Multi-quantum well heterostructures (MQWHs) of the novel Ga(NAsP)/GaP material system have been grown, pseudomorphically strained to GaP-substrate. The crystalline perfection is verified by transmission electron microscopy (TEM). For As-concentrations in excess of about 70%, a direct band structure and adequate luminescence efficiency for laser device application is observed. Temperature-dependent photoluminescence (PL) investigations show the influence of carrier localisation and non-radiative recombination processes typical for dilute nitride materials. With rising N content in the active material, the emission wavelength shifts towards longer wavelength, leading to Ga(NAs)/GaP MQW structures with photon energies below the indirect band gap of silicon (Si). At the same time the luminescence intensity drops due to an increase in non-radiative carrier traps and/or structural degradation. 相似文献
The scope and limitations of the Takai-Utimoto reagent to induce the cyclization of olefinic-esters is described. Critical is the steric environment about both the ester and the olefin. Mechanistically, these results support the hypothesis that cyclized product comes from an olefin metathesis, carbonyl-olefination sequence. 相似文献
In this work, the optical and structural properties of high k materials such as tantalum oxide and titanium oxide were studied by spectroscopic ellipsometry, where a Tauc-Lorentz dispersion model based in one (amorphous films) or two oscillators (microcrystalline films) was used. The samples were deposited at room temperature by radio frequency magnetron sputtering and then annealed at temperatures from 100 to 500 °C. Concerning the tantalum oxide films, the increase of the annealing temperature, up to 500 °C does not change the amorphous nature of the films, increasing, however, their density. The same does not happen with the titanium oxide films that are microcrystalline, even when deposited at room temperature. Data concerning the use of a four-layer model based on one and two Tauc-Lorentz dispersions is also discussed, emphasizing its use for the detection of an amorphous incubation layer, normally present on microcrystalline films grown by sputtering. 相似文献
Reactions of the hydrated electron, H atoms, 2-propanol, and methanol radicals with the TiO2 nano-particles have been studied either directly or by competition kinetics. The radicals were produced by radiolysis of 2-propanol, t-butanol, or methanol aqueous solutions in acid pH's. The reactions involve electron injection to the conduction band. As expected, the t-butanol radical is inert towards TiO2 under our conditions, while the other reducing radicals react with TiO2. The reactivity decreases in the order: eaq−>H>CH3COHCH3>CH2OH. Two TiO2 nanocrystallite sizes, with average diameters of 1.0 and 4.7 nm were compared. For equal concentrations (in terms of TiO2 molecules), the rate of electron injection shows relatively little dependency on particle size. The rates of interfacial electron transfer and transfer coefficient are also reported. 相似文献
X-ray photoelectron spectroscopy (XPS) was adopted for the analytical characterization of composite titanium dioxide–poly(vinylidenefluoride) (TiO2–PVDF) films developed for applications in the photocatalytic degradation of pollutants.
The composites were deposited on glass substrates by casting or spin coating from TiO2–PVDF suspensions in dimethylformamide (DMF). XPS data on the TiO2–PVDF surface composition were used to optimize preparation conditions (composition of the TiO2/PVDF suspension, deposition technique) in terms of titanium dioxide surface amount and film stability.
The use of spin-coating deposition and the increase of TiO2 amount in the DMF suspensions were found to improve the titanium surface content, although high TiO2/PVDF ratios led to film instability. PVDF–TiO2 films were also used in preliminary photocatalytic degradation tests on isoproturon, a phenylurea herbicide, under solar UV irradiation; the results were compared to direct photolysis to evaluate the catalytic efficiency of immobilized TiO2 and the role played by the PVDF film during the degradation process. 相似文献
Titanium tetrachloride promoted reaction of silyl ketene acetals with epoxides, followed by acidic work-up, affords butanolides in moderate/good yields. With epihalohydrins the reaction is regioselective and occurs at the less substituted end of the epoxide; the γ-haloalkyl-γ-butanolides thus obtained can be further transformed into various products. 相似文献
Synthesis and Structure of K3N Two phases in the binary system K/N have been obtained via co‐deposition of potassium and nitrogen onto polished sapphire at 77 K and subsequent heating to room temperature. The powder diffraction pattern of one of these phases can be satisfactorily interpreted by assuming the composition K3N, and the anti‐TiI3 structure‐type, which is also adopted by Cs3O. The resulting hexagonal lattice constants are: a = 779.8(2), c = 759.2(9) pm, Z = 2, P63/mcm. Comparison with possible structures of K3N generated by computational methods and refined at Hartree‐Fock‐ and DFT level, reveals that the energetically most favoured structure has not formed (presumable Li3P‐type), but instead one of those with very low density. In this respect, the findings for K3N are analogous to the results on Na3N. The thermal evolution of the deposited starting mixture has been investigated. Hexagonal K3N transforms to another K/N phase at 233 K. Its XRD can be fully indexed resulting in an orthorhombic cell a = 1163, b = 596, c = 718 pm. Decomposition leaving elemental potassium as the only residue occurs at 263 K. 相似文献
This case report describes a one-stage technique for long-term voice restoration and laryngeal reconstruction in the treatment of Teflon (Dupont, Wilmington, Delaware) granuloma. A patient who presented with severe dysphonia underwent resection of a Teflon granuloma via a lateral laryngotomy. A pedicled strap muscle flap was used to reconstruct the paraglottic space. The muscle flap was positioned through the lateral laryngotomy with direct endoscopic visualization of the endolarynx to ensure correct vertical positioning and medialization of the vocal fold. The muscle flap was secured in this position with suture fixation. The trapdoor piece of cartilage that was elevated to create the window in the lateral thyroid lamina was repositioned over the pedicled muscle flap and reinforced with a titanium miniplate, which was secured to the remaining thyroid cartilage. The patient had excellent voice results and has not required revision or augmentation. Reinforcement of the lateral thyroid lamina using titanium miniplate fixation helps to stabilize the muscle pedicle flap and the position of the vocal fold, in this case resulting in good long-term voice results after a single-stage reconstruction. 相似文献
The performance of high power transistor devices is intimately connected to the substrate thermal conductivity. In this study, the relationship between thermal conductivity and dislocation density is examined using the 3 omega technique and free standing HVPE GaN substrates. Dislocation density is measured using imaging cathodoluminescence. In a low dislocation density regime below 105 cm−2, the thermal conductivity appears to plateau out near 230 W/K m and can be altered by the presence of isotopic defects and point defects. For high dislocation densities the thermal conductivity is severely degraded due to phonon scattering from dislocations. These results are applied to the design of homoepitaxially and heteroepitaxially grown HEMT devices and the efficiency of heat extraction and the influence of lateral heat spreading on device performance are compared. 相似文献
Monoclonal antibodies specific for thiabendazole were immobilized to silicon, silicon dioxide, stoichiometric silicon nitride,
and silicon-rich silicon nitride surfaces. This work provides the foundation for the development of a homogeneous sensor system
for rapid detection and quantification of thiabendazole residues in produce and animal tissue. Immobilization was performed
via aqueous silanization of the substrate followed sequentially by treatment with glutaraldehyde and contact with antibody
solution in the presence of detergent. Surfaces were challenged with thiabendazole-horseradish peroxidase conjugate in an
ELISA format to estimate immobilized antibody load. A stable and reproducible surface loading of 2 x 1011 antibodies/cm2 was obtained only after surfaces received postimmobilization treatments to remove nonspecifically adsorbed antibody. No difference
in surface loading was noted when using 30% hydrogen peroxide rather than nitric acid for silanol activation. Little difference
was noted among the antibody loadings achieved on the various silicon substrates. Bound antigen-enzyme conjugate was eluted
with 0.1N acetic acid and reproducible surface activity was measured for up to four consecutive antigen challenges. Immobilized
antibody surfaces were stabilized with 2% sucrose, dehydrated at 37‡C and stored in vacuum or stored at 4‡C in phosphate buffered
saline containing 0.01% sodium azide without significant loss of activity. 相似文献