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141.
142.
In this paper,the density functional theory has been used to perform a comparative theoretical study of water monomer,dimer,trimer,and bilayer adsorptions on the Be(0001) surface.In our calculations,the adsorbed water molecules are energetically favoured adsorbed on the atop sites,and the dimer adsorption is found to be the most stable with a peak adsorption energy of ~ 437 meV.Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3a 1-like molecular orbital with the (s,p z) orbitals of the surface beryllium atoms.While in the case of the water dimer adsorption,the 1b 1-like orbital of the H2O molecule plays a dominant role. 相似文献
143.
Xinyu Zhang Zhouwen Chen Changzeng Fan Mingzhen Ma Qin Jing Riping Liu 《固体物理学:研究快报》2009,3(9):299-301
The energetic, mechanical and electronic properties as a function of composition for Rex W1–x C alloys in the WC structure have been investigated. It has been demonstrated that the shear modulus of WC can be enhanced by alloying with a small amount of Re, to a maximum shear modulus of 311 GPa at x = 0.23. The designed alloy is energetically stable and could be expected to be a potential extremely hard transition‐metal monocarbide, which is attributed to the strong metal–metalloid interaction with modulated valence electron concentration with respect to WC. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
144.
We present a gauge-independent quark mass counterterm for the on-shell renormalization of the Cabibbo–Kobayashi–Maskawa (CKM) matrix in the Standard Model that is directly expressed in terms of the Lorentz-invariant self-energy functions, and automatically satisfies the hermiticity constraints of the mass matrix. It is very convenient for practical applications and leads to a gauge-independent CKM counterterm matrix that preserves unitarity and satisfies other highly desirable theoretical properties, such as flavor democracy. 相似文献
145.
Cu-Zn/ZnO nanocomposites with a novel core-shell structure have been prepared by a surface precipitation process in aqueous solution. X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy are employed to analyze the structure and morphology of the present products. The influence of the annealing temperature on the core-shell structure of the nanocomposites is investigated, and a possible growth model is proposed. Furthermore, the gas sensors based on the Cu-Zn/ZnO nanocomposites are fabricated and tested, which exhibits high sensitivity and fast response to CO. The best results are obtained for the sensor based on the film annealed at 350 °C, which shows that the sensitivity is about 6.3 when the sensor is exposed to 100 ppm CO at the operating temperature of 240 °C. The possible sensing mechanism of the Cu-Zn/ZnO sensing film has also been discussed. 相似文献
146.
Epitaxial La1−xSrxMnO3 (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO3 (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm2 of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO3 (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La0.8Sr0.2MnO3 film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR. 相似文献
147.
The silver nanoparticles with about 10 nm diameter were immobilized onto the halloysite nanotubes (HNTs) via the in situ reduction of AgNO3 by polyol process. The silver nanoparticles supported halloysite nanotubes (Ag/HNTs), with Ag content of about 11%, were used for the catalyzed reduction of 4-nitrophenol (4-NP) with NaBH4 in alkaline aqueous solutions. The effect of the reduction of 4-NP catalyzed by the catalysts in the presence of variable concentration NaBH4 was investigated. It was found that the reduction rate increased with the increasing of the amounts of NaBH4. And the larger amounts of NaBH4 reduced the induction time. 相似文献
148.
K. Vijai Anand M. Karl Chinnu R. Mohan Kumar R. Jayavel 《Applied Surface Science》2009,255(21):8879-8882
A hydrothermal method has been optimized for the synthesis of ZnS nanoparticles. The nanoparticles were stabilized using Hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The self-assembling of the surfactant molecules in the water solution forms a unique architecture that can be adopted as the reaction template for the formation of nanomaterials. The average grain size of the nanoparticles calculated from the XRD pattern was of the order of 2 nm which exhibits cubic zinc-blende structure. TEM results showed that the synthesized nanoparticles were uniformly dispersed in the HMTA matrix without aggregation. The spectroscopic results revealed that the synthesized ZnS nanoparticles exhibits strong quantum confinement effect as the optical band gap energy increased significantly compared to the bulk ZnS material. Formation of HMTA capped ZnS nanoparticles were confirmed by FTIR studies. The PL spectra exhibit a strong green emission peak around 502 nm attributed to some self-activated defect centers related to Zn-vacancies. 相似文献
149.
The formation energies and electronic structures of Ni-rich Ni-Mn-Ga alloys have been investigated by firstprinciples calculations using the pseudopotential plane wave method based on density functional theory. The results show that the alloying Ni prefers to occupy the Mn site directly in Ni9Mn3Ga4 and to occupy the Mn site and drive the displaced Mn atom to the Ga site in NigMn4Ga3, which is in accordance with the experimental result. According to the lattice constants and the density of states analyses, these site preference behaviours are closely related to the smaller lattice distortion and the lower-energy electronic structure when the excess Ni occupies the Mn site. The effect of Ni alloying on martensitic transformation is discussed and the enhancement of martensitic transformation temperature by Ni alloying is estimated by the calculated formation energy difference between austenite and martensite phases. 相似文献
150.
Qiaoli Wu 《Physica B: Condensed Matter》2009,404(16):2499-2502
Stabled hexagonal phase Sr1−xBaxAl2O4:Eu2+ (x=0.37-0.70) was prepared by solid-state method. Result revealed that the structure behavior of the SrAl2O4:Eu2+ calcined at 1350 °C in a reducing atmosphere for 5 h strongly depended on the Ba2+ concentration. With increasing Ba2+ concentration, a characteristic hexagonal phase can be observed. When 37-70% of the strontium is replaced by barium, the structure of the prepared sample is pure hexagonal. Photoluminescence and excitation spectra of the samples with different x and doped with 2% Eu2+ were investigated. Changes in the emission spectra were observed in the two different phases. The green emission at 505 nm from Eu2+ was found to be quite strong in the hexagonal phase. The intensity and peak position of the green luminescence from Eu2+ changed with increasing content of Ba2+. The strongest green emission was obtained from Sr0.61Ba0.37Al2O4:Eu2+. The decay characteristics of Sr1−xBaxAl2O4:Eu2+ (x=0.37-0.70) showed that the life times also varied with the value of x. Furthermore, the emission colors and decay times varying with x could be ascribed to the variation of crystal lattice. 相似文献