Vol. 49, No. 7 (2000)
2000-04-05
GENERAL
2000, 49 (7): 1207-1210.
doi: 10.7498/aps.49.1207
Abstract +
Using the invariance of the algebraic equations and the differential equations under the infinitesimal transformations,we study the Lie symmetries and conserved quantities of the nonholonomic systems with servoconstraints.We establish the determining equations,the restriction equations and the structure equation,and give the form of conserved quantities.
2000, 49 (7): 1211-1214.
doi: 10.7498/aps.49.1211
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Double-wave function quantum theory is applied to describe the motion of charged particle in both uniform magnetic field and three-dimensional harmonic oscillat or potential field.Quantum results and classical limit results are derived respe ctively.A comparison between the classical limit results and those of classical mechanics is made.
2000, 49 (7): 1215-1220.
doi: 10.7498/aps.49.1215
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The riddled basin of the chaotic synchronized attractor in linear coupled standard tent maps is studied and proved.The notion of riddled factor is presented.Acc ording to it,the critical value of the coupling at which locally-globally bifurcation occurs is found and the analytical expression of transverse Lyapunov exponent is also revised.It is shown that in chaotic synchronization the riddled basin plays an important role.
2000, 49 (7): 1221-1227.
doi: 10.7498/aps.49.1221
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Based on the Volterra expansion of nonlinear dynamical system functions and the deterministic and nonlinear characterization of the chaotic signals,an adaptive higher-order nonlinear Fourier infrared(HONFIR)filter is proposed to make predic tion of chaotic time series.The time domain orthogonal algorithm is taken to upd ate filter's coefficients.A higher-order nonlinear adaptive filtering scheme is suggested in order to track current chaotic trajectory by using preceding predic tive error for adjustign filter parameters rather than approximating global or l ocal map of chaotic series.Experimental results show that:(1)this adaptive HONFI R filter can be successfully used to predict hyperchaotic time series;(2)the pre diction capacities of the HONFIR filter is related to its nonlinear function,but not determined by the HONFIR filter's degree of nonlinearity;(3)the adaptive pr ediction performance of the HONFIR filter is not confined by the Takens embeddin g dimension;(4)the proposed HONFIR filter can have some anti-noise ability.
2000, 49 (7): 1228-1234.
doi: 10.7498/aps.49.1228
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Crises in systems of ordinary differential equations are investigated by means o f Generalized Cell Mapping Digraph (GCMD) method. We show that a boundary crisis results from a collision between a chaotic attractor and a periodic saddle on i ts basin boundary. In such a case the chaotic attractor, together with its basin of attraction, is suddenly destroyed as the parameter passes through a critical value, leaving behind a nonattracting chaotic saddle in the place of the origin al chaotic attractor in phase space. We focus here on a sudden change in the siz e of a chaotic attractor, namely an interior crisis. We demonstrate that at an i nterior crisis the chaotic attractor collides with a chaotic saddle within its b asin of attraction. This chaotic saddle is an invariant and nonattracting set an d resembles the new portion of the larger chaotic attractor just after the inter ior crisis. We also investigate the origin and evolution of the chaotic saddle. The local refining procedures of persistent and transient self-cycling sets are given.
2000, 49 (7): 1235-1240.
doi: 10.7498/aps.49.1235
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Based on the nonlinear feedback approach for realizing any continuous time scalar(hyper)chaotic signal synchronization control,we have designed an adaptive feedback controller for controlling the scalar output signal of a smooth(hyper)chaotic system to synchronize with any continuous time scalar(hyper)chaotic signal under some assumptions.The result,which is rigorously proved by means of stability theory,not only can adaptively estimate the control parameter,but also has some robustness against parameter variations and external disturbances.An application to the synchronization of two(hyper)chaotic systems is given.
2000, 49 (7): 1241-1248.
doi: 10.7498/aps.49.1241
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In this paper,the hot-carrier effect in grooved gate NMOSFET and the device degr adation induced by it were simulated using device simulator MEDICI,and compared with those of counter conventional planar device.The hot-carrier effect and the device degradation were explained using the distribution of some internal physic al parameters.The simulation results indicated that hot-carrier effect was stron gly suppressed in grooved gate MOSFET,while grooved gate MOSFET's performance wa s sensitive to hot carrier.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2000, 49 (7): 1249-1255.
doi: 10.7498/aps.49.1249
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Starting from homogeneous scalar Helmholtz's equations associated with Borgnis p otential function in a cylindrical coordinate system, and based on the standing wave concept of slow-wave introduced in the paper, the analytic expressions of the dispersion relation and field distribution for azimuthally symmetric transverse magnetic modes in the resonant cavity chain with full-cavity terminations are derived, by using boundary conditions for Borgnis potential function in conjunction with field matching conditions at the common interface between adjacent sub regions. The resonance frequency of the four-cavity transit-time tube oscillator calculated by this analytic method is compared with that measured in experiment s and it is found that they are in agreement quite well. The field distribution of the oscillator developed by this analytic method is agreeable to that simula ted by numerical code.
ATOMIC AND MOLECULAR PHYSICS
2000, 49 (7): 1256-1259.
doi: 10.7498/aps.49.1256
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The knowledge of the hyperfine structure of 139LaⅡ has been very poo r until now.In our experiment,the atomic hyperfine structure spectra of 139 LaⅡ with 5d2 1Ｇ4 and 4f5d 1F 3 configurations have been measured using collinear fast-ion-beam las er spectroscopy,and the magnetic dipole and electric quadrupole coupling constan ts were determined.
CLASSICAL AREA OF PHENOMENOLOGY
2000, 49 (7): 1260-1266.
doi: 10.7498/aps.49.1260
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The morphology of random screens with different surface roughness is studied with atomic force microscope and it is found that their height distributions have very obvious fractal characteristics in short range regions.For screens with larger and smaller roughness,the fractals exist in the forms of random height fluctuations and small grains without characteristic size respectively.The self-affine fractal surface model is introduced to the quantitative descriptions of randomscreens.The light scattering measurements show that:(1)the scattered intensity in off-axis region descends in negative power functions,and the theoretical analy sis based on self-affine fractal model indicates that it originates from the sho rt-range fractal of the screens;and(2)there is a halo ring in the scattered fiel ds in the paraxial region .This phenomenon cannot yet be explained on the basis of the self-affine fractal model.
2000, 49 (7): 1267-1272.
doi: 10.7498/aps.49.1267
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Applying a genetic algorithm and taking the maximum output as an objective funct ion, a copper vapor laser with about 100W output is optimized and designed for reducing the “black center” of the radial laser intensity. The “black center ”, which results from the skin effect of the continuing pulsed field, is reduce d and the output is increased significantly by optimizing the laser tube radius- length and the LC circuit parameters.
2000, 49 (7): 1273-1276.
doi: 10.7498/aps.49.1273
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The infrared (λ0=830nm)nanosecond pulse is generated by pumping Ti:s apphire with diode-Q-YLF laser, and then the second-harmonic blue laser (λ 0=415nm)is obtained by frequency-doubling with the crystal Li BO20(LBO). In our experiments, the fundamental wave with a power of 960mW and cor responding harmonization of 285mW are output from the laser system when pumping power is only 3W. The high fundamental conversion efficiency of 32% and the seco nd harmonic conversion efficiency of 322% are reached, by optimizing the desig n of Ti:sapphire laser system and the focusing system in frequency-doubling. The influences of the bandwidth, the polarization and the focusing of the fundament al wave on the second-harmonic generation are discussed.
2000, 49 (7): 1277-1281.
doi: 10.7498/aps.49.1277
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By second-order and third-order perturbation theory, the one-photon and two-phot on absorption rates of conduction band electrons are calculated. The effects of nonlinear absorption and the absorption with electron-hole scattering on the dam age processes are discussed.
2000, 49 (7): 1282-1286.
doi: 10.7498/aps.49.1282
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The Bespalov-Talanov theory is extended to include the effects of gain and loss of the medium. An analytic expression for the growth rate of the ripples is obta ined and it reveals some new properties of small-scale self-focusing. For a give n input power, the cutoff spatial frequency, the fastest growing frequency and t he maximum perturbation growth, in an amplifying medium, increase with the incre ase of the gain of the medium and propagation distance. For a given output power , as the medium gain increases, the maximum perturbation growth, and thus the B- integral, decreases, while the fastest growing frequency shifts to lower frequen cy. Also, the expression for the distance at which the filaments are formed is o btained by means of a phenomenological approach, and it is found that the gain ( loss) of the medium extends (reduces) the distance. It is thus concluded that it is an effective way to suppress the small-scale self-focusing by increasing the gain of the medium.
2000, 49 (7): 1287-1291.
doi: 10.7498/aps.49.1287
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Assuming that the Raman gain profile of silica is a linear function, the authors have given analytic solutions of N-channel stimulated Raman scattering (SRS) st eady-state coupling wave equation. Considering the SRS cross coupling among the N-channels, the analytic solutions are applicable to systems with arbitrary chan nel separation and input light power. Theory shows, that the ratio of photon flu xes between arbitrary two channels is a base-e exponential function of the effct ive fibre length, the total input photon fluxes, and the Raman gain coefficient between the two channels. Finally, the analytic solution is compared with the nu merical one, both are in good agreement with each other.
2000, 49 (7): 1292-1296.
doi: 10.7498/aps.49.1292
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The development of Ti:sapphire femtosecond laser is reviewed. The basic principl es of its mode-locking, ultrashort pulse generation and its amplifiers are intro duced. The ultrafast time-resolved laser spectroscopy, including femtosecond flu orescence up-conversion and optical Kerr effect as well as its applications are presented.
2000, 49 (7): 1297-1302.
doi: 10.7498/aps.49.1297
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In conjunction with the transfer matrix techniques for modeling ultrasonic wave in multilayered composite medium, the spring model for a weak interface and the interface condition of the slip interface, we have the generalized frequency equ ations for low-order mode guided waves in ultra-thin layered composites structur e with a weak or slip interface in different depth, and the effect of the depth of the interface on the dispersion properties of low-order mode ultrasonic Lamb wave are analyzed. The “ultra-thin” here means that the thickness of the plate is only a fraction of the ultrasound wavelength so that the echoes from the fro nt and the back of the surface cannot be separated in the time domain.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2000, 49 (7): 1303-1306.
doi: 10.7498/aps.49.1303
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X-ray energy tansport along the cylindral cavity axis is measured. Many Kinds of experimental instruments are used to diagnose the X-ray radiation. The spatial distribution of soft X-ray spectra, X-ray intensities and radiation temperature are obtained.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2000, 49 (7): 1307-1311.
doi: 10.7498/aps.49.1307
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The shell model parameters and interionic non-Coulombic potential parameters in rutile TiO2 are determined by empirical parameterization, i.e.,by fit ting models to the structural and macroscopic data such as lattice formation ene rgies, dielectric constants and elastic constants. In terms of these obtained pa rameters the formation energies of point defects are calculated. It is shown tha t Schottky defect is the intrinsic defect in rutile TiO2.
2000, 49 (7): 1312-1315.
doi: 10.7498/aps.49.1312
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Small angle X-ray scattering (SAXS) with synchrotron radiation as X-ray source h as been used to study the structure of SiO2 xerogels prepared by sol-gel pr ocess. All SAXS profiles in this paper deviate from Porod's law and show negativ e or positive deviation. In order to obtain the information of pore in SiO2 xerogels, we have proposed the corresponding methods to correct the negat ive and positive deviations from Porod's law. Then, the average pore diameter of SiO2 xerogels is determined with Debye's method and Guinier's method , separately, and the results are found to be close to each other. The average d iameters fall in the rangl 3-25nm for samples prepared under various conditions. The results of SAXS are also close to that determined by N2 adsorption met hod at 77K with ASAP2000.
2000, 49 (7): 1316-1320.
doi: 10.7498/aps.49.1316
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Scanning tunneling microscopy (STM) has been used to study the adsorption of aspartic acid on the Cu(001) surface at room temperature.At lower coverage,there ex ist two different bonding states and the corresponding diffusion activation ener gies are 079±001eV and 088±005eV,respectively.When the coverage is inc reased,the aspartic acid molecules can finally form an overlayer with uniform co ntrast but could never form any ordered structures.It has been also found that t he adsorption of aspartic acid cannot make steps faceted.It is interesting that all these features are quite different from the adsorption behaviors of other am ino acids on Cu(001),such as glycine,alanine,phenylalanine and lysine,which do n ot have the β-caboxylate.
2000, 49 (7): 1321-1326.
doi: 10.7498/aps.49.1321
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Using Ritz method in obtaining the surface order parameters,we obtained a phase transition from Bc,a biaxial nematic along the film normal,to phase B a,a biaxial phase along the axis in the film plane.The result shows t hat as the biaxial part of the anchoring strength increases,the mechanism of the occurrence of Ba changes from temperature decreasing to surface anch oring.Within a certain range of uniaxial anchoring strength α,increasing α wil l make Ba occur at a higher temperature while further increasing of α will make the liquid crystal reenter Bc from Ba.
2000, 49 (7): 1327-1330.
doi: 10.7498/aps.49.1327
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The internal friction of the Pb-Sn alloys was measured during heating process fr om room temperature to high temperature.It is reported that there is a sudden dr op in the internal friction curves of the vibration systems with the presence of solid-liquid transition of the Pb-Sn alloys.The decrement of the internal frict ion varies with the content of tin.It is proposed that these variations are rela ted with the structure variation of the Pb-Sn alloys during solid-liquid transit ion.
2000, 49 (7): 1331-1334.
doi: 10.7498/aps.49.1331
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Effects of irradiation temperature are explored for metal-oxide-semiconductor de vice under γ-rays.Hardened CC4007 chips were irradiated under different tempera tures,gate bias and annealing conditions.Threshold voltage shift was divided int o Vot and Vit using mid-gap voltage method.Finally,the mec hanism of threshold shift was discussed.
2000, 49 (7): 1335-1343.
doi: 10.7498/aps.49.1335
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The roughness of Mo2C film surface is measured and the results are gi ven.By introduction of crystalline boundary correction,the rapid roughening phen omenon is explained theoretically.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2000, 49 (7): 1344-1347.
doi: 10.7498/aps.49.1344
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A model of 5.3° low angle grain boundaries in steel is set up by using elastict heory of dislocations.The first-principle calculations of energies and the elect ronic structures of impurities for a 5.3° low angle grain boundary (GB) in stee l have revealed important features of the impurity effect.In Fe,impurities such as S,P weaken the intergranular cohesion,resulting in ‘loosening’ of the GB.Th e presence of B,C,N on the contrary enhances the GB.Boron plays a dual role in s teel,not only does it presence at GBs enhance the intergranular cohesion,but als o accomplishes ‘site competition cleaning’ by displacing the other impurity at oms off the GB.
2000, 49 (7): 1348-1351.
doi: 10.7498/aps.49.1348
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The measurements of the specific contact resistance (ρc) were carrie d out for Ti/Au ohmic contact to heavily boron-doped p-diamond (～1020cm-3) by the transmission line model (TLM).I-V measurements were per formed before and after annealing at 500℃,as well as in big current cases.The a nnealing effects on the ρc value were investigated.It is shown that heavy doping of the semiconductor and annealing are effective means to improve o hmic contacts.The changes of ρc value with the operating temperature are discussed.We suggest that the dominant transport mechanism at the metal/sem iconductor interface is tunneling.No light effects on the ρc value h ave been observed,the results show that diamond can be an ideal window material. In our experiments,the smallest ρc value of the Au/Ti/p-diamond reac hes ～10-4Ωcm2.
2000, 49 (7): 1352-1355.
doi: 10.7498/aps.49.1352
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The ZrO2(Y2O3) thin film materials are studed b y slow positron beam.The ZrO2(Y2O3) thin film m aterials are made by r f puttering without biasing,heat treatment of liner being at 300℃ in pure Ar atmosphere.We discovered that the defects distribute themse lves in different depths of the thin film.The tempearture influences the distril ution of defects in the YSZ thin films.And we discuss briefly the method to make dense and high-quality YSZ films.
2000, 49 (7): 1356-1361.
doi: 10.7498/aps.49.1356
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This paper describes the method of artificial doping Y-211 phase and melt-textur ed growth with a top-seeded technique to prepare the quasi-single crystal domain YBCO bulk materials with various Y-211 particle contents.The specimens obtained have high density (more than 62g/cm3) and good mechanical toughnes s.The Jc of specimens reaches 123×106A/cm2 u nder 06T at 30K and 135×104A/cm2 under 2 T at 70K.The scanning electron microscope observation of specimens indicates that Y-211 part icles can improve the quality of melt-textured YBCO superconductor and reduce th e microcrack of specimens.Combining the microstructures with Jc measu rements shows that the smaller the particle size,the more homogeneous the partic le distribution,the higher the pinning effectiveness.The best ratio of Y-123 to Y-211 for the superconductor specimens is 1∶05 in moles,in which the Y-211 pa rticles are uniformly distributed and their size is about 200nm.
2000, 49 (7): 1362-1365.
doi: 10.7498/aps.49.1362
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On the basis of the single-ion model, a method of calculation on the magnetizati on curves for magnetically aligned rare-earth-Fe(Co) intermetallic compound is d eveloped. High-field magnetization curves for magnetically aligned Nd2Fe14B and Pr2Fe14B were calculated by using th e above method. In the calculations, the fitted exchange and crystalline field p arameters from magnetization curves of the single crystals were used. The calcul ated curves agree well with the experiments.
2000, 49 (7): 1366-1370.
doi: 10.7498/aps.49.1366
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This paper discusses the preparation of the colossal magnetoresistance samples L a0.7Sr0.3CrxMn1-xO3 (x=0, 0.10, 0.15) and La0.7Sr0.3FexMn1-xO 3 (x=0.05,0.10,0.16) by the sol-gel technique. The effects that the s ubstitution of Cr or Fe for Mn in La0.7Sr0.3MnO3 affects its structure, magnetic properties and magnetoresistance are also stud ied. Two peaks are observed on the resistance-temperature curves (R-T curves) of the two samples La0.7Sr0.3Cr0.15Mn0.85O3 and La0.7Sr0.3Fe0.05Mn0.9 5O3. The mechanism for the potential appearance of the double p eaks is discussed. A conclusion is drawn that with the increase of Cr (or Fe) s ubstituting for Mn, the samples' Curie temperature (TC), ferromagnetism and conductivity decrease， whereas their magnetoresistance strengthens. However, t he same amount of Cr produces less effect on the samples than the same amount of Fe.
2000, 49 (7): 1371-1376.
doi: 10.7498/aps.49.1371
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The TC of BaμSr1-μTiO3(BST) as a f unction of the composition and the lattice parameter γ is examined. It is compa red with the lattice parameter dependence of TC of BaTiO3 and SrTiO3 respectively. It is argued that the variation of TC in BST can be attributed to the change of cell volume. The order and the di ffuseness of the phase transition are also discussed from the volume effect view point. The fact that the Ba and Sr are ionized leads to the volume effect of BST .
2000, 49 (7): 1377-1382.
doi: 10.7498/aps.49.1377
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The electron traps in SrS:Eu and SrS:Eu, Sm were studied by the time dependence of their afterglow and the fluorescence rising process at the beginning of excitation. The numbers of traps in both phosphors were compared and the singly doped SrS:Eu was found to have approximately the same trap number as the latter at the absence of Sm inos. The absorption spectra of SrS:Eu,Sm at excited and bleached states were measured respectively. The difference at infrared region between them demonstrates the transitions of electrons from the traps to conduction band, which were studied by stimulated spectrum normally. The concentration dependence of Eu and Sm of this difference that we named stimulating absorption spectrum was examined. The results show that the complexes formed by combination of Sm ions and crystal defects such as anion impurity ions or vacancies act as the storageable traps, i.e.,Sm ions play a role of deepening the trap levels so that the trapped electrons can be stored stably.
2000, 49 (7): 1383-1385.
doi: 10.7498/aps.49.1383
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Blue light (449nm) has been observed at room temperature and it has been multip le enhanced (up to 6.3 times) in ion implanted samples. The quantum confinment-l uminence center model can well explain it. A new type of material that can emit blue light has been prepared.
2000, 49 (7): 1386-1389.
doi: 10.7498/aps.49.1386
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Hydrogenated amorphous SiOx films are fabricated via plasma enhanced chemical vapor deposition technique. After erbium implantation and rapid thermal annealing, photoluminescence (PL) are measured at 77K and room temperature (RT) , respectively. We observed the strong PL at 1.54μm at RT. The 1.54μm PL inten sity changes with the variation of concentration of oxygen. The most intense PL at 77K in a-SiOx∶H (Er) corresponds to O/Si=1.0 and at RT to O/Si=1. 76. Based on our results, we propose that Er ions contributed to PL come from O- rich region in the film. Er ions in Si-rich region have no relation with PL. Tem perature dependence of the intensity of the 1.54μm line of the Er3+ transition displays a very weak temperature quenching in Er-doped hydrogenated a morphous Si. The PL intensity at 250K is a little more one half of that at 15K.
2000, 49 (7): 1390-1393.
doi: 10.7498/aps.49.1390
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A composite oxide material Gd3Ga5O12:Ag was pre pared by solid state reaction. The composition and the crystallinity of phosphor were determined by X-ray diffraction. The thin film electroluminescence (EL) de vices based on Gd3Ga5O12:Ag were prepared by el ectron beam evaporation. We have obtained a good UV-blue EL emission with a peak at 397nm and a shoulder at 467nm. The EL peaks located at 397 and 467nm are fou nd to originate from the oxide vacancies and 4d95s0 to 4d10 of Ag+, respectively.
2000, 49 (7): 1394-1399.
doi: 10.7498/aps.49.1394
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We studied the dynamical behaviors of the depletion-mode AlGaAs/GaAs high-electr on-mobility transistor under optical illumination. The photovoltage effect and t he photogenerated carriers contribution to the space charge concentration were t aken into account. The pinch-off voltage, the sheet concentration of two-dimensi onal electron gas (2-DEG) located at the interface of the heterojunction, the I- V characteristic curve, and the transconductance were investigated by using the charge-controlling model. We found that the pinch-off voltage was lowered and th e sheet concentration of 2-DEG was increased because of the optical illumination , which, in turn, resulted in an increase in the current gain and the transcondu ctance of the device.
2000, 49 (7): 1400-1403.
doi: 10.7498/aps.49.1400
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Using Normaski polarization interference technique, the expansion process of a plasma generated by ultrashort laser pulses was optically diagnosed. Temporal resolved interferogram of the laser-plasma has been obtained. A strong pinch effect in the transverse dimension has been observed for a jet expansion of the laser- plasma. It is found that the pinch effect was due to the confinement of the magn etic fields generated in the laser-plasma.
2000, 49 (7): 1404-1408.
doi: 10.7498/aps.49.1404
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The (SiO2/Si/SiO2) nanoscale double-barrier/n+- Si structures with Si layers of various thicknesses were fabricated by the two-t arget alternative magnetron sputtering technique. The thicknesses of the Si laye rs in the structures are from 2nm to 4nm with an interval of 0.2nm. The control samples with Si layers of 0nm were also made. After these structures were anneal ed at 600℃ in a N2 ambient for 30min, electroluminescence (EL) from the Au/SiO2/Si/SiO2/n+-Si structures were obser ved under reverse biases (n+-Si is biased to positive). It was found that the current and EL intensity synchronously swing with increasing Si layer t hickness. All EL spectra of the samples can be decompounded into two Gaussian lu minescent spectra with peaks at 1.85eV (670nm) and 2.26eV (550nm). Analysis of e xperimental results indicates that the EL orginates from the recombination of el ectrons and holes, which are produced in an avalanche process in the Au/(SiO2/Si/SiO2) nanoscale double-barrier/n+-Si structure , via luminescence centers in the SiO2 layers.
