Browsing by Subject "Hydrogen intercalation"

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Open Access
Surface evolution of 4H-SiC(0001) during in-situ surface preparation and its influence on graphene properties
(Trans Tech Publications, Switzerland, 2013) Ul Hassan J.; Meyer, A.; Çakmakyapan, Semih; Kazar, Özgür; Flege J.I.; Falta J.; Özbay, Ekmel; Janzén, E.
The evolution of SiC surface morphology during graphene growth process has been studied through the comparison of substrate surface step structure after in-situ etching and graphene growth in vacuum. Influence of in-situ substrate surface preparation on the properties of graphene was studied through the comparison of graphene layers on etched and un-etched substrates grown under same conditions. © (2013) Trans Tech Publications, Switzerland.
Open Access
Visualization of one-dimensional diffusion and spontaneous segregation of hydrogen in single crystals of VO2
(Institute of Physics Publishing, 2016-07) Kasirga, T. S.; Coy, J. M.; Park, J. H.; Cobden, D. H.
Hydrogen intercalation in solids is common, complicated, and very difficult to monitor. In a new approach to the problem, we have studied the profile of hydrogen diffusion in single-crystal nanobeams and plates of VO2, exploiting the fact that hydrogen doping in this material leads to visible darkening near room temperature connected with the metal-insulator transition at 65 ï¿½C. We observe hydrogen diffusion along the rutile c-axis but not perpendicular to it, making this a highly one-dimensional diffusion system. We obtain an activated diffusion coefficient ∼ 0.01 e-0.6eV/kBT cm2s-1, applicable in metallic phase. In addition, we observe dramatic supercooling of the hydrogen-induced metallic phase and spontaneous segregation of the hydrogen into stripes implying that the diffusion process is highly nonlinear, even in the absence of defects. Similar complications may occur in hydrogen motion in other materials but are not revealed by conventional measurement techniques.