摘要:

A bathysphere consisting of an inverted Dewar flask for submersible operation in cryogenic fluids is used to measure the resistance of superconductors, including high‐Tcsuperconducting copper oxides, as a function of temperature from 4 to 300 K. We describe the cryostat incorporating the bathysphere and present data on NbTi (44% Ti) and YBa2Cu3O7−&dgr;with respective superconducting transitions temperatures of 9.5 and 91.5 K. There are several advantages of the bathysphere method. The cryostat is of simple, compact design easily adapted to high‐field applications where magnet bore size is a limiting factor. The sample and thermometer are thermolyzed in the dry vapor trapped at the top of the bathysphere. Temperature can be varied rapidly from 300 to 4 K at a rate of 1 K min with less than a 0.1 K thermal lag between the sample and thermometer.

ISSN:0034-6748    

DOI:10.1063/1.1139893

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new magnetic densimeter for cryogenic fluids has been developed by adapting a magnetic levitation of a high‐Tcsuperconductor. In this instrument, a superconducting material made of Y–Ba–Cu–O is sealed in a hollow glass buoy, and a stable levitation of the buoy is carried out with the Meissner effect of the superconductor simply by placing the buoy in the fluid above a ring‐shaped permanent magnet. The fluid density is obtained from the magnetic force required to levitate the buoy in the fluid. To measure this force, the magnet is suspended from an electronic balance and the reaction force acting on the magnet is determined directly as a change of the apparent weight of the magnet. Details are given of the theoretical calculation of the force acting on the superconductor in the magnetic field and of the construction of the apparatus. The measurements of the saturated liquid density of nitrogen have shown a standard deviation of 0.014%. The total uncertainty of the measurements is estimated to be less than 0.06%. The results agree with reliable literature values within the experimental uncertainty.

ISSN:0034-6748    

DOI:10.1063/1.1139894

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have developed a technique which allows optical absorption measurements to be made using a pulsed light source and offers a sensitivity significantly greater than that attained using stabilized continuous light sources. The technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined within a closed optical cavity. The decay of the light intensity within the cavity is a simple exponential with loss components due to mirror loss, broadband scatter (Rayleigh, Mie), and molecular absorption. Narrowband absorption spectra are recorded by scanning the output of a pulsed laser (which is injected into the optical cavity) through an absorption resonance. We have demonstrated the sensitivity of this technique by measuring several bands in the very weak forbiddenb1&Sgr;g−X3&Sgr;gtransition in gaseous molecular oxygen. Absorption signals of less than 1 part in 106can be detected.

ISSN:0034-6748    

DOI:10.1063/1.1139895

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A four‐segmented longitudinal discharge low pressure N2laser (337 nm) is reported in which automatic spark preionization and an LC inversion‐charge transfer excitation circuit are employed. Its laser output power was nearly doubled when the techniques developed here were used. The characteristics of the peak laser output powers are interpreted qualitatively, with the electron densities calculated from the observed discharge voltages and currents.

ISSN:0034-6748    

DOI:10.1063/1.1139896

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A microscopic imaging ellipsometer has been constructed based on use of a CCD camera and framegrabber board in a PC computer. The performance (sensitivity and speed) are described.

ISSN:0034-6748    

DOI:10.1063/1.1139897

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have designed and constructed an apparatus that combines hyperthermal energy ion scattering (<100 eV) with low‐energy ion scattering (a few hundred eV to several keV). The UHV scattering chamber possesses a full range of sample preparation and characterization capabilities, including LEED, Auger spectroscopy, a Kelvin probe for work function measurements, and facilities for gas or alkali‐metal deposition. The differentially pumped beamline provides well‐collimated, monoenergetic beams of gas or alkali‐metal ions ranging in energy from <10 eV to 10 keV. To illustrate the qualitative changes in the scattering behavior observed over this range, we present experimental results for Na+scattered off the Cu(110) surface with the incident ion energy ranging from 56 eV to 4 keV. We also show a comparison between 1 keV K+and 1 keV Ar+scattered from the same surface.

ISSN:0034-6748    

DOI:10.1063/1.1139898

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A theta‐two theta x‐ray diffractometer stage has been developed forinsitustructural characterization of thin‐film samples. This stage integrates an ultrahigh vacuum dc ion‐beam thin‐film sample preparation chamber with the Siemens D500 x‐ray diffractometer.Invacuosample translation and manipulation is provided. The stage incorporates resistive heating to 900 K and liquid nitrogen cooling to 150 K. The sample theta rotation is transmitted into the vacuum chamber by a rotary feedthrough. X rays enter the vacuum chamber through a beryllium window with allowed reflection angles from 0 to +168° two‐theta.

ISSN:0034-6748    

DOI:10.1063/1.1139899

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An IBM PC AT compatible computer is used to host the interface of a Fourier transform ion cyclotron resonance mass spectrometer or FTMS. A common fast memory bank for both ion‐excitation waveform and data acquisition is reserved in the computer’s system memory space. All the digital electronics circuitry is assembled on an IBM PC AT extension board. Neither an external frequency synthesizer nor a waveform digitizer is needed. Ion‐excitation waveforms can be generated in either frequency‐sweeping or inverse‐Fourier transform modes. Both excitation and data acquisition can be carried out at eight megawords per second.

ISSN:0034-6748    

DOI:10.1063/1.1139900

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A broadband, continuous‐sweep microwave spectrometer has been constructed for measurements of the absorption coefficient of aqueous solutions and other liquid media. The spectrometer makes use of the phase fluctuation optical heterodyne technique, which provides a direct measure of the microwave power deposited in the sample. Consequently, in contrast to the standard dielectrometric techniques that indirectly determine the absorption coefficient via separate measurements of the real and imaginary parts of the dielectric constant, this spectrometer directly measures the microwave absorption coefficient. Broadband spectra are obtained using a transmission line to couple microwave power into the liquid sample. The absorption spectrum for deionized water in the range 3–20 GHz is presented as an example and shows excellent agreement with calculated values of the absorption coefficient based on previously published dielectric data.

ISSN:0034-6748    

DOI:10.1063/1.1139901

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have studied pressure distributions and area of contact as a function of load in a diamond indentor cell consisting of a flat diamond plate and diamond indentors of two different radii of curvature. The measurements were conducted with type Ia, IIa, and uncharacterized diamonds. Samples investigated were either ruby or ruby on a tantalum foil. In both cases, the ruby fluorescence was used to determine the pressure distributions. Previous suggestions that the elastic Hertzian solutions are applicable for plastic samples are not supported by these data. We conclude with comments on the prospects of the system for experimental high‐pressure research.

ISSN:0034-6748    

DOI:10.1063/1.1139902

出版商:AIP    

年代:1988

数据来源: AIP