Fully reversible bias induced phase transition at the solid-liquid interface

FERNANDO P. COMETTO; GUSTAVO RUANO; KLAUS KERN; MAGALÍ A. LINGENFELDER

Antalya

Conferencia; 30th European Conference On Surface Science ECCOS; 2014

In this work we pursued the development of robust networks for catalysis and for host-guest applications. Structures such as metal-organic coordination networks produced in vacuum [1] as well as in the solid liquid interface [2,3] are suitable for this purpose and have been extensively studied using mainly STM. In this work we report a bias induced phase transformation in the solid-liquid interface for the system benzene tribenzoic acid (BTB) in n-nonanoic acid (NA) on HOPG. BTB solutions on HOPG constitute interesting transitioning system with temperature [6] and the nature of the solvent [1]. Additionaly some bias dependent phase transition have been observed in systems with permanent molecular dipoles [4] or allowing the adsorption/desorption of an ionic specie [5]. Given that the BTB/NA on HOPG system does not present permanently charged species the understanding of the phase transition results challenging. To explain the phase transition of the system we studied the thermodynamic stability of each phase exploring the Gibbs energy landscape applying quasi-adiabatic perturbations in the form of bias pulses. In this way we found out that there is a thermodynamically stable phase and a kinetically trapped one. For low concentrations of BTB (in which the energy of the electric field controls the electrochemical potential of the specie in the solution) a reversible transition between the phases is achieved by changing the bias. In an effort to provide some insight on the intrinsic mechanism linking the bias to the electrochemical potential of the solute we performed partial substitutions introducing non polar species as solute (4,4?-bis(4-pyridyl)-terphenyl Pyridine) as well as solvent(phenyl octane). [1] M. Lackinger, M. Heckl Langmuir 25 (19), 11307-11321 (2009) [2] S. Stephanow et al. Nature Materials 3, 229 - 233 (2004)