摘要:

It is demonstrated that microwave cutoff can be used to measure absolute electron densities for CHF3, Ar, and O2plasmas in a batch‐mode planar reactor excited at 13.56 MHz. The densities obtained are between 1015and 1016m−3for all gases and a large set of conditions (pressure, rf power, electrode spacing). A comparison with selective etching of SiO2over Si in the same reactor shows a qualitative agreement between the substrate ion flux calculated from the electron density and the etch rate of silicon oxide; the apparent sputter yield ranges from 0.4 to 1.4 molecules per ion.

ISSN:0021-8979    

DOI:10.1063/1.335458

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The collective acceleration of heavy ions (C, Al, Fe) from a laser produced plasma to energies in excess of 10 MeV/amu has been observed experimentally. In the experiments, an intense relativistic electron beam (1.2 MeV, 30 kA, 30 ns) is injected through an anode aperture into a downstream drift region. Ions to be accelerated are produced by firing aQ‐switched ruby laser (0.3–15 J, 15 ns) at a target material located immediately downstream of the anode aperture. Accelerated ion energies are measured by time of flight, range‐energy, and Thomson spectrometer techniques.

ISSN:0021-8979    

DOI:10.1063/1.334599

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A pulsed photothermal method is proposed for the detection of delaminations in layered materials. The surface of the material is heated by a focused laser pulse to a few degrees above the ambient temperature, and the induced thermoelastic displacement is detected by a laser interferometer. Unbonded areas are characterized by their thermoelastic bending behavior, in addition to their thermal expansion, because of the induced temperature gradients both in the radial and axial directions. A theoretical analysis and an experimental investigation of this behavior are described in order to point out the most significant parameters. An application of the nondestructive inspection of Al‐epoxy honeycomb panels is presented.

ISSN:0021-8979    

DOI:10.1063/1.334600

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In this paper the shot noise process is reformulated in terms of spatial correlation functions. In ‘‘ballistic’’ devices local noise sources remain correlated for separation distances on the order of device dimensions. The effect of randomizing collisions, is introduced as a decay of this correlation. The velocity distribution of carriers is taken into account. The effect of parameters such as injection velocity, scattering probability, and device length on noise in near‐ballistic devices could be calculated using this method.

ISSN:0021-8979    

DOI:10.1063/1.334601

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A general model of a solar thermophotovoltaic device is discussed both for improving the efficiency of one‐band‐gap photovoltaic cells by matching the photon energy to the band gap and for concentrating diffuse radiation. First we assume ideal components to calculate theoretical maximum efficiency. It corresponds to that of a perfect selective absorber in conjunction with a Carnot‐engine ranging from 53% for 1 sun to 85% for the highest possible irradiance of 5×104suns. The improvement over an ideal one‐gap device is roughly a factor of 2. Consideration of available materials shows that any improvement in efficiency can be expected only for high irradiance of 1000 suns. The sensitive parameter is the selectivity of the absorber‐emitter. Concentration of diffuse solar radiation is not feasible. Perspectives appear not much better than for existing technologies such as photovoltaics or solar tower applications.

ISSN:0021-8979    

DOI:10.1063/1.334602

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

High‐field critical current densitiesJcand pinning behavior are discussed for Nb‐63a/oTi, Nb‐61.7a/oTi‐3a/oHf, and Nb‐64.7a/oTi‐7.2a/oTa superconducting alloys.Jcproperties for 8–12 T in these alloy superconductors under superfluid helium environments can be even superior to those in Nb3Sn at 4.2 K, when they are heavily cold‐worked after final heat treatments. A temperature scaling law of the flux pinning forceFpis found to hold for these alloys in the form ofFP=K [Bc2(T)]nbp(1−b)q, whereBc2is the upper critical field andb≡B/Bc2. The peak reduced field,bm, in theFp−bcurve depends upon how the alloys have been processed. The origins ofn,p, andqare discussed in terms of the processing condition.

ISSN:0021-8979    

DOI:10.1063/1.334564

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Light absorption by a solid material and conversion of part, or all, of the optical energy into heat due to nonradiative deexcitation processes within the solid can give rise to an electrical signal in a pyroelectric thin film in contact with the sample. This effect forms the basis of a new spectroscopic technique for the study of condensed phase matter. A one‐dimensional theory is presented, which describes the dependence of the pyroelectric signal on the optical, thermal, and geometric parameters of the solid/pyroelectric system. Specifically, the theory examines the conditions under which the photopyroelectric signal exhibits a linear dependence on the optical absorption coefficient of the solid. Thus a theoretical basis for the technique of photopyroelectric spectroscopy is established. Qualitative comparisons between predictions of the theory and preliminary experimental observations are used to test the applicability of the theory to experimental configurations of practical interest.

ISSN:0021-8979    

DOI:10.1063/1.334565

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The absorption coefficient of a highly absorbing (&bgr;>105cm−1) new composite produced in our laboratory, namely manganese dioxide surface‐impregnated polyethylene (MnO2–PE) film, has been measured in the visible range. We have employed a combination of concurrently taken photoacoustic and beam transmission data. This combination proved to be an effective means for the optical evaluation of highly absorptive samples which dispenses with the need for prior knowledge of the sample reflectivity. Theoretical interpretation of MnO2–PE absorption profile, with due account of the processes underlining the photoacoustic signal generation, reveals a semiconductor behavior with an estimated effective gap wavelength of 8050 A˚. Technical implications of the availability of these highly absorptive flexible films are briefly considered.

ISSN:0021-8979    

DOI:10.1063/1.334566

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have measured the concentration of deuterium as a function of depth in a deuterium‐exchanged LiNbO3sample using nuclear analysis. From the shape of the concentration profile we calculate the concentration dependent effective diffusion coefficient for deuterium‐lithium counterdiffusion. Comparison of the concentration and refractive index profiles for this waveguide confirms that the index increase in exchanged material is a nonlinear function of concentration. We discuss implications of these results for optical waveguide fabrication.

ISSN:0021-8979    

DOI:10.1063/1.334567

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This paper presents the results of a theoretical study of the plasma‐activated chemical vapor deposition (PCVD) process used for the preparation of optical fibers. We show how the static deposition profile of silica can be computed by taking into account convection, reaction, and diffusion processes inside the glass tube. The parameters describing these processes are estimated. We examine how the deposition profile depends on the gas velocity, the reaction, and the diffusion constants. Theory and experiment are in good agreement. The calculations confirm the idea that in the PCVD process the deposit is formed from single molecules and not from clusters.

ISSN:0021-8979    

DOI:10.1063/1.334568

出版商:AIP    

年代:1985

数据来源: AIP