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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; BN, 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>
Connecting Dopant Bond Type with Electronic Structure in N-Doped Graphene
Schiros, Theanne,Nordlund, Dennis,Pá,lová,, Lucia,Prezzi, Deborah,Zhao, Liuyan,Kim, Keun Soo,Wurstbauer, Ulrich,Gutié,rrez, Christopher,Delongchamp, Dean,Jaye, Cherno,Fischer, Daniel American Chemical Society 2012 Nano letters Vol.12 No.8
<P>Robust methods to tune the unique electronic properties of graphene by chemical modification are in great demand due to the potential of the two dimensional material to impact a range of device applications. Here we show that carbon and nitrogen core-level resonant X-ray spectroscopy is a sensitive probe of chemical bonding and electronic structure of chemical dopants introduced in single-sheet graphene films. In conjunction with density functional theory based calculations, we are able to obtain a detailed picture of bond types and electronic structure in graphene doped with nitrogen at the sub-percent level. We show that different N-bond types, including graphitic, pyridinic, and nitrilic, can exist in a single, dilutely N-doped graphene sheet. We show that these various bond types have profoundly different effects on the carrier concentration, indicating that control over the dopant bond type is a crucial requirement in advancing graphene electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-8/nl301409h/production/images/medium/nl-2012-01409h_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl301409h'>ACS Electronic Supporting Info</A></P>
Imaging chiral symmetry breaking from Kekulé bond order in graphene
Gutié,rrez, Christopher,Kim, Cheol-Joo,Brown, Lola,Schiros, Theanne,Nordlund, Dennis,Lochocki, Edward ,B.,Shen, Kyle M.,Park, Jiwoong,Pasupathy, Abhay N. Nature Publishing Group, a division of Macmillan P 2016 NATURE PHYSICS Vol.12 No.10
Chirality—or ‘handedness’—is a symmetry property crucial to fields as diverse as biology, chemistry and high-energy physics. In graphene, chiral symmetry emerges naturally as a consequence of the carbon honeycomb lattice. This symmetry can be broken by interactions that couple electrons with opposite momenta in graphene. Here we directly visualize the formation of Kekulé bond order, one such phase of broken chiral symmetry, in an ultraflat graphene sheet grown epitaxially on a copper substrate. We show that its origin lies in the interactions between individual vacancies in the copper substrate that are mediated electronically by the graphene. We show that this interaction causes the bonds in graphene to distort, creating a phase with broken chiral symmetry. The Kekulé ordering is robust at ambient temperature and atmospheric conditions, indicating that intercalated atoms may be harnessed to drive graphene and other two-dimensional materials towards electronically desirable and exotic collective phases.
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.