The image above shows the undulations on a copper surface that was polished with ethanol. Tip bias was -1V (the sample being negative to the tip), and the tunnel current reference was 5nA. The sine wave modulation for the tip bias was switched on during the scan.
The scale indication was first calculated from the piezo characteristics, then confirmed in the Z-direction by counting the number of steps the stepper motor takes to traverse the maximum vertical range covered by the piezo. It is not clearly understood whether the surface is purely copper or rather a thin conductive layer of oxide.
The resolution of the image in the Y direction is half of that in the X direction. The quality of the image suggests that the next version of the scanning algorithm should increase the scan density in the Y direction, even at the expense of shortening the Y distance scanned.