Characterization of copper ion sensing thiacalix[4]arene films evaporated on semiconductor substrates

Thermal evaporation under vacuum of thin thiacalix[4]arene on electrolyte-insulator-semiconductor (EIS)- and ion-sensitive-field-effect-transistor (ISFET)-based structures allows to obtain sensitive and selective sensors for copper metal ions. The sensitivity of such devices, varying from a Nernstian response (30 mV/decade) to about 18 mV/decade was strongly dependent upon the film thickness. Such a film thickness influence onto the sensors behaviour was correlated to the morphology and the composition of the thiacalix[4]arene layer investigated using atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS) and diffraction of X-ray techniques. Furthermore, the complexation of copper ions by the thiacalix[4]ane layer, reported by electrochemical measurements, has been confirmed by Rutherford backscattering spectroscopy (RBS).