Confinement Effects on Optical Phonons in Polar Tetrapod Nanocrystals Detected by Resonant Inelastic Light Scattering

Krahne, Roman; Chilla, Gerwin; Schüller, Christian; Carbone, Luigi; Kudera, Stefan; Mannarini, Gianandrea; Manna, Liberato; Heitmann, D.; Cingolani, R.

doi:10.1021/nl0524492

Cited by 37 publications

(34 citation statements)

References 38 publications

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“…[18][19][20][21][22][23] Closer examination of Raman spectra obtained with a high signal-to-noise ratio reveals an additional, low-frequency shoulder on the LO phonon. This shoulder is seen quite consistently in nanocrystals with different sizes and shapes and with different surface chemistries, 6,[24][25][26][27][28][29][30][31][32][33][34][35][36] and also in many semiconductor materials other than CdSe. It was assigned as a "surface optical" (SO) phonon by comparison with predictions based on dielectric continuum theory for the optical phonon modes of ionic crystals.…”

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confidence: 76%

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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The “Surface Optical” Phonon in CdSe Nanocrystals

et al. 2014

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“…[29][30][31] Additionally, modes such as the ones associated with surface phonons have been detected. [32][33][34][35] In this work, scanning Raman spectroscopy is performed on GaAs nanowires with zinc-blende and wurtzite structures. The paper is structured as follows: after presenting theoretical considerations on the phonon dispersion and selection rules for both structures in Sec.…”

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confidence: 99%

Raman spectroscopy of wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects

et al. 2009

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Polarization-dependent Raman scattering experiments realized on single GaAs nanowires with different percentages of zinc-blende and wurtzite structure are presented. The selection rules for the special case of nanowires are found and discussed. In the case of zinc-blende, the transversal optical mode E 1 ͑TO͒ at 267 cm −1 exhibits the highest intensity when the incident and analyzed polarization are parallel to the nanowire axis. This is a consequence of the nanowire geometry and dielectric mismatch with the environment, and in quite good agreement with the Raman selection rules. We also find a consistent splitting of 1 cm −1 of the E 1 ͑TO͒. The transversal optical mode related to the wurtzite structure, E 2 H , is measured between 254 and 256 cm −1 , depending on the wurtzite content. The azimuthal dependence of E 2 H indicates that the mode is excited with the highest efficiency when the incident and analyzed polarization are perpendicular to the nanowire axis, in agreement with the selection rules. The presence of strain between wurtzite and zinc-blende is analyzed by the relative shift of the E 1 ͑TO͒ and E 2 H modes. Finally, the influence of the surface roughness in the intensity of the longitudinal optical mode on ͕110͖ facets is presented.

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“…A broad range of semiconductor nanowires, including Si, Ge [13,14], III-Vs [15,16] and II-VIs [17][18][19][20][21], have been grown using chemical vapor deposition (CVD), thermal evaporation, solvothermal synthesis and molecular-beam exitaxy (MBE) based on the metal-catalyzed vaporliquid-solid (VLS) mechanism [22]. However, only a few reports on the synthesis of tellurium-based NWs have been published so far.…”

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“…However, only a few reports on the synthesis of tellurium-based NWs have been published so far. ZnTe NWs [20] and CdTe NWs [19] have been obtained by using chemical synthesis or CVD methods. Recently, we have reported the first growth of ZnTe NWs by using the MBE technique [23].…”

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MBE Growth and Properties of ZnTe- and CdTe-Based Nanowires

Wójtowicz¹,

Janik²,

Zaleszczyk³

et al. 2008

J. Korean Phy. Soc.

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We review our results on the growth of ZnTe-and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)-and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diffractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was 111 , and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe-and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn 2+ transition between crystal-field-split energy levels ( 4 T1 → 6 A1) was observed in the ZnMnTe nanowires.

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Confinement Effects on Optical Phonons in Polar Tetrapod Nanocrystals Detected by Resonant Inelastic Light Scattering

Cited by 37 publications

References 38 publications

The “Surface Optical” Phonon in CdSe Nanocrystals

The “Surface Optical” Phonon in CdSe Nanocrystals

Raman spectroscopy of wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects

MBE Growth and Properties of ZnTe- and CdTe-Based Nanowires

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