Scanning tunneling microscope tip structures

Studies of electrochemically etched tungsten scanning tunneling microscope tips, using scanning electron microscopy, show that (i) the tips are often convolved or bent if the mass of the tungsten wire submerged in the etchant is large (an effect ascribed to surface plastic flow), (ii) bent tips nevertheless often produce good quality scanning tunneling microscopy images of Au films in air, but (iii) tips, once crashed clumsily into the Au films, no longer produce images.