Fluorinated graphene dielectric films obtained from functionalized graphene suspension: preparation and properties.

In the present study, we have examined the interaction between a suspension of graphene in dimethylformamide and an aqueous solution of hydrofluoric acid, which was found to result in partial fluorination of suspension flakes. A considerable decrease in the thickness and lateral size of the graphene flakes (up to 1-5 monolayers in thickness and 100-300 nm in diameter) with increasing duration of fluorination treatment is found to be accompanied by a simultaneous transition of the flakes from the conducting to the insulating state. Smooth and uniform insulating films with a roughness of ∼2 nm and thicknesses down to 20 nm were deposited from the suspension on silicon. The electrical and structural properties of the films suggest their use as insulating elements in thin-film nano- and microelectronic device structures. In particular, it was found that the films prepared from the fluorinated suspension display rather high breakdown voltages (field strength of (1-3) × 10(6) V cm(-1)), ultralow densities of charges in the film and at the interface with the silicon substrate in metal-insulator-semiconductor structures (∼(1-5) × 10(10) cm(-2)). Such excellent characteristics of the dielectric film can be compared only to well-developed SiO2 layers. The films from the fluorinated suspension are cheap, practically feasible and easy to produce.

Electronic structure of ß-RbSm(MoO4)2 and chemical bonding in molybdates.

Microcrystals of orthorhombic rubidium samarium molybdate, ß-RbSm(MoO4)2, have been fabricated by solid state synthesis at T = 450 °C, 70 h, and at T = 600 °C, 150 h. The crystal structure has been refined by the Rietveld method in space group Pbcn with cell parameters a = 5.0984(2), b = 18.9742(6) and c = 8.0449(3) Å (R(B) = 1.72%). Thermal properties of ß-RbSm(MoO4)2 were traced by DSC over the temperature range of T = 20-965 °C, and the earlier reported ß â†” α phase transition at T ∼ 860-910 °C was not verified. The electronic structure of ß-RbSm(MoO4)2 was studied by employing theoretical calculations and X-ray photoelectron spectroscopy. It has been established that the O 2p-like states contribute mainly to the upper part of the valence band and occupy the valence band maximum, whereas the Mo 4d-like states contribute mainly to the lower part of the valence band. Chemical bonding effects have been analysed from the element core level binding energy data. In addition, it was found that the luminescence spectrum of ß-RbSm(MoO4)2 is rather peculiar among the Sm(3+) containing materials. The optical refractive index dispersion in ß-RbSm(MoO4)2 was also predicted by the first-principles calculations.

Electronic structure of α-SrB4O7: experiment and theory.

The investigation of valence band structure and electronic parameters of constituent element core levels of α-SrB(4)O(7) has been carried out with x-ray photoemission spectroscopy. Optical-quality crystal α-SrB(4)O(7) has been grown by the Czochralski method. Detailed photoemission spectra of the element core levels have been recorded from the powder sample under excitation by nonmonochromatic Al Kα radiation (1486.6 eV). The band structure of α-SrB(4)O(7) has been calculated by ab initio methods and compared to XPS measurements. It has been found that the band structure of α-SrB(4)O(7) is weakly dependent on the Sr-related states.

The electronic structure of RbTiOPO4 and the effects of the A-site cation substitution in KTiOPO4-family crystals.

The electronic structure of RbTiOPO(4) has been investigated with x-ray photoemission spectroscopy. Detailed photoemission spectra of the element core levels have been recorded under excitation by nonmonochromatic Al Kα radiation (1486.6 eV). The chemical bonding parameters are compared to those reported for complex titanates and phosphates. The band structures of KTiOPO(4), RbTiOPO(4), K(0.535)R(0.465)TiOPO(4) and TlTiOPO(4) have been calculated by ab initio methods and compared to available experimental results. It is found that the band structure of KTP-type phosphate crystals is weakly dependent on the nature of the A-site (A=K, Rb, Tl) element.

The Investigation of Intermediate Stage of Template Etching with Metal Droplets by Wetting Angle Analysis on (001) GaAs Surface.

In this work, we study metal droplets on a semiconductor surface that are the initial stage for both droplet epitaxy and local droplet etching. The distributions of droplet geometrical parameters such as height, radius and volume help to understand the droplet formation that strongly influences subsequent nanohole etching. To investigate the etching and intermixing processes, we offer a new method of wetting angle analysis. The aspect ratio that is defined as the ratio of the height to radius was used as an estimation of wetting angle which depends on the droplet material. The investigation of the wetting angle and the estimation of indium content revealed significant materials intermixing during the deposition time. AFM measurements reveal the presence of two droplet groups that is in agreement with nanohole investigations. To explain this observation, we consider arsenic evaporation and consequent change in the initial substrate. On the basis of our analysis, we suggest the model of droplet evolution and the formation of two droplet groups.

Optical properties of LiGaS(2): an ab initio study and spectroscopic ellipsometry measurement.

Electronic and optical properties of lithium thiogallate crystal, LiGaS(2), have been investigated by both experimental and theoretical methods. The plane-wave pseudopotential method based on DFT theory has been used for band structure calculations. The electronic parameters of Ga 3d orbitals have been corrected by the DFT+U methods to be consistent with those measured with x-ray photoemission spectroscopy. Evolution of optical constants of LiGaS(2) over a wide spectral range was determined by developed first-principles theory and dispersion curves were compared with optical parameters defined by spectroscopic ellipsometry in the photon energy range 1.2-5.0 eV. Good agreement has been achieved between theoretical and experimental results.