Ray D. Twesten

Layered-structure nanoribbons with efficient electron transport and short lithium ion insertion lengths are promising candidates for Li battery applications. Here we studied at the single nanostructure level the chemical, structural, and electrical transformations of V2O5 nanoribbons. We found that transformation of V2O5 into the omega-Li3V2O5 phase depends not only on the width but also the thickness of the nanoribbons. Transformation can take place within 10 s in thin nanoribbons, suggesting a Li diffusion constant 3 orders of magnitude faster than in bulk materials, resulting in a significant increase in battery power density (360 C power rate). For the first time, complete delithiation of omega-Li3V2O5 back to the single-crystalline, pristine V2O5 nanoribbon was observed, indicating a 30% higher energy density. These new observations are attributed to the ability of facile strain relaxation and phase transformation at the nanoscale. In addition, efficient electronic transport can be maintained to charge a Li3V2O5 nanoribbon within less than 5 s. These exciting nanosize effects can be exploited to fabricate high-performance Li batteries for applications in electric and hybrid electric vehicles.

Abstract In many cases, electron counting with direct detection sensors offers improved resolution, lower noise, and higher pixel density compared to conventional, indirect detection sensors for electron microscopy applications. Direct detection technology has previously been utilized, with great success, for imaging and diffraction, but potential advantages for spectroscopy remain unexplored. Here we compare the performance of a direct detection sensor operated in counting mode and an indirect detection sensor (scintillator/fiber-optic/CCD) for electron energy-loss spectroscopy. Clear improvements in measured detective quantum efficiency and combined energy resolution/energy field-of-view are offered by counting mode direct detection, showing promise for efficient spectrum imaging, low-dose mapping of beam-sensitive specimens, trace element analysis, and time-resolved spectroscopy. Despite the limited counting rate imposed by the readout electronics, we show that both core-loss and low-loss spectral acquisition are practical. These developments will benefit biologists, chemists, physicists, and materials scientists alike.

Frataxin is a conserved mitochondrial protein required for iron homeostasis. We showed previously that in the presence of ferrous iron recombinant yeast frataxin (mYfh1p) assembles into a regular multimer of approximately 1.1 MDa storing approximately 3000 iron atoms. Here, we further demonstrate that mYfh1p and iron form a stable hydrophilic complex that can be detected by either protein or iron staining on nondenaturing polyacrylamide gels, and by either interference or absorbance measurements at sedimentation equilibrium. The molecular mass of this complex has been refined to 840 kDa corresponding to 48 protein subunits and 2400 iron atoms. Solution density measurements have determined a partial specific volume of 0.58 cm(3)/g, consistent with the amino acid composition of mYfh1p and the presence of 50 Fe-O equivalents per subunit. By dynamic light scattering, we show that the complex has a radius of approximately 11 nm and assembles within 2 min at 30 degrees C when ferrous iron, not ferric iron or other divalent cations, is added to mYfh1p monomer at pH between 6 and 8. Iron-rich granules with diameter of 2-4 nm are detected in the complex by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. These findings support the hypothesis that frataxin is an iron storage protein, which could explain the mitochondrial iron accumulation and oxidative damage associated with frataxin defects in yeast, mouse, and humans.