Nonequilibrium Electron Interactions in Metal Films

Ultrafast relaxation dynamics of an athermal electron distribution is investigated in silver films using a femtosecond pump-probe technique with 18 fs pulses in off-resonant conditions. The results yield evidence for an increase with time of the electron-gas energy loss rate to the lattice and of the free electron damping during the early stages of the electron-gas thermalization. These effects are attributed to transient alterations of the electron average scattering processes due to the athermal nature of the electron gas, in agreement with numerical simulations

A colloidal heterostructured quantum dot sensitized carbon nanotube-TiO 2 hybrid photoanode for high efficiency hydrogen generation

Solar-driven photoelectrochemical (PEC) hydrogen (H 2 ) generation is a promising approach to harvest solar energy for the production of a clean chemical fuel. However, the low photon-to-fuel conversion efficiency and long-term stability of PEC devices are major challenges to be addressed to enable large-scale commercialization. Here we report a simple, fast and cost-effective approach to fabricate high efficiency and stable PEC devices for H 2 generation, by fabricating a hybrid photoanode obtained by incorporating small amounts of multiwall carbon nanotubes (MWCNTs) into a TiO 2 mesoporous film and sensitizing with colloidal heterostructured CdSe/(CdSe x S 1-x ) 5 /(CdS) 2 quantum dots (QDs). The latter were specially designed to accelerate the exciton separation through a band engineering approach. The PEC devices based on the TiO 2 /QD-MWCNT (T/Q-M) hybrid photoanode with an optimized amount of MWCNTs (0.015 wt%) yield a saturated photocurrent density of 15.90 mA cm -2 (at 1.0 V RHE ) under one sun illumination (AM 1.5G, 100 mW cm -2 ), which is 40% higher than that of the reference device based on TiO 2 /QD (T/Q) photoanodes. This is attributed to a synergistic effect of the promising optoelectronic properties of the colloidal heterostructured QDs and improved electron transport (reduced charge transfer resistance) within the TiO 2 -MWCNT hybrid anodes enabled by the directional path of MWCNTs for the photo-injected electrons towards FTO. Furthermore, the PEC device based on the T/Q-M hybrid photoanode is more stable (∼19% loss of its initial photocurrent density) when compared with the T/Q photoanode (∼35% loss) after two hours of continuous one sun illumination. Our results provide fundamental insights and a different approach to improve the efficiency and long-term stability of PEC devices and represent an essential step towards the commercialization of this emerging solar-to-fuel conversion technology

Highly efficient and stable spray assisted nanostructured Cu2S/Carbon paper counter electrode for quantum dots sensitized solar cells

The counter electrode (CE) plays a significant role in determining the overall performance and long-term stability of quantum dots (QDs) sensitized solar cells (QDSCs) by collecting the electrons from the external circuit and catalyzing the regeneration of the oxidized electrolyte. In this work, we report a simple, low cost and large area scalable spray deposition approach to fabricate nanostructured Cu2S CE on a carbon fiber paper (CP). The QDSCs were assembled with optimized spray assisted nanostructured Cu2S/CP CEs, and yield a photoconversion efficiency (PCE) of 5.06%, which is 28% higher than QDSCs based on Cu2S/Brass CEs. The PCE can be further boosted to 5.89% upon optimization of the photoanode structure. In addition, QDSCs with Cu2S/CP CEs exhibit better long-term stability than QDSCs with Cu2S/Brass CE. This excellent performance and satisfactory long-term stability of QDSCs with Cu2S/CP CEs is mainly attributed to the synergistic effect of excellent conductivity of CP and high and stable catalytic activity of nanostructured Cu2S, which is confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Thus, our results define a cost-effective and large area scalable approach to fabricate highly efficient and stable CEs, which is an important step toward the fabrication of solar driven optoelectronic devices

Central blood pressure assessment using 24-hour brachial pulse wave analysis

Maria Lorenza Muiesan, Massimo Salvetti, Fabio Bertacchini, Claudia Agabiti-Rosei, Giulia Maruelli, Efrem Colonetti, Anna Paini Clinica Medica, Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy Abstract: This review describes the use of central blood pressure (BP) measurements during ambulatory monitoring, using noninvasive devices. The principles of measuring central BP by applanation tonometry and by oscillometry are reported, and information on device validation studies is described. The pathophysiological basis for the differences between brachial and aortic pressure is discussed. The currently available methods for central aortic pressure measurement are relatively accurate, and their use has important clinical implications, such as improving diagnostic and prognostic stratification of hypertension and providing a more accurate assessment of the effect of treatment on BP. Keywords: aortic blood pressure measurements, ambulatory monitoring, pulse wave analysi

Structural investigation of the Rh(110)-c(2x2)-CN phase

The Rh(110)-c(2x2)-CN phase has been examined by means of scanning tunneling microscopy (STM) and full dynamical low-energy electron diffraction (LEED). From STM large c(2x2) domains are observed. The detailed LEED-IV structural analysis indicates that CN is located in the grooves of the (110) surface, approximately atop second layer rhodium atoms. The CN molecules lie almost flat with their bond axes oriented perpendicular to the rhodium troughs. An outward relaxation of the first substrate interlayer distance and a strong buckling of the second Rh layer are induced by CN adsorption. Calculated and experimental intensity curves are in good agreement. An exhaustive set of other possible adsorption sites and configurations was tested and excluded on the basis of reliability-factor analysis

Observation of individual molecules trapped on a nanostructured insulator

For the first time, ordered polar molecules confined in monolayer-deep rectangular pits produced on an alkali halide surface by electron irradiation have been resolved at room temperature by non-contact atomic force microscopy. Molecules self-assemble in a specific fashion inside pits of width smaller than 15 nm. By contrast no ordered aggregates of molecules are observed on flat terraces. Conclusions regarding nucleation and ordering mechanisms are drawn. Trapping in pits as small as 2 nm opens a route to address single molecules

Enhanced Photocurrent Generation in Proton-Irradiated “Giant” CdSe/CdS Core/Shell Quantum Dots

Group II–VI quantum dots (QDs) possess tunable electrical and optical properties that make them very attractive for high-tech applications and power generation. The effects of proton irradiation on both the structural and physical properties of “giant” CdSe/CdS core–shell QDs (g-CS QDs) are investigated. These experiments shed light on photoelectron delocalization in g-CS QDs, where current linkages and strong variations in optical emission result from the spatial extension of the photoelectron wavefunctions over the conduction bands of CdSe and CdS. Monte Carlo simulations of ion–matter interactions show that the damaging rates can be set from the energy of impinging protons to promote the formation of structural defects in the core or shell. The formation of nanocavities is demonstrated after irradiation doses higher than ≈1017 H+ cm−2, while a continuous decrease in luminescence intensity is observed for increasing proton fluencies. This feature is accompanied by a concomitant lifetime decrease marking the rise of nonradiative phenomena and the occurrence of greater photocarrier transfers between CdS and CdSe. Current-to-voltage characterizations evidence that proton implantation can be implemented to enhance the photocurrent generation in g-CS QDs. This increase is attributed to the delocalization of photoelectrons in the CdS shell, whose improvement is found to promote electron–hole pair separation

Electronic structure of Nb-Mo alloys

Thermoreflectance measurements on NbxMo1−x alloys (x=0.2, 0.5, 0.8) have been carried out in the 0.5-5.0 eV energy region. Augmented-plane-wave (APW) calculations for Nb at two different lattice parameters and for Mo, as well as coherent-potential-approximation calculations (CPA), have been carried out and have been used in the interpretation of the experimental results. Several optical transitions [Σ1(EF)→Σ3, G4(EF)→G1,N2→N′1], have been identified, and their concentration dependence followed. These results contribute significantly toward putting the interpretation of the optical properties of Nb, Mo, and their alloys on a much more secure footing. In particular, it has been confirmed that while the lower conduction bands behave roughly as predicted by the rigid-band model, the higher-lying conduction bands show distinctly non-rigid-band-like behavior

The effect of pregnancy on subsequent relapse from Graves' disease after a successful course of antithyroid drug therapy.

OBJECTIVE: Pregnancy and the postpartum (PP) period are associated with profound changes of the immune system, which largely influence the clinical activity of autoimmune diseases. The aim of this study was to evaluate the effect of pregnancy and/or the PP period in driving a clinical relapse of hyperthyroidism in patients with Graves' disease (GD) who are in remission after antithyroid drug (ATD) treatment. Data were retrospectively collected from 150 female patients with GD, who were assigned to two groups according to the occurrence of a successful pregnancy after ATD withdrawal. RESULTS: Relapsing Graves' hyperthyroidism was observed in 70 of 125 patients in group I (no pregnancy after ATD withdrawal) (56.0%) and 21 of 25 patients in group II (pregnancy after ATD withdrawal) (84.0%) (P < 0.05). Logistic regression analysis (dependent variable: relapse/nonrelapse; covariates: age, positive family history for autoimmune thyroid disease, duration of treatment with ATD, number pregnancies at diagnosis, number of pregnancies after ATD withdrawal) showed a significant effect only for the number of pregnancies after ATD withdrawal [4.257 (1.315-13.782)]. The effect was ascribed to the PP period rather than to pregnancy itself because in 20 of 21 patients of group II (95.2%), the relapse of Graves' hyperthyroidism occurred between 4 and 8 months after delivery. CONCLUSIONS: The PP period is significantly associated with a relapse of hyperthyroidism in GD patients being in remission after ATD. We therefore recommend that patients with GD in remission after a course of ATD should have their thyroid function tested at 3 and 6 months after delivery