DIGITAL-FILTERS TO RESTORE INFORMATION FROM FAST SCANNING TUNNELING MICROSCOPY IMAGES

A transfer function-similar to that used in optical cases to correct blurring effects due to the circular aperture of the system-is presented here to restore scanning tunnelling microscopy (STM) images. Due to the conical geometry of the tip-sample system, we have established an analogy between the process of image formation in STM and in optical systems. The transfer function utilized, similar to that calculated by Stokseth, allows us to differentiate between the blurring effects introduced along the x and y axes. These effects are different due, mainly, to the different velocities achieved along the x and y directions. Furthermore we have measured the beta parameter that characterizes the classical 1/f-beta noise present in STM data, demonstrating its independence from experimental conditions. A Wiener filter is utilized to restore the images using the previous assumptions given for the transfer function and noise effects.