A novel strategy for efficient growth of nitrogen-doped graphene (N-graphene) on a large scale from s-triazine molecules is presented. The growth process has been unveiled in situ using time-dependent photoemission. It has been established that a postannealing of N-graphene after gold intercalation causes a conversion of the N environment from pyridinic to graphitic, allowing to obtain more than 80% of all embedded nitrogen in graphitic form, which is essential for the electron doping in graphene. A band gap, a doping level of 300 meV, and a charge-carrier concentration of ∼8×10(12) electrons per cm2, induced by 0.4 atom % of graphitic nitrogen, have been detected by angle-resolved photoemission spectroscopy, which offers great promise for implementation of this system in next generation electronic devices.
We show by angle-resolved photoemission spectroscopy that a tunable gap in quasi-free-standing monolayer graphene on Au can be induced by hydrogenation. The size of the gap can be controlled via hydrogen loading and reaches approximately 1.0 eV for a hydrogen coverage of 8%. The local rehybridization from sp(2) to sp(3) in the chemical bonding is observed by X-ray photoelectron spectroscopy and X-ray absorption and allows for a determination of the amount of chemisorbed hydrogen. The hydrogen induced gap formation is completely reversible by annealing without damaging the graphene. Calculations of the hydrogen loading dependent core level binding energies and the spectral function of graphene are in excellent agreement with photoemission experiments. Hydrogenation of graphene gives access to tunable electronic and optical properties and thereby provides a model system to study hydrogen storage in carbon materials.
We present an approach to monitor and control the strength of the hybridization between electronic states of graphene and metal surfaces. Inspecting the distribution of the π band in a high-quality graphene layer synthesized on Ni(111) by angle-resolved photoemission, we observe a new "kink" feature which indicates a strong hybridization between π and d states of graphene and nickel, respectively. Upon deposition and gradual intercalation of potassium atoms into the graphene/Ni(111) interface, the "kink" feature becomes less pronounced pointing at potassium mediated attenuation of the interaction between the graphene and the substrate.
Composite MoS 2 /carbon nanotube material has been produced by hydrothermal decomposition of a mixture of multiwall carbon nanotubes (CNTs) and a water solution of ammonium molybdate and thiourea. Transmission electron microscopy and Raman spectroscopy showed formation of MoS 2 layers on the CNT surface and MoS 2 flakes. X-ray photoelectron spectroscopy revealed a downshift of C 1s peak of the composite as compared to the pristine CNT sample that was related to charge transfer between the components. This fact was confirmed by near-edge X-ray absorption fine structure spectroscopy which detected a decrease of intensity of π* resonance in the C K-edge spectrum after the MoS 2 deposition. Quantum-chemical calculations of a CNT@MoS 2 model showed a positive charging of the CNT surface. Comparison of field emission characteristics of CNTs and the composite indicated lowering of the voltage threshold in the latter sample.
Applying time-dependent photoemission we unravel the graphene growth process on a metallic surface by chemical vapor deposition (CVD). Graphene CVD growth is in stark contrast to the standard growth process of two-dimensional films because it is self-limiting and stops as soon as a monolayer graphene has been synthesized. Most importantly, a novel phase of metastable graphene was discovered that is characterized by permanent and simultaneous construction and deconstruction. The high quality and large area graphene flakes are characterized by angle-resolved photoemission proofing that they are indeed monolayer and cover the whole 1×1 cm Nickel substrate. These findings are of high relevance to the intensive search for reliable synthesis methods for large graphene flakes of controlled layer number. 1 arXiv:0904.3220v2 [cond-mat.mtrl-sci]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.