Raman spectra of semiconductor nanoparticles: Disorder-activated phonons

Ingale, Alka; Rustagi, K. C.

doi:10.1103/physrevb.58.7197

Cited by 106 publications

(130 citation statements)

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“…The main (LO mode) peak does not show any significant variation in position and shape with exposure duration. This is in contrast to earlier work on CdS nanoclusters, [21][22][23] where large asymmetric broadening has been observed for cluster sizes less than 10 nm. The full width at half maximum (FWHM) of the LO mode peak in all the three cases lies in the range of 11 -14 cm − 1 , which is slightly larger than the bulk value of 8-10 cm .…”

Section: Resultscontrasting

confidence: 54%

Structure of CdS–arachidic acid composite LB multilayers

Kumar

Narang

Major

et al. 2002

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Langmuir-Blodgett (LB) multilayers of cadmium arachidate were used as precursors to grow semiconducting CdS nanoclusters. The formation of CdS in the multilayers was determined by Fourier transform-infrared (FT-IR), ultraviolet-visible (UV-vis) and Raman spectroscopy. The structural changes occurring as a consequence of CdS formation have been characterized using X-ray reflection (XR) and grazing incidence X-ray diffraction (GIXD) techniques. The CdS containing composite multilayers exhibit the presence of two types of molecular domains, one with close packed herringbone arrangement and the other with tilted molecular chains with no in-plane order. The structural and spectroscopic evidences together suggest that the CdS nanoclusters formed within the arachidic acid LB matrix are quasi two-dimensional in nature with lateral dimension 5-10 nm and thickness 1.1 nm.

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Section: Resultscontrasting

confidence: 54%

Structure of CdS–arachidic acid composite LB multilayers

Kumar

Narang

Major

et al. 2002

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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“…In NCs, these are the surface atoms with undercoordinated bonds, while in alloys these can be the atoms adjacent to the "impurity" atom or a structural defect. This kind of disorder can lead to activation in Raman scattering of vibrational modes forbidden for perfect crystal, particularly ZE phonons [22].The ZE phonons, that is, phonons from the boundary of the Brillouin zone, where TO and LO branches approach each other, are forbidden in Raman spectra due to their large k (compared to that of the probing light). However, they can be activated in Raman by a certain degree of disorder in the lattice.…”

mentioning

confidence: 99%

“…The nature of a low-frequency shoulder of the LO peak, commonly observed for different kinds of semiconductor NCs, is still under discussion. It is related either with phonons at k / = 0 [33], surface optical (SO) [23], zone-edge (ZE) [22] phonons, or quantized optical phonons (vibrons) with a quantum number n > 1 [17,34,35]. Fitting the Raman spectrum in the range of LO mode with two Lorentzians, corresponding to SO (or ZE) and LO phonon or to vibrons with different quantum numbers, is widely applicable for II-VI NCs [15,18,23,36].…”

mentioning

confidence: 99%

Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

Dzhagan

Valakh

Mel’nik

et al. 2012

International Journal of Spectroscopy

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Resonant Raman spectroscopy has been employed to explore the first-and higher-order phonon spectra of several kinds of II-VI nanocrystals (NCs), with the aim of better understanding of the nature of phonon modes and forming a unified view onto the vibrational spectrum of semiconductor NCs. Particularly, besides the previously discussed TO, SO, LO, and 2LO modes, the combinational modes of TO+LO and SO+LO can be assumed to account for the lineshape of the spectrum below 2LO band. No trace of 2TO or 2SO band was detected, what can be the result of the dominance of Fröhlich mechanism in electron-phonon coupling in II-VI compounds. The resonant phonon Raman spectrum of NCs smaller than 2 nm is shown to be dominated by a broad feature similar to the SO mode of larger NCs or phonon density of states of a bulk crystal.The understanding of the phonon spectrum of semiconductor nanocrystals (NCs), electron-phonon coupling (EPC), dependence of the phonon spectra on the NC size, surfacebound moieties, and extended environment is of a large fundamental and application significance [1][2][3][4][5][6][7][8][9][10][11] due to the determinant role phonons play in the optical and electrical properties of semiconductor nanostructures [12,13]. Though a number of in-depth studies have addressed the phonon spectra of colloidal [14][15][16][17][18][19][20], glass-embedded [21][22][23] NCs, and epitaxial nanostructures [24][25][26], a significant divergence of the results exists concerning both the nature of the modes and their response to such factors as size, surface conditions, properties of the hosting medium and so forth. In particular, the apparently similar Raman spectra of a wide range of compounds (e.g., II-VI, III-V, and IV) and NC morphologies (dots, rods, tetrapods, wires, and discs) have been assigned differently.Recently, attempts were made to build a general picture of the phonon spectrum of various semiconductor NCs, based on analysis of the experimental Raman data and appropriate models [14,27,28]. This paper further explores the first-and higher-order phonon spectra of several kinds of II-VI NCs, as well as their similarity to other compounds, with the aim of better understanding of the vibrational spectrum of small NCs. High-quality NC samples were selected for this study in order to resolve Raman features, which are usually smeared by size dispersion, structural disorder, or low signal-to-noise ratio.The NC samples studied in this work have been prepared by means of colloidal chemistry according to protocols reported elsewhere [29][30][31][32], and CdSe, CdS, and CdTe NC samples of the same mean diameter (∼4 nm) were selected. Another sort of NCs studied were ultrasmall NCs of about 1.8 nm mean diameter, which revealed distinct Raman spectra. The attempts to measure the size and shape of these NCs directly by electron microscopy were unsuccessful [19], obviously due to ultrasmall NC size and charging of the stabilizing polymer. The broad X-ray features of these ultrasmall NCs [3] indicated their small size or/and n...

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“…It is shown that the decrease of the nanocrystal concentration leads to the intensity decrease of the above mentioned bands, while the decrease of the nanocrystal size additionally leads to the low-frequency shift of the band formed by the Е and F 2 symmetry vibrations (Figs 2 and 3). It should be noted that in nanometric crystals the low-frequency shift of Raman bands and their broadening are most often explained by confinementrelated selection rules violation due to the small crystal size [15] and surface phonon modes [16]. In our case, the former factor seems to be hardly possible, because the minimal nanocrystal size studied here (15 nm) is, according to the calculations in [17], too big to ascribe the observed features of the size-related behaviour of the Raman band parameters to the phonon confinement.…”

Section: Resultsmentioning

confidence: 99%

Raman scattering studies of composites based on Cu6PS5X (X = I, Br) superionic nanocrystals

Studenyak¹,

Aleja²

2013

Semicond. Phys. Quantum Electron. Optoelectron.

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Abstract.Composites were prepared by mixing Cu 6 PS 5 X (X = I, Br) nanocrystalline powders obtained by ball milling with different polymers. The average nanocrystal size was estimated from X-ray diffraction; the composites were studied by scanning electron microscopy. Phonon spectra of nanocomposites with different polymer matrices, size and concentration of nanocrystals were studied using Raman spectroscopy. It has been revealed that the surface-to-bulk phonon integrated intensity ratio strongly varies with the type of polymer matrix, average grain size and concentration of nanocrystals.

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Raman spectra of semiconductor nanoparticles: Disorder-activated phonons

Cited by 106 publications

References 29 publications

Structure of CdS–arachidic acid composite LB multilayers

Structure of CdS–arachidic acid composite LB multilayers

Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

Raman scattering studies of composites based on Cu6PS5X (X = I, Br) superionic nanocrystals

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