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

In this work, we present experimental results about electrolyte-insulator-s emiconductor (EIS)-type sensors based on evaporated p-tert-butylcalix[4]are ne sensitive thin films devoted to sodium detection. Several calixarene fil ms of different thicknesses (10-1000 nm) were studied and a significant dec ay of their detection ability was pointed out for thick samples. To investigate the presence of sodium encaged in the sensitive receptors, d uring the contact with the electrolyte, two surface analytical methods were used, namely, Rutherford backscattering spectroscopy (RBS) sind low energy electron induced X-ray spectrometry (LEEIXS). Both methods show that sodiu m is incorporated within the membrane and that its surface concentration de creases as the calixarene film thickness increases, due to the growth of mi crocrystallites in the thickest films as pointed out by atomic force micros copy (AFM) observations. (C) 2000 Elsevier Science B.V. All rights reserved .