Temperature dependence of the first order Raman scattering in thin films of mc-Si:H

The temperature effect on microcrystalline silicon (mc-Si:H) films produced by R.F. magnetron sputtering has been studied by Raman spectroscopy. The thermal behaviour of mc-Si:H films and crystalline silicon is compared and interpreted on the basis of anharmonic effects. We have studied the first order Raman spectra of our films for several Ar+ laser powers. Our results show a blue shift and a broadening of the Raman spectra with increasing the laser power. This effect is not due to structural changes since it is reproducible. The sample temperature has been calculated according to the well known relation between Stokes and anti-Stokes components. Our results show that the temperature effect is stronger in mc-Si:H than in crystalline silicon. This difference can be attributed to the size of the microcrystals, which are imbedded in a amorphous matrix surrounded by a third phase called grain boundary

Identification of novel Cu, Ag, and Au ternary oxides from global structural prediction

We use ab initio global structural prediction, and specifically the minima hopping method, to explore the periodic table in search of novel oxide phases. In total, we study 183 different compositions of the form MXO2, where M=(Cu, Ag, Au) and X is an element of the periodic table. This set includes the well-known Cu delafossite compounds that are, up to now, the best p-type transparent conductive oxides known to mankind. Our calculations discover 81 stable compositions, out of which only 36 are included in available databases. Some of these new phases are potentially good candidates for transparent electrodes. These results demonstrate, on one hand, how incomplete is still our knowledge of the phase-space of stable ternary materials. On the other hand, we show that structural prediction combined with high-throughput approaches is a powerful tool to extend that knowledge, paving the way for the experimental discovery of new materials on a large scale

Active carboxymethyl cellulose-based edible coatings for the extension of fresh goldenberries shelf-life

Edible coatings based on natural sources are a good alternative to protect and increase the shelf-life of the fruits. In this work, active carboxymethyl cellulose (CMC)-based edible coatings enriched with functional ingredients, extracted from spent coffee grounds (SCG), were produced and used to increase the shelf-life of fresh goldenberries. Thus, three different treatments were tested on fresh goldenberries: (i) coating CMC (CMC-based edible coating); (ii) coating CMC-A (CMC-based edible coating with 0.2% (w/v) of polysaccharide-rich extract from SCG); and (iii) coating CMC-B (CMC-based edible coating with 0.2% (w/v) of polysaccharide-rich extract, and 0.2% (w/v) of phenolic compounds encapsulated from SCG), being compared with uncoated goldenberries. Physicochemical and microbiological properties of the fruits were evaluated throughout 12 and 28 days of storing at 20 °C and 65% relative humidity and 4 °C and 95% RH, respectively. The results showed that the temperature and relative humidity significantly influenced the quality of goldenberries, increasing their shelf-life almost two-fold when stored at 4 °C and 95% RH. Both CMC-A and CMC-B coatings controlled weight loss and decreased the gas transfer rates (O2, CO2, and C2H4), mainly when goldenberries were stored at 20 °C and 65% RH. Moreover, coating CMC-A was better for delaying microbial growth, while the edible coating CMC-B gave an extra content of phenolic compounds to goldenberries, increasing thus their antioxidant potential.This research was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit.info:eu-repo/semantics/publishedVersio

Photoluminescence of erbium doped microcrystalline silicon thin films produced by reactive magnetron sputtering

Microcrystalline silicon thin films doped with erbium were produced by RF sputtering and their structural, chemical and optical properties were studied by X-ray diffractometry at grazing incidence, Rutherford back scattering and optical transmission spectroscopy. The samples exhibit a sharp photoluminescence (PL) spectrum from the Er centres with the strongest peak positioned at 1.536 microm with a full width at half maximum of about 8 nm. When the temperature varies between 5K and 300K the photoluminescence decreases only five fold, in contrast to the behaviour reported for monocrystalline silicon

Structural studies and influence of the structure on the electrical and optical properties of microcrystalline silicon thin films produced by RF sputtering

Microcrystalline silicon thin films were produced by reactive magnetron sputtering on glass substrates under several different conditions (RF power and gas mixture composition). The film structure was studied by X-ray diffractometry (XRD), transmission electron microscopy (TEM) and Raman spectroscopy, allowing the determination of crystal sizes, crystallinity and mechanical strain. These parameters were evaluated by fitting a pseudo-Voigt function to the X-ray data, and by the application of the strong phonon confinement model to the Raman spectra. The degree of crystallinity and the presence of single crystals or crystal agglomerates, which was confirmed by TEM, depends on the preparation conditions, and strongly affects the optical spectra and the electrical transport properties.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XX

Development of active edible coatings for the preservation of Agaricus bisporus mushrooms

Mushrooms are highly perishable food products that tend to lose their unique organoleptic properties immediately after harvest ing. The ir short shelf - life is mainly explained by the high losses of water vapour that favour dehydration, high respiration and microbial colonization by bacteria or fungi. Furthe rmore, enzymatic acti vity and biochemical alteration lead to mushrooms quality losses [1]. The microorganisms most often associated with mushroom spoilage and colonization are gram - negative bacteria e specially those belonging to Pseudomon ae family such as Pseudomonas fluorescens [2]. Active edible coatings h ave been increasingly applied in the last years as an alternative method for the contr ol of microbial contamination in food products. The incorporation of antimicrobial compounds has potential for increasing food quality and safety thus extending its shelf - life [3 - 4]. Recently, several studies have been developed on the incorporation of natural antimicrobial compounds i n edible coatings, responding to an increasing demand by the consumers for foods without chemical additives. Some of the natural antimicrobials are e ssential oils , such as carvacrol and eugenol , which were shown to possess antimicrobial activity against P. f luorescens and E. coli [5]. Aiming at developing an active edible coating to increase the shelf - life of Agaricus bisporus mushrooms p olysaccharide - based coatings were developed using chitosan and alginate , glycerol (as plasticizer) and Tween 80 (as surfactant) . C oating formulations were evaluated through a 2 2 factorial experimental setup with one central point where the influence of the added compounds on W s ( spreading coefficient - wettability) was determined (Pareto charts analyses, p <0.05). W s was evaluated on the pileus of the mushroom once this is the main part of the mushroom and is a indicator of quality and freshness [6]. Tween 80 and polysaccharide concentrations showed to influence the value s of W s . The optimal coating formulation to be a pplied was selected through the determination of the coating that presents the minor value of W s (i.e. value close to zero) and need less quantity of ingredients (i.e. more economic coating) . Based on this, two coatings were selected, one containing 0.5% (w/v) of chitosan, 0. 125% (v/v) of glycerol and 0. 15% (v/v) of T ween 80 and other with 0.5% (w/v) of alginate, 0. 125% (v/v) of glycerol and 0.0 5% (v/v) of T ween 80, presenting W s values of - 62.4 and - 49.9 mN/m, respectively. Different concentrations (0 - 1% v/v) of eugenol and carvacrol and a com bination of both (1:1 – v/v) were incorporated i n chitosan and alginate coatings and their antimicrobial activity was evaluated through CLSI M7 - A7 [7] . I n the case of E. coli , the chitosan - based coatings containing eugenol showed higher antimicrobial activity than th e ones containing carvacrol, being this activity clear after 48 h of incubation . The same behaviour was observed for alginate - based coatings containing eugenol and carvacrol . R esults with P. fluorescens w ere similar to those obtained for E. coli , being the only difference registered for the re sults of inhibition at 24 and 48 h of incubation , w h ere the values of inhibition were similar for both times of incubation. There was a clearly the larger microbial i nhibition against P. fluorescens in comparison to E. c oli , for both coatings - in the presence of eugenol and carvacrol. These results suggest that active polysaccharide - based coatings may present a valuable solution for food packaging in order to prevent microbiological spoilage of Agaricus bisporus mushrooms by P. fluorescens and E. coli . Further studies will be addressed evaluating the effect of developed coatings on shelf - life parameters of Agaricus bisporus mushrooms during storage

Caracterização morfoagronômica de diferentes copas de maracujazeiro enxertadas em porta-enxerto de Passiflora gibertii.

Este trabalho teve como objetivo caracterizar morfoagronomicamente diferentes copas de maracujazeiro enxertadas em porta-enxertos de Passiflora gibertii, com vistas à seleção de copas superiores. Foi utilizado um porta-enxerto com 25 copas diferentes, previamente obtidos do trabalho de pesquisa desenvolvido pela equipe de Recursos Genéticos da Embrapa Mandioca e Fruticultura

Microstrucure and thermal features a-Si:H and nc-Si:H thin films produced by r.f. sputtering

Amorphous and nanocrystalline silicon thin films have been produced by reactive r.f. sputtering and their microstructure, optical and thermal properties were evaluated. A good correlation was found between the microstructure determined by Raman spectroscopy and X-ray diffraction and the thermal transport parametersFCT Project POCTI / CTM / 39395 / 200

The influence of electric field on the microstructure of nc-Si:H films produced by RF magnetron sputtering

Hydrogenated nanocrystalline silicon thin films were prepared by RF magnetron sputtering. Different bias fields (no bias–no ground, grounded and negative bias) were applied to the substrate. The effect of the ion bombardment on the structure, chemical composition and optical property were studied by Raman spectroscopy, X-ray diffraction, Rutherford backscattering (RBS) and optical transmission spectroscopy. The deposition rate and the optical bandgap decrease as the bias voltage increases from 0 to -50 V. The structural characterization indicates that compressive stress is developed in plane and tensile stress is induced in the growth direction. No significant variation on the chemical composition was observed.FCT Project POCTI/CTM/ 39395/2001INTAS Project #03-51-648