Si nanocrystallites

The near-infrared PL15 at 0.8 eV (below the bulk Si band gap) exhibits complex nonexponential dynamics, with a wide distribution of decay times, and has been assigned to deep level transitions associated with dangling bonds on the surface of the Si nanocrystallites.54... 

So, the present study has shown that a weak magnetic field affects the processes at the surface of PS during its ageing in air. The effect consists in acceleration of breakage of Si-H bonds and in suspending the process of Si surface oxidation. It is supposed that magnetic field affects the strength of chemical bonds in surface complexes of Si nanocrystallites. 

The influence of dimensionality on the optical band gap, especially the widening for chain-like CT-conjugated Si polymers [3] and for small Si nanocrystallites, is demonstrated in Fig. 2 Theoretical predictions from Delerue et al. [4] are also included Our experimental data agree fairly well with this theory... 

Chao Y, Krishnamurthy S, Montalti M, lie LH, Houlton A, Horrocks BR, Kjeldgaard L, Dhanak VR, Hunt MRC, Siller L (2005) Reactions and luminescence in passivated Si nanocrystallites induced by vacuum ultraviolet and soft-X-ray photons. 1 Appl Phys 98 044316... 

ENHANCED PHOTOLUMINESCENCE OF AND Eu INDUCED BY ENERGY TRANSFER FROM SnOj AND Si NANOCRYSTALLITES... 

The enhancement can be explained also by an excitation transfer from Si nanocrystallites to Eu ions. Other authors [10] have shown similar results by comparing the PL of Eu in silica gel and in silica gel with colloidal cadmium sulfide. They show that CdS nanoparticles enhanced Eu fluorescence due to energy transfer from a surface trap in the CdS particles to Eu ions. 

The PS host based complex contains a mixture of Si nanocrystallites with clusters of filling materials. Formation of Pt-Si composites with grain size of about 100 nm, and polymer-Si composites including the PS grains separated from the Si substrate and mixed with poly(p phenylene-vinylene) are described in [6, 10],... 

After impregnation, the PL band of PS does not quenched which can indicate that excitation transfer from Si nanocrystallites to Eu ions is not possible. Furthermore, in a previous work [7], we have shown that Eu emission in PS depends strongly on laser excitation which exclude the process of radiative excitation transfer from PS to Eu. ... 

To improve the energy excitation transfer from rare earth to Si nanocrystallites, we have studied the effect of co-doping of the PS layer with Eu and Tb in equal proportion. Fig. 4 displays the RBS spectra of PS samples after europium and terbium deposition and subsequent annealing. Due to the close atomic numbers of terbium and europium and to the overlapping of their respective isotopic... 

The PL spectra for A,exc= 488 nm of (Eu +Tb )/PS nanocomposite are shown in Fig. 5a. By increasing the concentration of Eu -Tb solution, we show an increase of the PL intensity for Eu and Tb " emission. Moreover, we confirm the RBS results in Fig. 4. It was found also, that the PL intensity of PS emission increases when the concentration of the solution increases. Nevertheless, the Eu ions in PS are directly excited by absorption of laser energy. The same result has been shovm with Tb ions in PS [6,8]. Each behavior suggests that energy transfer can occur from rare earth (Eu and Tb ) ions to Si nanocrystallites. 

We have developed PS doped Eu " or Tb and Eu by a simple impregnation method. RBS and EDX/TEM analysis reveal a complete penetration of rare earth (Eu and Tb ) in the nanometric pores of PS. The PL study shows that Eu are diffused in Si nanocrystallites and occupies crystallographic sites in the matrix after annealing at 1000°C. We show that the luminescence of (Eu + Tb )/PS depends directly on wavelength excitation, which suggests that a process of excitation transfer occurs from Tb to Eu and to Si nanocrystallites when the radiative resonant transfer does play a key role. 

The next two chapters deal with investigations concerning solid silicon monoxide. The application of thin films of this material is based on its unique mechanical, chemical, and dielectric properties. It is related to Si-Si systems in so far as solid SiO consists of small particles of Si and Si02. Depending on the conditions for synthesis, the material has different local structures. In the contribution of U. Schubert and T. Wieder (Chapter 18), the structure and reactivity of a special SiO modification (Patinal ) is described. This material consists of Si and Si02 regions of 0.25 - 0.5 nm in diameter, which are connected by a thin interface. Most of the SiO reactions are also observed for elemental silicon. H. Hofineister and U. Kahler (Chapter 19) show that thermal processing of solid SiO (from BALZERS) up to 1300°C leads to phase separation into Si nanocrystallites embedded in an SiOx matrix. Their internal structure is determined by solid-phase crystallization processes. 

Si Nanocrystallites in SiO Films by Vapour Deposition and Thermal Processing... 

Figure 19.8. HREM images of Si nanocrystallites in an SiOx film (x = 1.17) illustrating their random orientation (a) and examples of cyclic (b) and parallel (c) planar defects.

Figure 19.9. Size distribution of Si nanocrystallites in SiOx films as a function of their oxygen content.

Starting from SiO vapor-deposited films, which may be regarded as nano-disproportionate materials, we have studied the evolution of further disproportionation and phase separation into a nano-particulate Si/SiOx composite material within which at sufficiently high temperatures, Si nanocrystallites may form. The mean size and concentration of these nanocrystallites are mainly governed by the initial oxygen content of the films and the annealing temperature. 

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