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Abstract: A comprehensive study on the relationship between yield strength, relative density and ligament sizes is presented for nanoporous Au foams. Depth-sensing nanoindentation tests were performed on nanoporous foams ranging from 20% to 42% relative density with ligament sizes ranging from 10 to 900nm. The Gibson and Ashby yield strength equation for open-cell macrocellular foams is modified in order to incorporate ligament size effects. This study demonstrates that, at the nanoscale, foam strength is governed by ligament size, in addition to relative density. Furthermore, we present the ligament length scale as a new parameter to tailor foam properties and achieve high strength at low densities. [Copyright &y& Elsevier]

Scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) were used to study the interaction of sulfur dioxide with the bulk-terminated (1×1) and the reconstructed (1×2) structure of the TiO2(1 1 0) surface at 300 K. During exposure new features appear first on the added rows of the reconstructed (1×2) surface structure. In general these new features are randomly distributed, i.e., no ordered adsorbate phase builds up. However, in some areas locally ordered linear structures can be observed along the (1×2) rows with a periodicity two or three times higher than the substrate. Similar to these observations, randomly distributed spots also appear on single added rows of the (1×2) surface structure that are located on top of the (1×1) structure of the TiO2(1 1 0) surface. In contrast, additional features on the (1×1) structure itself can be seen only after higher SO2 exposure. Here, an ordered adsorbate phase with a (2×1) structure is formed. The new features of this (2×1) structure are located on top of the (1×1) rows along the [0 0 1] direction, which previously have been shown to represent the fivefold coordinated Ti surface cations. Subsequent AE spectra display a single peak in the sulfur region at 151.3 eV, confirming the predominant formation of Ti–S bonds during SO2 exposures. In LEED a diffuse (1×2) structure with faint (1×2) half-order reflections can be seen, demonstrating the overall disorder on the surface. Point defects on the stoichiometric (1×1) surface structure as well as on the reconstructed (1×2) surface structure are unaffected by SO2 exposure. [Copyright &y& Elsevier]

Abstract: Nanocrystalline diamond (NCD) films with a thickness of ~6 µm and average grain sizes ranging from 60 to 9 nm were deposited on silicon wafers using a hot-filament chemical vapor deposition (HFCVD) process. These samples were then characterized in order to identify correlations between grain size, chemical composition and mechanical properties. The characterization reveals that our films are phase pure and exhibit a relatively smooth surface morphology. The levels of sp 2-bonded carbon and hydrogen impurities are low, showing a systematic variation with the grain size. The hydrogen content increases with decreasing grain size, whereas the sp 2 carbon content decreases with decreasing grain size. The material is weaker than single crystalline diamond, since both stiffness and hardness decrease with the reduction in crystal size. These trends suggest gradual changes in the nature of the grain boundaries, from graphitic in case of 60 nm grain size material to hydrogen terminated sp 3 carbon in 9 nm grain size material. The films exhibit low levels of internal stress and free-standing structures with a length of several centimeters could be fabricated without noticeable bending [Copyright &y& Elsevier]