Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysics

CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures

Interstitial-phase precipitation in iron-base alloys: a comparative study

Recent developments have elucidated the atomistic mechanisms of precipitation of interstitial elements in simple alloy systems. However, in the more technologically important iron base alloys, interstitial phase precipitation is generally not well understood. The present experimental study was therefore designed to test the applicability of these concepts to more complex ferrous alloys. Hence, a comparative study was made of interstitial phase precipitation in ferritic Fe-Si-C and in austenitic phosphorus-containing Fe-Cr-Ni steels. These systems were subjected to a variety of quench-age thermal treatments, and the microstructural development was subsequently characterized by transmission electron microscopy

The Bending Behavior of NiTi

The bending behavior of superelastic and shape memory Nitinol wire with circular and rectangular cross sections was studied in three-point, four-point and pure bending. Four-point and pure bending results are in good agreement with each other, whereas those from three-point bending show marked differences. The stress-strain curves of the four-point and pure bending were also compared with uniaxial tensile results. As expected, the plateau stresses in bending were consistently higher than those in tension. The tensile data were then analyzed with the modified plasticity theory for pseudoelastic beams and further compared with the bending results. It was found that the linear elastic range and upper plateau stresses are in close agreement with the bending data. Differences were found, however, for the lower plateau and the springback strain, which may result from the different modes of deformation

An Apparatus to Measure the Shape Memory Properties of Nitinol Tubes for Medical Applications

A new apparatus has been developed to characterize the shape memory properties of Nitinol tubes and stents. In tests run on this apparatus, the samples are deformed in the radial direction in the martensitic state to a prescribed outer-fiber strain. Recovery strain and force are monitored continuously on heating. Values of properties as measured on this apparatus are compared to corresponding values from three-point and four-point bending tests, as well as DSC. We have found that this is a fast and reliable system to test transformation temperatures and recovery forces of tubes and stents