The infrared (IR) and Raman spectra of eight substitutional carbon defects in silicon are computed at the quantum mechanical level by using a periodic supercell approach based on hybrid functionals, an all electron Gaussian type basis set and the CRYSTAL code. The single substitutional Cs case and its combination with a vacancy (CsV and CsSiV) are considered first. The progressive saturation of the four bonds of a Si atom with C is then examined. The last set of defects consists of a chain of adjacent carbon atoms C, with i = 1–3. The simple substitutional case, Cs, is the common first member of the three sets. All these defects show important, very characteristic features in their IR spectrum. One or two C related peaks dominate the spectra: at 596 cm−1 for Cs (and CsSiV, the second neighbor vacancy is not shifting the Cs peak), at 705 and 716 cm−1 for CsV, at 537 cm−1 for C and C (with additional peaks at 522, 655 and 689 for the latter only), at 607 and 624 cm−1, 601 and 643 cm−1, and 629 cm−1 for SiC, SiC, and SiC, respectively. Comparison with experiment allows to attribute many observed peaks to one of the C substitutional defects. Observed peaks above 720 cm−1 must be attributed to interstitial C or more complicated defects. 相似文献
XRD and XPS are used to study the dispersion state of CuO on ceria surface. The dispersion capacity values of CuO measured
by the two methods are consistent, which are of 1.20 mmol CuO/100 m2 CeO2. In addition, the results reveal that highly dispersed Cu2+ ions are formed at low CuO loadings and that increasing the CuO content to a value higher than its dispersion capacity produces
crystalline CuO after the surface vacant sites on CeO2 are filled. The atomic composition of the outermost layer of the CuO/CeO2 samples has been probed by using static secondary ion mass spectroscopy (SSIMS), and the ratim of Cu/Ce are found to be 0.93
and 0.46 for the 1.22 and 0.61 mmol CuO/CeO2 samples respectively. Temperature-programmed reduction (TPR) profile with two reduction peaks at 156 and 165°C suggests that
the reduction of highly dispersed Cu2+ ions consists of two steps and is easier than that of CuO crystallites, in which the TPR profile has only one reduction peak
at about 249°C. The above experimental results are in good agreement with the prediction of the incorporation model.
Project supported by the National Natural Science Foundation of China. 相似文献
Comparative study of the regularities of the reaction and specific features of phase formation during electrochemical incorporation
of lithium from propylene carbonate solutions in intermetallic aluminum-based compounds (CuAl2, Mg2Al3, and NiAl) and pure metals (Al, Cu, Mg, and Ni) was performed. The initial stage of the process was shown to be dissolution
of lithium in the solid phase limited by diffusion for all studied substrates. Trace amounts of lithium-containing by-products,
were detected in NiAl, Ni, and Cu samples. The subsequent change in the limiting stage is related to the beginning of formation
of a new phase: metallic lithium (on Mg2Al3, NiAl, Mg, Ni, and Cu) or LiAl (on Al and CuAl2 cathodes). In the latter case, the solid-phase substitution occurs, which is formally described by the equation: CuAl2+2Li++2e→2LiAl+Cu. Thus, the specific features of phase formation on the CuAl2 electrode correspond to the highest (among three intermetallides studied) concentration of Al atoms in the crystal lattice
of the compound.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8. pp. 1525–1530, August, 1998. 相似文献
Surface‐diffusion‐induced spontaneous Ga incorporation process is demonstrated in ZnO nanowires grown on GaN substrate. Crucially, contrasting distributions of Ga atoms in axial and radial directions are experimentally observed. Ga atoms uniformly distribute along the ~10 μm long ZnO nanowire and show a rapidly gradient distribution in the radial direction, which is attributed substantially to the difference between surface and volume diffusion. The understanding on the incorporation process can potentially modulate doping and properties in semiconductor nanomaterials.
Irreversible processes accompanying the lithium incorporation into amorphous thin-film silicon are investigated. It is shown that the irreversible processes occurred during the cathodic polarization result in the formation of passive film at the silicon surface. The passive film at silicon is close, in its composition, to the passive film at carbonaceous materials. However, unlike the carbonaceous electrodes, no effect of electrolyte composition on the irreversible capacity of the silicon electrodes is observed. 相似文献
The incorporation of oxygen atoms in oxide films grown by pulsed laser deposition depends upon the oxygen pressure and laser power density. By carefully controlling these two parameters it is possible to control the oxygen deficiency in the samples, and thus to change their physical properties from insulating and transparent to absorbing and conducting. By using X-ray diffraction, Rutherford backscattering spectroscopy and resistivity measurements, we show that depending upon the oxide materials oxygen deficiency in the films can induce either the growth of stable sub-oxide phases or the formation of nanocomposite films by phase separation. The first case corresponds to oxides with a mixed valency cation like Ti, which leads to the formation of stable, crystalline and highly conductive TiOx sub-oxide phases. The second case is well described by the indium tin oxides (ITO) in which a large oxygen deficiency leads to metallic clusters embedded into a stoichiometric matrix, i.e. nanocomposite films. This phenomenon is due to the fact that sub-oxides of these compounds are not stable and thus the oxygen deficiency induced a phase separation. 相似文献