4 research outputs found
Controlling Spin Interference in Single Radical Molecules
Quantum interference (QI) dominates the electronic properties
of
single molecules even at room temperature and can lead to a large
change in their electrical conductance. To take advantage of this
for nanoelectronic applications, a mechanism to electronically control
QI in single molecules needs to be developed. In this paper, we demonstrate
that controlling the quantum interference of each spin in a stable
open-shell organic radical with a large Ļ-system is possible
by changing the spin state of the radical. We show that the counterintuitive
constructive spin interference in a meta-connected
radical changes to destructive interference by changing the spin state
of the radical from a doublet to a singlet. This results in a significant
change in the room temperature electrical conductance by several orders
of magnitude, opening up new possibilities for spin interference based
molecular switches for energy storage and conversion applications
Thermopower in Underpotential Deposition-Based Molecular Junctions
Underpotential deposition
(UPD) is an intriguing means for tailoring
the interfacial electronic structure of an adsorbate at a substrate.
Here we investigate the impact of UPD on thermoelectricity occurring
in molecular tunnel junctions based on alkyl self-assembled monolayers
(SAMs). We observed noticeable enhancements in the Seebeck coefficient
of alkanoic acid and alkanethiol monolayers, by up to 2- and 4-fold,
respectively, upon replacement of a conventional Au electrode with
an analogous bimetallic electrode, Cu UPD on Au. Quantum transport
calculations indicated that the increased Seebeck coefficients are
due to the UPD-induced changes in the shape or position of transmission
resonances corresponding to gateway orbitals, which depend on the
choice of the anchor group. Our work unveils UPD as a potent means
for altering the shape of the tunneling energy barrier at the moleculeāelectrode
contact of alkyl SAM-based junctions and hence enhancing thermoelectric
performance
Graphene Sculpturene Nanopores for DNA Nucleobase Sensing
To
demonstrate the potential of nanopores in bilayer graphene for
DNA sequencing, we computed the currentāvoltage characteristics
of a bilayer graphene junction containing a nanopore and found that
they change significantly when nucleobases are transported through
the pore. To demonstrate the sensitivity and selectivity of example
devices, we computed the probability distribution <i>P</i><sub>X</sub>(Ī²) of the quantity Ī² representing the change
in the logarithmic current through the pore due to the presence of
a nucleobase X (X = adenine, thymine, guanine, or cytosine). We quantified
the selectivity of the bilayer-graphene nanopores by showing that <i>P</i><sub>X</sub>(Ī²) exhibits distinct peaks for each
base X. To demonstrate that such discriminating sensing is a general
feature of bilayer nanopores, the well-separated positions of these
peaks were shown to be present for different pores, with alternative
examples of electrical contacts
Single-Molecule Conductance Behavior of Molecular Bundles
Controlling the orientation of complex molecules in molecular
junctions
is crucial to their development into functional devices. To date,
this has been achieved through the use of multipodal compounds (i.e.,
containing more than two anchoring groups), resulting in the formation
of tri/tetrapodal compounds. While such compounds have greatly improved
orientation control, this comes at the cost of lower surface coverage.
In this study, we examine an alternative approach for generating multimodal
compounds by binding multiple independent molecular wires together
through metal coordination to form a molecular bundle. This was achieved
by coordinating iron(II) and cobalt(II) to 5,5ā²-bis(methylthio)-2,2ā²-bipyridine
(L1) and (methylenebis(4,1-phenylene))bis(1-(5-(methylthio)pyridin-2-yl)methanimine)
(L2) to give two monometallic
complexes, Fe-1 and Co-1, and two bimetallic
helicates, Fe-2 and Co-2. Using XPS, all
of the complexes were shown to bind to a gold surface in a fac fashion through three thiomethyl groups. Using single-molecule
conductance and DFT calculations, each of the ligands was shown to
conduct as an independent wire with no impact from the rest of the
complex. These results suggest that this is a useful approach for
controlling the geometry of junction formation without altering the
conductance behavior of the individual molecular wires