Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene

Using the recently developed technique of microsoldering, we perform systematic transport studies of the influence of polymethylmethacrylate on graphene revealing a doping effect with a n-type dopant density Delta n of up to Delta n=3.8x10(12) cm(-2) but negligible influence on mobility and hysteresis. Moreover, we show that microsoldered graphene is free of contamination and exhibits very similar intrinsic rippling as found for lithographically contacted flakes. Characterizing the microsoldered sample by scanning tunneling spectroscopy, we demonstrate a current induced closing of the phonon gap and a B-field induced double peak attributed to the 0 Landau level.