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The influence of the bilayer number on the microstructure, mechanical properties, adhesion strength and tribological behaviors of the WB2/Cr multilayer films was systematically investigated in the present study. Five groups of WB2/Cr films with the same modulation ratio were synthesized by magnetron sputtering technique. The crystalline structure of the films was determined by X-ray diffraction. The morphologies and the microstructure of the films were observed by scanning electron microscopy, atomic force microscopy and transmission electron microscopy. Furthermore, Nano indenter, scratch tester and ball-on-disc tribometer were used to evaluate the mechanical and tribological properties. As bilayer numbers varied from 5 to 40, the hardness increased first and then decreased with the maximum hardness of 33.9 GPa when the bilayer number is 30. The H/E* and H3/E*2 values calculated to evaluate the fracture toughness showed the similar changing trend with hardness. The adhesion strength reached the maximum of 67 N when the bilayer number is 30. The surface roughness and friction coefficient decreased with increasing bilayer number. The wear mechanism was also investigated, and the results suggested that the multilayer film with bilayer number of 30 exhibited the best wear resistance (1.78 × 10–7 mm3/Nm), benefiting from the contribution of high hardness, fracture toughness and adhesion strength.

WB2/Cr multilayer films with different modulation ratios (λ = 1, 3, 5, 7, 12, and 20) were deposited by a combination of direct-current and pulse direct-current magnetron sputtering, and the number of bilayers was fixed at ten. The effect of the modulation ratio on the microstructure, mechanical and tribological properties of the multilayer films was investigated in detail. X-ray diffraction demonstrates that a preferred orientation of WB2 (101) and Cr (110) exists, and WB2 (101) dominates the film's growth with increasing of modulation ratio. The TEM results show that the multilayer films consist of nanograins dispersed in an amorphous matrix in WB2 layers and polycrystalline grains in Cr layers. The hardness increases with the increasing modulation ratio, and the maximum hardness (31.1 GPa) is obtained at λ = 20. The indentation toughness presents an opposite changing trend, and the maximum indentation toughness (1.264 MPa m1/2) is obtained in S1 at λ = 1 which conforms to the rule of mixture due to the relatively thick bilayer thickness (Λ = 160–192 nm). The wear mechanism is investigated, and the results suggest that the multilayer film with λ = 7 possesses the best wear resistance (2.06 × 10−7 mm3/Nm), benefiting from the balance of hardness and indentation toughness.

A fiber Fabry–Perot interferometer (FPI) is proposed and demonstrated for the measurement of gas pressure and temperature. The interferometer is fabricated by fusion splicing a short segment of capillary tube to a standard single mode fiber (SMF), followed by inserting a glass microsphere into the tube, the air gap between the SMF end face and the glass microsphere then forms a fiber FPI. Due to the additional reflection occurred on the rear surfaces of the microsphere, the reflection spectrum of the device is a three-beam interference pattern. Owing to the dependence of refractive index of gas on the pressure applied and the thermal-optical effect of glass microsphere, different dips in the interference fringe pattern exhibit different responses to the changes in gas pressure and temperature, which enables a simultaneous gas pressure and temperature sensing. The proposed device has the advantages of compact size, robust structure, easy fabrication, high gas pressure sensitivity, and supporting of range tunable operation.

In the current concept for disposal of high-level radioactive waste (HLW) in China, a barrier composed of blocks of highly compacted bentonite is constructed around the waste canisters. To develop this technique, uniaxial compaction of full-sized bentonite blocks has been initiated. Many factors affect the quality of bentonite blocks, including water ratio and granule size distribution of the bentonite, compaction pressure and rate, and form geometry. In the present study, compaction tests were conducted using powdered, pelleted, and mixed GMZ bentonite to evaluate the effects of granule size distribution on the integrity and uniformity of the block samples. Results show that high-quality blocks can be manufactured by adjusting the water content of the bentonite to 17%, in spite of different granule size distributions. The compaction in the mixed bentonite was better than that in the powdered and pelleted samples. However, the difference in final density was negligible when compacting at the same pressure. The block uniformity was not improved by adopting different granule size distributions when the height:diameter ratio of the bentonite samples reached 2. Blocks produced by powdered and mixed bentonite were prone to radial cracks when subjected to moisture loss; however, the cracks were healed after moisture redistribution.

Fabrication and efficiency enhancement of tubal field emission lamps (FELs) using multi-walled carbon nanotubes (MWNTs) as the cathode field emitters were studied. The cathode filaments were prepared by eletrolessly plating a nickel (Ni) film on the cathode made of a 304 stainless steel wire dip-coated with MWNTs. The 304 wire was dip-coated with MWNTs and nano-sized Pd catalyst in a solution, and then eletrolessly plated with Ni to form an MWNT-embedded composite film. The MWNTs embedded in Ni not only had better adhesion but also exhibited a higher FE threshold voltage, which is beneficial to our FEL system and can increase the luminous efficiency of the anode phosphor. Our results show that the FE cathode prepared by dipping three times in a solution containing 400 ppm Pd nano-catalysts and 0.2 wt.% MWNTs and then eletrolessly plating a Ni film at a deposition temperature of 60 °C, pH value of 5, and deposition time of 7 min has the best FE uniformity and efficiency. Its emission current can stay as low as 2.5 mA at a high applied voltage of 7 kV, which conforms to the high-voltage-and-low-current requirement of the P22 phosphor and can therefore maximize the luminous efficiency of our FEL. We found that the MWNT cathodes prepared by this approach are suitable for making high-efficiency FELs.

The electronic structures and optical properties of tin dioxide (SnO2) with different Al-doping concentrations (x = 0, 0·0185 and 0·0417) are investigated using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory under the local-density approximation. The results show that the Fermi level of Al-doped SnO2 goes into the valence band, indicating that Al-doped SnO2 is a typical p-type semiconductor. Moreover, with the increase in Al-doping concentrations, the band gap of SnO2 is broadened and the blueshift of the absorption spectrum becomes significant, which are in good agreement with the experiment results. In addition, the low reflectivity (

As a representative boundary, interphase-interface may affect the strength or ductility of multilayered composites dramatically. However, the effect of the interface with mismatch dislocations on the mechanical behavior of multilayered composites is still not clear. In the present work, we performed molecular dynamics simulations to investigate the effect of interface structures and layer spacing on the mechanical properties of the Ti/Al nanolaminate. The results indicate that there are two transitions of the plastic deformation mechanism in the Ti layer with the increase of layer spacing in the sample with a coherent interface. The plastic deformation mechanism evolves from one that is dominated by dislocation to the phase transformation from the hcp-Ti to the fcc-Ti mode, which transfers to the dislocation slip deformation again. For the samples with an incoherent interface, the plastic deformation is dominated by the transformation from hcp-Ti to fcc-Ti, regardless of the variation of layer spacing, while the plastic deformations in the Al layers are mainly dislocations confined in the layer slip in the samples with both coherent and incoherent interfaces. When the layer spacing is larger than 6.6 nm, an obvious second hardening is observed due to the superior dislocation storage ability of the Ti/Al laminate with the incoherent interface. Meanwhile, extraordinary ductility is obtained when optimal layer spacing is employed in the Ti/Al laminate. Moreover, the phase transformation mechanism of hcp-Ti to bcc-Ti has also been explicated in the present work. The general conclusions derived from this work may provide a guideline for the design of high-performance Ti/Al multilayer and alloy devices.As a representative boundary, interphase-interface may affect the strength or ductility of multilayered composites dramatically. However, the effect of the interface with mismatch dislocations on the mechanical behavior of multilayered composites is still not clear. In the present work, we performed molecular dynamics simulations to investigate the effect of interface structures and layer spacing on the mechanical properties of the Ti/Al nanolaminate. The results indicate that there are two transitions of the plastic deformation mechanism in the Ti layer with the increase of layer spacing in the sample with a coherent interface. The plastic deformation mechanism evolves from one that is dominated by dislocation to the phase transformation from the hcp-Ti to the fcc-Ti mode, which transfers to the dislocation slip deformation again. For the samples with an incoherent interface, the plastic deformation is dominated by the transformation from hcp-Ti to fcc-Ti, regardless of the variation of layer spacing, wh...

The non-destructive inspection method of scale on the inner wall of the ferritic steel and austenitic steel of high temperature boiler tube and the application effect were introduced in our work. The risk of scale exfoliation on the inner wall was also assessed. The risk of tube burst caused by scale exfoliation and accumulation, was reduced greatly, or even avoided by means of the change or treatment of high-risk tube confirmed by non-destructive inspection method.

Based on the effective-mass approximation, the acceptor binding energy in a cylindrical zinc-blende (ZB) InGaN / GaN single quantum dot (QD) is investigated variationally in the presence of the applied electric field. Numerical results show that the acceptor binding energy is highly dependent on the applied electric field, impurity positions and QD size. The applied electric field also induces an asymmetric distribution of the acceptor binding energy with respect to the center of the QD. Moreover, in the presence of the applied electric field, the acceptor binding energy is insensitive to dot height when the impurity is located at the left boundary of the ZB In 0.1 Ga 0.9 N / GaN QD with large dot height (H≥6 nm). In particular, the acceptor binding energy of the impurity located at the left boundary of the ZB In 0.1 Ga 0.9 N / GaN QD is identical for different dot height when the applied electric field F≥350 KV/cm. This result can be of interest for the technological purpose, as it could involve a source of control some impurity-related properties in these systems under the applied electric field.

High temperature interfacial evolution by reaction between liquid Al and solid Ti3Al has been studied by observation of reaction couples isothermally reacted at 700, 800 and 900°C for different time intervals between 1 and 60 min respectively. Only TiAl3 phase was detected in Al/Ti3Al reaction couples up to 900°C. The reaction zone consisted of aluminide particles dispersed in an Al rich matrix. However, microstructures in the inner, central and marginal regions of reaction zone were different and were continuously changing across the width of reaction zone. A model corresponding to evolution progress was drawn schematically. A water quenched experiment confirmed the restriction effect of dispersed TiAl3 particles to Al matrix and suggested that TiAl3p/Al composite could be fabricated by this in situ reaction method.

We present multiple-beam splitting to free space from a V groove in a two-dimensional photonic crystal waveguide (PCW) with a few additional dielectric rods at the exit of the PCW. Numerical study shows that ‘one-beam-in to two-beams-out’ (one-to-two, also denoted as Y-shaped), one-to-three, and one-to-five beam splittings can be easily realized over a wide bandwidth, and the split beams have remarkable properties such as symmetric energy distributions and high directional transmissions. Off-axis directional emission can also be achieved by simple displacements of the additional rods at the exit of the PCW.

Magnesium and its alloys are susceptible to corrosion, which has limited their use in automotive and aerospace industries. In the present study, ZM2 electrode was coated on ZM2 magnesium alloy using high energy microarc alloying (HEMAA) technique, and the influence of the coatings on the corrosion behaviour of the ZM2 alloy was examined. A potentiostat for electrochemical corrosion tests, X-ray diffractometer (XRD) for phase analysis, energy dispersive analysis (EDX) for compositional analysis of coating, scanning electron microscopy (SEM) for cross-section and a microhardness tester for microhardness were used. It was found that the material transfer depended on the voltage and the effective output power. It was determined that ZM2 HEMAA coatings on ZM2 magnesium alloy increased the corrosion resistance of the alloy. However, it was observed that, in the coating layers, small structural defects, e.g. pores, pinholes and cracks that could arise from the coating process or substrate and get the ability of protection from corrosion worsened were present. Microhardness of the alloyed layer was improved to 130 HV as compared with 100 HV of the as received ZM2. The phases in the coating layers were the same as those in the ZM2 alloy.

Laser surface engineering can be used to alter the surface of alloys and produce a fine microstructure, usually improving the corrosion resistance and wear resistance. In the present paper, a CO2 laser was used to melt preplaced Mg20Al80 powder with the objective of improving the corrosion resistance of ZM5 magnesium alloy in sea water solution. The corrosion behaviour of the ZM5 substrate and the laser cladding Mg20Al80 sample was studied with relating to their microstructures. Corrosion was studied in a 3·5 wt-%NaCl solution at pH 7 by observing the corrosion morphology. The results showed that the Mg17Al12 acted as galvanic cathode in both the ZM5 substrate and the cladding layer. The enhanced corrosion resistance was attributed to the fine dispersion of intermetallic phases and extended Al solid solutions by laser rapid solidification.

Embedded non-volatile memory (NVM) introduces additional thermal processes to a logic process flow and the impact from this extra thermal budget becomes more considerable with continued device scaling. This paper investigates the mechanism of SRAM V MIN degradation in a 40nm embedded NVM process and provides a solution to address the degradation caused. Failure analysis shows enlarged poly grain size for SRAM PMOS due to the NVM thermal processes, resulting in a large shift in threshold voltage. The results show that introduction of a p-poly boron pre-dope greatly helps to recover the SRAM V MIN . The mechanism for the V MIN recovery is also explained, with further high-temperature SRAM V MIN studies showing the effectiveness of p-poly pre-dope even at elevated temperatures.

The anomalous response of an elastic–plastic beam may occur in a narrow region of loading parameters (Symonds, Yu. ASME J Appl Mech 1985;52:517–22). The existence and the width of the anomalous region of loading parameter depend on system parameters. When the width of the anomalous region is less than the design or experimental tolerance, experimental results are uncertain (Li, Liu. Int J Impact Engng 2003;28(6):643–51). In the present paper, an elastic, linear plastic-strain-hardening Shanley model is used to understand the dependence of anomalous region on system parameters. Results show that there exist two anomalous regions when the strain-hardening parameter R varies between 0 and 0.18. The very closeness of ϕ 0 c and ϕ 0 b indicates that the beam response is extremely sensitive to the load parameter for the specifically selected system parameters.

Anisotropic damage evolution in a 0°/90° laminated Nicalon ™ SiC fiber-reinforced calcium aluminosilicate (CAS) glass–ceramic composite during uniaxial tensile deformation has been investigated using a variety of non-invasive characterization techniques. The elastic constant reduction in the three principal directions was measured from in situ laser-generated ultrasonic velocity measurements in various sound propagation directions. They indicate that, in addition to a large drop in elastic stiffness in the loading direction, the constants characterizing the nominal elastic stiffness transverse to the loading direction were also degraded. Surface replicas taken intermittently during loading revealed that transverse softening of the elastic stiffness was associated with fiber/matrix interface damage mainly in the 0° plies, while the large softening of the elastic stiffness in the loading direction was the result of multiple matrix cracking in both the 0° and 90° plies. While the ultrasonic data allowed a detailed characterization of the anisotropic damage evolution in this laminate, acoustic emission measurements and surface replica data identified the crack initiation stress in the 90° plies and correlated it to macroscopically observable deviations of the stress–strain curve from linear elastic behavior. These matrix cracks were found to have initiated preferentially in the weak 90° plies near the 90°/0° ply boundaries.

Damage transverse to the loading direction of a unidirectionally reinforced ceramic matrix composite has been observed and characterized by ultrasonic methods and acetate replicas. A laser-ultrasonic technique approach was developed and used to measure the ultrasonic velocity anisotropy, thus the complete elastic stiffness tensor, during uniaxial tensile loading/unloading of calcium aluminosilicate (CAS) composites reinforced by Nicalon™ SiC fibers. Acoustic emission and surface replica observations link degradation of the axial stiffness to the accumulation of matrix cracks normal to the loading (and fiber) direction. The substantial loss of transverse stiffness is proposed to originate from the fiber/matrix interface debonding near matrix cracks. These observations may significantly impact the constitutive models used to design multiaxially loaded ceramic matrix composites.

The elastic properties of unidirectional and 0°/90° crossply Nicalon-SiC-fiber-reinforced calcium aluminosilicate (CAS/SiC) ceramic-matrix composites have been measured using a resonant ultrasound spectroscopy (RUS) technique. This approach has allowed the nondestructive determination of the complete set of independent second-order elastic stiffness constants of these ceramic composites. These stiffness data have been used to obtain the orientation dependence of Young's modulus and the shear modulus. The results are in reasonably good agreement with the limited experimental data obtained from mechanical testing. The RUS measurements reveal that the unidirectional CAS/SiC composite is well modeled by transverse isotropic symmetry, indicating relatively isotropic fiber spacing in the transverse plane. The analysis indicates that the overall elastic anisotropy is also small for unidirectional and 0°/90° laminated CAS ceramic-matrix composites, a result that can be attributed to the relatively low modulus ratio of the Nicalon SiC fiber to the CAS matrix and to the moderate fiber volume fraction.

Analysis of a new fiber optic sensor based on the principle of Fresnel reflection is presented in order to develop a robust, flexible, readily embedded, high sensitivity and low-cost cure monitoring tool for intelligent control of composite manufacturing. This approach is distinct from previous work on on-line in-situ monitoring sensors in that the transducer is simply the fiber optic/epoxy interface. This leads to a more simple, less intrusive, and lower cost sensing system. The response of the sensor is a function of the mismatch in refractive index between the fiber optic end/resin interface. The refractive index of the resin is a nonlinear function of the temperature and the cure reaction of the resin. The sensing system detects the mismatch in the refractive index and generates a characteristic profile that gives the chemorheological information about the curing resin. Under isothermal cure conditions, the effect of the temperature on the refractive index mismatch can be eliminated. In this situation, the optical response of the sensor is only dependent on the cure kinetics and the state of the cross-linking in the material. A calibration method has been developed to interpret the optical response directly as the degree-of-cure of the resin. This work provides analysis of the fundamental sensor response and correlates it to the material state (degree-of-cure). These results provide a basis for extending the use of this sensor technology for on-line real-time cure monitoring and control.

Hybrid resins of unsaturated polyester/urethane were synthesized and characterized. Both the toughness and stiffness of the polyester were improved significantly by incorporating 20 wt% urethane. Unsaturated polyester, styrene, and ethane showed good compatibility during blending and probably formed a simultaneous interpenetrating network (IPN) during polymerization. The resultant IPN morphology possessed a unique glass transition temperature. This IPN morphology not only imparted great fracture resistance to the otherwise brittle polyester, but also changed the fracture mode of new resin composites. The molecular weight of unsaturated polyesters did not have significant effect on the mechanical properties, but did exert an apparent influence on the fracture mode. During the cure process the side reaction, an amine reaction, could be suppressed addition of suitable promoter and catalyst.

Graphite fiber reinforced epoxy composites normally exhibit low impact strength, poor delamination resistance, and low damage tolerance. Because delamination is a matrix-dominated failure mode, tougher matrix resins may be utilized to reduce or eliminate the adverse effects of delamination on the structural integrity of fiber composites. The effects of modifying epoxy network morphology by introducing polyurethane in the form of an interpentrating network were studied. The compatibility, toughness, and tensile properties of the matrix as well as the properties of the resultant laminates were evaluated. One of the conclusions arising was that the interpenetrating network morphology results in superior resin and composites toughness with increasing polyurethane content. However, the benefits of increased resin toughness did not necessarily translate into proportionally increased composite owing to the geomertical limitations placed on the plastic deformation zones in laminates.

The densification of a porous intermetallic alloy (Ti-14wt%Al-21wt%Nb) during the final stage of densification has been investigated under various states of stress and compared with the predictions of current models for densification by power-law creep. The experiments generally confirm the model predictions that the densification rate is a sensitive function of the stress state. Experimentally, unconstrained uniaxial compression resulted in the largest densification rates, while constrained uniaxial compression resulted in the lowest. Hydrostatic loading resulted in a densification rate similar (but slightly higher) than that of constrained compression. This ordering of the densification rates agreed well with the model predictions. However, the magnitudes of the measured densification rates are found not to be accurately predicted. A number of factors, including pore shape, pore spatial distribution and matrix microstructure have been observed to affect the densification rate, and the significance of each of these factors to predictive modelling of creep consolidation processes is assessed.

We demonstrate all-optical switching at 1.3 and 1.5 μm in the reflection mode of an asymmetric silicon Fabry–Perot etalon by a control beam at 0.85 μm. Both switch-on and switch-off operations are demonstrated at different locations of the etalon. Based on the free-carrier plasma effect, a modulation depth as large as 10% is obtained and a frequency response as high as 0.5 GHz is achieved.

Experimental results derived from early lots made with modified EEPROM masks are described. MIS structures formed with ferroelectric (FE) films grown on lightly doped silicon substrates have yielded FE switching properties demonstrated by hysteresis in capacitance vs voltage (CV) characteristics as the first step required to show suitability for use in high performance FEMFETs. In particular, switching attributable to polarization charge reversal inside the FE layer is observed, as opposed to tunnel injection of carriers from the silicon into the gate dielectric. Barium magnesium fluoride (BMF) and bismuth titanate FE films are currently under evaluation. Recent FEMFETs have achieved a 9.5V memory window using 20V programming, with Ion/Ioff > 105 for W/L = 12μm/3μm, after complete fabrication ∼ including Scratch-Protection. Some data loss is apparently associated with the BMF films having their primary P. vector nearly in the plane of the film and only a small component of P, experiencing reversa...

This paper reports the electrical tuning of a lasing in a liquid crystal (LC) sandwich structure. A dye-doped nematic LC (NLC) layer is sandwiched between two CLC layers to act as a phase retarder with the CLC layers acting as cavity mirrors, for the selective reflection of light in the photonic band with the same sense of helix handedness as that of the CLC layers. The transmittance spectrum of the sandwich cell provides a large range of modulation due to the wavelength dependent nature of phase retardation between the optical eigenmodes in the NLC layer. Lasing occurs at wavelengths corresponding to the maximum transmittance within the reflection band of the CLC layers. The application of voltage to the NLC layer makes it possible to shift the wavelengths of maximum transmittance, thereby tuning the wavelength of lasing. In these experiments, an applied voltage of 1.25 V was sufficient to shift the lasing peak wavelength by approximately 47 nm.

Diamond, having many advanced physical and mechanical properties, is one of the most important materials used in the mechanical, telecommunication and optoelectronic industry. However, high hardness value and extreme brittleness have made diamond extremely difficult to be machined by conventional mechanical grinding and polishing. In the present study, the microwave CVD method was employed to produce epitaxial diamond films on silicon single crystal. Laser ablation experiments were then conducted on the obtained diamond films. The underlying material removal mechanisms, microstructure of the machined surface and related machining conditions were also investigated. It was found that during the laser ablation, peaks of the diamond grains were removed mainly by the photo-thermal effects introduced by excimer laser. The diamond structures of the protruded diamond grains were transformed by the laser photonic energy into graphite, amorphous diamond and amorphous carbon which were removed by the subsequent laser shots. As the protruding peaks gradually removed from the surface the removal rate decreased. Surface roughness (Ra) was improved from above 1μm to around 0.1μm in few minutes time in this study. However, a scanning technique would be required if a large area was to be polished by laser and, as a consequence, it could be very time consuming.

Damage in composites can be defined as the more or less gradual development of microdefects such as matrix or fiber cracks that eventually leads to final fracture of a component.1 Associated with damage is a reduction of elastic stiffness.2, 3, 4 Knowledge of the overall stiffness degradation in composites is of great importance for predicting its serviceability, especially if the component is under a multiaxial stress state.

The mechanical properties of unidirectional Nicalon SiC fiber reinforced calcium aluminosilicate (CAS/SiC) and magnesium aluminosilicate (MAS/SiC) glass-ceramic composites have been investigated by tensile testing and a nondestructive laser-ultrasound technique. The barium-stuffed MAS was either undoped or doped with 5% borosilicate glass. The degradation of the elastic stiffness constant Cu in the transverse direction due to interface damage was monitored in-situ by measuring the laser-generated ultrasound wave velocity. The three composite materials show distinctly different macroscopic deformation characteristics, which are correlated strongly to the interface degradation. A stronger reduction trend of the elastic constant ?? is associated with a larger degree of inelastic deformation. Observations of the fracture surfaces also reveal the close relation between fiber pullout length and interfacial characteristics. Interfaces of these composites have been studied by TEM, and their influence on inhibiting and deflecting matrix cracks is discussed.

Local two-way magnetoelectric (ME) couplings of a multiferroic composite have been characterized at nanoscale using novel scanning probe microscopy techniques we developed. A bilayer multiferroic composite consisting of lead zirconate titanate (PZT) and TbDyFe (TDF) has been fabricated, and the evolution of ferroelectric domains in PZT induced by an external magnetic field is observed by piezoresponse force microscopy, while the evolution of magnetic domains in TDF induced by an external electric field is observed by magnetic force microscopy, confirming the two-way ME couplings in the multiferroic composite. The technique will be useful in characterizing nanoscale ME couplings in a wide range of multiferroic composites.

The lifetime of carriers injected optically in the extended states of amorphous silicon-germanium alloys has been measured by time-resolved pump and probe optical techniques using either a femtosecond dye laser or a picosecond free electron laser. When Ninj > 1018 cm-3, the lifetime of the carriers is in the picosecond time domain. Our results are comparable to what we have observed previously in a-Si:H and very recently in a-Si,C:H. There are two lifetime regimes: at high densities, the recombination is bimolecular and nonradiative, whereas at lower densities, the recombination tends to be monomolecular but still nonradiative. The origin of these lifetimes is discussed.

A computer aided design and manufacturing methodology, in conjunction with a multi-functional intelligent sensor, has been developed that can be used throughout the manufacturing and service-life cycles of thermoset composite materials. The concept of the sensor, called mechanical impedance analysis (MIA), involves measuring the relation between a force input (excitation) and a motion output (response) between various points in the material and therefore can provide a quantitative indication of the resin cure state and the structural health of the composite. Rapid measurements and analysis of the dynamic mechanical properties such as G’, Gil”, and tan δ of a composite can be obtained in real-time by using a multi-channel Fast Fourier Transform (FFT) spectrum analyzer interfaced with a microcomputer. This methodology, including the MIA concept, has proven to be effective in (1) the cure cycle design and optimization, (2) serving as a real time monitor for resin/prepreg aging/shelf life, (3) determining the processability of a resin/prepreg, (4) acting as an in-situ cure monitor for press curing and autoclaving of composites and (5) providing structural health state or condition monitoring of composites when subjected to various stressing conditions. In the present report, we will discuss the feasibility, advantages, and limitations of applying the computer-assisted MIA methodology for quality assurance, control and management before, during and after composite manufacturing.

A comprehensive thermodynamic study of a bilayer of HD adsorbed on graphite has been completed. Adsorption isotherm and adiabatic heat capacity measurements on different types of exfoliated graphite yield a phase diagram with a well defined solid-liquid-vapor triple point at 8.44K, and a liquid-vapor critical point at 11.45K, both intermediate between those of bilayer pure H2 and D2 on the same substrate.

We have developed a slow, highly collimated, and bright sodium atom beam suitable for orientation and alignment studies in cold collisions. A combination of transverse-optical collimation, longitudinal cooling, rapid decoupling from the longitudinal cooling cycle, and a final “optical-force extrusion” stage produces an atom density of 1×1010 cm−3 within a beam-divergence solid angle of 2×10−6 sr. Rapid Zeeman-cooler decoupling results in a narrow laboratory velocity distribution of 5 m/s full width at half maximum and a cold binary intrabeam collision temperature of 4 mK.

New data for the resistivity‐dopant density relationship for phosphorus‐doped silicon have been obtained for phosphorus densities between 1013 and 1020 cm−3 and temperatures of 296°K (23°C) and 300°K. For dopant densities less than 1018 cm−3, results were calculated from resistivity and junction capacitance‐voltage measurements on processed wafers. For more heavily doped material, data were obtained from Hall effect and resistivity measurements on specimens cut from bulk silicon slices. The results differ by 5–15% from the commonly used Irvin curve, always in the direction of lower dopant density for a given resistivity. For comparison with the electrical measurements, phosphorus densities were also obtained by neutron activation analysis and the photometric technique. The values from these methods were within 10% of the electrical results. Analytical fits were determined for the resistivity‐dopant density product as a function of resistivity and dopant density for temperatures of 23°C and 300°K. Similar fits were obtained for the calculated electron mobility as a function of resistivity and electron density.

The improved infrared response (IRR) technique has been used to qualitatively compare radiation effects on Si(Li) detectors with energy levels reported for silicon in the literature. Measurements have been made on five commercial silicon detectors and one fabricated in-house, both before and after irradiation with fast neutrons, l.9-MeV protons, and 1.6-MeV electrons. Effects dependent upon the extent of radiation damage have been observed. It seems likely that the photo-EMF, or photovoltage, effect is the basic mechanism for the observation of IRR in p-i-n diodes with a wide i-region. Experimental characteristics of the IRR measurement are in agreement with those of the photovoltage effect.

Defects in silicon p-n solar cells with Li diffused N region produced by electron irradiation and spontaneously annealed at room temperature interpreted as Li ions

Spontaneous annealing was observed at room temperature of the electron irradiation induced defect in lithium diffused oxygen‐rich silicon. Some implications of this observation are discussed.