Nanocrystalline structures properties

QD particles in a population can be entirely dark. The nonradiant properties probably are due to defects in their nanocrystalline structure that occurred during manufacture. The percentage of dark dots varies for each sample, but they can represent 44-47 percent of all dots in a population. Thus, the use of QD conjugates for biomolecule imaging may mean that nearly half of all particles in an assay do not contribute to the resultant fluorescence signal. 

Z. Dehouche, R. Djaozandry, 1. Huot, S. Boily, 1. Goyette, T.K. Bose, R. Schulz, Influence of cycling on the thermodynamic and structure properties of nanocrystalline magnesium based hydride, J. Alloys Compd. 305 (2000) 264-271. 

The chapters in this volume present detailed insights into the synthesis-structure-properties relationships of nanostructured materials. In particular, the catalytic and photocatalytic properties of nanoclusters and nanostructured materials with ultrahigh surface-to-volume ratio are demonstrated. The gas absorption characteristics and surface reactivity of nanoporous and nanocrystalline materials are shown for various separation and reaction processes. In addition, the structural manipulation, quantum confinement effects, transport properties, and modeling of nanocrystals and nanowires are described. The biological functionality and bioactivity of nanostructured ceramic implants are also discussed. 

Photoemission experiments that probe the electronic structure of the nanocrystals are indispensable if one wishes to gain insight into the electronic structure-property relationship. Though very few studies have been carried out on semiconducting nanocrystalline systems to date, techniques such as photoemission and X-ray absorption spectroscopies are of immense value in probing the electronic structure and also in verifying various theories proposed for the nanocrystals. In Section 11.6 we discuss these spectroscopic studies. 

A.S. Argon and S. Veprek, in Proc. 22nd Riso Intern. Symp. on Materials Science, Science of Metastable and Nanocrystalline Alloys - Structure, Properties and Modeling (Eds. A. R. Dinesen et al.), Riso National Laboratory, Roskilde, Denmark, 2001, p. 183. 

A second example of the application of laser ablation was reported by Chmielowska et al. [260]. The authors carried out structural analysis of thin cerium dioxide films doped with copper, which were produced for applications as catalytic gas sensors. The thin films deposited on a silicon substrate had a nanocrystalline structure with a well-developed texture. The morphology, as well as the preferred orientation of the films, changed with the volume fraction of copper. The observed variations were found to affect the catalytic properties of the materials. 

Influence of cycling on the thermodynamic and structure properties of nanocrystalline magnesium based hydride, Journal of Alloys and Compounds, 305, 264-271. 

The influence of the microstructure on electrieal transport and nonstoichiometry was reported for Ce02, Zr02 Ca bulk [12, 15, 16] and YSZ and ScSZ nanocrystalline thin films [7, 13, 14]. Bulk specimens are usually prepared by pressure-densified processing (l.lGPa, 600°C) from powders of 5nm crystallite size, while nanocrystalline thin films were obtained by the lymeric precursor spin coating technique, which has been proved to be particularly useful for the formation of dense nanocrystalline films at temperatures about 1000°C lower than those required to prepare micrometersized specimens [26]. The uniform distribution of grain size as well as the ability to control the thickness and microstructure of the films prepared by the polymeric precursor method allow comprehensive structure/property studies to be made on nanocrystalline materials [7]. 

NANOCRYSTALLINE ALUMINA FIBERS STRUCTURE, PROPERTIES, APPLICATION... 

In parallel to developments in the field of electronics, nanostmctured materials have been developed by materials scientists and chemists also. The concept of nanocrystalline structures emerged in the field of materials science, and polycrystals with ultrafine grain sizes in the nanometer range have been produced. These nanophase materials have been shown to have significant modifications of their mechanical properties compared with the coarse-grain equivalent materials. The huge surface area of nanoporous materials has attracted much attention for applications in chemistry such as molecular sieves, catalysis, and gas sensing. This has motivated intense research aimed at the fabrication of materials with a well-controlled composition and nanoscale stracture, such as synthetic zeolites. 

As shown by the studies on rare-earth permanent magnets, the non-equilibrium structures developed by mechanical alloying, with or without subsequent heat treatment, exhibit unique properties. There is thus much potential for the development of new mechanically alloyed materials for applications such as catalysts, electrodes, hydrogen-storage containers and other applications, where property improvements are associated with the amorphous and nanocrystalline structures developed by mechanical alloying. 

In order to investigate the possible differences in oxidation resistance along with any underlying mechanisms, understanding the nanocrystalline structure of a material is essential. This chapter will therefore first describe the structure of nanocrystalline materials, their thermodynamic properties and the possible effects of changes in the material structure (caused by such fine grain size) that may influence the oxidation resistance of a material. 

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