Improving the performance of printable carbon electrodes by femtosecond laser treatment

Low-cost carbon-conductive films were screen-printed on a Plexiglas® substrate, and then, after a standard annealing procedure, subjected to femtosecond (fs) laser treatments at different values of total accumulated laser fluence ΦA. Four-point probe measurements showed that, if ΦA > 0.3 kJ/cm2, the sheet resistance of laser-treated films can be reduced down to about 15 Ω/sq, which is a value more than 20% lower than that measured on as-annealed untreated films. Furthermore, as pointed out by a comprehensive Raman spectroscopy analysis, it was found that sheet resistance decreases linearly with ΦA, due to a progressively higher degree of crystallinity and stacking order of the graphitic phase. Results therefore highlight that fs-laser treatment can be profitably used as an additional process for improving the performance of printable carbon electrodes, which have been recently proposed as a valid alternative to metal electrodes for stable and up-scalable perovskite solar cells

Aluminum (Oxy)nitride thin films grown by fs-PLD as electron emitters for thermionic applications

Thin films based on aluminum nitride were obtained by fs-laser assisted Pulsed Laser Deposition (fs-PLD) at room temperature on tantalum substrates for studying the electron emission performance in the temperature range 700- 1600 °C, so to investigate the possibility of their exploitation as thermionic cathodes. Results of structural, chemical and morphological analyses show the growth of nanostructured thin films with a significant oxygen contamination, forming a mixture of crystalline aluminum nitride and aluminum oxide as well as metallic aluminum inclusions. Despite the considerable presence of oxygen, the developed cathodes demonstrate to possess promising thermionic emission characteristics, with a work function of 3.15 eV, a valuable Richardson constant of 20.25 A/(cm²K²), and a highly thermo-electronic stability up to operating temperatures of 1600 °C

Incidence and outcome of invasive candidiasis in intensive care units (ICUs) in Europe: results of the EUCANDICU project

BACKGROUND: The objective of this study was to assess the cumulative incidence of invasive candidiasis (IC) in intensive care units (ICUs) in Europe. METHODS: A multinational, multicenter, retrospective study was conducted in 23 ICUs in 9 European countries, representing the first phase of the candidemia/intra-abdominal candidiasis in European ICU project (EUCANDICU). RESULTS: During the study period, 570 episodes of ICU-acquired IC were observed, with a cumulative incidence of 7.07 episodes per 1000 ICU admissions, with important between-center variability. Separated, non-mutually exclusive cumulative incidences of candidemia and IAC were 5.52 and 1.84 episodes per 1000 ICU admissions, respectively. Crude 30-day mortality was 42%. Age (odds ratio [OR] 1.04 per year, 95% CI 1.02-1.06, p < 0.001), severe hepatic failure (OR 3.25, 95% 1.31-8.08, p 0.011), SOFA score at the onset of IC (OR 1.11 per point, 95% CI 1.04-1.17, p 0.001), and septic shock (OR 2.12, 95% CI 1.24-3.63, p 0.006) were associated with increased 30-day mortality in a secondary, exploratory analysis. CONCLUSIONS: The cumulative incidence of IC in 23 European ICUs was 7.07 episodes per 1000 ICU admissions. Future in-depth analyses will allow explaining part of the observed between-center variability, with the ultimate aim of helping to improve local infection control and antifungal stewardship projects and interventions

Dosimetric performance of single-crystal diamond X-ray schottky photodiodes

Single-crystal diamond Schottky photodiodes have been developed following a WC-diamond-TiC/Ti/Ag vertical structure for X-ray dosimetry with characteristics of low leakage current and the capability of zero-bias operations. Continuous and modulated X-ray measurements show that the devices developed provide a linear response to dose rate at low bias voltages ( 130 Hz. This supports their application in modulated radiotherapy treatments. © 1980-2012 IEEE

Optical characteristics of nanostructured aluminium/diamond composite systems in the visible range

The inclusion of aluminium (Al) nanoparticles (NPs) in chemical vapor deposition (CVD) diamond structures was achieved by depositing Al thin films on commercial CVD single-crystal diamond plates, and then covering them by a CVD diamond thin film to encapsulate the metal NPs formed by the dewetting occurring during the CVD process. Morphology and composition are investigated, showing a peculiar structure formed by an Al/diamond composite with both Al NPs and Al2O3 islands included and surrounded in the diamond matrix, respectively. A mosaic-patterned homoepitaxial growth occurs for the capping diamond layer. The experimentally measured reflectivity matches the simulation of a system where the thickness of the Al/diamond composite layer is 1.80 ± 0.05 μm and the composition is 95 ± 2 % diamond and 5 ± 2 % Al. Simulations of the plasmonic response of Al NPs embedded in the diamond layer suggest that the decrease in transmission of the sample in the blue region of the spectrum is unlikely to be due to plasmonic absorption by the NPs. It is concluded that the shape of the transmission spectrum follows a Rayleigh-like scattering induced by the nanoporous diamond film. Ultrafast transient absorption measurements allow us to identify a sharp feature at 700 nm which can be associated with a modification of an interband transition in Al due to heating after photon absorption at 380 nm

Transport properties of photogenerated charge carriers in black diamond films

Surface nanostructured diamond films by ultrashort pulse laser treatment, named black diamond, demonstrated a huge increase in the photogeneration capability for photons with sub-bandgap energy (<5.47 eV). Here we analyze in detail the transport properties of photogenerated charge carriers in several black diamond samples, in order to better understand the electronic behavior of defect levels introduced by the laser treatment. If compared with the pristine diamond films, the mean charge carriers’ mobility-lifetime product, evaluated from the over bandgap photocurrent characteristics, remarkably increases in every black diamond set up to a defined absorbed accumulated laser fluence before decreasing at the highest fluence values. We attribute this effect to the laser-induced introduction of fast traps for one charge carrier type, that increases with fluence. At the same time, an increasing density of recombination centers, capturing permanently the charge carriers, is formed. A trade-off treatment condition can be found in order to maximize the sensitivity to sub-bandgap photons and the mean mobility-lifetime product as well as to limit the effect of recombination centers

Black diamond for solar energy conversion

AbstractBlack diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, able to drastically modify the interaction with solar radiation from optical transparency up to solar absorptance values even >90%. Surface texturing, performed by the use of an ultra-short pulse laser, is demonstrated to induce an intermediate band within the diamond bandgap supporting an efficient photoelectronic conversion of sub-bandgap photons (<5.5 eV). The intermediate band introduction results in an external quantum efficiency enhanced up to 800 nm wavelengths (and up two orders of magnitude larger than the starting transparent diamond film), without affecting the film transport capabilities. The optical and photoelectronic outstanding results open the path for future application of black diamond as a photon-enhanced thermionic emission cathode for solar concentrating systems, with advantages of excellent electronic properties combined with a potentially very low work function and high thermal stability

Thermal Assessment of Dielectric Microspacer Technology Using an Advanced Three-Dimensional Simulation Model

Dielectric microspacers (DMS) are a novel micro-technology that can be used to achieve a fixed micron/sub-micron gap distance between two separated surfaces, such as the emitter (cathode) and the PV cell (anode) of a near-field thermophotovoltaic converter (TPV). One of the system&rsquo;s challenges is the flow of undesirable excess thermal energy from the cathode to the anode that might cause the PV cell to overheat. This work investigates the possibility of integrating this technology into a hybrid thermionic-photovoltaic (TIPV) converter operating at ultra-high temperatures (&gt;1000 &deg;C) without any risk of collector&rsquo;s overheating, which might lead to its mechanical failure. A steady-state 3-D CFD model was developed in Fluent v17.1 solver to assess the system&rsquo;s thermal behavior when the two electrodes were separated by a distance of 8&ndash;10 &mu;m. The heat transfer through conduction across the system components and the net photon/electron flux between the two electrodes were simulated. Different cathode temperatures within the range of 1500&ndash;2500 K and various DMS shapes (capillary, cylindrical), patterns (e.g., ring-shaped) and sizes were studied. Results show that thermal performance is not affected by the DMS pattern, even for thermal conductivities of 80 W/(m&middot;K), whereas the possibility of mechanical failure is considerable for Tcathode &gt; 2000 K

Thermal Assessment of Dielectric Microspacer Technology Using an Advanced Three-Dimensional Simulation Model

Dielectric microspacers (DMS) are a novel micro-technology that can be used to achieve a fixed micron/sub-micron gap distance between two separated surfaces, such as the emitter (cathode) and the PV cell (anode) of a near-field thermophotovoltaic converter (TPV). One of the system’s challenges is the flow of undesirable excess thermal energy from the cathode to the anode that might cause the PV cell to overheat. This work investigates the possibility of integrating this technology into a hybrid thermionic-photovoltaic (TIPV) converter operating at ultra-high temperatures (>1000 °C) without any risk of collector’s overheating, which might lead to its mechanical failure. A steady-state 3-D CFD model was developed in Fluent v17.1 solver to assess the system’s thermal behavior when the two electrodes were separated by a distance of 8–10 μm. The heat transfer through conduction across the system components and the net photon/electron flux between the two electrodes were simulated. Different cathode temperatures within the range of 1500–2500 K and various DMS shapes (capillary, cylindrical), patterns (e.g., ring-shaped) and sizes were studied. Results show that thermal performance is not affected by the DMS pattern, even for thermal conductivities of 80 W/(m·K), whereas the possibility of mechanical failure is considerable for Tcathode > 2000 K