摘要:

The design and performance of a magnetic susceptometer for thin films and surfaces is described. The device uses a 14‐MHz resonant circuit driven by a tunnel diode oscillator with a superconducting meander line as the inductive element. Magnetic properties of thin films deposited near the line in ultrahigh vacuum at low temperature affect the inductance of the meander line and thus the frequency. The device can detect a susceptibility change equal to that of a change in Fe thickness of 0.03 atomic layers. The minimum detectable change in the diamagnetism of superconducting Pb corresponds to a thickness difference of 10−3A˚. The effect of 10−6atomic layers of Fe can be detected by its depairing effect on a superconducting Pb film. The oscillator circuit including the film being studied is analyzed and the oscillation frequency calculated so that the effect of the various circuit elements can be determined. Suggestions for extending this technique are given.

ISSN:0021-8979    

DOI:10.1063/1.337754

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A small microwave ion source has been constructed to generate low‐energy (5–10 eV) oxygen beams. The source is fabricated from a quartz tube and is enclosed by a microwave cavity. The source is operated without an external extraction voltage. Positive ions effuse from the source with energies equal to the plasma potential. The source has been operated in a cw mode producing an atomic oxygen ion fluence >1×1014 cm−2 s−1with energies as low as 5.5 eV. The ‘‘self‐extracted’’ ion beam can be used to simulate the oxygen environment encountered in low earth orbits.

ISSN:0021-8979    

DOI:10.1063/1.337755

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The gas‐phase etch products of silicon and XeF2have been studied as a function of doping and XeF2flux using molecular beam mass‐phase spectrometry. In this experiment the product flux, not the incident reactant beam, is modulated, providing direct information on product identity and velocity, and indirect information on surface reaction kinetics. The data show that although the product ion distributions exhibit little change over the range of experimental conditions used, the neutral products from which the ions are formed vary significantly. More SiF4desorbs fromn‐type thanp‐type silicon at constant flux. The balance of the products mainly consists of Si2F6and SiF3, the relative amounts of which are flux dependent. These species have not been identified previously as etch products. Average product translational temperatures have also been determined, providing important information on surface interactions during etching. The stable molecules SiF4, Si2F6, and reflected (unreacted) XeF2all have translational temperatures of approximately 270 K. The free radical SiF3is much colder, having a temperature of about 200 K. Although etching of the two types of silicon is qualitatively similar, a quantitative comparison reveals intrinsic differences in their reactivity which are not attributable to field effects. The possible origin of these differences is discussed.

ISSN:0021-8979    

DOI:10.1063/1.337756

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Using standard multilayer and effective medium models, we determine microstructures that optimize the near‐IR‐visible normal‐incidence optical transmittance of electrically conducting metal films intended for use as semitransparent contacts for semiconductor devices such as photodetectors or photoelectrochemical converters. Various conditions are considered, including unpolarized and linearly polarized light and electrical conduction both parallel and perpendicular to the surface. For linearly polarized light, the optimum microstructure consists of parallel metal lines of nominally square cross section oriented perpendicular to the polarization vector of the incident light, regardless of the direction of electrical conduction. The line separation and cross‐sectional dimensions must both be small compared to the wavelength &lgr;. For unpolarized radiation, the optimum microstructure depends on the direction of electrical conduction. For conduction parallel to the surface, the optimum microstructure again consists of parallel lines with the lines oriented perpendicular to the residual linear polarization, if any, of the incident flux. For conduction perpendicular to the surface, the optimum microstructure consists of cylindrical metal posts of dimension small compared to &lgr;. Expressions are derived that allow the thicknesses and refractive indices of protective antireflection coatings to be calculated to first order in the thicknesses of the metal films. The more general case of antireflection coatings for anisotropic structures is briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.337757

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The TlBr‐TlI (thallium bromoiodide) crystal and its fiber preparation method were studied in order to develop a high power CO2laser beam fiber. As a result of this study, the most preferable composition for the fiber was determined to be 42 wt. % TlBr. The fiber (0.5 mm in diameter and 1.5 m in length) at that composition had the following excellent characteristics: (1) a high output power of 138 W (70 kW/cm2), (2) a high total transmissivity of more than 93%/1.5 m, and (3) a bending radius of ultimate 3.5 cm.

ISSN:0021-8979    

DOI:10.1063/1.337758

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Optical third harmonic generation measurements by transmission have been performed on thin films of polysilane deposited by a spinning technique with a thickness varying between 0.15 and 0.45 &mgr;m. The films have a good optical quality and support large laser power (∼200 MW/cm2at 1.064 &mgr;m). They are transparent in visible and near infrared. The measured average value of cubic susceptibility ⟨&khgr;(3)xxxx(−3&ohgr;; &ohgr;,&ohgr;,&ohgr;)⟩ is equal to (1.5±0.1)×10−12esu at 1.064 &mgr;m. The technique used for the third harmonic generation measurements allows determination of both modulus and phase of &khgr;(3). It is argued that the large value of &khgr;(3)is due to a three‐photon resonance at 1.064 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.337759

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Concepts from the theory of interacting continua are employed to develop constitutive relations for liquid and/or gas saturated elastic porous media. The model is formulated by defining intrinsic stress tensors and densities in terms of the partial stress tensors, partial densities, and actual volume fractions occupied by each component. It is assumed that the constitutive law for each component as a single continuum relates intrinsic pressure to intrinsic deformation. Relative motion between the constituents is allowed through simple Darcy‐type expressions. The governing equations together with the constitutive relations are used to investigate the propagation of both harmonic and transient pulses. In general three modes of wave propagation exist. In the case of a transient pulse, these modes lead to a three‐wave structure. Laplace transform techniques are used to derive closed‐form solutions for transient loading for two limiting values of viscous coupling (i.e., weak viscous coupling, strong viscous coupling). Strong viscous coupling results in the coalescence of the three wave fronts into a single front. Solutions for the general case of transient loading are obtained by numerical inversion of the Laplace transforms.

ISSN:0021-8979    

DOI:10.1063/1.337760

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The confinement properties of a low‐&bgr; (average) potassium plasma produced by contact ionization in a spindle cusp magnetic field were investigated. In this configuration,ne≊108–1010cm−3,Te≊Ti≊0.2 eV, and the ions are weakly magnetized. Electron and ion densities, space potentials, and plasma flow velocities were measured in the ring and point cusps. The leak width of the escaping plasma was measured over a wide range of magnetic field strengths and neutral pressures. The dependence of the leak width on neutral pressure and magnetic field strength is accounted for by a simple model in which the plasma streams out of the cusps along the magnetic field lines while diffusing across the magnetic field due to the combined effects of neutral‐particle collisions and Bohm diffusion. Measurements of broadband plasma noise suggest the presence of ion acoustic wave turbulence.

ISSN:0021-8979    

DOI:10.1063/1.337761

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Neutron time‐of‐flight techniques have been used to diagnose fuel ion temperatures of inertial confinement fusion plasmas. A new technique for making this measurement using an array of ‘‘single‐hit’’ detectors operating in single‐particle counting mode is described. This technique has some potential advantages over previous methods (faster timing, better energy resolution, good sensitivity) and can possibly be further developed to allow detailed measurements of neutron energy spectra to give other diagnostic information, such as fuel areal density (⟨&rgr;R⟩).

ISSN:0021-8979    

DOI:10.1063/1.337762

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Irradiation of the bulk plasma region in a 13.56‐MHz Cl2discharge with an XeCl laser increased the current through the discharge. The perturbed current waveform had the shape of an amplitude modulated waveform with a period long with respect to the rf cycle. This optogalvanic effect has been attributed to the photodetachment of electrons from Cl−, which perturbs the electron density. The optogalvanic signal depended on the square root of the pressure and was almost independent of the discharge current. The optogalvanic current has been correlated with the dependence of the Cl−density on pressure and discharge current as well as the changes in the electric field induced by the perturbation. Saturation of the signal at high laser intensity has been accounted for by the impedance mismatch induced by the increased electron density. From the relationship between the saturation and the impedance mismatch, the ratio of Cl−to the electron density was calculated. Probing various parts of the discharge with a laser beam having a smaller cross section than the discharge did not reveal any significant spatial variations in the discharge.

ISSN:0021-8979    

DOI:10.1063/1.337763

出版商:AIP    

年代:1986

数据来源: AIP