75 research outputs found
Characterization of the electrical and optical properties of the CrNxOy and AlNxOy thin films
Dissertação de mestrado em [FÃsica]The metallic oxynitrides have attracted the attention of many researchers in the last decade due their versatile properties. By controlling the oxide/nitride ratio, the electronic properties of materials can be tuned from those of low resistivity metallic nitrides to those of insulator oxides. In this thesis the optical and electrical properties of AlNxOy and CrNxOy thin films, deposited by DC reactive magnetron sputtering, were investigated and correlated with their compositional and structural features. Depending on the particular deposition parameters that were selected, it was possible to identify different types of films with different growth conditions and physical properties. The optical and electrical properties of both type of films, was found to depend strongly on the chemical composition of the samples
Preparation and characterization of CrNxOy thin films: The effect of composition and structural features on the electrical behavior
Metallic oxynitrides have attracted the attention of several researchers in the last decade
due to their versatile properties. Through the addition of a small amount of oxygen into a
transition metal nitride film, the material’s bonding states between ionic and covalent types
can be tailored, thus opening a wide range of electrical, optical, mechanical and tribological
responses. Among the oxynitrides, chromium oxynitride (CrN x O y ) has many interesting
applications in different technological fields. In the present work the electrical behavior of
CrN x O y thin films, deposited by DC reactive magnetron sputtering, were investigated and
correlated with their compositional and structural properties. The reactive gas flow, gas
pressure, and target potential were monitored during the deposition in order to control the
chemical composition, which depend strongly on reactive sputtering process. Depending on
the particular deposition parameters that were selected, it was possible to identify three types
of films with different growth conditions and physical properties. The electrical resistivity of the films, measured at room temperature, was found to depend strongly on the chemical
composition of the samples
RNA Aptamers Generated against Oligomeric Aβ40 Recognize Common Amyloid Aptatopes with Low Specificity but High Sensitivity
Aptamers are useful molecular recognition tools in research, diagnostics, and therapy. Despite promising results in other fields, aptamer use has remained scarce in amyloid research, including Alzheimer's disease (AD). AD is a progressive neurodegenerative disease believed to be caused by neurotoxic amyloid β-protein (Aβ) oligomers. Aβ oligomers therefore are an attractive target for development of diagnostic and therapeutic reagents. We used covalently-stabilized oligomers of the 40-residue form of Aβ (Aβ40) for aptamer selection. Despite gradually increasing the stringency of selection conditions, the selected aptamers did not recognize Aβ40 oligomers but reacted with fibrils of Aβ40, Aβ42, and several other amyloidogenic proteins. Aptamer reactivity with amyloid fibrils showed some degree of protein-sequence dependency. Significant fibril binding also was found for the naïve library and could not be eliminated by counter-selection using Aβ40 fibrils, suggesting that aptamer binding to amyloid fibrils was RNA-sequence-independent. Aptamer binding depended on fibrillogenesis and showed a lag phase. Interestingly, aptamers detected fibril formation with ≥15-fold higher sensitivity than thioflavin T (ThT), revealing substantial β-sheet and fibril formation undetected by ThT. The data suggest that under physiologic conditions, aptamers for oligomeric forms of amyloidogenic proteins cannot be selected due to high, non-specific affinity of oligonucleotides for amyloid fibrils. Nevertheless, the high sensitivity, whereby aptamers detect β-sheet formation, suggests that they can serve as superior amyloid recognition tools
Continuous Flow Reactor for the Production of Stable Amyloid Protein Oligomers
The predominant working hypothesis of Alzheimer's disease is that the proximate pathologic agents are oligomers of the amyloid β-protein (Aβ). "Oligomer" is an ill-defined term. Many different types of oligomers have been reported, and they often exist in rapid equilibrium with monomers and higher-order assemblies. This has made formal structure-activity determinations difficult. Recently, Ono et al. [Ono, K., et al. (2009) Proc. Natl. Acad. Sci. U.S.A. 106, 14745-14750] used rapid, zero-length, in situ chemical cross-linking to stabilize the oligomer state, allowing the isolation and study of pure populations of oligomers of a specific order (number of Aβ monomers per assembly). This approach was successful but highly laborious and time-consuming, precluding general application of the method. To overcome these difficulties, we developed a "continuous flow reactor" with the ability to produce theoretically unlimited quantities of chemically stabilized Aβ oligomers. We show, in addition to its utility for Aβ, that this method can be applied to a wide range of other amyloid-forming proteins
Graphene-porous semiconductor nanocomposites scalable synthesis for energy applications
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Epitaxial lift-off process for Ill-V solar cells by using porous germanium for substrate re-use
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AlNxOy thin films for electrical applications
Comunicação oralAluminium oxide (Al2O3) is an insulator material, with high electrical breakdown, large band gap and high permittivity. Its dielectric properties make it a promising candidate to be used as gate material instead of SiO2 in microelectronic applications, such as in flash memory circuits, organic thin film transistors (OTFT) and MOSFETs. On the other hand, aluminium nitride (AlN) is a ceramic piezoelectric material with high electrical resistivity and excellent thermal properties, that has been used in many applications such as substrate in microelectronic devices, fabrication of high power and high temperature electronic devices, surface acoustic wave (SAW) devices, and electronic packaging.
The interesting electrical properties of Al2O3 and AlN opens the door to study the electrical properties of the Al-N-O system, which, in a first approach, can combine some of both Al2O3 and AlN advantages by tailoring the concentrations of the three elements, according to the particular application envisaged. The use of aluminium oxynitride is not yet very common, despite some very few examples in the field of protective coatings, optoelectronics, and in microelectronics as a dielectric in multilayer capacitors.
The main objective of the present work is to study the variation of the electrical response of the AlNxOy thin films as a function of the composition of the prepared films, using as reference the two base binary systems: AlNx and AlOy. The films are deposited by DC magnetron sputtering, with the discharge parameters monitored during the deposition in order to control the chemical composition, according to the particular results of the electrical behavior. The electrical resistivity of the films is observed to depend strongly on film stoichiometry, composition and structure of the samples. Preliminary results show a smoth transition of the film’s electrical characteristics between those of closely metallic (similar to the response of pure Al films), towards those of AlN and Al2O3 films. These results confirm the possibility to tailor in a very smooth way the characteristics of materials between those of metallic towards insulting ones, opening thus a widespread of possible applications.Portuguese Foundation for Science and Technology (FCT) - SFRH/BD/47118/200
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