Optical investigation of CdS quantum dots in Langmuir-Blodgett films

Milekhin, A. G.; Friedrich, M.; Zahn, Dietrich R. T.; Sveshnikova, L. L.; Repinsky, S.M.

doi:10.1007/s003390050978

Cited by 25 publications

(24 citation statements)

References 3 publications

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“…This can be an evidence of a weak phonon confinement (PC) in these 6-7 nm NPs, in accordance with previous reports [12,13]. The second order 2LO peak is observed at about 600 cm -1 .…”

Section: Cds/cdse4supporting

confidence: 90%

“…3a). The higher-frequency component is attributed to the LO phonon [4,12,14,15], while the lower-frequency component is assigned either to surface optical (SO) phonon mode [14][15][16] or disorder-activated zone-edge (ZE) phonons [4]. Within the framework of the model [17], the vibrational modes of NP (vibrons) are classified according to the main quantum numbers l,n.…”

Section: Contributedmentioning

confidence: 99%

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Resonant Raman spectroscopy of confined and surface phonons in CdSe‐capped CdS nanoparticles

Dzhagan

Rayevskaya

Stroyuk

et al. 2009

Phys. Status Solidi (c)

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A series of colloidal CdS/CdSe heteronanoparticles are studied by Resonant Raman spectroscopy. The Raman‐active phonons of both CdS‐core and CdSe‐shell are monitored upon a gradual increase of the shell thickness. Noticeable differences between the Raman spectra taken at different excitation wavelengths are observed, which can be related to different resonant conditions for different vibrational modes at a certain excitation wavelength. The possible morphology transformation of the CdSe shell with increase of its thickness is discussed, based on the correlation between changes in phonon spectra of the nanoparticles and the spectra of photoluminescence and optical absorption. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…This can be an evidence of a weak phonon confinement (PC) in these 6-7 nm NPs, in accordance with previous reports [12,13]. The second order 2LO peak is observed at about 600 cm -1 .…”

Section: Cds/cdse4supporting

confidence: 90%

Section: Contributedmentioning

confidence: 99%

Resonant Raman spectroscopy of confined and surface phonons in CdSe‐capped CdS nanoparticles

Dzhagan

Rayevskaya

Stroyuk

et al. 2009

Phys. Status Solidi (c)

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“…23,24,29,30 The temperature-dependent measurement, from 250 down to 85 K (Figure 2, inset), reveals no noticeable spectral change, except for the expected increase in the peak intensities with decreasing temperature. 31,32 The temperature dependence of the optical phonon frequency is known to be determined by two main factors: the change in the lattice constant (bond length) and phonon−phonon coupling.…”

Section: ■ Results and Discussionmentioning

confidence: 91%

Raman and Infrared Phonon Spectra of Ultrasmall Colloidal CdS Nanoparticles

et al. 2014

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Raman and infrared phonon spectra of ultrasmall (1.8 nm) colloidal CdS nanoparticles (usNPs) are presented. Multiphonon scattering by optical phonons up to the third order is observed in the Raman spectra at low temperature and resonant (325 nm) excitation. The first-order optical phonon peak is a superposition of several components, two of which can be assigned to surface optical (SO) and longitudinal optical (LO) modes, respectively. The LO mode, being markedly broadened compared to that of spectra of regular (>2 nm) NPs, is related to phonon confinement and bond distortion induced by a significant structural relaxation in usNPs. A shoulder observed above the LO frequency is either due to the density of phonon states induced by distorted surface bonds or due to higher-order scattering processes involving optical and acoustic phonons. The Raman peaks of usNPs do not reveal the upward shift and narrowing upon decreasing temperature from 300 K down to 85 K typical for crystalline semiconductors, even though their intensity increases as expected. The abnormal thermal behavior of phonon peaks is likely related to the significant structural reorganization of the usNP lattice. A broad feature in the range of 200−300 cm −1 observed in the infrared phonon spectrum of usNPs correlates with the Raman data and is distinct from the SO mode previously reported for NPs of larger size. ■ INTRODUCTIONUltrasmall semiconductor nanoparticles (usNPs), or "magicsize" clusters, have recently attracted much attention due to their unique physical properties. 1−6 The growth rate of colloidal NPs deviates from the prediction of the classic thermodynamic growth theory as the NPs attain the magic closed-shell structure resulting from the existence of a chemical potential well. 6 For CdSe, CdS, and several other II−VI compounds, the most frequently observed magic structure comprises 32−34 molecular units corresponding to a diameter of around 1.7−1.9 nm. 1,6,7 The usNPs reveal either narrow blue 8 or broad-band quasi-white photoluminescence (PL), making this kind of NP promising for light-emission applications. [2][3][4]9,10 Studying NPs of such a small size is also of fundamental importance, as it allows the existing models to be verified in the regime of strong electron and phonon confinement. 11−15 Understanding and controlling the electronic and optical properties of usNPs is, however, complicated due to a considerable contribution from surface atoms, the number of which is comparable to the number of fully coordinated inner atoms, as well as due to the coupling between the electronic states in the NP and ligands. 16 The lattice vibration (phonon) spectra can provide valuable information on the structure and physical properties of semiconductor NPs and their interaction with the environment. 15−22 Here we report on resonant Raman scattering and infrared (IR) studies of phonons in CdS usNPs prepared by "wet" colloidal chemistry under mild conditions. We observe for the first time multiple Raman scattering by optical phonons up to the th...

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“…1). This is why just a single absorption peak near the Frö hlich frequency is normally observed for II-VI QDs (see, for example [10]). It should be emphasized that the Frö hlich mode is not an eigenmode of this problem considering the boundary conditions taken.…”

Section: Discussionmentioning

confidence: 99%

FIR Absorption in CdSe Quantum Dot Ensembles

Vasilevskiy

Rolo

Artemyev

et al. 2001

phys. stat. sol. (b)

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Absorption of far-infrared (FIR) radiation in very small CdSe crystallites (quantum dots, QDs) via excitation of confined dipolar vibrational modes was studied, both theoretically and experimentally. Spatial quantisation of optical phonons was analysed in the framework of a continuum model, which couples the phonon amplitude to the electrostatic potential via the Frö hlich interaction. The frequencies and oscillator strengths of the dipole-active optical vibration modes are presented calculated for a spherical QD, and for the first time for II-VI QDs these quantised modes were observed experimentally. Another effect studied in this work is the influence of the QD concentration on the FIR absorption of their ensemble. It is shown that the dipole-dipole interaction becomes very important in dense QD ensembles and leads to smearing of the structure in the CdSe phonon band as the QD concentration increases.

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Optical investigation of CdS quantum dots in Langmuir-Blodgett films

Cited by 25 publications

References 3 publications

Resonant Raman spectroscopy of confined and surface phonons in CdSe‐capped CdS nanoparticles

Resonant Raman spectroscopy of confined and surface phonons in CdSe‐capped CdS nanoparticles

Raman and Infrared Phonon Spectra of Ultrasmall Colloidal CdS Nanoparticles

FIR Absorption in CdSe Quantum Dot Ensembles

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