Competition as a design concept: Polymorphism in Self-Assembled Monolayers of Biphenyl-Based Thiols
- chair: Cyganik, P. / Buck, M. / Strunskus, T. / Shaporenko, A. / Wilton-Ely, J. D. E. T. / Zharnikov, M /. Wöll, Ch. (2006)
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place:
JACS, 128 (2006), 13868
- Date: 2006
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Cyganik, P. / Buck, M. / Strunskus, T. / Shaporenko, A. / Wilton-Ely, J. D. E. T. / Zharnikov, M /. Wöll, Ch. (2006): „Competition as a design concept: Polymorphism in Self-Assembled Monolayers of Biphenyl-Based Thiols“. In: JACS, 128 (2006), 13868
Abstract
Self-assembled monolayers (SAMs) of two ω-(4‘-methylbiphenyl-4-yl)alkanethiols (CH3(C6H4)2(CH2)nSH, BPn, n = 4, 6) on Au(111) substrates, prepared from solution at room temperature and subsequently annealed at temperatures up to 493 K under a nitrogen atmosphere, were studied using scanning tunneling microscopy (STM), high-resolution X-ray photoelectron spectroscopy (HRXPS), and near-edge X-ray absorption fine structure spectroscopy (NEXAFS).
In striking contrast to BPn SAMs with n = odd, for which only one phase is observed, the even-numbered BPn SAMs exhibit polymorphism. Irreversible phase transitions occur which involve three phases differing substantially in density and stability. Upon annealing, BP4 and BP6 transform into a β-phase, which is characterized by an exceptionally high structural quality with virtually defect-free domains exceeding 500 nm in diameter.
Exchange experiments, monitored by contact angle measurement, reveal that the β-phase exhibits a dramatically improved stability. The fundamental differences in the phase behavior of even- and odd-numbered BPn SAMs are discussed in terms of two design strategies based on cooperative and competitive effects.
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In striking contrast to BPn SAMs with n = odd, for which only one phase is observed, the even-numbered BPn SAMs exhibit polymorphism. Irreversible phase transitions occur which involve three phases differing substantially in density and stability. Upon annealing, BP4 and BP6 transform into a β-phase, which is characterized by an exceptionally high structural quality with virtually defect-free domains exceeding 500 nm in diameter.
Exchange experiments, monitored by contact angle measurement, reveal that the β-phase exhibits a dramatically improved stability. The fundamental differences in the phase behavior of even- and odd-numbered BPn SAMs are discussed in terms of two design strategies based on cooperative and competitive effects.
Download [PDF]