Clusters optoelectronic properties

Some of the major questions that semiconductor characterization techniques aim to address are the concentration and mobility of carriers and their level of compensation, the chemical nature and local structure of electrically-active dopants and their energy separations from the VB or CB, the existence of polytypes, the overall crystalline quality or perfection, the existence of stacking faults or dislocations, and the effects of annealing upon activation of electrically-active dopants. For semiconductor alloys, that are extensively used to tailor optoelectronic properties such as the wavelength of light emission, the question of whether the solid-solutions are ideal or exhibit preferential clustering of component atoms is important. The next... 

Optoelectronic properties of clusters and small supported particles... 

Total energy calculations have been performed to understand the role of oxidation on the structural, electronic and optical properties of Si nanoclusters. Our aim is to explain the peculiar properties of aged porous Si samples, heavily oxidized Si nanoparticles and embedded Si nanocrystals. We have studied two types of structures isolated H-covered clusters, replacing Si-H bonds with various Si-0 bonds and Si nanoclusters embedded in a SiOz matrix. Regarding the isolated clusters we find that the optoelectronic properties depend on the type and the number of Si-O bonds at the cluster surface. For the embedded systems our results show that a close interplay between chemical and structural effects plays a key role in the light emission processes. 

The different behavior is due to the fact that the Si=0 bond produces new states within the band gap, strongly localized on the O atom itself, whereas for the Si-O-Si this does not happen (see Fig. 1(b)). Moreover, the presence of Si-O-Si and Si=0 bonds demonstrates that it is this last bond that dominates the optoelectronic properties. Increasing the oxygen coverage level, i.e. adding new Si=0 bonds, the gap decreases. The reduction is not linear with the number of Si=0 bonds (Fig. 2). For all the cluster sizes the strongest red shift occms with the first Si=0 bond a second Si=0 bond produces a further reduction but weaker than the first and the... 

The quantum effect of reduction of particle size in reducing the band gap of semiconductors and so giving rise to novel optoelectronic properties has stimulated interest in quantum dot inclusion compounds of nanoparticles of semiconductors within zeolite pores.In a pioneering study, Herron and coworkers succeeded in introducing cadmium sulfide clusters within the pores of zeolite Y via the reaction of a cadmium-exchanged zeolite Y with hydrogen sulfide gas (Scheme 6.8). °... 

Stability of common polymers, and consequently, thermal degradation of mercaptide molecules ean be also carried out with the mercaptide dissolved into a polymeric medium. In this case, a finely dispersed inorganic solid phase, embedded in polymer, is generated. Materials based on clusters confined in polymeric matrices are called nanocomposites [Mayer, 1998 Caseri, 2000]. Both semiconductor-polymer and metal-polymer nanocomposites have unique functional properties that can be exploited for applications in several advanced technological fields (e.g., optics, nonlinear optics, magnetooptics, photonics, optoelectronics) [Caseri, 2000]. 

The study of colloidal systems is a large field with many facets applications of these systems include optoelectronics, thin film growth, and catalysis. This is due to their exotic physiochemical properties lending credibility to the claim that these systems are an intermediate state of matter [115]. Colloidal metal clusters have also been examined as materials suitable for quantum confinement and quantum dots which may serve as models for studying single electron tunneling (SET) and... 

The interest in the surface structures with their special properties has increased considerably due to extensive applications in micro- and optoelectronics. It is known that the properties of films of submicron size can be different from those of structures having macroscopic dimensions. The parameters that change the properties of films, are the thickness, number of layers, uniformity of the films, the size of clusters and nanocrystals. The presence of small particles and nano-sized elements leads to changes in material properties such as electrical conductivity, refractive index, band gap, magnetic properties, strength, and others (Suzdalev, 2006 Kobayashi, 2005). 

Trimetallic nitride endohedral fiiUerenes have been sought for use in MRl contrast agent ( Lanthanides Magnetic Resonance Imaging) and optoelectronic devices because of the wide variety of trimetallic nitride clusters that can be encapsulated in the fullerene, which can be used to tune properties of the material. ... 

In the last few decades, there has been a tendency toward the use of polymeric materials in the areas of science and technology where the manifestation of specific properties of molecular clusters or even individual macromolecules is required for example, in optoelectronic and data-recording devices, nanoelectronics [1-3] and nanomechanics, and biochemical [4] and biophysical technologies [5, 6]. 

Boranes and carboranes are comprised of a-aromatic cage-like structures with boron and carbon vertices ranging from small tetrahedral to supra-icosahedral clusters. Despite more than four decades of work with this class of inorganic compound, there have been few reports of their photophysical properties, with a distinct paucity of information regarding luminescence. Carboranes have nevertheless been incorporated into photophysically active metal complexes, usually as ancillary components. But what of boranes, carboranes, and metallacarboranes (where a transition metal atom can either be an integral vertex in the polyhedral skeletal framewoik or an exterior component thereof) as chromophores themselves and their resultant optoelectronic behavior In this arena, there are very few contributors. 

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