Photopolymerization of Self-Assembled Monolayers of Diacetylenic Alkylphosphonic Acids on Group-III Nitride Substrates

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• 作者：Feng Li ; Evgeniy Shishkin ; Michael A. Mastro ; Jennifer K. Hite ; Charles R. Eddy ; Jr. ; J. H. Edgar ; Takashi Ito
• 刊名：Langmuir
• 出版年：2010
• 出版时间：July 6, 2010
• 年：2010
• 卷：26
• 期：13
• 页码：10725-10730
• 全文大小：805K
• 年卷期：v.26,no.13(July 6, 2010)
• ISSN：1520-5827

文摘

This paper describes the fabrication and characterization of photopolymerizable alkylphosphonate self-assembled monolayers (SAMs) on group-III nitride substrates including GaN and Al_xGa_1−xN (AlGaN; x = 0.2 and 0.25). Contact angle goniometry, visible absorption spectroscopy, and atomic force microscopy were used to assess the formation, desorption, and photopolymerization of SAMs of diacetylenic alkylphosphonic acids (CH₃(CH₂)_n−C≡C−C≡C−(CH₂)_mPO(OH)₂; (m, n) = (3, 11), (6, 8), and (9, 5)). As with GaN substrates (Ito, T.; Forman, S. M.; Cao, C.; Li, F.; Eddy, C. R., Jr.; Mastro, M. A.; Holm, R. T.; Henry, R. L.; Hohn, K.; Edgar, J. H. Langmuir 2008, 24, 6630−6635), alkylphosphonic acids formed SAMs on UV/O₃-treated AlGaN substrates from their toluene solutions in contrast to other primary substituted hydrocarbons with a terminal −COOH, −NH₂, −OH, or −SH group. Diacetylenic alkylphosphonate SAMs on group-III nitrides could be polymerized by UV irradiation (254 nm), as indicated by the appearance of a visible absorption band around 640 nm and also by their significantly reduced desorption from the surface in a 0.1 M aqueous NaOH solution. A longer UV irradiation time was required to maximize the photopolymerization of a SAM having a diacetylene group close to the terminal phosphonate moiety, probably because of the hindrance of the topochemical polymerization due to the limited flexibility of the cross-linking moieties on an atomically rough substrate surface.