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Vol. 46, No. 6 (1997)

1997-03-20
GENERAL
SELF CONTROL FEEDBACK SYNCHRONIZATION OF CHAOS BYCOUPLING-DRIVING IN ACOUSTO-OPTIC BISTABLE SYSTEM
ZHOU LI-WEI, LIU JIN-GANG, SHEN KE
1997, 46 (6): 1041-1047. doi: 10.7498/aps.46.1041
Abstract +
The paper proposes theoretically the method of chaos synchronization by self-controlled feedback coupling-driving,and studies numerically on the condition of chaotic synchronization in two Bragg acousto-optic bistable (AOB) systems. The maximum conditional Lyapunov exponent (MCLE) are considered as the criteria of synchronization. It is found that one can gain the chaotic outputs synchronized of the two systems if one system is coupling-driven appropriately by another. When self-controlled feedback on parameter introduced, synchronization can be realized faster and the required minimum stiffness of coupling is decreased. The synchronization is also gained when the effect of noise is considered. The result of experimental test is also given.
LEEM STUDIES OF TWO-DIMENSIONAL OXIDATION ON W(110) SURFACE
CAI QUN, M.S.ALTMAN
1997, 46 (6): 1048-1054. doi: 10.7498/aps.46.1048
Abstract +
With increasing coverage,the adsorption of oxygen on W(110) surface can be- subdivided into chemisorption,two-dimensional oxidation and bulk oxidation. In this work,the new imaging technique low energy electron microscopy (LEEM) was used to investigate the two-dimensional oxidation on W(110) surface. With increasing O coverage,the low energy electron diffraction patterns change from (1×1) to p(2×1) structure,and then into p(2×2) with complex diffraction satellites. Using dark field LEEM mode,we have imaged the fractional spots near (00) beam. It was found that there were two kinds of regions with opposite contrast on the surface,i.e. the oxygen superstructure domains with different orientations. The distribution of these domains was related to surface defects,especially to surface steps. It was also indicated that the temperature played a very important role for surface oxidation.
ATOMIC AND MOLECULAR PHYSICS
EXACT SOLUTIONS OF SCATTERING STATES IN THE WEAKEST BOUND ELECTRON POTENTIAL MODEL
CHEN CHANG-YUAN, SHEN HONG-LAN, SUN GUO-YAO
1997, 46 (6): 1055-1061. doi: 10.7498/aps.46.1055
Abstract +
Characteristics of the scattering states in the most weakly bound electron potential model have been studied, and certain analytical solutions of a distorted Coulomb wave were obtained. The normalized wave functions of scattering states on the k /2π scale and the calculation formula of phase shift are presented. Analytical properties of the scattering amplitude are discussed, and analytical formulas for calculating bound continuous transition matrix elements are also given. The results may be useful in a wide class of scattering problems.
THEORETICAL ANALYSES OF A DOPPLER TYPE ATOMIC INTERFEROMETER
XU XIN-YE, WANG YU-ZHU
1997, 46 (6): 1062-1072. doi: 10.7498/aps.46.1062
Abstract +
Based on the analyses of a moving three-level atom interacting slantingly with a standing wave laser field, two kinds of atomic interferometries are designed. The coherent splitting, deflection, combination and free propagating of the atomic waves in the two atomic interferometers are studied in detail.The results show that the interference effects resulting from interaction between different internal states of the atom will occur when some conditions are met by both the atom and the light field. Finally, we have analysed theoretically how to realize and demonstrate the-atomic interferometry by using the two methods.
FERMI RESONANCES AND VIBRATIONAL SPECTRUM FOR METHANE
XIE MI, MA ZHONG-QI, HOU XI-WEN
1997, 46 (6): 1073-1078. doi: 10.7498/aps.46.1073
Abstract +
The boson realization model with Fermi resonances is used for explaining both stretching and bending vibrational spectra in methane. The interactions between stretching and bending vibrations are described by Td symmetric Fermi resonance terms that couple one creation (or annihilation) operator of stretching vibrations with two annihilation (or creation) operators of bending ones. This model provides a ten-parameter fit to the published experimental vibrational- eigenvalues of methane with the root-mean-square energy deviation 12.38cm-1.
MAKING LOCAL MODE VIBRATION LONG LIVED BY THE INTERACTION BETWEEN A STRONG MULTI-COLOR LASER FIELD AND MOLECULES
CHENG JI-XIN, SHI QIANG, SHUANG FENG, ZHU QING-SHI
1997, 46 (6): 1079-1087. doi: 10.7498/aps.46.1079
Abstract +
Trapping vibrational energy into one single bond is a key problem of bond-selective chemistry. We explored this possibility by means of restricting local mode wavepacket dephasing with multi-color laser field. The vibrational excitation and evolution of molecules in weak and strong multi-color laser fields are discussed by field-quantization method and semi-classical method. The results demonstrate that population can not be trapped in a local mode wave-packet using multi-color weak field, while it is possible to trap vibrational population between the ground state and local mode vibration by making use of power-broadening induced by strong laser field and the interference between two wave-packets excited by two strong laser of different frequencies.
THE SINGLE AND DOUBLE FREQUENCY MULTIPHOTON SPECTRUM OF IODINE
ZHANG LIAN-SHUI, LI YUN-JING, LI XIAO-WEI, FU GUANG-SHENG
1997, 46 (6): 1088-1095. doi: 10.7498/aps.46.1088
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Using both optical-optical doubl resonance multiphoton ionization spectroscopy (OODR-MPI) and fluorescence excitation spectroscopy techniques,we have measured and assigned the single and double frequecy five-photon ionization spectrum as well as three-photon fluorescence excitation spectrum of iodine molecule,and identified a regular progression with a spacing of 72cm-1 as the excitation of the high vibrational level in the F0+u state. Based on the experimental results,we discussed the channel of excitation,emission and ionization of- iodine- molecule.
THEORETICAL CALCULATIONS OF CROSS SECTIONS FOR ELECTRON CAPTURE IN COLLISIONS OF PROTON WITH- He+ AND Li++ IONS AT HIGH ENERGIES
ZHANG XIAN-ZHOU, ZHOU XIAO-XIN, CHEN HONG-SHAN, DONG CHEN-ZHONG
1997, 46 (6): 1096-1102. doi: 10.7498/aps.46.1096
Abstract +
We have computed the partial cross section ratios of electron capture into excited states to ground state in collisions of proton with He+ and Li++ ions using Oppenheimer Brinkman Kramers and continuum distorted wave methods. Our results show that the cross section ratios obtained by the two different methods are consistent with each other at high energies. Consequently, we propose a simple method to estimate the partial and total cross sections of electron capture by proton from any hydrogen like ions at high energies.
CLASSICAL AREA OF PHENOMENOLOGY
SPACE-RESOLVED STUDY OF NEON-LIKETITANIUM SOFT X-RAY LASING
LI YU-TONG, ZHANG QI-REN, GU YU-QIU, YANG SHANG-JIN, YIU YONG-LU, JI KANG-NING, ZHAO YONG-KUAN
1997, 46 (6): 1103-1107. doi: 10.7498/aps.46.1103
Abstract +
We report a spatially resolved investigation of lasing on the J=0—1,3p—3s transition in neon-like titanium at 32.6nm, with high-resolution erect field spectrometer. Experiments were carried out on the “Xingguang” Nd-glass laser with 1% prepules 5ns before the main pulse. The experimental results are compared with the theoretical simulations obtained by LASNEX and XRASER code. The dependence of lasing region on drive energy is also discussed.
THEORETICAL STUDY OF NON-EXPONENTIAL PHOTON ECHO DECAYS
WANG HAI-YU, HUANG SHI-HUA
1997, 46 (6): 1108-1113. doi: 10.7498/aps.46.1108
Abstract +
Photon echo decays of several impurity paramagnetic ions are calculated,the historical average of each lattice nuclear spin flip is described by a bivalued random telegraph process,and the spatial average is obtained according to the crystal structure. The results are very close to those of Monte Carlo simulations. From the experimental observations,we obtained that all samples have a universal decay form.
ENERGY- LEVEL-EXCITATIONS——THE ELEMENTARY EXCITATIONS IN THE CRYSTAL-OPTICAL- FIELD STRONG-COUPLED SYSTEM
DUAN LU-MING, GUO GUANG-CAN
1997, 46 (6): 1114-1117. doi: 10.7498/aps.46.1114
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It is found that a new kind of excitations,the energy-level-excitations,exist in a narrow-band crystal which strongly couples to the optical field. The energy spectrum and some other properties of the energy-level excitations are analyzed.
EXCITONIC OPTICAL NONLINEARITIES FOR ZnSe THIN FILM
ZHANG XI-QING, FAN XI-WU, CHEN YI-MIN, Lü YOU-MING, ZHENG ZHU-HONG
1997, 46 (6): 1118-1124. doi: 10.7498/aps.46.1118
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We present a simple,but highly sensitive,method for obtaining both the sign and magnitude of the nonlinear refractive index and the nonlinear absorption coefficient as a function of wavelength. It is shown theoretically that these paramters can be easily obtained from the linear and nonlinear thansmission spectra of the medium as well as the laser intensity distribution on the frequancy. This technique is demonstrated for ZnSe thin film at 77K and room temperature.
SECOND HARMONIC GENERATION FROM UNPOLED HEMICYANINE-DOPED SILICA THIN FILM
YU JING, LIU LI-YING, XU LEI, WANG WEN-CHENG, LI FU-MING
1997, 46 (6): 1125-1130. doi: 10.7498/aps.46.1125
Abstract +
Hemicyanine-doped silica film was fabricated by the sol-gel technique.It was demonstrated for the first time that the self-alignment of hemicyanine molecules in the above film existed in the interfacial area.A χ(2) value of 6.6pm/V was obtained for a 50nm thick film.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
SELF-GENERATED MAGNETIC FIELDPRODUCED IN PREPLASMA CHANNEL
ZENG GUI-HUA, YU WEI, SHEN BAI-FEI, XU ZHI-ZHAN
1997, 46 (6): 1131-1136. doi: 10.7498/aps.46.1131
Abstract +
An equation for self-generated magnetic field is derived,and is used to investigate the self generated magnetic field produced by an intense short laser pulse in preplasma channel.The results show that the magnetic field can be generated by the ponderomotive mechanism,and the cavitation influences the magnetic field.The structure of the magnetic field in a plasma channel is also demonstrated.
WAVEBREAKING DUE TO RESONANT ABSORPTION IN PLASMAS PRODUCED BY LASER BEAM
LIU DA-QING, CAO LI-HUA, CHANG WEN-WEI, YUE ZONG-WU
1997, 46 (6): 1137-1145. doi: 10.7498/aps.46.1137
Abstract +
Wavebreaking due to resonant absorption in plasmas produced by the laser beam is studied using theoretical analysis and particle simulation of plasma.The temperature effects on wavebreaking and resonant absorption are also considered.It is indicated that those electrons in the resonant region are not only oscillating heated,but also accelarated by Landau damping.There exists a turbulence accelaration mechanism in underdense plasma region.Second wavebreaking can also be observed in certain power density of laser light.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
DYNAMIC SCALING OF PHASE SEPARATION IN-AMORPHOUS Cu12.5Ni10Zr41Ti14Be22.5 ALLOY
LIU JUN-MING, WU ZHUANG-CHUN, LIU ZHI-GUO
1997, 46 (6): 1146-1152. doi: 10.7498/aps.46.1146
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The dynamic scaling of phase separation in amorphous Cu12.5Ni10Zr41Ti14Be22.5 alloy has been investigated by means of smallangle neutron scattering. A detailed scaling analysis of the scattering function indicates that the dynamic scaling state of the scattering is reached in the early stage of the phase separation. We demonstrate that the dynamic scaling hypothesis can be applied to the phase separation sequence in deeply supercooled liquid.
PREPARATION OF nc-Ge EMBEDDED IN SiO2 MATRIX AND OBSERVATION OF VISIBLE PHOTOLUMINESCENCE
HE ZHEN-HONG, CHEN KUN-JI, FENG DUAN
1997, 46 (6): 1153-1160. doi: 10.7498/aps.46.1153
Abstract +
The nanocrystalline(nc) Ge embedded in SiO2 matrix was attempted to synthesize from thermal oxidation of PECVD deposited a-GexSi1-x∶H films.The microstructures of the samples were detected by Fourier transform infrared spectroscopy,Raman spectroscopy and XRD.The results reveal that Ge nanocrystals form during oxidation and their numbers and sizes are varied with different Ge content in the as deposited a-GexSi1-x∶H alloy and also changed upon different-oxidation conditions.These characteristics may be due to the selective oxidation of Si in a-GexSi1-x∶H alloy and the reduction of hydrogen existing in the samples in view of chemical thermodynamic equilibrium. Some nc-Si samples display visible photoluminescence(PL) at room temperature.Based on Brus, exiton three-dimensional quantum confinement model,the nc-Ge size was evaluated from the PL peak positions and show a good agreement with the result of XRD.All the above analyses suggest that nc-Ge buried in SiO2 matrix can be obtained by the present method and its visible photoluminescence is related to the effect of quantum size on nc-Ge.The observation of nc-Ge with TEM is required to further confirm these facts.
MODIFIED EMBEDDED-ATOM METHOD FOR SIMULATING THE MULTILAYER RELAXATION AND SELF-DIFFUSION OF COPPER
WAN JUN, SHEN SAN-GUO, FAN XI-QING
1997, 46 (6): 1161-1167. doi: 10.7498/aps.46.1161
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The multilayer relaxation of Cu(100),(110),(111)and(311) surfaces are calculated- using the modified embedded atom method,from which the results obtained are in good agreement with the experiments. The self-diffusion mechanisms on the Cu(100) surface are investigated,and the result is colse to the available experimental data and that obtained by local density approximation method.In addition,the diffusion barrier heights on Cu(110) and (111) surface are predicted.
CHARACTERIZATION OF Hg1-xCdxTe EPITAXIAL FILMS ON VARIOUS VICINAL PLANES
LI BIAO, CHU JUN-HAO, ZHU JI-QIAN, CHEN XIN-QIANG, CAO JU-YING, TANG DING-YUAN
1997, 46 (6): 1168-1173. doi: 10.7498/aps.46.1168
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The Hg1-xCdxTe films were prepared by a dipping liquid phase epitaxy technique on spherical CdTe substrate with several different misoriented facets. They were characterized by means of micrograph,infrared absorption spectra, Raman scattering, and X ray double crystal diffraction. The results show that-near facet (δ<1°) and terrace free (δ≈1.2 °) growth modes are superior in both the planarity and the amount of precipitates.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
ELEMENTARY EXCITATIONS OF ONE-DIMENSIONALQUANTUM SINE-GORDON MODEL
CHEN YU-GUANG, YUAN QING-SHAN, CHEN HONG, ZHANG YU-MEI, WU XIANG
1997, 46 (6): 1174-1182. doi: 10.7498/aps.46.1174
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Using the-self-consistent quantum perturbation theory, we study the elementary excitaton of one-dimensional sine-Gordon model described by parameters α0 and β0. It is demonstrated in this article that the elementary excitations consist of quantum solitons and antisolitons.Under the condition α020≤8π,our results for the gaps agree with the exact results of the Thirring model and the half-filling Hubbard model based on the bosonization techniques.
ELECTRICAL PROPERTIES OF SULFUR-DOPED C60 FILMS
CHEN GUANG-HUA, YAO JIANG-HONG, WANG YONG-QIAN, ZOU YUN-JUAN
1997, 46 (6): 1183-1187. doi: 10.7498/aps.46.1183
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The temperature dependencies of electrical conductivity of sulfur-doped C60 films were measured after annealing at 433K. The results showed that the conductive activation energy decreased and electrical conductivity of C60 films increased after sulfur-doping. From the logarithmic curve of the electrical conductivity versus temperature,a transition zone was seen where the conductivity did not vary with temperature exponentially;however,when above 388K or below 368K,sulfur-doped C60 films showed obvious semiconductive properties. This phenomenon is due to the phase transformation of sulfur molecules in the film.
ELECTRICAL CHARACTERISTICS OF METAL CONTACTS ON DIAMOND FILMS
YAN HUI, CHEN GUANG-HUA, ZHANG XING-WANG, JI YA-YING
1997, 46 (6): 1188-1192. doi: 10.7498/aps.46.1188
Abstract +
The polycrystalline diamond films were synthesized by thermal filament chemical vapor deposition technique. The electrical characteristics of contacts between metal and diamond film and the effect of annealing have been investigated. Experimental results showed that the electrical characteristics of Cu contact on diamond film is similar to that of Ag,but different from that of Al. In addition,annealing has a great effect on the contact electrical characteristics.
INFLUENCE OF HEATING RATE DURING ANNEALING ON MAGNETIC PROPERTIES OF NANOCRYSTALLINE Fe-Cu- Nb(V)-Si-B ALLOYS
HE KAI-YUAN, HE SHU-LI, ZHANG YU-MEI, FU YU-JUN, WANG ZHI, ZHANG LUO
1997, 46 (6): 1193-1198. doi: 10.7498/aps.46.1193
Abstract +
Influence of heating rate on magnetic properties for Fe72.7Cu1Nb2V1.8Si13.5B9 alloy and Fe73.5Cu1Nb3Si13.5B9 alloy in nanocrystallization at 550℃ was investigated.Magnetic measurements showed that the effect of heating rate on permeability was significant,the initial permeability μi was significantly increased by quick heating.For Fe72.7Cu1Nb2V1.8Si13.5B9 alloy,when heating rate was raised from 2℃/min to 260℃/min, μi was increased from 42000 to 81000; for Fe73.5Cu1Nb3Si13.5B9 alloy,when heating rate was raised from 0.5℃/min to 260℃/min,μi was increased from 26000 to 92000.It was found that the grain size was decreased by quick heating.For Fe72.7Cu1Nb2V1.8Si13.5B9 alloy,when heating rate was raised from 2℃/min to 260℃/min,the grain size was decreased from 14.6nm to 13.1nm;for Fe73.5Cu1Nb3Si13.5B9 alloy,when heating rate was raised from 0.5℃/min to 260℃/min,the grain size was decreased from 13.1nm to 10.6nm.This suggested that the effect of heating rate on permeability was caused mainly by the changes of grain size.The plot of grain size and μi showed that μi∝D-6 ,where D is the average size of the grains.The nucleation frequency and growth rate of α-Fe(Si) vs.heating rate of annealing were also discussed.
DIELECTRIC PROPERTIES OF SiNx FILMS DEPOSITED AT LOW TEMPERATURE
YE CHAO, NING ZHAO-YUAN, SHEN MING-RONG, WANG HAO, GAN ZHAO-QIANG, MA YUN-XIU
1997, 46 (6): 1199-1205. doi: 10.7498/aps.46.1199
Abstract +
The dielectric properties of SiNx films,which were deposited at low temperature by microwave electron cyclotron resonance plasma chemical vapor deposition,have been investigated.The frequency dependence of ε′and ε″ have two kinds of power-law dependence in the frequency range of 5—106Hz due to the fractal structure in nanometer-sized amorphous films.The relationship between ε′and ωn-11 with n1=0.82—0.88- due to electron hopping are obtained at low frequency region,and the relationship between ε′ and- ωn-12 with n2=0.05 due to the fractal structure conduction are- obtained at high frequency region.
BLUE UPCONVERSION EMISSION IN Yb,Tm-DOPEDPENTAPHOSPHATE GLASSES
HAO ZHAO, CHEN XIAO-BO, HOU YAN-BING, SONG FENG, ZHANG GUANG-YIN, WANG HONG
1997, 46 (6): 1206-1211. doi: 10.7498/aps.46.1206
Abstract +
Much stronger blue emission have been observed in phosphate non-crystals at room temperature,co-doped with Yb3+ and Tm3+ when excited into the Yb3+ 2F7/2 state and the excited states of Tm3+ at 966nm by laser diode.Energy transfer and back transfer between the two rare earth ions,participation of phonons were demonstrated to be responsible for the upconversion process.
FLUORESCENCE SPECTRA OF Ge-NANOCRYSTALLITESEMBEDDED IN SiO2 THIN FILMS
YUE LAN-PING, HE YI-ZHEN
1997, 46 (6): 1212-1216. doi: 10.7498/aps.46.1212
Abstract +
The fluorescence spectra of Ge-nanocrystallites embedded in SiO2 thin films prepared by the ion-beam sputtering technique have been measured at room temperature.A strong visible photoluminescence with a peak at 2.95eV under exciting radiation of λ=300nm,and two luminescence peaks at about 2.95eV and 2.64eV under exciting radiation of λ=633nm are observed in the wavelength region of 380—520nm in the annealed samples.A possible mechanism for the photoluminescence in the visible region based on the quantum confinement of excitons in the nanometer-size Ge particles and recombination of the surface states has been proposed.The results also suggest that the interesting optical properties observed,of this new class of thin films with practical importance could be closely related to the new structure behavior of Ge-nanocrystallites,which is definitely different from that of the bulk Ge-crystals.
VISIBLE ELECTROLUMINESCENCE FROM SILICONNANOCRYSTALLITES PREPARED BY PLASMAENHANCED CHEMICAL VAPOR DEPOSITION
TONG SONG, LIU XIANG-NA, WANG LU-CHUN, YAN FENG, BAO XI-MAO
1997, 46 (6): 1217-1222. doi: 10.7498/aps.46.1217
Abstract +
We have observed visible electroluminescence (EL) from silicon nanocrystallites which are embedded in a-Si∶H films prepared in a plasma enhanced chemical vapor deposition system. The EL spectra are in the range of 500nm to 850nm with two peaks located at about 630—680nm and 730nm respectively. We found that the intensity of EL peaks is related closely to the conductivity of the deposited films. The carrier conduction path is discussed in terms of the material structural- characteristics, and a tentative explanation of the light emission mechanism is proposed.
TWO KINDS OF ELECTROLUMINESCENCE FROM POROUSSILICON IN ELECTROLYTE SOLUTIONS
LIU XIAO-BING, LIAO LIANG-SHENG, YUAN ZE-LIANG, HOU XIAO-YUAN
1997, 46 (6): 1223-1229. doi: 10.7498/aps.46.1223
Abstract +
Two kinds of different electroluminescence from the porous silicon grown on p-type silicon wafers were observed by applying a forward bias to porous silicon in acidic aqueous system containing strong oxidizing agents (such as 1mol·L-1HCl, 1mol·L-1 SnCl4, and 1mol·L-1 H2SO4+0.1mol·L-1 Na2S2O8). One was the red emission with low applied voltage (V+≈1.4V). Its red peak shifted to shorter wavelength as the operation time increases. It is most possibly related to the quantum size effect. The other was the white emission exhibited after the red one was quenched and when high voltage was applied on (V+>30V). It is resulted from the hot electron injection under high electric field to the thin and continuos SiO2 sub-layer formed in the porous silicon after the red emission was quenched in the electrolyte.
PHOTOEMISSION OF COLD-DEPOSITED Ag-BaO THIN FILMUNDER THE ACTION OF ULTRASHORT PULSE LASER
DAI ZHI-YONG, WU JIN-LEI, LIU WEI-MIN, XUE ZENG-QUAN, WU QUAN-DE
1997, 46 (6): 1230-1236. doi: 10.7498/aps.46.1230
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In this paper, the emission of photoelectrons in the Ag-BaO thin film prepared by a cold deposition method has been studied. The quantum yield of the film irradiated by an ultrashort pulse laser with a wavelength of 0.53μm is more than 10-4, and the photoemissive threshold of the film to laser intensity is 10W/cm2. The curve of photoelectric current density vs. laser intensity is not linear. It shows a slope which decreases with increasing light intensity. The quantum yield of the photoemission is variable. This phenomenon is related to the laser intensity and the film characteristics.
PHASE DIAGRAM CALCULATION OF DIAMONDGROWTH FROM LOW PRESSURE GASES
ZHANG WEI, WANG JI-TAO, WAN YONG-ZHONG
1997, 46 (6): 1237-1242. doi: 10.7498/aps.46.1237
Abstract +
The phase diagrams of diamond growth from CH4/H2, CO/H2 gases and oxyacetylene flames are calculated by non-equilibrium thermodynamic coupling model in the paper. These phase diagrams are different from those derived from classical equilibrium thermodynamic theory. A diamond growth region, which is the thermodynamic basis of diamond synthesis, exists in each calculated phase diagram. The diamond growth region reflects the roles of those activated particles such as super equilibrium atomic hydrogen during diamond deposition. The calculated phase diagrams are agreement with many reported experimental results, and they will be of favor of theoretical and experimental studies of diamond growth from gas mixtures.
SELECTION OF INITIAL PERTURBATION WAVELENGTHOF A PLANAR SOLID-LIQUID INTERFACE
DING GUO-LU, LIN XIN, HUANG WEI-DONG, ZHOU YAO-HE
1997, 46 (6): 1243-1248. doi: 10.7498/aps.46.1243
Abstract +
A transparent model alloy, succinonitrile-0.93wt.% salol is unidirectionally solidified under the accurately controled experimental conditions to investigate the selection of initial perturbation wavelength of a planar interface. The experimental data are compared with the Mullins-Sekerka (M-S) theory and the Warren-Langer (W-L) model. The following results are obtained: (1) Some experimental points do not lie within the wavelength range predicted by the M-S theory when Vcmsecms, where Ve is the pulling velocity, Vcms is the critical instability velocity of a planar interface given by M-S theory. When Ve》1.57Vcms, the experimental points are all within the wavelength range, but several times larger than the wavelength with the fastest amplitude developing speed predicted by the M-S theory. In short, the M-S theory cannot be used effectively to predict the selection of the initial perturbation wavelength of a planar interface. (2) The experimental results obtained in different alloys are all in good agreement with the W-L model, which proves that the initial perturbation of a planar interface is generated by the dramatic amplification of the ambient thermal micro-fluctuation with a characteristic wavelength.