Materials nanocrystalline

ReflEXAES can be used for near-surface structural analysis of a wide variety of samples for which no other technique is appropriate. As with EXAES, ReflEXAES is particularly suited for studying the local atomic structure around particular atomic species in non-crystalline environments. It is, however, also widely used for the analysis of nanocrystalline materials and for studying the initial stages of crystallization at surfaces or interfaces. ReflEXAES was first proposed by Barchewitz [4.135], and after several papers in the early nineteen-eighties [4.136, 4.168-4.170] it became an established (although rather exotic) characterization technique. Most synchrotron radiation sources now have beam-lines dedicated to ReflEXAES experiments. 

R. B. Schwarz and Y. He, Proc. International Symposium on Metastable, Mechanically Alloyed and Nanocrystalline Materials (ISMANAM-96), Rome, Italy, 20-24 May, 1996. 

National Creative Research Initiative Center for Oxide Nanocrystalline Materials and School of Chemical Engineering, Seoul National University, San 56-1, Shilim-dong, Kwanak-gu, Seoul 151-744, South Korea, Fax 82-2-888-1604, thyeon plaza.snu.ac.kr... 

More serious errors may result when the grain-size of a specimen is small compared with the size of an indentation. Then, since all crystals are elastically anisotropic a rigid indenter will produce differing amounts of elastic strain in the grains depending on their orientations. This will create an effective roughening of the surface and increase the friction coefficient. This may result in overestimates of hardnesses. For example, this may underlie reports of nanocrystalline materials being harder than diamond. 

There has been substantial interest in the preparation and characterization of materials consisting of particles with dimensions in the order of 2-100 nm, so-called nanocrystalline materials. 336-343 One factor driving interest in nanoparticle research is the perceived need for the further miniaturization of... 

One problem with methods that produce polycrystalline or nanocrystalline material is that it is not feasible to characterize electrically dopants in such materials by the traditional four-point-probe contacts needed for Hall measurements. Other characterization methods such as optical absorption, photoluminescence (PL), Raman, X-ray and electron diffraction, X-ray rocking-curve widths to assess crystalline quality, secondary ion mass spectrometry (SIMS), scanning or transmission electron microscopy (SEM and TEM), cathodolumi-nescence (CL), and wet-chemical etching provide valuable information, but do not directly yield carrier concentrations. 

In nanocrystalline materials, the electrons are confined in regions having one, two or three dimensions (Fig. 1) when the relative dimension is comparable with the De... 

N as a tracer, ammonia 106 exchange reaction 105 glutamic add 106 GOGAT system 106 radioactive tracer 106 N2 and HD formation 109 N2 fixation in non-leguminous plants, actinomycetes 110 actinorhizal systems 110 NAD 74 nanocrystal 263 nanocrystalline materials 171... 

Las but not least, sample preparation is also an important issue. If we want to examine nanocrystalline powder samples. The grain size must be just a few nanometers, the layer, formed by these nanocrystals must be as thin as possible (to minimize dynamic difiraction), continuous and self-supporting. In many cases not all these requirements are fulfilled simultaneously. The nanocrystalline material to be studied is frequently present on a thin supporting carbon layer. In such cases peak decomposition can not yield an acceptable fit unless the presence of the amorphous material (in the form of a few diffuse rings) is taken explicitly into account in the model to be fitted. The size of the background is also affected by scattering in such a carbon support. 

Key words nanocrystalline materials, Z1O2, Z1O2 -Y2O3, HRTEM, IP, Fourier filtering... 

R. Birringer, H. Gleiter, H.P. Klein, P. Marquardt, Nanocrystalline materials- an approach to a novel sohd structure with gas-like disorder Phys. Lett. A 102(8) (1984) 365-369. 

No XRD pattern was found for the films, and on this basis they were believed to consist of amorphous HgSe. Based on more recent XRD studies of nanocrystalline materials, the lack of an XRD pattern was likely due to very small crystal size (supported by the increased bandgap see later). Annealing at 200°C crystallized the HgSe to an extent that it was clearly identified by XRD. Optical spectroscopy gave a bandgap value of 1.42 eV. Bulk HgSe is a semimetal with... 

H2GaNH2)3 at 500 °C produces nanocrystalline GaN with a significant impurity of gallium metal.The nanocrystalline material slowly converts to the wurtzite phase at 900 °C. Since dimethylhydrazine H2NNMe2 decomposes at much lower temperatures than ammonia, the dimeric four-membered ring (H2GaNHNMe2)2 has also been considered as a precursor to GaN. ° ... 

A nanocrystalline material recently available on the commercial market was found and utilized in this process. When utilized as a closed flux path external to and closed on the two poles of a permanent magnet, the special nanocrystalline... 

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