Metal finger electrode fabrication: Glass microscope slides were used as substrates for the electrodes. The glass substrates were washed with distilled water and dried using hot air. Using an E-beam evaporator at a deposition rate of 2 Ås -1 under 5 × 10 -7 Torr at room temperature, 100 nm Au on 10 nm Cr were evaporated through shadow masks. Mats were placed on finger electrodes and gently dried with filter paper to remove excess water.