Solving a Long-Standing Problem Regarding Atomic Structure of Si(100)2×3-Ag.

The atomic structure of the Si(100)2×3-Ag reconstruction has remained unknown for more than 25 years since its first observation with scanning tunneling microscopy, despite a relatively small unit cell and seeming abundance of the available experimental data. We propose a structural model of the Si(100)3×2-Ag reconstruction which comfortably fits all the principal experimental findings, including our own and those reported in the literature. The model incorporates 3 Si atoms and 4 Ag atoms per the 2 × 3 unit cell forming linear atomic chains along the 3aSi-periodic direction. A peculiar feature of the Si(100)2×3-Ag structure is the occurrence of the inner Si dimers in the second atomic layer from the top of the Si(100) substrate. The reconstruction is proved to possess semiconducting properties.

Synthesis of two-dimensional Tl(x)Bi(1-x) compounds and Archimedean encoding of their atomic structure.

Crystalline atomic layers on solid surfaces are composed of a single building block, unit cell, that is copied and stacked together to form the entire two-dimensional crystal structure. However, it appears that this is not an unique possibility. We report here on synthesis and characterization of the one-atomic-layer-thick Tl(x)Bi(1-x) compounds which display quite a different arrangement. It represents a quasi-periodic tiling structures that are built by a set of tiling elements as building blocks. Though the layer is lacking strict periodicity, it shows up as an ideally-packed tiling of basic elements without any skips or halting. The two-dimensional Tl(x)Bi(1-x) compounds were formed by depositing Bi onto the Tl-covered Si(111) surface where Bi atoms substitute appropriate amount of Tl atoms. Atomic structure of each tiling element as well as arrangement of Tl(x)Bi(1-x) compounds were established in a detail. Electronic properties and spin texture of the selected compounds having periodic structures were characterized. The shown example demonstrates possibility for the formation of the exotic low-dimensional materials via unusual growth mechanisms.

Self-assembly of conductive Cu nanowires on Si(111)'5 × 5 '-Cu surface.

Upon room-temperature deposition onto a Cu/Si(111)'5 × 5' surface in ultra-high vacuum, Cu atoms migrate over extended distances to become trapped at the step edges, where they form Cu nanowires (NWs). The formed NWs are 20-80 nm wide, 1-3 nm high and characterized by a resistivity of ∼8 µΩ cm. The surface conductance of the NW array is anisotropic, with the conductivity along the NWs being about three times greater than that in the perpendicular direction. Using a similar growth technique, not only the straight NWs but also other types of NW-based structures (e.g. nanorings) can be fabricated.