Optical excitations in small hydrogenated silicon clusters: comparison of theory and experiment

Vasiliev, Igor

doi:10.1002/pssb.200303242

Cited by 17 publications

(8 citation statements)

References 44 publications

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“…In contrast to a great deal of theoretical studies 24–34 on the energy gap or absorption energy, studies on the emission gap are rather scarce, largely due to the lack of an efficient excited‐state (ES) geometric optimization method. However, a clear understanding of the excited state properties and its dynamics is of utmost necessity as the light emission properties of silicon nanoparticles is intimately related to it.…”

Section: Structure–(optical) Property Relationship: a Simple Model mentioning

confidence: 99%

Excited state properties of Si quantum dots

Sarkar

Niehaus

et al. 2011

Physica Status Solidi (b)

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Silicon is the cornerstone of the semiconductor industry. In the nanoscale, the surface gains considerable significance due to the large surface to volume ratio. Recent theoretical advances in the investigation of the excited state properties of silicon quantum dots (QDs) are reviewed in this article. The origin of optical properties in silicon QDs is attributed to the tetrahedral crystalline structure in the Si nanostructures. Consequently, passivating the surfaces of these Si nanostructures by a suitable species turns out to be the most effective avenue for the retention of their tetrahedral structural symmetry and in turn their photoluminescence (PL) properties. The passivating agent and the extent of surface passivation need to be chosen very judiciously for the purpose of realizing the practical applications of the dots. Structural relaxation in the excited state induces Stokes shift, which varies with the particle size, the degree of surface passivation, and the nature of the passivating species. Stokes shift needs to be minimized for maximizing the PL efficiency of the QDs. All these intermingled issues are briefly addressed in the article. 1 Introduction Silicon has been playing a ubiquitous role in our day-to-day lives through the use and application of modern technology. The continued trend for miniaturization of electronic devices induces the genesis of novel properties, which in turn integrate themselves into the devices. As the silicon-based materials shrink in size down to the nanoscale, manifold interesting changes show up: the indirect band gap (corresponding to the Si bulk crystal) gradually transforms itself into a direct band gap semiconductor, the energy or band gap widens, and the surface to volume ratio increases. The sum-total of the unprecedented bonuses accruing from the downsizing of Si-based materials is commonly known as quantum size effect or quantum confinement effect. The quantum size effect comes into play when the Si-based materials downsize to 5 nm and less than that. This critical dimension of 5 nm is referred to as the Bohr excition radius (or the de Broglie wavelength of an electron-hole pair) at which the Si-based nanomaterials turn into quantum dots (QDs). The properties of QDs are intermediate between those of bulk semiconductors and those of discrete

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Section: Structure–(optical) Property Relationship: a Simple Model mentioning

confidence: 99%

Excited state properties of Si quantum dots

Sarkar

Niehaus

et al. 2011

Physica Status Solidi (b)

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“…Depending on the choice of the exchange-correlation functional, TDDFT calculations predict the lowest two transition energies at 7.1-7.3 and 8.6-8.8 eV. 86…”

Section: A Disilanementioning

confidence: 99%

“…The TDLDA calculations in Ref. 84 lead to somewhat lower excitation energies of 8.2, 9.2, and 9.7 eV, while the usage of the asymptotically corrected exchange-correlation functionals LB94/ACLDA results in values of 8.8/8.5, 9.5/ 9.3, and 10.8/ 10.3 eV, respectively 86.…”

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confidence: 96%

Molecular electronic excitations calculated from a solid-state approach: Methodology and numerics

2005

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We investigate the applicability and accuracy of a solid-state approach, which was developed originally for the relatively homogeneous electron gas, to describe electronic single-particle and electron-hole pair excitations in molecules. Thereby we start from the determination of the molecular ground state within the local density functional theory using repeated supercells and pseudopotentials for the electron-ion interaction. The electronic spectra are obtained from the Green's function formalism. The exchange-correlation self-energy ⌺ is linearly expanded in the screened Coulomb interaction, i.e., the GW approximation is used. Optical spectra are obtained from the Bethe-Salpeter equation for the irreducible polarization propagator. The numerical implementation and possible pitfalls of this methodology are discussed using silane, disilane, and water molecules as examples. In particular the influence of the dynamics of the screening, the supercell size, and the number of empty states are studied. The resulting single-and two-particle excitation energies are compared with experiment and previous theoretical work.

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“…Then, Zhou and co-workers used the static and TD-DFT calculations to investigate the optical properties of the core/shell nanoclusters with F− and OH− passivations. , Reboredo and Galli discussed the energy gap of silicon nanoclusters with reconstructed surfaces completed by alkyl passivation . Vasiliev determined the excited-state properties of passivated silicon nanoclusters by the TD-DFT method . In particular, the interplay between quantum confinement effect in the Si core and the extrinsic passivation effect is still unclear.…”

Section: Introductionmentioning

confidence: 99%

Structural and Optical Properties of Passivated Silicon Nanoclusters with Different Shapes: A Theoretical Investigation

et al. 2008

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Optimized geometries and electronic structures of hydrogenated silicon nanoclusters, which include the Td and Ih symmetries, have been generated by using the semiempirical AM1 and PM3 methods, the density functional theory (DFT) B3LYP method with the 6-31G(d) and LANL2DZ basis sets from the Gaussian 03 package, and the local density functional approximation (LDA), which is implemented in the SIESTA package. The calculated diameters for these Td symmetric hydrogenated silicon nanoclusters are in the range from 6.61 A (Si5H12) to 23.24 A (Si281H172). For the Ih symmetry, we calculated Si20H20 and Si100H60 nanoclusters only. Theoretically, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is size dependent. The calculated energy gap decreases (Si5H12: 7.65 eV to Si281H172: 3.06 eV) while the diameter of silicon nanocluster increases. By comparing different calculated results, we concluded that the calculated energy gap by B3LYP/6-31G(d)//LDA/SIESTA is close to that from experiment and that the LDA/SIESTA result underestimates the experimental value. On the contrary, the AM1 and PM3 results overestimate the experimental results. For investigation of the optical properties of Si nanoclusters as a function of surface passivation, we carried out a B3LYP/6-31G(d)//LDA/SIESTA calculation of the Si35 and Si47 core clusters with full alkyl-, OH-, NH2-, CH2NH2-, OCH3-, SH-, C3H6SH-, and CN- passivations. The calculated optical properties of alkyl passivated Si35 nanoclusters (Si35(CH3)36, Si35(C2H5)36, and Si35(C3H7)36) are close to one another and are higher than those of oxide, nitride, and sulfide passivated Si 35 clusters. In conclusion, the alkyl passivant affects weakly the calculated optical gaps, and the electron-withdrawing passivants generate a red-shift in the energy gap of silicon nanoclusters. A size-dependent effect is also observed for these passivated Si nanoclusters.

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Optical excitations in small hydrogenated silicon clusters: comparison of theory and experiment

Cited by 17 publications

References 44 publications

Excited state properties of Si quantum dots

Excited state properties of Si quantum dots

Molecular electronic excitations calculated from a solid-state approach: Methodology and numerics

Structural and Optical Properties of Passivated Silicon Nanoclusters with Different Shapes: A Theoretical Investigation

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