Vol. 54, No. 5 (2005)
2005, 54 (5): 1965-1968. doi: 10.7498/aps.54.1965
In this paper, a fuzzy matching criterion of membership function based on shape description matrix (SDM) is presented to analyze and compare shape characteristi cs of images. Analysis and experimental result show that by applying this approa ch to image retrieval, more effective image retrieval can be achieved.
In this paper, we study the Hamiltonian Ermakov systems using the method of form invariance. In terms of the form invariance of the Hamiltonian Ermakov systems,the generator of point symmetry transformations and the partial differential equations for the potential energy are obtained by comparing the coefficients of all monomials.The result indicates that under the point symmetry transformations,only the autonomous Hamiltonian Ermakov systems possess form invariance.
2005, 54 (5): 1972-1976. doi: 10.7498/aps.54.1972
We have investigated the elliptic cylindrical quantum dot by adopting elliptic cylindrical coordinates and infinite-potential model, and presented the expressio ns for calculating the energy structures and wave-functions of the single electr on in the elliptic cylindrical quantum dot.
2005, 54 (5): 1977-1981. doi: 10.7498/aps.54.1977
The quantum state number and free energy of the scalar field at the horizon of g eneral non-stationary black hole with charges are calculated and the result show s that the entropy of black hole is proportional to the event horizon area. This implies that the black hole entropy is just identical to the entropy of the qua ntum field on the event horizon. Taking into account the effect of the generaliz ed uncertainty principle on the black hole entropy and adopting the 2-D membrane model, the divergence in the brick-wall model is removed, without any cut-off， and the little mass approximations appear in the brick-wall model and the thin f ilm model are removed. Calculating the scalar field on the 2-D membrane outside horizon by using progression method we obtained some interesting results.
2005, 54 (5): 1982-1987. doi: 10.7498/aps.54.1982
A dynamical model, based on the Lattice Boltzmann method, is presented for simul ating the two-dimensional moving elliptic cylinders in a Newtonian fluid. Using this model, we have simulated the motions of elliptic cylinders with different shapes in a Newtonian fluid under the same initial conditions, and the motions o f an elliptic cylinder under different initial conditions. The numerical simulat ions are compared with the results of moving cylinders under the same conditions . The characters of the two-dimensional moving elliptic cylinders are discussed, and some new results are obtained.
2005, 54 (5): 1988-1993. doi: 10.7498/aps.54.1988
In this paper, a new method is proposed to implement subband forecast within the nonlinear noisy time series based on abstracting and reconstruction of the sign al's main components and adaptive Volterra filter theory.By considering noise's wavelet transform characteristic,the main component of noise signal is abstracte d by using the wavelet package decomposition in an appropriate scale and the ma ximum module reconstruction algorithm,then the forecast components are brought f rom adaptive Volterra forecast filter to reconstruction the final signal.This m ethod improves the traditional blindness in selecting scale in wavelet decomposi ng denoise,avoids the shortage of antinoise capability of Volterra series model used singly.The simulated results show that it is a practicable and effective me thod for nonlinear noise signal.
Simulation and theoretical analysis on detection of the frequency of weak harmonic signals based on a special chaotic system
2005, 54 (5): 1994-1999. doi: 10.7498/aps.54.1994
In order to study a kind of chaotic system which is based on the special Duffing-Homes equation, and use it to detect the unknown frequency of weak harmonious s ignals, we prove the existence of the periodic solution and the exclusivism of the solution, carry out simulation experiments to detect harmonious frequency us ing the periodic trajectory of a stable phase state.We also compute the detectio n error |Δω|,when the damping ratio (α) changes and the frequency changes fro m 1Hz to 200Hz. The results show that we have to choose the value of α correspo nding to the different range of frequency by simulation experiments.
2005, 54 (5): 2000-2006. doi: 10.7498/aps.54.2000
In this paper, we present the synchronization of chaotic injected semiconductor lasers in an optical fiber system via phase-controllers controlling its lasing p hase shift, and a theoretical model for optical fiber chaotic secure communicati on system via chaos phase shift modulation by coupling a chaotic laser phase con trolled synchronization system and an optical fiber channel. Chaotic synchroniza tion is realized numerically under phase-controllers controlling in a long-haul optical fiber system. Optical fiber chaos propagation formula is demonstrated by analyzing theoretically the effect of optical fiber self-phase modulation on ch aotic signal and synchronization. Chaotic laser phase shift is controlled and it s signal is transmitted via continuous chaos shift keying modulation on end for optical fiber communication encoding. Chaotic laser demodulation is achieved via setting a phase shift of the receiver phase-controllers for optical fiber commu nication decoding. Application of chaotic digital encoding of 50Mbit/s rate is simulated numerically for long-haul optical fiber secure communication. The system parameter mismatch and robustness of anti-noise are analyzed numerically in long-haul optical fiber propagation, in particular.
2005, 54 (5): 2007-2012. doi: 10.7498/aps.54.2007
The coordinate and spectral integral representations of Hamiltonian in isotropic LandauLifschitz equation are given by a standard procedure.But,the problem of deriving the corresponding conserved quantity to connect two kinds of integral mentioned above is still open.In this paper,using the gauge invariance properties,the compatibility pair of LL equation is transformed to the form-ikσ3+O(1) by choosing an app ropriate tr ansformation.Hence,the conserved quantities are obtained.The zeroth conserved qu antity,I0,is zero.The first one,I1,which has coordinate an d spe ctral integral representations,coincide with the two desired integral representations of the Hamiltonian.
2005, 54 (5): 2013-2018. doi: 10.7498/aps.54.2013
The intensity of upconversion emissions of rareearth ions is determined by the maximum phonon energy of glass host. In this paper the intensities of upconversion emissions in Yb3+/Er3+codoped germanatetellurite glas ses upon the excitation of 980nm laser diode were extremely enhanced by replacing PbO wit h Bi2O3 and increasing the size of alkalimetal ions. Rama n spectra show tha t the maximum phonon energies of the glass hosts investigated keep unchanged, wh ile the maximum phonon density decreases on substituting Bi2O3 for PbO and i ncreasing the size of alkalimetal ions. Based on the nonradiative decay rate, it is found that the maximum phonon density is the main reason for the enhanceme nt of upconversion emissions in Yb3+/Er3+codoped germana tetellurite glasses.
ATOMIC AND MOLECULAR PHYSICS
Total cross sections for the scattering of electrons from methane and chloromethanes at intermediate and high energies
2005, 54 (5): 2019-2024. doi: 10.7498/aps.54.2019
A complex optical model potential modified by incorporating the concept of bonde d atom, which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule, is employed to calculate the total cross sect ions for electron scattering from methane and chloromethanes（CH4 , CCl4, CHCl3, CH2Cl2 and CH3Cl）over the incident energy r ange 30—5000eV by using additivity rule model at Hartree_Fock level. In the stu dy, the complex optical model potential composed of static, exchange, correlatio n polarization plus absorption contributions uses the bonded_atom concept. The quantitative molecular total cross_section results are compared with the experim ental data and other calculation results wherever available, and good agreement is obtained. It is shown that the additivity rule model together with the comple x optical potential model modified by incorporating the concept of bonded atom c an give better results than that unmodified. So, the introduction of the bonded_ atom concept in the complex optical model potential improves the accuracy of the total cross_section calculation results of electrons from molecules.
CLASSICAL AREA OF PHENOMENOLOGY
2005, 54 (5): 2025-2029. doi: 10.7498/aps.54.2025
Based on the generalized Lorenz_Mie theory(GLMT),the incident fundamental Gaussi an beam is expanded in terms of the vector spherical harmonics. The interaction of Gaussian beam with a cluster composed of spheres located on the propagation a xis is analyzed. The numerical results are discussed and compared with those obt ained in the plane wave incident case.
2005, 54 (5): 2030-2033. doi: 10.7498/aps.54.2030
In this paper, a uniform axial line_focus, which is important for the x_ray lase r amplification pumped by picosecond and femtosecond laser pulses, is generated by a binary_phase Fresnel zone plate. The performances of the plate are tested u sing a ultrashort_pulse laser. The results show that the length and the width of the line_focus are ～5mm and ～100μm respectively, when coupled with a 125mm f ocal length lens. The ratio of the peak intensity at the center of the line focu s to the intensity outside around the line focus is 7:1
2005, 54 (5): 2034-2037. doi: 10.7498/aps.54.2034
Since hard x_ray in_line phase_contrast imaging is based on Fresnel diffraction of x_ray, we propose to make phase retrieval calculations between arbitrary plan es interrelated through the Fresnel domain. The calculation of the free space pr opagation is based on the angular spectrum approach, which can be used with Gerc hberg_Saxton algorithm for phase retrieval. We call this method the iterative an gular spectrum approach. The new method is tested on simulated images in the cas e of uniform illumination and is demonstrated to be efficient for phase retrieva l.
2005, 54 (5): 2038-2042. doi: 10.7498/aps.54.2038
By using double-exposed holographic interferometry, the distribution of sound pr essure in the acoustic levitation field is analyzed. The holograms under differe nt conditions are obtained and compared with each other. It is shown that the me asured holograms are consistent with the theoretical ones, and the intensity dis tributions along their central axis are identical. Compared with other methods, double-exposed holographic interferometry has the merits of non-contact, non-int rusive and whole-field measurement; and it provides a more convenient and more i ntuitionistic approach to realize acoustic field and guarantees the optimization of acoustic levitation system.
2005, 54 (5): 2043-2048. doi: 10.7498/aps.54.2043
The time evolution of entanglement and disentanglement between a Λ-type three-l evel atom and a single-mode field initially in the number state in an ideal cavi ty are investigated by considering von Neumann entropy of the optical field. Res ults indicate that entanglement of the system displays periodicity; the maximal degree of entanglement depends on the initial atomic state, the initial photon n umber and the ratio of detuning to the coupling constant, while the number of ti mes for maximal entanglement and disentanglement in a period is independent of t he initial photon number. The initial relative phase between the two lower state s have effects on the time evolution of field entropy, while the initial relativ e phases between the excited state and the ground states of the atom does not.
2005, 54 (5): 2049-2058. doi: 10.7498/aps.54.2049
In this paper, the quantum statistical properties of the superposition state,a｜ β〉+beiφ｜mβeiδ〉,which involves two arbitrary coh erent states, are investigated. The results show that this kind of super-positio n states generally exhibits squeezing effect or anti-bunching effect. The quantu m effects of the superposed state depend on β2 and the amplitude coe fficient m, as well as the changes of the phase difference between two coherent states δ, and the phase difference between two superposition coefficients φ al so plays an important role in squeezing or anti-bunching effects.
Spontaneous emission properties of a two-level atom with an intense low-frequency field in a three-dimensional photonic crystal
2005, 54 (5): 2059-2065. doi: 10.7498/aps.54.2059
We have investigated spontaneous emissions from a two-level atom embedded in a p hotonic crystal with three-dimensional dispersion relation as well as interacted with a coherent intense low-frequency field .Due to this field, additional deca y channels with exchange of one low-frequency photon during an atomic transition are created, resulting in the spontaneously induced quantum interference. The s pontaneous emission can be suppressed significantly because of the combinational influences of the quantum interference effect and the band edge effect. The pop ulation in the upper levels depends on the relative position of the upper level from the band edge. The frequency of the low-frequency field and the relative in tensity of the coupling strength for the transitions can affect spontaneous emis sion from the atom.
2005, 54 (5): 2066-2071. doi: 10.7498/aps.54.2066
A novel scheme based on cross-gain modulation in cascaded single-port-coupled se miconductor optical amplifier(SOA) is studied theoretically and experimentally. Theoretical model for the single-port-coupled SOA is established for theoretical simulation and performance evaluation.The 10Gb/s all-optical logic AND operatio n has been demonstrated theoretically and experimentally. A parameter is exploit ed to evaluate the output performance. Results show that the output performance is tightly related to input power and input extinction ratio. Theoretical calcul ation results are in agreement with the experimental results.
2005, 54 (5): 2072-2078. doi: 10.7498/aps.54.2072
The electronic structures and dipole moments of para- nitroaniline molecule are calculated by use of density functional theory at ab initio level. We then inve stigate theoretically the interaction between the ultrashort pulse laser and the para-nitroaniline molecule medium by solving the full Maxwell-Bloch equations. The effects of permanent dipole moments on the pulse reshaping, the spectrum com ponents, and the evolutions of energy state populations are discussed in detail. The results show that the standing slowly varying envelope and the rotating-wav e approximations fail to give a good description for the propagation of an ultra short pulse in the molecule medium. Furthermore, the dipole moments of the molec ule make the propagation deviate from the area theorem further and make the pul se split more quickly. When the pulse with the excitation energy of the charge-t ransfer state propagates in the para-nitroaniline molecule medium, the second-ha rmonic spectral component appears obviously and becomes stronger as the propagat ing distance increases, which displays the high two-photon absorption properties of the molecule.
2005, 54 (5): 2079-2083. doi: 10.7498/aps.54.2079
Quasi-phase-matched second harmonic generation(SHG) in bulk periodically poled L iNbO3(PPLN) was studied , the coupled-wave equations for quasi-phase- matched S HG was accurately resolved, and the formula for calculating SHG conversion effic iency under focusing Gauss beams was given. The relations between focusing beams waist and crystal length were analyzed. Furthermore, the SHG cavity was opti mized to obtain the maximum conversion efficiency.
2005, 54 (5): 2084-2089. doi: 10.7498/aps.54.2084
The phase matching for second harmonic generation(SHG) in biaxial nonlinear-optical crystals is discussed and the accurate calculation of the corresponding effective nonlinear coefficients is presented, based on which the optimum phase matching can be determined. As an example, numerical treatment of phase matching and the corresponding effective nonlinear coefficients for SHG at fundamental wavelengths of 1.064μm and 0.808μm in the organic nonlinear-optical crystal benzophenone is performed, and accordingly the optimum phase matchings are found.
2005, 54 (5): 2090-2095. doi: 10.7498/aps.54.2090
We present a numerical study of coherent collisions of multi photovoltaic bright spatial solitons. The result shows that when the colliding solitons are in-phas e, they will attract each other and the inner ones will fuse together gradually. When the relative initial phase between any two adjacent solitons is π2, they will experience a power transfer which includes three basic interaction modes. When the colliding solitons are out of phase, they will propagate stably, which may be useful for the formation of soliton arrays and waveguide arrays.
2005, 54 (5): 2096-2101. doi: 10.7498/aps.54.2096
The photonic band structure of two-dimensional magnetic photonic crystals(MPCs) composed of magnetic pillars in different shapes (rectangular, square, hexagonal and circular) sitting on square lattice is investigated by use of the plane wa ve expansion method. The optimal MPCs, which possess the largest photonic band g ap and the lowest frequency in the middle of the photonic band gap, are picked u p when scanning the parameters (filling factor, orientation angle, and permeabil ity). Based on the results, we construct theoretically the mixed MPC heterostruc tures and investigate the guide modes at interface. The guide modes along the in terface of the heterostructures can be generated without any lattice distortion when the scattering pillars are in shapes of rectangle, hexagon, and circle.
The dispersive characteristics of impurity bands in coupled-resonator optical waveguides of photonic crystals
2005, 54 (5): 2102-2105. doi: 10.7498/aps.54.2102
We found that the dispersive properties of impurity bands in a coupled-resonator optical waveguide based on photonic crystals depend on the properties of the fields localized at the two neighboring defects instead of the distance of the defects. In fact, the seemingly anomalous dispersion of the impurity band in the first Brillouin zone is a result from band folding. After calculating the effective refractive index of the structure, we have verified that the impurity band has a normal dispersion.
2005, 54 (5): 2106-2110. doi: 10.7498/aps.54.2106
Phenomena of self-coherence and mutual-coherence of the distributed fiber optic sensor based on the principle of polarized-mode coupling are analyzed. The inter ference characteristics measured by experiment validate the theoretical analysis . The spatial resolution of the distributed fiber optic sensor is determined by the polarized dispersion coefficients of polarization-maintaining fiber and the spectral width of the light source. The spatial resolution of the polarized-mode s coupling distributed fiber optic sensor measured by experiment is 6cm.
2005, 54 (5): 2111-2117. doi: 10.7498/aps.54.2111
A piezoelectric strip of infinite length but with finite width and thickness is placed on top of an isotropic elastic half space. The piezoelectric strip is excited by an electrical signal and the acoustic field is generated. The piezoelectric strip is of type 6mm crystal system oriented along its length direction. The SH wave is studied for the structure of this piezoelectric transducer. At first, the field is expanded as a Fourier series in the piezoelectric strip and as a Fourier integral in the half space. Then, the response of the solution inside the piezoelectric strip and in the half space is obtained by the boundary conditions. The acoustic field distribution is analyzed and compared to that obtained by the traditional method. Finally, the acoustic radiation field at the far field is investigated by the saddle point method and the directional factor is analyzed. It is found that the traditional method is valid only in the case where the product of the frequency with the width of the piezoelectric strip is less than1kHz·m. The stress and displacement in the piezoelectric strip are oscillatory distributions when the frequency increases. The greater the frequency, the greater the difference between the traditional method and the present method.
2005, 54 (5): 2118-2122. doi: 10.7498/aps.54.2118
1/f noise in n-channel and p-channel metal_oxide_semiconductor field effect tran sistors(MOSFETs) with different channel areas, are studied in theory and experim ent. Experimental results demonstrate that the 1/f noise magnitude in n-channel MOSFETs is ten times than that in p_channel MOSFETs, but both magnitudes are al l in inverse proportion to the power of effective gate voltage and its active ar ea, while they are in direct proportion to the power of drain voltage. Based on these experimental results, the mechanisms are discussed that the 1/f noise in M OSFETs is attributed to the random trapping/detrapping processes between channel and oxide traps near the SiO2_Si interface about several nanometers, which ca use fluctuations in both the number and the mobility of channel carriers. Based on these mechanisms, a unified 1/f noise model for MOSFETs is developed, includi ng tunneling and thermal activation through which traps communicate carriers wit h channel. Experimental results agree well with the developed model.
2005, 54 (5): 2123-2127. doi: 10.7498/aps.54.2123
Chemical mechanical polishing(CMP) is a manufacturing process used to achieve th e high levels of global and local planarity required. Currently, the slurries us ed in CMP usually contain particles at nano scale to accelerate the material rem ove ratio (MRR) and to optimize the planarity. Micro polar theory will provide a feasible candidate to describe the rheology of these fluids. It will provide so me insights into the mechanism to solve the flow equation of CMP with the micro- polar effect considered. The effects of micro polarity on load and moments are s imulated and computation results are given. The results show that micro-polarity will give rise to an increase in load capacity to a certain extent by increasin g the equivalent viscosity of the slurries, through which the material removal c an be accelerated. The size-dependent feature can be seen since it becomes more prominent with low pitch height and low pad velocity. The effects of micro-polar ity on material removal rate in CMP process were experimentally investigated by altering the polarity of the slurries, which support the theoretical analysis.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (5): 2128-2132. doi: 10.7498/aps.54.2128
The basic idea of two-centre atomic orbital close coupling method is introduced in ion-atom collision process. We have found a systematic procedure to obtain th e parameter in close coupling calculation. We calculate the single electron capt ure cross sections for the collision of the multiply charged O6+ ion s with hydrogen atoms. The present calculations are in good agreement with exper imental data.
2005, 54 (5): 2133-2137. doi: 10.7498/aps.54.2133
The energy spectra of ion beams emitted from gas-puff Z-pinch plasma was experim entally studied with a compact Thomson spectrometer, which is composed of an inp ut window, deflecting electromagnetic fields,a rear pinhole, and a CR-39 track d etector. Ion beams were collimated by a front pinhole and the input window of Th omson spectrometer and deflected in the electromagnetic fields, and then they pa ssed through the rear pinhole to hit the CR-39 detector. Based on the detected p ictures of parabolas, we have calculated the energy spectra of ion beams and fou nd that the energy spectra move toward the direction of lower energy for a bad Z -pinch shot. A “bad Z-pinch shot" here means a shallower dip on the di/dt signal, which is the time derivative of Z-pinch current.
2005, 54 (5): 2138-2146. doi: 10.7498/aps.54.2138
The spatio temporal evolution of electromagnetic (Weibel-type) and electrostati c (two-stream) instabilities of electron beams propagating in collisionle ss plasmas were investigated by using electromagnetic relativistic particl e-in-cell simulations. The onset and nonlinear saturation of Weibel instability , the emergence of beams and magnetic field reconnection were discussed. T he excitation of longitudinal electric field plays an important role for the stable propagation of electron beams, which can be destructed by the transverse modulation due to two-stream instability. These results may be important for understanding the static magnetic field generation and fast electron propagati on in fast ignition physics.
Ions extraction and collection using the RF resonance method and taking into consideration the sputtering loss
2005, 54 (5): 2147-2152. doi: 10.7498/aps.54.2147
One_dimensional ions extraction and collection using the RF resonance method is studied by PIC-MCC simulation. The energy and angle distribution of extracted ions is recorded and the sputtering loss is calculated. The results show that compared with parallel electrode method, RF resonance method has advantages such as shorter extraction time, lower collision loss and sputtering loss and higher col lection ratio; the extraction time and collision loss are decreased with increas ing extraction voltage, but the sputtering loss increases and collection ratio d ecreases; collision loss is decreased with increasing magnetic field, but the sp uttering loss increases and collection ratio decreases.
Measurement of metastable state densities and electron temperatures in an electron cyclotron resonance argon plasma
2005, 54 (5): 2153-2157. doi: 10.7498/aps.54.2153
The number of metastable state densities obtained ranges from 1×1015to 4×1015 m-3 in the electron cyclotron resonance (ECR) argon plasma by measuring the optical absorption of the 8115 nm spectral line under the conditions of 02—08 Pa and 500—800 W. Taking into account the c ontribution of both the ground state and the 1s5 metastable state to the emiss ions, the electron temperature Te is measured by the ratio of emissio n lines. Results show that there are obvious differences compared with only considering t he metastable state densities.
2005, 54 (5): 2158-2161. doi: 10.7498/aps.54.2158
A method to prepare single-walled carbon nanotubes (SWNTs) by using a new type o f catalyst is presented. With a certain proportion, cerium oxide (CeO2) and gr aphite powders were mixed. The mixture was then filled into the longitudinal hol es of graphite sticks used as composite graphite electrode. With it as the anode , arc discharge was carried out in He atmosphere. The resultant collected was ob served and analyzed by using HRTEM and Raman spectroscopic analysis, indicating that a large amount of SWNTs with a uniform diameter were close-packed in bundl es and the average diameter of SWNTs was about 120nm—132nm.
2005, 54 (5): 2162-2166. doi: 10.7498/aps.54.2162
The secondary discharge is an important factor for power loss in the high-voltag e and high- power solar cell array. This paper studies the characteristics of th e secondary discharge and the breakdown mechanism through identifying the voltag e threshold where the secondary discharge will probably occur and monitoring the pulse current of the secondary discharge. The results show that increasing the operation voltage and string current will increase the possibility of the occurr ence of the secondary discharge on the solar array. The special structure design and the presence of RTV grouting between the solar cell strings can prevent th e secondary discharge incidents efficiently.
Temporal evolution of electron excited temperature in micro-discharge in argon at atmospheric pressure
2005, 54 (5): 2167-2171. doi: 10.7498/aps.54.2167
The temporal evolution of electron excited temperature of micro-discharge in die lectric barrier discharge (DBD) in argon at atmospheric pressure is studied by s pectroscopy method. The time-resolved spectra of 69654nm (2P2→1S5), 763 51nm (2P6→1S5) and 77242nm (2P2→1S3) Ar are measured. It is found th at the voltage decreases during the discharge, and increases after the discharge quenched. The transition of lower level 2P6 (76351nm) is some doze ns of ns ahead of the transitions of higher level 2P2 (77242nm and 69654nm ). Accord ing to the time-resolved spectrum, the electron excited temperature is estimated during the discharges. It is shown that the temperature is not a constant.It is variable with the time.The peak value of temperature exists about two hundred n s time_delay after the peak value of the discharge current.It is shown that the electron excited temperature does not reach its peak value when the electron den sity is at the peak value.And the electron excited temperature reaches the peak value 200ns late.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
The microstructure of hydrogenated microcrystalline silicon thin films studied by small-angle x-ray scattering
2005, 54 (5): 2172-2175. doi: 10.7498/aps.54.2172
The microstructures of hydrogenated microcrystalline silicon (μc-Si:H) thin fil ms, prepared by plasma-enhanced chemical vapor deposition (PECVD), hot wire CVD( HWCVD) and plasma assisted HWCVD (PE-HWCVD), have been analyzed by the small ang le x_ray scattering(SAXS) measurement. The SAXS data show that the microstructur es of the μc-Si:H films display different characteristics for different deposit ion techniques. For films deposited by PECVD, the volume fraction of micro-voids and mean size are smaller than those in HWCVD sample. Aided by suitable ion-bom bardment, PE-HWCVD samples show a more compact structure than the HWCVD sample. The microstructure parameters of the μc-Si:H thin films deposited by two-steps HWCVD and PE-HWCVD with Ar ions are evidently improved. The result of 45° tilti ng SAXS measurement indicates that the distribution of micro-voids in the film i s anisotropic. The Fouriertransform infrared spectra confirm the SAXS data.
2005, 54 (5): 2176-2182. doi: 10.7498/aps.54.2176
Structure and magnetic properties of the (Nd1-xErx)3Fe25Cr40 (x=0—10) compounds have been investigated by means of x -ray diffraction and magnetic measurements. It is found that the compounds with x =0—08 crystallize in Nd3(Fe,Ti)29-type structure, A 2/m space grou p, but those with 082Ni17-type structure, P63/mmc space group. Both the Curie tem perat ure Tc and the saturation magnetization Ms of (Nd1 -xErx)3Fe25Cr40 de crease monotonically with increasing Er content. The easy magne tization direction (EMD) of the Nd3Fe25Cr40 compound is close to the ［040］ direction at room temperature, but makes a tilted angle with the ba sal plane of 1∶5 structure. With increasing Er content the EMD changes to much close to the  direction and the tilted angle increases. AC susceptibility m easurement indicates the appearance of a spin reorientation at low temperatures for the compounds with x=0—04 and x=10, and the spin reorientation temperature Tsr increases monotonically as the Er content increas es fo r the compounds with x=0—04 First-order magnetization process (FOMP) is observed in the compounds with 0≤x≤08 and the critical field Bc rof the FOMP decreases with increasing Er content from 66T for x=0 to 20T for x=07
2005, 54 (5): 2183-2187. doi: 10.7498/aps.54.2183
Based upon the Landauer formula,we have studied electron transport properties of finite incommensurate and commensurate double_walled carbon nanotubes(DWNTs).The results obtained show that the geometrical structures of the tube may produce significant effects on their electron transport properties:Electron transport of the incommensurate DWNTs may be either ballistic or non_ballistic,depending on the energy region.The commensurate DWNTs formed by the armchair tubes may displa y quick and slow oscillation;however,those formed by the zigzag tubes have no re gular slow oscillation.
2005, 54 (5): 2188-2193. doi: 10.7498/aps.54.2188
A new model of medium is established,in which the elastic modulus is bigger when the sound wave is in the compressed area,while it is smaller in the expanding area.The strong nonlinear coupling effect occurs when the compressed wave and the expanding wave exist in the same area.The calculated results show that the coupling of compressed wave and expanding wave can result in the expanding of the system,which is related to the relative difference between the expanding elastic modulus and compressing elastic modulus.In addition,the results obtained from the elastic modulus of non_continuum are the same as the limit case of continuous elastic modulus.
Pressure and temperature dependence of shear modulus and yield strength for aluminum, copper and tungsten under shock compression
2005, 54 (5): 2194-2197. doi: 10.7498/aps.54.2194
Experimental data of shear modulus and yield strength of shocked aluminum, copper and tungsten were analyzed systematically. Comparison between these data and t he results calculated by using SCG(Steinberg-Cochran-Guinan) constitutive model (J.Appl.Phys.51(3):1498) shows that shear modulus and yield strength have simila r dependence on pressure and temperature under conditions for aluminum below 50 GPa, copper below 100 GPa and tungsten below 200 GPa shock pressures. So the as sumptions in the SCG model,Y′pY0=G′pG0,Y′TY0=G′TG0, are approximately correct in these pressure ranges, and the SCG model can be used to describe the shear modulus and yield strength of these metals at high shock pr essure and high temperature.
2005, 54 (5): 2198-2201. doi: 10.7498/aps.54.2198
Based on the negative eigenvalue theory we discuss the non-diagonal disorder and dimensional effects for the electronic structure in low-dimensional disordered systems. The result shows that: It is the non-diagonal disorder and the dimensio nal effect that strongly affects the electronic structure in the low-dimensional disordered system. The non-diagonal disordered mainly shows the changes of the structure and the boundary effects of the particles in the system. From one- dim ensional system to narrow gap one, the number of the electronic bandgap decrease s, the degree of local states increases, and the structure of the energy gap wil l be more complicated.
2005, 54 (5): 2202-2206. doi: 10.7498/aps.54.2202
Based on the static-friction model for solid-liquid-vapor contact line suggested by Adam and Jessop，one can calculate surface-tension coefficient of solids from the data of wetting angles, but the results depend on the friction condition adopted. Using the data reported on stainless steel and polypropylene samples as examples, we have compared the surface-tension coefficients given by the Mises yield condition and Amonton's friction law. It is found that only the latter pos sesses always the Wenzel behavior which claims an increase of surface-tension co efficient with surface roughness, as well as total wetting condition, namely rec eding angle vanishes when the difference of solid-liquid and solid-vapor coeffic ients equals that of liquid-vapor. This shows that the Amonton's law seems to be more reasonable for describing the static friction of contact line.
2005, 54 (5): 2207-2211. doi: 10.7498/aps.54.2207
The desorption spectrum of NO adsorbed on the surface of TiO2 powder was determined by temperature programmed desorption. The molecular orbital theory was u tilized to investigate the crystal cluster model of NO adsorbed on TiO2 and th e change of band gap in the adsorption process. The results indicate that there exist two peak temperatures, 450 and 980K, as N2 desorption followed by the NO adsorption on TiO2 The intensity of N2 desorption decre ases if the TiO2 powder is pretreated in an O2 atmosphere. The nitrogen atoms of the adsorbed NO gas recombine into N2 for desorption while oxygen atoms occupy th e oxygen vacancies in the TiO2 surface. The calculation analysis from the mole cular orb ital theory supports the deduction that the existence of oxygen vacancy on TiO2(110) surface offers a suitable condition of crystal surface for NO ad sorption.
2005, 54 (5): 2212-2219. doi: 10.7498/aps.54.2212
The two_dimensional thin film growth is simulated by modified diffusion_Limited_ aggregation method. The thin film morphologies such as fractal growth and dense growth are obtained by changing the parameters DT,DC an d ＤＶ. The number and the size of clusters changing with coverage are analyzed. The re sults are consistent with the experimental results.
2005, 54 (5): 2220-2225. doi: 10.7498/aps.54.2220
The preparation of silicon nanoporous pillar array (Si-NPA) and Fe3O 4 coated Si-NPA (Fe3O4/Si-NPA) is presented. The morphologies and microstructures of the two kinds of thin films were characterized and their corresponding capacit ive humidity sensing properties investigated. It was shown that both Si-NPA and Fe3O4/Si-NPA are typical micron/nanometer structural compo site systems. When the relative humidity increased from 11% to 95%, the capacitances reached 1500% and 5500% of their initial values measured with 100 Hz signal frequency, and 800% and 12000% measured with 1000 Hz signal frequency, for Si-NPA and Fe3O4/S i-NPA, respectively. At the same time, both of the two thin films exhibited quic k response speed, the response times in the humidity-increment and humidity-decr ement processes were determined to be 15 s and 5 s for Si-NPA, and 20 s and 15 s for Fe3O4/Si-NPA, respectively. These excellent humidity sensing properties of Si-NPA and Fe3O4/Si-NPA are explained based on thei r corresponding morph ological and structural properties. Our experiments strongly indicated that Si-N PA is an ideal thin film both for direct humidity sensing and as a substrate for growing composite humidity sensing materials.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Airy function and transfer matrix method in the study of quasi-bound levels of biased multi-barrier quantum structures
2005, 54 (5): 2226-2232. doi: 10.7498/aps.54.2226
The quasi-bound levels in biased/unbiased double/triple-barrier quantum structures have been exactly calculated based on the solution of the one_dimensional (1D) time-independent Schrdinger equation using Airy function and transfer matrix method, which is easily extended to multi-barrier quantum structures; furthermo re, the dependence of the quasi-bound levels on the effective masses and bias in biased/unbiased double/triple-barrier quantum structures has also been investig ated. In addition, errors of Airy function and transfer matrix method in the stu dy of quasi-bound levels of biased multi-barrier quantum structures in other let ters have been pointed out and verified.
Simulations of the structure characteristic of diamond-like carbon films formed by ion-beam-assisted deposition
2005, 54 (5): 2233-2238. doi: 10.7498/aps.54.2233
Molecular dynamics (MD) simulation was used to study the growth process of dia mond_like carbon (DLC) films synthesized via ion_beam_assisted deposition (IBAD ). The C2 molecules and Ar ions were selected as deposition and assis tance pr ojectiles, respectively. The influence of the impact energy of Ar as well as the assistance/deposition atomic ratio (Ar/C), on the film structure was investiga ted. The transient mobility and the migration of C adatoms caused by Ar impact were studied. Our results indicate that the impact-induced high recoil energy a nd displacement of deposited C atoms play a leading role in the growth of DLC f ilms. This can be attributed to the incident energy and momentum of assistance Ar. Our results agree well with the experimental observation. Furthermore, it e xplains the growth mechanism partly.
2005, 54 (5): 2239-2246. doi: 10.7498/aps.54.2239
A magnon-phonon interaction model is applied to two_dimensional insulating ferro magnets. By using Matsubara Green function theory, we have studied the magonon spectrum, and calculated the magnon dispersion curve on the main symmetric point and line in the Brillouin Zone for different parameters of the system. It is con cluded that at the boundary of Brillouin Zone there is a strong broadening in th e magnon linewidth and softening. The influences of longitudinal phonon and tran sverse phonon on the softening and broadening in the magnon linewidth are compar ed, and the influences of the parameters are also illustrated.
Beating patterns in the oscillatory magnetoresistance of a Si modulation-doped AlGaN/GaN heterostructure
2005, 54 (5): 2247-2251. doi: 10.7498/aps.54.2247
Magneto-transport measurements have been carried out on a Si modulation-doped Al 022Ga078N/GaN heterostructure in a temperature range between 1 5 and 25 K under magnetic field up to 10T. Striking beating patterns in magnetor esistance vs magnetic field are observed in the vicinity of a specific temperatu re. Theoretical simulation is performed and the comparison between numerical sim ulations and the experimental data reveals that the beating patterns are due to the interference of the magneto-intersubband scattering and the SdH oscillator o f first subband.
2005, 54 (5): 2252-2255. doi: 10.7498/aps.54.2252
A novel silicide technology to improve the thermal stability of the conventional Ni silicide is studied by adding a small quantity of Mo element in Ni flim.The results show that during rapid thermal annealing (RTA) temperature from 650 to 800℃,sheet resistance of Ni(Mo)Si silicide formed is low,whose value is about 2.4(Ω/□).X_ray diffraction(XRD) analysis identifies the existance of NiSi phase and no peak of NiSi2 phase for the above samples.Furthermore,accordin g to the theory on Gibbs free enery,the results show that adding 5.9 atomic% of Mo element can enhance thermal stability of nickel monosilicide.Finally,after annealed at temperatures ranging from 650 to 800℃,Ni(Mo)Si/Si Schottky barrier diodes(SBDs ) are fabricated.Good I_V characteristics of SBD that the range of Schotty b arrier height is from 0.64 to 0.66eV and the ideal factor is close to unity are shown.This further proves that the addition of a little amount of Mo in Ni film can improve the thermal stability of the NiSi film.
2005, 54 (5): 2256-2260. doi: 10.7498/aps.54.2256
The vacancy_dioxygen complex(VO2) is one of the main defects formed i n fast neutron irradiated CZ_Si during annealing in the temperature range 400—500℃. In this defect,two oxygen atoms share a vacancy,each of which is bonded to two s ilicon neighbors.With the increase of the 889cm-1(VO2),two infrared absorption bands at 919.6 and 1006cm-1 will arise in neutron irradia ted CZ _Si after annealed in the temperature range 300—500℃.IR vibrational bands at 9 19.6 and 1006cm-1 can be assigned to the metastable defect (O-V-O)th at is composed of a VO(A center) and a neighboring interstitial oxygen(Oi)atom.By prolonging the annealing time from 2h up to 10h or increasing the annealing temperature,the metastable defect(O-V-O)will be converted into V O2.During annealing in the temperature range 400—500℃,the main defe cts for med in the high dose(1019) neutron irradiated CZ_Si is the multi_vac ancy type of defects and the formation of the VO2 will be depressed.
2005, 54 (5): 2261-2266. doi: 10.7498/aps.54.2261
The current-voltage characteristics and the low frequency noise measured at 255 —293K are reported. The figures of merit increase from 45×103 t o 7×104Ωcm2 as the temperatures decreases. At low fre quencies the noise mainly cons ists of flicker noise and generation recombination (g-r) noise, while at high fr equencies thermal noise is the dominant component. The flicker noise current is proportional to the detector current at reverse bias, and the Hooge parameter αH of the device is (3—7)×10-4. In addition, the fluc tuation time co nstant τ of the g-r noise is extracted by fitting the curve of the low_freq uency noise. Therefore, the trap thermal activation energy of the deep level is obtained from the relation between τ and temperature.
2005, 54 (5): 2267-2271. doi: 10.7498/aps.54.2267
β-GaN nanocrystalline have been successfully synthesized from the nitridation of GaP nanocrystalline at low temperatures by gas_phase chemical reaction. The s tarting GaP nanocrystalline has a large specific surface and a high reactivity that can reduce remarkably the difficulty of nitridation. The results of GaP nan ocrystalline in N2 at different heating rates support the fact that β-GaN nan ocrystalline can form in GaP nanocrystalline via N-P metathesis gas_phase chemic al mechanism. The mechanism is different when different heating rate was used. T his method is very simple and is used generally to synthesize β-GaN nanopartic les or nanorods.
2005, 54 (5): 2272-2276. doi: 10.7498/aps.54.2272
The recombination dynamics of localized exciton in ZnS1-xTex ternary alloys has been investigated by time-resolved photoluminescence (PL) in a large Te concentration range from 0005 to 085. It is found that the radiativ e recombination lifetimes of different Te isoelectronic centers show a significa nt difference, varying from a few nanoseconds to tens of nanosecond. The lifetim e reaches a maximum of ～ 40 ns in the sample of x=015. The present result s could be understood in terms of the exciton localization effect. When the Te c oncentration is small, the Te isoelectronic centers evolve gradually from a sing le Te impurity (Te1) to the Te clusters (Ten). The exciton localization is enhanced, resulting in the increase of exciton recombination lifetime. When t he Te concentration is further increased, the Te clusters (Ten) becom e lar ge enough to hybridize the Te localized states and the host valence band states. Therefore, the excitons bound to Te isoelectronic centers become more or less d elocalized, resulting in a shorter lifetime. Furthermore, the concentration depe ndence of the exciton binding energy and the PL intensity variation with tempera ture have been mearsured. The results further confirm the above conclusion.
2005, 54 (5): 2277-2281. doi: 10.7498/aps.54.2277
There is a significant diminution in the hydrostatic pressure coefficients (PCs) of the photoluminescence (PL) for InAs/GaAs quantum dots (QDs) in comparison wi th that of bulk binary. We study this phenomenon with the nonlinear elasticity t heory. The variation of the lattice and elastic constants plays an important rol e in the change of PCs, which causes the obvious decrease of the built-in strain s in InAs/GaAs QD. Therefore, the energy gap and the electronic confined energy change with pressure subsequently. It is the main reason for the measured small PCs of PL from QDs. Also the calculation reveals that the PCs are sensitive to t he sizes of QD. The smaller the quantum dot is, the more greatly the change of t he electronic confined energy affects the PCs. This effect gives rise to the inc rease of PCs when dot size is reduced.
The self-consistent theoretical study of the effect of surface plasmon and polariton on electronic transport Ⅱ——The calculation and analysis of molecular orbital field in MIM system
2005, 54 (5): 2282-2290. doi: 10.7498/aps.54.2282
Adopting the self-consistent method to calculate the coefficient of molecular orbital (MO) field in a metal/insulator/metal (MIM) system under the effect of a static electric field, we obtain the result that the distribution of the MO coe fficient appears in the form of sine function. With increasing electric field, t he energy band shifts to the deep energy area, and the energy peaks separate fro m each other more evidently, and the overlap of hybrid states between the 3dm group atomic orbits constructing the current pass increases, which im prove s the power of charge transportation. This work provides the method for research ing the effect of surface plasmon and polariton on charge transportation.
2005, 54 (5): 2291-2295. doi: 10.7498/aps.54.2291
Based on the fact that a mesoscopic capacitor can be regarded as a mesoscopic tunnel junction, we quantized the mesoscopic LC circuit by using the rotating -wave approximation.The study shows: Considering the coupled energy of the meso scopic capacitor, the system of the mesoscopic LC circuit will be equivalent to a Kerr system. We also used the thermal field dynamic theory to investigate the thermal Kerr state at a definite temperature and calculated the quantum fluc tuation of both charge and magnetic flux, and discussed the results.
Analysis of the mechanism and characteristic for the transparent anode in a gate commutated thyristor
2005, 54 (5): 2296-2301. doi: 10.7498/aps.54.2296
The mechanism of the transparent anode in gate commutated thyristors (GCT) was i nvestigated by analyzing its current transportation theoretically, and the expre ssion of the electron current density at the transparent anode is deduced. The s imulation result of the CCT's switching characteristic validates the correctnes s of the mechanism analysis for the transparent anode. In addition, the characte ristic of the transparent anode in GCT devices was analyzed by compared with gen eral anode in GTO devices. The results show that the transparent anode can impro ve effectively the switching characteristic and reduce the switching loss, and t he transparent anode with an additional n buffer layer used in GCT can make the trade off among the on-state characteristic,blocking characteristic and switchin g characteristics,and improve further the characteristics of GCT.The conclusions are validated by the experiment results.
2005, 54 (5): 2302-2306. doi: 10.7498/aps.54.2302
AMPS (Analysis of microelectronic and photonic structures) mode,which was developed by Pennsylvania State University,has been used to module the light J_V c haracteristics of a_Si solar cells with a structure of TCO/p_a_SiC:H/i_a_Si:H/n_ a_Si:H/metal.The effects of valence band offset and contact barriers at p/i and TOC/p,n/metal interfaces on the light J_V characteristics have been examined .The modeling has qualitatively categorized and explained the non_ideal J_V behaviors (rollover,crossover,Voc shift,and rollunder) observed in a_Si based so lar cells.
2005, 54 (5): 2307-2312. doi: 10.7498/aps.54.2307
Flux jumps behavior in textured (Nd0.33Eu0.33Gd0.33)Ba2Cu3O7-δ （with high content of Gd-21 1 phase） have been studied. With the magnetic field parallel to the c axis, partial flux jumps have been obser ved in the temperature range 2—3K, and there were no jumps found above 5K. When ab plane is parallel to the field direction, no flux jumps have been observ ed in the whole temperature range (from 2K to Tc). The anisotropi c flux instability may be due to the anisotropic pinning force and geometrical demagnet ization factor. As the temperature increases,the number of flux jumps is decreas ed, and the third quadrant of M(H) curve is the most flux instability quadra nt. Finally we have studied the magnetic field sweep rate dependence of flux jum p, and discussed the influence of flux creep on flux jump.
Conductance peak with Zeeman splitting in normal metal-insulator-ferromagnet/superconductor tunnel junctions
2005, 54 (5): 2313-2317. doi: 10.7498/aps.54.2313
Using Bogoliubov-de Gennes equations, we obtain the self-consistent equation in a ferromagnetic superconductor. Taking into account the rough interface scatteri ng effects, in the framework of the Blonder-Tinkham-Klapwijk model，we present t he differential conductance of the normal metal-insulator-ferromagnet/supercondu ctor (N/I/FS ) tunnel junctions. It is shown that the exchange energy Eh i n FS can lead to the Zeeman splitting of the conductance peaks;the energy differ ence between the two splitting peaks is equal to 2Eh. The differentia l con ductances in N/I/FS are suppressed by the barrier strength and rough interface s cattering strength.
Effect of the insulating layer on the differential conductance in the normal metal/insulator/s-wave superconductor tunnel junctions
2005, 54 (5): 2318-2324. doi: 10.7498/aps.54.2318
Making use of the square-potential barrier to describe the influence of the insulating layer on the quasi-particle transport in normal metal/insulator/superconductor (NIS) tunnel junctions, we calculate the quasi-particle transport coeffic ients and the differential conductance using the Bogoliubov-de Gennes（BdG）equa tion and Blonder-Tinkham-Klapwijk(BTK) theory. It is found that the change of th e differential conductance with insulating layer thickness takes the form of the oscillation and attenuation, the period of oscillation and the speed of attenua tion depend strongly on the potential magnitude of the insulating layer and the bias value, the height of the conductance peaks and their positions are related to the insulating layer thickness intimately. It is shown that the tunneling spe ctra are different from those described by the δ-potential.
We have measured the microwave surface resistance Rs, the magnetic fi eld penetration depth λ(0) and the energy gap Δ(0) of MgB2 thin film s using the dielectric resonator technique. The c_axis textured sample, with superconducting transition temperature of 38K and transition width of 01K, w as prepared on MgO(111) substrates by the chemical vapor deposition method. The Rs value of the MgB2 thin film at 10K was found to be as low as 100 μΩ, which is comparable to that of a high_quality high_temperature thin film o f YBCO. BCS fits of the temperature dependence of Δλ of the MgB2 t hin film gave λ(0)=102nm and Δ(0)=113kTc.
Ground state properties of the one-dimensional spin-Peilers model with symmetric and antisymmetric superexchange interactions
2005, 54 (5): 2329-2333. doi: 10.7498/aps.54.2329
Ground-state properties of the one-dimensional spin-Peilers model with Dzyaloshi nskii-Moriya（DM）interaction and Kaplan-Shekhtman-Entin-Wohlman-Aharony（KSEA） interactions are studied by Lanczos numerical method. It is shown that the DM interaction acts against dimerization when the DM interaction is irrelative to dimerization. On the other hand, the DM interaction is favorable for dimerization when DM interaction depends on the dimerization. Otherwise, the KSEA interactio n is always against dimerization. The KSEA interaction affects the contribution of the DM interaction to dimerization, and even offsets the effect of DM interac tion. The dimerization vanishes when DM and KSEA interactions are large enough i n some special cases.
2005, 54 (5): 2334-2337. doi: 10.7498/aps.54.2334
The negative thermal expansion and spontaneous magnetostrictive deformation of Tb2Fe15.5Cr1.5 compound have been investigated by means of x-ray diffraction and magnetization measurements. The compound Tb2Fe15.5Cr1.5 has a hexagonal Th2Ni17-type structure from 293 to 672K. A negative thermal expansion was fou nd from 432 to 522K. The coefficient of the average thermal expansion is =-157 ×10-5/K. There exists a strong and anisotropic spontaneous magnetost riction in the magnetic state of Tb2Fe15.5Cr1.5 . The spontaneous volumetric magnetostrictive deformation is about 84×10-3 at 293K and the deformation occurs mainly in the directi on of c-axis. The result of magnetization measurement shows that the Curie tempera ture of Tb2Fe15.5Cr1.5 is 494K, which is by abo ut 80K higher than the mother compound Tb2Fe17.
2005, 54 (5): 2338-2341. doi: 10.7498/aps.54.2338
Planar Hall effect(PHE) in Ta(8nm)/NiFe(7nm)/Cu(2.4nm)/NiFe(4.4nm)/FeMn(14nm)/Ta(6nm) spin valve multilayer have been measured in magnetic fields rotating in the film plane. A “mixed” effect of the free and pinned layers on anisotropic magnetoresistance (AMR) has been obtserved. The result shows that the PHE can give more information about the magnetic configurations of the spin valve multilayers than the usual MR measurements.
2005, 54 (5): 2342-2345. doi: 10.7498/aps.54.2342
Simple p_n diodes have been fabricated by direct growth of La0.9Sr0.1MnO3 thin films on n_type silicon substrates.These junctio ns exhibit good rectifying characteristic in a wide temperature range from 50 to 280K.Large magnetoresistance up to 70% was observed in a low field of 3×10-2T in th ese junctions.The junction magnetoresistance depends on bias and temperature.
Microstructure, dielectric and piezoelectric properties of mixed-layered Bi7Ti4NbO21 ferroelectric ceramics
2005, 54 (5): 2346-2351. doi: 10.7498/aps.54.2346
Bi7Ti4NbO21, Bi4Ti3O 12 and Nb-doped Bi4Ti3O12 la yer-structure ferroelectric ceramics were prepared. Microstructure, dielectric and piezoelectric properties of Bi7Ti4NbO21 were investigated by comparing with the electrical properties of Bi4Ti3O12 and Nb-doped Bi4Ti3O12. High resolution transmission electron microsco py result of Bi7Ti4NbO21 showed an intergrowth structure of perovskite -like(Bi2Ti3O10)2-, (BiTiNbO7)2- layers and (Bi 2O2)2+ layer along c direction. Two dielectric anomalies of Bi7Ti4NbO 21 occurred at 668 and 845℃. The material underwent a ferroelectric-ferroelectric and a ferroe lctric-paraelectric phase transition at the low and high temperatures. They were attributed to the microstructure transition of (Bi2Ti3O10)2- an d (BiTiNbO7)2- perovskite layers, respectively. During the depolarizat ion, the piezoelectric coefficient d33 of Bi7Ti 4NbO21 decrease d by 10% of its initial value over 200℃. The reason was that the directional ar rangement of defect dipoles created by some vacancies was damaged. The results o f depolarization experiment and thermally stimulated current measurement indicat ed that the piezoelectric properties of Bi7Ti4NbO 21 came from the polarization of intrinsic dipoles and defect dipoles.
2005, 54 (5): 2352-2357. doi: 10.7498/aps.54.2352
A novel silicon-based micron/nanometer structural composite system, silicon nanoporous pillar array(Si-NPA), was prepared on the substrate of single-crystal si licon (sc-Si) wafers by a hydrothermal etching method; and the studies on its mo rphological structural and optical properties were carried out. Structural exper iments disclose that Si-NPA could be well described by triple hierarchical struc tures: the array composed of micron-sized silicon pillars, the nanopores densely distributing on each pillar, and the silicon nanocrystallites constructing the walls of nanopores. Optical measurements prove that Si-NPA has good performances on light absorption and photoluminescence(PL). Based on the experimental data o f the integral reflectance spectrum, the structural and optical parameters such as complex refractive index, complex dielectric constant and absorption coeffici ent of Si-NPA are calculated by adopting Kramers-Kronig transformation; based on which, the origin of the notable difference between the optical properties of S i-NPA and sc-Si is discussed. Through analyzing the function relation between th e absorption coefficient of Si-NPA and the photon energy of incident light, the characteristic of the electronic structure of Si-NPA is proved to be that of a d irect-band-gap semiconductor, and the calculated bandgaps agree well with the PL peak energies given by experiments.
2005, 54 (5): 2358-2363. doi: 10.7498/aps.54.2358
A method for designing two-dimensional photonic crystal polarization splitters is put forward. Optimal structure of a two-dimensional photonic crystal with a t riangular lattice of Ge rectanglular rods in BaF2 is presented. It is shown ho w a maximum photonic band-gap for TE mode is obtained by choosing the proper wid th of the rectangular rods. The two-dimensional bandgap for TE mode of this design is 0.083(2πc/a, here a is the period of grating). The polarization frequency band corresponds to a wavelength band ranging from 172 to 24μm, with the theoretical relative bandwidth being 33.1%. The fabrication of such a pho tonic crystal polarization splitter is an easy process based on coating films on the grating and is suitable for industrial making.
2005, 54 (5): 2364-2368. doi: 10.7498/aps.54.2364
The Al and O atomic vacancies on α-Al2O3(0001) surface an d the adsorption o f ZnO are calculated theoretically by using a plane wave ultrasoft pseudo-potent ial method based on density functional theory. The electron localization functio n(ELF) shows the electronic density changes at the atomic vacancies. There is an obvious absence of electronic areas where the vacancies of Al have the dangling bonds of oxygen, which are favourable for the adsorption of Zn atoms. In contra st, at the vacancies of O, there are more electron distribution(ELF:005—03) , forming lone electron pairs which are profitably available to combine O atoms or O2- ions. Through the dynamics calculation, we find that surface d efect s can significantly strengthen particle adsorption, and the vacancies are filled by adatoms(Al or O), with the adsorption energy much higher than the case of th e adsorption on a perfect surface. The surface Al-vacancies where the ZnO adsorp tion clearly breaks the hexagonal symmetry of oxygen on the α-Al2O3(0001) s urface because of the formation of the O double bonds, which apparently weakens the reaction diffusivity of O, and has a further negative impact on the regular ZnO films formation. Accordingly, more defects and dislocations in films growth might be produced. Contrarily, the O-vacancies on the α-Al2O3(0001) surface , the chemisorption and dissociation of ZnO do not have an effect on the surface hexagonal symmetry.
2005, 54 (5): 2369-2373. doi: 10.7498/aps.54.2369
Sr2CeO4 and Ca2+/Ba2+ doped Sr2 CeO4 samples with two different formation mechanisms were prepared by a solid-state method and their luminescent properties were investigated. For the Sr2CeO4(Ⅰ) sam ples formed by the direct reaction between SrO and CeO2, the peak of the strong excitat ion band appeared at about 256 nm while that for the Sr2CeO4(Ⅱ) sa mples obtained by the reaction between SrCeO3 and SrO was observed at about 279nm. It w as found that the solubility of Ca2+ in Sr2CeO4(Ⅱ) w as very low while Ca2+ could replace part of Sr2+ in Sr2CeO 4(Ⅰ). The substitution of Sr2+ by Ca2+ in Sr2CeO4(Ⅰ) led to r ed shift of the strong excitation band and its spectral shape approached that of Sr2CeO4(Ⅱ) with the in crease of Ca2+. The strong excitation band was attributed to the char ge tr ansfer transition of the terminal Ce4+—O2- bonds of CeO6 octahedr a. The peak of the weak excitation band located at about 340nm remained unchange d in all the samples, however, its intensity was found to increase with red shif t of the strong excitation band. This band might originate from the charge trans fer transition of the equatorial Ce4+—O2- bonds of CeO6 octahedra . The formation mechanism and the doping of Ca2+ had no effect on the emission spectra. Ba2+ was not incorporated in the Sr2CeO 4 phase in any formation mechanism and it only produced a second crystalline phase of BaCeO3.
2005, 54 (5): 2374-2378. doi: 10.7498/aps.54.2374
A new Er3+-doped tellurite glass has been studied. According to the a bsorp tion spectrum, Judd-Ofelt intensity parameters were determined and used to calcu late the radiation rates, fluorescent branch ratio and radiative lifetimes of Er 3+ in Er3+-doped tellurite glasses. The J-O parameters wer e o btained as follows, Ω2=479×10-20cm2,Ω 4=152×10 -20cm2,Ω6=070×10-20cm2. The stimulated emission cross-sections (σ e=1040×10-21cm2)， of the Er3+ io n 4I13/2→ 4I15/2 transition was calculated using the McCumber th eory. The FWHM(FWH M=655nm) of the 4I13/2→4I 15/2 emission and lifetimes of every level of Er3+ ion were measured and the lifetime of 4I1 3/2 level obtained is 399ms. The spectroscopic properties of Er3+ ion were compared with those in different glasses. These studies indicate that tellu rite glass is much more beneficial for optical fiber amplifiber to realize broad band and high gain amplification.
Investigation of spectral properties and thermal stability of Er3+/Yb3+ co-doped tungsten-tellurite glasses
2005, 54 (5): 2379-2384. doi: 10.7498/aps.54.2379
Er3+/Yb3+ co-doped tungsten-tellurite glasses, 65TeO2 -25WO3-10RmOn(RmOn= PbO,BaO), (65+x) TeO2-(25-x)WO3- 10La2O3(x=0,5,10),(60+x)TeO2-(30-x)WO3-10Bi2O3(x=0,5,10) have been prepared. The thermal stability and spectral properties, such as absorption spec tra, emission spectra and lifetimes of the 4I13/2 level of Er3+ were investigated. Results obtained show that tungsten-telluri te glasses have good thermal stability. All the glass samples except the Bi2O3-containing g lasses show no onset temperature of crystallization (Tx), indicating that they are stable for fiber drawing. Three intensity parameters Ωt(t= 2,4, 6) were calculated by Judd-Ofelt theory. It is shown that Ω2 is domi nated b y the covalency between the Er3+ and O2-, the effect of as ymmetry in the local structures around the Er3+ ions on Ω2 can be neglected. The full width at half maximum (FWHM=71—77 nm) of the 4I 13/2→ 4I15/2 emission and lifetimes of 4I 13/2 level(τm= 3—3.4 ms) of Er3+ ions were measured. The emission cross-section ( σpeak=068—103×10-20 cm2) of the 4I13/2→4I15/2 transitio n of Er3+ ions were calculated according to the McCum ber the ory. The FWHM and emission cross-section of Er3+ ions at 1.5 μm ba nd in d ifferent glass hosts were compared. The results show that tungsten-tellurite gla ss will be the promising host material for 1.5 μm broadband amplification.
2005, 54 (5): 2385-2388. doi: 10.7498/aps.54.2385
A set of GaNxAs1-x samples with a small content of nit rogen (N)( xAs1-x, which was extremely different from the N_related i mpurity states. At the same time, PR spectra were also studied in this work.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
The properties of the as-sputtered ZnO films under different deposition parameters after sulfidation
2005, 54 (5): 2389-2393. doi: 10.7498/aps.54.2389
ZnS films are produced on the glass and quartz substrates by sulfidation of the as-sputtered ZnO films in the H２S-H２-N2 mixtu re. The properties of the f ilms are characterized by using the XRD, SEM and transmission measurements. The results show that the ZnS films with a hexagonol structure have a (002) preferre d orientation. The crystallinity and optical transmission spectra of the ZnS fil ms are related to working pressure and Ar/O２ ratio during the deposi tion of t he ZnO films. At the pressure >1Pa, the thickness of the ZnS films is very sma ll, while at the pressure ２ ratio higher or lower than 4∶1 will leads to the poor crystalline ZnS films. Also it is found that the ZnS films formed from the unannealed ZnO films almost have the same grain size as those formed from th e in-air annealed ZnO films, due to the high (002) preferred orientation during the growth of the ZnS films.
Optical emission diagnosis of helicon-wave-plasma-enhanced chemical vapor deposition of nanocrystalline silicon
2005, 54 (5): 2394-2398. doi: 10.7498/aps.54.2394
Optical emission spectroscopy (OES) is used to diagnose the active species emission in the helicon_wave_plasma_enhanced chemical vapor deposition of nanocrystalline silicon. The effects of the experimental parameters on OES intensity of SiH *, Hβ and Hα have been studied. Ｅxperiment r esults indicate that the ma gnetic field confinement makes the reactant molecules dissociate efficiently. Ap propriate hydrogen dilution can increase the density of hydrogen active species, while higher dilution makes the concentration of silicon_contained active spec ies decrease. The density of the active species increases monotonically with in creasing input rf power, and a relatively higher concentration of hydrogen act ive species reaching the substrate surface can be achieved. Experiment results obtained are analyzed based on the dispersive relation and the characteristic o f the helicon wave plasma, which offer the basic data for the understanding of t he process of nanocrstalline silicon deposition and adjusting its experimental p arameters.
2005, 54 (5): 2399-2402. doi: 10.7498/aps.54.2399
The basic idea of the reactive plasma spray (RPS) was presented. The TiN coating was successfully deposited on Q235 steel substrate by using the gas_tunnel plasma spray gun via RPS. Micro_hardness of the TiN coating under different loads has been measured, revealing an obvious indentation size effect, and a weak work_hardening effect. XRD, TEM and HRTEM were employed to analyze the prepared coating samples. Results obtained show that nanocrystalline TiN coating has been achieved via RPS, which is composed of TiN crystals of about 57—70nm in diameter and the amorphous TiN.
Effect of multiwalled carbon nanotubes on the thermoelectric properties of p-type Ba0.3FeCo3Sb12 compounds
2005, 54 (5): 2403-2408. doi: 10.7498/aps.54.2403
The p_type Ba_filled Ba0.3FeCo3Sb１2 skutterudite compounds were synthesized using a two_step solid_state reaction method, and the Ba0.3FeCo3 Sb１2/multiwalle carbon nanotubes composites were prepared by spark plasma sintering (SPS). The structure of Ba0.3FeCo3Sb１2/multi walled carbon nanotube composites and effect of multiwalled carbon nanotubes on the thermoelectric properties of p_type Ba0.3FeCo3Sb１2 compounds w ere investigated. The dispersed distribution of multiwalled carbon nanotubes in the Ba0.3Fe Co3Sb１2 compounds was observed by SEM. With increasing content of multiwal led carbon nanotubes, the electrical conductivity of the Ba0.3FeCo 3Sb１2 compounds decreased, Seebeck coefficient reduced slightly and the lattice thermal conductivity decreased significantly. The minimum of lattice thermal conductivity was obtained when the content of carbon nanotubes was 5%. When the content of carbon nanotubes was 3%, the maximal ZT value of 078 was obtained for Ba0.3FeCo3Sb１2/multiwalled carbon nanot ube composites at 850K.
2005, 54 (5): 2409-2413. doi: 10.7498/aps.54.2409
Nano_scale ZnO green disks are prepared by continuous compaction process. Relation between green density, sintering time, densification temperature and compaction method is examined. Microstructure of the samples is characterized by an XL30S_FEG field esmission scanning electron microscopy. Hardness of the ZnO nano_bulk is measured as a function of sintering temperature. The results show that gree n density is increased by 56%, sintering time is decreased by 3h and densifica tion temperature is decreased by 200℃ after the continuous compaction process. Distributions of density and grain size within the sintered body are homogeneous through examination of the XL30S_FEG field esmission scanning electron microsco py. Hardness values imply that the relation between micro_hardness and sintering temperature is not monotonic, but first increasing then decreasing with increas ing sintering temperature in the ZnO nano_bulk. The grain size at the inflexion point is about 50—60nm.
2005, 54 (5): 2414-2417. doi: 10.7498/aps.54.2414
A formula of fatigue life for materials in seawater is derived based on the non-equilibrium statistical theory of fatigue. As an example, the results of soft steel under the ocean corrosive circumstance are compared with that when they ar e free of corrosion.
An approach to obtain the photofragment translational energy distribution from time-of-flight profile
2005, 54 (5): 2418-2423. doi: 10.7498/aps.54.2418
At the magic angle, the time_of_flight mass_spectrometer (TOF-MS) profile depends only on the translational energy distribution of photofragment, and is indep endent of the angle distribution of recoil momentum, therefore, the translationa l energy distribution is usually determined by fitting the measured TOF-MS profi le. Different from the above procedure, we take another approach in the present work. According to this method, by measuring three widths at half maximum (t 1/2), one-fourth maximum (t1/4) and three-fourth m aximum (t 3/4) of the TOF-MS profile, the averaged translational energy, th e width of translational energy distribution, as well as the width of instrumental func tion can be determined from numeric tables or mathematical expressions. In this method, both the translational energy distribution and the instrumental function are described by Gaussian functions.
2005, 54 (5): 2424-2428. doi: 10.7498/aps.54.2424
This paper presents a novel efficient charge pump composed of low Vth metal_oxide_semiconductor (MOS) field effect transistors (FET) in the course of realizing radio frequency (RF) energy AC/DC conversion. The novel structure eliminates tho se defects caused by typical Schottky_diode charge pumps, which are dependent on specific processes and inconsistent in quality between different product batche s. Our analyses indicate that an easy_fabricated, stable and efficient RF energy AC/DC charge pump can be conveniently implemented through reasonably configurin g the MOS transistor aspect ratio, and other design parameters such as capacit ance, multiplying stages to meet various demands on performance.
2005, 54 (5): 2429-2434. doi: 10.7498/aps.54.2429
A new model of collagen molecule is constructed, thus obtaining the Hamiltonian that can characterize its 3-dimensional structure properties better. The 4th Run ge-Kutta algorithm is used to numerically solve the obtained kinetic equations o f excited energy transport in the collagen molecules under an applied electric f ield. The results indicate that soliton waves of amide-I will be stimulated by t he electric field in collagen molecules with phonon emission.
2005, 54 (5): 2435-2440. doi: 10.7498/aps.54.2435
A multiple input-queued ATM switching fabrics (ASF) for scheduling cell based on Hopfield neural network (HNN) is proposed. This scheme eliminates degeneration of performance due to head-of-line (HOL) blocking. Simulation results show that, compared with the single first in_first out and window input-queued ASF, the pr oposed approach can greatly improve the throughput and reduce the cell delay.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2005, 54 (5): 2441-2447. doi: 10.7498/aps.54.2441
The complexity series of the Guliya (Tibetan plateau) ice core and Shihua cave (Beijing) stalagmite proxy records were respectively calculated in this paper, using a dynamical nonlinear analysis method for time series-Lemper-Ziv complexityalgorithm; and the physical implication of Lemper-Ziv complexity and its meaning in the study of climate change were also discussed. The wavelet analysis resul ts show that there exist distinctive quasi-periods of 780_, 380_, 160_, and 105_ year in the complexity series. Further investigations indicate that when differ ent window lengths are selected, the characters of the complexity series for a g iven time series are basically the same, and there exists the coherency between the jumps of the complexity series and the climatic jumps on various timescales . This paper presents, for the first time so far as we know, the oscillation on 380_year timescale in the recent millennium, with amplitude decaying and intri nsic period reducing. The complexity of the time series has gradually reduced si nce 1900. For the complexity of the stalagmite data,there has been the quasi-equ al-amplitude oscillation after 1920, which is similar to the circumstances of th e warming epochs over China in the middle of the sixth century and the middle o f the twelfth century. Consequently, the reason for the warming in the twentiet h century remains to be necessary to study.
2005, 54 (5): 2448-2452. doi: 10.7498/aps.54.2448
Polarimetric radiation of wind-roughened sea surfaces is modeled using a geometr ical approach combined with the statistical method. The focus is on the geophysi cal nature of azimuthal emission signatures of sea surfaces and their relation t o the wind direction. The geometrical optics model assumes that the surfaces are composed of tilted specularly reflecting facets with the reflecting fields from each facet contributing incoherently to the total upwelling radiation, and the total radiation is calculated as a statistical averaging of contributions from individual facets. The first three Stokes parameters of sea surfaces are derived . The bright temperature azimuthal variations are characterized by the second az imuthal harmonics, which can be explained by the asymmetry of wind-driven sea su rfaces. The simulation shows that the upwelling Stokes parameters are sensitive to the wind direction and exhibits azimuthal variations up to a few Kelvin in am plitude. Theoretical interpretation of sea surface emission signatures provides the potential possibility to facilitate ocean wind vector retrieval using purely passive means.
2005, 54 (5): 2453-2456. doi: 10.7498/aps.54.2453
The event horizon equation is given.Using Damour_Ruffini method improved by Zhao Zheng, the formula of temperature is obtained, which supports the result by Zhao Z (Acta Phys. Sin. 1990 39 1845) (in Chinese).