Vertically Aligned Few-Layered Graphene-Based Non-Cryogenic Bolometer

In this study, we report the photoresponse of vertically aligned few-layered graphene (VAG) upon infra-red (IR) irradiation at room temperature. Four probe measurements showed the current−voltage (I−V) characteristic of electrical switching during pulsed IR irradiation. The photoresponse reported here for VAG was significantly higher than that reported for carbon nanotube (CNT) samples. Our investigation shows that such a photoresponse arose solely from the bolometric effect, where the conductivity changed with temperature. The resistance magnitude of the VAGs increased ~two fold for each 6 °C increase in temperature. Also, the Thermal Coefficient of Resistance (TCR) in this region was ~11%/K, which is the highest TCR value reported for any carbon nanomaterial

Microbial surfactants: fundamentals and applicability in the formulation of nano-sized drug delivery vectors

Microbial surfactants, so-called biosurfactants, comprise a wide variety of structurally distinct amphipathic molecules produced by several microorganisms. Besides exhibiting surface activity at the interfaces, these molecules present powerful characteristics including high biodegradability, low toxicity and special biological activities (e.g. antimicrobial, antiviral, anticancer, among others), that make them an alternative to their chemical counterparts. Several medical-related applications have been suggested for these molecules, including some reports on their potential use in the formulation of nano-sized drug delivery vectors. However, despite their promises, due to the generalized lack of knowledge on microbial surfactants phase behavior and stability under diverse physicochemical conditions, these applications remain largely unexplored, thus representing an exciting field of research. These nano-sized vectors are a powerful approach towards the current medical challenges regarding the development of efficient and targeted treatments for several diseases. In this review, a special emphasis will be given to nanoparticles and microemulsions. Nanoparticles are very auspicious as their size, shape and stability can be manipulated by changing the environmental conditions. On the other hand, the easiness of formulation, as well as the broad possibilities of administration justifies the recent popularity of the microemulsions. Notwithstanding, both vector types still require further developments to overcome some critical limitations related with toxicity and costs, among others. Such developments may include the search for other system components, as the microbial surfactants, that can display improved features.The author acknowledges the financial support from the Strategic Project PEst-OE/EQB/LA0023/2013 and project ref. RECI/BBB-EBI/0179/2012 (project number FCOMP-01-0124-FEDER-027462) funded by Fundacao para a Ciencia e a Tecnologia

Controlling the morphology and efficiency of nanostructured molybdenum nitride electrocatalysts for the hydrogen evolution reaction

Among catalysts based on non-noble metals, Mo-based materials are important for hydrogen evolution because of their low cost, good conductivity, and catalytic efficiency. This study demonstrates a facile two-step synthesis of Mo₂N nanostructures assembled from 5–8 nm particles with graphitic carbon nitride as the nitrogen source. These Mo₂N nanostructures of various morphologies (hexagons, triangles, and nanowires) show a very high activity and stability in acidic media during water electrolysis. Their nanostructures were characterized by using powder XRD, electron microscopy, N<SUB>2</SUB> gas adsorption analysis, and X-ray photoelectron spectroscopy. Hydrogen evolution reaction parameters, which include the Tafel slope, charge transfer resistance, and stability, were analyzed by using linear sweep voltammetry and electrochemical impedance spectroscopy. Thin hexagonal sheets of Mo₂N show the highest apparent electrocatalytic activity (current density of 197 mA cm⁻²_geometric at −400 mV vs. the reversible hydrogen electrode) and excellent stability in an acidic medium with a small onset potential of 90 mV and a Tafel slope of 145 mV decade⁻¹. The lowest Tafel slope was observed for Mo₂N nanowires

Enhanced and stable field emission from in situ nitrogen-doped few-layered graphene nanoflakes

Vertically aligned few-layered graphene (FLG) nanoflakes were synthesized on bare silicon (Si) substrates by a microwave plasma enhanced chemical vapor deposition method. In situ nitrogen (N2) plasma treatment was carried out using electron cyclotron resonance plasma, resulting in various nitrogen functionalities being grafted to the FLG surface. Compared with pristine FLGs, the N2 plasma-treated FLGs showed significant improvement in field emission characteristics by lowering the turn-on field (defined at 10 μA/cm2) from 1.94 to 1.0 V/μm. Accordingly, the field emission current increased from 17 μA/cm2 at 2.16 V/μm for pristine FLGs to about 103 μA/cm2 at 1.45 V/μm for N-doped FLGs. Furthermore, N-doped FLG samples retained 94% of the starting current over a period of 10 000 s, during which the fluctuations were of the order of ±10.7% only. The field emission behavior of pristine and N2 plasma-treated FLGs is explained in terms of change in the effective microstructure as well as a reduction in the work function as probed by X-ray photoelectron valence band spectroscopy