Graphene Photonics and Optoelectronics

The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultra-wide-band tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Here we review the state of the art in this emerging field.Comment: Review Nature Photonics, in pres

Bio-inspired nanocatalysts for the oxygen reduction reaction

Electrochemical conversions at fuel cell electrodes are complex processes. In particular, the oxygen reduction reaction has substantial overpotential limiting the electrical power output efficiency. Effective and inexpensive catalytic interfaces are therefore essential for increased performance. Taking inspiration from enzymes, earth-abundant metal centres embedded in organic environments present remarkable catalytic active sites. Here we show that these enzyme-inspired centres can be effectively mimicked in two-dimensional metal-organic coordination networks self-assembled on electrode surfaces. Networks consisting of trimesic acid and bis-pyridyl-bispyrimidine coordinating to single iron and manganese atoms on Au(111) effectively catalyse the reduction and reveal distinctive catalytic activity in alkaline media. These results demonstrate the potential of surface-engineered metal-organic networks for electrocatalytic conversions. Specifically designed coordination complexes at surfaces inspired by enzyme cofactors represent a new class of nanocatalysts with promising applications in electrocatalysis.Fil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Max Planck Institute for Solid State Research; AlemaniaFil: Wurtser, Benjamin. Max Planck Institute for Solid State Research; AlemaniaFil: Stepanow, Sabastian. Max Planck Institute for Solid State Research; AlemaniaFil: Kern, Klaus. Max Planck Institute for Solid State Research; Alemania. Ecole Polytechnique Federale de Lausanne; Suiz

Effect of ACE inhibitors on endothelial dysfunction: Unanswered questions and implications for further investigation and therapy

Experimental studies have suggested that angiotensin-converting enzyme (ACE) inhibitors may have an important role in blocking the progression of and/or reversing endothelial dysfunction. The extrapolation of these experimental studies to the clinical situation has, however, been disappointing. Studies of forearm-mediated endothelial vasodilatation in patients with hypertension with captopril, enalapril, and cilazapril have been negative. The finding of the Trial in Reversing Endothelial Dysfunction (TREND) that the administration of quinapril to normotensive patients with coronary artery disease in part restores endothelial-mediated coronary vasodilation, as assessed by intracoronary administration of acetylcholine, has important implications for future therapy and raises several important questions. The differences in the TREND and previous studies of ACE inhibitors on endothelial dysfunction may be due to mechanistic differences in endothelial dysfunction in patients with coronary artery disease and hypertension. Although in general there has been a good correlation between endothelial dysfunction as assessed by forearm flow and coronary endothelial dysfunction as assessed by acetylcholine, these vascular beds may be affected differently by therapeutic interventions, especially with an ACE inhibitor, which may affect sheart stress and angiotensin II formation in different vascular beds differently. Third, one needs to question whether the effect of quinapril on coronary endothelial dysfunction is a class effect or unique to quinapril. It will be necessary to test the effectiveness of other ACE inhibitors on coronary endothelial dysfunction in humans before concluding that the beneficial effects of quinapril are due to a class effect.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44542/1/10557_2004_Article_BF00051113.pd

Cardiovascular disease, chronic kidney disease, and diabetes mortality burden of cardiometabolic risk factors from 1980 to 2010: A comparative risk assessment

Background: High blood pressure, blood glucose, serum cholesterol, and BMI are risk factors for cardiovascular diseases and some of these factors also increase the risk of chronic kidney disease and diabetes. We estimated mortality from cardiovascular diseases, chronic kidney disease, and diabetes that was attributable to these four cardiometabolic risk factors for all countries and regions from 1980 to 2010. Methods: We used data for exposure to risk factors by country, age group, and sex from pooled analyses of population-based health surveys. We obtained relative risks for the effects of risk factors on cause-specific mortality from meta-analyses of large prospective studies. We calculated the population attributable fractions for each risk factor alone, and for the combination of all risk factors, accounting for multicausality and for mediation of the effects of BMI by the other three risks. We calculated attributable deaths by multiplying the cause-specific population attributable fractions by the number of disease-specific deaths. We obtained cause-specific mortality from the Global Burden of Diseases, Injuries, and Risk Factors 2010 Study. We propagated the uncertainties of all the inputs to the final estimates. Findings: In 2010, high blood pressure was the leading risk factor for deaths due to cardiovascular diseases, chronic kidney disease, and diabetes in every region, causing more than 40% of worldwide deaths from these diseases; high BMI and glucose were each responsible for about 15% of deaths, and high cholesterol for more than 10%. After accounting for multicausality, 63% (10·8 million deaths, 95% CI 10·1-11·5) of deaths from these diseases in 2010 were attributable to the combined effect of these four metabolic risk factors, compared with 67% (7·1 million deaths, 6·6-7·6) in 1980. The mortality burden of high BMI and glucose nearly doubled from 1980 to 2010. At the country level, age-standardised death rates from these diseases attributable to the combined effects of these four risk factors surpassed 925 deaths per 100 000 for men in Belarus, Kazakhstan, and Mongolia, but were less than 130 deaths per 100 000 for women and less than 200 for men in some high-income countries including Australia, Canada, France, Japan, the Netherlands, Singapore, South Korea, and Spain. Interpretation: The salient features of the cardiometabolic disease and risk factor epidemic at the beginning of the 21st century are high blood pressure and an increasing effect of obesity and diabetes. The mortality burden of cardiometabolic risk factors has shifted from high-income to low-income and middle-income countries. Lowering cardiometabolic risks through dietary, behavioural, and pharmacological interventions should be a part of the global response to non-communicable diseases. Funding: UK Medical Research Council, US National Institutes of Health. © 2014 Elsevier Ltd

Dynamics of semiconducting nanocrystal uptake into mesoporous TiO2 thick films by electrophoretic deposition

Electrophoretic deposition (EPD) is a simple technique for the uptake of nanoparticles into mesoporous films, for example to graft semiconducting nanocrystals (quantum dots, QDs) on mesoporous oxide thick films acting as photoanodes in third generation solar cells. Here we study the uptake of colloidal QDs into mesoporous TiO2 films using EPD. We examined PbS@CdS core@shell QDs, which are optically active in the near infrared (NIR) region of the solar spectrum and exhibit improved long-term stability toward oxidation compared to their pure PbS counterpart, as demonstrated by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. We applied Rutherford backscattering spectrometry (RBS) to obtain the Pb depth profile into the TiO2 matrix. EPD duration in the range from 5 to 120 min and applied voltages from 50 to 200 V were considered. The applied electric field induces the fast anchoring of QDs to the oxide surface. Consequently, QD concentration in the solution contained in the mesoporous film drastically decreases, inducing a Fick-like diffusion of QDs. We modelled the entire process as a QD diffusion related to the formation of a QD concentration gradient, and a depth-independent QD anchoring, and were able to determine the electric field-induced diffusion coefficient D for QDs and the characteristic time for QD grafting, in very good agreement with the experiment. D increases from (1.5 +/- 0.4) x 10(-5) mu m(2) s(-1) at 50 V to (1.1 +/- 0.3) x 10(-3) mu m(2) s(-1) at 200 V. The dynamics of EPD may also be applied to other different colloidal QDs and quantum rod materials for the sensitization of mesoporous films. These results quantitatively describe the process of QD uptake during EPD, and can be used to tune the optical and optoelectronic properties of composite systems, which determine, for instance, the photoconversion efficiency in QD solar cells (QDSCs)

Probing the electronic structure of carbon nanotubes by nanoscale spectroscopy

Among the carbon allotropes newly discovered during the last few decades, carbon nanotubes (CNTs) have attracted enormous attention due to their structural and electronic properties with strong one dimensional character. The physical and chemical features of such systems are intrinsically rich and complex, and can only be probed by using multiple experimental and theoretical techniques. In this feature, we focus on the structural and electronic properties of CNTs that can be accessed by using transmission electron energy loss spectroscopies. The latter are complementary to optical and X-ray absorption techniques, yet allow to obtain the electronic structure with nanoscale spatial resolution. An improved understanding of the structure-electronic properties relationship of these unique 1D systems would represent a fundamental advance, and holds the promise of using CNTs in future applications

Tailoring the reaction path in the on-surface chemistry of thienoacenes

Oligothiophenes provide rich opportunities for surface confined reactions that can lead to two-dimensional materials. We have performed systematic studies of tetrathieno-anthracene (TTA) based molecules on different transition metal surfaces to reveal the details of their on-surface chemistry. On the (111) surfaces of Ni, Pd, and Cu, we observe the sulfur abstraction from the monomer following thermal activation, whose yield varies with the type of metal surface. On Ni(111) and Pd(111) the internal design of the 2TTA isomer promotes intramolecular rebonding to produce pentacene, whereas geometrical constraints prevent the 3TTA isomer from intramolecular rebonding, promoting oligomerization. On Cu(111), desulfurization is preceded by dehydrogenation, which introduces metal-mediated intermolecular coupling in 2TTA. This organometallic phase is stable up to 200 °C. On all surfaces, the desulfurization and dehydrogenation of the molecules are important reaction pathways which define the bonding geometries of the products