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Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)3 (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

Waste printed circuit boards (WPCBs) are an essential component in electronic waste (e-waste), and contain a number of valuable metals (e.g., Cu, Sn) as well as non-metal resources (e.g., brominated epoxy resin). Currently, most of the non-metals are disposed of in landfills, causing environmental problems. In this study, a combination of pyrolysis and physical separation is proposed to recover valuable resources, including both metals and non-metals, from WPCBs. The WPCBs were pyrolyzed at 700°C under a nitrogen atmosphere. Pyrolysis oil and gas can be reused as fuel for the pyrolysis of WPCBs. Metals like copper, tin, and iron in the pyrolysis residues were separated by selective crushing, sieving, gravity separation, and magnetic separation. Finally, rich copper (Cu 82.21%, Sn 1.47%), rich tin (Cu 53.20%, Sn 13.43%), rich iron (Fe > 63%), and non-metal products were obtained, and the total recoveries of copper, tin, and iron were 95%, 86%, and 76%, respectively.

As an effective and universal acaricide, amitraz is widely used on beehives against varroasis caused by the mite Varroa jacobsoni. Its residues in honey pose a great danger to human health. In this study, a sensitive, rapid, and environmentally friendly surface-enhanced Raman spectroscopy method (SERS) was developed for the determination of trace amount of amitraz in honey with the use of silver nanorod (AgNR) array substrate. The AgNR array substrate fabricated by an oblique angle deposition technique exhibited an excellent SERS activity with an enhancement factor of ~107. Density function theory was employed to assign the characteristic peak of amitraz. The detection of amitraz was further explored and amitraz in honey at concentrations as low as 0.08 mg/kg can be identified. Specifically, partial least square regression analysis was employed to correlate the SERS spectra in full-wavelength with Camitraz to afford a multiple-quantitative amitraz predicting model. Preliminary results show that the predicted concentrations of amitraz in honey samples are in good agreement with their real concentrations. Compared with the conventional univariate quantitative model based on single peak’s intensity, the proposed multiple-quantitative predicting model integrates all the characteristic peaks of amitraz, thus offering an improved detecting accuracy and anti-interference ability.

Polyphenylene sulfide (PPS) superfine fiber is a promising high efficient material for high temperature dedusting. In this paper, the PPS superfine fiber was prepared by melt-electrospinning for the first time. In order to produce the finer fibers, the polypropylene (PP) was added to PPS and the effects of blending ratio, spinning voltage, spinning temperature, and spinning distance on resultant fibers were investigated systematically. The superfine fibers of PPS with an average diameter of 4.12 μm were successfully prepared at the optimized condition, which was one third of that by melt-spinning method. With the decrease of 76.21 % fibers diameter, the filter efficiency increased from 87.03 % to 98.05 %. The presented method provides a new way for the scalable and green fabrication of PPS superfine fibers.

Pyrolysis has recently received much attention as a promising technology for recycling all the valuable materials from wastes. This study investigated the thermal degradation behaviors of the waste steel tailings and the recovery of iron from waste steel tailings using magnetic separation after pyrolysis. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were performed to study the mass loss characteristics. The main pyrolysis temperature range of the waste steel tailings was approximately from 100 to 800 ℃ and the total mass loss was about 30%. The pyrolysis process of waste steel tailings could be classified into four stages. The optimum pyrolysis temperature and pyrolysis time of waste steel tailings were at 700 ℃ for 60 min. The pyrolysis residues generated during the process under optimal condition were detailed analyzed by X-ray powder diffraction (XRD). The result showed that the phase composition of iron in the pyrolysis residues was magnetite. The results of magnetic separation showed that the recovery of iron was 92.66%.

In milk and milk products, the matrix is complex and the interfering components are large, so it is difficult to separate and enrich formaldehyde. In this study, combined with Surface-Enhanced Raman Scattering (SERS) technology, the self-developed green capture device was used to realize the integration of separation, enrichment and detection of formaldehyde. Firstly, we use fluid dynamics to simulate the heat-fluid coupling working mechanism of the enrichment chemical mechanical device. By exploring the steady-state and transient changes of separation and enrichment gas flow under different working conditions, we designed a purge and separation device with small dead volume and high separation efficiency. We further optimized the purge air velocity and heating voltage to increase sample recovery and shorten the separation and enrichment time of the target. As a result, we have realized the application of green and efficient pre-treatment, which is rapid and green. Finally, we used derivatization strategy to enhance the Raman scattering and combined with colloidal gold nanoparticles (AuNPs) to realize SERS analysis. According to this method, we detected formaldehyde in boxed milk, milk powder and raw milk. Thus, we realized a rapid detection method of formaldehyde in milk from various sources, including exogenous and endogenous formaldehyde.

For the polarity test of the CT for 1, 000kV ultra-high voltage(UHV) infrastructure projects, the polarity layout method and test program of a main transformer, etc. were discussed under 3/2 complete serial connection mode in an all-round manner. The protection of 1, 000kV bus difference, circuit breakers, lines and high resistance, the polarity of a metering device CT and the receiving method of a secondary circuit were discussed; and a reasonable point polarity method was provided before actual production. The polarity configuration of CTs at the low-voltage side of an ultra-high voltage transformer body bushing, common windings, a voltage regulation-compensation transformer, a house transformer and a main transformer, and the calculation logic of protective devices were studied. The effect of essential factors such as actual wring, equivalent impedance, etc. on polarity were analyzed, and the adverse factor of voltage regulation position was pointed out. When the polarity at the high-voltage side of the housing transformer was being studied, it is strongly interfered by electromagnetic coupling. The selection scheme of CT secondary circuit was studied according to the requirements of different ultra-high voltage protective devices, and the point polarity measures of the voltage regulation-compensation transformer were explored according to protection calculation logic. When the polarity of the main transformer and the auxiliary transformer for a compensation transformer were being tested, the cause of interference among three phases due to the Y/Δ wiring method at HV and low sides of the main transformer was mainly discussed.

Researchers’ work on computational materials is often hampered by the lack of suitable intera tomic potentials. In this paper, under the framework of Finnis-Sinclair (FS) potentials, the process of fitting, testing and correction of interatomic potential is given in detail by developing the FS potential for metal Nb. First, the relationship between the interatomic potential and the macroscopic properties of the material is established. Then, the Finnis-Sinclair potential of metal Nb is fitted by reproducing the experimental data, such as the cohesive energy, bulk modulus, surface energy, vacancy formation energy and equilibrium lattice constant, and the fitting mean square error is less than 10–7. In order to test the interatomic potential, the elastic constant, shear modulus and Cauchy pressure of metal Nb are calculated by the constructed interatomic potential. In addition, how the form of the interatomic potential function affects the interstitial performance is discussed, and the constructed interatomic potential is modified according to the results of density functional theory (DFT) of the interstitial formation energy. The treatment of cutoff distance is also discussed. In the paper, the results are as follows. 1) The original form of FS potential is not suitable for extending the atomic interaction to the third nearest neighbor. Through analysis and test, it is found that when the modified electron density function is in the form of the fourth power and the form of the pair potential function is in the form of the sixth power polynomial, the interatomic potential can better describe the interatomic interaction; 2) The result of interstitial formation energy is taken as the target value to modify the behavior of the pair potential function in the near distance, and the modified interatomic potential gives the interstitial formation energy close to the result of DFT. When the interstitial energy calculated by the interatomic potential is larger than the target value, the pair potential curve of near distance will be softened by the superposition of a polynomial term, otherwise, the pair potential curve will be stiffened; 3) When the physical quantity under equilibrium state is used as the fitting data, the fitted potential parameters and the elastic constant results will not be affected, while adjusting the curve form of the potential function, as long as none of the function value, the slope and the curvature of the function curve is changed at each neighbor position. The magnitude of interstitial energy will be affected by changing the shape of the curve that is less than the first neighbor range; 4) Under the cutoff strategy in this paper, changing the cutoff distance has almost no influence on the calculated results of potential parameters or crystal properties, but has a slight influence on the mean square error of the fitting results. The results of this paper provide some information for the construction of interatomic potentials database, and lay a foundation for constructing the Nb-related interatomic potential of alloy. And it also provides a method and basis for developing and improving the quality of interatomic potential.

Piezoelectric elements have been commonly used because of their wide applications in sensors, transducers, and some micro intelligent structures. However, in the fields of aviation, aerospace, and automation, some relevant equipment works in a harsh environment and is susceptible to the temperature change, thereby leading its performances to be greatly affected. Therefore, the problem of nonlinear wave relating to piezoelectric circular rods in different temperature fields is studied by modeling and numerical analysis. Firstly, based on the theory of finite deformation, we take infinite piezoelectric circular rod as a research object and consider the effects of transverse inertia and equivalent Poisson's ratio under the thermoelectric coupling action. Using the Hamilton principle and introducing the Euler equation, the longitudinal wave equation of piezoelectric circular rod is obtained. Secondly, Jacobi elliptic cosine function and Jacobi elliptic sine function expansion method are used to solve the wave equation of the piezoelectric circular rod, and the solitary wave solution and the exact periodic solution of the wave equation are obtained. It is found that the periodic solution can be reduced into a solitary wave solution under certain conditions, and it is proved theoretically that there may be solitary wave stably propagating in a piezoelectric circular rod. Finally, the dispersion curves of different wave velocity ratios and the curves about influences of temperature field on the waveform, amplitude and wave number of the piezoelectric rod are obtained by Matlab. The numerical results show that the wave velocity decreases with the increase of temperature when the wave velocity ratio is constant. Given the temperature is constant, it can be found that with the increase of the ratio, the amplitude of solitary wave gradually increases while the wavelength gradually decreases. In addition, the images obtained show that although temperature change can cause the characteristics of solitary waves to change, the solitary waves are always symmetrical bell shaped waves in the propagation process, reflecting the stability characteristics under the combined action of nonlinear and dispersion effects. Therefore, the variation of temperature field can influence and control some propagation characteristics of solitary waves. Moreover, the wave theory has been widely used in the nondestructive testing of structures and the improving of information transmission quality due to its special stability.

Space solar cell array is the only power source for satellites, and the mechanical impact on solar array during its in-orbit service will directly affect the normal operation of the satellites. Therefore, it is of great significance to study the stress and strain law of space solar array. In this paper, we establish a strain-testing system for space solar array, and this system can help test the strain data of space solar array under simulated space vacuum and thermal cycling field. We find that the space solar cells suffer compression deformation at high temperature and tensile deformation at low temperature. The total maximum strain of the free cell and pasted cell under the same conditions are 1270 and 1320 με, respectively. In addition, the strain of middle area is 113% higher than that of the edge area in one space solar cell. The rupturing strain of space solar cell is 2080 με. These measured data conduce to studying the deformation characteristics of solar cells in space environment, which can help researchers get the deformation regularity of space solar cells. They also provide experimental basis for stress-relieving arrangement of space solar array. This research provides technical support for studying the deformation resistance of space solar cells.

Waste printed circuit boards (WPCBs) are an integral part of e-waste, and they contain many valuable metals like Cu, Sn, etc. In order to recycle metal from WPCBs, electrostatic separation, wet gravity separation, air current separation, etc., have been used to separate metals from nonmetals, and the metal product has usually contained a high grade of copper and a low grade of tin. Because copper and tin can form an alloy, it is difficult to separate the two by smelting. Therefore, selective flotation of copper and copper-tin alloy (solder) was investigated in this study, with the aim of decreasing the content of tin in the rich copper product. Under optimized conditions, a rich copper concentrate with Cu grade of 61.12%, Cu recovery of 75.93%, Sn grade of 1.78%, Sn recovery of 8.46%, and a rich tin tailings with Sn grade of 40.93%, Sn recovery of 91.54%, Cu grade of 40.50%, Cu recovery of 24.07% were obtained. Moreover, during the flotation process, the adsorption capacity of ammonium dibutyl dithiophosphate (ADD) on the surface of copper was significantly higher than that on the surface of solder, which is the main reason for the flotation separation of copper and solder. Cu(II) on the surface of copper and solder was reduced to a lower valence state by ADD, and the ADD was oxidized to (ADD)2; but the (ADD)2 did not stably adsorb on the surface of either copper or solder. The adsorption product of ADD on the surface of copper and solder was Cu(I)-ADD precipitate; the adsorption sites of ADD on the solder surface were copper atoms.

Fin field effect transistor (FinFET) is a most widely used structure when the field effect transistor is scaled down to 30 nm or less. And there are few studies on single-event transient of FinFET devices with gate length below 30 nm. The single-event-transient on FinFET with gate length below 30 nm is worth studying. The single-event-transient responses of bulk FinFETs with 30 nm, 40 nm, 60 nm and 100 nm gate length are examined by using the pulsed laser and technology computer-aided design (TCAD) simulation in this article. First, we use the pulsed laser to ionize the gate of the FinFET device and detect the transient drain current of the FinFET device. The experimental results show that there are obvious platforms for the transient drain current tails of FinFETs with different gate lengths, and the platform current increases as the gate length of FinFET becomes shorter. The charges collected in the platform of FinFET devices with gate lengths of 100, 60, 40, and 30 nm are 34%, 40%, 51%, and 65% of the total charge collected in transient drain current, respectively. Therefore, when the FinFET device with the gate length below 100 nm, the platform current will seriously affect the device performance. Second, we use TCAD to simulate the heavy ion single-event effect of FinFET device and study the generation mechanism of platform region in transient drain current. The TCAD simulation explains this mechanism. Laser or heavy ions ionize high concentration electron-hole pairs in the device. The holes are quickly collected and the high concentration electrons are left under the FinFET channel. High concentration electrons conduct source and drain, generating the source-to-drain current at the tail of the transient drain current. Moreover the source-drain conduction enhances the electrostatic potential below the FinFET channel and suppresses high-concentration electron diffusion, making source-to-drain current decrease slowly and form the platform. The transient drain current tail has a long duration and a large quantity of collected charges, which seriously affects FinFET performance. This is a problem that needs studying in the single-event effect of FinFET device. It is also a problem difficult to solve when the FinFET devices are applied to spacecraft. And the generation mechanism of the transient drain current plateau region of FinFET device can provide theoretical guidance for solving these problems.

This paper proposes a novel method to derive the junction temperature of a Silicon Carbide Schottky Barrier Diode (SiC SBD) when it is in operation. There is a correlation between the switching waveforms and the temperature, due to the material parameters and the carrier vary with the temperature. Estimating the Turn-on-delay time as a temperature sensitive electrical parameter (TSEP), the chip temperature in operation can be evaluated. The experiment is based on signal loop — dealing with the output signal of the chip by the peripheral circuits, then putting it as the switching signal to the chip. Thus, each minimal turn-on-delay time — at nanosecond level — can be accumulated to be a time span at microsecond or second level and the value is averaged to evaluate the turn-on-delay time.

A modified ring spinning technology has been successfully applied to the production of yarns with reduced twist level and improved performance. Various US cottons and Chinese cottons have been covered in previous studies. In this paper, three combed rovings with different blending ratios of Upland and Extra Long cottons were adopted in a systematic investigation and evaluation on a fine modified ring yarn produced on a new modified spinning system that was developed to reduce the imperfections of fine yarns. The potentially important spinning parameters were proposed and their individual and interaction effects of spinning system parameters on the properties of fine modified ring yarn were quantitatively examined using the response surface methodology. Then with the optimum parameters, physical properties of the yarns and their knitted fabrics produced from three rovings were evaluated by comparing them with the conventional ones. Experimental results showed that yarns produced in the new modified spinning system had reduced imperfections; at low twist levels, fine modified yarns and resultant fabrics also showed improved performance. Moreover, properties of fiber materials and roving quality influenced the properties of modified yarns and knitted fabrics.

The influence of an Al interlayer on the crystalline quality and surface morphology of AlN epitaxial layers is investigated. 100 nm thick (0002) oriented AlN layers were grown on Si (111) substrates by metal organic chemical vapor deposition. Al interlayers were introduced through Al soaking, followed by nitridation for different lengths of time. When the nitridation time was 0 s, the AlN surface was uneven. At a nitridation time of 15 s, the AlN epilayer started to transform into a smooth surface. When the nitridation time was increased to 40 s, the AlN films had rough surfaces. X-ray diffraction measurements showed that the full width at half maximum of the (0002) peak decreased to 801.9 arcsec by introducing the Al interlayer for a nitridation time of 25 s. The roughness of the AlN surface was reduced from 5.30 nm to 1.91 nm compared with the films without an Al interlayer. The Al interlayer improved the crystalline quality and surface roughness of the AlN films. An optimized nitridation time was important in achieving an appropriate surface roughness for high quality crystals of AlN on Si (111) surfaces. Open image in new window

Medium frequency induction heating for large diameter pipe bending is an advanced technique that has been widely used. However, the thickness control of outer wall and inner wall of pipe is still difficult in the actual production: outer wall tends to be thinner and inner wall tends to be thicker. Therefore, it is necessary to optimize the process parameters of bending. Combined central composite experimental design and a proper selection of design parameters sample, an accurate response surface model was built in order to decrease ovality, thickness reduction ratio and forming load. The response value of objective function was analyzed; and important influence factors for system stability were found, i.e heating temperature, heating width and advance speed. The results indicate that the optimal value range were heating temperature of outer wall t=1030∼1070 °C, while advance speed v=0.3∼0.4 mm/sec. Practical results from multi-objective optimization could achieve qualified products.

Flavin mononucleotide (FMN) plays an important role in living systems. Accurate probing and characterizing of FMN is the key to understanding the contribution of FMN coenzyme in biological processes. We demonstrate a way to get a bright surface-enhanced Raman spectroscopy (SERS) signal while simultaneously quenching the fluorescence background through silver nanorod (AgNR) array substrates fabricated by the oblique angle deposition method. The AgNR array substrates show a good SERS activity with an enhancement factor of ∼4.2 × 104. Meanwhile, the characteristic peaks of FMN are assigned by the density function theory calculation. An exponential relationship is demonstrated between SERS intensity and FMN concentration in the concentration range of 0.1 to 100 mg / L. This SERS-based method enabled the rapid and highly sensitive detection of FMN, holding great promise for expanding SERS application in biochemistry and food safety fields.

Ultrathin nanostructures have attracted much attention in recent years due to their predictable novel properties and various potential applications. The improvement in synthetic skills has led to many successful syntheses of nanostructures including zero-dimensional (0D) nanoclusters, one-dimensional (1D) nanowires, two-dimensional (2D) nanosheets and other higher-level complex nanostructures, where cluster-assembly of primary nanocrystals is a common process. In this review, progress in ultrathin nanocrystals in the last decade and several important factors in the growth mechanisms are covered. By giving examples of cluster assembly from 1D to 3D nanostructures, the utility of cluster assembly in the synthesis of new materials has been demonstrated.

Friction stir welding (FSW) is a relatively new joining technique particularly for magnesium and aluminum alloys that are difficult to fusion weld. In this paper, an excellent friction stir weld of AZ31 magnesium alloy was obtained at proper parameter. In the friction stir zone (FSZ), the microstructure of the base material (BM) is replaced by fine grains and small particles of intermetallic compounds. The average microhardness of the friction stir zone is higher than that of the base material. The maximum tensile strength of joint can reach 93% that of the base material. And the failure locations are almost at the heating affected zone.

Fluorescence of Tm3+/Er3+ codoped bismuth-silica (BS) glasses and the sensitization of Ce3+ are investigated. It shows that Ce3+ codoping with Tm3+/Er3+ in BS glasses results in a quenching of Tm3+ ion emission from 3F4 to the 3H6 level. Consequently, the 1.47 μm emission occurs after the population inversion between the 3H4 and 3F4 levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum (FWHM) up to about 119 nm, as it combines 1.55 μm emission band of Er3+ with 1.47 μm emission band of Tm3+ under 800 nm excitation.

A novel method of codoping the Er3+, Yb3+, and Ho3+ ions in tellurite glasses is demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Three intense emission bands observed in Er3+, Yb3+, and Ho3+ codoped tellurite glasses centred at 525, 547, and 657 nm correspond to Er3+: 2H11/2→4I15/2, Er3+: 4S3/2→4I15/2+Ho3+: 5S2(5F4)→5I8, and Er3+: 4S3/2→4I15/2+Ho3+: 5F5→5I8 transitions, respectively. No visible upconversion quenching phenomenon is observed when three rare-earth ions are codoped together in tellurite glasses. In contrast, the upconversion intensity of red and green emissions in Er3+, Yb3+, and Ho3+ codoped glasses is enhanced largely when compared with Er3+/Yb3+-codoped glasses. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The three emissions are based on two-photon absorption processes.

Poly-phenylquinoxaline is used as the electroluminescent(EL) materials to fabricate the thin film electroluminescent devices by the spin coating method. Doped with 1, 3, 5-triphenyl-2-pyrazoline, the EL spectrum of the devices is shifted to the blue-green region with its peak located at 465nm. The incorporation of a hole transport layer, poly-vinylcarbazole, will enhance the EL intensity, and the quantum efficiency is estimated to be 0.2%. Thus, the devices can be driven by either positive or negative bias (or ac voltage) even though the currentvoltage curve possesses a rectifying property.

An Sb delta doping layer in silicon is grown at the temperature of 300°C by silicon molecular beam epitaxy and characterized by the small angle x-ray reflectivity measurement using synchrotron radiation beam. The oscillations of the reflectivity caused by dopant Sb at Q as large as 14.5 are detected. Simulation of this curve as a whole shows that the total amount of dopant Sb is 0.15 monolayer and is restricted to two atomic layers. An extremely narrow Sb delta doping structure without Sb segregation is thus obtained at the growth temperature of 300°C as verified by the experiment.

Frank's theory describes that a screw dislocation will produce a pit on the surface, and has been evidenced in many material systems including GaN. However, the size of the pit calculated from the theory deviates significantly from experimental result. Through a careful observation of the variations of surface pits and local surface morphology with growing temperature and V/III ratio for c-plane GaN, we believe that Frank's model is valid only in a small local surface area where thermodynamic equilibrium state can be assumed to stay the same. If the kinetic process is too vigorous or too slow to reach a balance, the local equilibrium range will be too small for the center and edge of the screw dislocation spiral to be kept in the same equilibrium state. When the curvature at the center of the dislocation core reaches the critical value 1/r 0, at the edge of the spiral, the accelerating rate of the curvature may not fall to zero, so the pit cannot reach a stationary shape and will keep enlarging under the control of minimization of surface energy to result in a large-sized surface pit.

Porous silicon samples were prepared for optical studies by using the photoluminescence (PL), Raman scattering (RS), as well as the absolute reflectance and ellipsometry methods. Results show that the porous Si has low optic constants, and can trap the visible photons of more than 95%, but give no evidence of a strong interband transition existing in the visible region. The Bruggeman effective-medium-approximation (EMA) and Lorentz oscillator models were used in data analyses. Calculations show that the layer dispersion effect may result in a red shift of the PL peak. The possible mechanism for the PL and Raman enhancement as well as the photon trap phenomenon was discussed, and was attributed mainly to the random multiple micro-reflections in the porous-Si layer having extremely large internal micro-surfaces.

We have investigated the optical transitions above the fundamental gap of a set of GexSi1-x/Si strained layer multiple-quantum wells by electroreflectance (ER). The samples were grown by molecular beam espitaxy (MBE). The thickness of the strained layer of GexSi1-x was 5nm with Ge concentration x in the range from 0.4 to 0.5, and the Si barrier layer greater than 16nm. Considering the energy shift caused by strain and quantum well confinement, we were able to clearly recognize the transitions from different quantum well structures associated with the critical points E0, E'0, and E1. The transitions of the critical points E0 and E'0, which are very weak in bulk materials, are apparently enhanced in the quantum well structures.

It is demonstrated in this paper that the infrared-up-conversion luminescence generation from porous silicon, considered as an enhanced third-order nonlinear optical effect by the recent work, is anisotropic as the polarization vector of normally incident fundamental light is rotated. A new method has been used to determine the anisotropy parameter σ of the third-order nonlinear optical tensor χ(3). Due to the sensitivity of σ to the crystal structure and microscopic electronic properties, the difference in σ's between porous and crystalline silicon, particularly in their phases, demonstrates that the nanometer structure of porous silicon induces a dramatic change of the electronic band structure, but the strongly anisotropic crystal property remains unchanged.

A new surface cleaning method for Si MBE is described in which a very weak Ge beam flux is deposited on the surface for removing the thin passivative layer of SiO2 on the Si substrate. It has proved that the SiO2 will react with Ge at a relatively low temperature (620° C), and as a result, the oxide layer becomes volatile. Here the high temperature annealing in the conventional Shiraki method is no longer required, and since the oxide layer is removed in ultra high vacuum, only very little carbon contamination may occur. Furthermore, to reduce the excessive Ge on the substrate surface, Ge is deposited at 620° C and then the sample is annealed at 700° C; the residual Ge atoms on Si substrate can be reduced to less than 0.1 monolayer (ML). Ge beam treatment turns out to be an effective low-temperature Si surface-cleaning method, especially for the heteroepitaxial growth of GexSi1-x/Si.

The absorption in Si1-xGex/Si multiple quantum-well structures is measured. Several separated well absorption peaks corresponding to both intersubband and intervalence band transitions in the samples are observed. In the normal incidence, two broadband peaks are attributed to intervalence band transitions HH0-SO0(2.5 µm), HH0-LH0(~3 µm), respectively. Using 45° incidence of unpolarized light, both the intervalence band and intersubband transitions are observed. The intervalence band transitions (HH0-LH0) are Ge composition dependent, but the intersubband transitions, HH0-HH1(5.9 µm) and HH0-HH2(4.3 µm), are not sensitive to the Ge composition.

It is well known that the excellent pollution performance of silicone rubber (SR) insulators originates from its hydrophobicity and hydrophobicity transfer properties. With the sustainable growth of composite insulator usage in China, a convenient method should be given to judge the hydrophobicity properties and to help the utilities choose proper products. In this paper, a four-parameter method used in the evaluation of hydrophobicity status was introduced. The four parameters are hydrophobicity on clean surface, hydrophobicity loss property, hydrophobicity recovery property and hydrophobicity transfer property named H/sub c,/ H/sub l,/ H/sub r/ and H/sub t,/ respectively. Relative values of the four parameters, which were based on the research work of hydrophobicity, were also given. This method has already been used in some parts of China for its easy operation and effectiveness regarded. In addition, the mechanism of hydrophobicity transfer property was further investigated and the difference of the results between contact angle and hydrophobicity classification was also discussed in detail.

In this paper,the degradation of irradiated GaAs/Ge single junction (SJ) solar cells is evaluated under the orbital environments using the displacement damage dose method. Firstly the electric-property changes of the SJ solar cells are experimentally obtained with the fluencies of electrons and protons of various energies under ground-based irradiation simulators. Based on the experimenal results and the calculated non-ionization energy losses (NIELs) of the electrons and protons in GaAs, the equivalent exponent n is obtained to be 1.7 for various electron energies,while the equivalent coefficient Rep for electron displacement damage converted into that of protons is 5.2. Furthermore, a degradation formula of the electrical property of the domestic SJ solar cell is established as a function of displacement damage dose during the particle irradiation. Using the displacement damage technique, the orbital evolution of the electric property degradation of the domestic SJ cell is predicted in this paper. In the meantime, the shielding effects of the cover glass with different thicknesses are also evaluated.

Erbium-doped SiOx is prepared by molecular beam epitaxy. The influence of Er on the incorporation of O is studied by using Auger specstrocopy. Photoluminescence(PL) peaks around the wavelength of 1.53μm have been observed within the temperature range of 18 to 300 K after annealing. The relationship between PL intensity and annealing temperature is discussed. The temperature dependence of the PL intensity shows an exponential decay with an activation energy of 12 meV at low temperatures (＜100 K) and 150 meV at high temperatures (＞100K).

The atomic configuration and electronic structure of erbium-doped silicon are studied theoretically by using local density formalism (LDF) and discrete variational method (DVM).The influence of codoping with oxygen is also investigated.The minimum-energy atomic configuration is that erbium occupies a tetrahedral interstitial site for an isolated erbium atom.In this configuration,Er 5d levels are located near the conduction band edge of Si in shallow resonance states. With the presence of oxygen,the binding energy of the structure decreases. In this case,the minimum-energy atomic configuration is that erbium occupies a hexagonal interstitial site with six nearest neighbors of oxygen atoms. An electronic state caused by the hybridization of Er 5d,O 2p and Si 2p electrons is located 0.3eV below the conduction band edge,which might be correlated with the deep level at Ec-0.15eV observed by the experimental measurement in Er and O codoped Si.

Ion implantation and annealing have been used to switch the luminescence in Si1-xGex/Si quantum wells from a band-edge exciton process to a broad well below the band edge. The damage introduced by silicon ion implants, which leads to the formation of the platelets correlated with broad band luminescence, is related to the track of an implanted ion and the recoiled atoms in the quantum well structures. The activation energy for defect clusters is about 0.1eV, which is larger compared with the activation energy of ～0.05 eV for interstitial atoms. This indicates that the defect clusters is responsible for the deep broad photoluminescence in early MBE samples.

The admittance spectroscopy technique has been used to study the hole confinement in Si/Si1-xGex/Si and boron highly doped superthin Si quantum wells. Based on the carrier thermal emission medel of the carriers in the well, the value of activation energy derived from the admittance spectra was considered as the distance from the position of the heavy hole ground state in the well to the top of it . For Si/Si1-xGex/Si quantum wells we found the value of activation energy increased with increasing annealing time at 800℃. The phenomena could be explained the annealing-induced interdiffusion of Si and Ge, the interface broadening, the weakening of quantum confinement, the decrease of the position of the heavy hole ground state, and so the increase of the activation energy. At the annealing temperature of 900℃, we only see the decrease of the value of activation energy with increasing annealing time. For boron highly doped superthin Si quantum wells due to quantum confinement effect, we observed the activation energy are different for samples with the same doping density but different well widths.

The effect of Sb on Ge epilayer grown on Si(001) is investigated in situ by RHEED and ex situ by X-ray diffraction.Without Sb,island formation takes place when Ge epilayer is 6nm thick,and the strain in Ge epilyer is totally relaxed.With Sb,the growth mode of Ge on Si is two- dimensional, and the strain is relaxed gradually.Even if the thickness of the Ge epilayer is 6nm, 42%- strain is still not relaxed.

The ion beam producing ionization of N= has been successfully utilized as the N source for nitride growth. Cubic GaN thin films are thus grown on GaAs(100) substrates. The width of the (200) X-ray diffraction peak of the epilayer is 23′ only, and the high-resolution electron energy loss spectroscopy measurements show that the optical surface phonon of cubic GaN appears at the loss energy of 82 meV.

Porous silicon of low porosity was oxidized in boiling HNO3 solution. Photo-luminescence, microluminescence and SEM studies show that the stability and the uniformity of the sample were greatly improved by such a treatment. This is a new method much easier to control than rapid thermal oxidation.

The typical Raman spectrum from light-emitting porous silicon shows a sharp peak near 520cm －１ . The peak wavenumber decreases with the increase of porosity. The lineshape analysis shows that both phonon confinment and strain effects in nanocrystal silicon must be taken into account for the measured Raman spectra. The strain in porous silicon film is estimated and the result is consistent with that given by X-ray diffraction studies. No light scattering from amorphous phase is observed.

The STM images of NaCl microcrystal at room temperature have been studied in the air. The results show that the ionic conductivity plays a crucial role in the image formation. The resolution of the microcrystals is restricted due to surface condensation of water molecules on the sample, and the phenomenon of "dragging effect" appears on the NaCl images. The effects of bias voltage and humidity to the tunneling process are also discussed.

A stable hydrogen-terminated Si (100) surface was obtained by using a modified mothed. The Si (100) surface was hydrogen passivated during the ex-situ HF-dip followed by the in-situ low-temperature desorption of physisorbed residues. It was found that this procedure is very effective to eliminate the boron spike at the Si MBE layer/p-Si substrate interface. The origon of the boron spike is also discussed.

In this paper, we report the results of the growth of a series of ZnSe films on (100) GaAs at different substrate temperatures by hot wall epitaxy. The quality of ZnSe films has been studied by X-ray diffraction, Raman scattering and photoluminescence. The results show that: 1) We have got (100)-oriented single crystal fillms, but the quality becomes worse when lowering the substrate temperature. When the substrate temperature is below 300℃ there appears the (111)-oriented twins in the (100ZnSe. 2) When the substrate temperature is 350℃, Ga atom diffusion from the substrate to the ZnSe epitaxial layer is serious.

The energy dispersive relation of surface dangling bond state on InP() clean surface has been measured by the angle resolved photomission. The theoretical calculation based on a slab model and extended Huckel theory agreed well with the experimental result if a surface relaxed atomic structure model for InP() (1×1) is postulated.