Room temperature conductance switching in a molecular iron(iii) spin crossover junction

Abstract

Molecular junctions are important because their operating mechanisms are complementary to semiconductor based technologies potentially enabling new technologies. In this context, it is important to develop molecular switches operating at room temperature that do not suffer from stochastic effects. Spin crossover (SCO) molecules are promising candidates to develop stable electrical switches, but so far it has been challenging to assemble molecular devices with robust SCO functionality due to the lack of control over the molecule¿electrode coupling strength diminishing the SCO functionality. This paper reports molecular tunnel junctions with SCO molecules, [FeIII(qsal-I)2]NTf2 (qsal-I = 4-iodo-2-[(8-quinolylimino)methyl]phenolate) adsorbed on graphene surfaces via physisorption with room temperature conductance switching of one order of magnitude associated with the high and low spin states of the SCO complex. Normalized conductance analysis of the current-voltage characteristics as a function of temperature reveals that the mechanism of charge transport across the SCO molecule is dominated by coherent tunneling. Temperature-dependent X-ray absorption spectroscopy and density functional theory confirm the SCO complex retains its SCO functionality on the surface implying that physisorbed molecule¿electrode contacts provide a good trade-off between junction stability while retaining SCO switching capability. These results could open the door to design other types of molecular devices based on SCO compounds.