Low wavenumber Raman scattering of nanoparticles and nanocomposite materials

Ivanda, Mile; Furić, Krešimir; Musić, Svetozar; Ristić, Mira; Gotić, Marijan; Ristić, Davor; Tonejc, Antun; Djerdj, Igor; Mattarelli, Maurizio; Montagna, M.; Rossi, F.; Ferrari, M.; Chiasera, Alessandro; Jestin, Y.; Righini, Giancarlo C.; Kiefer, W.; Gonçalves, Rogéria Rocha

doi:10.1002/jrs.1723

Cited by 79 publications

(57 citation statements)

References 36 publications

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“…It can furthermore be used to estimate diameter distributions in nanorod ensembles. In spherical particles of similar composition, the line-shape of the spherical equivalent to the RBM can be used to estimate the size distribution of the investigated particles [94]. There, the agreement between the distributions from the Raman spectra and TEM measurements is quite good.…”

Section: Raman Measurement Of the Radial Breathing Modementioning

confidence: 94%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

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Colloidal CdSe nanorods are nanoparticles synthesized in solution. The synthesis allows the growth of CdSe nanorods with well defined diameters and aspect ratios. They have many potential applications in the field of optoelectronics and biotechnology. The nanorods can be epitaxially covered with a graded CdS/ZnS shell of a few monolayers in thickness. The shell leads to an increased quantum efficiency and improved photostability of the nanorods. However, the lattice mismatch between the nanorod core material and the shell material introduces strain into the core lattice. In this work Raman spectroscopy, accompanied by ab-initio calculations, is used to determine the amount of this strain, the exciton-phonon coupling strength in the nanorods and to investigate confinement effects. The longitudinal optical phonons in a nanorod are confined to the nanorod volume. The confinement of a phonon wavefunction leads to a neutralization of the q = 0 rule and the phonon frequency is found to depend on the nanorod diameter. The coupling strength between longitudinal optical phonons and excitons is investigated. It also depends on the nanorod diameter. The total coupling strength is much lower than in bulk material due to a decrease of the influence of the Coulomb interaction in nanoparticles. However, the coupling strength is found to rise for decreasing diameters. This is due to the increasing contributions of higher frequency phonons for smaller nanoparticle sizes. A radial breathing mode with a diameter dependent frequency is deduced from ab-initio calculations and its existence in nanorods is verified experimentally. The diameter-dependence of the modes' frequency can be used to estimate the nanorod diameter from a Raman measurement. In core-shell structures, the coverage of a CdSe nanorod with a ZnS shell leads to a compressive strain of the CdSe core due to the smaller lattice parameter of ZnS compared to CdSe. Ab-initio calculations show that all bonds of the CdSe core are shortened. The bonds in the lateral direction are much more strongly compressed than the bonds parallel to the c-axis. The amount of strain is estimated from the Raman spectra. The compressive nature of the shell decreases for thicker nanorods. The exciton wave function changes with the modified boundary from air to ZnS. This is reflected in a altered exciton-phonon coupling strength and can be monitored in the Raman spectra. ZusammenfassungCdSe Nanorods sind Nanopartikel, die in einer kolloidalen Lösung synthetisiert werden. Für diese existieren viele mögliche Anwendungen im Bereich der Optoelektronik und der Biotechnologie. Der Durchmesser und die Länge der Nanorods lässt sich durch die Syntheseparameter festlegen. Die Nanorods können in eine epitaktische Hülle aus einem Halbleitermaterial mit einer größeren Bandlücke, ZnS, eingebettet werden. Diese Hülle verbessert die optischen Eigenschaften und ermöglicht eine weitere Funktionalisierung der Oberfläche. Der Unterschied der Gitterparameter zwischen ZnS und CdSe führt jedoch zu Verspannung...

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Section: Raman Measurement Of the Radial Breathing Modementioning

confidence: 94%

Optical phonons in colloidal CdSe nanorods

Lange

Mohr

Artemyev

et al. 2010

Physica Status Solidi (b)

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“…But, the signal at 564 cm -1 may also correspond to an NbO 2 -species for which a literature value of 580 cm -1 is given ( Table 2). The broadening of the Raman-modes is caused by the small particle size and their interaction with an elastic, non-complete crystalline crystall-lattice, leading to a shortening of the lifetime of vibrational excited states [30]. The Raman spectra of a highly oxidic sputtered film with the stoichiometry Nb 0,03 Ti 0,97 O 1,91 is presented by curve S2.…”

Section: Structural Characterisation Of the Nbmentioning

confidence: 99%

Niobium‐doped TiO₂ films as window layer for chalcopyrite solar cells

Neumann¹,

Bierau²,

Johnson³

et al. 2008

Physica Status Solidi (b)

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Smooth and semitransparent Nbx Ti1–x Oy (x = 0.03, y = 1.84–1.91) films have been prepared by reactive magnetron sputtering at temperatures below 420 K. Structural investigations by RAMAN‐spectroscopy together with resistivity‐ and temperature‐dependent Hall‐measurements were used in order to analyze the film structure and the nature of the charge transport in this material. These films can be used as a window layer (TCO) for thin film solar cells. Cu(In,Ga)Se2 solar cells equipped with the new window layer keep their functionality which excludes first, the presence of strong energetic barriers and second, a strong interfacial recombination. The development of TiO2‐based window layers is expected to make thin film solar cells less sensitive against corrosion after contact with humidity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…As a matter of fact, this distribution is often found when analyzing system of particles of nanometric size [12]. We have calculated…”

Section: Resultsmentioning

confidence: 95%