Direct measurement of electron transport features in cytochrome c via V-I characteristics of STM currents

The morphology of and electron tunneling through single and cluster cytochrome c molecules deposited on self-assembled dodecanthiol monolayer film on a gold substrate have been studied experimentally using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. STM images of a single cytochrome c molecule revealed a globular structure with a diameter of ∼4 nm and height of ∼1.5 nm. A spectroscopic study obtained by recording tunneling current-bias voltage (V-I) curves revealed that the STM current increases stepwise at asymmetric threshold sample bias voltages of +100 mV and -200 mV.