Practical considerations for EDS analysis in an AEM

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25860/1/0000423.pd

Some simple techniques for coating heat-sensitive SEM specimens

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22706/1/0000260.pd

On the structure of Au/Pd bimetallic nanoparticles

We performed a study on bimetallic Au/Pd nanoparticles using aberration corrected electron microscopy along with molecular dynamics simulations to investigate the features of specific atomic sites at the surface, which can be related to the high catalytic activity properties of the particles. The calculations mimic the growth of nanoparticles through a cooling process from a molten solid to a crystalline structure at room temperature. We found that the final structure for the alloy particles is neither a cuboctahedral nor an icosahedral,but a complex structure that has a very rough surface and unique isolated Pd sites surrounded by Au atoms. We also found that there is predominance of three specific Pd sites at the surface, which can be directly related to the catalytic activity of the nanoparticle

Alumina-supported triosmium clusters and ensembles: Characterization by high-resolution transmission electron microscopy

Structurally defined supported osmium clusters [HOs3(CO)10---O---Al3(CO)12] with the -OH groups of [gamma]-Al2O3. The supported clusters were heated to 200 [deg]C in argon and then reduced in hydrogen at 400 [deg]C, being characterized at different stages of the treatment by high-resolution transmission electron microscopy. After the sample had been heated to 200 [deg]C, scattering centers about 6 A in diameter were evident in the micrographs, their size being consistent with the expected geometry of three-atom ensembles of Os(II) complexes formed by cluster breakup. The ensembles were remarkably stable, and even prolonged exposure of the same area to the 100 keV electron beam caused neither disintegration nor agglomeration. After reduction of the osmium in hydrogen at 400 [deg]C, aggregates of similar size were observed. In contrast to the ensembles of Os(II) complexes, the aggregates seemed to disintegrate slowly under the impact of the electron beam. The difference in stability of the ensembles and the reduced osmium aggregates is attributed to the difference between the strong ionic bonds in the former sample and the weaker interaction between the reduced metal and the Al2O3 surface.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25063/1/0000494.pd

Extending the Canada-France brown Dwarfs Survey to the near-infrared: first ultracool brown dwarfs from CFBDSIR

We present the first results of the ongoing Canada-France Brown Dwarfs Survey-InfraRed, hereafter CFBDSIR, a Near InfraRed extension to the optical wide-field survey CFBDS. Our final objectives are to constrain ultracool atmosphere physics by finding a statistically significant sample of objects cooler than 650K and to explore the ultracool brown dwarf mass function building on a well defined sample of such objects. Candidates are identified in CFHT/WIRCam J and CFHT/MegaCam z' images using optimised psf-fitting, and we follow them up with pointed near infrared imaging with SOFI at NTT. We finally obtain low resolution spectroscopy of the coolest candidates to characterise their atmospheric physics. We have so far analysed and followed up all candidates on the first 66 square degrees of the 335 square degrees survey. We identified 55 T-dwarfs candidates with z'-J > 3:5 and have confirmed six of them as T-dwarfs, including 3 that are strong later-than-T8 candidates, based on their far-red and NIR colours. We also present here the NIR spectra of one of these ultracool dwarfs, CFBDSIR1458+1013 which confirms it as one of the coolest brown dwarf known, possibly in the 550-600K temperature range. From the completed survey we expect to discover 10 to 15 dwarfs later than T8, more than doubling the known number of such objects. This will enable detailed studies of their extreme atmospheric properties and provide a stronger statistical base for studies of their luminosity function.Comment: A&A, Accepte

Silicification of developing internodes in the perennial scouring rush (Equisetum hyemale var. affine)

An electron microprobe (EMP) analysis of silica (SiO2) deposition in the epidermis of developing internodes of the perennial scouring rush (Equisetum hyemale var. affine) indicates that SiO2 is first detected in the stomatal apparatus beginning with internode 3, then the epidermal papillae (internode 8), and finally in radial cell walls of the long epidermal cells (internode 10). This process is initiated in the intercalary growth regions at the bases of the elongating internodes. The deposition of SiO2 in long epidermal cell walls occurs after internodal extension has ceased and should therefore be considered as one of the final stages in internodal differentiation that involves strengthening the cellulosic framework of the cell wall. EMP measurements indicate that SiO2 in stomata is equivalent to 30% of a pure SiO2 standard and that SiO2 in the radial walls of long epidermal cells averages twice that measured on the tangential walls of these same cells. This study supports the view that silicification plays a major role in strengthening the developing perennial scouring rush internodal system and that regulation of this process in this and other species of Equisetum, whose SiO2 deposition patterns are markedly different, deserves further study.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33924/1/0000191.pd

Primeval very low-mass stars and brown dwarfs - III. The halo transitional brown dwarfs

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We report the discovery of an esdL3 subdwarf, ULAS J020858.62+020657.0 and a usdL4.5 subdwarf, ULAS J230711.01+014447.1. They were identified as L subdwarfs by optical spectra obtained with the Gran Telescopio Canarias, and followed up by optical to near infrared spectroscopy with the Very Large Telescope. We also obtained an optical to near infrared spectrum of a previously known L subdwarf, ULAS J135058.85+081506.8, and re-classified it as a usdL3 subdwarf. These three objects all have typical halo kinematics. They have $T_{\rm eff}$ around 2050-2250 K, $-$1.8 $\leq$ [Fe/H] $\leq -$1.5, and mass around 0.0822-0.0833 M$_{\odot}$, according to model spectral fitting and evolutionary models. These sources are likely halo transitional brown dwarfs with unsteady hydrogen fusions, as their masses are just below the hydrogen-burning minimum mass, which is $\sim$ 0.0845 M$_{\odot}$ at [Fe/H] = $-$1.6 and $\sim$ 0.0855 M$_{\odot}$ at [Fe/H] = $-$1.8. Including these, there are now nine objects in the `halo brown dwarf transition zone', which is a `substellar subdwarf gap' spans a wide temperature range within a narrow mass range of the substellar population.Peer reviewedFinal Accepted Versio