Nanocrystalline structures

This approach is an alternative to quantitative metallography and in the hands of a master gives even more accurate results than the rival method. A more recent development (Chen and Spaepen 1991) is the analysis of the isothermal curve when a material which may be properly amorphous or else nanocrystalline (e.g., a bismuth film vapour-deposited at low temperature) is annealed. The form of the isotherm allows one to distinguish nucleation and growth of a crystalline phase, from the growth of a preexisting nanocrystalline structure. 

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. 

Zr-based AB2 Laves phase alloys consist of cast polycrystalline and nanocrystalline structures. The nanocrystalline microstructure could be obtained for quenching the melt-spun alloys after annealing151. Figure 1 shows SEM Micrographs of the cast Polycrystalline ABi Alloys. Microstructures of AB2-1 alloys consist of cubic C15 Laves phase, hexagonal C14 Laves phase and of AB2-4 is only Cl5. The white one of non Laves in AB2-I and AB2-4 is the phase Zr9Nil 1 and Zr7NilO respectively. 

Finally, remanence enhancement has been achieved by producing a coherent nanocrystalline structure in mechanically alloyed isotropic Sm7Fe93-nitride powders consisting of a-Fe and Sm2Fei7N3 [100],... 

Figure 2a. Ordered nanocrystalline structure of a film of a zirconia-based solid electrolyte in the form of a parallelogram.

The simultaneous analysis of the results of the study into the structure and the formation of the solid-electrolyte films led to the following conclusion the nanocrystalline structure of the solid-electrolyte films at the initial stage of their formation caused the appearance of a columnar structure of the films of the zirconia-based solid electrolyte during their sputtering. 

J.M. Sanchez, J.L. Moran-Lopez, Statistical Thermodynamics of Surfaces and Interfaces, in Nanophases and Nanocrystalline Structures, R.D. Shull and J.M, Sanchez Eds., A publication of TMS, Warrendale, Pennsylvania, 1993. 

Another frequently employed and convenient way for the preparation of Ti02 thin films is pulsed laser deposition [180], although this technique does not produce nanocrystalline structures. 

Sc considerably lowers the glass forming ability of Al alloys compared to rare earth metals (Ce). No amorphous phase was formed in rapidly solidified binary Al-Sc alloys. An unstable quasicrystalline icosahedral phase was first found in the alloy A185Sci5. Substitution of Ce for Sc in Al91Ce9 xScx alloys caused a transfer to a mixed amorphous-nanocrystalline and then to nanocrystalline structure. In Al85Nii0Ce5 xScx alloys a mixed amorphous-nanocrystalline structure appeared in the alloy with x=5 at a lowered solidification rate (increased ribbon thickness). 

The appearance of mixed amorphous-nanocrystalline and nanocrystalline structures strongly increased the ribbon hardness. 

The nanohardness of 400 nm thickness chromium coatings with ultra-fine grain (nanocrystalline) structure is equal to 21.61 GPa (Table 1), which is 8-9 times higher than that of cast chromium. At the same time the nanohardness of molybdenum coatings, which characterized even more fine-grain structure, is equivalent to 9.98 GPa. It is necessary to note, that in a massive state hardness of polycrystalline chromium is lower than hardness of polycrystalline molybdenum (2 GPa and 1.3 GPa for poly crystalline molybdenum and chromium accordingly [7]). 

The extra-high hardness of chromium coatings cannot be explained only by presence of the nanocrystalline structures. As has been shown earlier [2] the... 

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. 

Nanocrystalline and amorphous nickel-boron films with different boron content were prepared by electrodeposition. Ability of various boron-containing compounds to be a source of boron was studied. Effects of boron content on the crystallite size, surface morphology, microhardness and wear resistance of the films were investigated. It was shown that the Ni-B films containing less than 14 at. % of boron had the nanocrystalline structure. The films became amorphous at boron content more than 14 at. %. Boron incorporation into nickel film and increasing the content of boron resulted in a decrease of the crystallite size, extension of grain boundaries and considerable increase in microhardness and wear resistance. 

Mechanism of Film Formation with a Nanocrystalline Structure.534... 

MECHANISM OF FILM FORMATION WITH A NANOCRYSTALLINE STRUCTURE... 

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