162 research outputs found
Electronics and Chemistry: Varying Single Molecule Junction Conductance Using Chemical Substituents
We measure the low bias conductance of a series of substituted benzene
diamine molecules while breaking a gold point contact in a solution of the
molecules. Transport through these substituted benzenes is by means of
nonresonant tunneling or superexchange, with the molecular junction conductance
depending on the alignment of the metal Fermi level to the closest molecular
level. Electron-donating substituents, which drive the occupied molecular
orbitals up, increase the junction conductance, while electron-withdrawing
substituents have the opposite effect. Thus for the measured series,
conductance varies inversely with the calculated ionization potential of the
molecules. These results reveal that the occupied states are closest to the
gold Fermi energy, indicating that the tunneling transport through these
molecules is analogous to hole tunneling through an insulating film.Comment: 14 pages, 4 figure
From Cyber to E-Mail Incivility: A Psychometric Assessment and Measure Validation Study
Conducting research on organizational communication, and on how e-mail is used and misused by employees, is an important question addressed by this research. Specifically, we assess and address the deficiency in the existing construct of cyber incivility. This research examines how the existing scale is lacking, explains why a new scale is needed, and then develops and tests a new measure of rude e-mail. In this study we perform a quantitative test of the quality of the existing cyber incivility scale. In addition, we develop and propose a new scale with improved psychometric properties and test its validity on a sample of Mechanical Turks (MTurks). Taken together, this research develops a much-needed construct and measure of rude e-mail that is empirically informed, validated, and more useful than the existing cyber incivility scale. Implications of these findings for theory and practice are discussed
Graphene Oxidation: Thickness Dependent Etching and Strong Chemical Doping
Patterned graphene shows substantial potential for applications in future
molecular-scale integrated electronics. Environmental effects are a critical
issue in a single layer material where every atom is on the surface. Especially
intriguing is the variety of rich chemical interactions shown by molecular
oxygen with aromatic molecules. We find that O2 etching kinetics vary strongly
with the number of graphene layers in the sample. Three-layer-thick samples
show etching similar to bulk natural graphite. Single-layer graphene reacts
faster and shows random etch pits in contrast to natural graphite where
nucleation occurs at point defects. In addition, basal plane oxygen species
strongly hole dope graphene, with a Fermi level shift of ~0.5 eV. These oxygen
species partially desorb in an Ar gas flow, or under irradiation by far UV
light, and readsorb again in an O2 atmosphere at room temperature. This
strongly doped graphene is very different than graphene oxide made by mineral
acid attack.Comment: 15 pages, 5 figure
Amine-Linked Single Molecule Circuits: Systematic Trends Across Molecular Families
A comprehensive review is presented of single molecule junction conductance
measurements across families of molecules measured while breaking a gold point
contact in a solution of molecules with amine end groups. A theoretical
framework unifies the picture for the amine-gold link bonding and the tunnel
coupling through the junction using Density Functional Theory based
calculations. The reproducible electrical characteristics and utility for many
molecules is shown to result from the selective binding between the gold
electrodes and amine link groups through a donor-acceptor bond to
undercoordinated gold atoms. While the bond energy is modest, the maximum force
sustained by the junction is comparable to, but less than, that required to
break gold point contacts. The calculated tunnel coupling provides conductance
trends for all 41 molecule measurements presented here, as well as insight into
the variability of conductance due to the conformational changes within
molecules with torsional degrees of freedom. The calculated trends agree to
within a factor of two of the measured values for conductance ranging from 10-7
G0 to 10-2 G0, where G0 is the quantum of conductance (2e2/h).Comment: Invited paper for forthcoming special issue of Journal of Physics:
Condensed Matte
Single-Molecule Circuits with Well-Defined Molecular Conductance
We measure the conductance of amine-terminated molecules by breaking Au point
contacts in a molecular solution at room temperature. We find that the
variability of the observed conductance for the diamine molecule-Au junctions
is much less than the variability for diisonitrile and dithiol-Au junctions.
This narrow distribution enables unambiguous conductance measurements of single
molecules. For an alkane diamine series with 2-8 carbon atoms in the
hydrocarbon chain, our results show a systematic trend in the conductance from
which we extract a tunneling decay constant of 0.91 +/- 0.03 per methylene
group. We hypothesize that the diamine link binds preferentially to
undercoordinated Au atoms in the junction. This is supported by density
functional theory-based calculations that show the amine binding to a gold
adatom with sufficient angular flexibility for easy junction formation but
well-defined electronic coupling of the N lone pair to the Au. Therefore, the
amine linkage leads to well-defined conductance measurements of a single
molecule junction in a statistical study
Interplay between local moment and itinerant magnetism in the layered metallic antiferromagnet TaFeTe
Two-dimensional (2D) antiferromagnets have garnered considerable interest for
the next generation of functional spintronics. However, many available bulk
materials from which 2D antiferromagnets are isolated are limited by their
sensitivity to air, low ordering temperatures, and insulating transport
properties. TaFeTe offers unique opportunities to address these
challenges with increased air stability, metallic transport properties, and
robust antiferromagnetic order. Here, we synthesize TaFeTe ( =
0.14), identify its structural, magnetic, and electronic properties, and
elucidate the relationships between them. Axial-dependent high-field
magnetization measurements on TaFeTe reveal saturation magnetic
fields ranging between 27-30 T with a saturation magnetic moment of 2.05-2.12
. Magnetotransport measurements confirm TaFeTe is metallic
with strong coupling between magnetic order and electronic transport.
Angle-resolved photoemission spectroscopy measurements across the magnetic
transition uncover a complex interplay between itinerant electrons and local
magnetic moments that drives the magnetic transition. We further demonstrate
the ability to isolate few-layer sheets of TaFeTe through
mechanical exfoliation, establishing TaFeTe as a potential
platform for 2D spintronics based on metallic layered antiferromagnets.Comment: 30 pages, 5 main figures, 23 supporting figures, and 3 supporting
table
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