Electrical rectification in a Langmuir-Blodgett monolayer of dimethyanilinoazafullerene sandwiched between gold electrodes

Asymmetries were observed across a monolayer of dimethylanilinoaza[C-60]fullerene, (DMA-NC60, 1) sandwiched between gold electrodes of relatively large size (0.265 mm(2)). 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 V-1 (approximate to0.6 to 1.0 V), a dramatic increase of current to 0.3 to 1 A (as high as 1.36 x 10(7) electrons molecule(-1) s(-1) at 1.5 V), followed by ohmic behavior from V-1 to a relatively smaller negative bias V-2 (approximate to -0.5 V to -0.6 V). At more negative potentials (e.g., at - 1.5 V) the current is very small (a few muA). 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 mum(2) area) are used. The defects could be stalagmitic filaments of gold. which grow from the bottom electrode above V-1 but are broken at the negative bias V-2, 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.