Abstract

It is well known that evaporated aluminum films develop a diffuse reflecting surface as their thickness increases, but it is not generally appreciated that the limiting thickness at which light scattering appears decreases as the incidence angle of the vapor atoms arriving at the condensing surface increases. Aluminum films formed at 80° incidence have a greater absorption than those condensed at normal incidence and develop a diffuse reflecting surface before becoming opaque. The film surface density at which diffuse reflection appeared at different vapor incidence angles was determined by measuring the specular reflectivity of the film for blue light at nearly normal incidence. It is shown that a diffuse reflecting surface is formed more easily as the vapor incidence angle approaches grazing incidence because the vapor atoms are mainly deposited on the upper surface of the film nuclei, the most elevated of which tend to grow in the direction of the vapor beam.

© 1953 Optical Society of America

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References

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  1. G. Hass, J. Opt. Soc. Am. 39, 179 (1949).
    [Crossref]
  2. S. Tolansky, Multiple Beam Interferometry (Clarendon Press, Oxford, 1948), first edition, p. 147.
  3. H. Levinstein, J. Appl. Phys. 20, 306 (1944).
    [Crossref]
  4. R. S. Sennett and G. D. Scott, J. Opt. Soc. Am. 40, 203 (1950).
    [Crossref]
  5. L. Holland, J. Opt. Soc. Am. 42, 686 (1952).
    [Crossref]
  6. W. Walkenhorst, Z. Tech. Phys. 22, 14 (1941).
  7. R. Beeching, Phil. Mag. 22, 938 (1936).
  8. L. Holland, J. Electrodepositors’ Tech. Soc. 28 (1952), advance copy No. 4.

1952 (2)

L. Holland, J. Opt. Soc. Am. 42, 686 (1952).
[Crossref]

L. Holland, J. Electrodepositors’ Tech. Soc. 28 (1952), advance copy No. 4.

1950 (1)

1949 (1)

1944 (1)

H. Levinstein, J. Appl. Phys. 20, 306 (1944).
[Crossref]

1941 (1)

W. Walkenhorst, Z. Tech. Phys. 22, 14 (1941).

1936 (1)

R. Beeching, Phil. Mag. 22, 938 (1936).

Beeching, R.

R. Beeching, Phil. Mag. 22, 938 (1936).

Hass, G.

Holland, L.

L. Holland, J. Electrodepositors’ Tech. Soc. 28 (1952), advance copy No. 4.

L. Holland, J. Opt. Soc. Am. 42, 686 (1952).
[Crossref]

Levinstein, H.

H. Levinstein, J. Appl. Phys. 20, 306 (1944).
[Crossref]

Scott, G. D.

Sennett, R. S.

Tolansky, S.

S. Tolansky, Multiple Beam Interferometry (Clarendon Press, Oxford, 1948), first edition, p. 147.

Walkenhorst, W.

W. Walkenhorst, Z. Tech. Phys. 22, 14 (1941).

J. Appl. Phys. (1)

H. Levinstein, J. Appl. Phys. 20, 306 (1944).
[Crossref]

J. Electrodepositors’ Tech. Soc. (1)

L. Holland, J. Electrodepositors’ Tech. Soc. 28 (1952), advance copy No. 4.

J. Opt. Soc. Am. (3)

Phil. Mag. (1)

R. Beeching, Phil. Mag. 22, 938 (1936).

Z. Tech. Phys. (1)

W. Walkenhorst, Z. Tech. Phys. 22, 14 (1941).

Other (1)

S. Tolansky, Multiple Beam Interferometry (Clarendon Press, Oxford, 1948), first edition, p. 147.

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Figures (5)

F. 1
F. 1

a: Deposition onto a cylinder with an extended vapor source “S” arranged parallel to the cylinder axis, i.e., normal to the plane of the paper. b: Deposition onto plane surface using a point vapor source.

F. 2
F. 2

The surface density of aluminum required at a given vapor incidence angle to form a diffuse reflecting film. The curve is for films whose reflectivity, measured at 10° light incidence and 4600A, is four percent less than that of normal aluminium (90 percent).

F. 3
F. 3

The reflectivity and transmission at 4600A of aluminum films as a function of surface density. The height of the vertical ordinates between the curves is the absorption (100−RT). All of the films deposited at a gas pressure < 0.1 micron Hg. Curves a: Aluminum deposited at normal incidence. Curve b: Aluminum deposited onto glass at 80° and 85° vapor incidence angle.

F. 4
F. 4

Reflectivity and transmission of two aluminum films of equal surface densities (2.7 μg/cm2) deposited at θ=0° and θ=85°.

F. 5
F. 5

Curve a is the reflectivity of an opaque aluminum film 16 μg/cm2 deposited at θ=0°, and curve b shows the effect on the mirror reflectivity of a thin aluminum film deposited at glancing incidence (2.7 μg/cm2 at θ=85°). Curve c is for a mirror prepared under similar conditions to that of curve a with the exception that the aluminium was deposited onto a heated substrate (150°C). Curve d shows the reduction of reflectivity after depositing on the mirror surface 2.7 μg/cm2 aluminum at θ=85°.