Based on a rigorous far-field solution of the Helmholtz equation,the dependence of the far-field of the light wave with a large divergence angle on the perturbation of the source profile is discussed,and the error formulas of the far-field amplitude and phase are also given.It is shown that the far-field errors must be described by using the “error area” of the source.In the paraxial region,the far-field amplitude and phase are not sensitive to the source perturbation,but,in off-axis region,they may be sensitive.
Based on a rigorous far-field solution of the Helmholtz equation,the dependence of the far-field of the light wave with a large divergence angle on the perturbation of the source profile is discussed,and the error formulas of the far-field amplitude and phase are also given.It is shown that the far-field errors must be described by using the “error area” of the source.In the paraxial region,the far-field amplitude and phase are not sensitive to the source perturbation,but,in off-axis region,they may be sensitive.
Laser ablation mass spectroscopy (LAMS) has been used to study yttrium contained fullerenes. Yttrium contained fuller enes were prepared by arc burning of Y2O3/graphite composite rods. The LAMS exper imental results confirm the presence of YC82．It was also shown that YC82 appears on the surface of the sample and that the yield of YC82 changes with the primitive weight ratio of Y2O3 to graphite in fabrication processing. In addition, the stability of YC82 in air was studied and the mechanism of YC82 formation was discussed.
Laser ablation mass spectroscopy (LAMS) has been used to study yttrium contained fullerenes. Yttrium contained fuller enes were prepared by arc burning of Y2O3/graphite composite rods. The LAMS exper imental results confirm the presence of YC82．It was also shown that YC82 appears on the surface of the sample and that the yield of YC82 changes with the primitive weight ratio of Y2O3 to graphite in fabrication processing. In addition, the stability of YC82 in air was studied and the mechanism of YC82 formation was discussed.
A pronounced odd-even alternation for Al－n clusters ranging from n=5 to n=17 has been observed in mass abundance spectra. The electron-pairing effect of the delocalized valence electrons determines intrinsically the alternation, while special source conditions enhance the alternation so dramaticaly that it is readily obseervable in mass abundance spectra. The ion group Al7O－ has also, for the first time as far as we know, been observed, and its geometric as well as electronic structure has been discussed.
A pronounced odd-even alternation for Al－n clusters ranging from n=5 to n=17 has been observed in mass abundance spectra. The electron-pairing effect of the delocalized valence electrons determines intrinsically the alternation, while special source conditions enhance the alternation so dramaticaly that it is readily obseervable in mass abundance spectra. The ion group Al7O－ has also, for the first time as far as we know, been observed, and its geometric as well as electronic structure has been discussed.
It is shown theoretically and experimentally that a weak signal light amplification is possible in thin photorefractive crystals with a local nonlinear response due to photovoltaic charge transport.The origin of the power exchange is that four wave interaction of the input beams and reflection beam at the rear will form two sets of bending gratings with certain spatial phase shift.When the grating written by the reflection wave and its diffracted wave is read by the input pump beam under off Bragg condition ,the weak signal beam achieves coherent amplification.Theoretical and experimental results are compared with each other.
It is shown theoretically and experimentally that a weak signal light amplification is possible in thin photorefractive crystals with a local nonlinear response due to photovoltaic charge transport.The origin of the power exchange is that four wave interaction of the input beams and reflection beam at the rear will form two sets of bending gratings with certain spatial phase shift.When the grating written by the reflection wave and its diffracted wave is read by the input pump beam under off Bragg condition ,the weak signal beam achieves coherent amplification.Theoretical and experimental results are compared with each other.
The superposition properties of generalized coherent states in the non harmonic oscillator potential is discussed in this paper. The necessary and sufficient condition of periodic squeezing is found, and the relation between antibunching effort and the superposition coefficient is shown.
The superposition properties of generalized coherent states in the non harmonic oscillator potential is discussed in this paper. The necessary and sufficient condition of periodic squeezing is found, and the relation between antibunching effort and the superposition coefficient is shown.
Theoretical calculations show that the generalized odd and even coherent states(OECS) of a non harmonic oscillator represent higher power (odd number power) squeezing effect and antibunching effect respectively, and these photon statistical characteristics are very different from those of the ordinary OECS.
Theoretical calculations show that the generalized odd and even coherent states(OECS) of a non harmonic oscillator represent higher power (odd number power) squeezing effect and antibunching effect respectively, and these photon statistical characteristics are very different from those of the ordinary OECS.
The closed expressions with a parameter of the Bogoliubov unitary transformation are derived. The reduced Hamiltonian of the quantum Bose fluid is diagonalized in the original particle number representation. The manifestation of nonclassical character in the two mode radiation is extended to the quantum Bose fluid. Finally, the eigenstates of the Hamiltonian are established to be the squeezed boson pair number states with a nonclassical character.
The closed expressions with a parameter of the Bogoliubov unitary transformation are derived. The reduced Hamiltonian of the quantum Bose fluid is diagonalized in the original particle number representation. The manifestation of nonclassical character in the two mode radiation is extended to the quantum Bose fluid. Finally, the eigenstates of the Hamiltonian are established to be the squeezed boson pair number states with a nonclassical character.
We first derive the state vector of a V-type three-level atom interacting with two-mode SU (1,1) coherent states in a Kerr-like medium. It is shown by numericl calculations that the Kerr effect results indifferent characters of the Rabi oscillation, as compared with the two-levelatom case, while the correlation of the two-mode coherent states is less affected by the the Kerr medium. We also discuss the influence of Kerr effect on the Cauchy-Schwartz inequality.
We first derive the state vector of a V-type three-level atom interacting with two-mode SU (1,1) coherent states in a Kerr-like medium. It is shown by numericl calculations that the Kerr effect results indifferent characters of the Rabi oscillation, as compared with the two-levelatom case, while the correlation of the two-mode coherent states is less affected by the the Kerr medium. We also discuss the influence of Kerr effect on the Cauchy-Schwartz inequality.
By using the two photon Bloch equation and quantum regression theorem, the second order correlation function of two photon fluorescence of a two level atom in a broad band squeezed vacuum is obtained. From this, the bunching and the antibunching effects of two photon fluorescence are investigated. We find that the second order correlation function is dependent on the squeezing parameter (|M|) of the squeezed vacuum. There is a critical value (Γ/4g) for |M|,above which the second order correlation function oscillates around 1. This indicates that the two photon fluorescence can exhibit both antibunching and bunching effects. Below the critical value, the second order correlation function does not oscillate and the two photon fluorescence exhibits the antibunching effect only.
By using the two photon Bloch equation and quantum regression theorem, the second order correlation function of two photon fluorescence of a two level atom in a broad band squeezed vacuum is obtained. From this, the bunching and the antibunching effects of two photon fluorescence are investigated. We find that the second order correlation function is dependent on the squeezing parameter (|M|) of the squeezed vacuum. There is a critical value (Γ/4g) for |M|,above which the second order correlation function oscillates around 1. This indicates that the two photon fluorescence can exhibit both antibunching and bunching effects. Below the critical value, the second order correlation function does not oscillate and the two photon fluorescence exhibits the antibunching effect only.
The rate equation theory for the dual wavelength pulsed laser is first put forward and the numerical calculation is made,the conclusions are agree with experimental results in references.
The rate equation theory for the dual wavelength pulsed laser is first put forward and the numerical calculation is made,the conclusions are agree with experimental results in references.
Effects of the multilayer heterostructures as the feedback end facets and quantum well structure as the active medium on the lasing behavior in the vertical cavity surface emitting laser (VCSEL) have been analyzed theoretically and systematically. It is shown that the degree of phase matching and the effective length of the distributed reflector have prominent effects on the laser characteristics, and the available low threshold VCSEL may not be due to the microcavity effect. The possible ways to improve the design and the device characteristics have been proposed, both for low threshold and simplified device technology, and for satisfying the condition of microcavity effect in VCSEL.
Effects of the multilayer heterostructures as the feedback end facets and quantum well structure as the active medium on the lasing behavior in the vertical cavity surface emitting laser (VCSEL) have been analyzed theoretically and systematically. It is shown that the degree of phase matching and the effective length of the distributed reflector have prominent effects on the laser characteristics, and the available low threshold VCSEL may not be due to the microcavity effect. The possible ways to improve the design and the device characteristics have been proposed, both for low threshold and simplified device technology, and for satisfying the condition of microcavity effect in VCSEL.
The parametric gain of the ring and standing cavities was studied in this paper. By using the strong output of frequency doubled and stabilized Nd:YAP laser at 0．54μm as the pump source and the fundamental output at 1．08μm as the signal and idler modes, strong coupling of three modes in the ring or standing cavities is demonstrated. An optical wedge and a temperature controller are used to realize the three mode resonance simultaneously. Parametric gain as high as 110 is obtained. The relation between the gain and the pump power is also measured and the result fits to the theory on the whole.
The parametric gain of the ring and standing cavities was studied in this paper. By using the strong output of frequency doubled and stabilized Nd:YAP laser at 0．54μm as the pump source and the fundamental output at 1．08μm as the signal and idler modes, strong coupling of three modes in the ring or standing cavities is demonstrated. An optical wedge and a temperature controller are used to realize the three mode resonance simultaneously. Parametric gain as high as 110 is obtained. The relation between the gain and the pump power is also measured and the result fits to the theory on the whole.
Y-G algorithm is used in the whole desigh of a new type phase-only-controlled wave length division multiplexer (WDM). According to the intensity distribution set up on the input (H1) and output(H2) faces, the phase distribution on H1 and H2 can be designed. By only phase modulation, The demultiplex and focusing etc. are realized, thus the WDM structure is simplified, and at the same time the Y-G algorithm is extende to the situation that the input beam is a 2-D Gaussian beam and the output beam is also a 2-D Gaussian beam.
Y-G algorithm is used in the whole desigh of a new type phase-only-controlled wave length division multiplexer (WDM). According to the intensity distribution set up on the input (H1) and output(H2) faces, the phase distribution on H1 and H2 can be designed. By only phase modulation, The demultiplex and focusing etc. are realized, thus the WDM structure is simplified, and at the same time the Y-G algorithm is extende to the situation that the input beam is a 2-D Gaussian beam and the output beam is also a 2-D Gaussian beam.
The crystalline quality of two SrTiO3 substrate wafers has been analyzed by X-ray double crystal rocking curve and topography.The surface structures of these two samples are investigated by grazing X-ray specular reflectivity and diffuse scattering.Results show that there are mosaic defects in both samples,but the crystalline quality of one sample is relatively high.There is big difference in the surface structures of these two samples.The root mean roughness σ of one sample is only (0.5±0.1)nm,while the other one is as high as (1.3±0.1)nm.The lateral correlation length of one sample is (1200±200)nm,but another is (300±20)nm.The rough surface will enhance the X-ray diffuse scattering and reduce the specular reflectivity.The substrate wafer with higher crystalline quality has also a relative smooth surface and is suitable for epitaxial growth.
The crystalline quality of two SrTiO3 substrate wafers has been analyzed by X-ray double crystal rocking curve and topography.The surface structures of these two samples are investigated by grazing X-ray specular reflectivity and diffuse scattering.Results show that there are mosaic defects in both samples,but the crystalline quality of one sample is relatively high.There is big difference in the surface structures of these two samples.The root mean roughness σ of one sample is only (0.5±0.1)nm,while the other one is as high as (1.3±0.1)nm.The lateral correlation length of one sample is (1200±200)nm,but another is (300±20)nm.The rough surface will enhance the X-ray diffuse scattering and reduce the specular reflectivity.The substrate wafer with higher crystalline quality has also a relative smooth surface and is suitable for epitaxial growth.
Polytetrafluoroethylene (PTFE) thin films have been grown successfully by rf magnetron sputtering technique. The infrared spectra of the as prepared films are consistent with those of the PTFE target. However, chains in the films become shorter than those in the bulk.
Polytetrafluoroethylene (PTFE) thin films have been grown successfully by rf magnetron sputtering technique. The infrared spectra of the as prepared films are consistent with those of the PTFE target. However, chains in the films become shorter than those in the bulk.
Ag ultrafine crystal films (AgUFCPs) of about 18nm thickness were deposited on a (111) monocrystalline silicon surface,by means of the vacuo-sputtering technique.The microstructure of AgUFCP and the interface morphology between the film and substrate were revealed by using of grazing incidence X-ray scattering (GIXS) method.A semi-crystalline structure of AgUFCP was- investigated by wide angle X-ray diffraction (WXRD) and radial distribution function(RDF).The surface atomic structure of Ag ultrafine crystal particle were analysed by DSC scans.and the temperature dependence of the growth dynamic mechanism of particle surface layer was explored.
Ag ultrafine crystal films (AgUFCPs) of about 18nm thickness were deposited on a (111) monocrystalline silicon surface,by means of the vacuo-sputtering technique.The microstructure of AgUFCP and the interface morphology between the film and substrate were revealed by using of grazing incidence X-ray scattering (GIXS) method.A semi-crystalline structure of AgUFCP was- investigated by wide angle X-ray diffraction (WXRD) and radial distribution function(RDF).The surface atomic structure of Ag ultrafine crystal particle were analysed by DSC scans.and the temperature dependence of the growth dynamic mechanism of particle surface layer was explored.
Specimens of 316L stainless steel are irradiated with 2.5 MeV He+ ions at temperatures of 400,500 and 550℃,respectively.For each implantation the dose and dose rate are separately 2.5×1021 ion/m2 and (3.2—3.8)×1016 ion/m2s-1.Bubble structures are investigated with cross sectional transmission electron microscopy(XTEM).The measured apparent activation energies provide evidence that the formation of bubbles is controlled by He diffusion via the self interstitial/He replacement mechanism.Good agreement is found between our results and other low dose experimental data,indicating that the underlying mechanism holds constant for different implantation conditions.The pre implantation cold working enhances significantly the nucleation of bubbles,and the dislocations are favorable sites for bubble nucleation in the investigated temperature range.
Specimens of 316L stainless steel are irradiated with 2.5 MeV He+ ions at temperatures of 400,500 and 550℃,respectively.For each implantation the dose and dose rate are separately 2.5×1021 ion/m2 and (3.2—3.8)×1016 ion/m2s-1.Bubble structures are investigated with cross sectional transmission electron microscopy(XTEM).The measured apparent activation energies provide evidence that the formation of bubbles is controlled by He diffusion via the self interstitial/He replacement mechanism.Good agreement is found between our results and other low dose experimental data,indicating that the underlying mechanism holds constant for different implantation conditions.The pre implantation cold working enhances significantly the nucleation of bubbles,and the dislocations are favorable sites for bubble nucleation in the investigated temperature range.
Strain rate and shear viscosity are measured for Zn-Al eutectoid alloy under continuous heating rate conditions.The minimum values of the shear viscosity accompanied by the eutectoid change process have been observed.The stress dependence of the strain rate and the heating rate dependence of minimum values of the shear viscosity have been investigated.It is found that the relation between strain rate and the stress in the temperature region of the phase transformation obeys Newtonian viscous flow law.The viscous flow behaviour of Zn-Al eutectoid alloy in the temperature region of phase transformation can be explained with the number and the property of the phase interface.Comparing the activation energy of the phase transformation with that of viscous flow of the phase interface,it is found that the fluidity of phase interface is likely to be a primary factor which influences phase transformation process.In a previous work,the minimum values of viscosity have been observed in glass transition and crystallization process of amorphous Pd-Cu-Si alloy.According to these results,it is shown that the minimum viscosity emerged in structural transition process has some universality.
Strain rate and shear viscosity are measured for Zn-Al eutectoid alloy under continuous heating rate conditions.The minimum values of the shear viscosity accompanied by the eutectoid change process have been observed.The stress dependence of the strain rate and the heating rate dependence of minimum values of the shear viscosity have been investigated.It is found that the relation between strain rate and the stress in the temperature region of the phase transformation obeys Newtonian viscous flow law.The viscous flow behaviour of Zn-Al eutectoid alloy in the temperature region of phase transformation can be explained with the number and the property of the phase interface.Comparing the activation energy of the phase transformation with that of viscous flow of the phase interface,it is found that the fluidity of phase interface is likely to be a primary factor which influences phase transformation process.In a previous work,the minimum values of viscosity have been observed in glass transition and crystallization process of amorphous Pd-Cu-Si alloy.According to these results,it is shown that the minimum viscosity emerged in structural transition process has some universality.
With cell model,the polarized order parameter is defined on cell center.By choice of interaction potential of biaxial molecules possessing a permanent electris dipole moment transverse to molecular axes,the system free energy is obtained.The approximate formula of spontaneous polarization and pitch is derived by calculation of variation to the free energy.We have calculated the temperature and the molecular transverse electric dipole dependence of the spontaneous polarization and pitch for four classic SmC* liquid crystals of DOBAMBC and 3M2CPOOB etc.The calculations agree satisfactorily with experimental results.It is shown that the spontaneous polarization is mainly due to the molecular biaxiality and transverse electric dipole of the SmC* liquid crystals.
With cell model,the polarized order parameter is defined on cell center.By choice of interaction potential of biaxial molecules possessing a permanent electris dipole moment transverse to molecular axes,the system free energy is obtained.The approximate formula of spontaneous polarization and pitch is derived by calculation of variation to the free energy.We have calculated the temperature and the molecular transverse electric dipole dependence of the spontaneous polarization and pitch for four classic SmC* liquid crystals of DOBAMBC and 3M2CPOOB etc.The calculations agree satisfactorily with experimental results.It is shown that the spontaneous polarization is mainly due to the molecular biaxiality and transverse electric dipole of the SmC* liquid crystals.
The effect of Sb on Ge epilayer grown on Si(001) is investigated in situ by RHEED and ex situ by X-ray diffraction.Without Sb,island formation takes place when Ge epilayer is 6nm thick,and the strain in Ge epilyer is totally relaxed.With Sb,the growth mode of Ge on Si is two- dimensional, and the strain is relaxed gradually.Even if the thickness of the Ge epilayer is 6nm, 42%- strain is still not relaxed.
The effect of Sb on Ge epilayer grown on Si(001) is investigated in situ by RHEED and ex situ by X-ray diffraction.Without Sb,island formation takes place when Ge epilayer is 6nm thick,and the strain in Ge epilyer is totally relaxed.With Sb,the growth mode of Ge on Si is two- dimensional, and the strain is relaxed gradually.Even if the thickness of the Ge epilayer is 6nm, 42%- strain is still not relaxed.
Using the quantum statistical Green's function approach,we have studied the giant magneto resistance effect in magnetic sandwich structure,and developed a unified conductivity fomula.The relation between the classical and quantum theories and the transition from classical to quantum result are also discussed.
Using the quantum statistical Green's function approach,we have studied the giant magneto resistance effect in magnetic sandwich structure,and developed a unified conductivity fomula.The relation between the classical and quantum theories and the transition from classical to quantum result are also discussed.
The InyGa1-y As/GaAs superlattice with an InxGa1-x As (xyGA1-yAs interface was narrower than that at the InyGa1-y As/GaAs interface; in InyGa1-yAs alloy layer, the composition near the GaAs/InyGa1-y As interface was larger than that near the other interface. For the first time, we have explained the composition profile in these kinds of superlattices based on the indium segregation theory. In addition, a new strain relaxation model was presented to explain the differences in the smoothness between the two interfaces.
The InyGa1-y As/GaAs superlattice with an InxGa1-x As (xyGA1-yAs interface was narrower than that at the InyGa1-y As/GaAs interface; in InyGa1-yAs alloy layer, the composition near the GaAs/InyGa1-y As interface was larger than that near the other interface. For the first time, we have explained the composition profile in these kinds of superlattices based on the indium segregation theory. In addition, a new strain relaxation model was presented to explain the differences in the smoothness between the two interfaces.
Synchrotron radiation photoelectron spectroscopy is used to measure the valence-band offsets for Si/ZnS(111) and (100) heterojunctions. The valence band discontinuities obtained from the measurements are both (1.9±0.1)eV for Si/ZnS(111) and Si/ZnS(100) interfaces,which is in excellent agreement with the theoretical predictions but considerably different from the experimental- result of ZnS/Si(111) reported by Maierhofer et al. This suggests that the commutativity rule of- band offset may not be valid for Si/ZnS polar interface and the reason is discussed.
Synchrotron radiation photoelectron spectroscopy is used to measure the valence-band offsets for Si/ZnS(111) and (100) heterojunctions. The valence band discontinuities obtained from the measurements are both (1.9±0.1)eV for Si/ZnS(111) and Si/ZnS(100) interfaces,which is in excellent agreement with the theoretical predictions but considerably different from the experimental- result of ZnS/Si(111) reported by Maierhofer et al. This suggests that the commutativity rule of- band offset may not be valid for Si/ZnS polar interface and the reason is discussed.
Hidden local gauge invariance for Osp (2,1) spin chain is studied in the frame work of the quantum inverse scattering method. It is found that this model admits an Abel U (1) gauge transformation and the energy spectrum is gauge invariant, where as the eigenvectors and Be the an satz equations are explicitly gauge dependent.
Hidden local gauge invariance for Osp (2,1) spin chain is studied in the frame work of the quantum inverse scattering method. It is found that this model admits an Abel U (1) gauge transformation and the energy spectrum is gauge invariant, where as the eigenvectors and Be the an satz equations are explicitly gauge dependent.
The magnetoresistance of magnetic granular alloys has been studied based on a quantum phenomenological model.We take into account the phase interference effectamong the impurity atoms in a grain to calculate the scattering cross section between conduction electron and atom.According to the size distribution data provided by the experiment reported,we have derived an expression for the magnetoresistance depending on the grain size,size distribution,and applied magnetic field.The calculated results for the Fe-Ag sample have shown that the variation character of magnetoresistance with the external field depends on the size distribution of the grains.At a size scale D0,the magnetoresistance shows a maximum value.The size scale D0 depends on the applied field,the sample materials and fabrication conditions.
The magnetoresistance of magnetic granular alloys has been studied based on a quantum phenomenological model.We take into account the phase interference effectamong the impurity atoms in a grain to calculate the scattering cross section between conduction electron and atom.According to the size distribution data provided by the experiment reported,we have derived an expression for the magnetoresistance depending on the grain size,size distribution,and applied magnetic field.The calculated results for the Fe-Ag sample have shown that the variation character of magnetoresistance with the external field depends on the size distribution of the grains.At a size scale D0,the magnetoresistance shows a maximum value.The size scale D0 depends on the applied field,the sample materials and fabrication conditions.
The spin valve [NiFe/Cu/Co/Cu]N multilayers were prepared by using electr on bean method. The influences of thickness on the magnetoresistance (MR) werestudied. We also investigated the stability of MR and tried to reduce the center field H0, which is the center magnetic field of the linear region in the MRH curve. Under optimum seeking conditions, we have deposited many samples with low center field H0 in range of (10—20)(103/4π)Am-1,the merit is larger than 0.2%×((103/4π)Am-1)-1. The variation of MR in the linear region in the MRH curve is reversible during repeatedly magnetizing. After annealed at 200℃ for 15 minutes, MR increased and Hrm reduced with a small amount. The change of MR is less than 0.3% for several samples after aging one year in the dry air chamber and room temperature.
The spin valve [NiFe/Cu/Co/Cu]N multilayers were prepared by using electr on bean method. The influences of thickness on the magnetoresistance (MR) werestudied. We also investigated the stability of MR and tried to reduce the center field H0, which is the center magnetic field of the linear region in the MRH curve. Under optimum seeking conditions, we have deposited many samples with low center field H0 in range of (10—20)(103/4π)Am-1,the merit is larger than 0.2%×((103/4π)Am-1)-1. The variation of MR in the linear region in the MRH curve is reversible during repeatedly magnetizing. After annealed at 200℃ for 15 minutes, MR increased and Hrm reduced with a small amount. The change of MR is less than 0.3% for several samples after aging one year in the dry air chamber and room temperature.
Lead lanthanum titanate(PLT) thin films with excess PbO were prepared by metal organic decomposition (MOD) process.The C-V characteristics and ferroelectric properties of the PLT films were investigated as functions of amount of excess PbO.The normal P-E hysteresis loops and butterfly shape C-V curves were obtained for the PLT films with stoichiometric composition.While abnormal ferroelectric and C-V properties were observed in the PLT films with excess PbO.The P-E hysteresis loops were pinched before the polarization of the films reached the saturation.Instead of two peaks (butterfly-shape) in the normal C-V curves,the C-V curves had four peaks. The abnormal behavior of the hysteresis loops and C-V curves became more serious with increasing amount of excess PbO in the films.The results can be explained by the ferroelectric pinning effect.A part of excess PbO may be accumulated at boundaries of crystalline grains and clusters and the interface between the bottom electrode and the film during the annealing process of the films.PbO may act as the pinning centers and has a strong effect on the ferroelectric domains.If the biased voltage is not large enough,then part of the electric domains cannot overcome the force of the pinning,and abnormal ferroelectric and C-V properties will be observed.Excess PbO may be one of the main causes of fatigue and aging of ferroelectric thin films.
Lead lanthanum titanate(PLT) thin films with excess PbO were prepared by metal organic decomposition (MOD) process.The C-V characteristics and ferroelectric properties of the PLT films were investigated as functions of amount of excess PbO.The normal P-E hysteresis loops and butterfly shape C-V curves were obtained for the PLT films with stoichiometric composition.While abnormal ferroelectric and C-V properties were observed in the PLT films with excess PbO.The P-E hysteresis loops were pinched before the polarization of the films reached the saturation.Instead of two peaks (butterfly-shape) in the normal C-V curves,the C-V curves had four peaks. The abnormal behavior of the hysteresis loops and C-V curves became more serious with increasing amount of excess PbO in the films.The results can be explained by the ferroelectric pinning effect.A part of excess PbO may be accumulated at boundaries of crystalline grains and clusters and the interface between the bottom electrode and the film during the annealing process of the films.PbO may act as the pinning centers and has a strong effect on the ferroelectric domains.If the biased voltage is not large enough,then part of the electric domains cannot overcome the force of the pinning,and abnormal ferroelectric and C-V properties will be observed.Excess PbO may be one of the main causes of fatigue and aging of ferroelectric thin films.
The transfer matrix method has been used to calculate the Raman spectra of acoustic phonons in nearly periodic SiGe/Si superlattices,including the supperlattices with finite number of periods,the coupled supperlattices,and those with layer-thickness fluctuations.The properties of the above nearly periodic systems are found to be very different from those of periodic or disordered systems.In stead of the folded acoustic phonons appearing in the Raman spectra from ideal superlattices (main peak),the other satellite peaks are also observable in the finite system due to the existence of boundaries.For the coupled superlattices,the main peaks split into two due to the interference of the acoustic waves in different superlattices.For the superlattices with layer-thickness fluctuation,the main Raman peaks show asymmetric broadening and a tail towards high wave number are observable.The calculated results are compared to the measured spectra and good agreement between them is obtained.
The transfer matrix method has been used to calculate the Raman spectra of acoustic phonons in nearly periodic SiGe/Si superlattices,including the supperlattices with finite number of periods,the coupled supperlattices,and those with layer-thickness fluctuations.The properties of the above nearly periodic systems are found to be very different from those of periodic or disordered systems.In stead of the folded acoustic phonons appearing in the Raman spectra from ideal superlattices (main peak),the other satellite peaks are also observable in the finite system due to the existence of boundaries.For the coupled superlattices,the main peaks split into two due to the interference of the acoustic waves in different superlattices.For the superlattices with layer-thickness fluctuation,the main Raman peaks show asymmetric broadening and a tail towards high wave number are observable.The calculated results are compared to the measured spectra and good agreement between them is obtained.