Tracer diffusion in ordered lattice-gas systems with defect-controlled transport mechanisms
Tracer diffusion in an ordered two-dimensional lattice-gas system with square lattice symmetry is studied theoretically and by means of computer simulations. It is well known that the ordering with c 2 2 symmetry formed in the vicinity of half-filling of lattice sites is due to strong nearest neighbor repulsive interaction. In this case, the tracer migration occurs mainly by elementary displacements of structural defects. This paper focuses on the dimer transport mechanism which was accounted for with insufficient accuracy in previous publications. The long-time asymptotics of the dimer-tracer correlation function i.e., a three-particle correlation function , which describes concerted tracer-dimer motion, is obtained analytically. We analyze a specific exchange mechanism, relevant to tracer diffusion only. Also, the contribution of generation-recombination jumps to tracer diffusion is taken into account. The theoretical data agree well with the results of intensive Monte Carlo simulations.
Accelerator Surface Phase Associated with Superconformal Cu Electrodeposition
Superconformal film growth is a key process in state-of-the-art Cu metallization of electronic devices. Superfilling of recessed surface features results from the competition between electrolyte additives that accelerate or inhibit Cu electroplating. In situ scanning tunneling microscopy is used to image the accelerating bis-(3-sodiumsulfopropyl disulfide) (SPS)-Cl- surfactant phase that is responsible for disrupting and preventing the formation of the inhibiting poly(ethylene glycol)-Cl- layer. Various aspects of competitive and coadsorption of Cl- and SPS on Cu(100) were examined for industrially relevant additive concentrations. At potentials associated with superfilling, a saturated, c(2 × 2) Cl - ordered adlayer forms on the surface. When as-received SPS is added, individual SPS and (3-mercaptopropyl)sulfonate (MPS) molecules are imaged as a mobile two-dimensional gas diffusing on the Cl- adlattice. The SPS-Cl - surfactant accounts for many aspects of the additive function previously observed and stipulated by the curvature enhanced accelerator model of superconformal film growth. SPS-derived species of differing mobility and tunneling contrast appear with exposure time. The lattice gas species are sensitive to the imaging conditions with tip-molecule interactions particularly evident at higher tunneling currents. At negative potentials, the c(2 × 2) Cl - adlayer is disrupted by an order-disorder transition, followed by desorption at more negative potentials. This allows direct access of SPS to the Cu metal whereupon irreversible sulfide formation occurs.
Determining the Jaw Relationship
Contacts between the upper and lower posterior teeth of complete dentures take place during the opening and closing strokes of mastication (Brudvik and Howell 1990). These contacts are fast, gliding impacts of the mandibular teeth which contact close to the position of maximal intercuspation of the teeth, called the “intercuspal occlusion”. The intercuspal position is the position adopted by the mandible when the teeth are in intercuspal occlusion.