TIP-INDUCED DISPLACEMENT AND IMAGING OF A MULTILAYERED BACTERIAL STRUCTURE BY SCANNING-TUNNELING-MICROSCOPY

A multilayered disk-shaped structure which separates and partitions th e cells of the archaeon Methanospirillum hungatei into individual comp artments (i.e., the spacer plug) was isolated, dried onto a graphite s urface and prepared for routine scanning tunneling microscopy imaging (tunneling conditons of 1 V or less and less than 1 nA current) with a conventional platinum-iridium (Pt-Ir) conductive overlay. During repe ated scans of a single whole plug, the uppermost layer with its Pt-Ir coating was entirely removed by tip displacement exposing the uncoated underlying layer to tip contact. Surprisingly, the signals generated over the uncoated surface remained extremely stable allowing the resol ution of molecular details of a hexagonally arrayed layer that were co mparable to those obtained by transmission electron microscopy.