Calibration of a BayardAlpert Gauge for ChlorineMarion L. Shaw Citation: Review of Scientific Instruments 37, 113 (1966); doi: 10.1063/1.1719926 View online: http://dx.doi.org/10.1063/1.1719926 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/37/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Bayard–Alpert vacuum gauge with microtips J. Vac. Sci. Technol. B 14, 2119 (1996); 10.1116/1.588883 Calibration and characterization of Bayard–Alpert gauges operating in high magnetic fields J. Vac. Sci. Technol. A 4, 1732 (1986); 10.1116/1.573967 The Sensitivity of Bayard–Alpert Gauges J. Vac. Sci. Technol. 6, 848 (1969); 10.1116/1.1492719 Modulation of Bayard-Alpert Gauges J. Vac. Sci. Technol. 4, 57 (1967); 10.1116/1.1492523 Modulated BayardAlpert Gauge Rev. Sci. Instrum. 31, 343 (1960); 10.1063/1.1716973

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NOTES 113

the Na sources by the observation that a clean Ge surface exposed to the hot source, but biased positively with respect to the latter, showed no significant change in work function.

A variety of ion guns have been used with the zeolite sources. In some cases a problem of neutral re-emission of ions collected by hot gun electrodes has been encountered and precautions must be taken to keep the gun electrodes from being heated by the source.

* Work supported by Aeronautical Systems Division, Air Force Systems Command, U. S. Air Force.

1 J. P. Blewett and E. J. Jones, Phys. Rev. 50,464 (1936). 2 The material referred to is in powder form, Le., it does not contain

the binder used in forming pellets. It was obtained through the courtesy of Dr. D. W. Breck of the Linde Company.

3 D. W. Breck, W. G. Eversole, R. M. Milton, T. B. Reed, and T. L. Thomas, J. Am. Chern. Soc. 78, 5963 (1956).

4 R. M. Barrer and W. M. Meier, Trans. Faraday Soc. 55, 1 (1958).

Calibration of a Bayard-Alpert Gauge for Chlorine MARION L. SHAW

Lyman.[.aboratory of Physics, Harvard University, Cambridge, Jt,f assachusetts, and Smithsonian Astrophysical Observatory,

Cambridge, Massachusetts 02138

(Received 16 July 1965; and in final form, 23 August 1965)

AN ionization gauge of the Bayard-Alpert type (model RG 75-P, Veeco Company) was calibrated for use in

chlorine against a Knudsen gauge (Type lA, Edwards Company). This calibration was motivated by several factors: there are no published data on the sensitivity of this type of ionization gauge for chlorine; the sensitivity of a gauge of a given design for a given gas can depend on its previous history due to the pumping action of its glass envelope and on contaminant gases evolving from its

20

18

16

14 N2

w A

'" ::0 <[

'"

10 12 14 16 18 p x 106 torr

ION GAUGE:

FIG.!. Ionization gauge calibration.

TABLE I. Ionization gauge characteristics.

Sensitivity relative to argon Schulz McGowan This

Kerwin experiment

Westinghouse Veeco RG75 Veeco RG75P Gauge WL5966

Electron 10-4 10-4 1Q-2 current A

Filament 30 22.5 30 voltage

Grid 170 150 180 voltage

Ion 0 0 0 collector voltage

11P, Torr 10-'-10-1 10-'-10-1 10-6-10-5

Ar 1.00 1.00 1.00

N z 0.67 0.80 0.56 He 0.14 0.16 0.15 Cl z 0.64

surfaces; and it was not obvious that the gauge would behave linearly or reproducibly in a corrosive atmosphere.

The Knudsen gauge was chosen as the standard because it makes absolute pressure measurements, is conveniently sensitive over the pressure range of interest (10-6-10-0

Torr) and was thought unlikely to deteriorate noticeably during brief exposures to chlorine at low pressures. To insure that it had not deteriorated, it was checked with a McLeod gauge before and after the chlorine calibration.

The calibration was carried out with a vacuum system which was kinetic in the sense that a constant pressure was maintained by equal input and output flows of test gas. A kinetic gas system was used because it was thought that the reactivity of the chlorine would make it impossible to maintain a static system. The two gauges were placed close together to minimize any pressure differential between them due to the flow of gas through the system.

Immediately after the gauge had been baked, the repro­ducibility of its response to chlorine was found to be poor until it had been operated in chlorine pressures of about 10-6 Torr for a period of minutes. After it reached the steady state for chlorine, its response to nitrogen, argon, and helium was also checked. All results are given in Table I and the graph (Fig. 1) and refer to the gauge un­baked after previous operation in chlorine at pressures of the order of 10-6 Torr. Here we see that the behavior com­pares roughly with that of other gauges1,2 of the Bayard­Alpert type, the only notable difference occurring for nitrogen. (The response of a second gauge of the same type did not show so marked a difference for nitrogen although it was similar with respect to other gases.) We observed that for pressures of chlorine above about 1.0 X 10-5 Torr the response of the ionization gauge was no longer linear with increase in pressure, whereas the response of this

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114 NOTES

same gauge was linear and reproducible up into the region of pressures ~SXlO-4 Torr for nitrogen and argon. It was not checked on helium at higher pressures.

1 G. J. Schulz, J. App!. Phys. 28, 1149 (1957). 2 W. McGowan and L. Kerwin, Can. J. Phys. 38, 567 (1960).

Miniature Oven for Galvanomagnetic Measurements

LAWRENCE S. LERNER· AND AUGUSTUS J. MOHR

Hughes Research Laboratories, Malibu, California 90265

(Received 11 August 1965; and in final form, 2 September 1965)

I N order to characterize highly extrinsic samples of large band gap semiconductors, it is often necessary to

measure their resistivities over a wide range above room temperature. We have designed and built a furnace for this purpose which has proved to be very convenient and reliable. It operates in the range from room temperature to 650°C, and could probably be made to operate at much higher temperatures, although we have not had occasion to try this. The furnace is small enough to fit easily into a 2.5 cm magnet pole gap, and the outside is cool enough to eliminate the possibility of damage to the pole faces.

Two views of the furnace are shown in Fig. 1. The sample ies in a slot in a Lavite block and is clamped between two

copper shim plates which serve as current contacts. The plates are so shaped as to allow for differential thermal ex­pansion. Small tungsten pins, held in small holes in the Lavite block by means of molybdenum leaf springs, serve as pressure contacts for potential and Hall measurements. Several extra holes in the block allow for various probe arrangements with minor modification.

A labyrinth milled in the bottom of the Lavite block contains the 0.4 mm diam Nichrome heating element, of about 20 g resistance, which is held in place by a mica sheet; this in turn rests on the molybdenum clamp which holds the entire assembly to the quartz tube.

A bundle of ceramic tubes, held together with glass tape, carries the nickel current, potential, and heater leads to the sample holder, where they are spot welded to the appropriate contacts. A pair of thermocouple wires runs through the center of the bundle; the junction is inserted in an axial hole in the center of the Lavite block.

The side arm on the quartz tube is used to introduce a gentle stream of nitrogen gas (about 10 liter/h) in order to prevent oxidation of the sample. The gas leaks out through the space between the quartz tube and insulating cover.

The insulating cover is based on an extension of the design of Prescott,! Alternate layers of wetted 0.5 mm asbestos paper and 0.05 mm metal foil are wrapped on a mandrel whose rectangular cross section is slightly larger than that of the sample holder. Six layers were used,

QUARTZ TUBE

FIG. 1. Two views of the minature oven.

although this number can be varied depending on the temperature to be reached, the maximum tolerable out­side temperature, and the space available. For the inner layers, molybdenum foil is used, since the melting point of aluminum is too low for this application. Aluminum is used for the ou ter layer.

The metal foil layers serve two purposes. The first is to provide mechanical strength and stability. The second, and more important, function is to give to the oven a high thermal conductivity in the axial direction, and thus to eliminate thermal gradients along the sample which would interfere with the galvanomagnetic experiments. Hall and resistivity measurements on CuGaSe2 and AgInSe22 were practically independent of current and magnetic field di­rection, indicating that significant thermal gradients are indeed absent; this is borne out by the consistency between the resistivity measurements and measurements carried out in another, larger furnace.

The thermocouple junction lies directly under the center of the sample, separated from it by approximately 0.5 mm of Lavite, with which both junction and sample are in good thermal contact. This configuration minimizes error due to a temperature difference between sample and thermocouple. The error is not known, but is certainly less than 0.1°C. This point is borne out by the lack of inertia between galvanomagnetic and temperature readings on cycling the temperature up and down.

Whether or not the metal layers of the insulating cover serve effectively as radiation shields depends upon the temperature.

The open end of the formed insulating cover is molded so that it fits snugly over the quartz tube, and the cover is baked overnight in a drying oven. The finished cover is

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