Ana Maria Botelho do Rego

High mobility indium free amorphous oxide thin film transistors

High mobility bottom gate thin film transistors (TFTs) with an amorphous gallium tin zinc oxide (a-GSZO) channel layer have been produced by rf magnetron cosputtering using a gallium zinc oxide (GZO) and tin (Sn) targets. The effect of postannealing temperatures (200, 250, and 300°C) was evaluated and compared with two series of TFTs produced at room temperature (S1) and 150°C (S2) during the channel deposition. From the results, it was observed that the effect of postannealing is crucial for both series of TFTs either for stability as well as for improving the electrical characteristics. The a-GSZO TFTs (W∕L=50∕50μm) operate in the enhancement mode (n-type), present a high saturation mobility of 24.6cm2∕Vs, a subthreshold gate swing voltage of 0.38V/decade, a turn-on voltage of −0.5V, a threshold voltage of 4.6V, and an Ion∕Ioff ratio of 8×107, satisfying all the requirements to be used as active-matrix backplane.

Physical immobilization of Rhizopus oryzae lipase onto cellulose substrate: Activity and stability studies

Rhizopus oryzae lipase (ROL) was immobilized by adsorption onto oxidized cellulose fibers and regenerated films. The maximum adsorption level increases with the raise in the amount of carboxylic groups on cellulose surface confirming that adsorption is being governed mainly by electrostatic interaction between the enzyme and the substrate. This hypothesis was further confirmed by zeta-potential measurements showing a decrease in the zeta-potential of the fibers after enzyme adsorption. XPS analysis showed an intensification of the N 1s peak attesting the presence of the enzyme on the surface. The effect of temperature, pH and solvent polarity on the immobilized enzyme activity and stability was investigated. The catalytic esterification of oleic acid with n-butanol has been carried on using hexane as an organic solvent. A high conversion yield was obtained (about 80%) at 37 degrees C with a molar ratio of oleic acid to butanol 1:1 and 150IU immobilized lipase. The adsorption achieved two successive cycles with the same efficiency, and started to lose its activity during the third cycle.

Interaction of Self-Assembled Monolayers of DNA with Electrons: HREELS and XPS Studies

We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.

Chapter 7 – PHOTONIC AND ELECTRONIC SPECTROSCOPIES FOR THE CHARACTERIZATION OF ORGANIC SURFACES AND ORGANIC MOLECULES ADSORBED ON SURFACES

Publisher Summary This chapter describes the synergetic effect obtained on putting together the larger number of available techniques to the service of characterizing surfaces. It describes optical spectroscopies in the ultraviolet visible infrared (UV–Vis–IR) range used in diffuse reflectance arrangement in combination with electronic spectroscopies, specifically X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy spectroscopy. XPS and UV/Vis absorption and luminescence studies have proved to be complementary techniques in the study of dyes in several environments: when adsorbed onto or bound to a natural polymer, microcrystalline cellulose, when forming inclusion complexes with cyclodextrins, and also when interacting with silicas with different pore sizes. UV/Vis ground-state diffuse-reflectance absorption and luminescence studies showed in most cases a huge increase of fluorescence emission quantum yield when compared to solution studies for several dyes, when they are entrapped into microcrystalline cellulose, because of the reduction of mobility and formation of planar and emissive conformers and of the amount and type of aggregates, which are formed. A complementary view is given by X-ray photoelectron studies that provide evidence for hydrogen bond formation as well as preferential attachment by one or two nitrogen atoms per cyanine molecule to the hydroxyl groups in the substrates.

Human mesenchymal stem cell behavior on femtosecond laser-textured Ti-6Al-4V surfaces.

AIM The aim of the present work was to investigate ultrafast laser surface texturing as a surface treatment of Ti-6Al-4V alloy dental and orthopedic implants to improve osteoblastic commitment of human mesenchymal stem cells (hMSCs). MATERIALS & METHODS Surface texturing was carried out by direct writing with an Yb:KYW chirped-pulse regenerative amplification laser system with a central wavelength of 1030 nm and a pulse duration of 500 fs. The surface topography and chemical composition were investigated by scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. Three types of surface textures with potential interest to improve implant osseointegration can be produced by this method: laser-induced periodic surface structures (LIPSSs); nanopillars (NPs); and microcolumns covered with LIPSSs, forming a bimodal roughness distribution. The potential of the laser treatment in improving hMSC differentiation was assessed by in vitro study of hMSCs spreading, adhesion, elongation and differentiation using epifluorescence microscopy at different times after cell seeding, after specific stainings and immunostainings. RESULTS Cell area and focal adhesion area were lower on the laser-textured surfaces than on a polished reference surface. Obviously, the laser-textured surfaces have an impact on cell shape. Osteoblastic commitment was observed independently of the surface topography after 2 weeks of cell seeding. When the cells were cultured (after 4 weeks of seeding) in osteogenic medium, LIPSS- and NP- textured surfaces enhanced matrix mineralization and bone-like nodule formation as compared with polished and microcolumn-textured surfaces. CONCLUSION The present work shows that surface nanotextures consisting of LIPSSs and NPs can, potentially, improve hMSC differentiation into an osteoblastic lineage.

Adhesion of façade coating colonisers, as mediated by physico-chemical properties.

Abstract The adhesion of Klebsormidium flaccidum, Stichococcus bacillaris and Chlorella cf. mirabilis, three strains of green microalgae isolated from biofilms on façade coatings were investigated in a parallel plate flow chamber. The model surfaces tested were glass slides, and −CH3 (mediated by octadecyltrichlorosilane [OTS] and hexamethyldisilazane [HMDZ] modification) and -NH2 (aminopropyltriethoxysilane [APS] modification) terminated self-assembled monolayers. Algal physicochemical properties were evaluated by the microbial adhesion to solvents (MATS) assay and by contact angle measurements. The model surfaces were characterised by X-ray photoelectron spectroscopy analysis and by contact angle measurements. Predicted adhesion trends were then compared to in vitro measurements. The adhesion strength of the three algal strains followed the trend: APS > OTS > HMDZ > glass. The adhesion process thus seemed to be mediated by hydrophobic and electrostatic interactions, and was shown to be influenced by the algal culture age and the initial contact time.

Grafting of Porphyrins on Cellulose Nanometric Films

Ultrathin films of cellulose were functionalized with iron protoporphyrin IX (FePP). Spin-coating allows the production of silylated cellulose films in a controlled way. Cellulose regeneration is achieved through the hydrolyzation of the silane groups, exposing the film to acidic vapors. To enhance the reactivity of the cellulose surface to the protoporphyrin, carbonyldiimidazole (CDI) was used as an activator. The effect of different spacers on the porphyrin grafting such as 1,8-diaminooctane and 1,4-phenylenediamine was studied. The highest level of cellulose functionalization with FePP was achieved when both the cellulose film and FePP were activated by CDI and a diaminoalkane was used as a spacer between the surface and the FePP. ATR/MIR (attenuated total reflection in multiple internal reflections) was performed in situ to follow the kinetics of the different chemical reactions with the cellulose surface. ATR/MIR proved again to be a powerful tool for probing the surface reaction. X-ray photoelectron spectroscopy permitted the elemental analysis of the cellulose surface after the chemical modification.

Development and characterization of a thermoresponsive polysulfone membrane using an environmental friendly technology

A new and environmentally friendly technology has been used successfully to produce thermoresponsive polysulfone membranes with good performance in terms of valve mechanism in the pores, with a complete on-off control of water permeability. Membranes were prepared using a CO2-assisted phase inversion method and their pores were coated/impregnated with a thermoresponsive polymer – poly(N-isopropylacrylamide) – using a new methodology for the preparation of these type of structures. The coating/impregnation efficiency was assessed by SEM and XPS analysis that confirmed the presence of nitrogen due to the thermoresponsive hydrogel. Contact angle measurements and phosphate buffer solution permeability were determined in order to characterize the structure hydrophobicity variations with temperature. The on-off mechanism was tested using a model protein (BSA) as a proof of concept for the ability to control pore apertures by temperature stimulus. A diffusion model based on Ficks law and Langmuir adsorption was developed.

Sugarcane bagasse cellulose fibres and their hydrous niobium phosphate composites: synthesis and characterization by XPS, XRD and SEM

AbstractCellulose fibres obtained from sugarcane bagasse were submitted to a purification process, which consisted of an acid hydrolysis for elimination of the major part of lignin and hemicellulose. This was followed by a delignification process carried out in two steps to yield crude cellulose (CCell) fibres in the first one and with a subsequent bleaching in order to yield bleached cellulose fibres (BCell). Composites of crude and bleached cellulose fibres with hydrous niobium phosphate, cell/NbOPO4·nH2O, were subsequently synthesized. Scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction characterization of the obtained materials showed CCell/NbOPO4·nH2O and BCell/NbOPO4·nH2O are real composites. The nature of the cellulose (CCell or BCell) has an important role on the composites obtained, namely on the niobium salt composition at the composite surface. The synthesis of membranes of both cellulose and mixed matrix cellulose/NbOPO4·nH2O was only possible when the bleached cellulose was used.

Room-Temperature Cosputtered HfO2 – Al2O3 Multicomponent Gate Dielectrics

Hafnium oxide-aluminum oxide (HFAIO) dielectric films were cosputtered using HfO 2 and Al 2 O 3 targets, and their properties are studied in comparison with pure HfO 2 films. The X-ray diffraction studies confirmed that the HfO 2 films are nanocrystalline with a monoclinic phase. The as-deposited HfAIO films with a chemical composition of (HfO 2 ) 0 . 86 (AI 2 O 3 ) 0 . 14 are amorphous even after annealing at 500°C. Further, the cosputtered films show a slight reduction in leakage current. The leakage current density may be significantly reduced below 3 × 10 -10 A cm -2 at an electric field of 0.25 MV/cm when applying the proper radio-frequency bias to the substrate.