The low-frequency 1/f noise in graphene transistors has been studied extensively owing to the proposed graphene applications in analog devices and communication systems [1-5]. The studies were motivated by the fact th...
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Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid‐phase catalytic reactions (e.g., hydrogenation of biomass‐derived furfural in alcoholic solvents or ...
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Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid‐phase catalytic reactions (e.g., hydrogenation of biomass‐derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid‐phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X‐ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ‐Al 2 O 3 . Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under‐coordinated copper atoms on the nanoparticle surface.
We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well-defined struc...
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We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well-defined structures. We use Brownian dynamics to model the assembly of N-clusters varying in size from two to twelve outer spheres and free energy calculations to predict the expected cluster sizes and shapes as a function of temperature and inner particle diameter. We show that the arrangements of outer spheres at finite temperatures are related to spherical codes, an ideal mathematical sequence of points corresponding to the densest possible sphere packings. We demonstrate that temperature and the ratio of the diameters of the inner and outer spheres dictate cluster morphology. We present a surprising result for the equilibrium structure of a 5-cluster, for which the square pyramid arrangement is preferred over a more symmetric structure. We show this result using Brownian dynamics, a Monte Carlo simulation, and a free energy approximation. Our results suggest a promising way to assemble anisotropic building blocks from constituent colloidal spheres.
The crystal structure of a metal plays an important role in its relationship to its macroscopic properties as well as atomic mechanisms of structural change. As such, students need to have an ability to visualize plan...
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ISBN:
(纸本)9781467313537
The crystal structure of a metal plays an important role in its relationship to its macroscopic properties as well as atomic mechanisms of structural change. As such, students need to have an ability to visualize planar crystal atomic packing features, but often find it difficult. Thus, the research question here is, "How can a student's baseline knowledge and misconceptions of planar atomic packing features for different metal structures be measured and how well can instruction promote conceptual change and misconception repair." Answering this question will provide insight for developing more effective pedagogy for crystal structures. A multiple-choice survey with six items was developed using misconceptions from students' pencil and paper sketches of face-centered cubic (FCC) and body-centered cubic (BCC) atoms on (100), (110), and (111) planes. Pretests and posttests of the survey were administered to students in a Spring 2012 introductory materialsengineering course. Misconceptions that were revealed included: missing atoms, extra atoms, misplaced atoms, "non-touching atoms where they should touch" and "touching atoms that should not touch". Students' difficulty in solving increased from (100) to (110) to (111) planes for both BCC and FCC structures. Details of the survey instrument and results are described in the paper.
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