Simultaneous measurement of tunneling current and force as a function of position through a lipid film on a solid substrate

We present a new method using a simultaneous AFM-STM setup to define the concept of distance as a tunneling tip first approaches and then penetrates an organic film on a solid surface. This provides a method to investigate the imaging of low intrinsic conductivity organic material with an STM. In a lipid film using small tip-to-sample voltages, on the order of 1 V, we find an upper thickness limit for tunneling of 30 Å. However using higher voltages, on the order of 6 V, we measure a current through a lipid thickness of several 100 Å.