摘要:

Electronic circuits have been developed to replace the mechanical servos and lock‐in amplifiers customarily used in a wavelength‐modulated derivative spectrometer. The result is a faster response and wider range of gain while maintaining a constant photomultiplier‐tube voltage.

ISSN:0034-6748    

DOI:10.1063/1.1137513

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We described a new electron spectrometer for time‐angle resolved photoemission. The apparatus consists of 44 electron detectors (microchannel plate) 4 mm in diameter, equally spaced on half a sphere (35‐mm internal radius), and acting in the so‐called ‘‘spherical retarding potential’’ method configuration. Resolution in energy is measured to be of the order of 0.3 eV and typical time resolution is 0.1 s. This spectrometer is conceived essentially for time‐resolved surface reaction studies. Preliminary results are presented for the Si (111) surface.

ISSN:0034-6748    

DOI:10.1063/1.1137514

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A strong, optically flat cell of fused silica has been developed which has routinely withstood internal pressures in excess of 60 atm at 900 °C. Construction details are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137515

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A totally computer‐controlled triple quadrupole mass spectrometer (TQMS) is described. It has a number of unique features not available on current commercial instruments, including: complete computer control of source and all ion axial potentials; use of dual computers for data acquisition and data processing; and capability for self‐adaptive control of experiments. Furthermore, it has been possible to produce this instrument at a cost significantly below that of commercial instruments. This triple quadrupole mass spectrometer has been constructed using components commercially available from several different manufacturers. The source is a standard Hewlett‐Packard 5985B GC/MS source. The two quadrupole analyzers and the quadrupole CAD region contain Balzers QMA 150 rods with Balzers QMG 511 rf controllers for the analyzers and a Balzers QHS‐511 controller for the CAD region. The pulsed‐positive‐ion‐negative‐ion‐chemical ionization (PPINICI) detector is made by Finnigan Corporation. The mechanical and electronics design were developed at LLNL for linking these diverse elements into a functional TQMS as described. The computer design for total control of the system is unique in that two separate LSI‐11/23 minicomputers and assorted I/O peripherals and interfaces from several manufacturers are used. The evolution of this design concept from totally computer‐controlled instrumentation into future self‐adaptive or ‘‘expert’’ systems for instrumental analysis is described. Operational characteristics of the instrument and initial results from experiments involving the analysis of the high explosive HMX (1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazacyclooctane) are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137516

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The automatic evaluation of grain boundary activity in a polycrystalline solar cell can be carried out by interfacing a microcomputer to a scanning electron microscope operating in the electron beam induced current mode (EBIC). The grain boundary surface recombination velocity and diffusion length in the neighboring grains are obtained by digital acquisition and processing of the related EBIC profile. The technique is applied to the evaluation of hydrogen passivation of a ribbon solar cell.

ISSN:0034-6748    

DOI:10.1063/1.1137517

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We present a unit which enables us to evaporate two different metals, rare gas, and atomic or molecular hydrogen at the same time onto a substrate held at a temperature of about 5 K. The deposition rates of the metals and the rare gas are measured by a quartz oscillator. The hydrogen deposition rate is calibrated by using the H‐concentration dependence of the superconducting transition temperature in Pd–H and Al–H, known from ion‐implantation experiments.

ISSN:0034-6748    

DOI:10.1063/1.1137518

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A surface acoustic‐wave (SAW) device for measuring high voltages is described. The device consists of two SAW oscillators fabricated on a 128° rotatedY‐cut LiNbO3substrate. The voltage to be measured is applied to one of the oscillators while the other oscillator acts as the reference oscillator for temperature compensation purposes. The frequency of the perturbed oscillator varies linearly with the applied voltage. An oscillator fabricated on a 0.5‐mm‐thick substrate can withstand greater than 9 kV of voltage giving a fractional frequency deviation greater than 1630 parts per million. Attractive features of this technique include: (1) direct measurement of high voltages without the need for resistive or capacitive voltage dividers, (2) very high input resistance, (3) direct conversion of voltage to frequency, and (4) resolution better than 0.01% of full scale. This paper will discuss the basic operation and present experimental data on the performance of the device. A technique for obtaining improved temperature compensation in SAW sensors will also be presented.

ISSN:0034-6748    

DOI:10.1063/1.1137519

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

This paper presents details of an unusual clip‐on nanoammeter. The device utilizes a toroidal magnetic flux sensor which is split to allow its placement around a continuous current carrying filament, and is coupled to a sensitive superconducting current amplifier. Optimization formulas allow the design of an instrument having the greatest possible signal‐to‐noise ratio consistent with the physical volume available for the sensing element. A prototype exhibited 125‐nA current sensitivity at 25 Hz with a noise level of 40 nA/Hz1/2. The performance of this instrument verified the predictions of the theory. The optimization analysis for this probe demonstrated that the signal‐to‐noise ratio could have been doubled by a slight change in toroid dimensions. It was shown that SQUID noise is negligible for this instrument, justifying the assumption of a noiseless amplifier in the original calculation. Finally, the conditions under which an impedance matching transformer can reduce the importance of the SQUID noise relative to the Johnson noise are derived, and the required inductances are given.

ISSN:0034-6748    

DOI:10.1063/1.1137520

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

This paper describes the design and operation of a new diamond‐anvil press that can conduct x‐ray diffraction investigations of polycrystalline materials at sustained pressure and temperature up to 30 GPa and 500 °C. Several improvements have been made in heating efficiency, uniformity of temperature, alignment operation of anvil faces, and elimination of preferred orientation effect. Examples of the application to the study of a high‐pressure phase of phosphorus are shown.

ISSN:0034-6748    

DOI:10.1063/1.1137521

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In conventional tensile or compressive tests of single crystals, plastic deformation by slip occurs nonuniformly owing to slip plane rotation and constraint of the specimen’s ends. To minimize these problems, a ‘‘load fixture’’ (LF) that employs an air bearing and magnetic field (to provide for free rotation of the ends of the specimen) has been designed and built. The frictionless air bearing minimizes the tendency of the system to develop internal torques during the deformation of single crystals, particularly those with low critical resolved shear stresses. The LF has been tested in tensile and compressive loading of mercuric iodide single crystals. By keeping the center of rotation on the ‘‘boundary of slip’’ (i.e., on the slip plane that separates slipped from unslipped material in the plastically deformed crystal), the line of action of the applied force is maintained coincident with the sample’s central axis. The LF is particularly useful for testing small, ductile crystals and for studying mechanical hysteresis.

ISSN:0034-6748    

DOI:10.1063/1.1137522

出版商:AIP    

年代:1983

数据来源: AIP