Controlled Growth of Ceria Nanoarrays on Anatase Titania Powder: A Bottom-up Physical Picture

Kim, Hyun You,Hybertsen, Mark S.,Liu, Ping American Chemical Society 2017 NANO LETTERS Vol.17 No.1

<P>The leading edge of catalysis research motivates physical understanding of the growth of nanoscale oxide structures on different supporting oxide materials that are themselves also nanostructured. This research opens up for consideration a diverse range of facets on the support material, versus the single facet typically involved in wide-area growth of thin films. Here, we study the growth of ceria nanoarchitectures on practical anatase titania powders as a showcase inspired by recent experiments. Density functional theory (DFT)-based methods are employed to characterize and rationalize the broad array of low energy nanostructures that emerge. Using a bottom up approach, we are able to identify and characterize the underlying mechanisms for the facet-dependent growth of various ceria motifs on anatase titania based on formation energy. These motifs include OD clusters, 1D chains, 2D plates, and 3D nanoparticles. The ceria growth mode and morphology are determined by the interplay of several factors including the role of the common cation valence, the interface template effect for different facets of the anatase support, enhanced ionic binding for more compact ceria motifs, and the local structural flexibility of oxygen ions in bridging the interface between anatase and ceria structures.</P>

Amine−Gold Linked Single-Molecule Circuits: Experiment and Theory

Quek, S. Y.,Venkataraman, L.,Choi, H. J.,Louie, S. G.,Hybertsen, M. S.,Neaton, J. B. American Chemical Society 2007 NANO LETTERS Vol.7 No.11

Mechanically controlled binary conductance switching of a single-molecule junction

Quek, Su Ying,Kamenetska, Maria,Steigerwald, Michael L.,Choi, Hyoung Joon,Louie, Steven G.,Hybertsen, Mark S.,Neaton, J. B.,Venkataraman, Latha Springer Science and Business Media LLC 2009 Nature nanotechnology Vol.4 No.4

<P>Molecular-scale components are expected to be central to the realization of nanoscale electronic devices. Although molecular-scale switching has been reported in atomic quantum point contacts, single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. To date, switching in single-molecule junctions has been attributed to changes in the conformation or charge state of the molecule. Here, we demonstrate reversible binary switching in a single-molecule junction by mechanical control of the metal-molecule contact geometry. We show that 4,4'-bipyridine-gold single-molecule junctions can be reversibly switched between two conductance states through repeated junction elongation and compression. Using first-principles calculations, we attribute the different measured conductance states to distinct contact geometries at the flexible but stable nitrogen-gold bond: conductance is low when the N-Au bond is perpendicular to the conducting pi-system, and high otherwise. This switching mechanism, inherent to the pyridine-gold link, could form the basis of a new class of mechanically activated single-molecule switches.</P>

Conductance and Geometry of Pyridine-Linked Single-Molecule Junctions

Kamenetska, M.,Quek, Su Ying,Whalley, A. C.,Steigerwald, M. L.,Choi, H. J.,Louie, Steven G.,Nuckolls, C.,Hybertsen, M. S.,Neaton, J. B.,Venkataraman, L. American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.19

<P>We have measured the conductance and characterized molecule−electrode binding geometries of four pyridine-terminated molecules by elongating and then compressing gold point contacts in a solution of molecules. We have found that all pyridine-terminated molecules exhibit bistable conductance signatures, signifying that the nature of the pyridine−gold bond allows two distinct conductance states that are accessed as the gold−molecule−gold junction is elongated. We have identified the low-conductance state as corresponding to a molecule fully stretched out between the gold electrodes, where the distance between contacts correlates with the length of the molecule; the high-conductance state is due to a molecule bound at an angle. For all molecules, we have found that the distribution of junction elongations in the low-conductance state is the same, while in the high-conductance state, the most likely elongation length increases linearly with molecule length. The results of first-principles conductance calculations for the four molecules in the low-conductance geometry agree well with the experimental results and show that the dominant conducting channel in the conjugated pyridine-linked molecules is through the π* orbital.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-19/ja1015348/production/images/medium/ja-2010-015348_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja1015348'>ACS Electronic Supporting Info</A></P>

Atomistic Interrogation of B–N Co-dopant Structures and Their Electronic Effects in Graphene

Schiros, Theanne,Nordlund, Dennis,Palova, Lucia,Zhao, Liuyan,Levendorf, Mark,Jaye, Cherno,Reichman, David,Park, Jiwoong,Hybertsen, Mark,Pasupathy, Abhay American Chemical Society 2016 ACS NANO Vol.10 No.7

<P>Chemical doping has been demonstrated to be an effective method for producing high-quality, large-area graphene with controlled carrier concentrations and an atomically tailored work function. The emergent optoelectronic properties and surface reactivity of carbon nanostructures are dictated by the microstructure of atomic dopants. Co-doping of graphene with boron and nitrogen offers the possibility to further tune the electronic properties of graphene at the atomic level, potentially creating p- and n-type domains in a single carbon sheet, opening a gap between valence and conduction bands in the 2-D semimetal. Using a suite of high-resolution synchrotron-based X-ray techniques, scanning tunneling microscopy, and density functional theory based computation we visualize and characterize B–N dopant bond structures and their electronic effects at the atomic level in single-layer graphene grown on a copper substrate. We find there is a thermodynamic driving force for B and N atoms to cluster into BNC structures in graphene, rather than randomly distribute into isolated B and N graphitic dopants, although under the present growth conditions, kinetics limit segregation of large B–N domains. We observe that the doping effect of these BNC structures, which open a small band gap in graphene, follows the B:N ratio (B > N, p-type; B < N, n-type; BN, neutral). We attribute this to the comparable electron-withdrawing and -donating effects, respectively, of individual graphitic B and N dopants, although local electrostatics also play a role in the work function change.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2016/ancac3.2016.10.issue-7/acsnano.6b01318/production/images/medium/nn-2016-01318z_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn6b01318'>ACS Electronic Supporting Info</A></P>

Edge Structures for Nanoscale Graphene Islands on Co(0001) Surfaces

Prezzi, Deborah,Eom, Daejin,Rim, Kwang T.,Zhou, Hui,Lefenfeld, Michael,Xiao, Shengxiong,Nuckolls, Colin,Heinz, Tony F.,Flynn, George W.,Hybertsen, Mark S. American Chemical Society 2014 ACS NANO Vol.8 No.6

<P>Low-temperature scanning tunneling microscopy measurements and first-principles calculations are employed to characterize edge structures observed for graphene nanoislands grown on the Co(0001) surface. Images of these nanostructures reveal straight well-ordered edges with zigzag orientation, which are characterized by a distinct peak at low bias in tunneling spectra. Density functional theory based calculations are used to discriminate between candidate edge structures. Several zigzag-oriented edge structures have lower formation energy than armchair-oriented edges. Of these, the lowest formation energy configurations are a zigzag and a Klein edge structure, each with the final carbon atom over the hollow site in the Co(0001) surface. In the absence of hydrogen, the interaction with the Co(0001) substrate plays a key role in stabilizing these edge structures and determines their local conformation and electronic properties. The calculated electronic properties for the low-energy edge structures are consistent with the measured scanning tunneling images.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-6/nn500583a/production/images/medium/nn-2014-00583a_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn500583a'>ACS Electronic Supporting Info</A></P>

Local Atomic and Electronic Structure of Boron Chemical Doping in Monolayer Graphene

Zhao, Liuyan,Levendorf, Mark,Goncher, Scott,Schiros, Theanne,Pá,lová,, Lucia,Zabet-Khosousi, Amir,Rim, Kwang Taeg,Gutié,rrez, Christopher,Nordlund, Dennis,Jaye, Cherno,Hybertsen, Mar American Chemical Society 2013 Nano letters Vol.13 No.10

<P>We use scanning tunneling microscopy and X-ray spectroscopy to characterize the atomic and electronic structure of boron-doped and nitrogen-doped graphene created by chemical vapor deposition on copper substrates. Microscopic measurements show that boron, like nitrogen, incorporates into the carbon lattice primarily in the graphitic form and contributes ∼0.5 carriers into the graphene sheet per dopant. Density functional theory calculations indicate that boron dopants interact strongly with the underlying copper substrate while nitrogen dopants do not. The local bonding differences between graphitic boron and nitrogen dopants lead to large scale differences in dopant distribution. The distribution of dopants is observed to be completely random in the case of boron, while nitrogen displays strong sublattice clustering. Structurally, nitrogen-doped graphene is relatively defect-free while boron-doped graphene films show a large number of Stone-Wales defects. These defects create local electronic resonances and cause electronic scattering, but do not electronically dope the graphene film.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-10/nl401781d/production/images/medium/nl-2013-01781d_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl401781d'>ACS Electronic Supporting Info</A></P>

Visualizing Individual Nitrogen Dopants in Monolayer Graphene

Zhao, L.,He, R.,Rim, K. T.,Schiros, T.,Kim, K. S.,Zhou, H.,Gutierrez, C.,Chockalingam, S. P.,Arguello, C. J.,Palova, L.,Nordlund, D.,Hybertsen, M. S.,Reichman, D. R.,Heinz, T. F.,Kim, P.,Pinczuk, A.,F American Association for the Advancement of Scienc 2011 Science Vol. No.