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The surface areas of evaporated metal films
VACUUM Classified A b s t r a c t s Abstract No. arid References
Article by 1). E. Clark
Brit. ,I. Appl. Phys. 6, May 1955 158-160
55]III
III
Trans. Faraday Soc. 5x, March 1955 368-370
270
Vacuum
Processing Contd.
Techniques
~
III
electrodes of silver; for microwave measurements, to compensate for the capacitance effect of the glass substratc, an a l u m i n i u m inductive d i a p h r a g m was used at I).92 x 10 t° c:'s and at 2.65 x 10 ~° c.:s, an identical cover slip at one q u a r t e r wavelength distance a w a y from the specimen. During m e a s u r e m e n t s the power used was low enough to ensure resistivity m e a s u r e m e n t s independent of current. Investigation of the standing-wave p a t t e r n on the generator side of the films which were placed at one q u a r t e r wavelength from the short-circuit termination gave directly the value of the wave impedance z at the surface of the film. The resistivity could then be calculated from z = 1.'¢rl, where c~--conductivity of the metal film and l - - thickness of fihn. The thickness of the film was determined by weighing the piece of metal used to prepare the film before evaporation and also weighing the deposit formed after evaporation of a b o u t 2 g. of metal. The density of the film was assumed to be t h a t of the metal in bulk. The results for a n t i m o n y show t h a t there is an initial decrease of resistance with time, p r o b a b l y due to crystallisation of the initially a m o r p h o u s films, and thereafter a slight increase of resistance after a b o u t one hour. The initial decrease was greatest for direct m e a s u r e m e n t and was less marked the thicker the film. A curve is given showing the relation between resistance and film thickness. In the case of a n t i m o n y there is no marked difference between resistivities measured by direct current or microwave method. The resistivity, of a film greater than 100 A is greater t h a n t h a t of bulk a n t i m o n y by. a factor of _.a.') ~" The results for b i s m u t h show an increase of resistance with time, greater for direct c u r r e n t measurements, for films less than 4,5 A which is a t t r i b u t e d to a tendency to form small grains. Thicker films showed c o n s t a n t resistance with time. There is an a p p r o x i m a t e l y linear relation between the reciprocal of film resistance, and thickness. The resistivity of the films show t h a t t h e y are greater by factors of 3.6 and 3.0 respectively for direct current and microwave cleterminations than t h a t for b i s m u t h in bulk.
The Surface Areas of E v a p o r a t e d Metal Films United Kingdom. Measurements of the adsorptive capacity of thin fihns by different workers show different results. This report aims to show the possible causes of these cliscrepancies. Films of Ni, Fe, Rh, Me, Ta and W were made by direct evaporation, at two different t e m p e r a t u r e s of formation (0~C and -- 183°C). The surface areas of Ni, i:e were measured by the sorption of hydrogen at --183~C, and the remainder by the sorption of oxygen at low t)ressures. A table, partly reprochlced below, shows the results for the above metals, given in
Fast :td.~orption at
Article by B. M. W. Trapnell
~
183C (Molecules :z 10-1s.100mg), and Percentage of Atoms Present in Film Surfaces.
Nystem
l"a.~t adsorption films prepared at O:C.
Ni/H 2 Me/U2 W/O:
5.1) 19.5 11.0
__Fa*t adsorption . _% surface atoms _.~£ .*urface atoms filnla prepared films prepared films prepared at -- 183°C. at O°C. at - 183°C. 9.3 28.5 14.9
1.0 6.2 6.7
1.8 9.1 9.1
t e r m s of the percentage surface atoms. These results have been plotted in a graph showing percentage surface a t o m s a s a function of metal melting point. With the exception of tungsten, these results confirm the theory t h a t the fraction of total evaporated a t o m s in the surface should increase with the melting point of the metai, because during deposition it is assumed t h a t the low melting point metals would be most mobile. The difference in the results at 0°C and -- 183°C shows t h a t the sintering of the fihn by the radiant heat of the filament m u s t also be i m p o r t a n t . This could account for the observed discrepancies.
50/111
Chemical Analysis of Thin Films b y X - R a y Emission Spectroscopy See Abstract No.: 157.I
57/111
S e m i c o n d u c t i v i t y and Catalysis in the Nickel Oxide S y s t e m See Abstract No.: 156/1
58/111
The Structure and G r o w t h of Oxide Layers F o r m e d on Beryllium United Kingdom. An electron-diffraction s t u d y of oxide layers (m beryllium has established t h a t on polycrystalline metal surfaces, at 300°C anti over, the oxide developed in a one-degree orientation which varied with the t e m p e r a t u r e of formation. On abradcd beryllium below 70WC, the Be0 grew in the (001) orientation, b u t above 700°C in (100). The oxide formed on smooth, electropolished, coarsely crystalline beryllium at t e m p e r a t u r e s up to 250°C hact a grain-size of a b o u t 10 A, b u t t h a t formed at 300°C ancl above measured 60 A of more, with preferred (001) orientation up to 700°C. G r o w t h of the oxide in air at room t e m p e r a t u r e was not increased by irradiation with ultra-violet light. On vacuum-deposited beryllium surfaces, the oxide grew epitaxially on the exposed (001) and (110) metal faces, even t h o u g h at room t e m p e r a t u r e the grain-size of the oxide crystals was only a b o u t l0 A. This striking case of epitaxy under conditions of extremely limited surface mobility was t h u s
Vacuum Vol. l'I
October, 1956
Article by 1). E. Clark
Brit. ,I. Appl. Phys. 6, May 1955 158-160
55]III
III
Trans. Faraday Soc. 5x, March 1955 368-370
270
Vacuum
Processing Contd.
Techniques
~
III
electrodes of silver; for microwave measurements, to compensate for the capacitance effect of the glass substratc, an a l u m i n i u m inductive d i a p h r a g m was used at I).92 x 10 t° c:'s and at 2.65 x 10 ~° c.:s, an identical cover slip at one q u a r t e r wavelength distance a w a y from the specimen. During m e a s u r e m e n t s the power used was low enough to ensure resistivity m e a s u r e m e n t s independent of current. Investigation of the standing-wave p a t t e r n on the generator side of the films which were placed at one q u a r t e r wavelength from the short-circuit termination gave directly the value of the wave impedance z at the surface of the film. The resistivity could then be calculated from z = 1.'¢rl, where c~--conductivity of the metal film and l - - thickness of fihn. The thickness of the film was determined by weighing the piece of metal used to prepare the film before evaporation and also weighing the deposit formed after evaporation of a b o u t 2 g. of metal. The density of the film was assumed to be t h a t of the metal in bulk. The results for a n t i m o n y show t h a t there is an initial decrease of resistance with time, p r o b a b l y due to crystallisation of the initially a m o r p h o u s films, and thereafter a slight increase of resistance after a b o u t one hour. The initial decrease was greatest for direct m e a s u r e m e n t and was less marked the thicker the film. A curve is given showing the relation between resistance and film thickness. In the case of a n t i m o n y there is no marked difference between resistivities measured by direct current or microwave method. The resistivity, of a film greater than 100 A is greater t h a n t h a t of bulk a n t i m o n y by. a factor of _.a.') ~" The results for b i s m u t h show an increase of resistance with time, greater for direct c u r r e n t measurements, for films less than 4,5 A which is a t t r i b u t e d to a tendency to form small grains. Thicker films showed c o n s t a n t resistance with time. There is an a p p r o x i m a t e l y linear relation between the reciprocal of film resistance, and thickness. The resistivity of the films show t h a t t h e y are greater by factors of 3.6 and 3.0 respectively for direct current and microwave cleterminations than t h a t for b i s m u t h in bulk.
The Surface Areas of E v a p o r a t e d Metal Films United Kingdom. Measurements of the adsorptive capacity of thin fihns by different workers show different results. This report aims to show the possible causes of these cliscrepancies. Films of Ni, Fe, Rh, Me, Ta and W were made by direct evaporation, at two different t e m p e r a t u r e s of formation (0~C and -- 183°C). The surface areas of Ni, i:e were measured by the sorption of hydrogen at --183~C, and the remainder by the sorption of oxygen at low t)ressures. A table, partly reprochlced below, shows the results for the above metals, given in
Fast :td.~orption at
Article by B. M. W. Trapnell
~
183C (Molecules :z 10-1s.100mg), and Percentage of Atoms Present in Film Surfaces.
Nystem
l"a.~t adsorption films prepared at O:C.
Ni/H 2 Me/U2 W/O:
5.1) 19.5 11.0
__Fa*t adsorption . _% surface atoms _.~£ .*urface atoms filnla prepared films prepared films prepared at -- 183°C. at O°C. at - 183°C. 9.3 28.5 14.9
1.0 6.2 6.7
1.8 9.1 9.1
t e r m s of the percentage surface atoms. These results have been plotted in a graph showing percentage surface a t o m s a s a function of metal melting point. With the exception of tungsten, these results confirm the theory t h a t the fraction of total evaporated a t o m s in the surface should increase with the melting point of the metai, because during deposition it is assumed t h a t the low melting point metals would be most mobile. The difference in the results at 0°C and -- 183°C shows t h a t the sintering of the fihn by the radiant heat of the filament m u s t also be i m p o r t a n t . This could account for the observed discrepancies.
50/111
Chemical Analysis of Thin Films b y X - R a y Emission Spectroscopy See Abstract No.: 157.I
57/111
S e m i c o n d u c t i v i t y and Catalysis in the Nickel Oxide S y s t e m See Abstract No.: 156/1
58/111
The Structure and G r o w t h of Oxide Layers F o r m e d on Beryllium United Kingdom. An electron-diffraction s t u d y of oxide layers (m beryllium has established t h a t on polycrystalline metal surfaces, at 300°C anti over, the oxide developed in a one-degree orientation which varied with the t e m p e r a t u r e of formation. On abradcd beryllium below 70WC, the Be0 grew in the (001) orientation, b u t above 700°C in (100). The oxide formed on smooth, electropolished, coarsely crystalline beryllium at t e m p e r a t u r e s up to 250°C hact a grain-size of a b o u t 10 A, b u t t h a t formed at 300°C ancl above measured 60 A of more, with preferred (001) orientation up to 700°C. G r o w t h of the oxide in air at room t e m p e r a t u r e was not increased by irradiation with ultra-violet light. On vacuum-deposited beryllium surfaces, the oxide grew epitaxially on the exposed (001) and (110) metal faces, even t h o u g h at room t e m p e r a t u r e the grain-size of the oxide crystals was only a b o u t l0 A. This striking case of epitaxy under conditions of extremely limited surface mobility was t h u s
Vacuum Vol. l'I
October, 1956