Keithley 2602

Surface topography was observed by Dimension FastScan Bio (atomic force microscopy (AFM)) (Bruker Corp., Billerica, Germany) using tapping mode, and Nova Nano SEM 450 (FEI Company, Hillsboro, OR, USA). Raman spectroscopy measurements were performed using Lab Ram HR800 (Horiba, Ltd., Kyoto, Japan) with a 514 nm laser. The binding energy was measured by ESCALAB 250XI (XPS) (Thermo Fisher Scientific Inc., Waltham, MA, USA). The measurements of electrical characterizations were performed by a Keithley 2602 source meter (Keithley Instruments LLC., Solon, OH, USA).

For electrical measurements, a digital source meter (Keithley 2602, Keithley Instruments, OH, USA) in combination with a probe station, consisting of two micromanipulators (Süss MicroTec, GArching, Germany) with tungsten needles, a microscope (Olympus, Tokyo, Japan), and a data acquisition system was employed. The experimental setup, including electrical circuit, is schematized in Figure S1A. Briefly, under ambient conditions, the source–drain current I_SD was recorded as a function of the gate voltage V_G that was swept from −10 to 10 V and back, while a fixed source–drain voltage V_SD = 25 mV was maintained. Data recording and analysis were performed with help of the software MATLAB© (R2012b, MathWorks, Natick, MA, USA).
For temperature-dependent measurements, a home-made Peltier element, coated with a thin metal layer, was used to heat the sensors.