Villeneuve-la-Rivière, France
Villeneuve-la-Rivière, France

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Habinshuti J.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Habinshuti J.,Laboratoire Of Spectrochimie Infrarouge Et Raman | Kilian O.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Kilian O.,Comenius University | And 8 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We have investigated the diameter dependence of the Raman spectra of lead selenide nanocrystals. The first-order Raman peak at about 136 cm-1 and its second-order overtone at twice this wavenumber move up in energy with decreasing nanocrystal diameter. This anomalous behavior is interpreted in terms of quantum confinement of the longitudinal optical (LO) phonon whose frequency displays a minimum at Γ in the dispersion of bulk PbSe. We perform ab initio calculations of the phonons of PbSe slabs with up to 15 layers. The LO mode perpendicular to the slab shifts indeed upwards with decreasing layer thickness, thus validating the interpretation of the anomalous radius dependence of the Raman spectra in terms of quantum confinement. © 2013 American Physical Society.


Nguyen T.H.,French National Center for Scientific Research | Habinshuti J.,French National Center for Scientific Research | Habinshuti J.,Laboratoire Of Spectrochimie Infrarouge Et Raman | Justo Y.,Ghent University | And 9 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Semiconductor PbSe/CdSe core-shell nanocrystals (NCs) in a double barrier tunnel junction have been investigated by means of scanning tunneling spectroscopy at low temperature. From the analysis of the differential conductance peak position as a function of the potential distribution in both potential barriers, we demonstrate a unipolar transport regime for a large amount of NCs. The same charge carriers are injected on both sides of the zero-conductance gap, and the peaks observed at higher energy arise from the charging of the NCs. Similar results are obtained for CdSe/CdS dot-in-rod NCs, indicating that the addition of a shell favors transitions between different charge states rather than single particle excited states. Further characterization of the PbSe/CdSe core-shell NCs by x-ray photoemission spectroscopy reveals that the variations in the transport properties from NC to NC are explained by the occurrence of unprotected PbSe facets that have different orientations in the junction. © 2011 American Physical Society.


Mortet V.,Hasselt University | Mortet V.,IMEC | Zhang L.,University of Antwerp | Eckert M.,University of Antwerp | And 14 more authors.
Materials Research Society Symposium Proceedings | Year: 2010

Nanocrystalline diamond films have generated much interested due to their diamond-like properties and low surface roughness. Several techniques have been used to obtain a high re- nucleation rate, such as hydrogen poor or high methane concentration plasmas. In this work, the properties of nano-diamond films grown on silicon substrates using a continuous DC bias voltage during the complete duration of growth are studied. Subsequently, the layers were characterised by several morphological, structural and optical techniques. Besides a thorough investigation of the surface structure, using SEM and AFM, special attention was paid to the bulk structure of the films. The application of FT1R, XRD, multi wavelength Raman spectroscopy, TEM and EELS yielded a detailed insight in important properties such as the amount of crystallinity, the hydrogen content and grain size. Although these films are smooth, they are under a considerable compressive stress. FTIR spectroscopy points to a high hydrogen content in the films, while Raman and EELS indicate a high concentration of sp2 carbon. TEM and EELS show that these films consist of diamond nano-grains mixed with an amorphous sp2 bonded carbon, these results are consistent with the XRD and UV Raman spectroscopy data. © 2010 Materials Research Society.

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