X-ray photoelectron spectroscopy investigation of nanoporous NiO electrodes sensitized with Erythrosine B

Nanoporous NiO thin films were prepared onto FTO glass substrates by means of screen-printing and were sensitized with Erythrosine B (EryB) dye. The obtained material was electrochemically treated and characterized with ex-situ X-ray photoelectron spectroscopy in order to gain information beneficial to the application of sensitized NiO as photocathodes of p-type dye-sensitized solar cells (p-DSCs). In particular, EryB-sensitized NiO films underwent a series of electrochemical treatments in LiClO4/Acetonitrile (ACN) electrolyte devised so as to simulate possible conditions the electrode might encounter during operation in the photoelectrochemical cell. Upon potential-cycling in a range where the two NiO faradic events Ni(II)→Ni(III) and Ni(III)→Ni(IV) occur, X-ray photoelectron spectroscopy revealed that Erythrosine B dye experiences a partial detachment from the NiO surface. This detachment seems to be paralleled by the formation of stable (Ni)+(ClO4)- couples. Overall, the EryB dye displayed an acceptable electrochemical stability onto the surface of NiO electrode up to 50 cyclic voltammetries in the range -0.27÷+1.13V vs. Ag/AgCl. These results are useful for the evaluation of electrochemical stability of the dye when this is immobilized onto an electrode surface and are beneficial for a better comprehension of the degradation phenomena operating in real photoconversion device. © 2017 Elsevier B.V

analysis and reliability study of luminescent materials for white lighting

In this work, we report on the characterization and reliability/stability study of phosphorescent materials for lighting applications. More specifically, we investigated (a) phosphors directly deposited over light-emitting diodes (LED) chip, (b) remote phosphor (RP) solutions encapsulated in plastic medium for LED lighting, and (c) phosphors without binder for extreme high-intensity laser diode white lighting. The optical and thermal properties of phosphors were studied to develop a sample based on a mix of phosphor compounds in order to achieve different correlated color temperatures (CCT) and high color rendering index (CRI) LEDs. Thermal properties of cerium-doped YAG (Yttrium Aluminum Garnet) phosphor materials were evaluated in order to study thermal quenching. A maximum phosphor operating temperature of 190–200 °C was found to cause a sensible efficiency degeneration. Reduced efficiency and Stokes shift also caused a localized temperature increase in the photoluminescent materials. In the case of remote phosphors, heat did not find a low thermal resistance path to the heatsink (as occurred through the GaN LED chip for direct phosphor-converted devices) and thermal analysis indicated that material temperature might therefore increase to values in excess of 60 °C when a radiation of 435 mW/cm2 hit the sample template. Reliability was also investigated for both plastic-encapsulated materials and binder-free depositions. Pure thermal reliability study indicated that phosphors encapsulated in polycarbonate material were stable up to temperature of approximately 100 °C, while binder-free phosphor did not show any sensible degradation up to temperatures of 525 °C

Effect of cracks on the service life of RC structures exposed to chlorides

To move towards a more sustainable concrete, the enhancement of its durability is strongly encouraged and, dealing in particular with reinforced concrete (RC), this mainly means to prevent the damage due to environmental actions, e.g. due to chloride-induced corrosion. Therefore, there is the need of models aimed at designing durable structures. Usually the service life design models consider concrete in uncracked condition. In real structures, however, several phenomena can generate cracks on concrete surface, leading to an acceleration of the corrosion of steel rebar. A number of studies have been recently carried out in order to evaluate the influence of cracks on reinforced concrete durability in chloride-contaminated environment, however the knowledge of the effect of cracks on the initiation and propagation periods is still lacking. Furthermore, few studies have considered additional protection strategies, such as the use of stainless steel rebar. In this work, experimental results are presented concerning the influence of cracks on the service life of reinforced concrete structures in order to evaluate if cracks lead to an earlier corrosion initiation induced by chlorides. Prismatic specimens, reinforced with carbon steel and 304L stainless steel bars, were longitudinally cracked and exposed to ponding with 3.5% NaCl solution. The monitoring of corrosion behaviour showed that when cracks reached the steel surface corrosion initiated immediately

Trapping phenomena and degradation mechanisms in GaN-based power HEMTs

Abstract This paper reports an overview of the most relevant trapping and degradation mechanisms that limit the performance and lifetime of GaN-based transistors for application in power electronics. Results obtained on state-of-the-art devices are described and discussed throughout the paper, with the aim of providing a clear description of the topic. The first part of the paper deals with the issue of dynamic-Ron: after describing a robust test strategy for the analysis of the pulsed characteristics of the devices, we discuss the voltage- and temperature-dependent pulsed I-V characteristics of 650 V-rated transistors, and the physical origin of dynamic Ron in these devices. The results demonstrate that through proper buffer optimization it is possible to reach negligible trapping at high voltage. The properties of the traps responsible for dynamic-Ron are also discussed in detail in the paper, based on drain-current transient data. A specific discussion is devoted to hot-electron trapping processes, that – under hard switching conditions – may lead to significant modifications in the resistance of the 2DEG. The second part of the paper deals with device degradation: based on a wide set of experimental results, we describe the physical mechanisms responsible for the worsening of the properties of the devices. More specifically, we demonstrate that stress in off-state conditions may result in measurable changes in the pinch-off voltage, mostly consisting in a negative-threshold instability (NBTI). The origin of this shift is discussed in detail; we also demonstrate that in a real-life cascode configuration (where a low, subthreshold leakage current flows through the device in the off-state), NBTI effects are mitigated. Finally, we discuss the stability of the gate-stack, induced by the exposure to positive gate bias

Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe

Continuing Medical Education A Case of Mechanical Failure with Proximal Perforation at the Time of Revision Surgeryj sm_1475 2629..2632

Background. Implantation of inflatable penile prosthesis (IPP) is a well-established treatment for medically refractory erectile dysfunction with proven long-term reliability. However, if an IPP fails, the subsequent surgery to fix the IPP can be more difficult with higher risks of complications than the primary implantation. Aims. To review and evaluate a case of a difficult IPP replacement surgery for ways to improve surgical techniques and outcomes. Materials & Methods. Perform a case report of a difficult IPP replacement surgery in which the patient had proximal perforation of the tunica albuginea with a review of the pertinent literature. Results. The rear tip sling is a successful way to repair proximal perforation of the tunica albuginea. Recent publications show new surgical techniques to lower infection rates in IPP revision surgery. Discussion. The rear tip sling appears to have better outcomes than a synthetic windsock for repairs of proximal perforation of the tunica albuginea. Recent publications have shown that the revision washout decreases penile prosthesis infection rates in revision surgeries

Electric Field and Self-Heating Effects on the Emission Time of Iron Traps in GaN HEMTs

In this paper we separately investigate the role of electric field and device self-heating (SHE) in enhancing the charge emission process from Fe-related buffer traps (0.52 eV from Ec) in AlGaN/GaN High Electron Mobility Transistors (HEMTs). The experimental analysis was performed by means of Drain Current Transient (DCT) measurements for either i) different dissipated power (PD,steady) at constant drain-to-source bias (VDS,steady) or ii) constant PD,steady at different VDS,steady. We found that i) an increase in PD,steady yields an acceleration in the thermally activated emission process, consistently with the temperature rise induced by SHE. On the other hand, ii) the field effect turned out to be negligible within the investigated voltage range, indicating the absence of Poole-Frenkel effect (PFE). A qualitative analysis based on the electric field values obtained by numerical simulations is then presented to support the interpretation and conclusions

Use of Bilayer gate insulator in GaN-on-Si Vertical Trench MOSFETs : impact on performance and reliability

We propose to use a bilayer insulator (2.5 nm Al2O3 + 35 nm SiO2) as an alternative to a conventional uni-layer Al2O3 (35 nm), for improving the performance and the reliability of GaN-on-Si semi vertical trench MOSFETs. This analysis has been performed on a test vehicle structure for module development, which has a limited OFF-state performance. We demonstrate that devices with the bilayer dielectric present superior reliability characteristics than those with the uni-layer, including: (i) gate leakage two-orders of magnitude lower; (ii) 11 V higher off-state drain breakdown voltage; and (iii) 18 V higher gate-source breakdown voltage. From Weibull slope extractions, the uni-layer shows an extrinsic failure, while the bilayer presents a wear-out mechanism. Extended reliability tests investigate the degradation process, and hot-spots are identified through electroluminescence microscopy. TCAD simulations, in good agreement with measurements, reflect electric field distribution near breakdown for gate and drain stresses, demonstrating a higher electric field during positive gate stress. Furthermore, DC capability of the bilayer and unilayer insulators are found to be comparable for same bias points. Finally, comparison of trapping processes through double pulsed and V-th transient methods confirms that the V-th shifts are similar, despite the additional interface present in the bilayer devices

Modeling of gate capacitance of GaN-based trench-gate vertical metal-oxide-semiconductor devices

We propose a model for the gate capacitance of GaN-based trench-gate metal-oxide-semiconductor transistors, based on combined measurements, analytical calculations and TCAD simulations. The trench capacitance is found to be equivalent to four different capacitors, used to model the various regions with different doping and orientation of the semiconductor/dielectric interface. In addition, we demonstrate and explain the characteristic double-hump behavior of the G-D and G-DS capacitance of trench-MOSFETs. Lastly, a TCAD simulation results accurately reproduce the experimental data, thus confirming the interpretation on the double hump behavior, and providing insight on the electron density at the gate interface. (C) 2020 The Japan Society of Applied Physic

Il back-reshoring manifatturiero nei processi di internazionalizzazione: inquadramento teorico ed evidenze empiriche

Obiettivo del paper. Il paper si prefigge di inquadrare il fenomeno del back-reshoring manifatturiero - ovvero la rilocalizzazione nel paese di origine delle attivit\ue0 produttive precedentemente delocalizzate all\u2019estero -nell\u2019ambito dei processi di internazionalizzazione dell\u2019impresa. Metodologia. L\u2019approccio metodologico utilizzato \ue8 di tipo esplorativo, data la mancanza di una letteratura consolidata specifica. In particolare si \ue8 fatto ricorso a dati secondari raccolti in maniera originale attraverso una pluralit\ue0 di fonti. Risultati. \uc8 stata identificata una definizione operativa di back-reshoring inserendo tale fenomeno in un framework teorico rappresentativo del processo evolutivo di internazionalizzazione dell\u2019impresa. Sulla base delle evidenze empiriche, sono state proposte delle direttrici di sviluppo per future attivit\ue0 di ricerca. Implicazioni manageriali. Sono state evidenziate le conseguenze che il fenomeno pu\uf2 avere sulla competitivit\ue0 e le performance economica delle imprese che adottano strategie di reshoring. Originalit\ue0 e limiti della ricerca. Il principale elemento di originalit\ue0 del lavoro \ue8 rappresentato dall\u2019utilizzo di una metodologia di ricerca esplorativa che ha coniugato l\u2019analisi della letteratura di International business e quella di Supply chain management con l\u2019analisi di evidenze empiriche raccolte in maniera originaria. Le scelte metodologiche effettuate rappresentano anche il principale limite del contributo, le cui conclusioni non sono generalizzabili ma costituiscono la base per ulteriori approfondimenti del dibattito scientifico, per i quali si sono identificate delle specifiche direttrici