3C-SiC(001)-3 × 2 reconstructed surface analyzed by high-resolution medium energy ion scattering

The atomic structure of the 3C-SiC(001)-3 × 2 reconstructed surface was analyzed precisely by high-resolution medium energy ion scattering (MEIS). The present MEIS analysis unambiguously shows that the (3 × 2) surface consists of Si adatoms (1/3 ML, 1 ML = 1.05 × 10¹⁵ atoms/cm²) on top and underlying Si adlayer (2/3 ML) on the bulk truncated Si plane. As the result, the most probable structure is focused on the Two Adlayer Asymmetric Dimer Model predicted by ab initio calculations and the modified versions with alternating long and short dimers in the 2nd adlayer proposed by photoelectron diffraction (PED) and by grazing incidence X-ray diffraction (GIXRD) analyses. Observed MEIS spectra are well reproduced by the structure relatively close to that determined by PED rather than GIXRD. Interestingly, the first principle calculations using VASP (Vienna ab initio simulation package) prefer symmetric dimers in the second Si adlayer and non-relaxed interplanar distance between the top Si and 2nd C plane of the bulk-truncated surface, which are, however, unable to reproduce the observed MEIS spectra. The distorted 2nd adlayer (asymmetric dimers) may correlate with the compressed interplanar distance between the underlying Si and C planes.     

Cesium adsorption on the β2-GaAs(001) surface

The results of first-principles calculations of the cesium adsorption energy on the β2-GaAs(001) surface performed within approaches of the density functional theory are presented for two possible terminations of the surface. It is shown that, among the considered high-symmetry positions, the energy-preferred position for cesium is position T ₃ when the surface layer contains arsenic and position T ₄ for gallium terminated surface. Cesium introduces insignificant perturbations in the positions of surface-layer atoms, and surface dimers do not break even in the case of adsorption at the dimer bridge and top positions. It is shown that cesium bonding to the GaAs (001) substrate can be explained by sp hybridization of arsenic and gallium orbitals as well as by formation of cesium states mixed with delocalized states of a clean surface. At low coverage, more preferable adsorbate sites are those with nearest neighbor arsenic atoms for both surface terminations.     

Effects of potassium on the adsorption of methanol on β-Mo2C(001) surface

We have studied the effect of K on the adsorption of methanol on the β-Mo₂C(001) surface and compared our experimental data with theoretical calculations. We have also performed high resolution electron energy loss spectroscopy (HREELS) (LK, ELS3000). For calculations we used the density functional theory under the VASP implementation. The most favorable sites for methanol adsorption are on top of a Mo atom in the clean surface and on top of a K atom in the pre-dosed surface. The changes in the work function fit our model as the surface withdraws charge from the adsorbate. The changes in the computed vibrational frequencies also agree with the HREELS results at very low coverage. The C–O bond distance increases while the O–H bond decreases making a C–O bond breakage a possibility on K covered surfaces.     

Splitting of optical mode in (NH_4)_2 PtBr_6 studied by Raman scattering

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Study on optical wave scattering from slightly Gaussian rough surface of layered medium

The optical wave scattering from the slightly rough surface of three-layer medium is studied.The formulaes of the scattering coefficients for different polarizations are derived using the small perturbation method. A Gaussian rough surface is presented for describing rough surface of layered medium,the influence of the permittivity of layered medium,the mean layer thickness of intermediate medium,the surface roughness parameters and the incident wavelength on the bistatic scattering coefficient of HH polarization are obtained and discussed by numerical implementation.     

Surface rumples and band gap reductions of cubic BaZrO3 （001） surface studied by means of first-principles calculations

Electronic properties of the （001） surface of cubic BaZrO3 with BaO and ZrO2 terminations have been studied using first-principles calculations. Surface structure, partial density of states, band structure and surface energy have been obtained. We find that the largest relaxation appears in the first layer of atoms, and the relaxation of the BaO-terminated surface is larger than that of the ZrO2-terminated surface. The surface rumpling of the BaO-terminated surface is also larger than that of the ZrO2-terminated surface. Results of surface energy calculations reveal that the BaZrO3 surface is likely to be more stable than the PbZrO3 surface.     

The magnetic phases and structures of Ce(Ru1-xFex)2Ge2 studied by μ-SR

We report on the structures of the magnetic phases of CeRu₂Ge₂ and their evolution in the series Ce(Ru_1-xFe_x)₂Ge₂. The crossover behavior between the ferromagnetic ground state of CeRu₂Ge₂ to the paramagnetic ground state of CeFe₂Ge₂ is compared to the behavior in the series CeRu₂(Ge_1-xSi_x)₂. A profound difference is observed between these two series, which is in contradiction to the uniform behavior predicted by the Doniach-necklace model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Weathering of Martian and Earth surface studied by Mössbauer spectroscopy

Martian regolith and Earth’s basaltoid samples have been investigated by means of Mössbauer spectroscopy. The identification of the same minerals: olivine, pyroxene, magnetite, hematite and confrontation of the Fe^3?+?/Fe^2?+?, Fe^3?+?/Fe_tot, Fe^2?+?/Fe_tot ratios are presented. Co-existence of olivine and hematite in Martian regolith, absent in presented by authors terrestrial samples has been tentatively explained.     

Influence of the scattering potential model on low energy electron diffraction from Cu(001)−c(2 × 2)-Pb

A dynamical LEED intensity analysis is reported for Cu(001)−c(2 × 2)-Pb. The adsorbate layer distance from the substrate is determined as 2.29 Å, and the topmost interlayer spacing for the substrate is the same as in bulk Cu, in contrast to a contraction for clean Cu(001). This structural result is, within the accuracy reached, insensitive to changes in the assumed scattering potential models. The r-factors suggest a weak preference for an energy-dependent exchange correlation and a moderate one for adding a localized adsorption part inside the muffin-tin spheres. The sensitivity of spectra and r-factors to changes in the assumed isotropic Debye temperature for Pb suggests that vibrational anisotropy should be taken into account in order to improve the accuracy of the analysis. Calculated spin polarization spectra are very sensitive to the exchange approximation, the localized absorption and the Debye temperature. Together with experimental data, they should be useful in particular for determining the vibrational anisotropy.     

Self-organized patterning on Si(001) by ion sputtering with simultaneous metal incorporation

This report focuses on the effect of simultaneous Fe incorporation in the self-organized pattern formation on Si(001) by low-energy ion-beam sputtering. Experimental observations giving evidence for the correlation between different ion-beam parameters, Fe concentration on the substrate, and the resulting topography are shown. It was observed that the incorporation of Fe affects the evolution of the topography and it is a requisite for the formation of ripples at near-normal incidence. It is shown also that Fe is not homogeneously distributed on the surface, but there is a higher concentration at the crests of the ripples than at the valleys. For the experimental setup used for this study, the Fe flux that reaches the surface is determined mainly by the acceleration voltage (U _acc), while the ion energy (E _ion) and ion-beam incidence angle (α) control the concentration of Fe in the steady state. The adjustment of these operational parameters of the ion source enables the fine-tuning of surface patterns.     

Initial stage of Pd adsorption on Si(111)7 × 7 surface studied by AES and EELS

The initial stage of adsorption of Pd on a Si(111)7 × 7 surface has been studied by means of Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and surface work-function change. For Pd deposition at room temperature (RT) the Si(LVV) Auger signal intensity decays in a broken linear line. The structure factor, defined as the intensity ratio of the subpeak to the main one in Si(LVV) Auger spectra, increases up to a maximum around one monolayer coverages. In EELS spectra two peaks, characteristics of Pd, appear at the completion of the first Pd layer. Pd atoms deposited on Si(111) at RT form initially flat layers of a few monolayers height without mixing with substrate Si atoms. For Pd deposition at a moderately high temperature (MT) of about 300°C, however, the structure factor for Si(LVV) Auger spectra does not change. EELS peaks, characteristic of Si substrate, remain clearly even beyond one monolayer coverage. Pd atoms deposited at MT are unstable and easily diffuse into the bulk. We present evidences to support the “screening” model for the bond-breaking mechanism at the Pd/Si interface.     

Excitation of surface elasticity waves in piezoelectric media by ion beams∗

Kinetically it has been shown that by considering a semi-bounded piezoelectric medium with hexagonal symmetry with an ion beam flowing on its free surface, the surface elasticity waves can be excited on their surface-vacuum interface as a result of the piezoelectric effect.     

Photoluminescence properties of Er-doped β-FeSi2 grown by ion implantation

Photoluminescence (PL) properties of Er-doped β-FeSi₂ (β-FeSi₂:Er) and Er-doped Si (Si:Er) grown by ion implantation were investigated. In PL measurements at 4.2 K, the β-FeSi₂:Er showed the 1.54 μm PL due to the intra-4f shell transition of ⁴I_13/2→⁴I_15/2 in Er³⁺ ions without a defect-related PL observed in Si:Er. In the dependence of the PL intensity on excitation photon flux density, the obtained optical excitation cross-section σ in β-FeSi₂:Er (σ=7×10⁻¹⁷ cm²) is smaller than that in Si:Er (σ=1×10^-15 cm²). In the time-resolved PL and the temperature dependence of the PL intensity, the 1.54 μm PL in β-FeSi₂:Er showed a longer lifetime and larger activation energies for non-radiative recombination (NR) processes than Si:Er. These results revealed that NR centers induced by ion implantation damage were suppressed in β-FeSi₂:Er, but the energy back transfer from Er³⁺ to β-FeSi₂ was larger than Si:Er.     

Atomic structure of Cs grown on Si(0 0 1)(2×1) surface by coaxial impact collision ion scattering spectroscopy

The atomic structure and the saturation coverage of Cs on the Si(0 0 1)(2×1) surface at room temperature have been studied by coaxial impact collision ion scattering spectroscopy (CAICISS). For the atomic structure of saturated Cs/Si(0 0 1)(2×1) surface, it is found that Cs atoms occupy a single adsorption site at T3 on the Si(0 0 1) surface. The height of Cs atoms adsorbed at T3 site is 3.18±0.05 Å from the second layer of Si(0 0 1)(2×1) surface. The saturation coverage estimated from the measured CAICISS intensity ratio and the proposed atomic structure is found to be 0.46±0.06 ML.     

Kinetics of energy deactivation in the O2(1Δ)-I medium

The kinetics of energy-exchange and quenching processes in the O₂(¹Δ)-I medium plays an important role in the operation of the chemical oxygen-iodine laser. However, up to now, many of the key processes in this medium are not fully understood. In this work, the flow tube technique is used to determine the rate of excitation energy deactivation in the O₂(¹Δ)-I medium in the presence of small concentrations of water and carbon dioxide. The concentrations of electronically excited species are measured with spectrometers calibrated in absolute spectral responsivity. The effective rate constant for the deactivation of O₂(¹Δ) molecules in processes involving iodine atoms is determined. The results are compared to those obtained in previous works.     

Planarization of a surface of nanoporous silica–titania composition by atomic-molecular chemical assembly

The processes involved in the planarization of the surface of nanoporous SiO₂ by the atomicmolecular deposition of nanoscale TiO₂ films were studied in regimes with different degrees of penetration of TiO₂ into SiO₂ nanopores. The technological process parameters that correspond to different regimes of surface planarization were examined. The degree of penetration of TiO₂ into SiO₂ nanopores was monitored using reflection ellipsometry by measuring the depth distribution of the refraction index within the two-layer model.     

Self-assembly behaviour of amphiphilic diblock copolymer in selective solvents studied by synchrotron small-angle x-ray scattering

The aggregation behaviour of styrene-vinyl benzoic acid (PSm-b-PVBAn) amphiphilic diblock copolymers in selective solvents with different m and n was investigated by synchrotron small-angle x-ray scattering (SAXS). We have carried out a detailed analysis of scattering intensity, dimension, shape and microstructure of the diblock copolymers of narrow distribution in water, methanol, ethanol and isopropanol selective solvents, respectively. We have found that the aggregation behaviour of the copolymer depends on the nature of the solvent and the micelle forms fiat disc objects with the ratio of radius ω=0.4. The average radius gyration Rg of the copolymer decreases as solvents change from isopropanol to ethanol and to methanol, and increases with increasing pH in aqueous solution, but decreases with the addition of COCl2 in ethanol solvent. The scattering intensity of diblock copolymer micelle follows I(h) ∝ h^-α in different selective solutions, suggesting that the PSm-b-PVBAn coils have self-similar structure behaviour or a fractal structure in the selective solvents. All of these revealed that the aggregation behaviour of the diblock copolymer changes dramatically with experimental condition in the selective solvent. The increase of mass fractal dimension (Dm) from 2.12 to 2.47 indicates that the copolymer chain changes from a swollen coil to a rather compact disc in the course of changing solvents, decreasing surface fractal dimension (Ds) from 2.98 to 2.58 indicates that the copolymer micelle change from a rather rough surface to a smooth form in the course of increasing pH in aqueous solutions, and increasing Dm and Ds from 2.29 to 2.35 and 2.70 to 2.90, respectively, indicates the shrinkage of copolymer micelle to a rather compact and rough disc form by adding COCl2 in ethanol solvents.