Biexciton emission and crystalline quality of ZnO nano-objects.

The design of cost-effective standards for the quality of nano-objects is currently a key issue toward their massive use for optoelectronic applications. The observation by photoluminescence of narrow excitonic and biexcitonic emission lines in semiconductor nanowires is usually accepted as evidence for high structural quality. Here, we perform time-resolved cathodoluminescence experiments on isolated ZnO nanobelts grown by chemical vapor deposition. We observe narrow emission lines at low temperature, together with a clear biexciton line. Still, drastic alterations in both the CL intensity and lifetime are observed locally along the nano-object. We attribute these to non-radiative recombinations at edge dislocations, closing basal plane stacking faults, inhomogeneously distributed along the NB length. This leads us to the conclusion that the observation of narrow excitonic and biexcitonic emission lines is far from sufficient to grade the quality of a nano-object.

The morphology of submicronsized core-shell latex particles: an electron microscopy study.

The core-shell structure of a range of acrylic-acrylic latexes has been investigated by combining different specimen preparation methods with transmission electron microscopy (TEM), dark-field scanning transmission electron microscopy (DSTEM) and low-voltage scanning electron microscopy (LV-SEM), including the first reported use of LV-SEM to observe composite latex particles at ambient and subambient temperatures. Spin-coating of liquid latex dispersions directly onto TEM grids or SEM stubs is shown to be a relatively straightforward mean of avoiding film formation during specimen preparation. In conjunction with double staining techniques, it has been found to be particularly convenient for characterizing the fine structure of particles with diameters down to below 100 nm.

Practical method for high-resolution imaging of polymers by low-voltage scanning electron microscopy.

Morphologic characterization of polymers by scanning electron microscopy (SEM) is often made difficult by their sensitivity to electron beam damage. We describe here a specimen preparation method for the imaging of polymer blends by low-voltage SEM (LV-SEM) that improves their stability in the electron beam and hence facilitates focusing and recording of high magnification images. Its application to nanosized core-shell latexes embedded in a polymethylmethacrylate matrix and semi-crystalline polypropylene/ethylene-propylene rubber blends is discussed.