Temperature Dependent Structural Phase Transition at the Perfluoropentacene/Ag(111) Interface

• Published in: Journal of physical chemistry. C Vol. 116; no. 2; pp. 1904 - 1911
• Main Authors: Marks, Manuel, Schmidt, Christian, Schwalb, Christian H, Breuer, Tobias, Witte, Gregor, Höfer, Ulrich
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 19.01.2012
• Subjects: C: Surfaces, Interfaces, Catalysis; Condensed matter: structure, mechanical and thermal properties; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Physics; Specific phase transitions; Ultrathin films; Photoelectron spectra; Temperature dependence; Crystalline phase; Transition temperature; Multilayer; Weak interactions; Phase transformations; Electron diffraction; Diffraction pattern; Desorption; Coverage rate; Phase transitions; Inclination; Interfaces; Multilayers; Image potential; X-ray absorption spectra; Photoemission; Monolayers; LEED; Two-photon processes; Quantitative chemical analysis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp2094577

Monolayers of perfluoropentacene (PFP) on Ag(111) undergo a reversible structural transition from a crystalline (6 × 3) phase at low temperatures to a disordered phase at room temperature. Two-photon photoemission (2PPE) of the low temperature phase revealed a distinct signal of the first image-potential state (n = 1) of Ag(111), thus showing the presence of bare substrate regions between the crystalline PFP islands. At higher temperatures, the entire surface is covered by a disordered phase of diffusing molecules causing a complete suppression of the (n = 1) signal and the electron diffraction (LEED) pattern. X-ray absorption spectroscopy showed that neither a change of the weak chemical interaction nor a change of the molecular tilt angle occurs during this phase-transition. The quantitative analysis of the 2PPE signal and the LEED contrast yields a transition temperature of T C = 145 ± 5 K. The present experiment shows that desorption of excess multilayers leads to an effective coverage of less than a dense monolayer.