Fabrication and characterization of platinum nanoparticle arrays of controlled size, shape and orientation

We present a rigorous approach for the shape design of supported metal nanoparticle catalysts, morphologically identical to each other and epitaxially grown on strontium titanate substrates using electron beam lithography. We predict the particle shapes using Wulff construction based on density functional theory calculations of surface energies. Then, according to the theoretical predictions, we are able to tweak morphologies of the already produced nanocrystals by changing annealing conditions. The ability to design, produce and characterize the catalyst nanoparticles allows us to relate microscopic morphologies with macroscopic oxygen-reduction activities in perchloric acid [Komanicky et al., J. Am. Chem. Soc. 131 (2009) 5732]. The unexpectedly high oxygen-reduction activities proportional to inactive (1 0 0) facets led us to suggest a model where the reaction intermediates can cross over to neighboring facets in nanoscale proximity.     

Compression behavior of micro-scale truss structures formed from self-propagating polymer waveguides

The structure–property relationships in newly developed polymer micro-truss structures were investigated, correlating compressive behavior with structural features, including density, cell size and truss angle. These open-cellular polymer micro-truss structures were formed from an interpenetrating array of self-propagating polymer waveguides. Compression experiments verified that the effective modulus scaled linearly with the measured relative density of the micro-trusses and was reliably predicted from a simple analytical model. However, the measured peak strength at initial truss member buckling was well below the values predicted from inelastic buckling theory, which was attributed to imperfections in the structure and the nonlinear compressive behavior of the solid polymer. In addition, a micro-truss structure was post cured at a higher temperature in an oxidizing environment which suppressed the tendency for truss members to prematurely buckle. The polymer modulus increased by approximately 40% and the peak strength of the micro-truss structure nearly doubled to 5.9 MPa.     

Direct Surface Patterning from Solutions: Localized Microchemistry Using a Focused Laser

A method for creating microscale‐patterned surfaces by direct‐write lithography is described. A tightly focused, low‐power infrared laser beam is applied to a homogeneous precursor solution containing soluble reagents. When the laser is focused directly at a glass–solution interface, it initiates the local precipitation of a solid product that attaches firmly to the substrate. Operating the laser momentarily forms isolated spots, whereas moving the microscope stage or the laser spot draws continuous lines. The method has been demonstrated for metallic silver and gold, for oxidized copper, and for molybdenum disulfide, suggesting a broad range of suitable materials. Silver patterns were further modified by chemical reactions. Their morphology and physical properties can be altered during deposition by the use of capping agents, which may provide an onset for further functionalization.