摘要:

The results of the determination of the pumping speed employing conventional methods deviate from the productACefbased on concepts of the kinetic theory of gases, whereACe=Aυav/4is the conductance of an orifice, if the capture probabilityfis not small. This deviation may be attributed to the technique of pressure measurement. In order to obtain proportionality between capture probability and speed with a unique constant of proportionality in the whole range0≤f≤1it is recommended that the pumping speed be defined using the pressure in a large vessel at a place where the isotropic state is maintained to a high degree. This speed is named intrinsic speed and it may be measured using Knudsen's large chamber fitted with a proper gas inlet system. The measurement of very large pumps according to this definition however may be carried out by applying a conversion for the incidence density in the pump mouth to an isotropic pressure. The considerations presented in this paper are intended as a contribution to an international standardization of the speed measurement of high-vacuum pumps. They are based on molecular flow in the test dome.

ISSN:0022-5355    

DOI:10.1116/1.1492458

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

A Monte Carlo method was used to calculate the probability that a molecule passes through a cylindrical tube with wall sorption. This probability is presented as a function of the ratio of length to radius and the sticking coefficientsof the wall. Fors=0, the results confirm those of Clausing for the conductance of a tube of finite length. Fors≠0, wall pumping can greatly reduce the flow of gas, even for very small values ofs. The backscattering, total flux retained by the wall, and its distribution along the tube also are presented. Finally, the collimation of the emerging beam is investigated.

ISSN:0022-5355    

DOI:10.1116/1.1492459

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

The performance of an alloy of 85% Ti 15%Mo as a filament material for subliming titanium in getter pumps is described. Using 2.1-mm-diam filaments, evaporation rates of up to 1 mg/cm/min have been achieved at filament currents of 57A. The upper limit in the evaporation rate is caused by filament failure which is attributed to crystal growth, but at values below this limit the evaporation is extremely uniform and reproducible. Comparison has been made between the performance of this alloy and a number of filaments of the type in which titanium is wrapped over a tungsten or tantalum core. The alloy was found to compare favorably in terms of peak evaporation rate and efficiency, and to be considerably better in terms of expense, reproducibility, and mechanical strength.

ISSN:0022-5355    

DOI:10.1116/1.1492460

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

The development of cryosorption panels consisting of Molecular Sieve adsorbents bonded to refrigerated aluminum plates is described. The sticking coefficient of hydrogen on a cryosorption panel refrigerated with liquid hydrogen was found to be 0.16 in the high-vacuum range, corresponding to a pumping speed of6600 liter/sec per ft2of panel. A higher sticking coefficient, near unity, can be obtained with a more efficient shielding of the adsorbent surface against thermal radiation. The pumping speed decreases markedly when the surface is contaminated with more condensable gases, such as nitrogen. Therefore, the cryosorption panels must also be shielded from condensable contaminants. The panels can be mounted directly inside vacuum chambers, and can be scaled up without difficulty.

ISSN:0022-5355    

DOI:10.1116/1.1492461

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

Gold thin films of 1800 Å to be used as lubricants were vapor deposited on Ni, Ni-Cr, and Ni-Re substrates. Strong bonding (adhesion) and durability between the film and substrate were found to be essential when thin films are used as a lubricant. Factors that were investigated included the selection of the film and substrate material. Strong durability of the thin film is directly related to the type and structure of the interfacial region. Two methods of substrate preparation prior to vapor deposition were investigated: (1) mechanically polished surface and (2) electron bombarded surface. Gold was vapor deposited on the mechanically polished surface at room temperature and on the thermally etched surface at an elevated temperature approximately (800 °F). Strength and durability of the films were investigated in sliding friction experiments with a hemispherical niobium rider sliding on the films at a velocity of 5 ft/min. Results obtained in these friction experiments indicated that the film endurance life was considerably better on the thermally etched surface. This increased film durability with the thermally etched surface is believed to be owing to the formation of a diffusion type interface between the film and the substrate. Because of the disregistry at grain boundaries, a higher rate of diffusion and preferential trapping in and around the grain boundaries occurs, with these regions acting aslubricant reservoirsduring the friction experiments.

ISSN:0022-5355    

DOI:10.1116/1.1492462

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

Results of experiments with several types of adhesives that withstand bakeout temperatures of 300 °C in vacuum are given. The experiments included measurements of outgassing rates, mass spectra of evolved gases, and electrical and mechanical properties. Certain polyimide and silicone resins were found to have outgassing rates below10−7Torr litersec−1 cm−2at temperatures up to 155 °C. With the addition of trace amounts of uniform small glass spheres to obtain reproducible electrical characteristics, some of these materials also exhibited good insulating and bonding properties when used to join metal surfaces. Possible applications in the construction of experimental electron devices and other high-vacuum apparatus are discussed.

ISSN:0022-5355    

DOI:10.1116/1.1492463

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

A discussion is given of the scanning-electron-diffraction technique. The importance of energy analysis of the diffracted beams in both reflection and transmission diffraction is emphasized. Details are given of the results of experiments in which intensity patterns are recorded while metal films are being deposited onto room-temperature carbon substrates inside the electron-diffraction system. Intensity profiles across the Debye-Scherrer rings have been obtained at 10- to 20-sec intervals, corresponding typically to 10-Å increments in film thickness; thus, diffraction patterns corresponding to the earliest stages of growth could be recorded. Representative specimens were examined by electron microscopy. Growth sequences have been recorded for Al, Ag, An, Ni, 80/20 Ni/Fe, Fe, and Ge. The growth characteristics are discussed and correlated with observations by electron microscopy. Attention is given to the interpretation of electron-diffraction patterns from very thin films and from (so-called) amorphous films.

ISSN:0022-5355    

DOI:10.1116/1.1492464

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

Films of gold, silver, copper, nickel, palladium, and platinum were prepared by evaporation of the metals in ultrahigh vacuum onto hot, vacuum cleaved, sodium chloride substrates. Nickel, palladium, and platinum films that completely covered the surface were single crystals in the orientation of the substrate. Complete gold, silver, and copper films were polycrystals in which there was a tendency for the (111) metal plane to be parallel to the (001) salt surface. Later, it was found that single crystal foils of gold, silver, and copper were obtained if the salt substrate was exposed to air prior to the deposition of metal upon it. Careful comparison of the growth of gold on clean and on air-contaminated salt surfaces has shown that the effect of air is not to improve the alignment of the initial gold nuclei, but is to increase the number of nuclei generated per unit area. This increase causes nuclei to coalesce earlier in film growth. The stage in film growth at which coalescence occurs influences the orientation changes that accompany coalescence, and thereby influences the orientation of the complete film.

ISSN:0022-5355    

DOI:10.1116/1.1492465

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

Nearly perfect, single-crystal thin platelets of nickel and nickel alloy are readily grown non-epitaxially by the reduction of the halide. Thicknesses range from about 500 Å to over105Å; areas extend to over1 mm2. Etching in HCl reveals dislocation densities generally either of zero or of103–104 cm−2. Ferromagnetic domain studies with the platelets have yielded the following results: (1) 180 ° walls with mixed NéelBloch character may coexist with Bloch walls in both nickel and NiCo platelets at least 7000 Å thick. The presence of a geometrically required crosstie spot establishes the partially Néel-wall character. (2) one may precisely determine the applied field required to drive out a nucleus of reverse magnetization from the corner of a platelet by noting the form of the returning domain structure. (3) the 180 ° wall in a rectangular Ni-Co platelet with a simple closure pattern forms the arc of a circle in an applied field; i.e., there is a uniform effective pressure acting along its length. (4) Topological restraints are largely responsible for hysteresis in nickel platelets several thousand angstroms thick. In small driving fields Ni-Co rectangular platelets may have virtually no hysteresis or coercive force(Hc<0.01 Oe). In large fields there is hysteresis from irreversible topological changes, but there may still be no coercive force. (5) Near the transitional thickness for crosstie walls the platelets show both coercive forces of several tenths of an oersted and an after-effect. The ferromagnetic resonance experiments of Rodbell with nickel platelets are also briefly mentioned.

ISSN:0022-5355    

DOI:10.1116/1.1492466

出版商:American Vacuum Society    

年代:1966

数据来源: AIP

摘要:

The technique of direct observation of the growth of thin films involving the deposition of films inside the electron microscope, is described. Its merits, disadvantages, and limitations are discussed. The application of the technique to the study of the growth and intergrowth of the initial nuclei of a deposit, and also of larger compound islands, is described. It is shown that this can lead to appreciable “liquidlike” coalescence. The technique also provides detailed information on the manner in which the imperfection structure in the deposit changes as growth proceeds. The mechanisms of imperfection formation are discussed. If two islands of very different orientation coalesce, a recrystallization process can occur so that the fined compound island is in one single orientation. The general significance of this effect is discussed. The above phenomena are illustrated throughout by means of results obtained for the growth of gold on molybdenite(MoS2).

ISSN:0022-5355    

DOI:10.1116/1.1492467

出版商:American Vacuum Society    

年代:1966

数据来源: AIP