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Full-Text Articles in Physics

Reshaping Of Truncated Pd Nanocubes: Energetic And Kinetic Analysis Integrating Transmission Electron Microscopy With Atomistic-Level And Coarse-Grained Modeling, King C. Lai, Minda Chen, Benjamin Williams, Yong Han, Chia-Kuang Tsung, Wenyu Huang, James W. Evans Jul 2020

Reshaping Of Truncated Pd Nanocubes: Energetic And Kinetic Analysis Integrating Transmission Electron Microscopy With Atomistic-Level And Coarse-Grained Modeling, King C. Lai, Minda Chen, Benjamin Williams, Yong Han, Chia-Kuang Tsung, Wenyu Huang, James W. Evans

Chemistry Publications

Stability against reshaping of metallic fcc nanocrystals synthesized with tailored far-from-equilibrium shapes is key to maintaining optimal properties for applications such as catalysis. Yet Arrhenius analysis of experimental reshaping kinetics, and appropriate theory and simulation, is lacking. Thus, we use TEM to monitor the reshaping of Pd nanocubes of ∼25 nm side length between 410 °C (over ∼4.5 h) and 440 °C (over ∼0.25 h), extracting a high effective energy barrier of Eeff ≈ 4.6 eV. We also provide an analytic determination of the energy variation along the optimal pathway for reshaping that involves transfer of atoms across ...


Shapes Of Fe Nanocrystals Encapsulated At The Graphite Surface, Ann Lii-Rosales, Yong Han, Scott E. Julien, Olivier Pierre-Louis, Dapeng Jing, Kai-Tak Wan, Michael C. Tringides, James W. Evans, Patricia A. Thiel Feb 2020

Shapes Of Fe Nanocrystals Encapsulated At The Graphite Surface, Ann Lii-Rosales, Yong Han, Scott E. Julien, Olivier Pierre-Louis, Dapeng Jing, Kai-Tak Wan, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

We describe and analyze in detail the shapes of Fe islands encapsulated under the top graphene layers in graphite. Shapes are interrogated using scanning tunneling microscopy. The main outputs of the shape analysis are the slope of the graphene membrane around the perimeter of the island, and the aspect ratio of the central metal cluster. Modeling primarily uses a continuum elasticity (CE) model. As input to the CE model, we use density functional theory to calculate the surface energy of Fe, and the adhesion energies between Fe and graphene or graphite. We use the shaft-loaded blister test (SLBT) model to ...


Fabricating Fe Nanocrystals Via Encapsulation At The Graphite Surface, Ana Lii-Rosales, Yong Han, King C. Lai, Dapeng Jing, Michael C. Tringides, James W. Evans, Patricia A. Thiel Nov 2019

Fabricating Fe Nanocrystals Via Encapsulation At The Graphite Surface, Ana Lii-Rosales, Yong Han, King C. Lai, Dapeng Jing, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

In this paper, the authors describe the conditions under which Fe forms encapsulated nanocrystals beneath the surface of graphite, and they characterize these islands (graphite + Fe) thoroughly. The authors use the experimental techniques of scanning tunneling microscopy (STM) plus x-ray photoelectron spectroscopy (XPS) and the computational technique of density functional theory (DFT). Necessary conditions for encapsulation are preexisting ion-induced defects in the graphite substrate and elevated deposition temperature of 875–900 K. Evidence of encapsulation consists of atomically resolved STM images of a carbon lattice, both on top of the islands and on the sloping sides. The nature of the ...


Kinetics, Energetics, And Size Dependence Of The Transformation From Pt To Ordered Ptsn Intermetallic Nanoparticles, Minda Chen, Yong Han, Tian Wei Goh, Rong Sun, Raghu V. Maligal‐Ganesh, Yuchen Pei, Chia‐ Kuang Tsung, James W. Evans, Wenyu Huang Jan 2019

Kinetics, Energetics, And Size Dependence Of The Transformation From Pt To Ordered Ptsn Intermetallic Nanoparticles, Minda Chen, Yong Han, Tian Wei Goh, Rong Sun, Raghu V. Maligal‐Ganesh, Yuchen Pei, Chia‐ Kuang Tsung, James W. Evans, Wenyu Huang

Chemistry Publications

The outstanding catalytic activity and chemical selectivity of intermetallic compounds make them excellent candidates for heterogeneous catalysis. However, the kinetics of their formation at the nanoscale is poorly understood or characterized, and precise control of their size, shape as well as composition during synthesis remains challenging. Here, using well-defined Pt nanoparticles (5 nm and 14 nm) encapsulated in mesoporous silica, we study the transformation kinetics from monometallic Pt to intermetallic PtSn at different temperatures by a series of time-evolution X-ray diffraction studies. Observations indicate an initial transformation stage mediated by Pt surface-controlled intermixing kinetics, followed by a second stage with ...


Squeezed Nanocrystals: Equilibrium Configuration Of Metal Clusters Embedded Beneath The Surface Of A Layered Material, Scott E. Julien, Ann Lii-Rosales, Kai-Tak Wan, Yong Han, Michael C. Tringides, James W. Evans, Patricia A. Thiel Jan 2019

Squeezed Nanocrystals: Equilibrium Configuration Of Metal Clusters Embedded Beneath The Surface Of A Layered Material, Scott E. Julien, Ann Lii-Rosales, Kai-Tak Wan, Yong Han, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

Shapes of functional metallic nanocrystals, typically synthesized either free in solution or supported on surfaces, are key for controlling properties. Here, we consider a novel new class of metallic nanocrystals, copper islands embedded near the surface of graphite, which can be considered a model system for metals embedded beneath surfaces of layered materials, or beneath supported membranes. We develop a continuum elasticity (CE) model for the equilibrium shape of these islands, and compare its predictions with experimental data. The CE model incorporates appropriate surface energy, adhesion energies, and strain energy. The agreement between the CE model and the data is ...


Reverse-Engineering Of Graphene On Metal Surfaces: A Case Study Of Embedded Ruthenium, Ann Lii-Rosales, Yong Han, Ka Man Yu, Dapeng Jing, Nathaniel Anderson, David Vaknin, Michael C. Tringides, James W. Evans, Michael S. Altman, Patricia A. Thiel Oct 2018

Reverse-Engineering Of Graphene On Metal Surfaces: A Case Study Of Embedded Ruthenium, Ann Lii-Rosales, Yong Han, Ka Man Yu, Dapeng Jing, Nathaniel Anderson, David Vaknin, Michael C. Tringides, James W. Evans, Michael S. Altman, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy, we show that Ru forms metallic nanoislands on graphite, covered by a graphene monolayer. These islands are air-stable, contain 2–4 layers of Ru, and have diameters on the order of 10 nm. To produce these nanoislands two conditions must be met during synthesis. The graphite surface must be ion-bombarded, and subsequently held at an elevated temperature (1000–1180 K) during Ru deposition. A coincidence lattice forms between the graphene overlayer and the Ru island top. Its characteristics—coincidence lattice constant, corrugation amplitude, and variation of carbon lattice appearance ...