Relating Energy Level Alignment and Amine-Linked Single Molecule Junction Conductance

Using photoemission spectroscopy, we determine the relationship between electronic energy level alignment at a metal-molecule interface and single-molecule junction transport data. We measure the position of the highest occupied molecular orbital (HOMO) relative to the Au metal Fermi level for three 1,4-benzenediamine derivatives on Au(111) and Au(110) with ultraviolet and resonant x-ray photoemission spectroscopy. We compare these results to scanning tunnelling microscope based break-junction measurements of single molecule conductance and to first-principles calculations. We find that the energy difference between the HOMO and Fermi level for the three molecules adsorbed on Au(111) correlate well with changes in conductance, and agree well with quasiparticle energies computed from first-principles calculations incorporating self-energy corrections. On the Au(110) which present Au atoms with lower-coordination, critical in break-junction conductance measurements, we see that the HOMO level shifts further from the Fermi level. These results provide the first direct comparison of spectroscopic energy level alignment measurements with single molecule junction transport data

Determination of the structure and geometry of N-heterocyclic carbenes on Au(111) using high-resolution spectroscopy

N-heterocyclic carbenes (NHCs) bind very strongly to transition metals due to their unique electronic structure featuring a divalent carbon atom with a lone pair in a highly directional sp(2)-hybridized orbital. As such, they can be assembled into monolayers on metal surfaces that have enhanced stability compared to their thiol-based counterparts. The utility of NHCs to form such robust self-assembled monolayers (SAMs) was only recently recognized and many fundamental questions remain. Here we investigate the structure and geometry of a series of NHCs on Au(111) using high-resolution X-ray photoelectron spectroscopy and density functional theory calculations. We find that the N-substituents on the NHC ring strongly affect the molecule-metal interaction and steer the orientation of molecules in the surface layer. In contrast to previous reports, our experimental and theoretical results provide unequivocal evidence that NHCs with N-methyl substituents bind to undercoordinated adatoms to form flat-lying complexes. In these SAMs, the donor-acceptor interaction between the NHC lone pair and the undercoordinated Au adatom is primarily responsible for the strong bonding of the molecules to the surface. NHCs with bulkier N-substituents prevent the formation of such complexes by forcing the molecules into an upright orientation. Our work provides unique insights into the bonding and geometry of NHC monolayers; more generally, it charts a clear path to manipulating the interaction between NHCs and metal surfaces using traditional coordination chemistry synthetic strategies

Tuning ultrafast electron injection dynamics at organic-graphene/metal interfaces

We compare the ultrafast charge transfer dynamics of molecules on epitaxial graphene and bilayer graphene grown on Ni(111) interfaces through first principles calculations and X-ray resonant photoemission spectroscopy. We use 4,4'-bipyridine as a prototypical molecule for these explorations as the energy level alignment of core-excited molecular orbitals allows ultrafast injection of electrons from a substrate to a molecule on a femtosecond timescale. We show that the ultrafast injection of electrons from the substrate to the molecule is 3c4 times slower on weakly coupled bilayer graphene than on epitaxial graphene. Through our experiments and calculations, we can attribute this to a difference in the density of states close to the Fermi level between graphene and bilayer graphene. We therefore show how graphene coupling with the substrate influences charge transfer dynamics between organic molecules and graphene interfaces

Length-Independent Charge Transport in Chimeric Molecular Wires

Advanced molecular electronic components remain vital for the next generation of miniaturized integrated circuits. Thus, much research effort has been devoted to the discovery of lossless molecular wires, for which the charge transport rate or conductivity is not attenuated with length in the tunneling regime. Herein, we report the synthesis and electrochemical interrogation of DNA-like molecular wires. We determine that the rate of electron transfer through these constructs is independent of their length and propose a plausible mechanism to explain our findings. The reported approach holds relevance for the development of high-performance molecular electronic components and the fundamental study of charge transport phenomena in organic semiconductors

Sex- and age-related differences in the management and outcomes of chronic heart failure: an analysis of patients from the ESC HFA EORP Heart Failure Long-Term Registry

Aims: This study aimed to assess age- and sex-related differences in management and 1-year risk for all-cause mortality and hospitalization in chronic heart failure (HF) patients. Methods and results: Of 16 354 patients included in the European Society of Cardiology Heart Failure Long-Term Registry, 9428 chronic HF patients were analysed [median age: 66 years; 28.5% women; mean left ventricular ejection fraction (LVEF) 37%]. Rates of use of guideline-directed medical therapy (GDMT) were high (angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, beta-blockers and mineralocorticoid receptor antagonists: 85.7%, 88.7% and 58.8%, respectively). Crude GDMT utilization rates were lower in women than in men (all differences: P\ua0 64 0.001), and GDMT use became lower with ageing in both sexes, at baseline and at 1-year follow-up. Sex was not an independent predictor of GDMT prescription; however, age >75 years was a significant predictor of GDMT underutilization. Rates of all-cause mortality were lower in women than in men (7.1% vs. 8.7%; P\ua0=\ua00.015), as were rates of all-cause hospitalization (21.9% vs. 27.3%; P\ua075 years. Conclusions: There was a decline in GDMT use with advanced age in both sexes. Sex was not an independent predictor of GDMT or adverse outcomes. However, age >75 years independently predicted lower GDMT use and higher all-cause mortality in patients with LVEF 6445%

Tailoring SAM-on-SAM Formation

We present the formation, under ultrahigh vacuum conditions, of a three-dimensional organic architecture on a Au(111) surface based on the NH(2)-COOH interaction. The surface is first functionalized with a self-assembled monolayer (SAM) of an amine-terminated molecule (cysteamine, CA); then, a layer of benzoic acid (BA) is grown on top. We characterized this self-assembled structure by means of X-ray photoemission and absorption spectroscopy. The formation of a hydrogen bond between the two molecular species anchors the BA molecules to the CA. The structure is homogeneous in terms of its morphology and chemical properties. We also show that the structure (molecular orientation) of the BA SAM formed on the CA SAM is different from that of the BA SAM on the bare Au surface. The chemical recognition and molecular ordering nature of the BA-CA self-assembly makes it a promising candidate for the bottom-up parallel fabrication of hierarchically assembled nanodevices starting from fimctionalized building blocks

Structure and Energy Level Alignment of Tetramethyl Benzenediamine on Au(111)

We investigate the binding and energy level alignment of 2,3,5,6-tetramethyl-1,4-benzenediamine (TMBDA) on Au(111) through a combination of helium atom scattering (HAS), X-ray photoemission (XPS), and scanning tunneling microscopy (STM). We show that TMBDA binds to step edges and to flat Au (111) terraces in a nearly flat-lying configuration. Through combination of HAS and STM data, we determine that the molecules are bound on step edges with an adsorption energy of about 1.2 eV, which is about 0.2 eV stronger than the adsorption energy we measure on flat surface. Preferential bonding to the under-coordinated Au atoms on step edges suggests that the molecules bind to Au through the nitrogen lone pair. Finally, STM measurements on TMBDA in these two different adsorption configurations show that the highest-occupied molecular orbital is deeper relative to Fermi for the more strongly bound molecules on step edges, confirming that the nitrogen bonds through charge donation to the Au