摘要:

The understanding of the phenomena of ferroelectricity requires profound knowledge of the ferroelectric domain structure. In this paper we report on the progress of studying ferroelectric domains and domain walls with scanning force microscopy (SFM). Domains and domain walls of ferroelectric crystals of guanidinium aluminum sulfate hexahydrate (GASH) are imaged with SFM. Two sets of complementary results are obtained depending on the operation mode of the instrument. In the non‐contact imaging mode (attractive force regime), domain walls are imaged. In the contact imaging mode (repulsive force regime) in addition to the domain wall structure, information about the polarity of the domains is obtained. In these latter images, the opposing contrast of the ferroelectric positive and negative domains is superimposed on the GASH cleavage structure. The imaging mechanism of the contact and noncontact modes are discussed. Corroborating scanning electron microscopy images are presented as well.

ISSN:0021-8979    

DOI:10.1063/1.354969

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Structural and optical properties of InAs/AlSb strained‐layer superlattices (SLSs) grown by molecular‐beam epitaxy (MBE) are described. Either an interface bond of InSb or AlAs was selectively made in the SLSs by controlling the beam supply sequence during growth. Characterization of the SLSs was performed using Raman scattering and photoluminescence (PL) spectroscopy in addition to theinsituanalysis of reflection high‐energy electron‐diffraction signals. The Raman signals consisted of three different types of lattice vibrations: InSb‐ or AlAs‐like phonons localized at the interface bonds, InAs‐ and AlSb‐like optic phonons confined in the respective layers, and zone‐folded acoustic phonons extending through the constituent layers. The energy shift of the optic phonons was used to determine the strain in SLSs. This analysis revealed a considerable dependence of the SLS structure on the interface bond. The Raman analysis was also supported by the PL data. These optical properties are discussed in relation to the MBE‐growth conditions of SLSs.

ISSN:0021-8979    

DOI:10.1063/1.354970

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Light of wavelength 632.8 nm andp‐polarization is incident on a prism–air gap (varied from 0.7 to 7 &mgr;m)–Al‐GaAs arrangement. Both the photosignal generated by the Schottky diode and the reflectance are measured as a function of the internal angle of incidence in the prism. There is significant, well‐defined enhancement of the photosignal, up to a factor of ∼7.5, associated with two different types of enhanced absorption modes. For air gaps <1.5 &mgr;m there is photosignal enhancement due to an enhanced absorption feature (reflectance dip) that occurs at an angle of incidence just above critical angle in the prism; this feature corresponds to the excitation of a surface plasmon polariton at the Al‐air interface. For air gaps ≳1 &mgr;m there are between one and ten photoresponse peaks at input angles less than the critical angle. The corresponding enhanced absorption features are due to leaky guided wave modes set up in the air gap.

ISSN:0021-8979    

DOI:10.1063/1.354971

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The magnetic and magneto‐optical properties of Fe‐Si/Pd multilayers prepared by rf sputtering were studied. For Fe‐Si/Pd multilayers with a fixed Fe‐Si layer thicknessdmof 15 A˚ and the Pd layer thicknessdpincreasing from 10.8 to 18 A˚, the saturation magnetizationMsand the Kerr rotation &thgr;kdecrease sharply and reach a minimum. Withdpfurther increasing, the multilayers increase.Msis almost constant and &thgr;kdecreases slightly whendp≳36 A˚. For Fe‐Si/Pd (54 A˚) multilayers the room temperatureMsdecreases and &thgr;kincreases, respectively, with increasingdm. This is caused by the spin‐polarization effect of Pd atoms near the interfaces.

ISSN:0021-8979    

DOI:10.1063/1.354972

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A theoretical model for the surface photovoltage effect (SPV) in undoped semi‐insulating (SI) GaAs is presented. This model accounts for the large measured SPV signals for SI material compared withn‐type material. The SPV effect in undoped SI GaAs is shown to originate predominantly from the large difference in mobilities between electrons and holes. The low dark conductivity of SI GaAs also plays an important role in determining the large measured signal. In this article experimental SPV data for undoped SI GaAs are presented and explained using the proposed model, providing a value for the ambipolar diffusion length of 1.4 &mgr;m. The native surface field contribution to the measured SPV signal is estimated experimentally and found to be negligible in undoped SI GaAs compared with the aforementioned effects.

ISSN:0021-8979    

DOI:10.1063/1.354973

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The ablated flux characteristics of PbZr0.52Ti0.48O3(PZT), La0.5Sr0.5CoO3(LSC), and MgO ceramic targets have been studied as functions of the ablation time, the ablation energy, and the chamber gas pressure. The time dependence of the ablation rate shows an initial exponential decay, reaching a steady‐state value at longer times. The energy dependence of the ablation rate (in vacuum) reveals a distinct ablation threshold energy for MgO ablation, while for PZT and LSC no ablation threshold is evident. The differences in the ablation characteristics of these materials are explained mainly by differences in their melting points, thermal conductivities, and absorption coefficients. Upon adding O2gas, a visual change in the color and shape of the PZT ablation plume is evident. The color change indicates a gas phase reaction of the ablated species with the O2gas, while the shape change implies a change in the angular distribution of the ablated species. We have measured a narrowing of the ablated flux distribution from a PZT target as O2is added, from a cos40 &thgr; distribution in a low pressure, up to a cos260 &thgr; distribution in an O2pressure of 300 mTorr. This narrowing, or focusing, of the ablation plume is observed with high laser energies and high pressures of O2or noble gases. At low laser power, the deposition rate decreases and the plume broadens as the gas pressure is increased. The plume narrowing and plume broadening regimes are both controlled by gas scattering effects. The angular distribution of depositing species, and the ratio of deposition flux to O2flux, are very different in each of these regimes.

ISSN:0021-8979    

DOI:10.1063/1.354974

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A microscopic model for low energy electron interaction in alkali halides was used to simulate secondary electron emission from CsI induced by x rays with energies up to 100 keV. The integral ‘‘current’’ and ‘‘pulse’’ yields were calculated as function of the x‐ray energy, CsI convertor thickness, and angle of incidence. We observe a decrease in true low energy (<50 eV) secondary electron yields at increasing x‐ray energies and discuss the effectiveness of CsI convertors coupled to gaseous electron multipliers developed for fast, high resolution x‐ray imaging.

ISSN:0021-8979    

DOI:10.1063/1.354975

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

One‐dimensional‐imaging laser‐induced fluorescence spectroscopy (1D‐LIF) has been applied to investigate the dynamics of the nonemissive neutral particles (YO molecules) during the ArF excimer laser ablation of YBa2Cu3O7−&dgr;in an ambient oxygen gas. Investigating the 1D‐LIF observation, the propagation of particles through the ambient gas at appropriately high pressures is categorized into two phases, the propagation phase and the diffusion phase. In the propagation phase, the point source blast wave model (shock model) describes well the dynamics at high background gas pressures. Particles propagate according to the shock model over a finite distance from the pellet surface after the ablation, and almost stop there. The propagation distance depends on the ambient gas pressure and the ablation fluence. After the propagation ceases, the particles start to diffuse through the background gas; that is the diffusion phase. Rotational temperature variations of YO molecules in the different phases are also measured. Rotational temperatures as high as 1000 K are observed even in the diffusion phase.

ISSN:0021-8979    

DOI:10.1063/1.354976

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In a reactive ion beam etching system, gas phase collision processes in the reaction chamber were identified from the energy distributions of positive ions originating from source plasmas with O2, SF6, and CF4as feed gases. The ion energy distributions are determined by a quadrupole mass spectrometer for main beam energies below 500 eV at typical working pressures in the reaction chamber of 1–10×10−2Pa. Besides near thermal ions a considerable amount of high energy fragmentation products were detected for a number of primary molecular ions. The relative intensities of these products compared to the parent ions suggest a non‐negligible influence of gas phase dissociation processes on the etch or deposition characteristics of molecular ion beams and the resulting properties of surfaces treated under elevated working pressure conditions.

ISSN:0021-8979    

DOI:10.1063/1.354977

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Reaction products contained in the exhaust gas of a dc plasma jet reactor system were detected using mass spectrometry. The major reaction products formed from a feed gas mixture of 96% H2, 3% CH4, and 1% O2injected into an argon plasma jet were CH4, C2H2, C2H6, CO, and H2O. The products formed without O2in the reactor feed were CH4, C2H2, and C2H6. Addition of O2to the reactor gas feed increased the diamond deposition rate by ∼30% with no degradation in quality. A chemical kinetics model for flames was adapted to this reactor and accurately predicted the major reaction products formed for a reactor feed without O2, indicating the gas phase chemistry may be described by a reaction set developed for hydrocarbon combustion and the chemistry is thermally driven. When compared to experimental results, the model predicts: (1) a maximum temperature in the gas of 3000 K, (2) only 1.2% of the H2in the reactor feed is dissociated, and (3) CH3is the primary diamond growth precursor.  

ISSN:0021-8979    

DOI:10.1063/1.354978

出版商:AIP    

年代:1993

数据来源: AIP