Epitaxy and chainlength dependent strain in self-assembled monolayers
- Physics Dept. and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544 (United States)
- Exxon Corporate Research, Annandale, New Jersey 08801 (United States)
We use grazing incidence x-ray diffraction to systematically study the structure of an archetypal self-assembled monolayer as a function of the hydrocarbon chain length, n. The monolayers consists of n-alkyl thiol molecules, CH{sub 3}(CH{sub 2}){sub n{minus}1}SH (C{sub n}, 10{le}n{le}30), self-assembled on single crystal Au(111) surfaces. At room temperature, the 2D structure is described by a C(4{times}2) unit mesh for all chain lengths. However, we demonstrate that there is a systematic dependence of the tilt structure (i.e., the tilt angle and tilt direction) of the hydrocarbon chains as a function of the chain length. Furthermore, we show that the monolayer structures are characterized by distinct {open_quotes}long{close_quote}{close_quote} (n{ge}16) and {open_quotes}short{close_quote}{close_quote} (n{le}14) chain length regimes, as well as a smooth variation of the structural parameters within each regime. We associate these systematic structural changes with the conflicting requirements of epitaxy and molecular packing, and argue that the driving force is the changing intra-layer interaction strength (which is proportional to hydrocarbon chain length). We believe that these phenomena should be characteristic of the behavior of self-assembled monolayers, as well as the more general class of {open_quotes}soft/hard{close_quote}{close_quote} interfaces. {copyright} {ital 1997 American Institute of Physics.}
- Research Organization:
- Brookhaven National Laboratory
- DOE Contract Number:
- AC02-76CH00016; FG02-93ER45503
- OSTI ID:
- 435136
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 4 Vol. 106; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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