8 research outputs found
Influência da temperatura e do tipo de substrato em filmes de GaN depositados por magnetron sputtering reativo
Semicondutores de gap largo são materiais de grande interesse devido às suas amplas aplicações tecnológicas. Entre os semicondutores de gap largo se destaca o GaN que apresenta características desejáveis para tais aplicações, como valor de energia de bandgap de 3,4 eV, alta condutividade térmica e alta dureza. As técnicas convencionais para a produção de filmes finos de GaN são a epitaxia por feixe molecular (MBE) e deposição de vapor químico de precursores metalorgânicos (MOVPE), porém tais técnicas possuem um elevado custo. Este trabalho discorre sobre a preparação e caracterização de filmes policristalinos de GaN pela técnica alternativa de RF magnetron sputtering reativo com diferentes temperaturas e tipos de substratos. Analisou-se o efeito da variação destes dois parâmetros sobre estrutura e propriedades ópticas destes filmes. Utilizou-se medidas de difração de raios-X, microscopia de força atômica, transmitância no ultravioleta/visível/infravermelho e espectroscopia de espalhamento Rutherford (RBS). As medidas realizadas reportaram que tanto a temperatura quanto o tipo de substrato influenciaram na textura de orientação, morfologia e propriedades ópticas dos filmes. Medidas de transmitância no infravermelho indicaram a presença de bandas relacionadas à contaminação com higrogênio e oxigênio em filmes depositados em temperaturas de substratos menores que 500ºC. As referidas contaminações são compatíveis com a análise residual da água detectada no sistema de deposições, e não foram observadas em temperaturas maiores de substrato. Os diafratogramas de raios-X revelaram que somente em temperaturas altas (Ts>500ºC) a textura de orientação dos filmes é influenciada pelo substrato utilizado, podendo apresentar indícios de crescimento epitaxial. As medidas...Wide bandgap semiconductor materials are of great interest due to the broad range of their technological applications. Among the wide bandgap semiconductor GaN stands out due to its desirable characteristics for such aplications as the value of energy bandgap of 3.4 eV, high thermal conductivity and high hardness. Conventional techniques for producing GaN thin films are the molecular beam epitaxy (MBE) and chemical vapor deposition of metalorganinc precursors (MOVPE), nevertheless these are high techniques. This work brings into focus the preparation and characterization of polycrystalline GaN films by the alternative technique of reactive RF magnetron sputtering with different temperatures and substrates. The effects of varying theses two parameters on structured and optical properties of these films were analysed. Therefore, X-ray diffraction, atomic force microscopy, optical transmittance in the ultraviolet/visible/infrared, and Rutherford Backscattering Spectrometry (RBS) were used to characterize the samples. The results show that temperature, substrate type, and substrate orientation influence the texture, morphology and optical properties of the films. The X-ray diffraction patterns revealed that the orientation texture of films is influenced by the substrate used only at high substrate temperature (Ts>500ºC). This evidences a tendency of epitaxial growth. Besides, the atomic force microscopy at temperature above 500ºC showed that the surface morphology is different for amorphous and crystalline substrates. It also became evident that the decrease of deposition rate and bandgap of the films with increasing deposition temperature is possibly due to nitrogen deficiency by the high rate of desorption at these temperatures. In addition, measurements of trasmisttanc in the infrared Fourier Transform indicated the presence... (Complete abstract click electronic access below)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES
Discarded cell phone lithium ion batteries state of health quick method analysis by galvanostatic intermittent titration technique (GITT) concept
The state of health (SOH) is a important evaluation parameter to rechargeable batteries, because determine its cycle life and help on electric devices supplied by batteries maintenance. In this work the lithium ion discards cell phones batteries state of health and apparent diffusion coefficient (Dap) were measured and correlated which purpose is diminish the batteries analyze time. The apparent diffusion coefficient is a ionic diffusion coefficient modification from GITT technique. The SOH and Dap correlation is well behaved, disclosing a cubic dependency. The time analyze was reduced by more than 1 h
Método rápido de análise do estado de saúde (SOH) de baterias de íon lítio de telefones celulares descartados empregando os conceitos da técnica de titulação galvanostática intermitente (GITT).
O estado de saúde (state of health - SOH) é um importante parâmetro de avaliação de uma bateria recarregável, pois determina seu tempo de vida útil (número de ciclos) e auxilia na manutenção dos sistemas eletrônicos abastecidos com estas baterias. Neste trabalho o estado de saúde e o coeficiente de difusão aparente Dap de baterias de íon lítio descartadas de telefones celulares foram medidos e correlacionados com o objetivo de diminuir o tempo de análise do SOH para as baterias. O coeficiente de difusão aparente é uma modificação do coeficiente de difusão iônico obtido pela técnica GITT. A correlação entre SOH e Dap é bem comportada revelando uma dependência cúbica. O tempo de análise pode, portanto, ser reduzido em mais de 1 h
Functionalization of hydrophobic surfaces with antimicrobial peptides immobilized on a bio-interfactant layer
The design of functionalized polymer surfaces using bioactive compounds has grown rapidly over the past decade within many industries including biomedical, textile, microelectronics, bioprocessing and food packaging sectors. Polymer surfaces such as polystyrene (PS) must be treated using surface activation processes prior to the attachment of bioactive compounds. In this study, a new peptide immobilization strategy onto hydrocarbonaceus polymer surfaces is presented. A bio-interfactant layer made up of a tailored combination of laccase from trametes versicolor enzyme and maltodextrin is applied to immobilize peptides. Using this strategy, immobilization of the bio-inspired peptide KLWWMIRRWG-bromophenylalanine-3,4- dihydroxyphenylalanine-G and KLWWMIRRWG-bromophenylalanine-G on polystyrene (PS) was achieved. The interacting laccase layers allows to immobilize antimicrobial peptides avoiding the chemical modification of the peptide with a spacer and providing some freedom that facilitates different orientations. These are not strongly dominated by the substrate as it is the case on hydrophobic surfaces; maintaining the antimicrobial activity. Films exhibited depletion efficiency with respect to the growth of Escherichia coli bacteria and did not show cytotoxicity for fibroblast L929. This environmentally friendly antimicrobial surface treatment is both simple and fast, and employs aqueous solutions. Furthermore, the method can be extended to three-dimensional scaffolds as well as rough and patterned substrates
Polarity-Induced Selective Area Epitaxy of GaN Nanowires
We present a conceptually
novel approach to achieve selective area
epitaxy of GaN nanowires. The approach is based on the fact that these
nanostructures do not form in plasma-assisted molecular beam epitaxy
on structurally and chemically uniform cation-polar substrates. By <i>in situ</i> depositing and nitridating Si on a Ga-polar GaN
film, we locally reverse the polarity to induce the selective area
epitaxy of N-polar GaN nanowires. We show that the nanowire number
density can be controlled over several orders of magnitude by varying
the amount of predeposited Si. Using this growth approach, we demonstrate
the synthesis of single-crystalline and uncoalesced nanowires with
diameters as small as 20 nm. The achievement of nanowire number densities
low enough to prevent the shadowing of the nanowire sidewalls from
the impinging fluxes paves the way for the realization of homogeneous
core-shell heterostructures without the need of using <i>ex situ</i> prepatterned substrates
Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene
We demonstrate an
all-epitaxial and scalable growth approach to
fabricate single-crystalline GaN nanowires on graphene by plasma-assisted
molecular beam epitaxy. As substrate, we explore several types of
epitaxial graphene layer structures synthesized on SiC. The different
structures differ mainly in their total number of graphene layers.
Because graphene is found to be etched under active N exposure, the
direct growth of GaN nanowires on graphene is only achieved on multilayer
graphene structures. The analysis of the nanowire ensembles prepared
on multilayer graphene by Raman spectroscopy and transmission electron
microscopy reveals the presence of graphene underneath as well as
in between nanowires, as desired for the use of this material as contact
layer in nanowire-based devices. The nanowires nucleate preferentially
at step edges, are vertical, well aligned, epitaxial, and of comparable
structural quality as similar structures fabricated on conventional
substrates