The aim of a joint research activity in the FP6-ANNA project (http://www.i3-anna.org) is to develop and improve metrologies for the measurement of nanocrystal properties. Within the framework of this cooperation we optimized the sample preparation techniques to obtain a range of structures containing nanocrystals. Based on these samples we have optimized our characterization methods. In this work we focus on ellipsometry and X-ray diffraction measurements for the characterization of nanocrystal sizes in silicon rich oxide and porous silicon. We demonstrate the capabilities of dielectric function parametrizations in the ellipsometric evaluations, revealing the correlation between the broadening parameters of the critical point features and the nanocrystal size. ©The Electrochemical Society.

We study theoretically the optical properties of embedded Ge and Si nanocrystals (NCs) in wide band-gap matrix and compared the obtained results for both NCs embedded in SiO2 matrix. We calculate the ground and excited electron and hole levels in both Ge and Si nanocrystals (quantum dots) in a multiband effective mass approximation. We use the envelope function approximation taking into account the elliptic symmetry of the bottom of the conduction band and the complex structure of the top of the valence band in both Si and Ge (NCs). The Auger recombination (AR) in both nanocrystals is thoroughly investigated. The excited electron (EE), excited hole (EH) and biexciton AR types are considered. The Auger recombination (AR) lifetime in both NCs has been estimated and compared. Crown Copyright © 2009.

Different silicon nanocrystal (Si NC) systems in which Si NCs were either entirely isolated or loosely interconnected were studied by photoluminescence (PL) and time-resolved PL decay measurements in the range between 70 and 290 K, in order to investigate the role of exciton migration in the PL properties. We examined three kinds of samples: (a) two light emitting mesoporous Si (PSi) films with different porosities, grown on p -type Si, (b) a heavily oxidized light emitting anisotropic macroporous Si film, and (c) a film consisted of a Si NC superlattice with six Si NC/ SiO2 bilayers, grown by low pressure chemical vapor deposition of amorphous Si (α-Si), followed by high temperature thermal oxidation. In the two mesoporous Si films of the first case, the Si NCs show a degree of interconnection that depends on the porosity, whereas in the two other cases the NCs were isolated by SiO2, the degree of electrical isolation depending on the thickness of the SiO2 interlayer between them. Temperature dependent PL spectra and PL decay times of the different systems correlate well with the ability of excitons to migrate from one NC to another (case of loosely correlated NCs) or remain strongly localized within the Si NCs (case of effectively isolated NCs). © 2009 American Institute of Physics.

We study the effect of a red shift and a considerable enhancement of photoluminescence (PL) intensity from a freshly etched porous Si (PS) thin film after prolonged laser irradiation or after aging in atmosphere. Both effects coincide with the appearance of Si-OH and Si-O-Si vibration modes in the Fourier transform infrared (FTIR) absorption spectra. The red shift is attributed to a pinning of the band gap of the light-emitting Si nanocrystals (NCs) due to the formation of Si-OH and Si-O-Si bonds. Using theoretical calculations, we estimated the electron and hole energy shifts caused by the interaction of the electronic states of the Si NCs with the surface vibrations, and correlated the observed PL enhancement with resonant coupling between the quantized valence sub-levels in the Si NCs and surface vibration modes. © 2008 Elsevier B.V. All rights reserved.