A SCANNING TUNNELING MICROSCOPE SUITABLE FOR BIOLOGICAL APPLICATIONS

We have designed and built a scanning tunneling microscope (STM) suita ble for biological applications. A sound-isolated chamber contains the STM unit; the chamber can be evacuated or filled with inert gas, afte r the sample and tip are loaded, in order to reduce contamination on s ample and tip. The STM unit is mounted inside two separable cylindrica l supports. The lower cylinder contains the sample holder mounted on t op of a step-motor controlled x-y-z stage, while the upper one contain s the piezoelectric tip scanner. An I/V converter preamplifier mounted inside the x-y-z stage and a completely digitized feedback circuit, t ogether with a full software package in UNIX X-window environment and data processing, allow fast sample-tip approach and reduced acquisitio n time. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) in air and reproducible large scan on a platinum grating are r outinely obtained. Images of human liver ferritin deposited on an acti vated gold substrate have also been obtained.