely different from the PL of Si QDs under other conditions. The transition dipole moment decomposition analysis shows that the additional emission peak originates from the single Si-Si stretched bond of Si QDs induced by the dipole-dipole interaction between the cyclic water trimer and Si QDs. Moreover, the PL characteristics are size dependent. As the size increases from Si17H24 (the diameter of 0.6 nm) to Si52H52 (1.4 nm), the dipole-dipole interaction energy between (H2O)3 and Si QDs rapidly decreases from 19.1 × 10-22 J to 6.0 × 10-26 J, resulting in a single peak of PL of (H2O)3 adsorption on Si52H52. This study not only gives a deep understanding of PL of Si QDs under humid conditions, but also provides a new perspective on the development of optical devices based on Si QDs.
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Affiliation(s)
- Jinrong Yang
- Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, 100029 Beijing, People's Republic of China
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6
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Zhao LZ, Lu WC, Qin W, Zang QJ, Ho KM, Wang CZ. Theoretical Prediction of Si2–Si33 Absorption Spectra. J Phys Chem A 2017; 121:6388-6397. [DOI: 10.1021/acs.jpca.7b04881] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Li-Zhen Zhao
- College
of Physics and Laboratory of Fiber Materials and Modern Textile, the
Growing Base for State Key Laboratory, Qingdao University, Qingdao, Shandong 266071, P. R. China
| | - Wen-Cai Lu
- College
of Physics and Laboratory of Fiber Materials and Modern Textile, the
Growing Base for State Key Laboratory, Qingdao University, Qingdao, Shandong 266071, P. R. China
- Institute
of Theoretical Chemistry, Jilin University, Changchun, Jilin 130021, P. R. China
| | - Wei Qin
- College
of Physics and Laboratory of Fiber Materials and Modern Textile, the
Growing Base for State Key Laboratory, Qingdao University, Qingdao, Shandong 266071, P. R. China
| | - Qing-Jun Zang
- College
of Physics and Laboratory of Fiber Materials and Modern Textile, the
Growing Base for State Key Laboratory, Qingdao University, Qingdao, Shandong 266071, P. R. China
| | - K. M. Ho
- Ames
Laboratory-U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States
| | - C. Z. Wang
- Ames
Laboratory-U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States
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7
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Yang W, Lü W, Xue X, Zang Q, Wang C. Studies on optical properties of Si220 nanoclusters via time-dependent density functional theory calculations. Chem Res Chin Univ 2016. [DOI: 10.1007/s40242-016-6085-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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8
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Yang J, Fang H, Gao Y. Effect of Water Adsorption on the Photoluminescence of Silicon Quantum Dots. J Phys Chem Lett 2016; 7:1788-1793. [PMID: 27117881 DOI: 10.1021/acs.jpclett.6b00574] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The optical properties of silicon quantum dots (Si QDs) are strongly influenced by circumjacent surface-adsorbed molecules, which would highly affect their applications; however, water, as the ubiquitous environment, has not received enough attention yet. We employed the time-dependent density functional calculations to investigate the water effect of photoluminescence (PL) spectra for Si QDs. In contrast with the absorption spectra, PL spectra exhibit distinct characteristics. For Si32H38, PL presents the single maximum in the dry and humid environment, while the emission spectrum displays a dual-band fluorescence spectroscopy in the low-humidity environment. This phenomenon is also observed in the larger Si QDs. The distinct character in spectroscopy is dominated by the stretching of the Si-Si bond, which could be explained by the self-trapped exciton model. Our results shed light on the Si-water interaction that is important for the development of optical devices based on Si-coated surfaces.
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Affiliation(s)
- Jinrong Yang
- Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201800, China
- University of Chinese Academy of Sciences , Beijing 100049, China
| | - Haiping Fang
- Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201800, China
- Shanghai Science Research Center, Chinese Academy of Sciences , Shanghai 201204, China
| | - Yi Gao
- Division of Interfacial Water and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201800, China
- Shanghai Science Research Center, Chinese Academy of Sciences , Shanghai 201204, China
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9
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Brabec J, Lin L, Shao M, Govind N, Yang C, Saad Y, Ng EG. Efficient Algorithms for Estimating the Absorption Spectrum within Linear Response TDDFT. J Chem Theory Comput 2016; 11:5197-208. [PMID: 26894238 DOI: 10.1021/acs.jctc.5b00887] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We present a special symmetric Lanczos algorithm and a kernel polynomial method (KPM) for approximating the absorption spectrum of molecules within the linear response time-dependent density functional theory (TDDFT) framework in the product form. In contrast to existing algorithms, the new algorithms are based on reformulating the original non-Hermitian eigenvalue problem as a product eigenvalue problem and the observation that the product eigenvalue problem is self-adjoint with respect to an appropriately chosen inner product. This allows a simple symmetric Lanczos algorithm to be used to compute the desired absorption spectrum. The use of a symmetric Lanczos algorithm only requires half of the memory compared with the nonsymmetric variant of the Lanczos algorithm. The symmetric Lanczos algorithm is also numerically more stable than the nonsymmetric version. The KPM algorithm is also presented as a low-memory alternative to the Lanczos approach, but the algorithm may require more matrix-vector multiplications in practice. We discuss the pros and cons of these methods in terms of their accuracy as well as their computational and storage cost. Applications to a set of small and medium-sized molecules are also presented.
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10
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Das D, Samanta A. Quantum size effects on the optical properties of nc-Si QDs embedded in an a-SiOx matrix synthesized by spontaneous plasma processing. Phys Chem Chem Phys 2015; 17:5063-71. [DOI: 10.1039/c4cp05126b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
An energy blue shift due to quantum confinement effects in tiny nc-Si QDs accompanied by larger Stokes shifts in PL at smaller dimensions.
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Affiliation(s)
- Debajyoti Das
- Nano-Science Group
- Energy Research Unit
- Indian Association for the Cultivation of Science
- Jadavpur
- India
| | - Arup Samanta
- Nano-Science Group
- Energy Research Unit
- Indian Association for the Cultivation of Science
- Jadavpur
- India
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11
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Rocca D, Vörös M, Gali A, Galli G. Ab Initio Optoelectronic Properties of Silicon Nanoparticles: Excitation Energies, Sum Rules, and Tamm–Dancoff Approximation. J Chem Theory Comput 2014; 10:3290-8. [DOI: 10.1021/ct5000956] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Dario Rocca
- Université de Lorraine, CRM2, UMR 7036,
Institut Jean Barriol, 54506 Vandoeuvre-lès-Nancy, France
- CNRS,
CRM2, UMR 7036,
54506 Vandoeuvre-lès-Nancy, France
| | - Márton Vörös
- Department
of Physics, University of California, Davis, California 95616, United States
- Department
of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111, Budapest, Hungary
| | - Adam Gali
- Department
of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111, Budapest, Hungary
- Institute
for Solid State Physics and Optics, Wigner Research Center for Physics,
Hungarian Academy of Sciences, P.O. Box
49, H-1525 Budapest, Hungary
| | - Giulia Galli
- Institute
for Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States
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12
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Yin H, Ma Y, Hao X, Mu J, Liu C, Yi Z. Quasiparticle electronic structure and optical absorption of diamond nanoparticles from ab initio many-body perturbation theory. J Chem Phys 2014; 140:214315. [PMID: 24908016 DOI: 10.1063/1.4880695] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The excited states of small-diameter diamond nanoparticles in the gas phase are studied using the GW method and Bethe-Salpeter equation (BSE) within the ab initio many-body perturbation theory. The calculated ionization potentials and optical gaps are in agreement with experimental results, with the average error about 0.2 eV. The electron affinity is negative and the lowest unoccupied molecular orbital is rather delocalized. Precise determination of the electron affinity requires one to take the off-diagonal matrix elements of the self-energy operator into account in the GW calculation. BSE calculations predict a large exciton binding energy which is an order of magnitude larger than that in the bulk diamond.
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Affiliation(s)
- Huabing Yin
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Yuchen Ma
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Xiaotao Hao
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
| | - Jinglin Mu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Chengbu Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Zhijun Yi
- Department of Physics, China University of Mining and Technology, Xuzhou 221116, China
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14
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15
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DAI YING, HUANG BAIBIAO, YU LIN, HAN SHENGHAO, DAI DADI. EFFECTS OF SURFACE OXYGEN ON THE ELECTRONIC PROPERTIES OF SILICON NANOCLUSTERS. INTERNATIONAL JOURNAL OF NANOSCIENCE 2011. [DOI: 10.1142/s0219581x06004085] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We have studied the effects of surface oxygen and its bond structure on the electronic properties of silicon nanoclusters by means of density functional theory calculations. The results of the energy gap as a function of the nanocluster size in hydrogen-terminated and oxygen-adsorbed silicon clusters provide a well interpretation of several experiments. The nature of electronic and optical properties of silicon nanoclusters has been discussed and attributed to the oxygen in both the Si=O double bond structure and Si–O–Si bridge structure.
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Affiliation(s)
- YING DAI
- School of Physics and Microelectronics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China
| | - BAIBIAO HUANG
- School of Physics and Microelectronics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China
| | - LIN YU
- School of Physics and Microelectronics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China
| | - SHENGHAO HAN
- School of Physics and Microelectronics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China
| | - DADI DAI
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina, 27695-8204, USA
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16
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Zdetsis AD. Functionalizable magnetic/luminous silicon/bismuth core/shell nanocrystalline particles. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.04.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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17
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Stein T, Eisenberg H, Kronik L, Baer R. Fundamental gaps in finite systems from eigenvalues of a generalized Kohn-Sham method. PHYSICAL REVIEW LETTERS 2010; 105:266802. [PMID: 21231698 DOI: 10.1103/physrevlett.105.266802] [Citation(s) in RCA: 280] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Indexed: 05/30/2023]
Abstract
We present a broadly applicable, physically motivated, first-principles approach to determining the fundamental gap of finite systems from single-electron orbital energies. The approach is based on using a range-separated hybrid functional within the generalized Kohn-Sham approach to density functional theory. Its key element is the choice of a range-separation parameter such that Koopmans' theorem for both neutral and anion is obeyed as closely as possible. We demonstrate the validity, accuracy, and advantages of this approach on first, second and third row atoms, the oligoacene family of molecules, and a set of hydrogen-passivated silicon nanocrystals. This extends the quantitative usage of density functional theory to an area long believed to be outside its reach.
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Affiliation(s)
- Tamar Stein
- Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, Hebrew University, Jerusalem, Israel
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18
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Khoo KH, Zayak AT, Kwak H, Chelikowsky JR. First-principles study of confinement effects on the Raman spectra of Si nanocrystals. PHYSICAL REVIEW LETTERS 2010; 105:115504. [PMID: 20867585 DOI: 10.1103/physrevlett.105.115504] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 08/05/2010] [Indexed: 05/29/2023]
Abstract
The Raman spectra of Si nanocrystals are studied as a function of nanocrystal diameter using pseudopotential density functional theory and the Placzek approximation. Our calculations reproduce the redshift and broadening of the optical Raman peak with decreasing nanocrystal size, and calculated peak frequencies show good agreement with experimental values. We also find that a surface induced softening of vibrational modes is largely responsible for the Raman redshift, with relaxation of momentum conservation playing only a minor role.
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Affiliation(s)
- K H Khoo
- Center for Computational Materials, Institute for Computational Engineering and Sciences, University of Texas, Austin, Texas 78712, USA
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19
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Zope RR, Baruah T, Richardson SL, Pederson MR, Dunlap BI. Optical excitation energies, Stokes shift, and spin-splitting of C24H72Si14. J Chem Phys 2010; 133:034301. [PMID: 20649324 DOI: 10.1063/1.3459056] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
As an initial step toward the synthesis and characterization of sila-diamondoids, such as sila-adamantane (Si(10)H(16),T(d)), the synthesis of a fourfold silylated sila-adamantane molecule (C(24)H(72)Si(14),T(d)) has been reported in literature [Fischer et al., Science 310, 825 (2005)]. We present the electronic structure, ionization energies, quasiparticle gap, and the excitation energies for the Si(14)(CH(3))(24) and the exact silicon analog of adamantane Si(10)H(16) obtained at the all-electron level using the delta-self-consistent-field and transitional state methods within two different density functional models: (i) Perdew-Burke-Ernzerhof generalized gradient approximation and (ii) fully analytic density functional (ADFT) implementation with atom dependent potential. The ADFT is designed so that molecules separate into atoms having exact atomic energies. The calculations within the two models agree well, to within 0.25 eV for optical excitations. The effect of structural relaxation in the presence of electron-hole-pair excitations is examined to obtain its contribution to the luminescence Stokes shift. The spin-influence on exciton energies is also determined. Our calculations indicate overall decrease in the absorption, emission, quasiparticle, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, ionization energies, Stokes shift, and exciton binding energy when passivating hydrogens in the Si(10)H(16) are replaced with electron donating groups such as methyl (Me) and trimehylsilyl (-Si(Me)(3)).
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Affiliation(s)
- Rajendra R Zope
- NSF CREST Center for Nanomaterials Characterization Science and Process Technology, Howard University, School of Engineering, 2300 Sixth Street, N.W. Washington, D.C. 20059, USA.
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20
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Ren J, Kaxiras E, Meng S. Optical properties of clusters and molecules from real-time time-dependent density functional theory using a self-consistent field. Mol Phys 2010. [DOI: 10.1080/00268976.2010.491489] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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21
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Vasiliev I, del Puerto ML, Jain M, Lugo-Solis A, Chelikowsky JR. Application of time-dependent density-functional theory to molecules and nanostructures. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/j.theochem.2009.04.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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22
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Landt L, Klünder K, Dahl JE, Carlson RMK, Möller T, Bostedt C. Optical response of diamond nanocrystals as a function of particle size, shape, and symmetry. PHYSICAL REVIEW LETTERS 2009; 103:047402. [PMID: 19659398 DOI: 10.1103/physrevlett.103.047402] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Indexed: 05/28/2023]
Abstract
The optical spectra of hydrogen-passivated diamond clusters (diamondoids) precisely defined in size and shape have been measured in the gas phase, i.e., under an environment similar to boundary conditions typically assumed by theory. Characteristic optical properties evolve for these wide band-gap semiconductor nanocrystals as a function of size, shape, and symmetry in the subnanometer regime. These effects have not previously been theoretically predicted. The optical response of the tetrahedral-shaped C_{26}H_{32} diamond cluster [1(2,3)4] pentamantane is found to be remarkably similar to that of bulk diamond.
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Affiliation(s)
- Lasse Landt
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Eugene-Wigner Building EW 3-1, 10623 Berlin, Germany
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Guillaume M, Champagne B, Bégué D, Pouchan C. Electrostatic interaction schemes for evaluating the polarizability of silicon clusters. J Chem Phys 2009; 130:134715. [DOI: 10.1063/1.3104629] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Kumar S, Gope J, Kumar A, Parashar A, Rauthan CMS, Dixit PN. High pressure growth of nanocrystalline silicon films. JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 2008; 8:4211-4217. [PMID: 19049205 DOI: 10.1088/0953-8984/20/33/335215] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Nanocrystalline silicon thin films were grown using gaseous mixture of 5% silane (SiH4) diluted in hydrogen (H2) and argon (Ar) in a radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition technique. These films were deposited as a function of pressure and were characterized using AFM, Laser Raman, UV-VIS transmission, photoluminescence and electrical conductivity techniques. AFM micrographs shows that these films contain nanocrystallites of 30-60 nm size. Laser Raman peaks at 520 cm(-1) and photoluminescence peaks at 2.75 and 2.85 eV have been observed. The crystalline fraction in these films was varied from 30% to 80% with the variation of deposition pressure from 2 Torr to 8 Torr. There is an optimum pressure of 4 Torr where the maximum growth of nanocrystalline phases was observed. It has been found that nanocrystallites in these film enhanced the optical band gap and electrical conductivity. Also a voltage-current (V-I) probe was used to evaluate the various electrical parameters of the plasma used to deposit the nc-Si:H films for the present investigation. Growth via a SiH3 precursor, diffusion of hydrogen in the sub-surface and argon etching of weak bonds are some of the processes that may be involved in the nano crystallization process.
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Affiliation(s)
- Sushil Kumar
- Plasma Processed Materials Group, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India
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Abstract
Silicon nanocrystals (NCs) represent one of the most promising material systems for light emission applications in microphotonics. In recent years, several groups have reported on the observation of optical gain or stimulated emission in silicon NCs or in porous silicon (PSi). These results suggest that silicon-NC-based waveguide amplifiers or silicon lasers are achievable. However, in order to obtain clear and reproducible evidence of stimulated emission, it is necessary to understand the physical mechanisms at work in the light emission process. In this paper, we report on the detailed theoretical aspects of the energy levels and recombination rates in doped and undoped Si NCs, and we discuss the effects of energy transfer mechanisms. The theoretical calculations are extended toward computational simulations of ensembles of interacting nanocrystals. We will show that inhomogeneous broadening and energy transfer remain significant problems that must be overcome in order to improve the gain profile and to minimize nonradiative effects. Finally, we suggest means by which these objectives may be achieved.
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Wang BC, Chou YM, Deng JP, Dung YT. Structural and Optical Properties of Passivated Silicon Nanoclusters with Different Shapes: A Theoretical Investigation. J Phys Chem A 2008; 112:6351-7. [DOI: 10.1021/jp8006975] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Bo-Cheng Wang
- Department of Chemistry, Tamkang University, Tamsui 251, Taiwan, and Department of Physics, Chinese Culture University, Taipei 110, Taiwan
| | - Yu-Ma Chou
- Department of Chemistry, Tamkang University, Tamsui 251, Taiwan, and Department of Physics, Chinese Culture University, Taipei 110, Taiwan
| | - Jin-Pei Deng
- Department of Chemistry, Tamkang University, Tamsui 251, Taiwan, and Department of Physics, Chinese Culture University, Taipei 110, Taiwan
| | - Yu-Tsai Dung
- Department of Chemistry, Tamkang University, Tamsui 251, Taiwan, and Department of Physics, Chinese Culture University, Taipei 110, Taiwan
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27
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Hu C, Hirai H, Sugino O. Nonadiabatic couplings from time-dependent density functional theory. II. Successes and challenges of the pseudopotential approximation. J Chem Phys 2008; 128:154111. [DOI: 10.1063/1.2900647] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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28
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Absorption Mechanisms of Silicon Nanocrystals in Cosputtered Silicon-Rich–Silicon Oxide Films. ACTA ACUST UNITED AC 2008. [DOI: 10.1149/1.2828207] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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29
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Walker B, Gebauer R. Ultrasoft pseudopotentials in time-dependent density-functional theory. J Chem Phys 2007; 127:164106. [DOI: 10.1063/1.2786999] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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30
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Hu C, Hirai H, Sugino O. Nonadiabatic couplings from time-dependent density functional theory: Formulation in the Casida formalism and practical scheme within modified linear response. J Chem Phys 2007; 127:064103. [PMID: 17705584 DOI: 10.1063/1.2755665] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present an efficient method to compute nonadiabatic couplings (NACs) between the electronically ground and excited states of molecules, within the framework of time-dependent density functional theory (TDDFT) in frequency domain. Based on the comparison of dynamic polarizability formulated both in the many-body wave function form and the Casida formalism, a rigorous expression is established for NACs, which is similar to the calculation of oscillator strength in the Casida formalism. The adiabatic local density approximation (ALDA) gives results in reasonable accuracy as long as the conical intersection (ci) is not approached too closely, while its performance quickly degrades near the ci point. This behavior is consistent with the real-time TDDFT calculation. Through the use of modified linear response theory together with the ground-state-component separation scheme, the performance of ALDA can be greatly improved, not only in the vicinity of ci but also for Rydberg transitions and charge-transfer excitations. Several calculation examples, including the quantization of NACs from the Jahn-Teller effect in the H3 system, have been given to show that TDDFT can efficiently give NACs with an accuracy comparable to that of wave-function-based methods.
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Affiliation(s)
- Chunping Hu
- Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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31
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Li QS, Zhang RQ, Niehaus TA, Frauenheim T, Lee ST. Theoretical Studies on Optical and Electronic Properties of Propionic-Acid-Terminated Silicon Quantum Dots. J Chem Theory Comput 2007; 3:1518-26. [DOI: 10.1021/ct700041v] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Q. S. Li
- Centre of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China, Bremen Center for Computational Material Science, University Bremen, 28334 Bremen, Germany, and Department of Molecular Biophysics, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - R. Q. Zhang
- Centre of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China, Bremen Center for Computational Material Science, University Bremen, 28334 Bremen, Germany, and Department of Molecular Biophysics, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - T. A. Niehaus
- Centre of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China, Bremen Center for Computational Material Science, University Bremen, 28334 Bremen, Germany, and Department of Molecular Biophysics, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - Th. Frauenheim
- Centre of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China, Bremen Center for Computational Material Science, University Bremen, 28334 Bremen, Germany, and Department of Molecular Biophysics, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - S. T. Lee
- Centre of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China, Bremen Center for Computational Material Science, University Bremen, 28334 Bremen, Germany, and Department of Molecular Biophysics, German Cancer Research Center, D-69120 Heidelberg, Germany
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32
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Hu C, Sugino O. Average excitation energies from time-dependent density functional response theory. J Chem Phys 2007; 126:074112. [PMID: 17328598 DOI: 10.1063/1.2436887] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The authors present an occupation number averaging scheme for time-dependent density functional response theory (TD-DFRT) in frequency domain. The known problem that TD-DFRT within the local (spin) density approximation (LDA/LSDA) inaccurately predicts Rydberg and charge-transfer excitation energies has been reexamined from the methodology of linear response, without explicit correction of the exchange-correlation potential. The working equations of TD-DFRT are adapted to treat arbitrary difference of orbital occupation numbers, using the nonsymmetric matrix form of Casida's formulation of TD-DFRT [M. E. Casida, in Recent Advances in Density Functional Methods, edited by D. P. Chong (World Scientific, Singapore, 1995), Pt. I, p. 155]. The authors' scheme is applied to typical closed-shell and open-shell molecular systems by examining the dependence of excitation energies on the fraction of excited electron. Good performance of this modified linear response scheme is shown, and is consistent with the authors' previous examination by the real-time propagation approach, suggesting that the calculation of average excitation energies might be one of the ways to better decode excitation energies from LDA/LSDA. Different techniques for treating singlet, triplet, and doublet states are discussed.
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Affiliation(s)
- Chunping Hu
- Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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33
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Ng MF, Zhang RQ. Dimensionality Dependence of Optical Properties and Quantum Confinement Effects of Hydrogenated Silicon Nanostructures. J Phys Chem B 2006; 110:21528-35. [PMID: 17064103 DOI: 10.1021/jp063895w] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The excited state properties of linear, planar, and spherical hydrogenated silicon nanostructures are studied systematically with use of a time-dependent Hartree-Fock (TDHF) approach with a semiempirical Hamiltonian. The calculated optical gaps decrease significantly from linear, planar, to spherical silicon structures, showing that the optical gap is dimensionality dependent and hence it can be varied by solely managing the shape of the nanostructures. Remarkably, the calculated exciton sizes of the lowest dipole-allowed excited states for both silicon chains and planes are approximately 26 A, revealing that the quantum confinement effect should be significantly enhanced when the sizes of silicon nanostructures are smaller than this value but not dependent on the dimensionality. A similar trend is also observed for hydrogenated silicon spherical clusters.
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Affiliation(s)
- Man-Fai Ng
- Center of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China
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34
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Garoufalis CS, Zdetsis AD. High accuracy calculations of the optical gap and absorption spectrum of oxygen contaminated Si nanocrystals. Phys Chem Chem Phys 2006; 8:808-13. [PMID: 16482321 DOI: 10.1039/b513184g] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report accurate high level calculations of the optical gap and absorption spectrum of small Si nanocrystals, with hydrogen and oxygen at the surface. Our calculations have been performed in the framework of time dependent density functional theory (TDDFT) using the hybrid nonlocal exchange and correlation functional of Becke and Lee, Yang and Parr (B3LYP). The accuracy of these calculations has been verified by the high level multi-reference second order perturbation theory. The effect of oxygen contamination is studied by considering several different bonding configurations of the surface oxygen atoms. We show that for nanocrystals of sizes smaller than 20 angstroms, the widening of the gap due to quantum confinement facilitates the stabilization of Si[double bond, length as m-dash]O double bonds. For this type of bonding, the oxygen related states determine the value of the optical gap and make it significantly lower compared to the corresponding gap of oxygen-free nanocrystals. For diameters larger than 20 angstroms, the double bonds delocalize inside the valence band. We find that for small amounts of oxygen, the size of the optical gap depends strongly on their relative distribution and bonding type, while it is practically insensitive to the exact number of oxygen atoms.
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Affiliation(s)
- C S Garoufalis
- Department of Physics, University of Patras, 26500 Patras, Greece
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35
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36
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37
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Furche F, Rappoport D. Density Functional Methods for Excited States: Equilibrium Structure and Electronic Spectra. THEORETICAL AND COMPUTATIONAL CHEMISTRY 2005. [DOI: 10.1016/s1380-7323(05)80020-2] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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38
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Abstract
We have carried out a series of ab initio calculations to investigate changes in the optical properties of Si quantum dots as a function of surface passivation. In particular, we have compared hydrogen-passivated dots with those having alkyl groups at the surface. We find that, while on clusters with reconstructed surfaces complete alkyl passivation is possible, steric repulsion prevents full passivation of Si dots with unreconstructed surfaces. In addition, our calculations show that steric repulsion may have a dominant effect in determining the surface structure and eventually the stability of alkyl-passivated clusters, with results dependent on the length of the carbon chain. Alkyl passivation weakly affects optical gaps of silicon quantum dots, while it substantially decreases ionization potentials and electron affinities and affects their excited state properties. On the basis of our results, we propose that alkyl-terminated quantum dots may be size selected, taking advantage of the change in ionization potential as a function of the cluster size.
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39
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Bechstedt F, Weissker HC, Ramos LE, Furthmüller J. Electronic excitations in Si and Ge nanocrystals: Parameterfree calculations. ACTA ACUST UNITED AC 2004. [DOI: 10.1002/pssc.200405136] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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40
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de Sousa JS, Freire VN, da Silva EF. Quantum dot electronic devices: modeling and simulation. ACTA ACUST UNITED AC 2004. [DOI: 10.1002/pssc.200405137] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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41
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Draeger EW, Grossman JC, Williamson AJ, Galli G. Optical properties of passivated silicon nanoclusters: The role of synthesis. J Chem Phys 2004; 120:10807-14. [PMID: 15268108 DOI: 10.1063/1.1738633] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effect of preparation conditions on the structural and optical properties of silicon nanoparticles is investigated. Nanoscale reconstructions, unique to curved nanosurfaces, are presented for silicon nanocrystals and shown to have lower energy and larger optical gaps than bulk-derived structures. We find that high-temperature synthesis processes can produce metastable noncrystalline nanostructures with different core structures than bulk-derived crystalline clusters. The type of core structure that forms from a given synthesis process may depend on the passivation mechanism and time scale. The effect of oxygen on the optical of different types of silicon structures is calculated. In contrast to the behavior of bulklike nanostructures, for noncrystalline and reconstructed crystalline structures surface oxygen atoms do not decrease the gap. In some cases, the presence of oxygen atoms at the nanocluster surface can significantly increase the optical absorption gap, due to decreased angular distortion of the silicon bonds. The relationship between strain and the optical gap in silicon nanoclusters is discussed.
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Affiliation(s)
- Erik W Draeger
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
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42
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Xie RH, Bryant GW, Sun G, Nicklaus MC, Heringer D, Frauenheim T, Manaa MR, Smith VH, Araki Y, Ito O. Excitations, optical absorption spectra, and optical excitonic gaps of heterofullerenes. I. C60, C59N+, and C48N12: Theory and experiment. J Chem Phys 2004; 120:5133-47. [PMID: 15267383 DOI: 10.1063/1.1647532] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Low-energy excitations and optical absorption spectrum of C(60) are computed by using time-dependent (TD) Hartree-Fock, TD-density functional theory (TD-DFT), TD DFT-based tight-binding (TD-DFT-TB), and a semiempirical Zerner intermediate neglect of diatomic differential overlap method. A detailed comparison of experiment and theory for the excitation energies, optical gap, and absorption spectrum of C(60) is presented. It is found that electron correlations and correlation of excitations play important roles in accurately assigning the spectral features of C(60), and that the TD-DFT method with nonhybrid functionals or a local spin density approximation leads to more accurate excitation energies than with hybrid functionals. The level of agreement between theory and experiment for C(60) justifies similar calculations of the excitations and optical absorption spectrum of a monomeric azafullerene cation C(59)N(+), to serve as a spectroscopy reference for the characterization of carborane anion salts. Although it is an isoelectronic analogue to C(60), C(59)N(+) exhibits distinguishing spectral features different from C(60): (1) the first singlet is dipole-allowed and the optical gap is redshifted by 1.44 eV; (2) several weaker absorption maxima occur in the visible region; (3) the transient triplet-triplet absorption at 1.60 eV (775 nm) is much broader and the decay of the triplet state is much faster. The calculated spectra of C(59)N(+) characterize and explain well the measured ultraviolet-visible (UV-vis) and transient absorption spectra of the carborane anion salt [C(59)N][Ag(CB(11)H(6)Cl(6))(2)] [Kim et al., J. Am. Chem. Soc. 125, 4024 (2003)]. For the most stable isomer of C(48)N(12), we predict that the first singlet is dipole-allowed, the optical gap is redshifted by 1.22 eV relative to that of C(60), and optical absorption maxima occur at 585, 528, 443, 363, 340, 314, and 303 nm. We point out that the characterization of the UV-vis and transient absorption spectra of C(48)N(12) isomers is helpful in distinguishing the isomer structures required for applications in molecular electronics. For C(59)N(+) and C(48)N(12) as well as C(60), TD-DFT-TB yields reasonable agreement with TD-DFT calculations at a highly reduced cost. Our study suggests that C(60), C(59)N(+), and C(48)N(12), which differ in their optical gaps, have potential applications in polymer science, biology, and medicine as single-molecule fluorescent probes, in photovoltaics as the n-type emitter and/or p-type base of a p-n junction solar cell, and in nanoelectronics as fluorescence-based sensors and switches.
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Affiliation(s)
- Rui-Hua Xie
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8423, USA.
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43
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Zhou Z, Friesner RA, Brus L. Electronic Structure of 1 to 2 nm Diameter Silicon Core/Shell Nanocrystals: Surface Chemistry, Optical Spectra, Charge Transfer, and Doping. J Am Chem Soc 2003; 125:15599-607. [PMID: 14664607 DOI: 10.1021/ja036443v] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Static and time-dependent density functional calculations, geometrically optimized and including all electrons, are described for silicon nanocrystals as large as Si(87)H(76), which contains 163 atoms. We explore and predict the effect that different sp(3) passivation schemes-F or H termination, thin oxide shell, or alkane termination-have on the HOMO and LUMO, on the optical spectra, and on electron transfer properties. Electronegativity comparisons are a useful guide in understanding the observed deviation from the simple quantum size effect model. Nanocrystals containing Al or P impurity atoms, either on the surface or in the interior, are explored to understand electrical doping in strongly quantum-confined nanocrystals. Surface dangling bonds are found to participate in internal charge transfer with P atom dopant electrons.
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Affiliation(s)
- Zhiyong Zhou
- Chemistry Department, Columbia University, New York, NY 10027, USA
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44
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Chen XR, Bai YL, Zhou XL, Yang XD. First-principles simulations for structures and optical spectra of carbon cluster C8. Chem Phys Lett 2003. [DOI: 10.1016/j.cplett.2003.09.032] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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45
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Troparevsky MC, Kronik L, Chelikowsky JR. Optical properties of CdSe quantum dots. J Chem Phys 2003. [DOI: 10.1063/1.1585013] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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46
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Oğüt S, Burdick R, Saad Y, Chelikowsky JR. Ab initio calculations for large dielectric matrices of confined systems. PHYSICAL REVIEW LETTERS 2003; 90:127401. [PMID: 12688897 DOI: 10.1103/physrevlett.90.127401] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2002] [Indexed: 05/22/2023]
Abstract
Calculations for optical excitations in confined systems require knowledge of the inverse screening dielectric function epsilon(-1)(r,r(')), which plays a crucial role in determining exciton binding energies. We present a new efficient real-space method of inverting and storing large ab initio dielectric matrices of confined systems, which relies on the separability of epsilon matrix in r and r('). The method has allowed, for the first time, full ab initio calculation of epsilon(-1)(r,r(')) of dimension N approximately 270 000, and for quantum dots as large as Si35H36. The effective screening in Si quantum dots up to 1.1 nm in diameter is found to be very ineffective with average dielectric constants ranging from 1.1 to 1.4.
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Affiliation(s)
- Serdar Oğüt
- Department of Physics, University of Illinois at Chicago, 845 West Taylor Street (M/C 273), Chicago, Illinois 60607, USA
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47
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Puzder A, Williamson AJ, Grossman JC, Galli G. Computational studies of the optical emission of silicon nanocrystals. J Am Chem Soc 2003; 125:2786-91. [PMID: 12603167 DOI: 10.1021/ja0293296] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have computed absorption and emission energies of silicon nanocrystals as a function of size and of surface passivants, using both density functional theory and quantum Monte Carlo calculations. We have found that the ionic rearrangements and electronic relaxations occurring upon absorption and emission are extremely sensitive to surface chemistry. In particular, nanoclusters with similar sizes and similar absorption gaps can exhibit strikingly different emission energies. Our results provide a unifying interpretation of several recent measurements, which have observed significantly different emission energies from clusters with similar sizes. Our calculations also show that a combination of absorption and emission measurements can provide a powerful tool for identifying both the size and the surface passivants of semiconductor nanocrystals.
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Affiliation(s)
- Aaron Puzder
- Lawrence Livermore National Laboratory, 7000 East Avenue L-415, Livermore, CA 94550, USA
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48
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Weissker HC, Furthmüller J, Bechstedt F. Excitation energies and radiative lifetimes of Ge1-xSix nanocrystals: alloying versus confinement effects. PHYSICAL REVIEW LETTERS 2003; 90:085501. [PMID: 12633435 DOI: 10.1103/physrevlett.90.085501] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2002] [Indexed: 05/24/2023]
Abstract
The composition dependence of the optical and structural properties of Ge1-xSix nanocrystals is investigated by means of ab initio total-energy and electronic-structure calculations. A trimodal distribution of the Ge-Ge, Ge-Si, and Si-Si bond lengths is found. The pair-excitation energies and the Stokes shift are calculated taking into account many-body and alloying effects. They show a distinct nonlinear behavior with changing composition. The radiative lifetime decreases exponentially with increasing Ge molar fraction. The theoretical results explain recent photoluminescence measurements. They show that composition and confinement effects can be discussed nearly separately.
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Affiliation(s)
- H-Ch Weissker
- Institut für Festkörpertheorie und Theoretische Optik, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 Jena, Germany
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49
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Raty JY, Galli G, Bostedt C, Van Buuren TW, Terminello LJ. Quantum confinement and fullerenelike surface reconstructions in nanodiamonds. PHYSICAL REVIEW LETTERS 2003; 90:037401. [PMID: 12570521 DOI: 10.1103/physrevlett.90.037401] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2002] [Indexed: 05/24/2023]
Abstract
We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addition, our calculations show that the surface of nanodiamond particles larger than approximately 1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features observed in measured absorption spectra.
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Affiliation(s)
- Jean-Yves Raty
- Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550, USA
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50
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Williamson AJ, Grossman JC, Hood RQ, Puzder A, Galli G. Quantum Monte Carlo calculations of nanostructure optical gaps: application to silicon quantum dots. PHYSICAL REVIEW LETTERS 2002; 89:196803. [PMID: 12443140 DOI: 10.1103/physrevlett.89.196803] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2002] [Indexed: 05/24/2023]
Abstract
Quantum Monte Carlo (QMC) calculations of the optical gaps of silicon quantum dots ranging in size from 0 to 1.5 nm are presented. These QMC results are used to examine the accuracy of density functional (DFT) and empirical pseudopotential based calculations. The GW approximation combined with a solution of the Bethe-Salpeter equation performs well but is limited by its scaling with system size. Optical gaps predicted by DFT vary by 1-2 eV depending on choice of functional. Corrections introduced by the time dependent formalism are found to be minimal in these systems.
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