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Structural Phases and Phase Transitions of Alkanethiol Monolayers on Au (111)



G Poirier


Using ultrahigh vacuum scanning tunneling microscopy, we have characterized assembly of decanethiol monolayers on Au(111). Our results show that the monolayer adopts six discrete structural phases during assembly. At low surface coverage, alkanethiols exist as a lattice gas. Above a critical surface coverage, the molecules condense into islands of a commensurate crystalline lattice; these islands grow in equilibrium with the lattice gas until saturation. Above saturation, the surface sequentially undergoes two first-order phase transitions to higher density phases. These first three solid phases are characterized by alignment of the molecular axes with the surface plane but with discretely increasing degrees of out-of-plane interdigitation. Above saturation coverage of the densest surface-aligned phase, the monolayer undergoes an edge-mediated melting trating transition. This fluid is not an equilibrium phase, rather, it is a supercooled 2-dimensional liquid. The densest phase, characterized by surface-normal-aligned molecular axes, grows by homogeneous nucleation from the supercooled melt. These results highlight the importance of interface energy and molecular degrees-of-freedom on the process of molecular self-assembly.
Science Journal


2-dimentional liquid, alkanethiol, growth, monolayer, nucleation, phase transitions, self-assembly, tunneling microscopy


Poirier, G. (2008), Structural Phases and Phase Transitions of Alkanethiol Monolayers on Au (111), Science Journal (Accessed April 22, 2024)
Created October 16, 2008