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

Abstract

Asymmetries were observed across a monolayer of dimethylanilinoaza[C 60 ]fullerene, (DMA-NC 60 , 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 (≈0.6 to 1.0 V), a dramatic increase of current to 0.3 to 1 A (as high as 1.36 × 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 (≈ -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 µm 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.

HOMO–LUMO coupling: the fourth rule for highly effective molecular rectifiers

“…Azafulleroids have been shown to be stable in the solution phase at liquid/liquid interfaces, and Langmuir-Blodgett monolayers of a similar azafulleroid have previously displayed highly asymmetric current-voltage profiles. 15 It is further possible to attach these molecules between metallic contacts, as the protocols for grafting fullerenes to gold surfaces have been well documented in the literature. 16,17 We note that 4TPA-C 60 fulfills all three rules laid out above.…”

Single‐Walled Carbon Nanotube Based Molecular Switch Tunnel Junctions

“…The nanotube interacts noncovalently with a monolayer of bistable, nondegenerate [2]catenane tetracations, self-organized by their supporting amphiphilic dimyristoylphosphatidyl anions which shield the mechanically switchable tetracations from a twomicrometer wide metallic top electrode. The resulting 0.002 mm 2 area tunnel junction addresses a nanometer wide row of % 2000 molecules.…”

Molecular orbital analysis of frontier orbitals for molecular electronics: a case study of unimolecular rectifier and photovoltaic cell

“…4 clearly indicates that HOMO and LUMO are delocalized on a whole polymer. A rectifier is reported in the case of a D(donor)-p-A(acceptor) structure [33,34], even though, this porphyrin polymer does not exhibit the localized frontier orbital. However, a nonconjugated chain displays rectifying features (Cr -Cu and Zn -Fe).…”