The tensile fractures of ultrafine-grained (UFG) Al-Mg alloy with a bimodal grain size were investigated at the micro- and macroscale using transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with focused ion beam (FIB), and optical microscopy. The nanoscale voids and crack behaviors near the tensile fracture surfaces were revealed in various scale ranges and provided the evidence to determine the underlying tensile deformation and fracture mechanisms associated with the bulk bimodal metals. The bimodal grain structures exhibit unusual deformation and fracture mechanisms similar to ductile-phase toughening of brittle materials. The ductile coarse grains in the UFG matrix effectively impede propagation of microcracks, resulting in enhanced ductility and toughness while retaining high strength. In view of the observations collected, we propose a descriptive model for tensile deformation and fracture of bimodal UFG metals.

Self-assembled monolayers (SAMs) of octanethiol and benzeneethanethiol were deposited on clean Pt(111) surfaces in ultrahigh vacuum (UHV). Highly resolved images of these SAMs produced by an in situ scanning tunneling microscope (STM) showed that both systems organize into a super-structure mosaic of domains of locally ordered, closely packed molecules. Analysis of the STM images indicated a (square root 3 x square root 3)R30 degrees unit cell for the octanethiol SAMs and a 4(square root 3 x square root 3)R30 degrees periodicity based on 2 x 2 basic molecular packing for the benzeneethanethiol SAMs under the coverage conditions investigated. SAMs on Pt(111) exhibited differences in molecular packing and a lower density of disordered regions than SAMs on Au(111). Electron transport measurements were performed using scanning tunneling spectroscopy. Benzeneethanethiol/Pt(111) junctions exhibited a higher conductance than octanethiol/Pt(111) junctions.