| Autor: |
Volkmann, U. G., Pino, M., Altamirano, L. A., Taub, H., Hansen, F. Y. |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 2/1/2002, Vol. 116 Issue 5, p2107, 9p, 1 Black and White Photograph, 4 Graphs |
| Abstrakt: |
Using high-resolution ellipsometry and stray light intensity measurements, we have investigated during successive heating-cooling cycles the optical thickness and surface roughness of thin dotriacontane (n-C[sub 32]H[sub 66]) films adsorbed from a heptane (n-C[sub 7]H[sub 16]) solution onto SiO[sub 2]-coated Si(100) single-crystal substrates. Our results suggest a model of a solid dotriacontane film that has a phase closest to the SiO[sub 2] surface in which the long-axis of the molecules is oriented parallel to the interface. Above this “parallel film” phase, a solid monolayer adsorbs in which the molecules are oriented perpendicular to the interface. At still higher coverages and at temperatures below the bulk melting point at T[sub b]=341 K, solid bulk particles coexist on top of the “perpendicular film.” For higher temperatures in the range T[sub b]T[sub s], a uniformly thick fluid film wets to the parallel film phase. This structure of the alkane/SiO[sub 2] interfacial region differs qualitatively from that which occurs in the surface freezing effect at the bulk alkane fluid/vapor interface. In that case, there is again a perpendicular film phase adjacent to the air interface but no parallel film phase intervenes between it and the bulk alkane fluid. Similarities and differences between our model of the alkane/SiO[sub 2] interface and one proposed recently will be discussed. Our ellipsometric measurements also show evidence of a crystalline-to-plastic transition in the perpendicular film phase similar to that occurring in the solid bulk particles present at higher coverages. In addition, we have performed high-resolution ellipsometry and stray-light measurements on dotriacontane films deposited from solution onto highly oriented pyrolytic graphite substrates. After film deposition, these... [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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