%0 DATA
%A Kung-Ching, Liao
%A Liang-Yan, Hsu
%A Carleen M., Bowers
%A Herschel, Rabitz
%A George M., Whitesides
%D 2015
%T Molecular
Series-Tunneling Junctions
%U https://acs.figshare.com/articles/Molecular_Series_Tunneling_Junctions/2167333
%R 10.1021/jacs.5b00448.s001
%2 https://ndownloader.figshare.com/files/3801232
%K SAM
%K density
%K junction
%K groups R 1
%K R 1
%K R 2
%K AgTS
%K R 2 units
%K tunneling decay constants
%K HOMO
%K 6H
%X Charge transport through junctions
consisting of insulating molecular
units is a quantum phenomenon that cannot be described adequately
by classical circuit laws. This paper explores tunneling current densities
in self-assembled monolayer (SAM)-based junctions with the structure
Ag^{TS}/O_{2}C–R_{1}–R_{2}–H//Ga_{2}O_{3}/EGaIn, where Ag^{TS} is template-stripped silver and EGaIn is the eutectic alloy of gallium
and indium; R_{1} and R_{2} refer to two classes of
insulating molecular units(CH_{2})_{n} and (C_{6}H_{4})_{m}that are connected in series and have different tunneling
decay constants in the Simmons equation. These junctions can be analyzed
as a form of series-tunneling junctions based on the observation that
permuting the order of R_{1} and R_{2} in the junction
does not alter the overall rate of charge transport. By using the
Ag/O_{2}C interface, this system decouples the highest occupied
molecular orbital (HOMO, which is localized on the carboxylate group)
from strong interactions with the R_{1} and R_{2} units.
The differences in rates of tunneling are thus determined by the electronic
structure of the groups R_{1} and R_{2}; these differences
are *not* influenced by the order of R_{1} and
R_{2} in the SAM. In an electrical potential model that rationalizes
this observation, R_{1} and R_{2} contribute independently
to the height of the barrier. This model explicitly assumes that contributions
to rates of tunneling from the Ag^{TS}/O_{2}C and
H//Ga_{2}O_{3} interfaces are constant across the
series examined. The current density of these series-tunneling junctions
can be described by *J*(*V*) = *J*_{0}(*V*) exp(−β_{1}*d*_{1} – β_{2}*d*_{2}), where *J*(*V*) is the current density (A/cm^{2}) at applied
voltage *V* and β_{i} and *d*_{i} are the parameters
describing the attenuation of the tunneling current through a rectangular
tunneling barrier, with width *d* and a height related
to the attenuation factor β.