摘要:

The adsorption of CO2on polycrystalline molybdenum is blocked even by the partial (aproximately two‐thirds) presence of the strongly bound β2oxygen. Pre‐adsorption of CO2at room temperature does not impede subsequent oxidation. The CO2adsorption kinetics at room temperature can be explained by a two‐site adsorption model with rapid dissociative chemisorption and carbon and oxygen in equivalent sites. On heating the CO2‐saturated surface above 900 K, CO is lost from the surface. Interaction of CO2at 1200 K gives a small buildup of carbon until the surface oxygen concentration increases sufficiently that the loss rate exceeds the deposition rate.

ISSN:0022-5355    

DOI:10.1116/1.569861

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

The surface composition of a series of iron–chromium alloys was analyzed by Auger electron spectroscopy as a function of Ar and Ne ion etching conditions. The relative sensitivity factor was determined from iron and chromium and from an Fe–25%Cr alloy and was found to be independent of composition. No preferential sputtering of either alloy component was observed as long as the surface was free from any impurities. When small quantities of CO are adsorbed onto the alloys’ surfaces, the Cr content appeared to decrease markedly, much more than when H2O adsorbed. It is suggested that the preferential adsorption of CO onto Cr atoms of the alloy surface can account for this effect. Similar effects are likely during ion etching of other alloy systems.

ISSN:0022-5355    

DOI:10.1116/1.569869

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Thin films of electron‐beam‐vaporized silicon were deposited on fine‐grained tungsten substrates under a pressure of ∠1×10−10Torr. Mass spectra from a quadrapole residual gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. During separate silicon depositions, the atomically clean substrates were maintained at various temperatures between 400° and 780° C and deposition rates were between 20 and 630 Å min−1. Surface contamination and interdiffusion wer monitored byinsituAuger electron spectrometry before and after cleaning, deposition, and annealing. Auger depth profiling, x‐ray analysis, and SEM in the topographic and channeling modes, were utilized to characterize the samples with respect to silicon–metal interface, interdiffusion, silicide formation, and grain size of silicon. The onset of silicide formation was found to occur at approximately 625° C. Above this temperature tungsten silicides were formed at a rate faster than the silicon deposition. Fine‐grain silicon films were obtained at lower temperatures.

ISSN:0022-5355    

DOI:10.1116/1.569860

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

The rf sputtering of Nd–glass films from targets containing low dissociation energy oxides has been investigated, and factors affecting optical quality and process time are discussed. These include gas composition and pressure, input power density, substrate temperature, annealing, surface damage, and thermal properties of both host glass and substrate. Several methods for overcoming anion depletion in the films and reducing waveguide losses are evaluated.

ISSN:0022-5355    

DOI:10.1116/1.569862

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Thin film layers of Cr–Au were subjected to temperatures in the range 423–573 K for various periods of time and the morphology of the Cr layer was examined with optical and scanning electron microscopy. A preferential depletion of Cr was found beneath the Au grain boundaries and intergranular spaces which was not fully compensated by diffusion of Au into the Cr. Since the Au grain boundaries intersect, this results in islands of remaining Cr surrounded by a labyrinth of voids or channels. This phenomenon renders the entire Cr–Au interface vulnerable to the entry of corrosives. By using transmission optical microscopy in conjunction with a photometer, the optical transmission of the Cr layer was measured and related to the Cr depletion as a function of time and temperature. From these measurements two mathematical models were devised to calculate the activation energy for the Cr diffusion resulting in values of 1.30 and 1.36 eV, respectively.

ISSN:0022-5355    

DOI:10.1116/1.569863

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Friction and wear experiments on 440‐C steel surfaces that had been rf sputtered with titanium carbide when a small percentage of nitrogen was added to the plasma were conducted. X‐ray photoelectron spectroscopy and x‐ray diffraction were used to analyze the resultant coatings. Results indicate that a small partial pressure of nitrogen (∠0.5%) markedly improves the adherence, friction, and wear properties when compared with coatings applied on sputter‐etched, oxidized surfaces or in the presence of a small oxygen partial pressure. The improvements are related to the formation of an interface containing a mixture of the nitrides of titanium and iron which are harder than their corresponding oxides.

ISSN:0022-5355    

DOI:10.1116/1.569864

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

This paper discusses extended x‐ray absorption fine‐structure (EXAFS) measurements using monochromatized synchrotron radiation in the 300–1000‐eV range. EXAFS spectra were obtained by detecting the secondary electron yield from the sample. The electron yield technique is shown to exhibit several unique advantages over conventional absorption measurements. In particular, no thin‐film samples are needed and, more important, measurements of surface phemonema become feasible. Results are presented for the NK‐edge EXAFS in Si3N4and for the OK‐edge surface EXAFS of an oxygen monolayer on Ni (100).

ISSN:0022-5355    

DOI:10.1116/1.569865

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Microstructural investigations on hexagonal cadmium films, considering a number ofH−K=3N(namely, 00.2, 10.0, 11.0, 00.4,N1.2, and 20.0) andH−K= 3N±1 (namely, 10.1, 10.2, 10.3, 20.1, 10.4, 20.2 and 20.3) x‐ray diffraction profiles recorded in a counter diffractometer, were done by detailed Fourier analysis of lineshape and also integral breadth measurements. The films, in the thickness range of ∠200–3300 Å, were vapor deposited for both normal and oblique (∠46° to the substrate normal) vapor incidences. For both the source positions Fourier lineshape analysis of the fault‐unaffected (H−K=3N) reflections indicate that the effects from the average domain size and rms strain are relatively large in the thin range ≲600 Å, and these decrease at higher thickness ∠3300 Å. The size and strain values along [00.2] are found to be close to the average ones depicting the near isotropy in these parameters. As regards the effective domain size values evaluated for fault‐affected (H−K=3N±1) reflections, it has been observed that the size values forL0odd reflections are more than those ofL0even for films ≲1000 Å thick for both the source positions, and this implies the possibility of the presence of stacking faults. For both the source positions, there is a tendency for the growth‐stacking fault to be present in appreciable concentration (probability β ∠60.0×10−3in the thin range only,<1000 Å with total absence of intrinsic stacking fault (probability α). The dislocation density ρavis found to be ∠1011cm/cm3for both the cases of normal and oblique incidences. The integral breadth studies also yield similar observations on the microstructural parameters. The preferential orientation of these cadmium films is along [00.2], and the effect decreases with increasing thickness for oblique incidence case but increases for normally deposited films. The recovery effect as studied by analysing two films ∠680 and ∠930 Å, deposited normally on substrates preheated to about 383 K, is shown by considerable gains in size and strain parameters with a reduced probability of growth faulting.

ISSN:0022-5355    

DOI:10.1116/1.569866

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

A rate equation describing the desorption of particles from substrates has been formulated using a simple classical model in terms of the particulate escape probabilities and escape velocities. Numerical results for desorption rates as a function of temperature using simple two‐body potentials are calculated for various metallic systems. These results were obtained for the low coverage limits and are found to be in good agreement with experimental findings. The present formulation also provides an improved picture of the physical nature of the commonly discussed parameters, such as the frequency factor, desorption energy, and desorption temperature in relation to observed desorption phenomena.

ISSN:0022-5355    

DOI:10.1116/1.569867

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

The problems of tritium permeation through and loading of the TFTR vacuum vessel wall structural components are considered for various TFTR operating scenarios and outgassing modes. A general analytical solution to the time‐dependent diffusion equation which takes into account the boundary conditions arising from the tritium filling gas as well as the source function associated with implanted energetic charge exchange tritium is presented. Expressions are derived for two quantities of interest: (1) the total amount of tritium leaving the outer surface of a particular vessel component as a function of time, and (2) the amount retained as a function of time. These quantities are evaluated for specific TFTR cases. The results are that permeation through the vessel is important only for the bellows during discharge cleaning if the wall temperature rises above ∠150 °C. At 250 °C, after 72 hours of discharge cleaning ∠200 Ci would be lost. The wall loading is most severe in the stainless‐steel plate sections during normal pulsed operation where ∠600 Ci would be retained after 1000 shots if the walls were at 20 °C. Maintaining the temperature of the walls above 100 °C greatly lessens the problem. The 600 Ci in the wall would be reduced to ∠10 Ci if the wall were heated to 250 °C for about 60 h.

ISSN:0022-5355    

DOI:10.1116/1.569868

出版商:American Vacuum Society    

年代:1979

数据来源: AIP