Figure 4.

Transfer characteristics of graphene FET devices as a function of the number of PAH/PSS multilayers measured in (a) 1 mM NaCl and (b) 100 mM NaCl at V_ds = 0.1 V. Transfer characteristics of the device before (black dashed and dotted line) and after polymer coating with PAH (blue lines) and PSS (green lines). 1^st and 2^nd layers are solid lines. 3^rd and 4^th layers are dotted lines. 5^th and 6^th layers are dashed lines. Measured (red triangles) and predicted (black squares) device Dirac point voltage shift vs. the number of coating polymer layers for (c) 1 mM NaCl and (d) 100 mM NaCl. The Dirac point voltage of the uncoated device is regarded as the reference point.