SHALLOW RIPPLES WITH GIANT WAVELENGTHS OBSERVED BY ATOMIC-FORCE MICROSCOPY - REAL EFFECTS AND THE REPORT OF A NEW ARTIFACT

The (210) surface of ammonium perchlorate has been studied with an ato mic force microscope. Unexpected surface ripples with shallow amplitud es (typically less than 3 nm) and giant wavelengths (typically between 0.5 and 1.3 mu m) have been discovered. The dominant type shows a wav e vector along the [001] direction, and a second type forms a pattern in which two wave vectors make an angle of similar to 60 degrees with each other. The amplitude and wavelength of the ripples are clearly co rrelated. Their size depends on the local surface structure, but their direction is usually keyed to the main crystalline directions. Unfort unately we have also discovered a new artifact that can produce simila r images. We discuss the evidence we have gathered thus far to support the existence of the ripples in addition to that of the artifact. (C) 1996 American Vacuum Society.