摘要:

The distribution of resonant frequencies in single cavity and acoustically coupled surface acoustic wave grating resonators is investigated. The axial mode distribution is calculated using the transverse resonance method. The components of the resonator are represented by equivalent circuits whose parameters can be adjusted to conform to experimental values. Results showing the effect of cavity design parameters on the distribution of the resonant frequencies in resonators of bilaterally symmetric construction are presented.

ISSN:0021-8979    

DOI:10.1063/1.347185

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper, the three‐dimensional theory of pulsed photothermal deformation is presented; by taking two appropriate assumptions, the rigorous solutions of three‐dimensional thermal conduction and thermoelastic equations are given for the first time. The theoretical shape of the signal of two different samples is calculated, and the effects of pulse width, radius of pump beam, and sample thickness are discussed. As an example, the potential application of pulsed photothermal deformation for thin‐film thickness measurement is analyzed.

ISSN:0021-8979    

DOI:10.1063/1.346817

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In this paper, a number of the methods of nonlinear dynamics are applied to the study of electrostatic turbulence in a magnetized, steady‐state, partially ionized plasma. Electrostatic potential fluctuations were obtained by using a capacitative probe. These signals were captured, digitized, and recorded with a LeCroy transient recorder system interfaced to an IBM‐AT personal computer. A commercially available software program was used to calculate power spectra, to reconstruct and plot phase portraits, take Poincare´ sections, compute correlation dimensions and Lyapunov exponents, and to perform other manipulations of the time series of electrostatic potential fluctuations obtained from the plasma. Evidence of low‐dimensional chaos was sought, and trends were investigated which related the state of the turbulence to such plasma parameters as the anode voltage (rms electrostatic potential), background gas pressure (collisionality), and magnetic induction. These variables were found to have a significant effect on the nonlinear dynamics of the plasma.

ISSN:0021-8979    

DOI:10.1063/1.346818

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The reactive ion etching of small features in a planar substrate produces a wide range of profiles which depend on many factors. Of underlying importance is the energetic positive ion flux incident on any substrate exposed to the plasma. Therefore, the nature of this directed ion flux is of interest when trying to understand the microscopic nature of dry etching where ion‐enhanced surface chemistry and physical sputtering contribute to the etching performance. This paper uses a simple model to examine the influence of the local electric fields at the substrate on ion trajectories. It is found that the presence of trenches in the substrate distorts the local electric field, and the nature of this field is such that positive ions arriving normal to the substrate surface are deflected towards the sidewalls of the trench. The deflection is largest for those ions arriving near the trench sidewalls, the magnitude of which is calculated to be a few degrees. From the results of this investigation a new technique is proposed where in principle the positive ion flux can be influenced by externally applied potentials in an attempt to control the ion trajectories.

ISSN:0021-8979    

DOI:10.1063/1.346819

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Laser‐induced‐fluorescence spectroscopy was used to detect SO and SO2molecules in the active volume of 13.56‐MHz discharges through mixtures of sulfur hexafluoride and oxygen. A KrF laser was used to excite the SOB3&Sgr; state and the SO2B˜1B1andC˜1B2states. 235‐nm light was used to directly monitor the ground‐state densities of these molecules. For a 100‐W discharge through a 12.5% oxygen mixture (42 sccm SF6, 6 sccm O2, 340‐mTorr total pressure), the SO and SO2densities were determined to be ∼2×1014/cm3and ∼4×1013/cm3, respectively. For the same discharge conditions, the SO vibrational temperature was ∼880 K. The SO vibrational temperature was independent of oxygen content in our experiments.

ISSN:0021-8979    

DOI:10.1063/1.346820

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The penetration and equilibration of the velocity distribution function of an initially monoenergetic electron beam with energies of 50, 100, and 500 eV which is injected into a Maxwellian ‘‘bulk’’ hydrogen pseudospark or back‐lighted thyratron plasma ( j≊104A/cm2,Te≊1 eV,ne=1–3×1015cm−3) is evaluated using a Fokker–Planck equation. The electron beam considered here is the part that is produced during the conductive phase by the electric field in the cathode fall. The beam is estimated to traverse the electrode gap without equilibration with the background plasma if the plasma density is ≤2.5×1015cm−3.

ISSN:0021-8979    

DOI:10.1063/1.346821

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The location of Yb atoms in indium (InP, Ga0.51In0.49P) and gallium (GaAs, Al0.35Ga0.65As, GaAs0.6P0.4) III–V semiconducting compounds was investigated. It has been shown that Yb atoms occupy substitutional lattice positions only in indium compounds. Solid solubility of Yb in InP is of the order of 1020cm−3, as estimated from Rutherford backscattering spectroscopy (RBS) measurements and is high by a factor of 2.5 than in 50% GaInP alloy. In gallium compounds the substitutional fraction of Yb is much below the detection limit of the RBS method, even in the case of elevated temperature (250 °C) implantation. It is suggested that optical activity of Yb is related to its substitutional location in the lattices and/or to the character of the YbP bond. The reasons for the material dependent behavior of Yb atoms in III–V crystal hosts are discussed.

ISSN:0021-8979    

DOI:10.1063/1.346822

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The lattice constants of Nd14Fe78−xMnxC8compounds decrease with the increase of Mn contextxand have a minimum at aboutx=14. The Curie temperatureTcdecreases linearly and falls off below room temperature beyondx=14. The strong reduction of the saturation magnetization andTcare attributed to the antiparallel alignment of the Mn and Fe atoms moments. The behavior of magnetization and magnetization reversal in the high‐Mn‐containing samples at low temperature can be interpreted by the narrow domain wall effect. The relationship of the intrinsic coercive forcei Hcon temperature agrees well with the exponential formula of the narrow Bloch wall.

ISSN:0021-8979    

DOI:10.1063/1.346823

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Fourier synthesis is employed to obtain solutions to the coupled singular integrations which, according to the method of dislocation continua, represent equilibrium. The cases of screw and edge dislocations totally contained within parallel planar surfaces are considered first. An initial extension of the method to problems in three dimensions is then made and exemplified by the treatment of an edge dislocation which lies normal to a free surface.

ISSN:0021-8979    

DOI:10.1063/1.346824

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The elastic distortion field in (001)‐grown lattice mismatched heterostructures of diamond or zinc‐blende structure having misfit dislocations at the interface is calculated within the linear elasticity theory. Not only the misfit dislocation densities in the two ⟨110⟩ directions but also the distribution of the possible Burgers vectors are taken into consideration. A transition layer where the elastic field is appreciably laterally nonuniform extends from the interface up to a distance of the same order of the mean dislocation spacing. It is shown that this transition layer affects x‐ray diffraction measurements. Beyond this region, the elastic distortion field is uniform and is found to depend only on the mean values of the Burgers vectors associated with the two dislocation distributions. In particular it is shown that in general the strain field, i.e., the symmetric part of the elastic distortion field, is not biaxial. The three independent parameters describing the lattice deformations in the epilayer depend not only on the projections on the interface of the edge components but also on the screw components of the Burgers vectors. The predictions of this model are tested on InxGa1−xAs/GaAs samples analyzed by means of channeling and double crystal x‐ray diffractometry. The unbalance of the dislocation densities in the two ⟨110⟩ directions measured by the dechanneling behavior of the samples agrees rather well with the prediction of the model on the basis of the measured asymmetries of the strain field.

ISSN:0021-8979    

DOI:10.1063/1.346825

出版商:AIP    

年代:1990

数据来源: AIP