摘要:

A technique for measuring the thickness of silicon films grown epitaxially on sapphire is described. The method is nondestructive, is performedin situ, and can be used to monitor film thickness while the film is growing. The method utilizes the infrared emission from the sapphire substrate and from the growing film. The radiation from the sapphire substrate is partially transmitted through the silicon and partially reflected in the silicon, establishing an interference pattern which can be used to determine silicon film thickness. Using a detector with peak sensitivity at 2.4 &mgr;, silicon film thicknesses to the nearest ±0.1 &mgr; are readily measurable. The absolute accuracy of ±0.1 &mgr; is independent of film thicknesses. Films in the range from 0.1 to 15 &mgr; have been measured. Increased detector sensitivity can extend the maximum measurable film thickness.

ISSN:0034-6748    

DOI:10.1063/1.1720978

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A superconducting magnet spectrometer using lithium drifted silicon detectors has been constructed for the the measurement of electron spectra. The spectrometer has a 4&pgr; geometry for electrons and a resolution limited only by the detectors. Spectral distortions arising from electron backscattering and gamma‐ray interactions are eliminated by the achromatic focusing properties of a solenoidal magnet.

ISSN:0034-6748    

DOI:10.1063/1.1720979

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An apparatus for measuring excess volumes of dissolved gases in liquids at low temperature, for pressures below 100 atm and for concentrations about 1%, is described. The apparatus has been tested measuring the excess volume for A‐N2and H2‐N2systems.

ISSN:0034-6748    

DOI:10.1063/1.1720980

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The performance of a surface electric field strength meter, utilizing a broad unfocused beam of electrons, has been evaluated analytically and experimentally. The meter is capable of measuringEfields up to 100 V/cm and possesses a sensitivity of ∼0.1 V/cm in the field regime nearE=0. The meter response to time varying electric fields is limited by the finite transit time (<10−7sec) of the electrons from the source to the detector plates. Simple formulae for the errors introduced in the measurement of time dependent electric fields by finite transit time effects and by displacement currents are presented and indicate errors of ∼0.1 V/cm forEfields rising at 106V/cm sec. Sensitivity of the meter to magnetic field perturbations along three mutually perpendicular directions has been evaluated. The meter response has been examined in a plasma flow simulating spacecraft through the ionosphere.

ISSN:0034-6748    

DOI:10.1063/1.1721032

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper describes a system which can photographically record with one dual‐beam oscilloscope the amplitudes of 10 simultaneous photomultiplier pulses over a four‐decade dynamic range with an accuracy of ±1.5% over the entire range. The signal processing time is 2.2 &mgr;sec. The basic circuit is a logarithmic pulse‐height‐to‐time converter with two triggering levels, requiring twelve transistors per input channel. The dynamic range of the device could be easily extended to six decades, and the two‐level technique can be applied to digitized recording systems and pulse height analyzers. The circuit has been found to meet the above specifications over a temperature range from −19 to +38°C.

ISSN:0034-6748    

DOI:10.1063/1.1721033

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A method which allows measurements of the photoemissive quantum yield of a Cs3Sb cathode of a photomultiplier is described. The method consists of an accurate control of the photocathode polarization to separate its eventual effects from the dependence of the quantum yield on the temperature. Measurements thus performed on four 56AVP phototubes have been interpreted as an up‐to‐now unknown variation of the quantum yield due to the temperature. The measurements suggest that the Cs3Sb could exist in two states, one of which, never noticed before, is stable only below (260±2)°K (the transition temperature), and which moreover is very sensitive to the absorbed energy. This low temperature state has a low quantum yield (for whitish‐blue light), which, depending on the absorbed energy, can be even five to seven times lower than the yield of the usual high temperature state of Cs3Sb.

ISSN:0034-6748    

DOI:10.1063/1.1721034

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A Langmuir probe system has been developed for measurement of electron densities and electron temperatures in the lower ionosphere. While the probe works like the Smith probe, it has various practical advantages. It is an all electron system working on a single floating power supply. This makes the actual system simpler and allows for more thorough prelaunch checkouts while the rocket is on the launch pad. Further, this system can feed an additional guard electrode without the use of any additional electronics. It has greatly helped in reducing the current leakage and the effect of the distributed capacity at the input of the amplifier. Also the sweep used is such that capacitive discharge currents between the sensor and the rest of the system do not appear in that part of the sweep where retarding potential analysis is done for determination of electron temperature. Within this system it is possible to control the sensor voltage with the output of the amplifier and keep it at space potential. In principle this method can be used to determine both the electron density and electron temperature simultaneously and continuously.

ISSN:0034-6748    

DOI:10.1063/1.1721035

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper describes a simple and reliable thyratron circuit capable of generating high energy pulses at repetition rates of 5000/sec or higher. Design considerations and factors limiting the maximum repetition rate are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1721036

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Circuit modifications are described which enable a Varian A‐60 spectrometer to be used for relaxation studies of chemically‐shifted protons.T1andT2values greater than 0.1 sec can be measured on the modified instrument at ambient temperature. Owing to severe convection effects in the probe assembly, relaxation measurements are made with difficulty at other temperatures. Methods of time‐averaging relaxation data are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1721037

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A passive pressure transducer has been developed which utilizes the acoustic emission effect. This effect is noted when a suitable solid material is placed under increasing stress, causing permanent deformation processes to occur which are accompanied by emission of acoustic energy. These processes are irreversible, so if the stress is released and then reapplied, no acoustic energy will be emitted on the second cycle until the stress reaches its previous maximum level. The instrument described here contains a diaphragm of anodized aluminum which is first exposed to the pressure that is to be measured and then withdrawn and read by subjecting it to steadily increasing known pressure while monitoring it for acoustic emission. The pressure at which acoustic emission begins is taken as the pressure originally measured by the instrument. Pressure transducers of this type are inexpensive and require no calibration. Accuracy is within a few percent and can probably be improved. Possible applications include deep ocean depth measurements, measurements of peak acceleration, and tellatale uses for monitoring peak pressures.

ISSN:0034-6748    

DOI:10.1063/1.1721038

出版商:AIP    

年代:1967

数据来源: AIP