Silicon dioxide (SiO2) layers with a thickness more than 10 nm can be formed at ∼120 °C by direct Si oxidation with nitric acid (HNO3). Si is initially immersed in 40 wt.% HNO3 at the boiling temperature of 108 °C, which forms a ∼1 nm SiO2 layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO3 at 121 °C), resulting in an increase in the SiO2 thickness. The nitric acid oxidation rates are the same for (1 1 1) and (1 0 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO2 thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO2 layers with a uniform thickness are formed even on a rough surface of poly-Si thin film. 相似文献
La0.7Ce0.3MnO3 epitaxial films were successfully fabricated via a pulsed laser deposition method by controlling the experimental conditions. A series of experiments with varying the oxygen pressure and the substrate temperature demonstrated that the use of appropriate conditions is crucial for fabricating the epitaxial thin films. The existence of such suitable conditions was thermodynamically interpreted in terms of the stability of Mn2+ ion. Both XRD and EPMA measurements indicated that La0.7Ce0.3MnO3 thin films fabricated herein form single phases, although it was difficult to present the direct experimental evidence to prove that Ce ion can really exist within the perovskite structure. The resultant films with oxygen annealing showed a metal-insulator transition and ferromagnetic property with Curie temperature of 275 K. 相似文献
Chemically induced dynamic electron polarization (CIDEP) created in the quenching of triplet naphthalene by galvinoxyl were investigated by time-resolved Fourier-transform electron paramagnetic resonance (FT-EPR) measurements with monitoring a free induction decay signal of a pulsed microwave irradiation. Transient FT-EPR spectra of galvinoxyl with CIDEP were observed in various nonpolar solvents with different viscosity. A transient FT-EPR signal phase shows remarkable dependence on the viscosity: FT-EPR signal phases were absorption and emission in the solvents with low and high viscosity, respectively. Time evolutions of the FT-EPR signal of galvinoxyl were well simulated by a model of the radical-triplet pair mechanism (RTPM) for CIDEP. A sign of theJ value in the triplet naphthalene-galvinoxyl system in various solvents were discussed on the basis of the sign rule in the RTPM and the transient FT-EPR signal phase. One of possible explanation for the solvent viscosity dependence of the transient FT-EPR signal phase was pressented on the basis of hypothetical model of theJ value. 相似文献
Conformations of two dodecameric porphyrin wheels adsorbed on a Cu(1 0 0) were probed by using scanning tunneling microscopy (STM). Whereas a wheel consisting of six meso-meso linked diporphyrins was detected as uniform ring structure, several different images with three discrete molecular heights were detected for a wheel consisting of six meso-meso, β-β,β-β triply-linked planar diporphyrins. These results indicate that the former has a conformation similar to that in a free space, while the latter has various conformations with respect to orientation of planar diporphyrin units toward the metal surface. Several discrete STM images of the latter have been interpreted in terms of possible eight conformations, which vary as to relative orientation of neighboring diporphyrin units. 相似文献
We study the enzymatic degradation of xenobiotic polymers mathematically. As a mathematical model, we derive a linear second-order hyperbolic partial differential equation which governs the evolution of the weight distribution with respect to the molecular weight. Given an initial weight distribution and a final weight distribution, we formulate a problem to determine a degradation rate. We establish a necessary and sufficient condition for which the problem has a local solution. We also introduce a numerical technique based on our analysis, and present a numerical result that we obtained applying weight distributions before and after enzymatic degradation of polyvinyl alcohol. 相似文献
A numerical simulation was done to check the possibility of using planar C/C/C multilayers with density contrast 0.2 and 0.7 g/cm3 as an X-ray waveguide. After an optimization procedure, suitable waveguide layer thicknesses were found which provide a high degree of resonant standing wave field intensity enhancement in the core layer at incident beam energy of 13 keV. The obtained results were compared with those of the Mo/Be/Mo waveguide, whose high waveguiding capability at the same energy value was reported in the 1990s. The comparison shows that standing wave field intensity resonant enhancement provided by C/C/C planar multilayers is very high and, consequently, a guided beam can be well detected. 相似文献
The nickel Kalpha spectra of oxides, halides (NiF2, K2NiF6, NiCl2, NiBr2), complex compounds, and metal are measured with two different double-crystal X-ray fluorescence spectrometers. The peak shifts and line width changes due to the changes in the chemical states are reported. High reproducibility has been shown for the chemical shift and line width measurements. The DV-Xalpha molecular orbital calculation at the ground and the 1s(-1) hole states was performed to prove that the chemical effect originats from the charge-transfer mechanism. 相似文献
The adenosine derivative of 2‐oxo‐1,3‐diazaphenoxazine (Adap) exhibits a superb ability to recognize and form base pairs with 8‐oxo‐2′‐deoxyguanosine (8‐oxo‐dG) in duplex DNA. In this study, the triphosphate of Adap (dAdapTP) was synthesized and tested for single nucleotide incorporation into primer strands using the Klenow Fragment. The efficiency of dAdapTP incorporation into 8‐oxo‐dG‐containing templates was more than 36‐fold higher than with dG‐containing templates, and provides better discrimination than does the incorporation of natural 2′‐deoxyadenosine triphosphate (dATP). The selective incorporation of dAdapTP into 8‐oxo‐dG templates was therefore applied to the detection of 8‐oxo‐dG in human telomeric DNA sequences extracted from H2O2‐treated HeLa cells. The enzymatic incorporation of dAdapTP into 8‐oxo‐dG‐containing templates may provide a novel basis for sequencing oxidative DNA damage in the genome. 相似文献
This work is focused on montmorillonite (MMT)‐based “support‐activators” (S‐As) for the metallocene‐catalyzed propylene polymerization. This catalyst was previously industrialized; however, for further technological advances, the activation mechanism is investigated. The chemical and morphological requirements of the S‐A are surveyed using both commercially available raw clay minerals (non‐acid‐treated) and acid‐treated clay minerals. The S‐A possessing strong‐acid sites (pK a < ?8.2) gives a highly active catalyst. Acid treatment of MMT induces morphological changes as well as the formation of strong acid sites. Based on pore size distribution analysis and atomic force microscopy observations, it is concluded that the strong acid sites are located in the small pores around the edge of the clay mineral (not in the interlayer), where the structure is disordered by the acid treatment.
The synthesis of the C22-C37 segment of prorocentin, isolated from the dinoflagellate Prorocentrum lima, was achieved. Because the relative stereochemical relationship between C26 and other stereocenters (C28/C31/C32 established as R*/R*/R*) in the C22-C37 region of natural prorocentin has not yet been determined, both epimers at C26 of the C22-C37 segment were selectively constructed. The synthesis was based on a 5-exo epoxide ring opening reaction to form an oxolane (E-ring), Brown asymmetric methallylation to install the C26-stereocenter, acryloylation of the resulting alcohol, and ring-closing olefin metathesis to establish the Z-olefin at C23/C24. 相似文献