Phosphonic acid derivatives are used for surface modification on oxidized metals such as Al2O31), TiO22), ZrO23), SiO24), Mica5), stainless(SS316L) 6), nitinol7), hydroxyapatite8), AgO9), ZnO10), ITO11,12).
For a long time, organosilanes have been used to form self assembled monolayer (SAM) on the metal oxide. However, it is not always adaptable in the applications due to the poor stability and polymerization of the reagent with each other. On the other hand, phosphonic acid derivatives equally form a SAM on the metal oxide despite being very stable compounds. Also, phosphonic acid derivatives have been reported to use formation of more stable and dense SAM than organosilanes. Klauk et. al. and Sekitani et. al. show alkyl phosphonate SAM on Al2O3 is more useful than the trichlorosilane derivatives SAM as an conductor film of an organic transistor13).
Sharma et. al. have reported the work function of ITO substrate increases by the oxygen plasma treatment or modifying ITO substrate with phosphonic acid (FOPA) containing perfluoroalkyl group. However, the increased level of work function maintains with FOPA modified substrate for 246 hours, while the work function immediately decreases with the substrate treated by oxygen plasma11). In addition, the organic thin-film solar cell fabricated using the modified TO with FOPA increase the stability of light intensity, the driving voltage, and life time.
There are three perfluoro based phosphonic acids available with different alkyl lengths.
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8) S. C. D’Andrea and Al. Y. Fadeev, “Covalent surface modification of calcium hydroxyapatite using n-alkyl- and n-fluoroalkylphosphonic acids EB>, Langmuir, 2003, 19, 7904.
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10) B. Zhang, T. Kong, W. Xu, R. Su, Y. Gao and G. Cheng, “Surface functionalization of zinc oxide by carboxyalkylphosphonic acid self-assembled monolayers E Langmuir, 2010, 26(6), 4514.
11) A. Sharma, B. Kippelen, P. J. Hotchkiss and S. R. Marder, “Stabilization of the work function of indium tin oxide using organic surface modifiers in organic light-emitting diodes E Appl. Phys. Lett., 2008, 93, 163308.
12) A. Pulsipher, N. P. Westcott, W. Luo, and M. N. Yousaf, “Rapid in situ generation of two patterned chemoselective surface chemistries from a single hydroxy-terminated surface using controlled microfluidic oxidation E J. Am. Chem. Soc., 2009, 131(22), 7626
13) a) H. Klauk, U. Zschieschang, J. Pflaum, M. Halik, E/SPAN>Ultralow-power organic complementary circuits E Nature, 2007, 445, 745. b) T. Sekitani, Y. Noguchi, U. Zschieschang, H. Klauk, T. Someya, “Organic transistors manufactured using inkjet technology with subfemtoliter accuracy E Proc. Natl. Acad. Sci. USA, 2008, 105, 4976