ABSTRACT
Ionic liquids have recently been used as means of modulating the charge carrier properties of cuprates. The mechanism behind it, however, is still a matter of debate. In this paper we report experiments on ionic liquid gated ultrathin La2-xSrxCuO4 films. Our results show that the electrostatic part of gating has limited influence in the conductance of the cuprate in the gate voltage range of 0 to - 2 V. A non-electrostatic mechanism takes over for gate voltages below - 2 V. This mechanism most likely changes the oxygen concentration of the film. The results presented are in line with previous X-ray based studies on ionic liquid gating induced oxygenation of the cuprate materials YBa2Cu3O7-x and La2-xSrxCuO4.
Subject(s)
Ionic Liquids/chemistry , Copper/chemistry , Electric Conductivity , Lanthanum/chemistry , Oxides/chemistry , Oxygen/chemistry , Static Electricity , Strontium/chemistryABSTRACT
Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are performed on heptathioether ß-cyclodextrin (ß-CD) self-assembled monolayers (SAMs) on Au. The ß-CD molecules exhibit very rich dynamical behavior, which is not apparent in ensemble-averaged studies. The dynamics are reflected in the tunneling current-time traces, which are recorded with the STM feedback loop disabled. The dynamics are temperature independent, but increase with increasing tunneling current and sample bias, thus indicating that the conformational changes of the ß-CD molecules are induced by electrons that tunnel inelastically. Even for sample biases as low as 10 mV, well-defined levels are observed in the tunneling current-time traces. These jumps are attributed to the excitations of the molecular vibration of the macrocyclic ß-CD molecule. The results are of great importance for a proper understanding of transport measurements in SAMs.
