The change in the electronic structure of germanium nanocrystals is investigated as their concentration is increased from noninteracting, individual particles to assembled arrays of particles. The electronic structure of the individual nanoclusters shows clear effects due to quantum confinement which are lost in the concentrated assemblies of bare particles. When the surface of the individual particles is passivated, they retain their quantum confinement properties also upon assembly. These effects are interpreted in terms of a particle-particle interaction model. (C) 2004 American Institute of Physics.
"An especially interesting system is a Ge QD lattice embedded in amorphous alumina (Al 2 O 3 ) matrix. Ge shows a very strong carrier confinement, and therefore the electronic properties of Ge QDs are strongly tunable by changing their sizes (Bostedt et al. 2004). Ge QDs also exhibit electro-and photoluminescence, non-linear optical properties; they are capable to retain electric charge for a long time and have unusual melting-freezing conditions (Shen et al. 2002; Maeda 1995; Dowd et al. 1999; Xu et al. 2006; Kanjilal et al. 2003; Chang et al. 2004). "
[Show abstract][Hide abstract] ABSTRACT: In this article, we show how to produce materials consisting of regularly ordered Ge quantum dot lattices in an amorphous alumina matrix with a controllable Ge quantum dot size, shape, spacing, crystalline structure, and degree of regularity in their ordering. The production of such materials is achievable already at room temperature by magnetron sputtering deposition of a (Ge + Al2O3)/Al2O3 multilayer. The materials show photoluminescence in the visible and ultraviolet light range, a size-dependent blue shift of the photoluminescence peak and an enhancement of its intensity by size reduction, indicating the quantum dot origin of the photoluminescence. The materials also exhibit excellent mechanical properties due to the alumina matrix. Their internal structure is shown to be highly resistive to irradiation with energetic particles for a large range of the irradiation parameters.
Journal of Nanoparticle Research 03/2013; 15(3). DOI:10.1007/s11051-013-1485-9 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Condensed-phase hydrogen-terminated diamond clusters (diamondoids) have been studied with soft-x-ray emission and x-ray-absorption spectroscopy. The occupied and unoccupied electronic states measured with these methods imply an increasing highest occupied molecular orbital-lowest unoccupied molecular orbital gap with decreasing diamondoid size, with the shifting entirely in the occupied states, in contrast to other semiconductor nanocrystals. These experimental results are compared with theoretical calculations on the electronic structure of diamondoids.
[Show abstract][Hide abstract] ABSTRACT: Germanium nanocrystals may be of interest for a variety of electronic and optoelectronic applications including photovoltaics, primarily due to the tunability of their band gap from the infrared into the visible range of the spectrum. This letter discusses the synthesis of monodisperse germanium nanocrystals via a nonthermal plasma approach which allows for precise control of the nanocrystal size. Germanium crystals are synthesized from germanium tetrachloride and hydrogen entrained in an argon background gas. The crystal size can be varied between 4 and 50 nm by changing the residence times of crystals in the plasma between ∼30 and 440 ms . Adjusting the plasma power enables one to synthesize fully amorphous or fully crystalline particles with otherwise similar properties.
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