67 research outputs found
Data Sharing: How Much Doesn't Get Submitted to GenBank?
Funding agencies and journals require researchers to deposit DNA sequences in public databases such as GenBank when the paper is published, but how often do authors fail to do so
Molecularly Resolved Electronic Landscapes of Differing Acceptor-Donor Interface Geometries
Organic semiconductors are a promising class of materials for numerous
electronic and optoelectronic applications, including solar cells. However,
these materials tend to be extremely sensitive to the local environment and
surrounding molecular geometry, causing the energy levels near boundaries and
interfaces essential to device function to differ from those of the bulk.
Scanning Tunneling Microscopy and Spectroscopy (STM/STS) has the ability to
examine both the structural and electronic properties of these interfaces on
the molecular and submolecular scale. Here we investigate the prototypical
acceptor/donor system PTCDA/CuPc using sub-molecularly resolved pixel-by-pixel
STS to demonstrate the importance of subtle changes in interface geometry in
prototypical solar cell materials. PTCDA and CuPc were sequentially deposited
on NaCl bilayers to create lateral heterojunctions that were decoupled from the
underlying substrate. Donor and acceptor states were observed to shift in
opposite directions suggesting an equilibrium charge transfer between the two.
Narrowing of the gap energy compared to isolated molecules on the same surface
are indicative of the influence of the local dielectric environment. Further,
we find that the electronic state energies of both acceptor and donor are
strongly dependent on the ratio and positioning of both molecules in larger
clusters. This molecular-scale structural dependence of the electronic states
of both interfacial acceptor and donor has significant implications for device
design where level alignment strongly correlates to device performance
Electrically driven photon emission from individual atomic defects in monolayer WS2.
Quantum dot-like single-photon sources in transition metal dichalcogenides (TMDs) exhibit appealing quantum optical properties but lack a well-defined atomic structure and are subject to large spectral variability. Here, we demonstrate electrically stimulated photon emission from individual atomic defects in monolayer WS2 and directly correlate the emission with the local atomic and electronic structure. Radiative transitions are locally excited by sequential inelastic electron tunneling from a metallic tip into selected discrete defect states in the WS2 bandgap. Coupling to the optical far field is mediated by tip plasmons, which transduce the excess energy into a single photon. The applied tip-sample voltage determines the transition energy. Atomically resolved emission maps of individual point defects closely resemble electronic defect orbitals, the final states of the optical transitions. Inelastic charge carrier injection into localized defect states of two-dimensional materials provides a powerful platform for electrically driven, broadly tunable, atomic-scale single-photon sources
Designing optoelectronic properties by on-surface synthesis: formation and electronic structure of an iron-terpyridine macromolecular complex
Supramolecular chemistry protocols applied on surfaces offer compelling
avenues for atomic scale control over organic-inorganic interface structures.
In this approach, adsorbate-surface interactions and two-dimensional
confinement can lead to morphologies and properties that differ dramatically
from those achieved via conventional synthetic approaches. Here, we describe
the bottom-up, on-surface synthesis of one-dimensional coordination
nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed
from functional metal-organic complexes used in photovoltaic and catalytic
applications. Thermally activated diffusion of sequentially deposited ligands
and metal atoms, and intra-ligand conformational changes, lead to Fe-tpy
coordination and formation of these nanochains. Low-temperature Scanning
Tunneling Microscopy and Density Functional Theory were used to elucidate the
atomic-scale morphology of the system, providing evidence of a linear tri-Fe
linkage between facing, coplanar tpy groups. Scanning Tunneling Spectroscopy
reveals highest occupied orbitals with dominant contributions from states
located at the Fe node, and ligand states that mostly contribute to the lowest
unoccupied orbitals. This electronic structure yields potential for hosting
photo-induced metal-to-ligand charge transfer in the visible/near-infrared. The
formation of this unusual tpy/tri-Fe/tpy coordination motif has not been
observed for wet chemistry synthesis methods, and is mediated by the bottom-up
on-surface approach used here
How Substitutional Point Defects in Two-Dimensional WS Induce Charge Localization, Spin-Orbit Splitting, and Strain
Control of impurity concentrations in semiconducting materials is essential
to device technology. Because of their intrinsic confinement, the properties of
two-dimensional semiconductors such as transition metal dichalcogenides (TMDs)
are more sensitive to defects than traditional bulk materials. The
technological adoption of TMDs is dependent on the mitigation of deleterious
defects and guided incorporation of functional foreign atoms. The first step
towards impurity control is the identification of defects and assessment of
their electronic properties. Here, we present a comprehensive study of point
defects in monolayer tungsten disulfide (WS) grown by chemical vapor
deposition (CVD) using scanning tunneling microscopy/spectroscopy, CO-tip
noncontact atomic force microscopy, Kelvin probe force spectroscopy, density
functional theory, and tight-binding calculations. We observe four different
substitutional defects: chromium (Cr) and molybdenum
(Mo) at a tungsten site, oxygen at sulfur sites in both bottom and
top layers (O top/bottom), as well as two negatively charged
defects (CDs). Their electronic fingerprints unambiguously corroborate the
defect assignment and reveal the presence or absence of in-gap defect states.
The important role of charge localization, spin-orbit coupling, and strain for
the formation of deep defect states observed at substitutional defects in
WS as reported here will guide future efforts of targeted defect
engineering and doping of TMDs
Spatially resolved star formation and inside-out quenching in the TNG50 simulation and 3D-HST observations
We compare the star-forming main sequence (SFMS) of galaxies – both integrated and resolved on 1 kpc scales – between the high-resolution TNG50 simulation of IllustrisTNG and observations from the 3D-HST slitless spectroscopic survey at z ∼ 1. Contrasting integrated star formation rates (SFRs), we find that the slope and normalization of the star-forming main sequence in TNG50 are quantitatively consistent with values derived by fitting observations from 3D-HST with the Prospector Bayesian inference framework. The previous offsets of 0.2–1 dex between observed and simulated main-sequence normalizations are resolved when using the updated masses and SFRs from Prospector. The scatter is generically smaller in TNG50 than in 3D-HST for more massive galaxies with M*> 1010 M⊙, by ∼10–40 per cent, after accounting for observational uncertainties. When comparing resolved star formation, we also find good agreement between TNG50 and 3D-HST: average specific star formation rate (sSFR) radial profiles of galaxies at all masses and radii below, on, and above the SFMS are similar in both normalization and shape. Most noteworthy, massive galaxies with M*> 1010.5 M⊙, which have fallen below the SFMS due to ongoing quenching, exhibit a clear central SFR suppression, in both TNG50 and 3D-HST. In contrast, the original Illustris simulation and a variant TNG run without black hole kinetic wind feedback, do not reproduce the central SFR profile suppression seen in data. In TNG, inside-out quenching is due to the supermassive black hole (SMBH) feedback model operating at low accretion rates
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Characteristics of European adults who dropped out from the Food4Me Internet-based personalised nutrition intervention
Objective To characterise participants who dropped out of the Food4Me Proof-of-Principle study.
Design The Food4Me study was an Internet-based, 6-month, four-arm, randomised controlled trial. The control group received generalised dietary and lifestyle recommendations, whereas participants randomised to three different levels of personalised nutrition (PN) received advice based on dietary, phenotypic and/or genotypic data, respectively (with either more or less frequent feedback).
Setting Seven recruitment sites: UK, Ireland, The Netherlands, Germany, Spain, Poland and Greece.
Subjects Adults aged 18–79 years (n 1607).
Results A total of 337 (21 %) participants dropped out during the intervention. At baseline, dropouts had higher BMI (0·5 kg/m2; P<0·001). Attrition did not differ significantly between individuals receiving generalised dietary guidelines (Control) and those randomised to PN. Participants were more likely to drop out (OR; 95 % CI) if they received more frequent feedback (1·81; 1·36, 2·41; P<0·001), were female (1·38; 1·06, 1·78; P=0·015), less than 45 years old (2·57; 1·95, 3·39; P<0·001) and obese (2·25; 1·47, 3·43; P<0·001). Attrition was more likely in participants who reported an interest in losing weight (1·53; 1·19, 1·97; P<0·001) or skipping meals (1·75; 1·16, 2·65; P=0·008), and less likely if participants claimed to eat healthily frequently (0·62; 0·45, 0·86; P=0·003).
Conclusions Attrition did not differ between participants receiving generalised or PN advice but more frequent feedback was related to attrition for those randomised to PN interventions. Better strategies are required to minimise dropouts among younger and obese individuals participating in PN interventions and more frequent feedback may be an unnecessary burden
The ocean sampling day consortium
Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits
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