Low-Dimensional Dynamical Systems for a Wake-Type Shear Flow with Vortex Dislocations

Low-dimensional systems are constructed to investigate dynamics of vortex dislocations in a wake-type shear flow. High-resolution direct numerical simulations are employed to obtain flow snapshots from which the most energetic modes are extracted using proper orthogonal decomposition (POD). The first 10 modes are classified into two groups. One represents the general characteristics of two-dimensional wake-type shear flow, and the other is related to the three-dimensional properties or non-uniform characteristics along the span. Vortex dislocations are generated by these two kinds of coherent structures. The results from the first 20 three-dimensional POD modes show that the low- dimensional systems have captured the basic properties of the wake-type shear flow with vortex dislocation, such as two incommensurable frequencies and their beat frequency.

In-situ Boron-doped Low-stress LPCVD Polysilicon for Micromechanical Disk Resonator

Polycrystalline silicon (polysilicon) has been used as an important structural material for microelectro-mechnical systems (MEMS) because of its compatibility with standard integrated circuit (IC) processes. As the structural layer of micromechanical high resonance frequency (high-f) and high quality factor (high-Q) disk resonators, the low residual stress and low resistivity are desired for the polysilicon thin films. In the present work, we investigate the effect of deposition and annealing conditions on the residual stress and resistivity for in-situ deposited low pressure chemical vapor deposition (LPCVD) polysilicon films. Low residual stress (-100 MPa) was achieved in in-situ boron-doped polysilicon films deposited at 570 degrees C and annealed at 1000 degrees C for 4 hr. The as-deposited amorphous polysilicon films were crystallized by the rapid thermal annealing and have the (111)-preferred orientation, the low tensile residual stress is expected for this annealed film, the detailed description on this work will be reported soon. The controllable residual stress and resistivity make these films suitable for high-Q and bigh-f micro-mechanical disk resonators.

A note on the heat-transfer to nonspherical particles from plasma

Heat transfer from plasma to a nonspherical partical in the free-molecular regime is studied in the present paper under thin plasma sheath condition. Analytical expressions for the floating potential charge and heat fluxes of an ellipsoid particle of revolution are derived and curves are given for key parameters for arbitrary plasma flow direction. On the basis of these results, an equivalent sphere with the same surface area as the nonspherical particle is suggested to be used for calculating the total heat flux of nonspherical particle in engineering application with acceptable accuracy. Furthermore, the effects of particle rotation, which occurs in most aerosol systems, on the heat transfer are also discussed.

Plume Parameters and Thruster Properties of a Low Power Arcjet

Abstract. A low power arcjet-thruster of 1 kW-class with gas mixture of H2-N2 or pure argon as the propellant is fired at a chamber pressure about 10 Pa. The nozzle temperature is detected with an infrared pyrometer; a plate set perpendicular to the plume axis and connected to a force sensor is used to measure the thrust; a probe with a tapered head is used for measuring the impact pressure in the plume flow; and a double-electrostatic probe system is applied to evaluate the electron temperature. Results indicate that the high nozzle temperature could adversely affect the conversion from enthalpy to kinetic energy. The plume flow deviates evidently from the LTE condition, and the rarefied-gas dynamic effect should be considered under the high temperature and low-pressure condition in analyzing the experimental phenomena.

Fracture Properties of LPCVD Silicon Nitride and Thermally Grown Silicon Oxide Thin Films From the Load-Deflection of Long Si3N4 and SiO2/Si3N4 Diaphragms

The bulge test is successfully extended to the determination of the fracture properties of silicon nitride and oxide thin films. This is achieved by using long diaphragms made of silicon nitride single layers and oxide/nitride bilayers, and applying comprehensive mechanical model that describes the mechanical response of the diaphragms under uniform differential pressure. The model is valid for thin films with arbitrary z-dependent plane-strain modulus and prestress, where z denotes the coordinate perpendicular to the diaphragm. It takes into account the bending rigidity and stretching stiffness of the layered materials and the compliance of the supporting edges. This enables the accurate computation of the load-deflection response and stress distribution throughout the composite diaphragm as a function of the load, in particular at the critical pressure leading to the fracture of the diaphragms. The method is applied to diaphragms made of single layers of 300-nm-thick silicon nitride deposited by low-pressure chemical vapor deposition and composite diaphragms of silicon nitride grown on top of thermal silicon oxide films produced by wet thermal oxidation at 950 degrees C and 1050 degrees C with target thicknesses of 500, 750, and 1000 mn. All films characterized have an amorphous structure. Plane-strain moduli E-ps and prestress levels sigma(0) of 304.8 +/- 12.2 GPa and 1132.3 +/- 34.4 MPa, respectively, are extracted for Si3N4, whereas E-ps = 49.1 +/- 7.4 GPa and sigma(0) = -258.6 +/- 23.1 MPa are obtained for SiO2 films. The fracture data are analyzed using the standardized form of the Weibull distribution. The Si3N4 films present relatively high values of maximum stress at fracture and Weibull moduli, i.e., sigma(max) = 7.89 +/- 0.23 GPa and m = 50.0 +/- 3.6, respectively, when compared to the thermal oxides (sigma(max) = 0.89 +/- 0.07 GPa and m = 12.1 +/- 0.5 for 507-nm-thick 950 degrees C layers). A marginal decrease of sigma(max) with thickness is observed for SiO2, with no significant differences between the films grown at 950 degrees C and 1050 degrees C. Weibull moduli of oxide thin films are found to lie between 4.5 +/- 1.2 and 19.8 +/- 4.2, depending on the oxidation temperature and film thickness.

Doped polycrystalline 3C-SiC films deposited by LPCVD for radio-frequency MEMS applications

Polycrystalline 3C-SiC films are deposited on SiO2 coated Si substrates by low pressure chemical vapour deposition (LPCVD) with C3H8 and SiH4 as precursors. Controlled nitrogen doping is performed by adding NH3 during SiC growth to obtain the low resistivity 3C-SiC films. X-ray diffraction (XRD) patterns indicate that the deposited films are highly textured (111) orientation. The surface morphology and roughness are determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface features are spherulitic texture with average grain size of 100 nm, and the rms roughness is 20nm (AFM 5 x 5 mu m images). Polycrystalline 3C-SiC films with highly orientational texture and good surface morphology deposited on SiO2 coated Si substrates could be used to fabricate rf microelectromechanical systems (MEMS) devices such as SiC based filters.

Effects of V/III ratio on InGaAs and InP grown at low temperature by LP-MOCVD

Effects of V/III ratio on heavily Si doped InGaAs and InP were studied using low pressure metalorganic chemical vapor deposition (LP-MOCVD) at a growth temperature of 550degreesC. In InGaAs, as the V/III ratio decreases from 256 to 64, the carrier concentration increases from 3.0 x 10(18) to 5.8 x 10(18) cm(-3), and the lattice mismatch of InGaAs to InP was observed to vary from -5.70 x10(-4) to 1.49 x 10(-3). In InP, when the V/III ratio decreases from 230 to 92, the same trend as that in Si doped InGaAs was observed that the carrier concentration increases from 9.2 x 10(18) to 1.3 x 10(19) cm(-3). The change of AsH3 was found to have stronger effect on Si incorporation in InGaAs at lower growth temperature than at higher growth temperature. (C) 2003 Elsevier B.V. All rights reserved.

Low threshold current density 1.5 mu m strained-MQW laser by n-type modulation-doping

1.5 mu m. n-type modulation-doping InGaAsP/InGaAsP strained multiple quantum wells grown by low pressure metalorganic chemistry vapor decomposition technology is reported for the first time in the world. N-type modulation-doped lasers exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 1052.5 A/cm(2) for 1000 mu m long lasers with seven quantum wells. The estimated threshold current density for an infinite cavity length was 94.72A/cm(2)/well, reduced by 23.3% compared with undoped barrier lasers. The n-type modulation doping effects on the lasing characteristics in 1.5 mu m devices have been demonstrated.

Effects of reactor pressure on GaN nucleation layers and subsequent GaN epilayers grown on sapphire substrate

The influence of reactor pressure on GaN nucleation layer (NL) and the quality of subsequent GaN on sapphire is studied. The layers were grown by low-pressure metalorganic chemical vapor deposition (MOCVD) on c-plane sapphire substrates and investigated by in situ laser reflectometry, atomic force microscope, scanning electron microscope, X-ray diffraction and photoluminescence. With the increase of reactor pressure prior to high-temperature GaN growth, the size of GaN nuclei formed after annealing decreases, the spacing between nucleation sites increases and the coalescence of GaN nuclei is deferred. The optical and crystalline qualities of GaN epilayer were improved when NLs were deposited at high pressure. The elongated lateral overgrowth of GaN islands is responsible for the quality improvement. (C) 2003 Elsevier Science B.V. All rights reserved.

Structural and optical properties of InAlGaN films grown directly on low-temperature buffer layer with (0001)sapphire substrate

Quaternary InAlGaN film has been grown directly on top of low-temperature-deposited GaN buffer layer by low-pressure metalorganic vapor phase epitaxy. High-resolution X-ray diffraction and photoluminescence (PL) results show that the film has good crystal quality and optical property. Temperature-dependent PL and time-resolved PL (TRPL) have been employed to study the carriers recombination dynamics in the film. The TRPL signals can be well fitted as a stretched exponential function exp[-(t/tau)(beta)] from 14 to 250 K, indicating that the emission is attributed to the radiative recombination of excitons localized in disorder quantum nanostructures such as quantum disks originating from indium (In) clusters or In composition fluctuation. The cross-sectional high-resolution electron microscopy measurement further proves that there exist the disorder quantum nanostructures in the quaternary. By investigating the dependence of the exponential parameter beta on the temperature, it is shown that the multiple trapping-detrapping mechanism dominates the diffusion among the localized states. The localized states are considered to have two-dimensional density of states (DOS) at 250 K, since radiative recombination lifetime tau(r) increases linearly with increasing temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Stress and resistivity controls on in situ boron doped LPCVD polysilicon films for high-Q MEMS applications

The simultaneous control of residual stress and resistivity of polysilicon thin films by adjusting the deposition parameters and annealing conditions is studied. In situ boron doped polysilicon thin films deposited at 520 ℃ by low pressure chemical vapor deposition (LPCVD) are amorphous with relatively large compressive residual stress and high resistivity. Annealing the amorphous films in a temperature range of 600-800 ℃ gives polysilicon films nearly zero-stress and relatively low resistivity. The low residual stress and low resistivity make the polysilicon films attractive for potential applications in micro-electro-mechanical-systems (MEMS) devices, especially in high resonance frequency (high-f) and high quality factor (high-Q MEMS resonators. In addition, polysilicon thin films deposited at 570 ℃ and those without the post annealing process have low resistivities of 2-5 mΩ·cm. These reported approaches avoid the high temperature annealing process (> 1000℃), and the promising properties of these films make them suitable for high-Q and high-f MEMS devices.

High brightness AlGaInP orange light emitting diodes

Orange AlGaInP high brightness light emitting diodes (LEDs) were fabricated by low pressure metalorganic chemical vapor deposition(LP-MOCVD) technology. AlGaInP double heterojunction structure was used as active layer. 15 pairs of Al0.5Ga0.5As/AlAs distributed Bragg reflector and 7 mu m Al0.8Ga0.2As current spreading layer were employed to reduce the absorption of GaAs substrate and upper anode respectively. At 20mA the LEDs emitting wavelength was between 600-610nm with 18.3nm FWHM, 0.45mW radiation power and 1.7% external quantum efficiency. Brightness of the LED chips and LED lamps with 15 degrees viewing angle(2 theta(1/2)) reached 30mcd and 1000mcd respectively.

P wave velocity of the pumice from the Okinawa Trough at high temperature and high pressure.

P wave velocity of the pumice sample from the middle Okinawa Trough and andesite sample from vicinity Yingdao volcanic island, Kyushu Japan were measured at temperature (from room temperature to 1500 C) and pressure (from room pressure to 2.4GPa) using a multi-anvil pressure apparatus called the YJ-3000 press. The measured data shows that at low temperature and low pressure (<1GPa, <800degreesC), the P wave velocity of pumice is lower than that of andesite, while at high temperature and high pressure (>1GPa, >800degreesC) the P wave velocity of pumice and andesite. becomes consistent (5.9km/s). The paper points out that 1GPa/800degreesC is the point of thermodynamic phase transformation Okinawa Trough pumice and vicinity andesite, and the point is deeper than 18km.

孤北洼陷沙三-沙四段隐蔽油藏形成机制及其预测

Based on the study of sequence stratigraphy, modern sedimentary, basin analysis, and petroleum system in Gubei depression, this paper builds high resolution sequence stratigraphic structure, sedimentary system, sandbody distribution, the effect of tectonic in sequence and sedimentary system evolution and model of tectonic-lithofacies. The pool formation mechanism of subtle trap is developed. There are some conclusions and views as follows. 1.With the synthetic sequence analysis of drilling, seismic, and well log, the highly resolution sequence structure is build in Gubei depression. They are divided two secondary sequences and seven three-order sequences in Shahejie formation. They are include 4 kinds of system traces and 7 kinds of sedimentary systems which are alluvial fan, under water fan, alluvial fan and fan-delta, fan-delta, lacustrine-fan, fluvial-delta-turbidite, lakeshore beach and bar, and deep lake system. Sandbody distribution is show base on third order sequence. 2.Based on a lot of experiment and well log, it is point out that there are many types of pore in reservoir with the styles of corrosion pore, weak cementing, matrix cementing, impure filling, and 7 kinds of diagenetic facies. These reservoirs are evaluated by lateral and profile characteristics of diagenetic facies and reservoir properties. 3.The effect of simultaneous faulting on sediment process is analyzed from abrupt slope, gentle slope, and hollow zone. The 4 kinds of tectonic lithofacies models are developed in several periods in Gubei depression; the regional distribution of subtle trap is predicted by hydro accumulation characteristics of different tectonic lithofacies. 4.There are 4 types of compacting process, which are normal compaction, abnormal high pressure, abnormal low pressure and complex abnormal pressure. The domain type is normal compaction that locates any area of depression, but normal high pressure is located only deep hollow zone (depth more than 3000m), abnormal low pressures are located gentle slope and faulted abrupt slope (depth between 1200~2500m). 5.Two types dynamic systems of pool formation (enclosed and partly enclosed system) are recognized. They are composed by which source rocks are from Es3 and Es4, cap rocks are deep lacustrine shale of Esl and Es3, and sandstone reservoirs are 7 kinds of sedimentary system in Es3 and Es4. According to theory of petroleum system, two petroleum systems are divided in Es3 and Es4 of Gubei depression, which are high or normal pressure self-source system and normal or low pressure external-source system. 6.There are 3 kinds of combination model of pool formation, the first is litholgical pool of inner depression (high or normal pressure self-source type), the second is fault block or fault nose pool in marginal of depression (normal type), the third is fault block-lithological pool of central low lifted block (high or normal pressure type). The lithological pool is located central of depression, other pool are located gentle or abrupt slope that are controlled by lithological, faulting, unconfirmed. 7.This paper raise a new technique and process of exploration subtle trap which include geological modeling, coring description and logging recognition, and well log constrained inversion. These are composed to method and theory of predicting subtle trap. Application these methods and techniques, 6 hydro objects are predicted in three zone of depression.

鄂尔多斯盆地上古生界包裹体研究及天然气成藏特征分析

Based on the study of types, even temperature, the character of age-old fluid and fluid pressure of the reservoir fluid-inclusion in the Upper Paleozoic of Ordos Basin , combining with the diagenesis and character of gas geochemistry, reservoir sequence, cause of the low pressure reservoir formation and formation environment have been studied, the following knows are acquired: Abundant fluid-conclusions have developed in sandstone reservoir in Upper Paleozoic of Ordos Basin,and its kinds is numerous , also taking place some changes such as shrinking rock, cracking, stretching after formation. According to formation cause, fluid inclusion is divided into two types:successive and nonsuccessive inclusion. Nonsuccessive inclusion is further divided into brine inclusion, containing salt crystal inclusion, gaseity hydrocarbon conclusion and liquid hydrocarbon conclusion and so on. The gaseity hydrocarbon conclusion distributes at all the Basin, the liquid hydrocarbon conclusion mainly distributes at the East of Basin, and its two kinds of fluorescence color: blue and buff reflects at least two periods of oil filling and oil source of the different maturity. The study of diagenesis has indicated that five periods of diagenesis correspond to five periods inclusion's growth.The first and second period conclusions mainly distribute at the increasing margin of quartz, little amount and low even temperature, containing little gaseity hydrocarbon conclusion; The third and fourth conclusions are very rich, and having multiplicity forms, gaseity hydrocarbon conclusion of different facies, distributing at the increasing margin and crevice of quartz, its even temperature is between 85℃and 135℃;The fifth inclusion is relatively few ,mainly distributing at vein quartz and calcite, and developing few gaseity hydrocarbon conclusion. The fluid in the inclusion is mainly NaCl brine:low and high salinity brine fluid(containing salt crystal).The former salinity is between 0.18% and 18.55%,and mainly centralized distributing at three sectongs: from 0% to 4%, from 6% to 8%, from 10% to 14%, expressing that the alternation of the underground fluid was not intense, the conservation condition was good in different periods. The trapping pressure of the gaseity hydrocarbon conclusion calculated by PVTsim(V10)simulation is between 21.39 MPa and 42.58MPa,the average is 28.99MPa,mainlydistributes at between 24 MPa and 34MPa,and having a character of gradually lower from early to late time. The pressure of SuLiGe and WuShenQi dropped quickly in early time, and YuLin, ShenMu-MIZhi gas area dropped slowly in early and quickly in late time, ha portrait the change of trapping pressure can be divided into three old-age pressure systems: TaiYuan-ShanXi formation, low ShiHeZi formation and high ShiHeZi-ShiQianFeng formation. In plane, the trapping pressure dropped lowly from south to north in main reservoir period, and this reflects the gas migrating direction in the geohistory period. The analysis of gas component and monnmer hydrocarbon isotope indicates that the gas in Upper Paleozoic of Ordos Basin is coal-seam gas. The gas C_1-C_4 rnonnmer hydrocarbon isotopes has distinct differences in different stratums of different areas, and forming YuLin, SuLiGe and ShenMu-MIZhi three different distributing types. To sum up, gas reservoir combination in Upper Paleozoic of Ordos Basin can be divided into three sets of combination of reservoir formation: endogenesis type, near source type and farther source type,and near source gas combinations of reservoir formation is the main gas exploration area for its high gas filling intensity, large reservoir size.