摘要:

A short summary on recent developments in semiconducting temperature sensors is given. A thin‐film germanium resistor is described in detail, which is used for fast and accurate thermometry in a nonadiabatic microcalorimeter. The use of only standard vapor deposition techniques makes this sensor also available to research groups lacking access to semiconductor technology. The general good performance and its good mechanical properties have the potential of numerous applications in fast and accurate low‐temperature thermometry.

ISSN:0034-6748    

DOI:10.1063/1.1139321

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A recent discovery about a well‐studied phenomenon leads to the formation of ultracoherent streams of liquid drops. A remarkably straightforward, although previously unreported, method of drop generation from capillary streams, which involves the imposition of an amplitude modulated sinusoidal carrier disturbance, is discussed. The amplitude‐modulated disturbance results in the production of highly stable droplet streams over a previously unattainable range of wavenumbers. A decrease in the speed variation of the drops within the stream, which is a result of the amplitude modulation, is demonstrated over a range of nondimensional wavenumbers from 0.4 to 0.04. The nondimensional wavenumber is the ratio of stream circumference to disturbance wavelength. It is suggested that amplitude modulating the capillary stream’s disturbance may also decrease the diameter variation of the drops.

ISSN:0034-6748    

DOI:10.1063/1.1139322

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Conventional apparatus for the dipping and raising of slides usually uses an electric motor with the slides fixed in a rigid holder. Most of the devices create a great deal of vibrations and this produces a nonuniform film deposition. We have used a new apparatus, which does not produce any vibrations of the slide, to build up Langmuir–Blodgett films. To move the slide, we employ a column of water and use the siphon principle, with speeds that can be varied between 3.0 and 120.0 mm min−1. An electronic circuit controls the automatic dipping and raising of the slide. A relay switches the solenoid valve to move the piston in the opposite direction. A machined Teflon trough and antivibration mount are used for the monolayer preparation. With this method, the deposition ratio usually obtained for the cadmium arachidate and chlorophyllais 1.00±0.05. The absorption spectrum of multilayers of chlorophyllagive a linear relation between the absorbance at 680 nm and the number of layers up to 10. The nonlinear relation for the number of layers higher than 10 is explained by the presence of aggregates.

ISSN:0034-6748    

DOI:10.1063/1.1139323

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The design and performance of an effusion cell used to deposit low melting point metals under UHV conditions is described. A novel feature of the cell is a transfer rod and pretreatment chamber that allow for the rapid loading and retrieval of crucibles containing low melting point source elements. This feature of our cell makes it ideal for depositing the highly reactive alkali metals. The performance of the effusion cell is evaluated for the deposition of the metal potassium.

ISSN:0034-6748    

DOI:10.1063/1.1139272

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The operation of a proportional counter filled with helium gas has been investigated at low temperatures down to 5 K. It has been found for the first time that a helium‐filled counter cooled at temperatures below 30 K works well in the proportional region, but with low gas gains (≤100). The operation at low temperatures (≤30 K) is attributed to the complete removal of impurities from helium gas as well as the extreme depression of the reaction frequency of metastable heliums. The absence of impurities results in eliminating the Penning effect, i.e., an ionization process of impurity atoms or molecules by collisions with metastable helium, which spreads electron avalanches in both space and time if helium gas contains a slight amount of impurities (1–103ppm). Continuous discharges caused by the photoeffect of ultraviolet photons, which are mostly produced in decay channels of metastable helium, arethermallyquenched at low temperatures below 30 K. The helium‐filled counter provides us with a new method to detect nuclear radiations at very low temperatures. The present counter technique has been successfully applied to the resonance‐electron Mo¨ssbauer spectroscopy near liquid‐helium temperature (∼5 K).

ISSN:0034-6748    

DOI:10.1063/1.1139273

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The increase in output measurement error of lock‐in amplifiers with decreasing input signal‐to‐noise ratio, which has been shown to be linear over several orders of magnitude [G. T. Gillies and S. W. Allison, Rev. Sci. Instrum.57, 268 (1986)], is a consequence of the function of a lock‐in amplifier as a bandwidth reduction filter.

ISSN:0034-6748    

DOI:10.1063/1.1139274

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The device reported here allows the researcher the opportunity of gaining primitive yield information, threshold voltages, emission stability, and other information, e.g., gas effects, on field emitter arrays (FEA) which are microminiature ‘‘vacuum tubes’’ fabricated by microelectronic processing methods on silicon wafers, without scribing, dicing, and mounting each device on individual vacuum‐compatible headers. This device also speeds up the entire data‐acquisition process by requiring only one ultrahigh‐vacuum pumpdown and one set of vacuum feedthroughs.

ISSN:0034-6748    

DOI:10.1063/1.1139275

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Apriorirequirements and compatible, optimized design considerations for a high‐performance low‐cost absorption cell for the spectrometry of liquid samples are discussed. A new cell model is presented.

ISSN:0034-6748    

DOI:10.1063/1.1139276

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A double‐pass high‐resolution vibrational electron energy loss spectrometer of 127° cylindrical electrostatic deflection type has been constructed for surface studies. In the direct mode, an electron current at the detector of 1.3×10−14A is obtained with the energy spread (full width at half‐maximum) of 2.4 meV for electrons whose energy at the sample position is 5 eV.

ISSN:0034-6748    

DOI:10.1063/1.1139654

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have constructed a large differentially pumped platform for use in ultrahigh vacuum. The design utilizes spring‐loaded Teflon seals to permit differential pumping between two horizontal stainless‐steel disks. This allows the rotation of the upper disk and the items built into it directly inside a vacuum chamber while maintaining a pressure of 2×10−10Torr. The following design parameters are discussed: conductance across the seals, deflection of the seals, rotational friction, and differential thermal expansion during bakeout.

ISSN:0034-6748    

DOI:10.1063/1.1139277

出版商:AIP    

年代:1987

数据来源: AIP