Calix[4]arene sensitive thin films for detecting sodium. Surface studies

In this work, we present experimental results about electrolyte-insulator-semiconductor (EIS)-type sensors based on evaporated p-ter-butylcalix[4]arene sensitive thin films devoted to sodium detection. Several calixarene films of different thicknesses (10-1000 nm) were studied and a significant decay of their detection ability was pointed out for thick samples. To investigate the presence of sodium encaged in the sensitive receptors, during the contact with the electrolyte, two surface analytical methods were used, namely, Rutherford backscattering spectroscopy (RBS) and low energy electron induced X-ray spectrometry (LEEIXS). Both methods show that sodium is incorporated within the membrane and that its surface concentration decreases as the calixarene film thickness increases, due to the growth of microcrystallites in the thickest films as pointed out by atomic force microscopy (AFM) observations. (C) 2000 Elsevier Science B.V. All rights reserved.