Current-Voltage characteristics in macroporous silicon/SiOx/SnO2:F heterojunctions

ABSTRACT: We study the electrical characteristics of Macroporous Silicon/Transparent Conductor Oxide junctions obtained by the deposition of fluorine doped SnO2 onto macroporous silicon thin films, using the spray pyrolysis technique. Macroporous silicon was prepared by the electrochemical anodization of a silicon wafer to produce pores sizes ranging between 0.9 to 1.2 mum diameter. Scanning electronic microscopy was performed to confirm the pore filling and surface coverage. The transport of charge carriers through the interface was studied by measuring the current-voltage curves in dark and under illumination. In the best configuration we obtain a modest open circuit voltage of about 70 mV and a short circuit current of 3.5 mA/cm2 at illumination of 110 mW/cm2. In order to analyze the effects of the illumination on the electrical properties of the junction, we proposed a model of two opposing diodes, each one associated with an independent current source. We obtain a good accordance between experimental data and the model. The current-voltage curves on illumination conditions are well fitted with the same parameters obtained in dark where only the photocurrent intensities in the diodes are free parameters.     

Advances in the study of nano-structured Co/MCM-41 materials: surface and magnetic characterization

Co-modified mesoporous supports with MCM-41 structure and several metal loadings were successfully synthesized by a fast wet impregnation method. The nature and location of different Co species formed on the solids were inferred by TEM/SEM, XPS, XANES/EXAFS, adsorption of pyridine coupled to FT-IR spectroscopy and temperature dependence of magnetization. The presence of Co oxide species (clusters and Co₃O₄ nanoparticles) inside the channels of all the samples could be evidenced by TEM, XPS and XANES/EXAFS. In this sense, the surface Co/Si atomic ratios obtained by XPS were notably lower than the corresponding bulk Co/Si ratios obtained by ICP, indicating that the Co atoms are mostly incorporated inside the mesopores channels of the silica matrix. Nevertheless, by TEM, Co₃O₄ nanoparticles of small size segregated on the external surface of the silicate were also observed for the higher metal loadings. The temperature dependence of the magnetization performed for the Co/M(2.5) sample allowed to assign its superparamagnetic behavior to the presence of clusters and Co₃O₄ nanoparticles of very small size that grow inside the MCM-41 mesopores. Therefore, the analyses presented in this work indicate that a Co theoretical loading of 2.5 wt% leads to the formation of Co oxide nanospecies in the MCM-41 support with a particular superparamagnetic behavior. This sample with improved structural and magnetic properties result an attractive porous solid for drug hosting, to be applied in the field of the controlled release of medicaments.     

Tap Water Costs and Service Sustainability, a Close Relationship

Water is currently an essential and strategic resource for society and its importance will rise in the future due to the increasing number of threats. However, water management is not currently up to par taking into consideration this well acknowledged importance. Generally speaking, water use is not efficient and loss figures are often too high. The reasons behind this situation are complex and diverse, however, in principle, they can be divided into four categories: cultural, political, social and economic. Since the latter are of most importance, this paper focuses on water costs from source to tap. The economic analysis presented quantifies the costs of a sustainable urban water service in a structured way. The second part of the paper present a case study in which the economic losses linked to leakage are assessed as a function of how expenses are recovered. The cost of apparent losses could also be assessed in a similar way and will always be higher, since apparent losses (unlike real ones) are present throughout the whole water cycle, thus increasing the unit costs.     

Bidirectional connectivity via fish ladders in a large Neotropical river: Response to a comment

In a recent article, we described fitting electronic tags to the fish Prochilodus lineatus to document how a fishway connected aquatic habitats downstream and upstream of a major dam. Moreover, given that tagged fish remained upstream or downstream for periods extending months and years before returning to the fishway, and that observed patterns of passage were consistent with seasonal migratory cycles, and building on existing literature, we speculated that the fishway allows fish access to spawning habitats upstream and feeding habitats downstream. Our interpretation of the movement data resulted in several comments from Pelicice, Pompeu, and Agostinho (2020) and they outline various reasons by which, in their opinion, some of our conclusions may be mistaken. Their critique is threefold. First, they argue that the percentage of fish attracted into the fishway is too low to consider the fishway an effective link between the reservoir and the river downstream. We contend that without estimates of population size it is impossible to judge if 28% passage is “limited”; conceivably, the absolute number of fish passed may still be enough to maintain a viable population. Second, they assert that because receivers were located only in the fishway it is unknown if fish that used the fishway remained near the dam, or if they continued their migration. We counter with a brief literature review that documents P. lineatus migrating through reservoirs and spawning in tributaries. Third, they advocate for a broader conservation perspective and for additional research. We agree and, in the article, had already expressed this view that fishways are only a temporary fix and that we support their use only as an element of a broader environmental management package. We also agree with the need for more research but argue that procrastinating on conservation action may not be wise because we do not know if the research will be done, how long it will take, or what the cost may be of waiting.     

The sanitizing action of essential oil-based solutions against Salmonella enterica serotype Enteritidis S64 biofilm formation on AISI 304 stainless steel

Bacterial adhesion and biofilm formation by Salmonella enterica serovar Enteritidis is a serious concern in the food processing industry; organism persistence in biofilms represents a continual source of contamination. Due to unsuccessful disinfection processes and emerging resistance, conventional control methods are rapidly becoming ineffective, necessitating the development of new control strategies. The following study evaluated the anti-biofilm effect of disinfectant solutions formulated with essential oils (EOs) of peppermint (Mentha piperita) and lemongrass (Cymbopogon citratus) against biofilm formation by S. enterica serotype Enteritidis S64 on stainless steel surface AISI 304 (#4) after 10, 20 and 40 min of contact. A minimum inhibitory concentration (MIC) of 7.8 μL/mL was found for both EOs and disinfectant solutions were formulated based on these MIC values. Ten minutes of sanitizing solution contact significantly reduced (p ≤ 0.05) adhered bacterial populations for both EOs tested. After 20 and 40 min of treatment, cell counts were not detected. Thus, M. piperita and C. citratus EOs can be considered convenient, quality alternatives to the application of conventional sanitizing agents in the food industry; further, use of these EOs addresses the increasing consumer demand for natural products.     

Prompt phonon signals from particle interactions in Si crystals

We discuss the prompt (ballistic and quasidiffuse) phonon physics associated with elementary particle interactions within silicon crystals at temperatures below 1 K, and the differences in the ballistic and quasidiffuse phonon production from primary electron recoils versus primary nuclear recoils within these crystals. We then summarize the results from a growing body of direct experimental evidence on prompt phonon signals from particle detectors bombarded with alphas, x-rays, and neutrons.     

Lower body temperatures in infants delivered by caesarean section than in vaginally delivered infants

Clinical experience suggests that infants delivered by caesarean section have difficulties maintaining normal body temperature during the first hours after birth. To test this hypothesis, body and skin temperatures were measured and compared in healthy full-term caesarean section and vaginally delivered newborn infants. The babies were studied during the first 90 min after birth. Axillary and skin temperatures were significantly higher in the vaginally delivered group than in infants delivered by caesarean section. Infants born by non-elective caesarean section were slightly warmer during the first 90 min after birth compared to infants born by elective caesarean section. There were no significant differences in temperatures between infants cared for in a cot as compared to those cared for in an incubator. An incubator creates a physical barrier between babies and parents and incubator care might cause parental anxiety. Thus the routine of putting healthy, full-term caesarean section infants in incubators can be abandoned from a thermoregulatory point of view.     

Experimental control of deformability at short-term loadings in testing large-span prestressed structures

The problems in giving significance to the experimental control of deformability at short-term loadings of large-span prestressed structures in order to draw reliable conclusions on their static behaviour have been examined. With this aim the necessity of an exact evaluation of the elastic modulus of concrete together with the importance of its experimental measurement, which is too imprecise if deduced from the strength of concrete, have been pointed out. The work also shows how, by reducing uncertainty in calculating deflection, modulus measurement directly on the structure's concrete (and not only on specimens cast during construction) improves reliability in the evaluation of the static validity of the construction and the exactness of its modelling. In this regard the ultrasonic method can prove very useful. However, we have shown that it can give wrong results—especially when the load test is carried out long after the casting—if we do not make suitable corrections to take into account the evolution with time of the correlation between static and dynamic moduli, an aspect that is usually neglected.