Search

Seven bis(phosphine) cobalt complexes and one tris(phosphine) cobalt complex were tested for hydrosilylation of 1,3-diynes, among which dppp-CoCl2 (1 mol %) exhibited the best regio- and stereosele...

Four Ru(II)-NC complexes were tested as catalysts for semihydrogenation of internal alkynes to (E)-alkenes with ethanol, and the complex {(C5H4N)(C6H4)}RuCl(CO)(PPh3)2 (1a) showed the highest activ...

Thermal treatment of Ru3(CO)12 with 3-(6-ethyl-2-pyridyl)indene in refluxing toluene gave a triruthenium carbonyl complex {μ2-η5:η1-(C2H5C5H4N)(C9H5)}Ru3(CO)9 (1) via regioselective C(sp2)–H activation. While reaction of 2-methyl-3-(6-ethyl-2-pyridyl)indene with Ru3(CO)12 generated a dinuclear ruthenium complex {(C2H5C5H4N)(μ2-η5,η1-C9H5CH2)}Ru2(CO)5 (2) via regioselective C(sp3)–H bond activation. When the pyridyl rings were replaced by more bulky quinolinyl rings, only η5-indenyl ruthenium complexes were produced. The molecular structure of 2 was determined by X-ray diffraction analysis.

Thermal treatment of the trinuclear ruthenium complex {μ2-η5:η1-(C5H4N)(C9H5)}Ru3(CO)9 (1) with 1,5-heptadiene, diallyl sulfide, 1,4-hexadiene, and 1,7-octadiene respectively generated the series of diruthenium products {(C5H4N)(μ2-η5,η1-C9H5CHCH2CH2R)}Ru2(CO)x (4, R = −CH2CH═CHCH3; 6, R = SCH2CH═CH2; 7, R = −CH═CHCH3; 8, R = −(CH2)3CH═CH2) via the insertion of an terminal C═C bond into the Ru–C(η1) bond of 1. When 1 was treated with diallyl ether, the complex {(C5H4N)(μ2-η5,η3-C9H5CCH2CH2OCCHCH3)}Ru2(CO)4 (5) with a five-membered oxygen-containing heterocycle was produced. Reactions of 2-methyl-3-(2-pyridyl)indene or 2,5-dimethyl-3-(2-pyridyl)indene with Ru3(CO)12 gave the cycloruthenated complexes {(C5H4N)(μ2-η5,η1-RC9H4CH2)}Ru2(CO)5 (9, R = H; 10, R = CH3) with structures similar to those of 4, 7, and 8, via C(sp3)–H activation. The molecular structures of 5–7 and 10 were determined by X-ray diffraction.

DeepLab v3+ neural network shows excellent performance in semantic segmentation. In this paper, we proposed a segmentation framework based on DeepLab v3+ neural network and applied it to the problem of hyperspectral imagery classification (HSIC). The dimensionality reduction of the hyperspectral image is performed using principal component analysis (PCA). DeepLab v3+ is used to extract spatial features, and those are fused with spectral features. A support vector machine (SVM) classifier is used for fitting and classification. Experimental results show that the framework proposed in this paper outperforms most traditional machine learning algorithms and deep-learning algorithms in hyperspectral imagery classification tasks.

A combined experimental and computational investigation of the CO dissociation properties of three [Fe]-hydrogenase models, [(2-CH2CO-6-HOC5H3N)Fe(CO)3I] (1), [(2-CH2CO-6-MeOC5H3N)Fe(CO)3I] (2), and [(2-CH2CO-6-t-BuOC5H3N)Fe(CO)3I] (3), shows equilibria of tricarbonyl and dicarbonyl complexes in solution. In CH3CN, 1 transforms to the solvated product [(2-CH2CO-6-HOC5H3N)Fe(CO)2(CH3CN)I] (7). The reactivity of 2 with PPh3 was also explored, giving [(2-CH2CO-6-MeOC5H3N)Fe(CO)2(PPh3)I] (8) via one CO substitution by PPh3.

Five ruthenium(ii) complexes were synthesized, including (HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)Cl2 (3), [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2Cl][PF6] (4) and [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2OH][PF6] (5) bearing an unsymmetrical pincer NNN ligand with a 2-hydroxypyridylmethylene fragment, and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][Cl]2 (6) and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][PF6]2 (7) containing 2-methoxypyridylmethylene moieties. 4 reacts with H2O at room temperature to give 5 whose crystal structure reveals the existence of intramolecular hydrogen-bonding between its two -OH groups. 3 exhibits high catalytic activity for transfer hydrogenation of ketones.

In this paper, 850V breakdown voltage LDMOS fabricated on Simbond SOI wafer are reported. Simbond SOI wafers with 1.5@mm top silicon, 3@mm buried oxide layer, and n-type heavy doped handle wafers are used. In order to achieve uniform lateral electric field and shorten the vertical impact ionization integration path simultaneously, an optimized 60@mm drift region implant mask is designed to realize a linearly graded doping profile, and silicon thickness in the drift region is reduced from 1.5@mm to about 0.26@mm by thick field oxide process. CMOS compatible SOI LDMOS processes are designed and implemented successfully. Off-state breakdown voltage of SOI LDMOS can reach 850V, and the specific on-resistance is 56@Wmm^2. Experimental results also show the thickness of the top silicon in the drift region has a good uniformity. The performance of SOI LDMOS indicated that Simbond SOI wafers are good choice for thin film high voltage devices.

Photocatalytic degradation of phenanthrene and pyrene on soil surfaces in the presence of nanometer rutile TiO2 was investigated. After being spiked with phenanthrene and pyrene, soil samples loaded with different dosages of nanometer rutile TiO2 (0, 1, 2, 3, and 4 wt%) were exposed to UV-irradiation for 25 h. The results indicated that the photocatalytic degradation of phenanthrene and pyrene followed the pseudo-first-order kinetics. The catalyst dosage of 2 wt% was chosen as the optimal one for further studies. According to the half-life, the degradation rate of the phenanthrene and pyrene on soil surfaces was related to their absorption spectra in soil and oxidation-half-wave-potential. In addition, the degradation of phenanthrene and pyrene increased along with increasing H2O2, light intensity and humic acids. All results indicated that the photocatalytic method in the presence of nanometer rutile TiO2 was an advisable choice for the treatments of PAHs polluted soil in the future.

Titanium dioxide nanotubes, made by anodization, are highly sensitive to hydrogen; for example, cycling between nitrogen atmosphere and 1000 ppm hydrogen a variation in measured resistance of 10 3 is seen for 46 nm diameter nanotubes at 290 °C. The hydrogen sensors are completely reversible and have response times of approximately 150 s. Field emission scanning electron microscopy and Glancing angle X-ray diffraction (GAXRD) are used to study the surface morphology and crystal structure of the nanotubes.

The effect of pore size and uniformity on the response of nanoporous anodized alumina to ammonia at room temperature, 23 °C, is reported. Pore sizes examined range from 13.6 to 48 nm, with pore size standard deviations ranging from 2.6 to 7.8 nm. The nanoporous alumina films were used in conjunction with 98.5 and 32.5 MHz surface acoustic wave (SAW) devices, and as impedance-based sensors, both of which were found sensitive to ammonia. The SAW devices showed a frequency shift of approximately 0.001% per percentage change in ammonia concentration. Similarly, at 5 kHz an alumina sensor with an average pore size of 13.6 nm, standard deviation 2.6 nm, exhibits a factor of two change in impedance magnitude as it is cycled between an ammonia and argon environment. The nanoporous alumina-based sensors demonstrated a fast response time (≈30–40 s) and recovery time (≈60–80 s), and complete recovery upon removal from an ammonia ambient. We believe the enhanced physisorption of ammonia on alumina films due to the large surface area, provided by the mesoporous topology, is responsible for the sensing behavior.

The use of mechanically robust nanoporous alumina capsules, with highly uniform pores of 25 nm to 55 nm, for controled drug delivery is demonstrated. The nanoporous alumina capsules were fabricated by anodization of an aluminum tube, resulting in a highly uniform, large surface area, relatively inexpensive device suitable for biofiltration applications. Characterization of diffusion from the nanoporous capsules using fluorescein isothiocyanate and dextran conjugates of varying molecular weight, showed that molecular transport could be readily controlled by selection of capsule pore size. A branched membrane structure, with a stepwise change in pore size from large to small, is used to provide small pore-sized membranes with sufficient mechanical strength for handling.

The stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments. The tubes crystallized in the anatase phase at a temperature of about 280 °C irrespective of the ambient. Anatase crystallites formed inside the tube walls and transformed completely to rutile at about 620 °C in dry environments and 570 °C in humid argon. No discernible changes in the dimensions of the tubes were found when the heat treatment was performed in oxygen. However, variations of 10% and 20% in average inner diameter and wall thickness, respectively, were observed when annealing in a dry argon atmosphere at 580 °C for 3 h. Pore shrinkage was even more pronounced in humid argon environments. In all cases the nanotube architecture was found to be stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotube array.

The effect of pore size and uniformity on the humidity response of nanoporous alumina, formed on aluminum thick films through an anodization process, is reported. Pore sizes examined range from approximately 13 to 45 nm, with a pore size standard deviations ranging from 2.6 to 7.8 nm. The response of the material to humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm (standard deviation 2.6 nm) exhibits a well-behaved change in impedance magnitude of 103 over 20% to 90% relative humidity. Increasing pore size decreases the humidity range over which the sensors have high sensitivity and shifts the operating range to higher humidity values. Cole–Cole plots of 5 to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of water adsorption and ion migration within the adsorbed water layer. The presence of impurity ions within the highly ordered nano-dimensional pores, accumulated during the anodization process, appear highly beneficial for obtaining a substantial variation in measured impedance over a wide range of humidity values.

The effect of pore size and uniformity on the response of nanoporous alumina, formed on aluminum thick films through an anodization process, to ammonia and humidity at room temperature is reported. Pore sizes examined range from 13 nm to 48 nm, with pore size standard deviations ranging from 2.6 nm to 7.8 nm. The response of the material to ammonia and humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm, standard deviation 2.6 nm, exhibits a factor of two change in impedance magnitude as it is cycled between an ammonia and argon environment. At 5 kHz the same sensor exhibits a well-behaved change in impedance magnitude of 10 3 over 20% to 90% relative humidity. Cole-Cole plots of the 5 Hz to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of adsorption and ion migration. Key words: Ammonia, Nanoporous, Impedance spectroscopy, Alumina, Humidity, Mesoporous.

Titanium oxide nanotubes were fabricated by anodic oxidation of a pure titanium sheet in an aqueous solution containing 0.5 to 3.5 wt% hydrofluoric acid. These tubes are well aligned and organized into high-density uniform arrays. While the tops of the tubes are open, the bottoms of the tubes are closed, forming a barrier layer structure similar to that of porous alumina. The average tube diameter, ranging in size from 25 to 65 nm, was found to increase with increasing anodizing voltage, while the length of the tube was found independent of anodization time. A possible growth mechanism is presented.

The influence of boron atoms on the growth of self-organized Ge quantum dots (QDs) on Si(100) substrate is studied by atomic force microscopy (AFM). The boron coverage varied from 0 monolayers (ML) to 0.3 ML. AFM observation shows that the boron atoms have a great influence on the size, uniformity and the density of Ge QDs. In the presence of 0.2 ML of boron atoms, the growth of quite uniform Ge QDs is achieved with a mean base diameter of 60 nm and areal density of 6×10 9 cm −2 . The mechanism of B atom influence on the growth of Ge QDs is discussed.

The thermal stability of a SiGe/Si quantum well grown by molecular-beam epitaxy is studied by using the admittance spectroscopy technique. The values of activation energies of hole emission from the subbands in the SiGe/Si quantum well are derived from the admittance spectra. After annealing the sample at different temperatures, the activation energy varies in different behaviors. There is no significant change of the activation energy after annealing at 700 °C for 40 min. At the annealing temperature of 900 °C, the decrease of the activation energy with annealing time could be attributed to the interdiffusion of Ge, Si atoms at the heterointerfaces and the strain relaxation effect. An unexpected phenomenon is observed at the annealing temperature of 800 °C, i.e., the activation energy increases with the annealing time. This extraordinary phenomenon is supposed to be caused by the change of the well potential shape due to the B out-diffusion from the well to the Si barrier.

Synchrotron radiation x-ray reflectivity measurement is used to study the concentration profile of a delta-doped Er layer in Si epitaxial film grown by molecular-beam epitaxy. The oscillation of the reflectivity amplitude as a function of reflection angle is observed in the experiment. By doing a theoretical simulation, the concentration profile of Er atoms could be derived. It is shown that the originally grown delta-doped Er layer changes into an exponentially decayed function due to the Er segregation. The temperature dependence of the 1/e decay length indicates that the segregation is a kinetically limited process. The activation energy is determined to be 0.044 +/- 0.005 eV. [S0163-1829(99)11515-7].

The defects induced by boron-ion implantation with a relatively low dosage of 1 x 10 12 cm -2 in Si 1-x Ge x /Si single quantum wells are studied by deep level transient spectroscopy (DLTS). For low Ge content x, a defect level H 2 at an energy of 0.52 eV above the silicon valence band edge was found in the well region and its boundaries. For samples with higher Ge content, such that the strain is released, an electron trap E 2 rather than H 2 is formed by the ion implantation. Rapid thermal annealing at 600°C removes most of the H 2 defects induced by the ion implantation without changing the properties of the quantum well.

Photoabsorption and photoresponse of Si Si 1−x Ge x quantum wells are studied by using 45° unpolarized light field. Besides the free carrier absorption, the absorption peaks corresponding to both intersubband and intervalence band transitions are observed. We find that the intervalance band transitions are Ge composition dependent, but the intersubband transitions are not sensitive to Ge composition.

The admittance spectroscopy technique has been used to study the hole confinement in boron δ-doped Si quantum wells. A carrier thermal emission model is proposed to derive the activation energies of holes confined in the quantum wells from the measured conductance spectra. For the same peak doping concentration, the conductance peak shifts towards higher temperatures as the thickness of the δ-doped layer increases. The activation energies obtained from the measurements coincide well with the results of a self-consistent calculation of the subbands in the quantum wells. It verifies that the conductance peaks correspond to the hole emissions from the hole ground states in the δ-quantum wells to the Si valence band.

The interfacial defects at the p‐Si epitaxial layer/p‐Si substrate interface have been studied by deep‐level transient spectroscopy (DLTS). By solving Poisson equation, the electron concentration at the defect level varied with external voltage is derived. The emission and capture of electrons at the defect level, which are not observable in conventional DLTS, can be detected simultaneously in a single temperature scan by properly choosing the experimental parameters. The experimental results show that the energy level of the interfacial defects is located at Ec−0.30 eV.

The ion beam channeling technique has been used to characterize the SiGe/Si structure. It reveals different relative yield between and aligned spectra for strained SiGe layer, silicon buffer layer and silicon substrate which depends on different atomic arrangement.

A low temperature substrate surface cleaning procedure for silicon MBE has been studied. By using HF dipping followed by a two-step annealing, we achieved great suppression of the interfacial boron spike down to the concentration below 1015 cm-3 and reduction of the density of deep level defects down to below 1012 cm-3. The preheating temperature to obtain a clear (2 × 1) RHEED pattern can also be lowered to 300–400°C.

Aligned, open-tipped carbon nanotube arrays of high density and uniformity were synthesized via a flame method on silicon substrates using a nanoporous template of anodized aluminum oxide from which the nanotubes were grown. The diameter and length of the nanotubes are controlled by the geometry of the aluminum oxide template. These results show the feasibility of integration between carbon nanotube arrays and silicon microelectronics.

An ethylene-air laminar diffusion flame successfully provided silicon substrates of anodic aluminum oxide (AAO) template with vertically oriented well-aligned carbon nanotubes. Field emission scanning electron microscopy (SEM) showed that open-tipped carbon nanotubes consisting of tube elements with the same length and diameter uniformly coated the template. High-resolution transmission electron microscopy (TEM) analyses revealed these nanotubes to be multiwalled carbon nanotubes, some well graphitized. It was found that cobalt catalyst particles, but not the porous aluminum templates, helped the growth of carbon nanotubes through graphitization and bonding of carbon nanotubes to the silicon substrates.

Grazing incidence x-ray diffraction measurements at different grazing angles for self-organized Ge dots grown on Si(001) are carried out by using synchrotron radiation as a light source. Deformation strains in the substrate underneath or surrounding the dots induced by formation of Ge quantum dots are investigated. Besides a tensile strain existing underneath the dots, a peak located at the higher angle side of Si(220) or Si(400) is observed for the first time, the origin of this peak is attributed to the near surface compressive strain in the peripheral substrate regions surrounding the Ge dots. This compressive strain corresponds to a -0.8% lattice constant change parallel to the interface.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Observation of the hole-confinement effect in boron \ensuremath{\delta}-doped Si quantum wells has been demonstrated using the deep-level transient spectroscopy (DLTS) technique, based on the concept of treating the quantum well as a big ``trap.'' For the same doping thickness but different doping densities, i.e., different boron sheet doping concentrations, the well depths and the subband positions are different and the peak shift of DLTS spectra is thus expected and is observed experimently for two samples with sheet doping concentrations of about 2.4\ifmmode\times\else\texttimes\fi{}${10}^{13}$ and 6.0\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, respectively. A self-consistent calculation of the subbands in the quantum wells verifies that the detected activation processes in DLTS correspond to the hole emissions from the hole ground states in the \ensuremath{\delta}-doped quantum wells to the top of the wells. \textcopyright{} 1996 The American Physical Society.

x.J. Chen**, Q.H. Wang, D.W. Gong, Y. Yang H.Q. LU, F. Lu, Y.L. Fan, X.K. Lu, Z.M. Jiang, X.J. Zhang,and Xun WangSurface Physics Laboratory and Fudan T.D. Lee Physics Laboratory, Shanghai 200433, ChinaABSTRACTWe have successfully realized boron 84unctionshaped doping in the silicon epilayer by molecular beam epitaxy(MBE) with a B203 doping source. The sheet boron concentration NB of the boron o doping layer can exceed3.4x1O'4cm2 The transmission electron microscopy (TEM) crosssection image shows the width of the o dopinglayer is about 1.5nm. Meanwhile, we have applied in situ Auger electron spectroscopy (AES) to quantitatively

An oxygen δ-doped Si multilayer structure has been grown by molecular beam epitaxy (MBE). Thermal oxidation of a Si layer prepared by an MBE system at a low oxygen partial pressure resulted in a thin ordered oxide layer with a very flat surface. On the ordered oxide, Si was epitaxied through the solid phase epitaxy. Five periods of Si(2 nm)/SiO x (1 nm) multilayers were grown successfully. The O-doped Si layer (SiO x ) was composed of 7 atomic layers and the crystalline structure of the SiO x layer was the same as that of the Si substrate but had a relatively transverse displacement. The in-plane stress restricted the number of the oxide layers grown to a thickness of less than 6 atomic layers. This structure may be the gateway for realizing Si-based quantum wells.

Interfacial defects related to the residual carbon on the hydrogenterminated Si(100) surface have been studied using the deep-level transient spectroscopy (DLTS) technique. The defect level is found to be donorlike which compensates the acceptor impurity at the interface. With a fast load-in and a two-step annealing, the defect density can be suppressed below the DLTS detection limit of 1012 cm-3.

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F2 alpha (PGF2 alpha) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 +/- 3 mm Hg (n = 11) in SHR and 32 +/- 2 mm Hg (n = 12) in WKY (P less than 0.005). The perfusion pressures at all flow rates tested (2.5-6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to serotonin compared with phenylephrine and PGF2 alpha. EC50 values (-logM) for serotonin in the perfused brains of SHR and WKY were 7.0 +/- 0.06 (n = 10) and 6.5 +/- 0.06 (n = 11), respectively (P less than 0.01). There were no differences in EC50 values for phenylephrine or PGF2 alpha between SHR and WKY. Exogenous serotonin and phenylephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF2 alpha was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY. and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.