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Janus Reversal and Coulomb Blockade in Ferrocene-Perylenebisimide and N,N,N′,N′-Tetramethyl-para-phenylenediamine-Perylenebisimide D-σ-A Rectifiers

Author(s):

Marcus S. Johnson, Rajesh Kota, Daniell L. Mattern, Robert M. Metzger

Journal:

Langmuir

Year:

2016

Volume:

32

Pages

6851-6859

DOI:

10.1021/acs.langmuir.6b01567

Abstract:

Sandwiches “EGaIn|Ga2O3|LB monolayer of 2|Au” and “EGaIn|Ga2O3|LB
monolayer of 3|Au” rectify. They are formed from a Langmuir−Blodgett (LB) monolayer
of 2 or 3 transferred onto thermally evaporated gold. Molecules 2 and 3 are of the donorsigma-acceptor (D-σ-A) type and have the same perylenebisimide (PBI) acceptor as
previously studied molecule 1. Molecule 1 has the weak donor pyrene, 2 has the good
donor ferrocene, and 3 has the very strong donor N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD). All three molecules have a long swallowtail ending in a thioacetyl group,
which ensures slow chemisorption onto the Au electrode. These molecules were contacted
directly by a gallium indium eutectic (EGaIn) drop, covered by a defective oxide Ga2O3
layer. As before for 1, the direction of rectification for 2 is bias-dependent. In the ±1.0 V
range, the rectification is at positive V, with a rectification ratio (RR) that is initially greater
than 5 and then decreases on successive scans to 2, while the currents decrease by as much
as 2 orders of magnitude. In the ±2.5 V range, the rectification direction for 2 reverses,
while upon repeated scanning the rectification ratio (in the negative direction) increases
and the currents decrease. For molecule 3, both directions have a charge-trapped state (Coulomb blockade) leading to Voffset in
both biases, but at high potentials rectification set is, with large RR (up to 2,800) at ±2.5 V.

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