Number 42 (Story #4), July 24, 1991 by Phillip F. Schewe and Ben Stein SILICON ATOMS, DESPITE THEIR TIGHT COVALENT BONDS , can now be manipulated with scanning tunneling microscopes. In a mechanism known as field evaporation, silicon ions rise up to the STM's tip as a result of both the strong electric fields set up by the STM and the chemical interactions between the tip and the sample. In-Whan Lyo and Phaedon Avouris of IBM report that at longer tip-sample distances a mound of atoms forms a bridge between the silicon surface and the STM tip; clusters of atoms can then be removed, leaving behind a gaping hole. At shorter tip-sample distances, individual atoms can be removed, but with less reproducible results. By reversing the polarity of the voltage, the atoms can be re-deposited anywhere on the silicon surface. This new process promises many applications, including the fabrication of new semiconductors and the creation of locally-doped silicon materials. (Science, 12 July 1991.)