Yutaka Tuzi

Conductance modulation method for the measurement of the pumping speed and outgassing rate of pumps in ultrahigh vacuum

A new method, named the conductance modulation method (CM method), was developed for the measurement of pumping speeds (intrinsic and net) and outgassing rates in vacuum systems. The details of the formulation and the procedure of the CM method are described. The principle of the method lies in the measurement of the pressure modulation with the change of the conductance between a chamber and a pump. The pumping speed is obtained from the ratio of the modulated pressures and the value of the conductance without measurements of absolute pressures. This feature makes the method quite appropriate for measurements in ultrahigh vacuum. The CM method was applied to the measurement of the gas balance in a vacuum system pumped with a Ti getter pump. The intrinsic and the net speed of the Ti getter pump were measured for H2 in a wide pressure range down to ultimate pressure under various conditions of getter films and the amount of H2 sorbed. The outgassing rates from the wall of the chamber and the pump were simultaneously evaluated. These results confirmed the usefulness of the CM method for the quantitative analysis on the gas balance in vacuum systems.

Vibrational excitation of physisorbed CO2 on a Ag(111) surface

Vibrational excitations of CO2 molecules physisorbed on Ag(111) at 40 K were measured by high‐resolution electron energy‐loss spectroscopy (EELS). Measurements of EELS were performed at an incident electron energy of 1.5 to 30 eV for exposures of CO2 ranging from 0.5 to 5 L. Vibrational energies of three fundamental vibrational modes coincided with the values for CO2 molecules in the gas phase within ±3 meV. Resonance excitation of the symmetric stretch mode was observed at incident electron energies of 1.5 to 3 and 9 eV. The excitations of (n00) and (n10) progressions were significant at the incident energy of 2 eV, which is related to a 3.8‐eV resonance known for electron–molecule collision in the gas phase.

Variation of the yield of electron emission from a silicon single crystal with the diffraction condition of exciting x-rays

Abstract An anomalous variation of the yield of K-, L-photoelectrons and KLL Auger electrons emitted from a surface of a silicon single crystal has been studied under the diffraction condition of exciting X-rays of Cu Kα radiation.

Calibration of an axial symmetric transmission gauge in ultrahigh and extreme high vacuum

The sensitivity factor of an axial symmetric transmission gauge (AT gauge) was determined by the conductance modulation method (CMM) in the pressure range from 10−10 to 10−6 Pa. The gauge has a Bessel-box type energy filter between a Bayard–Alpert gauge type ionizer and an ion detector to eliminate the limiting factors of pressure measurement in extreme high vacuum such as the soft x-ray effect and the electron stimulated desorption of ions. The lower limit of the pressure measurement of the gauge is estimated to be about 10−12 Pa or lower. The sensitivity factor showed a slight pressure dependence caused mainly by outgassing from the gauge itself. The sensitivity factor of the AT gauge, which was further corrected for the effect of outgassing by the CMM, is almost constant in the pressure range from 10−10 to 10−6 Pa and is (2.3±0.1)×103 Pa−1 for hydrogen.

Double‐crystal, vacuum x‐ray diffractometer

An x‐ray double‐crystal diffractometer installed in a high‐vacuum chamber is designed and constructed for the study of photoelectron emission accompanying x‐ray dynamical diffraction. The rotation mechanism of the second crystal, based on torsion of a cylinder, provides an accuracy of 0.1 s of arc.

Axial-symmetric transmission gauge: Extension of its pressure measuring range and reduction of the electron stimulated desorption ion effect in ultrahigh vacuum

The basic characteristics of the axial-symmetric transmission gauge (AT gauge), that were modified for measurement over a wide pressure range, are reported. A Faraday cup ion collector is used instead of a secondary electron multiplier to extend the measurable pressure range to 10−3Pa. The sensitivity of the gauge was determined by a conductance modulation method, and by direct comparison against an extractor gauge and a spinning rotor gauge as well. When operating in O2, there was systematic disagreement between pressure readings with the AT gauge and the extractor gauge. This is due to the difference in the elimination efficiency of the electron stimulated desorption ion.

Performance of a simplified directional detector for gas molecules

A simplified directional detector for gas molecules was developed which does not use the collimator, described in a previous article,1 but has bundled capillaries at the entrance of the detector. The detector’s performance with capillaries is analyzed and compared with some experimental results. The directivity depends on the pumping speed of the bell jar, as in the case of the collimator, and on the length‐to‐diameter ratio of the capillary. The directivity of the detector can be increased ∠20 times or more than that of the detector with an orifice of the same diameter. Response time of the detector can be reduced by increasing the number of the capillaries. This detector has been applied to the measurement of the angular distributions of desorbed H2 molecules from Si (111) surfaces.

Measurement of Field-Emission Current-Fluctuations by Digital Autocorrelation of Electron-Counting

A new method of field-emission current-fluctuation analysis is presented. Digital autocorrelation of counting-fluctuations of field-emitted electrons is discussed on the basis of the theory of photon-counting fluctuations. The measurement of the digital autocorrelation function is made by using a pulse-counting system of field-emitted electrons and a microcomputer. The surface diffusion of Xe adsorbed on a (110) vicinal plane of W is studied with the present method. Measured digital autocorrelation function agrees well with the theory and surface diffusion coeffcient of 2.9×10-7cm2/s is obtained at 78 K.

A Zr–Al composite‐cathode sputter‐ion pump

The performance of a diode sputter‐ion pump which has a pair of cathode plates made of Zr and Al has been studied. The main purpose of the study was to reduce the memory effect of prepumped gases, especially hydrogen. Sputtered Zr and Al atoms from each cathode plate form deposits of Zr–Al alloy which have gettering properties superior to those of pure Zr or Al. Results showed that trapping on the sputtered deposits reduced the re‐emission of trapped gases from the sputtered region by ion bombardment. The composition of the deposited layers was determined by Auger electron spectroscopy. The pumping characteristics of the Zr–Al cathode were compared to a Ti cathode of the same configuration. Ratios of the pumping speeds (SZr–Al/STi), at 10−5 Pa are 1.8 and 3.3 for N2 and Ar, respectively. Re‐emission of D2 by subsequent pumping of Ar was measured after 1.3×10−2 Pa m3 of D2 were pumped by each cathode. At an Ar pressure of 1×10−5 Pa, re‐emission of D2 for the Zr–Al cathode is less than 40% of that for the T...

Effects of thermal spikes on the characteristics of cryosorption pumps with condensed carbon dioxide layers

The pumping characteristics of the condensed CO2 layers for He at low temperature depend on the structure of the layers which is determined by the formation conditions and the thermal history after deposition. During the continuous condensation process of CO2 on the cryosurface kept at the temperatures lower than about 8 K, abrupt temperture changes, ’’thermal spikes,’’ are repeatedly observed. The amount of heat generated at each thermal spike is directly proportional to the amount of condensed CO2 in the period subsequent to the last spike. The thermal spikes reduce the adsorption capacities of the condensed CO2 layers for He, assumed to depend on the inner surface area of the layers. Thus the spikes seem to be caused by some structure changes of the condensed CO2 layers.