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A ceramic membrane with multichannel generally has a higher specific area and a larger throughput compared to that with a single channel, which is beneficial to the industrialization of ceramic mem...

Postcombustion SO2 capture—from a high-volume flue gas—calls for a separator which should possess a high gas/liquid ratio concurrently without causing liquid flooding and entrainment. This study ai...

Membrane gas absorption (MGA) based on ceramic membranes is considered to be an effective technology for removing SOx from ship exhaust. To develop a convenient method for designing and amplifying a membrane contactor, the critical gas velocity was defined. Two simple connection modes, series and parallel modules, were assembled and compared with a single-tube membrane contactor. The critical gas velocity is associated with the size of the membrane element and module, based on which an empirical equation can be formulated to optimize the gas velocity in different membrane contactors. In addition, another amplifying method, using multiple tubes in one shell, was also studied with computational fluid dynamics (CFD) simulations. The results imply that the addition of baffles improves the desulfurization performance of the membrane contactor at the critical gas velocity. The methods and conclusions presented herein provide a design basis for using the contactor at an industrial scale.

Removal of SO2 from ship exhaust gas requires a specifically designed device due to the limitations of narrow space and inconvenient replacement of absorbent. Therefore, the scrubber should be high-efficient and the absorbent for SO2 removal should be efficiently utilized. In this work, a hydrophilic membrane (HIM) contactor was employed to selectively remove SO2 using NaOH solution from simulated ship exhaust gas. Mass transfer analysis demonstrated that the wetted membrane layer contributes to lower mass transfer of CO2 by limiting the diffusion of OH−, but it can improve the mass transfer of SO2 in the membrane phase. Experimental data showed that a SO2/CO2 selectivity factor of ~114 and a SO2 absorption flux over 0.2 mol·m−2·h−1 can be stably obtained using the HIM contactor and 0.4 mol·L−1 NaOH. These values were higher than those obtained in a hydrophobic membrane (HOM) contactor under the same conditions. The performance of selective removal of SO2 under various parameters were also investigated, including NaOH concentration, inlet SO2 concentration and packing density of membrane module.

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.

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 growth of Si-doped GaN films was performed by MOCVD using a homemade reactor operating at atmospheric pressure on (0 0 0 1) oriented sapphire. A study of the effect of Si-doping indicated that the intensity of yellow band emission in GaN : Si films decreased with the increasing of SiH4/TMGa ratio, and it was largely influenced by the parasitic reactions in the gas phase. The yellow band intensity was depressed when the parasitic reactions were reduced. We also observed that the growth rate of GaN : Si films was influenced by the Si doping and the parasitic reactions. The growth rate decreased with the increase of SiH4/TMGa ratio and was larger in larger parasitic reactions reactor. Sidoped GaN films with carrier concentration of 2 10 19 cm @3 , electron mobility of 120 cm 2 /V s, FWHM of the bandedge emission of only 60 meV at room temperature, and no yellow emission were obtained. r 2001 Elsevier Science

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.

The theoretical expressions of the capacitance-voltage (C-V) characteristics of a single quantum well are derived in different bias voltage regions based on solving analytically Poisson's equation. A method to determine the parameters, including the doping concentrations in the well and the barrier, the location of the well, and the thickness of the cap layer, as well as the band offset at the heterointerface from an experimental C-V curve is presented. By carefully constructing a testing sample with the structure of the Al/(thin nitride layer)/Si/${\mathrm{Si}}_{0.67}$${\mathrm{Ge}}_{0.33}$/Si single quantum well, the measurement of a complete C-V curve in a wide voltage range is achieved. The structural parameters of the quantum well derived from the measured C-V curve agree well with the nominal values set by the experimental growth conditions. \textcopyright{} 1996 The American Physical Society.

A thin SiGe buffer layer grown on a Ge-island-decorated Si(100) surface has been prepared and used as the substrate for growing the ${\mathrm{Si}}_{6}$${\mathrm{Ge}}_{4}$ short-period superlattice with symmetrically distributed built-in strains. The Si/Ge superlattice is found to be free of threading dislocations, which is in favor of suppressing the intermixing of Ge and Si atoms at the superlattice interfaces. The Raman spectrum shows a very weak Si-Ge vibration mode, narrow peak widths of the Ge-Ge and Si-Si modes, and the disappearance of the Si optical-phonon mode from the substrate, which are indicative of the great improvement of the interfacial quality. \textcopyright{} 1996 The American Physical Society.

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 single‐frequency admittance spectroscopy technique is presented to determine the band discontinuity of the Si/Si1−xGex/Si single quantum well. The accuracy of determining the activation energy for thermionic emission of holes over the Si barrier is improved as compared with the multiple‐frequency admittance spectroscopy measurement. To derive the band offset from the activation energy, the Fermi energy with respect to the band edge is calculated more exactly by solving the Poisson equation which accounts for the carrier transfer at the heterointerface. The accuracy of this technique is verified by the reconstruction of the temperature dependence of capacitance and conductance by the computer simulation.

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.

HV LDMOS on SOI has found wide applications such as lighting electronics and motor control due to its advantages over conventional LDMOS on bulk silicon. However, the design of optimized junctions with high breakdown voltages is commonly recognized to be difficult. This is partly because of the lack of analytical knowledge for the junctions design. In this study, various junctions were simulated by TCAD and analyzed from semiconductor physics point of view. It includes not only the junctions showing high breakdown voltages (>600V) but also the junctions showing relatively low breakdown voltages. The electrical field distribution, electrostatic potential distribution, depletion region and mobile carriers etc. were compared and analyzed to explain the reasons why a high breakdown voltage can be achieved for some junctions. Additionally, the breakdown voltage dependence on drift region doping profile was also studied.

Photovoltaic effect measurements have been carried out for the strained Si1−xGex/Si multiple quantum well samples. The absorption structures of the transitions from heavy‐hole ground state (HH0) to the unconfined conduction (EC) states, light‐hole ground state to EC states as well as the transitions of phonon (transverse acoustic and transverse optical)‐assisted HH0‐EC excitons of the sample with x=0.25 are identified by the photovoltaic measurement at the temperature of 18 K. The agreement between the experimental results and the calculations based on simple theoretical models is fairly good. Due to the rapid increase of the background absorption, the structures of the transitions from excited hole subbands to the conduction states are very difficult to identify. For the sample with x=0.5, the absorption related to the defects originated from the partial relaxation of the large misfit strain between Si0.5Ge0.5 and Si gives a great influence upon the identification of the interband absorption structures o...

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.

Two wireless, passive remote query magnetism-based glucose sensors, which operate in combination with a mass and volume changing glucose responsive polymer, are presented. One sensor design is based upon the magnetostatic coupling of magnetically soft thin-film elements, as the polymer volume changes in response to glucose concentration so does the magnetostatic coupling between elements. In response to a time varying magnetic field, upon reversal of the magnetization vector of the elements the magnetostatic coupling determines the time rate of change of magnetic flux, and hence the amplitude of the voltage spike generated in a pick-up coil. The other sensor consists of a free-standing magnetoelastic thick-film, coated with a thin layer of the glucose responsive polymer. In response to a time varying magnetic field the sensor mechanically vibrates at a characteristic resonant frequency, the characteristic resonant frequency of the sensor linearly tracks the change in mass of the glucose responsive polymer.

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.

The capacitance-voltage (C-V) characteristics of SiGe/Si quantum wells located near or in the space-charge region of a Schottky barrier have been numerically simulated by solving the Poisson equation. A physical picture of the variations of energy band and charge density in the quantum-well structure under the bias voltage is presented. The predominant feature of the C-V curves of quantum-well structures is the appearance of a capacitance plateau for single quantum wells or a series of plateaus for multiple-quantum-well samples. From the coincidence between the measured C-V curve and the simulated one, the band offset at the heterointerface could be derived. Moreover, the structural parameters of the quantum-well sample could be obtained from the measured C-V curves. It is found that the carrier-concentration profile derived from the C-V curve by the ordinary differential method does not coincide with the real carrier distribution in the quantum well; only the peak height of the C-V carrier concentration profile is related to the average carrier concentration in the well. \textcopyright{} 1996 The American Physical Society.

It is found that Er could only be deposited on a Si cathode by electrolysis of near neutral ErCl3 electrolyte with a large current density. The deposited Er hydrolytic layer reacts with Si at 1200 °C to form the activated Er centers that emit a 1.533 μm photoluminescence peak at room temperature. By applying this process to porous Si, an apparent doping concentration of Er larger than 1019/cm3 in the whole porous Si layer and a strong PL intensity with little temperature quenching are achieved.

We reported deep-level-free band edge luminescence from strained SiGe/Si multiple quantum well structures grown by conventional solid source Si MBE. No-phonon (NP) transitions due to symmetry-breaking alloy disordering in SiGe layers and transverse optical (TO) phonon replicas were clearly identified. A high quality of crystallinity is essential to the efficient luminescence. The choice of a higher growth temperature, Ts equals 870 degree(s)C, beyond the conventional growth temperature window 400-600 degree(s)C, was found to be important for radioactive recombination in SiGe/Si QWs structures.

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.