摘要:

A new method has been investigated for ultrahigh-vacuum calibration (molecular beam calibration) of vacuum gauges and mass spectrometers over the range10−6−10−15Torr with less than 5% probable error. The method is applicable, in principle, to all gases but limited in practise to gases with critical temperatures greater than or equal to that of nitrogen. It combines the techniques of pressure attenuation and molecular beaming from a nearly ideal aperture to generate a precisely known molecular density in a volume, the walls of which have a capture coefficient of near unity. The upstream (reference) pressure is measured by an instrument for which NBS has a test schedule. Direct beam to background density ratios in excess of 800:1 were measured for a 304 K argon beam. The conductance of the porous Vycor pressure-attenuating element is constant to pressures exceeding 5000 Torr. Determination of the magnitude of deviations from free molecular flow as the gas mean-free path λ in the furnace approaches the furnace orifice diameterdshowed no greater than12%deviation forλ/d≥25. The measured density distribution in the cryopumped beam tunnel agrees with the expectations of kinetic theory.

ISSN:0022-5355    

DOI:10.1116/1.1315866

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Equations are derived which allow the prediction of the thickness distribution of thin films deposited from sources possessing vertical sides and axial symmetry. These equations are in the form of three double integrals which must be integrated over a variable region of integration. Some correlation with experiment is also reported.

ISSN:0022-5355    

DOI:10.1116/1.1315867

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Sputter-ion pumped vacuum systems are commonly roughed with sorption pumps. This paper describes the design and performance of a new pump that is tailored for use with small systems. The new pump is designed to maximize heat transfer between the liquid-nitrogen coolant and the Molecular Sieve by means of an aluminum pump housing and by providing internal aluminum rods welded to the bottom of the housing. The performance of the new pump was assessed by three series of tests on a small (4.65-liter) vacuum system. These tests showed that the pump performs satisfactorily without internal gas access screens or prechilling, and that it can repeatedly (>20 times) evacuate the test system without loss of maximum (1×10−2Torr in 7.5 min and1×10−3Torr in 40 min) performance.

ISSN:0022-5355    

DOI:10.1116/1.1315868

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Electrical breakdown of thin (60–100 Å) titania films under high dc fields in high (10−9Torr) vacuum is discussed. Titania coatings were applied toAl2O3insulators, using the same process as in coating ofAl2O3microwave windows to reduce multipactoring. Recorded breakdown voltages and current dependence, along with the appearance of the coatings after testing, suggest the occurrence of a reduction of the titania films to a lower-order semiconducting oxide similar to what would happen in bulk titania. It is therefore evident that such coatings are not feasible on insulators subjected to high tangential dc fields.

ISSN:0022-5355    

DOI:10.1116/1.1315869

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Surfaces of mirrors or other optical devices employed in satellite programs will in time become contaminated with thin layers of polymer films. These films orginate most probably from outgassing followed by polymerization by uv radiation. The contaminant films degrade the reflectance of mirrors and the performance of critical optical surfaces. Atomic oxygen from an rf plasma restores optical surfaces to their original properties by rapid noncontaminating, nondestructive oxidation of the polymer film.

ISSN:0022-5355    

DOI:10.1116/1.1315870

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Nb–Zr thin films (3000–4000 Å thick) have been prepared by dc sputtering at 350 °C and 630 °C. Measurements of theJc–Hcharacteristics in transverse fields of up to 85 kOe and ofTc’s were carried out as a function of composition. We also investigated the effects of different substrate materials and deposition rates on the superconducting properties of Nb-66 at.% Zr thin films deposited at 630 °C. The results show a distinct dependence ofJc–Hdata on the substrate temperature: Maximum critical fields of up to 60 kOe at103 A/cm2are observed for films deposited at 350 °C, whereas some films deposited at 630 °C are still superconducting at 85 kOe with current densities of105 A/cm2. TheTcvs composition curve has a maximum at approximately 30 at.% and appears to be insensitive to deposition temperature at higher Zr concentrations. Additional annealing after deposition seems to increaseTc. The lower deposition rates yielded films with higherTc’s and betterJc–Hcharacteristics.

ISSN:0022-5355    

DOI:10.1116/1.1315871

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Due to the many conflicting reports on the structure of evaporated Pt on Si substrates, a study of the system was made with special emphasis on possible experimental errors. It is shown that for annealing temperatures up to 700 °C the only phases present are Pt and PtSi for evaporated and sputtered Pt.

ISSN:0022-5355    

DOI:10.1116/1.1315872

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The kinetics of the sulphidation and oxidation of evaporated zinc and cadmium films in sulphur and oxygen have been investigated. Between 100 ° and 250 °C a rapid gas uptake occurs which may be described byk·log(t−t0). Subsequently, a slow reaction is observed, the time dependence being represented by a logarithmic expression or by a general power law of the typek·t1/n. Electron-optical and x-ray studies reveal a substantial effect of nucleation and recrystallization processes on the kinetics of the layer growth. The following phases of layer growth could be confirmed: (1) coating of the metal with a very thin (d≈ 50 Å) nonoriented layer; (2) growth of oriented sulphide or oxide nuclei with diameters of102–103Å; (3) coalescence of these nuclei and formation of a coherent layer; in the case of CdS and CdO, formation of medium-size epitaxial crystallites; (4) formation of whiskers at elevated temperatures. (5) Measurements of zinc and cadmium single crystals gave similar results, but the reaction rate is much slower and the degree or orientation depends strongly on the pretreatment of the metal surfaces. The results show that nucleation and recrystallization processes affect considerably the kinetics of the formation of thin films on metals. From this it can be concluded that it is necessary to modify models of film growth, which in most cases are based on a homogeneous layer structure.

ISSN:0022-5355    

DOI:10.1116/1.1315873

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The efficiency of glow discharges in He, Ne, and Ar for the removal ofH2O, CO, andCO2from the surface of vacuum systems has been demonstrated. However, re-emission of the rare gas and of hydrogen atoms trapped in the surface during the discharge cause the total outgassing rate not to be significantly reduced. In general, as the pressure of the discharge increases, the efficiency of cleaning decreases, and this has been correlated with a decrease in the number of energetic ions hitting the surfaces.

ISSN:0022-5355    

DOI:10.1116/1.1315874

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1315875

出版商:American Vacuum Society    

年代:1970

数据来源: AIP