Dongxia Shi †, Wei Ji †, Bing Yang †, Huanyao Cun †, Shixuan Du †, Lifeng Chi ‡, Harald Fuchs ‡, Werner A. Hofer § and Hong-Jun Gao
† Institute of Physics, Chinese Academy of Sciences.
‡ Physics Institute and Center for Nanotehnology (CeNTech), University Muenster.
§ Surface Science Research Centre, The University of Liverpool
DOI:10.1021/jp902416r Publication Date: 17 Sep 2009
By precise control of substrate temperature, two kinds of structures (structure I and structure II) of coronene on Ag(110) are alternatingly observed by in situ molecular beam epitaxy−low energy electron diffraction. This series of alternating structural transition is confirmed by scanning tunneling microscopy images and density functional theory calculations. As the substrate temperature increases after the molecular monolayer growth at 250 K, the first transition from structure I to structure II occurs around 335 K, which is due to the different vibrational contributions of structures I and II to their free energy. The second transition from structure II to structure I around 367 K is due to the molecule−molecule repulsion, at that temperature the molecular island dissociation and the molecular desorption are dramatically activated and thus the molecule−molecule interaction becomes the dominant effect to the molecular structure. Comprehension of the underlying physics processes behind this alternating structural transition helps establish an understanding of the structural evolution and thermal stability of functional molecular thin films.