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In the present paper, we develope a 3-D Msrf-integral to evaluate the surface energy that is corresponding to formation of multiple surface cracks. The Msrf-integral is formulated by modifying the conventional 3-D M-integral with deliberate origination of the coordinate system and proper delimitation of the integral surface. The integral is demonstrated to be surface-independent in a modified manner and so can be accurately evaluated provided an integration surface remote from the crack fronts is selected. With this feature, the theory of integration can be straightforwardly incorporated into the finite element method. In fact, it is not necessary to simulate the near-front regions with very fine FE simulations to obtain accurate solutions of Msrf.

Microcantilever has been increasingly used as microsensor thanks to its fast response, low cost and parallel implementation in large quantity. The principle of sensing lies in the positive correlation between the resonant frequency of microcantilever and the target mass loading. The shape of cantilever determines the resonant frequency. Therefore it plays a vital role in microsensing. In the present study three basic geometric shapes (rectangle, triangle and half-ellipse) with innovative inner cut are investigated. The micro-cantilever beams are cut to external aspect ratios of 0.5, 1, and 2, and inner cut at aspect ratios of 0, 0.5, 1, and 2, with equal sensing area. Both numerical and experimental analysis indicates that the low-aspect-ratio cantilever with high-aspect-ratio inner cut achieved high sensitivity. The half-ellipse being the highest followed by the rectangle. The results are useful for optimal shape design of a micromechanical cantilever sensor.

In this paper, an energy parameter based on the concept of the M -integral is proposed for describing the fracture behavior of a multi-cracked solid subjected to nonconservative and nonuniform crack surface tractions. By using the M -integral with a suitably chosen closed contour, one can evaluate the ‘surface creation energy’ (SCE) required for creation of the stressed cracks. Also, it is demonstrated that the property of path-independence holds even under the action of crack surface tractions. Therefore, the singular stress field in the near-tip areas is not directly involved in the calculation so that a complicated finite element model around the crack tips is not required in evaluation of the M -integral.

The experiment described in this paper used vacuum induction melting (VIM) to coat Ni alloyNi alloy onto AISI 4140 steel. X-ray diffraction (XRD), scanning electron microscope (SEM), electron probe micro analyzer (EPMA), and transmission electron microscope (TEM) were used to identify the different phases of VIM Ni alloyNi alloys. Then, a ball-on-disc system and different dry sliding wear conditions were used to test VIM Ni alloyNi alloys. Results indicate that Ni 3 Si particles were scattered inside the γ-Ni solid solution, Ni 3 B and dendrite Ni 3 Si appeared in the lamellar structures, and Cr 7 C 3 and CrB were scattered in the lamellar structures of Ni 3 B and dendrite Ni 3 Si. Cr 7 C 3 and CrB were more wear resistant compared to other phases. The wear loss of VIM Ni alloys was lower when the sliding velocity was 0.1 m/s compared to when the velocity was 0.7 m/s. In the former case, the formation of a continuous oxidation layer protected the original surface from direct wear. A further increase in sliding distance caused, in both the cases, the formation of tumorous oxides, which led to delamination. Regardless, wear loss at 0.1 m/s was still lower than at 0.7 m/s.

An induction-melted Ni-based alloy (NiCrBSi) coating on AISI 4140 steel was prepared using induction melting under different melting conditions. To determine the microstructure and bonding behavior of their interfaces, the techniques of micro-diffraction, X-ray mapping and wavelength dispersive spectrometry (WDS) were employed. The experimental results showed that a white zone appears on the Ni-based alloy side of the final interface, becoming wider and wider with increasing temperature and time, which was identified as a solid solution of γ-Ni at 1000 °C and 1180 °C. A higher heating temperature and time caused a more severe iron dilution in the Ni-based alloy and decreased the microhardness.

Direct- and pulse-current (DC and PC) chromium electroplating on Cr–Mo steel were performed in a sulfate-catalyzed chromic acid solution at 50 °C using a rotating cylinder electrode (RCE). The electroplating cathodic current densities were at 30, 40, 50 and 60 A dm−2, respectively. The relationship between electroplating current efficiency and the rotating speed of the RCE was studied. The cross-sectional microstructure of Cr-deposit was examined by transmission electron microscope (TEM). Results showed that DC-plating exhibited higher current efficiency than the PC-plating under the same conditions of electroplating current density and the rotating speed. We found the critical rotating speed of RCE used in the chromium electroplating, above this rotating speed the chromium deposition is prohibited. At the same plating current density, the critical rotating speed for DC-plating was higher than that for PC-plating. The higher plating current density is, the larger difference in critical rotating speeds appears between DC- and PC-electroplating. Equiaxed grains, in a nanoscale size with lower dislocation density, nucleate on the cathodic surface in both DC- and PC-electroplating. Adjacent to the equiaxed grains, textured grains were found in other portion of chromium deposit. Fine columnar grains were observed in the DC-electroplated deposit. On the other hand, very long slender grains with high degree of preferred orientation were detected in PC-electroplated deposit.

The annealing behavior of electroplated copper deposits is reported in this study. The copper deposits were electroplated with a current density of 0.7 A/cm 2 at 53 °C in a sulfuric acid bath containing various concentrations of thiourea. The hardness values of the copper deposits were measured before and after annealing, and the differential scanning calorimetry (DSC) diagrams of the as-electroplated copper deposits were recorded. An improvement of the softening resistance of the copper deposits was observed when the bath contained thiourea ≥3 mg/L. By adding thiourea in the plating bath, smaller grain size of the copper deposits can be achieved. As thiourea content increased ≥3 mg/L, the twin boundary of the copper deposits was significantly increased, and many sulfur-rich particles were deposited along the grain boundaries and a few within the grains of the deposit. These sulfur-rich particles are capable of impeding migration of the grain boundaries and improving the softening resistance of the copper deposits during annealing. The aforementioned microstructures of the copper deposits were examined with transmission electron microscope (TEM) integrated with energy-dispersive X-ray spectrometer (EDX) for chemical composition analysis.

We propose ZnSe/BeTe:N superlattice (SL) as a new p-type cladding layer with improved p-type dopability, in which nitrogen-doped BeTe (N-doped) layers are inserted into undoped ZnSe layers. We have optimized the growth temperature for ZnSe/BeTe:N SLs. Both equivalent beam pressure (BEP) ratio and growth rate are further optimized in low-temperature growth of BeTe:N layers. The structural properties of BeTe:N layers were analyzed by reflection high-energy electron diffraction and high-resolution X-ray diffraction. Electrical properties were evaluated by the van der Pauw method and capacitance–voltage ( C – V ) measurements. We achieve the net acceptor concentrations of 1.2×10 19 cm −3 at the growth temperature of 350°C, BEP ratio of around 6, and growth rate of 35 nm/h.

We study the electrical properties of heavily Al-doped ZnSe grown by molecular beam epitaxy, whose electron concentration is saturated. Hall measurements show that electron mobility decreases with the increase of Al cell temperature, while it is almost independent of measurement temperature. These phenomena can be explained in terms of scattering mechanisms by ionized impurities and point defects. The point defects, which are induced by the incorporation of excess Al atoms, result in carrier compensation in heavily Al-doped ZnSe and decrease the electron mobility. As Al concentration increases, deep level emission around 2.25 eV, associated with a point defect such as a self-activated center [Al Zn –V Zn ], develops in photoluminescence spectrum. The line width of (0 0 4) X-ray rocking curve is broadened due to degradation of crystal quality, which is induced by the increase of point defects with an increase of Al concentration. As a result, it is suggested that the carrier compensation in highly Al-doped ZnSe is dominated by generation of complex point defects such as self-activated centers [Al Zn –V Zn ].

Highly efficient luminescence at room temperature is achieved from a novel CdTe(thickness ≤2 ML)/ ZnSe fractional monolayer heterostructures (FMS) grown by atomic layer epitaxy. Various optical spectroscopic methods such as, photoluminescence (PL), PL-excitation, spatially-resolved PL and temperature-dependent PL are used to investigate the origin of the luminescence. Structural inhomogeneities such as alloying and thickness fluctuation affect the line width and line shape of luminescence, also the luminescence intensity is greatly enhanced by the localization of excitons at disorder induced localized states. The radiative recombination mechanism is explained in terms of a simple model which includes localized states originating from the inhomogeneity of CdTe FMS.

Low dislocation density ZnTe heteroepitaxial layers are achieved by inserting a thin ZnTe buffer layer at low growth temperature (LT-buffer) followed by annealing. The ZnTe heteroepitaxy layer with a LT-buffer shows a narrow line width of X-ray rocking curve as narrow as 42 arcsec in (0 0 4) reflection and the dislocation density is estimated as 1.3×10 6 cm −2 . A cross-sectional view of transmission electron microscopy shows high structural quality of ZnTe layer with LT-buffers.

Direct computation of the mixed-mode dynamic asymptotic stress field around a notch tip is difficult because the mode I and mode II stresses are in general governed by different orders of singularity. In this paper, we propose a pair of elastodynamic contour integrals J kR ( t ). The integrals are shown to be path-independent in a modified sense and so they can be accurately evaluated with finite element solutions. Also, by defining a pair of generalized stress intensity factors (SIFs) K I, β ( t ) and K II, β ( t ), the relationship between J kR ( t ) and the SIF’s is derived and expressed as functions of the notch angle β . Once the J kR ( t )-integrals are accurately computed, the generalized SIF’s and, consequently, the asymptotic mixed-mode stress field can then be properly determined. No particular singular elements are required in the calculation. The proposed numerical scheme can be used to investigate the dynamic amplifying effect in the near-tip stress field.

We report growth optimization of molecular beam epitaxy (MBE) grown ZnSe on GaAs (0 0 1) substrate tilted by 15° toward [1 1 0] in terms of beam equivalent pressure (BEP) ratio and growth temperature. A LT-ZnSe buffer was grown to reduce the formation of Ga–Se bonding, a well-known source of defect generation, due to interdiffusion through the heterointerface in the initial stage of growth. The ZnSe layer was further optimized by low-temperature-grown (LT-ZnSe) buffer. The optical and structural properties of the ZnSe film with LT-ZnSe and GaAs buffer are also analyzed by photoluminescence spectroscopy (PL), X-ray diffraction (XRD), and secondary ion mass spectroscopy (SIMS), which show very large intensity ratio of near-band-edge emission to deep level emission, narrow XRD peak width of (0 0 4) rocking curves, and abrupt ZnSe/GaAs heterointerface under the optimum growth condition, respectively. The optimum growth conditions are BEP ratio ( P Se / P Zn ) of 3 and growth temperature of 310°C with an LT-ZnSe buffer grown at 250°C.

This article demonstrates the effect of the thin low-temperature-grown ZnSe buffer layer (LT-ZnSe) in improving crystallinity of ZnSe-based films grown on GaAs substrate. Especially, the density of stacking fault defects, which is normally observed in ZnSe-based films grown on GaAs substrate, can be well reduced by inserting a thin ZnSe buffer layer grown at sufficiently low temperature between ZnSe/GaAs heterostructure. A ZnSe film with stacking fault densities as low as ∼2×10 6 /cm 2 was obtained by growing on the LT-ZnSe/GaAs buffer layers, in contrast, ∼8×10 8 /cm 2 was obtained by directly growing on GaAs substrate. The Frank-type stacking faults was dominant for films grown with LT-ZnSe, meanwhile, Shockley-type stacking faults was dominant for films grown without LT-ZnSe buffer. At the initial stages of ZnSe growth, three-dimensional growth mode is considerably suppressed with LT-ZnSe buffer. The improvement of crystallinity in the ZnSe film with LT-ZnSe and GaAs buffer is also evidenced by low-temperature photoluminescence spectroscopy and high-resolution X-ray diffraction, which show very large intensity ratio of near-band-edge emission to deep level emission and narrow X-ray diffraction peak width of (0 0 4) rocking curve with 92 arcsec, respectively.

Self-assembled InAs quantum dots (QDs) on In 0.52 Al 0.48 As layer lattice matched to (1 0 0) InP substrates have been grown by molecular beam epitaxy (MBE) and evaluated by transmission electron microscopy (TEM) and photoluminescence (PL). TEM observations indicate that defect-free InAs QDs can be grown to obtain emissions over the technologically important 1.3–1.55 μm region. The PL peak positions for the QDs shift to low energy as the InAs coverage increases, corresponding to increase in QD size. The room temperature PL peak at 1.58 μm was observed from defect-free InAs QDs with average dot height of 3.6 nm.

We have investigated the effects of band filling and thermal escape on the temperature dependence and excitation power dependence of photoluminescence of CdTe QDs grown by molecular beam epitaxy on ZnTe(100) substrate. The absorption spectrum indicates that the PL spectrum consists of two peaks. The experimental results of excitation power dependence were well simulated by the rate equation model taking into account the effect of band filling. The temperature dependence of PL showed significant difference for different excitation powers. It is suggested that either the wetting layer or excited states play an important role in band filling and thermal escape.

We have investigated the ZnTe-based material system for the application to light-emitting devices. To this end, ZnTe homoepitaxy techniques have been developed to grow high-quality epitaxial layers. The conductivity control of ZnTe and ZnMgSeTe layers have been investigated. High structural quality n-type ZnTe layers with high carrier concentration are achieved by aluminum doping. Ambipolar conductivity control of quaternary layers is achieved. Aluminum doped ZnMgSeTe layers show a net carrier concentration of 5 × 10 16 cm -3 , while a high hole concentration of 2.5 x 10 19 cm -3 is achieved by p-type doping using a nitrogen plasma source. Based on those results, Zn 1-x Cd x Te/ZnMgSeTe triple-quantum-well(TQW) LED structures were fabricated. Bright electroluminescence was obtained at room temperature at the wavelength of 604 nm from Zn 0.7 Cd 0.3 Te and at 566 nm from Zn 0.85 Cd 0.15 Te TQW-LED.

Molecular beam epitaxy of Al doped n-type ZnSe is studied. Growth conditions such as Al cell temperature and substrate temperature are systematically examined. The electrical, optical and structural properties of ZnSe : Al layers are investigated. ZnSe : Al layers show high electron concentration of 8.37 × 10 18 cm -3 with low electrical conductivity of 6.92 x 10 -3 Ω cm along with high crystallinity.

The linear electro-optic (LEO) or Pockels coefficient above the fundamental edge E 0 of ZnTe has not been determined yet as far as we know. In this work, we have measured the LEO coefficient of ZnTe in the absorbing region by reflectance difference or reflectance anisotropy spectroscopy (RDS or RAS), and we have obtained two remarkable peaks near the E, and E 1 + Δ 1 critical points.

Self-assembled InAs quantum dots (QDs) on In 0.52 Al 0.48 As lattice matched to (1 0 0) InP substrates were grown by solid-source molecular beam epitaxy. We present in situ reflection high-energy electron diffraction studies of the initial growth processes and strain relaxation behaviors of the InAs QDs. The growth process of an InAs layer at the initial stage is clearly divided into two-dimensional (2D) growth and QD formation. It was found that the critical thickness for the 2D–3D transition is about two monolayers. The photoluminescence peak energies from the QDs were found to depend strongly on the InAs coverage, and the emission wavelength can be controlled over the 1.3–1.55 μm range.

We have studied the growth and properties of ZnSe/BeTe superlattices by molecular beam epitaxy for two interface configurations, which are basically characterized by a “ZnTe” and a “BeSe” interface layer. The interface properties for the two interface configurations have been studied by means of reflection high energy electron diffraction, high resolution X-ray diffraction, and photoluminescence. It is shown that the optical and structural properties of ZnSe/BeTe superlattices are improved with a ZnTe interface compared to a BeSe interface.

We have fabricated ZnCdSe/ZnMgBeSe single quantum well (SQW) light emitting diode (LED) structures with ZnSe:N/BeTe:N p-contact layers. The electrical properties of this p-contact layer scheme were evaluated for the use in ZnSe-based II–VI LDs. The specific contact resistance for Au/p-ZnSe/p-BeTe ohmic contact layers, which was measured by the transmission line model (TLM) method, was as low as 4.2 × 10–4 Ωcm2 even without annealing when the ZnSe layer thickness is 5 nm. The composition of quaternary ZnMgBeSe was determined using a ZnBeSe/ZnMgBeSe layer structure by PL and X-ray measurements. The p-type doping property was investigated for ZnMgBeSe with different compositions, and Na–Nd drastically decreases with increasing band gap energy the same as that of the ZnMgSSe:N system. The fabricated LEDs show a strong electroluminescence under dc bias at room temperature.

The selective-area growth of ZnSe is performed by molecular beam epitaxy on oxide-masked GaAs(0 0 1) substrates. Single-crystalline layers are obtained on a bare surface of the GaAs substrate, while poly-crystalline layers are deposited on an SiO 2 -covered region. The growth rate of a single-crystalline layer is faster than that of a poly-crystalline layer at least up to a substrate temperature of 340°C. The difference in growth rate increases with increasing the substrate temperature. The low-temperature photoluminescence of a single-crystalline layer shows dominant excitonic emission.

The phonon properties of Zn 1 −x Mg x Se 1 −y Te y quaternary alloys grown on GaAs(1 0 0) and ZnTe(1 0 0) substrates by molecular beam epitaxy have been studied by Raman scattering. ZnSeTe- and MgSeTe-like longitudinal optical phonon modes and ZnSeTe-like transverse optical phonon mode were observed in the room-temperature Raman spectra. The Raman scattering in Zn 1 −x Mg x Se 1 −y Te y quaternary alloys exhibits a two-mode behavior.

The correlated function expansion (CFE) methodology has been used to estimate the energy band gap and the alloy bond length of Zn1−xMgxSeyTe1−y over the entire composition space (x , y) . The lattice matching condition was obtained by optimizing the alloy bond length to the bond length of the substrates (ZnTe, InAs and InP), and the corresponding band gap and its bowing effect were identified. Excellent agreement was obtained between the CFE-estimated band gap and the recent photoluminescence data for the alloy grown on ZnTe and GaAs. As the CFE only requires ternary input data, it can accelerate efforts to find desirable quaternary alloy compositions.

Non-alloyed Au/p-ZnSe/p-BeTe ohmic contact layers for ZnSe-based blue–green laser diodes with contact resistivity as low as 4.2×10 −4 Ω cm 2 are reported. This contact layer is basically dislocation free due to small lattice misfit as long as the thickness is thinner than 500 A, as confirmed by transmission electron microscopy (TEM) observation. The ZnSe layer serves as a contact layer for BeTe and protecting layer against oxidation as well. The electrical properties of the contact layers are strongly dependent on the ZnSe layer thickness. Au diffusion through the ZnSe layer down to the BeTe layer at room temperature is found to be responsible for ohmic properties. A series of ZnBeTe epilayers with different x values have been grown on GaAs by molecular beam epitaxy (MBE). We can easily control the composition by changing the Zn or Be cell temperatures. Hall effect measurement was performed on as-grown Zn 0.05 Be 0.95 Te epilayer doped with nitrogen. Hole concentration as high as 2×10 19 cm −3 has been achieved.

Lattice-matched high crystal quality Zn 1-x Mg x Se y Te 1-y quaternary alloys are grown on ZnTe substrates. For high crystalline and homogeneous alloy growth, the molecular beam pressure ratio is controlled as P Se > 1. The lattice-matching condition to ZnTe substrates is obtained as y = 0.63 x by both the correlated-function-expansion method and experiment. The growth temperature is optimized in terms of the X-ray rocking curve and photoluminescence line width. The observed narrow temperature window (300-320°C) for high-quality crystal growth is explained in terms of the bond energy difference of the binary alloys, which compose ZnMgSeTe. Mg composition is determined by RHEED intensity oscillations of ZnTe and ZnMgTe, which shows good agreement with the values estimated from X-ray analysis and RHEED intensity oscillations of MgTe. The photoluminescence properties of ZnMgSeTe are characterized by strong excitonic luminescence intensity with a narrow line width (5.95meV) and very weak deep level luminescence. The luminescence intensity of typical ZnMgSeTe is 3.5 times stronger than that of bulk ZnSe under the same experimental condition. The narrow luminescence line width and small Stokes shift of ZnTe/ZnMgSeTe quantum wells are indicative of the homogeneity of the quaternary alloy.

The molecular motions of carbons in two polycarbodiimides were studied by 13 C cross-polarization, magic angle spinning nuclear magnetic resonance. From these results, the 13 C spin-lattice relaxation times in the rotating frame were measured. In this paper we discuss the molecular motions for each carbon of the two polycarbodiimides. The main-chain carbon of polycarbodiimide (I) with methyl has higher activation energy, 23.12 kJ/mol, than that of polycarbodiimide (II) with the methoxy side chain, 10.47 kJ/mol. From these results, we surmise that polycarbodiimide (I) has a bigger steric interaction with the main-chain carbon since the methyl group is located in the meta -position of the aromatic ring.

We have investigated the optical and structural properties of ZnMgBeSe/ZnSe/ZnMgBeSe quantum-well (QW) structures grown on GaAs (001) substrates by molecular beam epitaxy. The structural property of the QWs is confirmed by a sharp (line width is 21 arcsec) X-ray diffraction peak from ZnMgBeSe cadding layer. Photoluminescence (PL) and photoluminescence-excitation (PLE) spectra of QWs suggest the effective collection of excited carriers due to Type-I band alignment and high quality of ZnMgBeSe cladding layers. The bandoffset in these samples are evaluated as ΔEc=0.6ΔEg(ΔEv=0.4ΔEg) from the optical investigation of multi-quantum-well (MQW) structures and numerical calculation of the optical transition energies. From the optical pumping experiment, room temperature stimulated emission is observed at short wavelength (444 nm) with low threshold (16kWcm−2). Laser action is observed up to 473 K and the characteristic temperature (T0) is determined to be as high as 166 K. We believe that the low threshold and high characteristic temperature are due to the efficient electron and hole confinement in the quantum-well and high crystalline quality of the cladding layer as revealed from high excitation pumping experiments at low temperature.

MgSe is an important component in Mg-based ternary or quaternary alloys, but is less understood due to its hygroscopy and unstable zinc blende structure. In order to get a clear knowledge of this material, we have investigated the growth of MgSe films of ZB,(zinc blende), structure on ZnTe substrates by MBE (molecular beam epitaxy). The surface reconstruction of MgSe under different flux ratios and growth temperatures have been studied systematically by RHEED (reflected high-energy electron diffraction). (4×1) reconstruction is observed under VI/II flux ratios of 16–30, while (2×1) reconstruction appears at higher VI/II ratios. The oscillation of RHEED intensity at the first stage of MgSe growth indicated that 2D growth was achieved, and thereafter the growth mode changed to 3D growth due to the lattice mismatch. The structure of the MgSe layer is further confirmed by XRD (X-ray diffraction). The XRD results indicated the growth of a MgSe film having a ZB structure for a layer below 2000 A thick. No diffraction is observed from 2000 to 4000 A thick MgSe films. Thicker samples show the formation of MgSe layers having a rock salt structure.

We have carried out detailed investigation on the growth of Be-chalcogenides alloys and evaluated the device characteristics of optically pumped ZnSe/ZnMgBeSe SQW. A lattice-matched ZnMgBeSe ( E g =2.975 eV) layer shows a narrower X-ray diffraction (XRD) peak, the FWHM (full-width at half-maximum) value of which is 21 arcsec. The variation of FWHM of X-ray rocking curve (XRC) due to lattice misfit is investigated for ZnMgBeSe quaternaries with various lattice misfits extending from compressive-to-tensile strain, which shows that the FWHM value under compressive strain increases more steeply with lattice misfit than that under tensile strain. We report on the optically pumped lasing of a ZnSe/ZnMgBeSe single quantum well at 444 nm with a low threshold of 16 kW/cm 2 at room temperature and high-temperature lasing up to 473 K. The characteristic temperature is estimated to be 166 K from the exponential relation between threshold and temperature.

In this experiment, after the test specimens are preloaded at different first-step rolling cycles, the surface layer of the lower speed roller is ground to different depths by a grinder along the radial direction. With a new higher speed roller, the effects of the ground depth and first-step rolling cycle on the fatigue life of lubricated rolling/sliding contact are investigated using a 0.45% carbon steel pair. Results show that the prerolling cycles with metal removal can improve the rolling fatigue life. It is found that when the surface hardness of the specimen starts to approximate the saturated value at the first-step rolling cycle with the ground depth to the position of its maximum hardness, the rolling fatigue life with this preloading operation is 3.3 times that with the normal operation for the second-step load of 588 N. This increment in the rolling fatigue life can be reasonably explained by the measured plastic flow of the surface layer and the theoretical results of the residual stress below the contact surface.

This paper presents a numerical method to solve the electromechanically coupled equations in a brushless DC (BLDC) motor, i.e. Maxwell equation, voltage equation and Newton's equations by introducing the nonlinear finite element analysis and the time stepping method. It also investigates the coupling effect of the eccentric motion of a rotor on the characteristics of the magnetic force and the resulting motion of a BLDC motor by analyzing the free response and Fourier transform of the excitation force and the resulting displacement.

A study of field-induced coupled quantum-well oscillators due to the interwell coherent oscillation is presented. The evolution of an electron wave packet in an asymmetric coupled quantum-well structure is described by the application of the time-development operator of the time-dependent Schrodinger equation. By adjusting the applied field, various resonant conditions giving rise to different oscillation frequencies can be obtained in a single device. Direct frequency tuning, amplitude variation, and dipole matrix element due to the external field are also investigated. >

Although the application of semiconductor quantum dots to light emitters has been expected, only a few successful achievements have been reported mainly due to the low luminescence efficiency. This paper will report on the strong luminescence of CdTe/ZnSe fractional-monolayer (FM) heterostructures. Various optical-spectroscopic methods are used to investigate the origin of the luminescence in this structure.

We report on the correlation of surface chemistry of GaAs substrates with growth mode and stacking fault density in ZnSe epilayers. High quality ZnSe epilayers with low stacking fault density have been directly grown on commercial epiready GaAs (001) substrates without GaAs buffer layer growth. It is found that proper pregrowth treatments of epiready GaAs (001) substrates to obtain clean surfaces are crucial to two-dimensional layer-by-layer growth and suppression of generation of stacking faults. The surface oxide layers of epiready GaAs substrates before and after chemical etching using a NH4OH-based solution are carefully characterized by angle-resolved x-ray photoelectron spectroscopy. The surface oxide layer is composed of Ga2O3 and As2O3. The chemical etching is found to reduce not only the thickness of the oxide layers but also the ratio of Ga2O3 to As2O3 to about half of that before etching. A clean GaAs (001) surface typically characterized by a (4×1) reconstruction is obtained in the present case after thermal cleaning. Prior to ZnSe growth Zn preexposure is carried out. Reflection high-energy electron diffraction intensity oscillations with more than 50 periods are observed even from the beginning of ZnSe growth on such cleaned GaAs substrates. High quality ZnSe layers with a stacking fault density of low-105 cm−2 range are grown.

When the crack surfaces are traction-free, there is only one constant term T in the near-tip stress field, which contributes uniformly to the stress component acting in the direction parallel to the crack flank. As to pressurized cracks, the non-singular part of the asymptotic stresses appears to be more complicated and is no longer characterized only by the constant T. In this work, an effective numerical approach is developed for calculation of the non-singular parts of the asymptotic near-tip stresses under the action of nonuniform crack surface pressures. With this approach, the near-tip non-singular stress field can be accurately evaluated by direct use of regular numerical methods such as finite elements.

In this paper, a numerical procedure, incorporated with the finite element method, is developed for calculation of the mixed-mode stress intensity factors along a 3D curved crack with non-planar surfaces. The approach is formulated by modifying the concept of the Jk- and GIII-integrals. Note that the property of path-independence for curved cracks does not hold in a manner as that for straight cracks and needs to be properly modified. As a consequence, the near-front region is always included in the integration. An appropriate numerical method is therefore developed for simulating the associated singular behavior. Since no extra auxiliary solutions are required for the computation, the proposed method appears to be versatile and can be used for evaluation of the stress intensity factors associated with crack front and crack surfaces of arbitrary curvatures.