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941.
Recent developments in quantitative surface analysis by Auger (AES) and x-ray photoelectron (XPS) spectroscopies are reviewed and problems relating to a more accurate quantitative interpretation of AES/XPS experimental data are discussed. Special attention is paid to consideration of elementary physical processes involved and influence of multiple scattering effects on signal line intensities. In particular, the major features of core-shell ionization by electron impact, Auger transitions and photoionization are considered qualitatively and rigorous approaches used to calculate the respective transition probabilities are analysed. It is shown that, in amorphous and polycrystalline targets, incoherent scattering of primary and signal Auger and photoelectrons can be described by solving analytically a kinetic equation with appropriate boundary conditions. The analytical results for the angular and energy distribution, the mean escape depth, and the escape probability as a function of depth of origin of signal electrons as well as that for the backscattering factor in AES are in good agreement with the corresponding Mote Carlo simulation data. Methods for inelastic background subtraction, surface composition determination and depth-profile reconstructions by angle-resolved AES/XPS are discussed. Examples of novel techniques based on x-ray induced photoemission are considered. 相似文献
942.
{(MesGa)3[GaP(H)Mes](PMes)4}, a Phosphorus-substituted Ga? P-Heterocubane A mixture of MesGaCl2/GaCl3 (ratio 3:1) reacts with 5 equivalents of MesPLi2 in THF at ?78°C to the title compound {(MesGa)3[GaP(H)Mes](PMes)4} ( 1 ) by use of the “dilution principle”. 1 can be obtained in 30% yield. Recrystallization of 1 from DME and toluene, respectively, gives 1 · 0.5 DME and 1 · toluene. 1 was characterized by NMR-, IR-, and MS-techniques. According to the X-ray structure determination of 1 · toluene, 1 has a heterocubane structure, one corner of which is substituted with an P(H)Mes group. 相似文献
943.
Xin-hua Wan Hui-lin Tu Ying-feng Tu Dong Zhang Ling Sun Qi-feng Zhou Yu-ping Dong Mao Tang Department of Polymer Science & Engineering College of Chemistry Peking University Beijing China Department of Materials & Chemical Engineering Beijing Institute of Technology Beijing China 《高分子科学》1999,(2):189-192
The first TEMPO-mediated "living" free radical polymerization of liquid crystallinemonomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene(MPCS), was carried out at 130℃ withBPO as an initiator. The molecular weight of the polymer can be varied from rather low values to highvalues while maintaining narrow polydispersity. It was observed that the polymerization of MPCSproceeded much faster than that of styrene. A tentative explanation for this fast polymerization wassuggested. 相似文献
944.
The combination of ethyl diazoacetate with aryl aldehydes in the presence of copper(I) or rhodium(II) catalysts results in
the formation of 1,3-dioxolane products in moderate to good yields. These reactions occur through a pathway that involves
ylide intermediates. Catalyst-dependent diastereocontrol is observed and suggests that metal-associated ylides are involved
in the product-determining step. The influence of aryl aldehyde substituents has been determined.
Current address.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 961–965, May, 1998. 相似文献
945.
V. D. Sheludyakov Z. V. Belyakova V. M. Shevchenko E. A. Chernyshev 《Russian Chemical Bulletin》1997,46(5):997-1002
Novel dialkylaminocarbenium salts with metallocomplex counter ions were prepared by the reaction of phosgene with either DMF
or tetramethylurea in the presence of metal chlorides. Reactions of organosilicon amides with phosgene gave corresponding
carbenium salts, while organosilicon ureas yielded aminoiminocarbenium salts. Dialkylaminochlorocarbenium salts were reduced
with hydrosilanes to give dialkylaminocarbenium, salts and can be easily hydrolyzed to afford either amides or ureas. Pathways
of the reaction with water and alcohols depend on the nature of reagent and the reaction conditions.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1040, May 1997. 相似文献
946.
采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。 相似文献
947.
Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer 总被引:2,自引:0,他引:2
A piezoelectric quartz sensor coated with molecularly imprinted polymer (MIP) for caffeine was developed. The MIP was prepared by co-polymerizing methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) in the presence of azobis(isobutyronitrile) as initiator, caffeine as template molecule, and chloroform as solvent. The MIP suspension in polyvinyl chloride/tetrahydrofuran (6:2:1 w/w/v) solution was spin coated onto the surface of the electrode of a 10 MHz AT-cut quartz crystal. The sensor exhibited a linear relationship between the frequency shift and caffeine concentration in the range of 1×10–7 mg mL–1 up to 1x10–3 mg mL–1 [correlation coefficient (r)=0.9935] in a stopped flow measurement mode. It has a sensitivity of about 24 Hz/ln(concentration, mg mL–1). A steady-state response was achieved in less than 10 min. The performance characteristic of the sensor shows a promising and inexpensive alternative method of detecting caffeine. Surface studies were carried out for the reagent phase of the sensor using SEM, AFM, and XPS analysis in order to elucidate the imprinting of the caffeine molecule. The SEM micrograph, AFM image, and XPS spectra confirmed the removal of caffeine by Soxhlet extraction in the imprinting process and the rebinding of caffeine to the MIP sensing layer during measurement. 相似文献
948.
A new derivative of 2,5-piperazinedione, 1,4-di(2-methoxyphenyl)-2,5-piperazinedione (I), was synthesized by the cyclocondensation reaction of N-2-methoxyphenyl chloroacetamide, and its structure was characterized by elemental analysis, IR, ^1H NMR and single crystal X-ray diffraction method. The crystal belongs to monoclinic system, space group P21/c with unit cell dimensions a=0.56934(10) nm, b=1.3880(2) nm, c=1.00329(17) nm, β= 90.376(3)°, V= 0.7928(2) nm^3, Z=2, Dc = 1.367 g·cm^-3,μ = 0.98 cm^-1, R and wR being 0.0606 and 0.1564 respectively for 1549 unique reflections with 1247 observed reflections [I〉2σ(I)]. The molecule has a crystallographically imposed symmetry center. The three rings in the molecule are each coplanar with their attached groups, excluding methyl H atoms and the H atoms attached to the piperazinedione ring, while the whole molecule is not planar, with dihedral angles of 74.7(1)° between the piperazinedione and each of the two aromatic rings. The crystal structure is stabilized by van der Waals and dipole-dipole forces. 相似文献
949.
Chihiro Kachi‐Terajima Dr. Takamasa Akatsuka Masa‐aki Kohbara Satoshi Takamizawa Dr. 《化学:亚洲杂志》2007,2(1):40-50
The crystalline one‐dimensional compound, [RhII2(bza)4(pyz)]n ( 1 ) (bza=benzoate, pyz=pyrazine) demonstrates gas adsorbency for N2, NO, NO2, and SO2. These gas‐inclusion crystal structures were characterized by single‐crystal X‐ray crystallography as 1 ?1.5 N2 (298 K), 1 ?2.5 N2 (90 K), and 1 ?1.95 NO (90 K) under forcible adsorption conditions and 1 ?2 NO2 (90 K) and 1 ?3 SO2 (90 K) under ambient pressure. Crystal‐phase transition to the P space group that correlates with gas adsorption was observed under N2, NO, and SO2 conditions. The C2/c space group was observed under NO2 conditions without phase transition. All adsorbed gases were stabilized by the host lattice. In the N2, NO, and SO2 inclusion crystals at 90 K, short interatomic distances within van der Waals contacts were found among the neighboring guest molecules along the channel. The adsorbed NO molecules generated the trans‐NO???NO associated dimer with short intermolecular contacts but without the conventional chemical bond. The magnetic susceptibility of the NO inclusion crystal indicated antiferromagnetic interaction between the NO molecules and paramagnetism arising from the NO monomer. The NO2 inclusion crystal structure revealed that the gas molecules were adsorbed in the crystal in dimeric form, N2O4. 相似文献
950.
三齿单核三(3,5-二甲基-1-吡唑)硼氢钼配合物Tp*Mo(O)Cl2 (1)(Tp*=三(3,5-二甲基-1-吡唑)硼氢HB(C3H(Me2)N2)3)与含硫族元素碳硼烷的锂盐[(THF)2LiE2C2B10H10(THF)]< 相似文献