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

This paper describes the fabrication and characterization of photopolymerizable alkylphosphonate self-assembled monolayers (SAMs) on group-III nitride substrates including GaN and Al x Ga1−x N (AlGaN; x = 0.2 and 0.25). Contact angle goniometry, visible absorption spectroscopy, and atomic force micr...

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Bibliographic Details
Published in:Langmuir 2010-07, Vol.26 (13), p.10725-10730
Main Authors: Li, Feng, Shishkin, Evgeniy, Mastro, Michael A, Hite, Jennifer K, Eddy, Charles R, Edgar, J. H, Ito, Takashi
Format: Article
Language:English
Subjects:
Chemistry
Exact sciences and technology
General and physical chemistry
Interfaces: Adsorption, Reactions, Films, Forces
Solid-liquid interface
Surface physical chemistry
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Summary:This paper describes the fabrication and characterization of photopolymerizable alkylphosphonate self-assembled monolayers (SAMs) on group-III nitride substrates including GaN and Al x Ga1−x N (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) m PO(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.
ISSN:0743-7463
1520-5827
DOI:10.1021/la100273q