Study of quasi-1D SnO2 nanowires

The descriptions of SnO2 nanowires growth procedures are getting more and more frequent in the current literature. However, studies on the growth mechanisms are still lacking. In particular, no investigation has been reported on the growth process when the growth mechanisms are not based, as in the case of whiskers, on vapour-liquid-solid (VLS) transitions. In this paper, a new procedure is reported by the authors for growing SnO2 nanowires, based on the presence of liquid-tin droplets on the substrate. The Sn vapour pressure developed by these droplets, which find themselves very close to the growing tip of the wire, gives rise to a sufficiently high supersaturation to enable the fast growth rate usually observed. The principal features and results of this new procedure, as well as possible growth mechanisms, are also discussed

Near-infrared photoluminescence enhancement in Ge/CdS and Ge/ZnS core/shell nanocrystals: Utilizing IV/II-VI semiconductor epitaxy

Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II-VI, III-V and IV-VI semiconductor quantum dots. Here, we use relatively unexplored IV/II-VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II-VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II-VI nanocrystals are reproducibly 1-3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II-VI nanocrystals. We expect this synthetic IV/II-VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials

The Atomistic Nature of Crystal Growth, by B.Mutaftschiev, Springer, Berlin, 2001

Acta Cryst. A ISSN 0108-767

Vapour phase chemical transport properties of the cadmium telluride-iodine system

The vapour phase chemical transport properties of the CdTe : I2 system have been investigated. By comparing the experimental transport rate with the theoretical transport rate calculated on the basis of a three reaction transport model, it was shown that no iodine chemical transport is possible in closed tubes in the hot-cold direction, but only vapour phase transport controlled by the source sublimation. Thin platelets with large smooth surfaces were observed growing on the source charge under small temperature gradients. Their growth was explained in terms of a reverse (cold-hot) iodine transport associated with a reduced sublimation tendency of the facetted crystallized material with respect to the unfacetted powdered material of the charge.On a étudié les possibilités de croissance de cristaux par transport en phase gazeuse du système CdTe : I2. En comparant les taux de transport trouvés expérimentalement à ceux calculés à partir d'un modèle à 3 réactions, on a pu montrer qu'aucun transport d'iode n'est possible en tube scellé dans la direction allant de la zone chaude vers les régions plus froides, seul un transport par voie gazeuse contrôlé par la sublimation de la source est possible. Des plaquettes de grandes surfaces peuvent croître sur la charge constituant la source lorsque les gradiants de température sont faibles. Leur formation a été attribuée à un transport d'iode allant à contre-sens (froid-chaud) associé à une réduction de la sublimation des facettes cristallisées par rapport à la poudre constituant la charge

Theoretical and Technological Aspects of Crystal Growth, Proc. ISSCG-10 (The10-th Intern. Summer School on Crystal Growth, promoted by IOGG)

Materials Science Foru