In Situ Study of Hydrogenation of Graphene and New Phases of Localization between Metal–Insulator Transitions

• Published in: Nano letters 2013-11, Vol.13 (11), p.5098-5105
• Main Authors: Jayasingha, Ruwantha, Sherehiy, Andriy, Wu, Shi-Yu, Sumanasekera, G. U
• Format: Article
• Language: English
• Subjects: Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Conductance; Cross-disciplinary physics: materials science; rheology; Electron states; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Graphene; Hydrogenation; Localization; Materials science; Metal-insulator transitions and other electronic transitions; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Position (location); Specific materials; Thermal properties of condensed matter; Thermal properties of small particles, nanocrystals, nanotubes; Transport; Transport properties; X-ray photoelectron spectroscopy
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl402272b

Monolayer graphene synthesized by chemical vapor deposition was subjected to controlled and sequential hydrogenation using RF plasma while monitoring its electrical properties in situ. Low-temperature transport properties, namely, electrical resistance (R), thermopower (S), Hall mobility (μ), and magnetoresistance (MR), were measured for each sample and correlated with ex situ Raman scattering and X-ray photoemission (XPS) characteristics. For weak hydrogenation, the transport is seen to be governed by electron diffusion, and low-temperature transport properties show metallic behavior (conductance G remains nonzero as T → 0). For strong hydrogenation, the transport is found to be describable by variable range hopping (VRH) and the low T conductance shows insulating behavior (G → 0 as T → 0). Weak localization (WL) behavior is seen with a negative MR for weakly hydrogenated graphene, and these WL effects are seen to diminish as the hydrogenation progresses. A clear transition to strong localization (SL) is evident with the emergence of pronounced negative MR for strongly hydrogenated graphene.