SATF 2014 POSTER

Physical Review B, 2009

We compare, through first-principles pseudopotential calculations, the structural, electronic and optical properties of different size silicon nanoclusters embedded in a SiO2 crystalline or amorphous matrix, with that of free-standing, hydrogenated and hydroxided silicon nanoclusters of corresponding size and shape. We find that the largest effect on the opto-electronic behavior is due to the amorphization of the embedded nanocluster. In that, the amorphization reduces the fundamental gap while increasing the absorption strength in the visible range. Increasing the nanocluster size does not change substantially this picture but only leads to the reduction of the absorption threshold, following the quantum confinement rule. Finally, through the calculation of the optical absorption spectra both in a indipendent-particle and many-body approach, we show that the effect of local fields is crucial for describing properly the optical behavior of the crystalline case while it is of minor importance for amorphous systems.

Superlattices and Microstructures, 2009

Within a first-principles framework we show the dependence of the optical properties of silicon nanocrystallites embedded in a silica matrix on the crystalline vs. amorphous order of the system. Moreover we calculate how many-body effects modify the electronic and optical properties of the embedded silicon nanodots. A discussion about the different roles played by dimensionality, interface properties, disorder and excitonic effects on the electronic and optical properties of the confined nanostructures is presented.

MRS Proceedings

Si nanocrystals (Si-nc) embedded in amorphous silica matrix have been obtained by thermal annealing of substoichiometric SiOx films, deposited by PECVD (plasma enhanced chemical vapour deposition) technique with different amount of Si concentrations (42 and 46 at.%). Both nucleation and evolution of Si-nc together with the changes of the amorphous matrix have been studied as a function of the annealing temperature. The comparison of x-ray absorption measurements in Total Electron Yield (TEY) mode at the Si k-edge with photoluminescence (PL), FTIR and Raman spectra, allowed clarifying the processes of Si-nc formation and structural evolution as a function of the annealing temperature and Si content.

Applied Surface Science, 2006

Silicon nanocrystals (nc-Si) have gained great interest due to their excellent optical and electronic properties and their applications in optoelectronics. The aim of this work is the study of growth mechanism of nc-Si into a-SiO 2 matrix from SiO/SiO 2 multilayer annealing, using nondestructive and destructive techniques. The multilayer were grown by e-beam evaporation from SiO and SiO 2 materials and annealing at temperatures up to 1100 8C in N 2 atmosphere. X-rays reflectivity (XRR) and high resolution transmission electron microscopy (HRTEM) were used for the structural characterization and spectroscopic ellipsometry in IR (FTIRSE) energy region for the study of the bonding structure. The ellipsometric results gave a clear evidence of the formation of an a-SiO 2 matrix after the annealing process. The XRR data showed that the density is being increased in the range from 25 to 1100 8C. Finally, the HRTEM characterization proved the formation of nc-Si. Using the above results, we describe the growth mechanism of nc-Si into SiO 2 matrix under N 2 atmosphere. #

Materials Science and Engineering: C, 2002

Nanocrystal-based devices are possible candidates for future electronics. In this context, we have studied the electronic properties of Si Ž . nanocrystals nc-Si embedded in a SiO matrix. This work is devoted to the characterization of nc-Si by means of morphological, optical 2 and electrical techniques.

Nanotechnology, 2004

Silicon nanocrystals have been fabricated by annealing amorphous hydrogenated silicon-rich oxynitride (SRON) films in vacuum for 4 h over the temperature range 850-1150 • C. X-ray photoelectron spectroscopy confirmed the composition of the film to be SiO 0.17 N 0.07 . Glancing angle x-ray diffraction results revealed consistent silicon crystallite sizes of ∼5 nm for films annealed at temperatures 1050 • C, increasing to ∼12 nm for films annealed at 1150 • C. The room temperature photoluminescence spectra of the samples annealed at 850 and 950 • C comprised luminescent peaks from silicon nanocrystals and luminescence from the defects in Si-O system. However, only peaks from defects in Si-O system were present in the luminescence spectra from samples annealed at temperatures greater than 950 • C. For the samples annealed at 850 and 950 • C, the presence of strong Si-N bonds prevented the coalescence of smaller silicon crystallites into larger crystallites. Larger, non-luminescent silicon crystallites were only formed in films annealed at temperatures greater than 950 • C, where the energetics of coalescing particles overcame the strong Si-N bonding in SRON films. High-resolution transmission electron microscopy analysis confirmed the presence of silicon nanocrystallites. A proposed growth mechanism of silicon nanocrystals is discussed.

Chemistry of Materials, 2017

Silicon nanocrystals exhibit size-dependent optical and electronic properties that may be exploited for applications ranging from sensors to photovoltaics. In addition, they can be utilized in biological and environmental systems thanks to the nontoxicity of silicon. Synthesis of silicon nanocrystals has been accomplished using a variety of methods. However, creating near monodisperse systems of high purity has been a challenge. The high temperature processing of hydrogen silsesquioxane method of particle synthesis reproducibly provides pure, near monodisperse particles in scalable quantities. These particles can then be liberated using HF etching and functionalized using a variety of methods. This paper outlines our lab procedures for creating silicon nanocrystals, the various functionalization methods and the most commonly used characterization techniques.

Optoelectronics - Materials and Techniques, 2011

physica status solidi (a), 2012

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Journal of Molecular Structure, 2007

The Si-rich silicon oxide (SiO x ) thin films are prepared on silicon crystalline substrates by low pressure chemical vapor deposition (LPCVD) method. The oxygen concentration x are controlled by the ratio of the partial pressures of N 2 O and SiH 4 gases in the reaction chamber. In order to induce the phase separation on SiO 2 and Si nanostructures the samples are annealed at the temperatures 900-1100°C. The structural and optical properties of the samples are investigated by Raman and infrared spectroscopy and scanning electron microscopy.