Sounds of Atoms

Abstract

Early in setting up our nanoscience laboratory at Penn State, we were frustrated because we could not peer into the tunneling junctions of our scanning tunneling microscopes (STMs) to see what the atoms were doing. We were particularly vexed when singular events, such as an atom moving on the end of the STM probe tip, confounded our data and forced us to start over. Such an event was very difficult to identify; it would be just a blip in a recorded image or a flash on an oscilloscope, and it would not be recognizable at all in the frequency spectrum of noise monitored on our spectrum analyzer. ![Figure][1] CREDIT: PETER HOEY The solution to our problem was right there in the mirror every morning but had nothing to do with sight. Humans can hear a wide dynamic range and have a fantastic ability to recognize patterns in sounds. Borrowing a trick from electrophysiology, we sent the tunneling current of our microscopes into an audio amplifier and then turned our probe tip height into a tune by applying that signal to a voltage-controlled oscillator. One stereo channel corresponds to tunneling current and the other to STM tip height. This way, we could hear when imaging was proceeding well and when something was amiss. We applied this approach to every aspect of our microscopy and spectroscopy. The dreaded sound of an atom moving on the tip of a low-temperature STM has a characteristic rising “whoook” that is unmistakable (and sometimes heartbreaking). Every student, postdoc, and visitor in the group became familiar with the songs of his or her microscope—they learned which tune meant which problem and always rejoiced when they heard the best melody of all: the sound of a happily working microscope. Such ideas were also developed independently at the IBM Zurich and IBM Almaden Laboratories, and elsewhere. If you would like to hear some of the sounds of our microscopes and of imaging molecules, please listen to the media files in the supporting online material ([1][2]). 1. 1.[↵][3]Some of the sounds of our microscopes, recorded by P. Han, A. Kurland, and P. S. Weiss of Penn State, are available as supporting material on Science Online ( ). 2. 2.Our original work was supported by the National Science Foundation, the Office of Naval Research, the Petroleum Research Fund administered by the American Chemical Society, and G. Marcotrigiano of Gary's Electronics. [1]: pending:yes [2]: #ref-1 [3]: #xref-ref-1-1 View reference 1. in text