Local thickness determination of thin insulator films via localized states

We propose measuring the lifetime of localized states below the conduction band to determine the local thickness of thin insulating films using scanning tunneling microscopy. The lifetime, which is a characteristic fingerprint of the film thickness, is inversely proportional to the saturation value of the tunnel current through the localized state at close tip-sample separation and is readily measured using scanning tunneling spectroscopy. We demonstrate the method for 5-11 monolayer thick NaCl films grown on Cu(111). © 2014 AIP Publishing LLC.