Transition between direct and indirect band gap in silicon nanocrystals

Kocevski, Vancho; Eriksson, Olle; Rusz, Ján

doi:10.1103/physrevb.87.245401

Cited by 43 publications

(43 citation statements)

References 37 publications

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“…The integration is performed in a realspace three-dimensional (3D) grid, the fineness of which is determined by the plane-wave cutoff. We used a plane-wave cutoff of 160 Ry, the same cutoff as in our previous calculations [3]. Numerical atomic orbitals are used as a basis set, single ζ with polarization orbital (SZP) for Si, double ζ (DZ) for H, and SZP for each of the other considered elements (O, C, F, Cl, S).…”

Section: Structural Models and Methodologymentioning

confidence: 99%

“…We refer the reader to Ref. [3] for a more detailed discussion of basis sets for different elements. Furthermore, we explicitly evaluated the dipole transition matrix elements between each occupied and unoccupied eigenstate up to 15 eV, from where the imaginary part of the dielectric tensor is calculated.…”

Section: Structural Models and Methodologymentioning

confidence: 99%

“…In the previous study we showed that having a spherical shape or a NC made using the Wulff construction has a rather weak effect on the DOS and absorption indices of the Si NCs [3]. Therefore, in this study we consider only spherical silicon NCs with surface impurities, and as a starting model we used already-relaxed, fully hydrogenated spherical Si NCs from Ref.…”

Section: Structural Models and Methodologymentioning

confidence: 99%

“…This property of bulk silicon can be greatly influenced by making nanocrystals (NCs) [1], where it has been shown that the wave function (WF) of the lowest unoccupied eigenstate (LUMO) becomes more localized around the point, attaining a similar character to the WF of the highest occupied eigenstate (HOMO) [2][3][4]. This change in the character of the LUMO WF increases the probability of direct transitions from the LUMO to the HOMO level, largely enhancing the photoluminescence (PL) efficiency of Si NCs [5][6][7], compared to that of bulk Si.…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4]32,33,[44][45][46][47][48][49][50][51][52][53][54][55], to name a few. However, there have been only a limited number of theoretical studies concerning the size dependence of the electronic and optical properties of Si NCs with different surface impurities [4,[33][34][35][52][53][54][55][56][57][58].…”

Section: Introductionmentioning

confidence: 99%

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Size dependence of the stability, electronic structure, and optical properties of silicon nanocrystals with various surface impurities

2015

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We present a comprehensive, ground-state density functional theory study of the size dependence of the optical and electronic properties and the stability of spherical silicon nanocrystals (NCs) with different impurities on the surface. We vary the size of the NCs from 1.0 to 3.5 nm, considering single-bonded (CH 3 , F, Cl, OH) and double-bonded (O, S) impurities and bridged oxygen. We show that the density of states (DOS) and absorption indices of the NCs with single-bonded impurities are very similar to each other and the fully hydrogenated NCs, except for the 1.0-nm NCs, where a slight difference is present. In the case of the NCs with double-bonded impurities, the DOS and absorption indices exhibit a significant difference, compared to the fully hydrogenated NCs, for sizes up to 2.5 nm. We argue that this difference arises from the difference in the contribution from the impurity to the states around the gap, which can considerably change the character of the states. We demonstrate that the double-bonded impurities contribute significantly to the states around the gap, compared to the single-bonded impurities, causing changes in the symmetry of these states. This observation was further supported by analyzing the changes of the Fourier transform of the charge densities of the highest occupied and lowest unoccupied eigenstate. We also show that the formation energies of NCs with bridged oxygen and fluorine are the lowest, regardless of the size. Furthermore, we show that high hydrogen concentration can be used to suppress the addition of oxygen and fluorine on the surface of the Si NCs.

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Section: Structural Models and Methodologymentioning

confidence: 99%

Section: Structural Models and Methodologymentioning

confidence: 99%

Section: Structural Models and Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Size dependence of the stability, electronic structure, and optical properties of silicon nanocrystals with various surface impurities

2015

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Tracking the Fate of Porous Silicon Nanoparticles Delivering a Peptide Payload by Intrinsic Photoluminescence Lifetime

et al. 2018

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A nanoparticle system for systemic delivery of therapeutics is described, which incorporates a means of tracking the fate of the nanocarrier and its residual drug payload in vivo by photoluminescence (PL). Porous silicon nanoparticles (PSiNPs) containing the proapoptotic antimicrobial peptide payload, [KLAKLAK] , are monitored by measurement of the intrinsic PL intensity and the PL lifetime of the nanoparticles. The PL lifetime of the PSiNPs is on the order of microseconds, substantially longer than the nanosecond lifetimes typically exhibited by conventional fluorescent tags or by autofluorescence from cells and tissues; thus, emission from the nanoparticles is readily discerned in the time-resolved PL spectrum. It is found that the luminescence lifetime of the PSiNP host decreases as the nanoparticle dissolves in phosphate-buffered saline solution (37 °C), and this correlates with the extent of release of the peptide payload. The time-resolved PL measurement allows tracking of the in vivo fate of PSiNPs injected (via tail vein) into mice. Clearance of the nanoparticles through the liver, kidneys, and lungs of the animals is observed. The luminescence lifetime of the PSiNPs decreases with increasing residence time in the mice, providing a measure of half-life for degradation of the drug nanocarriers.

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Role of doping and sheet size in tailoring optoelectronic properties of germanene: A TDDFT study

Bhandari

Hassan

Al-Hashimi

et al. 2018

Int J of Quantum Chemistry

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Germanene is a novel 2D material with promising optoelectronic properties, tuning of which is to be explored. This work demonstrates that doping and increasing the sheet size can alter optical and electronic properties of germanene via perturbation of the band structure. This feature has also been observed in other nanostructures, notably, silicon nanostructures, and may be attributed to quantum confinement effects. Our main findings on H-terminated germanene are, (i) band gap can be reduced by 30%, (ii) exciton binding energy can be reduced by 60%, and (iii) absorption spectra can be tuned from UV to visible range. We employ time-dependent density functional theory to investigate the role of dopants, boron (B), phosphorus (P), carbon (C), silicon (Si), and zirconium (Zr). Width of the germanene sheet is varied from 0.78 nm to 2.78 nm. Frequency and energy calculations are carried out to analyze the infrared (IR) and ultra-violet (UV)-visible (VIS) spectra.

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Transition between direct and indirect band gap in silicon nanocrystals

Cited by 43 publications

References 37 publications

Size dependence of the stability, electronic structure, and optical properties of silicon nanocrystals with various surface impurities

Size dependence of the stability, electronic structure, and optical properties of silicon nanocrystals with various surface impurities

Tracking the Fate of Porous Silicon Nanoparticles Delivering a Peptide Payload by Intrinsic Photoluminescence Lifetime

Role of doping and sheet size in tailoring optoelectronic properties of germanene: A TDDFT study

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