*2.3. Measurements*

The current density-voltage (J-V) characteristics of the devices were measured in response to a voltage sweep from 0.0 to +1.0 V, using a Keithley 2636 source meter. The capacitance of EHCz was also measured with Agilent 4284A Precision LCR Meter (Agilent, Santa Clara, CA, USA), to evaluate the dielectric constant.
