Effect of Chain Length and Substrate Temperature on the Growth and Morphology of n-Alkane Thin Films

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• 作者：Juxia Fu ; Stephen G. Urquhart
• 刊名：Langmuir
• 出版年：2007
• 出版时间：February 27, 2007
• 年：2007
• 卷：23
• 期：5
• 页码：2615 - 2622
• 全文大小：579K
• 年卷期：v.23,no.5(February 27, 2007)
• ISSN：1520-5827

文摘

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and microscopy has been used to study theorientational morphology of thin films of the linear alkanes n-C₃₆H₇₄ and n-C₆₀H₁₂₂, prepared by vacuum depositiononto NaCl (001) surfaces at ambient and elevated substrate temperatures. The orientational morphology, specifically,the nature of domains with lateral and normal orientation, is explored as a function of the chain length and the substratetemperature. It is found that the longer n-C₆₀H₁₂₂ molecules are laterally oriented on the substrate surface within theinvestigated substrate temperatures but that the morphology of these thin films varies with substrate temperature. Theshorter n-C₃₆H₇₄ molecules are partially laterally oriented at low substrate temperature and are completely normallyoriented at high substrate temperature. The relative magnitude of "side-by-side" and "end-to-end" intermolecularinteractions leads to the formation of highly ordered alkane structures with a high aspect ratio. The formation ofcomplex, nanoscale orientational morphologies are rationalized by considering kinetic and thermodynamic effects,in particular, the relative enthalpic and entropic contributions to the free energy associated with the different molecularorientations.