The constant height and constant current Scanning Tunneling Microscopy(STM) images of W, Mo, Pt and Pd tips were simulated respectively by the method of exciton dynamics. The results show that, for the constant current STM images, the spacial resolution is independent of the types of the tips' materials; but for the constant height STM images, the spacial resolution of the current densities is strongly dependent on the types of the tips' materials. The spacial resolution of the current density of the Pd tip is better than that of W and Mo tips, and the spacial resolution of the current density...
