摘要:

This paper presents the results of experiments designed to carefully assess the merits of the metastable time-of-flight method of measuring velocity distributions in free molecule flows. The technique is particularly well suited to gas surface interaction work where high resolution, compactness, and cleanliness of the apparatus are appealing. Our measurements are of the absolute sensitivity of the technique when applied to He, Ne, Ar, Kr, Xe,N2,H2, CO,CO2, andO2at various electron impact energies when a tungsten Auger detector is used. Analysis of one component of a gas mixture by selecting an appropriate electron impact energy is also demonstrated. Second order effects such as those due to finite lifetime in the case ofN2and recoil from the electron impact in the case of light gases have been observed and a solution to these problems is indicated.

ISSN:0022-5355    

DOI:10.1116/1.1315826

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Chemisorption trends established using LEED techniques have shown that, at least for tungsten and melybdenum, the most densely packed planes are not the most reactive. The body-centered cubic (110), (100), and (112) planes are the most densely packed in this system and they contain surface atoms in density ratios of 1.4:1.0:0.8. Adsorption studies on the molybdenum (112) plane were concerned mainly withO2,N2,H2, and CO. Oxygen was the most reactive gas on this particular surface and formed(2×1),(2×1)+(1×2),(1×2),(1×3), andC(4×2)patterns. The(2×1),(2×1)+(1×2), and(1×2)coverages were obtained upon exposing the sample at room temperature to oxygen while the latter two patterns were obtained by heating the sample after very long oxygen exposures. No adsorption was found upon room temperature exposure to nitrogen while room temperature hydrogen exposure gave rise to a(1×2)LEED pattern. Carbon monoxide adsorbed only in an amorphous state at room temperature. Slight heating caused ordering of this amorphous structure resulting in complex LEED patterns. Changes in the intensity distribution of specularly reflected beams differed greatly depending on the gaseous species adsorbed.

ISSN:0022-5355    

DOI:10.1116/1.1315827

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1315828

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The following paper presents a summary of a number of experimental studies of the interaction of neutral molecules with solid surfaces. Several different experimental configurations are discussed, all of which have the common property that the parameter measured is the flux of molecules leaving the surface after interacting with it. In all cases the signal so obtained contains information on both the number flux of molecules and their mean thermal energy. Parameters measured include the thermal accommodation coefficient, mean stay-time for adsorption, equilibrium adlayer coverage, and critical supersaturation for condensed phase nucleation. Results are discussed both in terms of their fundamental physical significance and in terms of the versatility and the limitations of the experimental techniques used.

ISSN:0022-5355    

DOI:10.1116/1.1315829

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1315830

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Kinetic investigations of surface reactions are performed by field pulse desorption. The mass of field ions is analyzed by time-of-flight techniques. The apparatus is sensitive enough to detect single particles which are field desorbed from a small surface area(<100 Å2)of a defined single crystal plane. By variation of the field pulse repetition rate and the pulse width at sufficient pulse amplitude, the time dependence of surface processes as well as of the field desorption is investigated. The interaction of hydrocarbons with various single crystal planes of tungsten or platinum shows a selective behavior, and the deposition of carbon or high polymers alters the chemical reactivity. Time dependences are observed for surface reactions ofn-butane and ethylene.

ISSN:0022-5355    

DOI:10.1116/1.1315831

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Copper, nickel, a 20/80, and a 50/50 copper-nickel alloy were argon-ion bombarded in a 400-V glow discharge. The rate of thermal evolution of the argon was determined during a linear temperature rise. At least three peaks in the thermal evolution curves of all samples were found below 800 K. This thermal evolution was influenced by the alloy composition and by carbon monoxide adsorption after bombardment. After hydrogen bombardment, evolution occurred only at low temperatures. After nitrogen bombardment, evolution occurred only at high temperatures. Greatly enhanced uptake of hydrogen occurred after previous nitrogen bombardment.

ISSN:0022-5355    

DOI:10.1116/1.1315832

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

Measurement of the energy distribution of backscattered noble gas ions yields information regarding the elemental composition of the first atomic surface layer. An instrument based on this principle and designed for routine surface analysis will be described. This flange-mounted device is comprised of an electron bombardment ion source, an electrostatic energy analyzer, a channel electron multiplier, and a multiple sample holder. Primary ion beam energies range from 100–2000 eV at current densities up to50 μA/cm2. A depth profile of the surface constituents is obtained by utilizing the probe beam to selectively sputter clean the surface. Observations show the ability to resolve elemental isotopes, such asCu63fromCu65. Surface analyses are shown for 304 stainless steel, Cu, Ni, and ZnTe.

ISSN:0022-5355    

DOI:10.1116/1.1315833

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1315834

出版商:American Vacuum Society    

年代:1970

数据来源: AIP

摘要:

The Auger spectrum of a cleaved (111) Si surface shows the same transitions as those of an annealed surface having a Si (111)7 structure. The presence of these same Auger peaks from the cleaved surface and their behavior on annealing and gas exposure indicate that the previously observed transitions in the Auger spectrum of Si (111)7 surfaces are all due to Si and that there is no evidence that the Si (111)7 structure is impurity stabilized.

ISSN:0022-5355    

DOI:10.1116/1.1315835

出版商:American Vacuum Society    

年代:1970

数据来源: AIP