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排序方式: 共有136条查询结果,搜索用时 15 毫秒
11.
12.
Krill CE Helfen L Michels D Natter H Fitch A Masson O Birringer R 《Physical review letters》2001,86(5):842-845
Measurements of grain growth in nanocrystalline Fe reveal a linear dependence of the grain size on annealing time, contradicting studies in coarser-grained materials, which find a parabolic (or power-law) dependence. When the grain size exceeds approximately 150 nm, a smooth transition from linear to nonlinear growth kinetics occurs, suggesting that the rate-controlling mechanism for grain growth depends on the grain size. The linear-stage growth rate agrees quantitatively with a model in which boundary migration is controlled by the redistribution of excess volume localized in the boundary cores. 相似文献
13.
Stefan Eibl Andrew Fitch Michela Brunelli Alexander Dominic Evans Philip Pattison Marie Plazanet Mark Robert Johnson Christiane Alba‐Simionesco Helmut Schober 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(6):o278-o280
The title compound, C10H18, a decalin stereoisomer, crystallizes with Z′ = 0.5 in the space group P21/n. The trans‐decalin molecule is located on an inversion centre with both rings in a chair conformation, making for a quasi‐flat overall shape. Despite the absence of hydrogen bonds, it crystallizes easily. In this work the unknown crystal structure of trans‐decalin has been solved and refined using X‐ray powder diffraction data. 相似文献
14.
Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm−1 region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined.
We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed
in these distances is an indication of the substitution effect.
It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the
case of o-disubstituted benzenes it is only 80% of the para-substituted shift. 相似文献
15.
D. Wardecki R. Przeniosło A. N. Fitch M. Bukowski R. Hempelmann 《Journal of nanoparticle research》2011,13(3):1151-1161
The microstructure of electrodeposited nanocrystalline chromium (n-Cr) was studied by using synchrotron radiation (SR) diffraction,
SEM, TEM, and EDX techniques. The as-prepared n-Cr samples show the standard bcc crystal structure of Cr with volume-averaged
column lengths varying from 25 to 30 nm. The grain growth kinetics and the oxidation kinetics were studied by time resolved
SR diffraction measurements with n-Cr samples annealed at 400, 600, and 800 °C. The grain growth process is relatively fast
and it occurs within the first 10 min of annealing. The final crystallite size depends only on the annealing temperature and
not on the initial grain size or on the oxygen content. The final volume-averaged column lengths observed after 50 min annealing
are 40(4), 80(1), and 120(2) nm for temperatures 400, 600, and 800 °C, respectively. It is shown that annealing ex situ of
n-Cr at 800 °C both under vacuum and in air gives a grain growth process with the same final crystallite sizes. The formation
of the Cr2O3 and CrH phases is observed during annealing. 相似文献
16.
Fitch A Agyeman A Wagdy A Terranova Z 《Langmuir : the ACS journal of surfaces and colloids》2011,27(1):452-460
Electroactive planar waveguide (EAPW) instrumentation was used to perform potential modulated absorbance (PMA) experiments at indium tin oxide (ITO) electrodes coated with 0-, 300-, 800-, and 1200-nm-thick SWy-1 montmorillonite clay. PMA experiments performed at low potential modulation monitor mass transport events within 100 nm of the ITO surface and, thus, when used in conjunction with cyclic voltammetry (CV), can elucidate charge transport mechanisms. The data show that at very thin films electron transfer is controlled by electron hopping (sensitive to the anion species in the electrolyte) in an adsorbed Ru(bpy)(3)(2+) layer. As the thickness of the clay film grows, electron transfer may become controlled by mass transfer of Ru(bpy)(3)(2+) within the clay film to and from the electrode surface, a mechanism that is affected by the swelling of the film. Film swelling is controlled by the cation of the electrolyte. Films loaded with Ru(bpy)(3)(2+) while being subjected to evanescent wave stimulation demonstrate a large hydrophobic layer. The growth of the hydrophobic layer is attributed to the formation of Ru(bpy)(3)(2+*), which has negative charge located at the periphery of the molecule enhancing clay/complex repulsion. The results suggest that the structure of the film and the mechanism of charge transport can be rationally controlled. Simultaneous measurements of the ingress of Ru(bpy)(3)(2+) into the clay film by CV and PMA provide a means to determine the diffusion coefficient of the complex. 相似文献
17.
Since Ghosh and Bard [80] first established the field of clay-modified electrodes some 15 years ago, great strides have been made in understanding the nature of the clay structural units and their impact on transport of a variety of electroactive probes (anions, neutrals, small cations, large cations, and compounds with distributed charge). Great strides have also been made in understanding the nature of the layered material in creating access of interlayer sites (size, charge, iron content, pillaring, and organic tailoring). In the last five years several successful applications of clay-modified electrodes have been achieved. Given the explosive growth in tailoring and construction of novel clay structures it seems reasonable to predict further significant advances in applications involving clay-modified electrodes. 相似文献
18.
[reaction: see text] An expedient, atom-economical, asymmetric synthesis of 1-aryl-3-azabicyclo[3.1.0]hexanes, including (+)-Bicifadine and DOV21947, in a single-stage through process without isolation of any intermediates has been developed. The key of this synthesis is the in-depth mechanistic understanding of the complicated epoxy nitrile coupling at each reaction stage. Therefore, the desired trisubstituted cyclopropane can be prepared in high ee and yield by controlling the reaction pathway through manipulating the nitrile anion aggregation state. 相似文献
19.
John S. C. Kearney Miglė Graužinytė Dr. Dean Smith Daniel Sneed Christian Childs Jasmine Hinton Dr. Changyong Park Dr. Jesse S. Smith Dr. Eunja Kim Samuel D. S. Fitch Prof. Dr. Andrew L. Hector Prof. Dr. Chris J. Pickard Dr. José A. Flores‐Livas Prof. Dr. Ashkan Salamat 《Angewandte Chemie (International ed. in English)》2018,57(36):11623-11628
The application of pressure allows systematic tuning of the charge density of a material cleanly, that is, without changes to the chemical composition via dopants, and exploratory high‐pressure experiments can inform the design of bulk syntheses of materials that benefit from their properties under compression. The electronic and structural response of semiconducting tin nitride Sn3N4 under compression is now reported. A continuous opening of the optical band gap was observed from 1.3 eV to 3.0 eV over a range of 100 GPa, a 540 nm blue‐shift spanning the entire visible spectrum. The pressure‐mediated band gap opening is general to this material across numerous high‐density polymorphs, implicating the predominant ionic bonding in the material as the cause. The rate of decompression to ambient conditions permits access to recoverable metastable states with varying band gaps energies, opening the possibility of pressure‐tuneable electronic properties for future applications. 相似文献
20.
Ultrasound promoted the Kornblum reaction of silver nitrite or sodium nitrite with haloalkyl acetals to afford the corresponding C-nitro compounds. The acetalprotected nitro compounds were used as reactants in a 'double Henry' reaction to produce the key intermediate nitrocyclohexane diol with a masked aldehyde side chain. The nitrodiol was then subjected to an ultrasound-promoted one-pot/single operation sequence involving a reduction deprotection followed by a cyclization-reduction. The entire sequence provided the core spiropiperidine substructure of the histrionicotoxins. 相似文献