Fumio Watanabe

Ion spectroscopy gauge: Total pressure measurements down to 10−12 Pa with discrimination against electron‐stimulated‐desorption ions

The hot‐cathode magnetron gauge by Lafferty (which presently holds the possibility of making the lowest‐pressure measurements, 10−15 Pa) and the improved Helmer gauge by Benvenuti and Hauer (which carried out the lowest‐pressure measurements to date, 2.5×10−12 Pa) have been examined regarding the measurement limit due to electron‐stimulated‐desorption (ESD) ions. On the basis of this examination, a new hot‐cathode total pressure gauge, called an ion spectroscopy gauge, which substantially avoids errors caused by ESD ions down to 10−12 Pa, has been developed. Discrimination against ESD ions is accomplished by combining three technical elements: (i) a spherical grid ion source; (ii) a spherical 180° ion energy analyzer; and (iii) burying the ion source in an aluminum alloy flange. The ion source plays an important role in the generation of a large kinetic energy difference between gas‐phase ions and ESD ions, by using electron space charge. The 180° analyzer, which has a high energy resolution, promotes ion...

Total pressure measurement down to 10−12 Pa without electron stimulated desorption ion errors

In order to measure a total pressure as low as 10−12 Pa, the avoidance of electron stimulated desorption (ESD) ion errors is more important than the x‐ray limit, because even if we can contrive to reduce ESD ions in a gauge, we do not know what fraction the ESD ion error makes in the measured pressure value. This is the largest defect in the reliability of the measurements. Therefore, the development of the ion spectroscopy gauge which avoids ESD ion errors, was recalled with a historical review of the limiting processes in a hot‐cathode gauge. The most advanced ion spectroscopy gauge was constructed with a fine platinum alloy spherical grid ion source, immersed in a copper block with stainless steel flanges. Gas phase ions were effectively separated from ESD ions by the actions of electron space charge in the grid and a hemispherical 180° ion energy analyzer. The x‐ray limit of the advanced gauge was approximately 2.5×10−13 Pa, and the outgassing rate of 2×10−9 Pa l/s (about 1/100 that of an ordinary nud...

Low outgassing residual gas analyzer with a beryllium–copper‐alloy‐flanged ion source

By using a newly developed beryllium–copper (BeCu)‐alloy ConFlat flange to house the hot‐cathode ion source, a remarkable decrease in the outgassing from a quadrupole residual gas analyzer (RGA) has been achieved. The reduction in outgassing between the new BeCu‐flanged RGA and an ordinary stainless‐steel RGA of otherwise similar design was a factor of 60 or more in the 10−9 Pa total pressure range. From these results, the possibility of high accuracy residual gas analysis below 10−9 Pa is introduced.

Extremely low-outgassing material: 0.2% beryllium copper alloy

Exploration for low-outgassing materials for use in ultrahigh vacuum and extreme high-vacuum systems is one of the most important topics of a vacuum researcher. We have found that a copper alloy containing 0.2% beryllium (0.2% BeCu) can attain an extremely low hydrogen outgassing rate of 10−14 Pa (H2) m/s order. Almost the entire surface of 0.2% BeCu is dominated by a BeO layer, after a 400 °C×72 h prebakeout treatment in an ultrahigh vacuum. This layer functions as a barrier to the processes of oxidization and permeation of hydrogen. In addition, this layer resists carbon contamination. Temperature-programmed desorption spectra show only a single peak for water at 150 °C and small quantities of any other desorption gases. Therefore, an in situ bakeout process in which the temperature simply ramps up to 150 °C and immediately ramps back down is enough for degassing; it does not require an ordinary sustained-temperature bakeout. Using an outgassing sample consisting of 0.2% BeCu disks housed in a 0.2% BeCu...

Attaining an ultralow outgassing rate of 10−12 Pa m3 s−1 m−2 from an oxygen‐free high conductivity copper chamber with beryllium–copper–alloy flanges

A vacuum sealing technique using beryllium–copper (BeCu)–alloy Conflat flanges with an oxygen‐free copper gasket has been developed, and an outgassing rate from a vacuum cast oxygen‐free high conductivity (OFHC) copper chamber has been measured using the throughput method. The outside surface of the test chamber was protected against oxidation during bakeout by an electroless nickel plating (Ni–P alloy). The outgassing rate from the electropolished internal OFHC copper surface of the test chamber was about 4×10−8 Pa m3 s−1 m−2 nitrogen equivalency after 10 h evacuation at 20 °C, and reached a value of 2.9×10−11 Pa m3 s−1 m−2 nitrogen equivalency after bakeout at 100 °C for 24 h. After a 300 °C additional bakeout for 48 h, the outgassing rate decreased to the ultralow level of 6.2×10−13 Pa m3 s−1 m−2 nitrogen equivalency. This value is a hydrogen equivalency of 5.4×10−12 Pa m3 s−1 m−2, which is one of the lowest outgassing rates ever attained using any material and the throughput method.

Mechanism of ultralow outgassing rates in pure copper and chromium–copper alloy vacuum chambers: Reexamination by the pressure-rise method

Mechanisms influencing the ultimate outgassing rate of hydrogen from a metal chamber into a vacuum have been clarified by results from a reexamination using the pressure-rise method. The condition of the oxide surface of the metal plays a central role in determining the ultimate outgassing rate. Measurements were made for three materials, oxygen-free high-conductivity (pure) copper, chromium(0.6%)–copper(99.4%) alloy, and stainless steel 304, and are compared with previously published work by the throughput method. In the case of pure copper, the ultimate outgassing rate is dependent on in situ bakeout temperature. When the bakeout temperature is at least 250 °C, the oxide film on the copper surface is completely deoxidized and the ultimate outgassing rate is determined only by the concentration of hydrogen remaining in the bulk. As a result, this pure copper requires over a week in vacuum to attain its ultimate outgassing rate. In the case of chromium–copper alloy, however, the bulk content of hydrogen i...

SEPARATION OF ELECTRON-STIMULATED-DESORPTION NEUTRALS FROM OUTGASSING ORIGINATING FROM THE GRID SURFACE OF EMISSION-CONTROLLED GAUGES : STUDIES WITH A HEATED-GRID GAUGE

With the construction of a heated-grid gauge, whose grid temperature can be varied independent of the electron emission, the two major barriers against precise pressure measurements in the extremely high vacuum (XHV) region, i.e., electron-stimulated-desorption neutrals and outgassing, have been successfully separated. In XHV, these two processes are both dominated by hydrogen molecules, while their strengths depend strongly on the grid temperature and the grid material. At elevated temperatures, outgassing caused by the out-diffusion of hydrogen atoms dissolved in the grid begin to dominate. This suggests use of a metal with low hydrogen solubility for XHV-compatible grid material.

Comparative effects of gauge-wall materials on the outgassing rate of a hot-cathode ionization gauge

Using a newly developed spherical‐grid Bayard–Alpert gauge, a comparative test of gauge‐wall material (stainless steel, gold on stainless steel, aluminum, gold on aluminum, and copper) on the outgassing rate and pumping speed of a hot‐cathode ionization gauge has been carried out. (1) Outgassing was primarily related to electron emission and, in the ultrahigh vacuum (UHV) range, the existence of the hot‐cathode filament was a small factor, compared to electron emission. (2) At a low emission of 1 mA, an aluminum gauge wall had a very high pumping speed at UHV after degassing by electron bombardment. (3) At a high emission of 10 mA, the lowest outgassing rate was obtained with a vacuum‐cast oxygen‐free copper gauge wall. (4) Using low emissivity metals such as gold, copper, and aluminum for the gauge wall, the filament heating power was reduced to approximately half the power required with a stainless‐steel gauge wall for the same emission. (5) The outgassing rate of the spherical grid gauge with a low emi...

New x‐ray limit measurements for extractor gauges

A new x‐ray limit measurement method for extractor gauges has been developed using modulation of the hemispherical ion reflector. The measurement is possible from pressures as high as the 10−8 mbar range. X‐ray limits for commercial extractor gauges have been examined for various emission currents and different gauge port geometries. The scatter in the x‐ray limits measured is about 30% and the effect of gauge port geometry is more than 70%.

Investigation and reduction of spurious peaks caused by electron-stimulated desorption and outgassing by means of a grid heating method in a hot-cathode quadrupole residual gas analyzer

In the year 2001, two issues remain for extreme high vacuum (XHV) pressure measurements with hot-cathode ionization gauges: measurement limits caused by electron-stimulated desorption (ESD) and outgassing. The limit caused by ESD is significantly clarified and at least partially solved by means of a grid heating method in a residual gas analyzer. After system bakeout and at 10−9 Pa, when the surface of a platinum alloy grid remains contaminated with F and Cl atoms and CO molecules, the mass spectrum is dominated by spurious peaks (which set the measurement limit for a total pressure gauge) caused by ESD species of F, Cl, and O, with a yield of 10−11 (species/electron, with neutral/ion ≅0.3) and by CO molecule ESD, with a yield of 10−11 (species/electron, with CO neutral/O ion ≅18). In this condition, a spurious H peak caused by hydrogen ESD is still low. However, once the grid surface is thoroughly cleaned at over 900 °C by ohmic heating or electron bombardment, the major ESD species observed for both neu...