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排序方式: 共有300条查询结果,搜索用时 31 毫秒
241.
We present different relaxation mechanisms of Ge and SiGe quantum dots under excimer laser annealing. Investigation of the coarsening and relaxation of the dots shows that the strain in Ge dots on Ge films is relaxed by dislocation since there is no interface between the Ge dots and the Ge layer, while the SiGe dots on Si0.77Ge0.23 film relax by lattice distortion to coherent dots, which results from the obvious interface between the SiGe dots and the Si0.77Ge0.23 film. The results are suggested and sustained by Vanderbilt and Wickham's theory, and also demonstrate that no bulk diffusion occurs during the excimer laser annealing. 相似文献
242.
Martin Valldor Saeid Esmaeilzadeh Magnus Andersson Andrzej Morawski 《Journal of magnetism and magnetic materials》2006
The presented compound, Sr2TaMnO6, has a weak, disordered magnetic structure. The metal oxide was prepared under high isostatic oxygen pressure. The doubling of the perovskite structure was proven with electron diffraction and powder neutron diffraction. Combining neutron- and X-ray diffraction data, the room-temperature structure was modelled with the Rietveld method. Both octahedral positions are partially occupied by Mn and Ta, but with different Mn/Ta ratios. AC- and DC-magnetic measurements indicate a magnetic transition at about 17 K and the AC-magnetic susceptibility, both real and imaginary part, is frequency dependent, suggesting that the material has a spin-glass feature. The magnetic spins freeze during a wide temperature range and a possible explanation is a competative situation between the double exchange (ferromagnetism) and the super-exchange (anti-ferromagnetism). 相似文献
243.
ZnO films were deposited on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). Annealing treatments for as-deposited samples were performed in different atmosphere under various pressures in the same chamber just after growth. The effect of annealing atmosphere on the electrical, structural, and optical properties of the deposited films has been investigated by means of X-ray diffraction (XRD), atomic force microscope (AFM), Hall effect, and optical absorption measurements. The results indicated that the electrical and structural properties of the films were highly influenced by annealing atmosphere, which was more pronounced for the films annealed in oxygen ambient. The most significant improvements for structural and electrical properties were obtained for the film annealed in oxygen under the pressure of 60 Pa. Under the optimum annealing condition, the lowest resistivity of 0.28 Ω cm and the highest mobility of 19.6 cm2 v−1 s−1 were obtained. Meanwhile, the absorbance spectra turned steeper and the optical band gap red shifted back to the single-crystal value. 相似文献
244.
V.H. Méndez-García F.J. Ramirez-Arenas E. Cruz-Hernandez J.S. Rojas-Ramirez 《Applied Surface Science》2006,252(15):5530-5533
We have studied the surface atomic structure of GaAs(6 3 1), and the GaAs growth by molecular beam epitaxy (MBE) on this plane. After the oxide desorption process at 585 °C reflection high-energy electron diffraction (RHEED) showed along the [−1 2 0] direction a 2× surface reconstruction for GaAs(6 3 1)A, and a 1× pattern was observed for GaAs(6 3 1)B. By annealing the substrates for 60 min, we observed that on the A surface appeared small hilly-like features, while on GaAs(6 3 1)B surface pits were formed. For GaAs(6 3 1)A, 500 nm-thick GaAs layers were grown at 585 °C. The atomic force microscopy (AFM) images at the end of growth showed the self-formation of nanoscale structures with a pyramidal shape enlarged along the [5−9−3] direction. Transversal views of the bulk-truncated GaAs(6 3 1) surface model showed arrays of atomic grooves along this direction, which could influence the formation of the pyramidal structures. 相似文献
245.
Surface enhanced Raman scattering (SERS) from samples prepared by spreading para-nitrobenzoic acid (PNBA) and adenosine powders over silver thin films was achieved. The SERS intensities of the ionized PNBA on the silver film increase with increased applied pressure through a cover-glass and reach a maximum at 0.6 MPa. In contrast, the signals caused by adenosine remain nearly unchanged under applied pressures of 0-0.6 MPa. Beyond 0.6 MPa, the signals attributable to samples decrease in intensity. Atomic force microprobe images reveal that nanometer-scale surface morphology is changed by 0.8 MPa pressure, suggesting that the decrease in SERS intensity is related to pressure-induced morphological changes. Results obtained in this study indicate that SERS spectra are obtainable easily, without solvents, under ambient conditions using dispersion of the sample powder. 相似文献
246.
T.S. Chan R.S. Liu G.Y. Guo J.G. Lin L.-Y. Jang C.Y. Huang 《Solid State Communications》2004,131(8):531-535
We report on the preparation and characterization of the variation of B′-site transition metal in Sr2CrMO6 (M=Mo, W) with double perovskites structure. The magnetic susceptibility shows that Sr2CrMoO6 and Sr2CrWO6 are antiferromagnets with TN=40 and 30 K at H=1 T, respectively. In addition, a large magnetoresistance ratio (MR) of ∼38% (H=3 T) at 5 K was observed in the Sr2CrWO6 compound. However, the Sr2CrMoO6 compound does not show any significant MR even at high fields (MR∼4%; H=3 T and 5 K). The measured O K-edge X-ray absorption is in agreement with the calculated O p-density of states for both compounds. 相似文献
247.
H. Lippert V. Stert L. Hesse C.P. Schulz W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):445-448
The H atom transfer reaction in electronically excited indole(NH
3
)
n
clusters is studied in pump-probe experiments with femtosecond laser pulses. By applying different probe photon energies
we are able to detect the dissociation products (NH
3
)
n - 1
NH
4
for n
= 1-6. Furthermore we show that the analysis of the corresponding ion signals is not distorted by contributions from larger cluster
ions due to evaporation of NH
3
molecules. The formation times of the products are ca. 140ps for n
= 2-4 and about 80ps for n
= 5, 6.
Received 30 April 2002 / Received in final form 29 May 2002 Published online 13 September 2002 相似文献
248.
Langmuir-type films of poly(5-amino-1-naphthol) conductive polymer were formed at the air/water interface. The surface pressure versus molecular area isotherms of the polymeric layers showed a high tendency to aggregate and non-monomolecular behavior on the water surface. Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) procedures have been successfully used to transfer the Langmuir films of this polymer onto hydrophilic silicon substrates. Atomic force microscopy images showed that the films obtained by the LS method have much better quality than those obtained by the LB one. In particular, we have obtained uniform and smooth LS films covering practically all the substrate, while the LB films showed rather aggregated material, only partially covering the substrate. 相似文献
249.
We compare the foaming characteristics induced by irradiation with single ns and fs laser pulses of UV, VIS and IR wavelengths on gelatines differing in gel strength (bloom values 75 and 225) and in crosslinking degree. We have observed that while laser irradiation with nanoseconds leads to the formation of a microfoam layer at 266 nm, and melting and crater formation at longer wavelengths (532 and 1064 nm), fs pulse irradiation leads to submicron foaming at all wavelengths studied (266, 400 and 800 nm). These results show the possibility of controlling the submicrometric foam structure in this biomaterial and can shed light into the working mechanisms of fs laser nanoprocessing in biomaterials, where increase of temperature, thermoelastic stress generation, and stress-induced bubble formation are mediated by the generated plasma. 相似文献
250.
J. Lozeille A. Fioretti C. Gabbanini Y. Huang H. K. Pechkis D. Wang P. L. Gould E. E. Eyler W. C. Stwalley M. Aymar O. Dulieu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(2):261-269
We present detailed experimental spectra and accurate theoretical interpretation of resonance-enhanced
two-photon ionization of ultracold rubidium molecules in the
14000–17000 cm-1 transition energy range. The dimers are formed in a
magneto-optical trap by photoassociation followed by radiative decay into the a 3Σu+
lowest triplet state. The theoretical treatment of the process, which reproduces the main features
of the spectra, takes into account the photoassociation and decay steps as well as the resonant ionization through the manifold
of intermediate gerade states correlated to the 5S + 4D limit. In particular, the energy of the v=1 level of the
potential well has been determined for the first time. In addition, a tight constraint has been put on the position of the
a 3Σu+
repulsive wall. Finally, magnetic trapping of
rubidium molecules in the a 3Σu+ state is demonstrated.
Electronic supplementary material Online Material 相似文献