Dimensional measurements from secondary electron (SE) images were compared with those from backscattered electron (BSE) and low-loss electron (LLE) images. With the commonly used 50% threshold criterion, the lines consistently appeared larger in the SE images. As the images were acquired simultaneously by an instrument with the capability to operate detectors for both signals at the same time, the differences cannot be explained by the assumption that contamination or drift between images affected the SE, BSE, or LLE images differently. Simulations with JMONSEL, an electron microscope simulator, indicate that the nanometer-scale differences observed on this sample can be explained by the different convolution effects of a beam with finite size on signals with different symmetry (the SE signal’s characteristic peak versus the BSE or LLE signal’s characteristic step). This effect is too small to explain the > 100 nm discrepancies that were observed in earlier work on different samples. Additional modeling indicates that those discrepancies can be explained by the much larger sidewall angles of the earlier samples, coupled with the different response of SE versus BSE/LLE profiles to such wall angles.

Although their parent stars no longer exist, the isotopic and chemical compositions and microstructure of individual stardust grains identified in meteorites provide unique constraints on dust formation and thermodynamical conditions in stellar outflows 1-4. Novae are stellar explosions that take place in the hydrogen-rich envelope accreted onto the surface of a white dwarf in a close binary system 5. The energy released by a suite of nuclear processes operating in the envelope 2 powers a thermonuclear runaway, resulting in the ejection of processed material into the interstellar medium. Spectral fitting of features observed in the infrared spectra of dust-forming novae provided the first evidence of the co-condensation of both carbonaceous and silicate dust in stellar outflows within the 50 to 100 days after explosion 6-11. Here we report the identification of an O-rich inclusion, composed of both silicate and oxide nanoparticles, inside a graphite spherule that originated in the ejecta of a low-mass CO nova 12. This observation provides laboratory evidence of the co-condensation of O-and C-rich dust in nova outbursts, and is consistent with the transport and mixing of materials between chemically distinct clumps within the nova ejecta. Dust in stellar and interstellar environments is traditionally studied using space or ground-based telescopes but the laboratory study of circumstellar (presolar) grains identified in extraterrestrial materials (e.g., meteorites) has opened up a new field in astronomy and astrophysics, providing direct ground-truth information on individual stars. Such presolar grains are nanometer-to micrometer-sized minerals, amorphous grains, or aggregates of them, and can include materials such as nanodiamond, SiC, graphites, oxides, and silicates 1,2. Over the last two decades, about 2000 presolar graphite spherules have been identified and studied exclusively from the acid-resistant residues of the three carbonaceous chondrites: Murchison (CM2), Orgueil (CI1), and Qingzhen (EH3) 13-15. While most presolar graphite spherules originated from lowmetallicity asymptotic-giant-branch stars (∼50%) and core-collapse supernovae (∼25%), the remaining grains are hypothesized to have also originated from other types of stars, e.g., born-again AGB and Jtype stars 14,15. A few presolar graphite grains also have isotopic compositions suggesting possible origins in the ejecta of novae 16. Novae are traditionally classified as neon and non-neon, which reflects the composition of the white dwarf that hosts the explosion, i.e., ONe (O-and Ne-rich) and CO (C-and O-rich), respectively 5. Similarly to other SiC, silicates, and oxides with putative nova origins, these

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Zinc oxide (ZnO) thin films have been reported to suffer from degradation in electrical properties, when exposed to elevated heat and humidity, often leading to failures of electronic devices containing ZnO films. This degradation appears to be linked to water and oxygen penetration into the ZnO film. However, a direct observation in the ZnO film morphological evolution detailing structural and chemical changes has been lacking. Here, we systematically investigated the chemical and morphological heterogeneities of ZnO thin films caused by elevated heat and humidity, simulating an environmental aging. X-ray fluorescence microscopy, X-ray absorption spectroscopy, grazing incidence small angle and wide angle X-ray scattering, scanning electron microscopy (SEM), ultra-high-resolution SEM, and optical microscopy were carried out to examine ZnO and Al-doped ZnO thin films on two different substrates—silicon wafers and flexible polyethylene terephthalate (PET) films. In the un-doped ZnO thin film, the simulated environmental aging is resulting in pin-holes. In the Al-doped ZnO thin films, significant morphological changes occurred after the treatment, with an appearance of platelet-shaped structures that are 100–200 nm wide by 1 μm long. Synchrotron x-ray characterization further confirmed the heterogeneity in the aged Al-doped ZnO, showing the formation of anisotropic structures and disordering. X-ray diffraction and X-ray absorption spectroscopy indicated the formation of a zinc hydroxide in the aged Al-doped films. Utilizing advanced characterization methods, our studies provided information with an unprecedented level of details and revealed the chemical and morphologically heterogeneous nature of the degradation in ZnO thin films.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.