Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition

The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. Since large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman "D" peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material

Von der 'schweren Geburt' bis zur 'orangenen Revolution' : zehn Jahre ukrainische Verfassung

Since the end of Communism, the Constitutional question in Ukraine has been and continues to be difficult. The independence achieved, the country lived for several years under a provisional and transitional constitutional regime. A full post-Soviet constitution was enacted as late as in 1996. As it was drafted as a political compromise, the following years saw a continuous debate about the interpretation, the implementation and the amendment of numerous articles.The orange revolution gave the Constitutional question a new impetus. One of the results of the revolutionary change was a comprehensive amendment which was to redesign the balance of power in the Ukrainian Constitution towards a Parliamentarian system. Yet, the low technical quality of the amendment jeopardizes the implementation of this legislative aim. Furthermore, already now, a comparatively short time after the revolution, some politicians fall back into ways of behaviour which were typical of the Ukrainian pre-revolutionary presidential system and which conform to the political culture of Russia and Belarus rather than to the expectations that Western Europe has towards a future close partner