Theoretical investigation of the surface vibrational modes in germanium nanocrystals

Cheng, Wei; Ren, Shang‐Fen; Yu, Peter Y.

doi:10.1103/physrevb.68.193309

Cited by 45 publications

(41 citation statements)

References 13 publications

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“…Although there have been a number of large-scale atomistic simulations of phonon modes in other types of semiconductor nanocrystals, [48][49][50][51][52][53] nearly all discussions of phonons in CdSe nanocrystals have referred to dielectric continuum models such as described in refs. 37 and 38.…”

Section: Discussionmentioning

confidence: 99%

The “Surface Optical” Phonon in CdSe Nanocrystals

et al. 2014

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The origin of the ubiquitous low-frequency shoulder on the longitudinal optical (LO) phonon fundamental in the Raman spectra of CdSe quantum dots is examined. This feature is usually assigned as a "surface optical" (SO) phonon, but it is only slightly affected by modifying the surface through exchanging ligands or adding a semiconductor shell. Here we present excitation profile data showing that the lowfrequency shoulder loses intensity as the excitation is tuned to longer wavelengths, closer to resonance with the lowest-energy 1S e À1S 3/2 excitonic transition. Calculations of the resonance Raman spectra are carried out using a fully atomistic model with an empirical force field to calculate the phonon modes and the standard effective mass approximation envelope function model to calculate the electron and hole wave functions.When a force field of the Tersoff type is used, the calculated spectra closely resemble the experimental ones in showing mainly the higher-frequency LO phonon with 1S e À1S 3/2 resonance but showing intensity in lower-frequency features with 1P e À1P 3/2 resonance. These calculations indicate that the main LO phonon peak involves largely motion of the interior atoms, while the low-frequency shoulder is more equally distributed throughout the crystal but not surface-localized. Interestingly, very different results are obtained with the widely used Coulomb plus Lennard-Jones force field developed by Rabani, which predicts far more disordered structures and more localized phonon modes for the nanocrystals compared with the Tersoff-type potential.

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Section: Discussionmentioning

confidence: 99%

The “Surface Optical” Phonon in CdSe Nanocrystals

et al. 2014

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“…Microscopic lattice dynamical calculations have also been carried out for GaP quantum dots 35 and Ge nanocrystals. 36 The phonon spectrum obtained using the atomistic potential has been separated into bulklike (dot-interior) or surface-like depending on the spatial localization. The wavenumbers of the bulk-like zone-centre longitudinal optic (LO) and transverse optic (TO) phonons were found to decrease with decreasing dot size.…”

Section: Microscopic Lattice Dynamical Calculationsmentioning

confidence: 99%

Raman spectroscopy of optical phonon confinement in nanostructured materials

Arora

Rajalakshmi

Ravindran

et al. 2007

J Raman Spectroscopy

362

294

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If the medium surrounding a nano-grain does not support the vibrational wavenumbers of a material, the optical and acoustic phonons get confined within the grain of the nanostructured material. This leads to interesting changes in the vibrational spectrum of the nanostructured material as compared to that of the bulk. Absence of periodicity beyond the particle dimension relaxes the zone-centre optical phonon selection rule, causing the Raman spectrum to have contributions also from phonons away from the Brillouin-zone centre. Theoretical models and calculations suggest that the confinement results in asymmetric broadening and shift of the optical phonon Raman line, the magnitude of which depends on the widths of the corresponding phonon dispersion curves. This has been confirmed for zinc oxide nanoparticles. Microscopic lattice dynamical calculations of the phonon amplitude and Raman spectra using the bond-polarizability model suggest a power-law dependence of the peak-shift on the particle size. This article reviews recent results on the Raman spectroscopic investigations of optical phonon confinement in several nanocrystalline semiconductor and ceramic/dielectric materials, including those in selenium, cadmium sulphide, zinc oxide, thorium oxide, and nano-diamond. Resonance Raman scattering from confined optical phonons is also discussed.

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“…When the size of NCs is small, in the range of a few nm, the continuum dielectric models are intrinsically limited. In recent years, we have developed a microscopic valence force field model (VFFM) [11] to study phonon modes in NCs [7,[12][13][14][15][16][17][18][19].…”

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confidence: 99%

Microscopic phonon theory of Si/Ge nanocrystals

2008

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Microscopic phonon theory of semiconductor nanocrystals (NCs) is reviewed in this paper. Phonon modes of Si and Ge NCs with various sizes of up to 7 nm are investigated by valence force field theory. Phonon modes in spherical SiGe alloy NCs approximately 3.6 nm (containing 1147 atoms) in size have been investigated as a function of the Si concentration. Phonon density-ofstates, quantum confinement effects, as well as Raman intensities are discussed.

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Theoretical investigation of the surface vibrational modes in germanium nanocrystals

Cited by 45 publications

References 13 publications

The “Surface Optical” Phonon in CdSe Nanocrystals

The “Surface Optical” Phonon in CdSe Nanocrystals

Raman spectroscopy of optical phonon confinement in nanostructured materials

Microscopic phonon theory of Si/Ge nanocrystals

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