Toward Mechanosynthesis of Diamondoid Structures:Simple Strategy of Building Atomically Perfect SPM Tip Through Attachment of C_(60) Molecule to Commercial Silicon Tip by Controlled Hydrogen Atom Desorption from Tip Asperity Si(111) Silicon Surface

摘要

Tip manufacturers offer micro-fabricated silicon tips in three geometries, i.e., pyramidal, tetrahedral and conical. Conical tips can be made sharp, with high aspect ratios and radii as small as 50 A. Pyramidal tips have lower aspect ratios and nominal tip radii of a few hundred angstroms, but they are more durable. However, even commercial conical tip manufacturers supply the tip structure only at the micrometer scale, and there is no direct method for imaging the very end of the tip, i.e., the "nano-tip." In this paper a very simple strategy of building atomically defined asperity on Si(111) surface of the commercial silicon tip is described. The strategy consists of four simple steps. In the first step, the silicon tip is irradiated with ultraviolet light in the atmosphere of oxygen to remove carbon contaminants. During the second step, a thermally oxidized SiO_2 layer is eliminated by HF etching to sharpen the tip apex and hydrogenation of its surface. In the third step, controlled electron-stimulated desorption of hydrogen from the tip asperity surface is applied. Finally, in the step four, the C_(60) molecule docking to surface dangling bonds is performed. In the final part of this work PM6 modeling was used to show positional mechano-synthetic capabilities of the described SPM tip.