DETAILED EXPERIMENTAL INVESTIGATION OF THE BARRIER-HEIGHT LOWERING AND THE TIP-SAMPLE FORCE GRADIENT DURING STM OPERATION IN AIR

Using a combined scanning-tunnel-microscopy (STM)/atomic-force microscopy (AFM) setup, we have measured simultaneously the apparent barrier height and the tip-sample force gradient for various tip-sample distances of an STM configuration in air. Our results reconfirm the existence of repulsive tip-sample forces during the STM operation with inert metal systems in air. Also, the gradient of such forces is of the correct sign that is necessary to cause the lowering of the apparent barrier heights through elastic deformations. However, our results indicate that the model that is based on the elastic deformation due to the tip-sample forces does not provide a satisfactory explanation of the lowering of the barrier heights for the case of gold in air.