We present results on the photoluminescence ͑PL͒ properties of silicon nanocrystals as a function of their size. The nanocrystals are synthesized by laser pyrolysis of silane in a gas flow reactor and deposited at low energy on a substrate after a mechanical velocity and size selection. Both the photoluminescence spectroscopy and yield have been studied as well as the effect of aging of the samples in air. The measurements show that the PL of the silicon nanocrystallites follows the quantum confinement model very closely. The apparent PL yields are rather high ͑up to 18%͒. From evaluation of the size distribution obtained by atomic force microscopy it is concluded that the intrinsic PL yield of the nanocrystals can reach almost 100%. These results enabled us to develop a simple theoretical model to describe the PL of silicon nanocrystals. This model can also explain the changes of PL with aging of the sample, just by invoking a decrease of the size of the crystalline core as a result of oxidation.

In this article, we show how the well-known one-phonon confinement model can be improved to determine the diameter of silicon nanocrystalline spheres from the optical phonon wave-number shift, even using a physical-meaning weighting function. We show that the fundamental parameter is the knowledge of the phonon dispersion. The accuracy of our approach is supported by experimental data obtained by selective UV Raman scattering on nanocrystalline silicon thin films produced by size-selected silicon cluster beam deposition.

This paper presents an embedded vision system for object tracking applications based on a 128×128 pixel CMOS temporal contrast vision sensor. This imager asynchronously responds to relative illumination intensity changes in the visual scene, exhibiting a usable dynamic range of 120dB and a latency of under 100µs. The information is encoded in the form of Address-Event Representation (AER) data. An algorithm for object tracking with 1 millisecond timestamp resolution of the AER data stream is presented. As a realworld application example, vehicle tracking for a trafficmonitoring is demonstrated in real time. The potential of the proposed algorithm for people tracking is also shown. Due to the efficient data pre-processing in the imager chip focal plane, the embedded vision system can be implemented using a low-cost, low-power digital signal processor.

Silicon clusters and nanocrystals have been generated by CO 2 -laser-induced decomposition of SiH 4 in a flow reactor. By introducing a conical nozzle into the reaction zone, the clusters are extracted into a molecularbeam machine and analyzed with a time-of-flight mass spectrometer ͑TOFMS͒. Since the clusters have a size-dependent velocity, a mechanical velocity selector is used to further narrow their size distribution and to select a specific mean size. Employing this technique, silicon clusters with different preselected mean sizes have been deposited at low energy on various substrates. Photoluminescence ͑PL͒ and resonant Raman spectra of the resulting films are presented. The crystallite sizes deduced from the Raman spectra confirm the TOFMS measurements. The PL spectra are shifted with decreasing cluster size to smaller wavelengths. Our results agree very well with theoretical predictions for silicon quantum dots. ͓S0163-1829͑97͒08035-1͔

We used laser-induced decomposition of silane for the fabrication of nanosized Si particles and studied in detail their structural characteristics by conventional and high resolution electron microscopy. The silane gas flow reactor incorporated in a molecular beam apparatus was operated without size selection to achieve a broad size distribution. Deposition at low energy on carbon substrates yielded single crystalline, spherical Si particles almost completely free of planar lattice defects. The particles, covered by thin amorphous oxide shells, are not agglomerated into larger aggregates. The lattice of diamond cubic type exhibits deviations from the bulk spacing which vary from distinct contraction to dilatation as with decreasing particle size the oxide shell thickness is reduced. This effect is discussed in terms of the strong Si/oxide interfacial interaction and compressive stresses arising upon oxidation. A negative interface stress, as determined from the size dependence of the lattice spacing, limits the curvature of the interface, i.e., at small sizes Si oxidation must be considered as a self-limiting process.