摘要:

The aluminum electromigration drift velocity was measured at the temperature range 250–400 °C. A threshold current density was found inversely proportional to the stripe length. An activation energy of 0.65 eV was found for the drift velocity. The occurrence of the threshold is explained by opposing chemical gradients created by the atom pile‐up and depletion at the stripe ends. The threshold may explain several observations reported previously. The threshold is increased by decreasing the temperature or by enclosing the aluminum in silicon nitride. Virtually no electromigration is seen for very short aluminum stripes even at current densities above 106A/cm2.

ISSN:0021-8979    

DOI:10.1063/1.322842

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The nonlinear interaction between two oppositely directed surface acoustic waves (SAW) of frequencies &ohgr;1and &ohgr;2and wave vectors &kgr;1and &kgr;2is analyzed theoretically. It is shown from the general theory of thermoelasticity that nonlinear volume forces and surface stresses are created at the frequencies &ohgr;1±&ohgr;2and wave vectors &kgr;1∓&kgr;2, respectively. For the difference frequency case the forces and stresses are relieved by evanescent SAW. In the sum frequency case, up to three bulk waves are generated depending on the value of &kgr;2/&kgr;1. The nonlinear interaction is characterized by normalized surface displacement and bulk‐wave power parameters. The upshift case is examined as a function of &kgr;2/&kgr;1for fused quartz,yzsapphire, andzxsapphire and the cross sections for bulk‐wave generation are discussed in detail. Numerical calculations are presented (with &ohgr;1=&ohgr;2) for the (001), (110), and (111) planes of gallium arsenide, the principal planes of sapphire, and for some cuts of piezoelectric &agr;‐quartz and lithium niobate (in the quasi‐static approximation). The quantity and type of bulk modes generated is discussed in light of SAW propagation plane reflection symmetry, rotational symmetry, and confinement of SAW displacements to the saggital plane.

ISSN:0021-8979    

DOI:10.1063/1.322843

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Bubblelike patterns associated with polar domains have been observed in Fe‐doped LiNbO3single crystals quenched with a temperature drop of approximately 50 °C or more. Exploitation of this effect for a nondestructive domain identification is indicated.

ISSN:0021-8979    

DOI:10.1063/1.322844

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The generation of charge build‐up, caused by bombardment of insulating samples with energetic particles, and its role in altering the relative secondary‐ion currents and reducing their absolute values, sometimes even to zero, are discussed. Proposed methods for charge reduction by bombardment with negative ions or with neutral particles, or by use of an auxiliary electron beam or spray gun, are shown to be not useful in every experimental situation. A further method involving introduction of an auxiliary conducting electrode when using negative primary ions is considered mechanistically, and tested by placing tantalum diaphragms onto the surface of yttrium iron garnet (YIG). The final charging values and mass spectra thus obtained are compared to those measured when using bare and metallic grid‐covered surfaces of the same YIG sample. The satisfactory results achieved with the diaphragm show that SIMS analyses of insulators can be performed in a simple, quick, and inexpensive manner.

ISSN:0021-8979    

DOI:10.1063/1.322845

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The pyroelectric effect (PE) in faulted ZnS crystals was studied experimentally in the temperature range from 100 to 300 °K. It has been found that the observed voltage pulses are due to a special pyroelectric effect which is not connected with the temperature dilation of the unit cell or any resulting change in the value of its dipole moment. The observed pyroelectric effect has been correlated with built‐in electric fields in faulted ZnS crystals. Its temperature dependence is attributed to the different magnitude of the temperature dependence of the dielectric constants in the different ZnS crystal structures.

ISSN:0021-8979    

DOI:10.1063/1.322768

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Acoustic surface waves (ASW) scattered at a region with density and elastic parameter variations are studied in view of the newly developed techniques to fabricate ASW reflectors by ion implantation and metal impurity diffusion. The scattering problem is formulated in a perturbation theory. The first‐order vector equation and the solution are obtained in terms of a source which is due to the interaction of the incident wave and the material perturbation. An example is given to illustrate the application of the theory. Results are found to agree closely with experimental observation.

ISSN:0021-8979    

DOI:10.1063/1.322846

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The influence of surface roughness on the intensity of elastically scattered low‐energy noble‐gas ions has been determined for surfaces whose surface displacements are normally distributed. This has been done by modeling the effect of shadowing on the scattered‐ion intensity. The experimental results are in good agreement with the values predicted by the model.

ISSN:0021-8979    

DOI:10.1063/1.322847

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A beam ofunpolarizedlight is shown to be split into three distinctpolarizedbeams when it passes through the core region of a smectic liquid crystal which is oriented so that its planes form concentric cylinders. InN‐p‐cyanobenzylidene‐p‐octylozyaniline (CBOOA) the angle between two adjacent exit beams is ∼22° whereas forN‐p‐cyano‐p‐octylbiphenyl (COB) it is ∼14°. Knowing this angle, we are able to deduce the ratio of the extraordinary to ordinary index of refraction,ne/no, for CBOOA and COB.

ISSN:0021-8979    

DOI:10.1063/1.322848

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The late stages of sintering of a linear array of rods by viscous flow have been studied theoretically. An approximate model in which the actual interface profile is assumed to be locally planar has been developed. Within the framework of the model, analytic solutions to the steady‐state Navier‐Stokes equations have been derived and the course of sintering followed by advancing the profile through a sequence of short‐duration time intervals. After each step the profile is mathematically redefined and new values for the velocities and pressure calculated. In the later stages a logarithmic plot of the reduced neck radius versus time displays a distinctly nonlinear character. Thus the kinetics cannot be described by a simple exponential function as can the early stages when Kuczynski’s geometric simplifications remain valid. A comparison between the two models reveals the rate of neck growth in the later stages to be significantly less for the locally planar interface model. It is suggested that this reduction is due to a lower stress gradient for the flow or material into the neck as a result of the dependence of stress in the neck region upon the changing curvature everywhere.

ISSN:0021-8979    

DOI:10.1063/1.322849

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The scattering of plane shear and compressional waves incident normally upon an infinitely long circular cylindrical obstacle in an isotropic homogeneous elastic solid medium is examined in the case in which the incident wavelength is large compared to the obstacle diameter. The scatterer can be either an empty cavity, a nonviscous‐fluid‐filled cavity, or an elastic solid cylinder. Explicit approximate expressions for the scattering cross sections are derived from the general theory formulated by White. The cross sections are proportional to (ka)3, wherekis the compressional or shear wave‐vector amplitude, andais the cylinder radius.

ISSN:0021-8979    

DOI:10.1063/1.322823

出版商:AIP    

年代:1976

数据来源: AIP