Electrical Rectification in a Langmuir−Blodgett Monolayer of Dimethyanilinoazafullerene Sandwiched between Gold Electrodes

Abstract

Asymmetries were observed across a monolayer of dimethylanilinoaza[C60]fullerene, (DMA-NC60, 1) sandwiched between gold electrodes of relatively large size (0.265 mm2). Two modes of behavior are observed: (1) a sigmoidal and slightly asymmetric behavior, bespeaking of a moderate unimolecular rectifier (rectification ratio of about 2), and (2) above a threshold voltage V1 (≈0.6 to 1.0 V), a dramatic increase of current to 0.3 to 1 A (as high as 1.36 × 107 electrons molecule-1 s-1 at 1.5 V), followed by ohmic behavior from V1 to a relatively smaller negative bias V2 (≈ −0.5 V to −0.6 V). At more negative potentials (e.g., at −1.5 V) the current is very small (a few μA). This high asymmetry in current persists for between 10 and 20 cycles of voltage scan. This increased, but ohmic conductivity is probably due to defects that grow at domain boundaries, since this behavior is not seen when very small electrodes (1 μm2 area) are used. The defects could be stalagmitic filaments of gold which grow from the bottom electrode above V1 but are broken at the negative bias V2, or else they could be due to some unknown electrochemical couple. This device is vaguely reminiscent of Zener diodes or varistors: if operated between, say, + 2 V and −2 V, it is a super-rectifier, with a rectification ratio of up to 20 000 at 1.5 V.