η5-Phospholylgallium: The First Monomeric Polyhapto Compound between a Phospholyl Ligand and a Main Group Metal

Monomeric polyhapto-bound phospholyl compounds were hitherto unknown for the main group elements. Use of a solution of metastable GaBr has allowed the synthesis of monomeric η⁵-phospholylgallium, which has been characterized by X-ray structure analysis as the Cr(CO)₅ complex 1 .     

Enantioselective Ring Opening of Epoxides with 4-Methoxyphenol Catalyzed by Gallium Heterobimetallic Complexes: An Efficient Method for the Synthesis of Optically Active 1,2-Diol Monoethers

Useful chiral building blocks such as 1,2-diols can be obtained by the enantioselective ring opening of achiral epoxides with oxygen nucleophiles. The ring opening is carried out effectively (up to 94 % ee) with 4-methoxyphenol and catalytic amounts of gallium complexes. The novel complex GaSO 1 displays a particularly high catalytic activity.     

Theoretical investigation of the GaF molecule and its positive ion

Coupled pair approximation and configuration interaction calculations were carried out on the gallium fluoride molecule and its positive ion with flexible basis sets. Spectroscopic constants of these species were examined in detail through step-wise extensions of correlating space. The contribution from correlations of the semi-core 3d electrons in Ga was found to be sizable. The bonding character was revealed to be highly ionic even for the positive ion. Received: 13 June 1998/Accepted: 28 August 1998 / Published online: 7 December 1998     

Influence of deposition temperature on morphological, optical, electrical and opto-electrical properties of highly textured nano-crystalline spray deposited CdO:Ga thin films

This study investigated the effect of deposition temperature on the morphological, optical, electrical and opto-electrical properties of CdO:Ga films prepared by a cost effective spray pyrolysis deposition method. The substrate temperature was varied from 275 to 375 °C, in steps of 25 °C. The XRD patterns reveal that films are polycrystalline with cubic structure and are highly textured along (2 0 0) preferential orientation. The crystallinity and crystallite size increases with deposition temperature. The SEM images confirmed these results and showed larger grains and more crystallization for the higher deposition temperature. The electrical studies show degenerate, n-type semiconductor nature with minimum resistivity of 1.93 × 10⁻⁴ Ω cm. Temperature dependence of electrical conductivity shows a semiconducting behavior with a spectrum of activation energy. The electrical conductivity of the film dependence of temperature shows the thermally activated band conduction mechanism. The optical gap varies from 2.54 to 2.74 eV. The highest figure of merit observed in the present study is 9.58 × 10⁻³ Ω⁻¹ and shows improvement than our previous reports. The blue shift of absorption edge (or bandgap widening BGW) can be described by the Moss-Burstein (M-B) effect in which the optical absorption edge of a degenerate n-type semiconductor is shifted towards higher energy.     

Fabrication of microchannels in single-crystal GaN by wet-chemical-assisted femtosecond-laser ablation

We investigated micro- and nano-fabrication of wide band-gap semiconductor gallium nitride (GaN) using a femtosecond (fs) laser. Nanoscale craters were successfully formed by wet-chemical-assisted fs-laser ablation, in which the laser beam is focused onto a single-crystal GaN substrate in a hydrochloric acid (HCl) solution. This allows efficient removal of ablation debris produced by chemical reactions during ablation, resulting in high-quality ablation. However, a two-step processing method involving irradiation by a fs-laser beam in air followed by wet etching, distorts the shape of the crater because of residual debris. The threshold fluence for wet-chemical-assisted fs-laser ablation is lower than that for fs-laser ablation in air, which is advantageous for improving fabrication resolution since it reduces thermal effects. We have fabricated craters as small as 510 nm by using a high numerical aperture (NA) objective lens with an NA of 0.73. Furthermore, we have formed three-dimensional hollow microchannels in GaN by fs-laser direct-writing in HCl solution.     

碱性品红分子在纳米磷化镓粒子表面的吸附取向(英文)

利用表面增强拉曼光谱,初步确定了吸附于纳米磷化镓(GaP)粉体表面的碱性品红分子的取向。在295K时,将50 mg GaP粉体分别置于50 ml,4.7×10-3M和50 ml,4.74×10-6M碱性品红水溶液中。对由较高浓度溶液形成的吸附系统持续搅拌24小时;而对极稀溶液吸附系统则连续搅拌处理7天。在经过过滤、干燥处理后,吸附有染料分子的GaP粉体被直接用于碱性品红的表面拉曼光谱测试。通过对染料分子中央碳原子呼吸振动和氮-苯环伸缩振动模式的相对强度进行分析可知:在较高浓度的溶液中,染料分子主要以一种混合取向方式吸附于GaP粉体表面上,即“端基接触”和“平躺”两种方式;而在极稀溶液中,染料分子则仅以“端基接触”方式吸附于GaP粉体表面上。     

Hydrogen adsorption on GaAs(0 0 1)-c(4 × 4)

Exposure of the As-terminated GaAs(0 0 1)-c(4 × 4) reconstructed surface to atomic hydrogen (H) at different substrate temperatures (50-480 °C) has been studied by reflection high-energy electron diffraction (RHEED) and scanning tunnelling microscopy (STM). Hydrogen exposure at low temperatures (∼50 °C) produces a disordered (1 × 1) surface covered with AsH_x clusters. At higher temperatures (150-400 °C) exposure to hydrogen leads to the formation of mixed c(2 × 2) and c(4 × 2) surface domains with H adsorbed on surface Ga atoms that are exposed due to the H induced loss of As from the surface. At the highest temperature (480 °C) a disordered (2 × 4) reconstruction is formed due to thermal desorption of As from the surface. The results are consistent with the loss of As from the surface, either through direct thermal desorption or as a result of the desorption of volatile compounds which form after reaction with H.     

Growth behavior of GaN film along non-polar [1 1 -2 0] directions

We studied the atomic assembly mechanisms of non-polar GaN films by the molecular dynamics method as a function of the N:Ga flux ratio at a fixed adatom energy on non-polar planes. Our study revealed that high quality crystal growth occurred only when off-lattice atoms (which are usually associated with amorphous embryos or defect complexes) formed during deposition were able to move to unoccupied lattice sites by thermally activated diffusion processes, which attests to the experimental difficulties in obtaining smooth surfaces due to dense stacking faults lying in non-polar GaN. Furthermore, surface structures on different planes played an important role. We further suggested favorable conditions for growing high quality GaN films and nano-structures along non-polar directions.     

Efficient excitation and amplification of the surface plasmons

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (Λ = 700 nm) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module.Apart from this, grating devices of smaller periodicity (Λ = 280 nm) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).     

Surface reactions of 2-iodopropane on GaAs(1 0 0)

The surface reactions of 2-iodopropane ((CH₃)₂CHI) on gallium-rich GaAs(1 0 0)-(4 × 1), was studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). CH₃CHICH₃ adsorbs molecularly at 120 K but dissociates below room temperature to form chemisorbed 2-propyl ((CH₃)₂CH) and iodide (I) species. Thermal activation causes desorption of the molecular species at 240 K, and this occurs in competition with the further reactions of the (CH₃)₂CH and I chemisorbed species. Self-coupling of the (CH₃)₂CH results in the formation of 2,3-dimethylbutane ((CH₃)₂CH-CH(CH₃)₂) at 290 K. β-Hydride elimination in (CH₃)₂CH yields gaseous propene (CH₃CHCH₂) at 550 K while reductive elimination reactions of (CH₃)₂CH with surface hydrogen yields propane (CH₃CH₂CH₃) at 560 K. Recombinative desorption of the adsorbed hydrogen as H₂ also occurs at 560 K. We observe that the activation barrier to carbon-carbon bond formation with 2-propyls on GaAs(1 0 0) is much lower than that in our previous investigations involving ethyl and 1,1,1-trifluoroethyl species where the β-elimination process was more facile. The difference in the surface chemistry in the case of 2-propyl species is attributable to its rigid structure resulting from the bonding to the surface via the second carbon atom, which causes the methyl groups to be further away from the surface than in the case of linear ethyl and 1,1,1-trifluoroethyl species. The β-hydride and reductive elimination processes in the adsorbed 2-propyl species thus occurs at higher temperatures, and a consequence of this is that GaI desorption, which is expected to occur in the temperature range 550-560 K becomes suppressed, and the chemisorbed iodine leaves the surface as atomic iodine.