Ann N. Chiaramonti

Behavior of molecules and molecular ions near a field emitter

The cold emission of particles from surfaces under intense electric fields is a process which underpins a variety of applications including atom probe tomography (APT), an analytical microscopy technique with near-atomic spatial resolution. Increasingly relying on fast laser pulsing to trigger the emission, APT experiments often incorporate the detection of molecular ions emitted from the specimen, in particular from covalently or ionically bonded materials. Notably, it has been proposed that neutral molecules can also be emitted during this process. However, this remains a contentious issue. To investigate the validity of this hypothesis, a careful review of the literature is combined with the development of new methods to treat experimental APT data, the modelling of ion trajectories, and the application of density-functional theory (DFT) simulations to derive molecular ion energetics. It is shown that the direct thermal emission of neutral molecules is extremely unlikely. However, neutrals can still be formed in the course of an APT experiment by dissociation of metastable molecular ions.

Effects of annealing on local composition and electrical transport correlations in MgO-based magnetic tunnel junctions

The effects of annealing on the electrical transport behavior of CoFe/MgO/CoFe magnetic tunnel junctions have been studied using a combination of site-specific in situ transmission electron microscopy and three-dimensional atom-probe tomography. Annealing leads to an increase in the resistance of the junctions. A shift in the conductance curve (dI/dV) minimum from 0 V for the as-grown specimen correlates with a sharply defined layer of CoFe oxide at the lower ferromagnetic interface. Annealing decreases the asymmetry in the conductance by making the interfaces more diffuse and the tunnel barrier more chemically homogeneous.

Engineering plant cell walls: tuning lignin monomer composition for deconstructable biofuel feedstocks or resilient biomaterials

Advances in genetic manipulation of the biopolymers that compose plant cell walls will facilitate more efficient production of biofuels and chemicals from biomass and lead to specialized biomaterials with tailored properties. Here we investigate several genetic variants of Arabidopsis: the wild type, which makes a lignin polymer of primarily guaiacyl (G) and syringyl (S) monomeric units, the fah1 mutant, which makes lignin from almost exclusively G subunits, and a ferulate 5-hydroxylase (F5H) overexpressing line (C4H:F5H) that makes lignin from S subunits. We employ multiscale, multimodal imaging techniques that reveal the biomass of the C4H:F5H transgenic to be more susceptible to deconstruction by maleic acid treatment than the other variants. Enzymatic saccharification assays of the treated materials show that C4H:F5H transgenic tissue is significantly more digestible than the wild type, while the fah1 mutant is clearly the least digestible of these materials. Finally, we show by contact resonance force microscopy, an atomic force microscopy technique, that F5H overexpression in C4H:F5H transgenic plants significantly reduces the stiffness of the cell walls in the region of the compound middle lamella relative to wild type and fah1.

Epitaxial (111) films of Cu, Ni, and CuxNiy on α−Al2O3 (0001) for graphene growth by chemical vapor deposition

Films of (111)-textured Cu, Ni, and Cu

Atomically thin layers of B-N-C-O with tunable composition

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Effects of elemental distributions on the behavior of MgO-based magnetic tunnel junctions.

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Applicability of post-ionization theory to laser-assisted field evaporation of magnetite

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Atomic resolution transmission electron microscopy of surfaces

were evaluated as substrates for chemical vapor deposition of graphene. A metal thickness of 400 nm to 700 nm was sputtered onto a substrate of

Enhanced magnetoresistance in naturally oxidized MgO-based magnetic tunnel junctions with ferromagnetic CoFe/CoFeB bilayers.

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In situ TEM studies of local transport and structure in nanoscale multilayer films.

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