One-dimensional atomic chains on Au/Si(557) feature two proximal 1D bands near the Fermi level, which were controversially attributed as a spinon-holon pair of a Luttinger liquid. Angle-resolved photoemission shows that only one band is metallic with the neighboring one gapped at room temperature. Furthermore, even the metallic branch is found to undergo a metal-insulator transition upon cooling, which follows a mean-field-type behavior. Scanning tunneling microscopy observes two apparently unequivocal chains on the surface, one of which exhibits periodicity doubling accompanying the metal-insulator transition. The surface 1D structure is thus concluded to be insulating at low temperature with a Peierls-type instability.

The controlled manipulation of silicon at the nanometer scale will facilitate the fabrication of new types of electronic devices. The scanning tunneling microscope (STM) can be used to manipulate strongly bound silicon atoms or clusters at room temperature. Specifically, by using a combination of electrostatic and chemical forces, surface atoms can be removed and deposited on the STM tip. The tip can then move to a predetermined surface site, and the atom or cluster can be redeposited. The magnitude of such forces and the amount of material removed can be controlled by applying voltage pulses at different tip-surface separations.

Adsorption of B induces a (VJxV3)/£30° reconstruction on Si(lll). By combining scanningtunneling-microscope topographs and spectra with first-principles calculations we are able to follow the different stages of B incorporation in the Si surface and the corresponding changes to the surface electronic states. We find that the thermodynamically stable configuration consists of a B substitutional atom directly below a Si adatom at a T* site. The stability of this configuration is due to the relief of subsurface strain by the short B-Si bonds and the passivation of the surface obtained through charge transfer from the Si adatom to the substitutional B.

Negative differential resistance (NDR) is the essential property that allows fast switching in certain types of electronic devices. With scanning tunneling microscopy (STM) and scanning tunneling spectroscopy, it is shown that the current-voltage characteristics of a diode configuration consisting of an STM tip over specific sites of a boron-exposed silicon(111) surface exhibit NDR. These NDR-active sites are of atomic dimensions ( approximately 1 nanometer). NDR in this case is the result of tunneling through localized, atomic-like states. Thus, desirable device characteristics can be obtained even on the atomic scale.

Scanning tunneling microscope (STM)-induced selective bond breaking in individual molecules and conventional STM imaging are combined to determine the nature of chemisorbed O 2 species formed during the initial stages of silicon (111)-(7×7) oxidation. A selective atomic-scale modification mechanism that involves dissociative electron attachment of tip-emitted electrons to empty adsorbate orbitals is introduced. Two molecular species were found: one involves O 2 bonded to an already oxidized silicon adatom, and the other involves an O 2 molecule that is bonded to a second-layer rest atom and interacting with two silicon adatoms.