ČERMÁK Jan Institute of Physics AS CR, v.v.i.

Microscopic Characterization of Graphene Electronic Quality Across Neighbouring, Differently Oriented Copper Grains

Co-authors YAMADA Takatoshi, GANZEROVÁ Kristína, REZEK Bohuslav

A graphene layer is prepared on a copper foil by thermal chemical vapor deposition (CVD). The high temperature (1000 °C) during the CVD process causes re-crystallization of the copper substrate leading to a granular structure with grains of several tens or even hundreds of um in diameter, typically. After the CVD, optical microscopy shows that each grain is differently coloured. In this study, we focus on a 50x50 um2 area covering three such grains (darkest, dark, and brightest) and their junctions. Raman micro-spectroscopy proves the presence of mostly a monolayer graphene at all the three grains by detecting both 2D and G bands of intensity ratio (I2D/IG) around 2.5. Yet their absolute intensities are grain-dependent: highest at the darkest grain and lowest at the brightest one. Different properties are also observed by current sensing atomic force microscopy (CS-AFM) which detects highest electric current at the brightest grain. The same trend is further seen by local current as a function of voltage characteristics measured by an AFM probe. The phase imaging AFM at the same area reveals differences in mechanical properties not only between the grains, but an internal structuring within a single grain as well. The thermal CVD on a copper foil in fact results in three types of graphene on a single substrate. We discuss the above experimental results and compare them with similar experimental set of data obtained on CVD graphene layers prepared on variously treated and prepared copper substrates.