Visualization of nucleation and growth of molecular networks by LEEM and microLEED: BDA/Cu(001)

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Date/Time:Friday, 26 Oct 2012 - Sunday, 28 Oct 2012
Location:Room 19 PHYSICS HALL
Phone:515-294-5630
Channel:Condensed Matter Physics
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Prof. Bene Poelsema
University of Twente

We have studied the growth of 4,4’-biphenyldicarboxylic acid (BDA) molecular networks on Cu(001) using Low Energy Electron Microscopy, LEEM. LEEM is the method of choice since it provides microscopic information on the density in the 2D dilute phase, by making use of diffuse scattering of probing electrons, and simultaneously on the 2D structure, using selected area diffraction (µLEED). This combined ability allows to extract the 2D gas-solid coexistence line from the shape of which one can derive the 2D cohesive energy of the BDA molecules in their characteristic c(8x8) structure. The latter is governed by H-bonds between, respectively, the carboxylate group and the phenyl rings of adjacent molecules. The real time microscopic information also allows to monitor in-situ fluctuations of near-critical nuclei. Whilst these fluctuations are larger than predicted, the measured critical nucleus size compares well with that derived from accepted nucleation theory, on the basis of the measured super-saturation and line tension of BDA c(8x8). Finally, I will discuss growth anomalies occurring at relatively high temperature. We have detected a novel Mullins-Sekerka type growth instability, as well as reentrant (periodic) nucleation. These features are believed to be of general importance for the growth of molecular films, provided preexisting substrate steps are permeable for diffusing molecules and the growth of crystalline molecular networks terminates at these steps.



**Prof. Bene Poelsema is a well-known expert in several areas in surface science. He has pioneering work in epitaxial growth and growth manipulation using several state of the art techniques ( He scattering, Scanning Tunneling Microscopy, Low Energy Electron Microscopy, He ion microscopy). He has held previous appointment as a staff scientist in Julich research center Germany and at the University of Twente, Netherlands. His current interests include ultrathin film growth , organic molecule growth, graphene, colloids, etc.