排序方式: 共有118条查询结果,搜索用时 15 毫秒
1.
Lakshmi Vijayan 《Physica B: Condensed Matter》2009,404(20):3539-3543
The ac electrical conductivity properties of LiTi2(PO4)3 (LTP) polycrystalline material in two different crystallite sizes are compared. Micrometer sized LTP is prepared by conventional solid-state reaction. LTP crystallites of 71 nm size are prepared by solid-state reaction of 40 h planetary milled stoichiometric mixture. The XRD and SEM are used as characterization techniques. Electrical properties are studied using impedance spectroscopic technique. Ball-milled LTP shows one order increase in grain-interior conduction compared to microcrystalline LTP at 388 K. The increase in conduction results from decreased crystallite size. 相似文献
2.
Further investigation on the formation mechanisms of (NH4)2SiF6 synthesized by dry etching technique
The validity of two formation mechanisms of ammonium silicofluoride (ASF), which are proposed to take place when a silicon surface is exposed to the vapor of HNO3/HF acid mixture is investigated. Of the two proposed mechanisms regarding the synthesis of ASF on silicon surface, validity of the first predicting the release of hydrofluosilicic acid (H2SiF6) at the intermediate stage is examined by FTIR spectroscopy and the second mechanism suggesting O2 release is investigated using the Winkler technique. IR absorbance bands of SiF62+ are observed on the fresh samples prepared at low (1/100) HNO3/HF volume fractions. No significant amount of oxygen is detected during the synthesis of ASF films on silicon surface by dry etching technique. These two observations together provide firmer support for the validity of the second mechanism. 相似文献
3.
V.M. Gun’ko V.V. Turov D. Palijczuk S.V. Kerus E.M. Pakhlov 《Applied Surface Science》2008,254(10):3220-3231
The behaviour of water and water/organic mixtures adsorbed onto activated microporous carbons or a carbon adsorbent with narrow intraparticle micropores and broad mesopores and macropores between nanoparticles was studied using low-temperature adsorption method and 1H NMR spectroscopy with layer-by-layer freezing-out of liquids at 190-273 K. These investigations revealed concentration-dependent effects of benzene, DMSO, acetone, chloroform, methane and acetonitrile on the characteristics of adsorbed water and the influence of this water on the interfacial behaviour of adsorbed organics. The influence of organics causes the structural and energetic differentiations of adsorbed water. The latter can be displaced by organics from micropores into broader pores and/or form mixture with polar solvents in meso and macropores. Freezing of adsorbed water can affect the adsorbent structure because ice crystallites have a larger size than that of liquid water droplets that lead to changes in the behaviour of adsorbed water/organic mixtures observed by the 1H NMR and adsorption methods. 相似文献
4.
L. Toniutti 《Applied Surface Science》2008,255(1):170-173
The structural evolution of nanoporous silica thin films was studied by Doppler broadening spectroscopy (DBS), 2-3 gamma ratio of positronium (3γ-PAS) and Fourier transform infrared spectroscopy (FT-IR). Four series of silica films with thickness in the 300-600 nm range were deposited by spin coating on Si substrate changing the content of sacrificial porogen in the sol precursors. The effect on the porosity of different amount of porogen and of the thermal treatments in the 400-900 °C temperature range have been highlighted. The evolution of the porosity is discussed considering the removal of porogen and of the silanol Si-OH groups by thermal treatments as pointed out by FT-IR. Pores with size from less than 1 nm up to sizes larger than 2.0 nm have been detected. In samples with maximum porogen load oPs escaping was observed indicating onset of connected porosity. At temperatures higher than 700 °C a decrease of the porosity due to a progressive pore collapsing was evidenced. A strong correlation was found between the shift of the Si-O-Si transversal optical (TO3) mode in the FT-IR spectra and the pore size in the porous silica films as revealed by DBS and 3γ-PAS. 相似文献
5.
V. V. Artamonov M.Ya. Valakh B. N. Romanyuk I. V. Rudskoy V. V. Strelchuk 《Applied Physics A: Materials Science & Processing》1990,51(3):264-267
Raman scattering spectroscopy is used to study the elastic stress distribution in the epitaxial silicon operating areas in the vicinity of planar getter areas, the latter being created by previous ion implantation of the substrate. Data concerning the effect of the operating element size and the dose of implantation into the getter area are obtained. The results are compared with those of X-ray topographic analysis of the structures. 相似文献
6.
Amale Nezzal Luc Aerts Marleen Verspaille Geert Henderickx Andreas Redl 《Journal of Crystal Growth》2009,311(15):3863-3870
The polymorphism of sorbitol was investigated, confirming the existence of four anhydrous crystalline phases plus the hydrate. The crystallised melt (CM), the alpha form, and the gamma form were obtained via a dry route. The CM was confirmed to be a crystalline state with a spherulite morphology. The alpha form was obtained via direct conversion from the CM, in contrast to more complicated routes previously reported, and was found to have a very high crystallinity. Gamma crystals were obtained by seeding the melt at high temperature; however, crystallinity was clearly less than for alpha crystals. 相似文献
7.
V.V. Mourzenko J.-F. Thovert P.M. Adler 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):75-85
Two-scale porous media are generated by filtering a Gaussian random correlated field with a random correlated threshold field.
The percolation threshold and the critical exponent ν are derived with the help of a finite-size scaling method. The percolation
threshold for the three-dimensional media is a decreasing function of the variance and correlation length of the threshold
field. A simplified model predicts these trends in 3d; moreover, it suggested some effects in 2d which were all numerically
verified.
Received 17 August 2000 相似文献
8.
M. Olivares-Marín C. Fernández-González V. Gómez-Serrano 《Applied Surface Science》2006,252(17):5980-5983
Using cherry stones, the preparation of activated carbon has been undertaken in the present study by chemical activation with potassium hydroxide. A series of KOH-activated products was prepared by varying the carbonisation temperature in the 400-900 °C range. Such products were characterised texturally by gas adsorption (N2, −196 °C), mercury porosimetry, and helium and mercury density measurements. FT-IR spectroscopy was also applied. The carbons prepared as a rule are microporous and macroporous solids. The degree of development of surface area and porosity increases with increasing carbonisation temperature. For the carbon heated at 900 °C the specific surface area (BET) is 1624 m2 g−1, the micropore volume is 0.67 cm3 g−1, the mesopore volume is 0.28 cm3 g−1, and the macropore volume is 1.84 cm3 g−1. 相似文献
9.
In the present work, the effect of the oxidizing treatment with nitric acid on three activated carbon samples has been studied. The influence of the acid treatment on the surface groups of the different samples has been investigated by means of FT-IR spectroscopy. The pore size distributions of the different samples were determined by means of the HK and DFT methods. The HK method points out a moderate increment of the microporosity due to the action of the nitric acid, whereas the DFT method shows an increase in the microporosity range above 17 Å. Finally, the values of the fractal dimension reveal that the treatment of the samples with nitric acid leads to chemical reactions of a limited extent. 相似文献
10.
R. Navarrete Casas A. García Rodríguez F. Rey Bueno A. Espínola Lara C. Valenzuela Calahorro A. Navarrete Guijosa 《Applied Surface Science》2006,252(17):6026-6030
In the present work, we have studied the adsorption of xanthine derivatives by activated carbon sorbents in aqueous solutions. The study comprised both kinetic, equilibrium and thermodynamic aspects. The kinetic results were reported in a previous paper; the equilibrium-related results are discussed here. The two types of carbon used exhibit some differences but the equilibrium isotherms obtained are all of the H-3 type in the classification of Giles. This suggests a high affinity of the sorbents for the sorbates. We also found that the overall adsorption process comprises more than one individual adsorption-desorption process of which one leads to the formation of a “monolayer” and the other to the “precipitation” of the sorbate on the sorbent surface (multilayer adsorption); the amount of sorbate adsorbed in monolayer form was seemingly greater in C-A14. 相似文献