摘要:

Like EXAFS, extended appearance potential fine structure (EAPFS) probes the immediate neighborhood of a particular element and thus, unlike most other structural probes, does not require long‐range order. Furthermore, the use of low‐energy electron makes the technique surface sensitive. Because no dipole selection rules apply to electron excitation, explicit calculation must determine the angular momentum of the outgoing final‐state electron and thus the feasibility of Fourier inversion of the data. For excitation of the O 1score, we find the outgoing electron is overwhelmingly s‐wave. Reaction of Al(100) with about 1‐1/2 equivalent monolayers of oxygen disorders the surface completely (i.e., extinguishes the LEED pattern). For this surface, analysis of the O 1sedge gives an O–Al distance of 1.98±0.05 Å, the longer of the two Al–O spacings in bulk Al2O3, which indicates that the oxygen goes under the top layer of Al. For a thick oxide layer on Ni(100), diffraction effects precluded use of the O 1sedge. From Ni 2pdata, for which the angular momentum selection is weaker, we can extract the bulk Ni–O distance by using plausible phase shifts.

ISSN:0022-5355    

DOI:10.1116/1.570504

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.570505

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

A comprehensive high‐vacuum system has been set up and operated in an advanced undergraduate laboratory for students majoring in physics and microelectronics. The aim of the experiment is to provide the students with both practical experience and basic theoretical understanding of the production and measurement of low pressures. The students measure the pumping speed of a rotary forepump and of an oil diffusion pump, as a function of pressure, using procedures adopted by the AVS. A hot‐cathode ionization gauge and a thermocouple gauge are calibrated against a McLeod (absolute) manometer for several gases. The compositions of ambient air, of an isotopic mixture of neon, and of the residual gases in an oil‐diffusion‐pumped system are determined with the aid of a mass spectrometer. The influence of a liquid‐nitrogen‐cooled surface is assessed. Helium leak detection is demonstrated, and the response and sensitivity of the mass spectrometer as a leak detector are evaluated.

ISSN:0022-5355    

DOI:10.1116/1.570506

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

This paper outlines a two quarter laboratory course in integrated circuit design and fabrication offered by the Department of Electrical and Computer Engineering at the University of Cincinnati. Included in this course is an introduction to the operation and use of a wide range of vacuum system technology. The course also covers integrated circuit device design and layout, computerized mask generation, hands‐on processing, and evaluation of the finished IC chips. Traditional instruction is supplemented by video tapes of both lectures and demonstrations of the use of various pieces of equipment. Labortory facilities include high‐vacuum systems containing diffusion, ion and turbomolecular pumps used in several chemical vapor deposition systems, sputtering systems, and in an ion implantation system. The laboratory also features leak detection equipment, diffusion furnaces, photolithographic equipment, and a scanning electron microscope. Senior graduate students are given responsibility for routine maintenance of laboratory equipment including vacuum systems.

ISSN:0022-5355    

DOI:10.1116/1.570507

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

An overview of the topical coverage of a one‐semester, three‐hour course on solid surfaces, surface processes, and the solid/gas interface is presented. The main topical areas embracing the nature of the surface phase include topography, shape, depth, composition, purity, and structure, and the methods used to elucidate these parameters. The various theoretical and experimental categories for understanding adsorbate–adsorbent interactions are considered with particular attention focused on physical and chemical adsorption, desorption, and thermal desorption. Surface processes include surface diffusion and chemisorption as a precursor to oxidation and catalysis. The general emphasis of the course is on the experimental aspects of studying surfaces and the harmonious blending of backgrounds in physics, chemistry, materials, mathematics, and engineering for applied and fundamental surface science. The course is designed for graduate students and well qualified seniors majoring in science or engineering, or the equivalent, and has been taught several times.

ISSN:0022-5355    

DOI:10.1116/1.570508

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

The kinetics of the pack aluminizing of René 80 have been studied with emphasis on the early stages of the process. NH4F activated packs containing 2% Al and 5% Ni–40 Al were evaluated. It was found that for the 2% Al (high activity) pack that a weight gain of ∠5.6 mg/cm2was reached during the initial 10 min of processing; thereafter, there was essentially no further weight gain. In contrast, the 5% Ni–40 Al (low activity) pack showed a gradual weight gain to ∠3.0 mg/cm2during the 185 min process. Electron microprobe analyses of the coatings were used to characterize the composition profiles of the coatings formed in the two packs. The outer region of coatings formed in a 2% Al pack are of relatively uniform composition for the elements measured: Ni, Co, Cr, and Al. In contrast, the coatings formed in a 5% Ni–40 pack showed sharp compositional gradients in the outer region.

ISSN:0022-5355    

DOI:10.1116/1.570509

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

Alloys of composition Ni–20Cr, Ni–35Cr, Ni–50Cr, Co–35Cr, Ni–5Co–20Cr, and Ni–20Co–20Cr have been aluminided by pack cementation. Morphology of the coatings varies considerably among the different alloys. The most striking differences are the avoidance of formation of Kirkendall‐type voids in the Ni–Co–Cr alloys, and the degree of continuity of the α‐Cr layer formed. Both features need to be controlled to avoid coating loss by cracking and spallation. From the appropriate phase diagrams, the sequence of morphologies formed by aluminization can be rationalized. The relation of total aluminum deposition to alloy composition results from phase equilibria and phase solubilities, and phase diagrams can be used to rationalize this relation as well.

ISSN:0022-5355    

DOI:10.1116/1.570510

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

By means of vacuum annealing in the range 525–775 K and under well controlled oxidative conditions the chemical composition of protective films of an AISI 316 stainless steel has been modified in order to increase the resistance to crevice corrosion. Independent of surface pretreatment the increase in critical potential for crevice corrosion in a neutral sodium chloride solution after thermal passivation in controlled vacuum is at least 250 mV. Due to selective oxidation of chromium and nickel during such thermal treatments the beneficial effect in corrosion resistance is attributed to a marked chromium film enrichment and a less marked nickel film enrichment. In combination with any chemical surface pretreatment, which aims at reducing the amount of certain nonmetallic inclusions where localized corrosion attacks frequently start, this thermal surface treatment will result in a protective film with extraordinarily high corrosion resistance. The vacuum annealing process presented is suggested to act as the finishing manufacturing step in certain applications where the steel article is not subjected to any further high temperature annealing.

ISSN:0022-5355    

DOI:10.1116/1.570511

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.570512

出版商:American Vacuum Society    

年代:1980

数据来源: AIP

摘要:

The survey deals with the application of gravimetric measuring techniques to the investigation of physical adsorption processes. The principal topics covered in this paper are the definition of the term ’’adsorption’’; the types of surfaces under investigation; the most important measuring procedures, i.e. measuring isotherms, measuring isobars, and evaluating the results; the advantages, limitations, and typical errors involved in gravimetry compared with competing methods; and limitations and development perspectives of gravimetric investigations of physisorption.

ISSN:0022-5355    

DOI:10.1116/1.570513

出版商:American Vacuum Society    

年代:1980

数据来源: AIP