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

Optical modulation spectroscopy of hydrogenated microcrystalline silicon

The properties of microcrystalline silicon thin films prepared by RF sputtering were investigated by optical modulation spectroscopy at room temperature and the results were correlated with Raman and conductivity measurements. For comparative purposes, a number of good quality PECVD microc-Si:H samples were also investigated. For PECVD samples the OMS signal is very weak, and only measurable for probe beam energies comparable to the gap of amorphous silicon. This indicates the absence of gap states and therefore a very high crystalline fraction, as confirmed by Raman and TEM measurements. In what concerns RF-sputtered samples, different behaviors can be distinguished: Some samples show a low OMS signal which can be attributed either to a high crystallinity (low density of gap states) or to high recombination rates. These two cases can be distinguished by electrical conductivity values and analysis of the Raman spectra. Other samples exhibit a OMS signal similar to a-Si:H and have low conductivity values, consistent with a Raman spectrum typical of a-Si:H.FCT-grant from PRAXIS XX

Películas a base de proteínas de salvado de arroz enriquecidas por el extracto fenólico de salvado de arroz fermentado y por la arcilla montmorillonítica

Proteins extracted from rice bran were used to prepare bio-base films where a factorial experimental design was performed in order to evaluate the effect of protein and glycerol concentrations, and the addition of phenolic extract and montmorillonite (MMT) clay on their physicochemical properties. The phenolic extract was obtained from fermentation of rice bran in solid state with the fungus Rhizopus oryzae. Results showed that protein concentration affected (p < 0.05) the luminosity, opacity and solubility of the films. An increase of glycerol concentration strongly affects (p < 0.05) the values of mechanical properties and water vapor permeability of the films. The addition of phenolic extract to the films affected (p < 0.05) opacity, tensile strength, elongation, Youngs modulus and water vapor permeability, while addition of MMT decreased (p < 0.05) the mechanical properties of the films. Films presented solubility values of less than 25%, luminosity above 80 (L*), opacity above 14%, tensile strength of 8.6 MPa, elongation of 70%, elasticity above 600 MPa and water vapor permeability of 7.5 g.mm/d.m2.kPa. These results show that rice bran protein can be used in the production of bio-based films to further use in food applications.Con el fin de evaluar el efecto que sobre las propiedades fisicoquímicas de las proteínas extraídas del salvado de arroz tienen distintas concentraciones de proteína y de glicerol, así como la adición de extracto fenólico y de arcilla montmorillonítica, las mismas se utilizaron para preparar películas de base biológica en el marco de un diseño experimental factorial. Mediante la fermentación de salvado de arroz en estado sólido con el hongo Rhizopus oryzae, se obtuvo el extracto fenólico. Los resultados demuestran que la concentración proteica afectó significativamente (p < 0,05) la luminosidad, la opacidad y la solubilidad de las películas. Asimismo, un aumento de la concentración de glicerina afectó fuertemente (p < 0,05) los valores de las propiedades mecánicas y de la permeabilidad al vapor de agua de las mismas. La adición de extracto fenólico a las películas afectó de manera significativa (p < 0,05) la opacidad, la fuerza de tensión, el alargamiento, el módulo de Young y la permeabilidad al vapor de agua, mientras que la adición de montmorillonita disminuyó (p < 0,05) sus propiedades mecánicas. Se constató que las películas mostraron valores de solubilidad inferiores a 25%, de luminosidad superiores a 80 (L*), de opacidad superiores a 14%, de fuerza de tensión de 8,6 MPa, de alargamiento de 70%, de elasticidad superiores a 600 MPa y de permeabilidad al vapor de agua de 7,5 g.mm/d.m2 .kPa. Estos resultados demuestran que, en el ámbito de los alimentos, la proteína de salvado de arroz puede utilizarse para la producción de películas de base biológica con el fin de adjudicarle usos adicionales.Authors Cristiano G. Schmidt and Miguel A. Cerqueira are thankful to Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES, Brazil; BEX 9730/11-7) and Fundacao para a Ciencia e Tecnologia, POPH-QREN and FSE (FCT, Portugal) (SFRH/BPD/72753/2010) for financial support. The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013 and the project "BioInd - Biotechnology and Bioengineering for improved Industrial and Agro-Food processes", REF.NORTE-07-0124-FEDER-000028 Co-funded by the Programa Operacional Regional do Norte (ON. 2 - O Novo Norte), QREN, FEDER

Physical properties of edible coatings and films made with a polysaccharide from Anacardium occidentale L.

The effect of the concentrations of the polysaccharide from Anacardium occidentale L. (Policaju) and a surfactant (Tween 80) on relevant properties of edible coatings/films, in view of their application on apples (cv. Golden) was evaluated. The influence of the interactions between those two constituents on apples’ surface properties and on the coating/film’s wettability, water vapor permeability, opacity and mechanical properties was evaluated. The effects of the studied variables (polysaccharide and surfactant concentrations) were analyzed according to a 2² factorial design. Pareto bar charts were used to understand the most significant factors on the studied properties. The addition of surfactant reduced the cohesion forces, therefore reducing the surface tension and increasing the wettability; this resulted in an improved compatibility between the solution and the fruit skin surface. The opacity was also reduced. The results of each of the analyzed properties were adjusted to a polynomial, multifactor model, which provided a good fitting accuracy. This model is important once it will reduce the characterization work needed in subsequent applications of these coatings/films on foods.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes, Brazil)Fundação para a Ciência e a Tecnologia (FCT)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazi

Electrochemically gated graphene field-effect transistor for extracellular cell signal recording

This work presents an experimental characterization of electrochemically gated graphene field-effect transistors (EGFETs) to measure extracellular cell signals. The performance of the EGFETs was evaluated using cardiomyocytes cells. Extracellular signals with a peak value of 0.4 pico-amperes (pA) embedded in a noise level of 0.1 pA were recorded. Signals in current mode were compared with signals recorded as a voltage. Signals below 28 μV of magnitude can be detected in a noise floor of 7 μV with a signal-to-noise ratio of 4

Novel edible films made of polysaccharide from Anarcadium occidentale L.

Edible and/or biodegradable films have been evaluated in applications such as transportation of active materials, selective barrier to gases and solutes, and as an alternative to synthetic non-renewable packaging materials. This work aimed at producing and evaluating the mechanical characteristics of films of polysaccharide from the Anarcadium ocidentale L. tree gum (POLICAJU), in view to their application as protection to increase the shelf life of fruits and vegetables and as cutaneous dressing. Films with different POLICAJU concentrations (1% - 3% w/v) were cast using different plasticizers (sorbitol, glycerol and polyethylene glycol), at different concentrations (0.02 to 0.5% g/g of POLICAJU), in the presence and in the absence of Tween 80 as surfactant (0.05% w/w). The solution of 3.0% (w/v) of POLICAJU, 0.4% (w/w) sorbitol and 0.05% (w/w) Tween 80 was the one featuring a better flexibility and mechanical resistance (to traction). This has been determined with an INSTRON (model 4505) machine, with a load cell of 2.5 N. The film, of 0.07 mm thickness, stretched for a length 62 % higher than its original length, while resisting to a force of 0.2 N. These results suggest that this material has enough resistance to be used for the intended applications

The mechanism of formate oxidation by metal-dependent formate dehydrogenases

J Biol Inorg Chem (2011) 16:1255–1268 DOI 10.1007/s00775-011-0813-8Metal-dependent formate dehydrogenases (Fdh) from prokaryotic organisms are members of the dimethyl sulfoxide reductase family of mononuclear molybdenum-containing and tungsten-containing enzymes. Fdhs catalyze the oxidation of the formate anion to carbon dioxide in a redox reaction that involves the transfer of two electrons from the substrate to the active site. The active site in the oxidized state comprises a hexacoordinated molybdenum or tungsten ion in a distorted trigonal prismatic geometry. Using this structural model, we calculated the catalytic mechanism of Fdh through density functional theory tools. The simulated mechanism was correlated with the experimental kinetic properties of three different Fdhs isolated from three different Desulfovibrio species. Our studies indicate that the C–H bond break is an event involved in the rate-limiting step of the catalytic cycle. The role in catalysis of conserved amino acid residues involved in metal coordination and near the metal active site is discussed on the basis of experimental and theoretical results

Photoluminescence from ultrathin Ge-rich multi-quantum wells observed up to room-temperature: experiments and modeling

Employing a low-temperature growth-mode, we fabricated ultrathin Si1-xGex/Si multiple quantum well (QW) structures with a well thickness of less than 1.5 nm and a Ge concentration above 60 % directly on a Si substrate. We identified an unusual temperature-dependent blueshift of the photoluminescence (PL) and an exceptionally low thermal quenching. We find that this behavior is related to the relative intensities of the no-phonon (NP) peak and a phonon-assisted replica that are the main contributors to the total PL signal. In order to investigate these aspects in more detail, we developed a strategy to calculate the PL spectrum employing a self-consistent multi-valley effective mass model in combination with second-order perturbation theory. According to our investigation, we find that while the phonon-assisted feature decreases with temperature, the NP feature shows a strong increase in the recombination rate. Besides leading to the observed robustness against thermal quenching, this causes the observed blueshift of the total PL signal.T.W. and K.B. were supported by the Stiftung der Deutschen Wirtschaft (sdw) and by the Deutsche Forschungsgemeinschaft (DFG) through project B10 within the Collaborative Research Center (CRC) 951 Hybrid Inorganic/Organic Systems for Opto-Electronics. HRTEM measurements were financed by Xunta de Galica Grant No. GRC2014/008

Room temperature paramagnetism of ZnO:Mn films grown by RF-sputtering

ZnO:Mn transparent thin films (thickness b1 μm) with the Mn contents ranging from 1.8 to 3.25 at.% were grown by RF magnetron co-sputtering. The films are nanocrystalline, with wurtzite-structure grains of a typical size of 20 nm and with a preferential orientation of the c-axis perpendicular to the surface. According to the Raman spectroscopy data, Mn mostly substitutes Zn in the lattice sites. In spite of these factors, the nanostructure and the Mn(Zn) substitution, that are considered favorable for ferromagnetism in this material, both magnetic resonance and Faraday effect measurements show paramagnetic behavior of the ZnO:Mn films and the absence of ferromagnetic order at room temperature.FCT throughproject PTDC/FIS/72843/200