Abstract

Ellipsometer, surface-tension, and contact-potential measurements were made simultaneously at and below monolayer coverage (θ = 1 to 0.05) on a clean mercury surface at room temperature. It has been demonstrated with molecules of known dimensions (caproic, lauric, stearic, behenic, and adamantane-carboxylic acids, and α bromonaphthalene and pentane) that the classical Drude equation for the relationship between the phase shift ( Δ¯ − Δ) of reflected polarized light and the average effective film thickness d is valid below monolayer coverage. This is so even though the Drude equation was derived for thick films that are considered to be a continuum with index and density independent of thickness. The equation for the three-dimensional model is Δ¯ − Δ = αd, where for less than monolayer coverage d is the hypothetical thickness the film would have if it were a continuum with index and density independent of d. The equation for the 3-D model remains valid below monolayer coverage, where the continuum property is not approximated, because the 2-D model gives essentially the same equation Δ¯ − Δ = αd0θ. In the 2-D model, the molecules are contained between the substrate surface and a plane d0Å above the surface, where d0 is the molecular diameter. The phase shift ( Δ¯ − Δ) decreases as the fraction of the surface covered (θ) decreases because the index of refraction is a function of the surface density. Values of α, calculated with the bulk-liquid index of refraction (sodium D line) and the first-order Drude relation (for films with only a real part of the refractive index) can be used to calculate d (0.05d0 to d0) or θ (0.05 to 1) within a few percent with the equations above. The same values are obtained if the relationship between α and the film index (based on the 2-D model) is used to calculate α. The ellipsometer measurements indicate changes of orientation of the molecules on the surface. A technique is described for automatically recording ellipsometer measurements for very thin films (0–30 Å).

© 1968 Optical Society of America

Full Article  |  PDF Article
OSA Recommended Articles
Ellipsometry of an Absorbing Film below Monolayer Coverage: Cs/W

Tennyson Smith
J. Opt. Soc. Am. 62(2) 291-292 (1972)

Optical Constants of a Clean Mercury Surface as a Function of Temperature

Tennyson Smith
J. Opt. Soc. Am. 57(10) 1207-1210 (1967)

Ellipsometry of Anisotropic Films

D. den Engelsen
J. Opt. Soc. Am. 61(11) 1460-1466 (1971)

References

You do not have subscription access to this journal. Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Cited By

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Figures (9)

You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Tables (5)

You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Equations (37)

You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription