摘要:

This paper presents the characteristics of an optical pressure transducer using fiber optics. The transducer consists of a cylindrical housing with a reflective mylar diaphragm attached at one end and fiber‐optic bundle at the other. The fiber‐optic bundle used is the bifurcated type, in which two bundles of randomly distributed fibers are joined at one end to form a Y‐shaped geometry. The common end is attached to the end of the transducer housing, opposite to the diaphragm. At the branched ends, one bundle is connected to a dc light source, while the other bundle carries the light reflected from the diaphragm to a photodetector. By keeping the input light source at constant intensity, the amount of reflected light depends on the distortion of diaphragm due to pressure differential across the diaphragm surface. This pressure transducer can measure both the static pressure level and the fluctuating pressure. A simple ‘‘homemade’’ diaphragm was used in this experiment, and a sensitivity of approximately 10 mV per mm Hg was obtained over a range of 20 mm Hg. The dynamic response was linear to about 2 kHz. Both the sensitivity and the frequency response can be much increased by improving the diaphragm performance.

ISSN:0034-6748    

DOI:10.1063/1.1143989

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Depositions at rates higher than 1 nm/s show differences in properties when one deposits with a vapor stream that is modulated against those that are deposited with a steady vapor stream. For carrying out investigations along these lines, it was necessary to develop a real‐time, noninvasive, and sensitive technique for determining the nature and extent of flux variations in atomic streams close to the deposition plate. A pulsed laser based resonant photoionization technique is proposed for meeting these requirements. The paper describes the method and its application to a case where modulation is caused by residual ripple in high voltage accelerating supply used in the electron gun of the evaporator. The proposed technique overcomes the limitation on sensitivity due to background pressure experienced in the nonresonant approach. Other attractive features are the use of much lower laser intensities for a given sensitivity and the employment of a simpler ion detection system.

ISSN:0034-6748    

DOI:10.1063/1.1143990

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A simple deposition monitor has been incorporated into a thin‐film evaporator. The compact evaporator uses electron bombardment of the tip of a source wire to create an atomic beam. The current of ions in that portion of the atomic beam which falls on a collimating aperture is used to monitor the film deposition. The ion current is linearly related to the atomic beam flux, therefore allowing more precise control of the deposition rate than is obtained by monitoring the heating power delivered to the source wire. Calibration of the ion monitor within limits of ±6% requires positioning of the tip of the source wire within ±0.3 mm. This is readily accomplished using a plot of the current of bombarding electrons versus wire position. For the evaporation of iron, the calibration constant of this ion monitor is (2.50±0.15)×10−4ions/atom.

ISSN:0034-6748    

DOI:10.1063/1.1143991

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

On the basis of detailed considerations of the relevant effects and parameters, we describe techniques which have been developed to accurately set, maintain, and measure the temperature of a small sample (typically a single‐crystal disk of about 1 cm in diameter and 1 mm thick) in a strongly nonisothermal surrounding in ultrahigh vacuum, such as required by surface science experiments, in the temperature range from at least 6.5 K up. The resettability and resolution are 30–70 mK and the absolute error is estimated as about 0.7 K at 10 K and about 1.5 K at 100 K. Controlled linear heating with rates from 10−2to 50 K/s and high constancy (deviations below 0.1 K up to 5 K/s and below 0.5 K up to 50 K/s), and stepwise heating (≳100 K/s) without measurable overshoot can be carried out in this whole cryogenic range.

ISSN:0034-6748    

DOI:10.1063/1.1143992

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A simple apparatus for liquefying neon is described for use in experiments that require a stable thermal environment at 27 K. This apparatus makes use of a closed‐cycle refrigerator attached to an insulated cold finger inserted into a conventional stainless steel Dewar to liquefy a quantity of neon gas stored previously in a tank. The system is inexpensive and easy to use. Furthermore, the neon is recovered for subsequent reuse upon completion of the experiment. Starting with a Dewar holding a small coil that had not been precooled, and using a refrigerator with rated cooling capacity of 15 W at 26 K, approximately 0.5lof liquid neon was condensed into the Dewar in ∼4 h. The apparatus has been used to measure the critical currents of highTcoxide tape coils both with and without the application of an external magnetic field.

ISSN:0034-6748    

DOI:10.1063/1.1143993

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The construction of a high‐voltage (up to 1000 V) bipolar metal‐oxide‐semiconductor field‐effect transistor square‐wave generator is described. This generator is capable of producing both positive and negative going square waves with variable amplitude, repetition rate, and width. The circuit was designed for ferroelectrics research, however other applications are possible. The rise time of the prototype was 200 ns which was quite satisfactory for the present ferroelectric research project however the rise time can be decreased to 50 ns if necessary. The reader with a modest knowledge of electronics should be able to construct the circuit. Possible pitfalls and critical points are discussed.  

ISSN:0034-6748    

DOI:10.1063/1.1143994

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A compact grazing incidence grating spectrometer with spectral range of 2–32 nm resolution of 0.0005 nm, and about 3.6‐kg weight has been manufactured, which can meet the requirements of current x‐ray laser experimental research. During the construction, as a new method, we used a 3D measuring machine to finish the adjustment of spectral elements and invented a new method of alignment with a fiducial plane when using the spectrometer in an experiment.

ISSN:0034-6748    

DOI:10.1063/1.1143943

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A method is presented by which photoacoustic measurements can be done fast and with small effort. All operations are performed by an automatic measurement system based on an IBM PC personal computer. The structure and principles of the system operation are presented. The main advantages of the method described are: short time of measurement, wide chopping frequency range, high accuracy, and low error level. Owing to the computer some operations like hardware averaging, filtering, etc. can be replaced by software. This results in simplicity of the setup.

ISSN:0034-6748    

DOI:10.1063/1.1143944

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We demonstrate a system for collecting high quality x‐ray absorption spectroscopy data on microsecond and longer timescales. The method uses a fast‐multiscaling board to partition output pulses from a germanium energy resolving detector into a microsecond timebase. Full spectra accumulation and kinetic spectrophotometry are demonstrated for 1–4 mM biological samples. The use of an energy resolving detector promises that the dynamic behavior of a wide range of chemical elements (in conjunction with photochemical, rapid mixing, and temperature jump perturbations) can be observed with this method. We have successfully tested the system by examining the structural evolution of the iron atom of a myoglobin‐carbon monoxide complex subsequent to photolysis at low temperature.

ISSN:0034-6748    

DOI:10.1063/1.1144461

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report on the specific heats of typeEthermocouple wires, constantan (55% Cu–45% Ni) and chromel (10% Cr–90% Ni), measured using ac calorimetry in the temperature range 18–290 K. Data were normalized to values at 200 K determined by differential scanning calorimetry. The constantan values are close to those of other Cu/Ni alloys, while this is the first reported low‐temperature result for chromel.  

ISSN:0034-6748    

DOI:10.1063/1.1143945

出版商:AIP    

年代:1993

数据来源: AIP