35 research outputs found
Self-assembly in solution of a reversible comb-shaped supramolecular polymer
We report a single step synthesis of a polyisobutene with a bis-urea moiety
in the middle of the chain. In low polarity solvents, this polymer
self-assembles by hydrogen bonding to form a combshaped polymer with a central
hydrogen bonded backbone and polyisobutene arms. The comb backbone can be
reversibly broken, and consequently, its length can be tuned by changing the
solvent, the concentration or the temperature. Moreover, we have proved that
the bulkiness of the side-chains have a strong influence on both the
self-assembly pattern and the length of the backbone. Finally, the density of
arms can be reduced, by simply mixing with a low molar mass bis-urea
Fourier Transform Scanning Tunneling Spectroscopy: the possibility to obtain constant energy maps and the band dispersion using a local measurement
We present here an overview of the Fourier Transform Scanning Tunneling
spectroscopy technique (FT-STS). This technique allows one to probe the
electronic properties of a two-dimensional system by analyzing the standing
waves formed in the vicinity of defects. We review both the experimental and
theoretical aspects of this approach, basing our analysis on some of our
previous results, as well as on other results described in the literature. We
explain how the topology of the constant energy maps can be deduced from the FT
of dI/dV map images which exhibit standing waves patterns. We show that not
only the position of the features observed in the FT maps, but also their shape
can be explained using different theoretical models of different levels of
approximation. Thus, starting with the classical and well known expression of
the Lindhard susceptibility which describes the screening of electron in a free
electron gas, we show that from the momentum dependence of the susceptibility
we can deduce the topology of the constant energy maps in a joint density of
states approximation (JDOS). We describe how some of the specific features
predicted by the JDOS are (or are not) observed experimentally in the FT maps.
The role of the phase factors which are neglected in the rough JDOS
approximation is described using the stationary phase conditions. We present
also the technique of the T-matrix approximation, which takes into account
accurately these phase factors. This technique has been successfully applied to
normal metals, as well as to systems with more complicated constant energy
contours. We present results recently obtained on graphene systems which
demonstrate the power of this technique, and the usefulness of local
measurements for determining the band structure, the map of the Fermi energy
and the constant-energy maps.Comment: 33 pages, 15 figures; invited review article, to appear in Journal of
Physics D: Applied Physic
Solid-state reference electrodes based on carbon nanotubes and polyacrylate membranes
A novel potentiometric solid-state reference electrode containing single-walled carbon nanotubes as the transducer layer between a polyacrylate membrane and the conductor is reported here. Single-walled carbon nanotubes act as an efficient transducer of the constant potentiometric signal originating from the reference membrane containing the Ag/AgCl/Clâ ions system, and they are needed to obtain a stable reference potentiometric signal. Furthermore, we have taken advantage of the light insensitivity of single-walled carbon nanotubes to improve the analytical performance characteristics of previously reported solid-state reference electrodes. Four different polyacrylate polymers have been selected in order to identify the most efficient reservoir for the Ag/AgCl system. Finally, two different arrangements have been assessed: (1) a solid-state reference electrode using photo-polymerised n-butyl acrylate polymer and (2) a thermo-polymerised methyl methacrylate:n-butyl acrylate (1:10) polymer. The sensitivity to various salts, pH and light, as well as time of response and stability, has been tested: the best results were obtained using single-walled carbon nanotubes and photo-polymerised n-butyl acrylate polymer. Water transport plays an important role in the potentiometric performance of acrylate membranes, so a new screening test method has been developed to qualitatively assess the difference in water percolation between the polyacrylic membranes studied. The results presented here open the way for the true miniaturisation of potentiometric systems using the excellent properties of single-walled carbon nanotubes
In silico analysis of polymorphic microsatellites in penaeid shrimp and construction of a free-access database
Physical and electrochemical properties of vanadium alloy oxide layers prepared by anodic passivation
Development of redox glasses and subsequent processing by means of pulsed laser deposition for realizing silicon-based thin-film sensors.
In this work, two different redox-sensitive glass materials have been fabricated for the development of a production friendly redox electrode. The specific glass targets have been prepared by glass pouring process. The transducer structure is fabricated via conventional silicon-based semiconductor technology. The glass bulk material was deposited for the first time by means of pulsed laser deposition process into the thin-film state on the sensor structures. The fabricated sensors have been physically and electrochemically characterized by X-ray photoelectron spectroscopy, determination of expansion coefficient, impedance and potentiometric measurements
Untersuchungen von PreuĂisch Blau-modifizierten Elektroden zur H2O2-Bestimmung
Zur empfindlichen quantitativen elektrochemischen Bestimmung von Wasserstoffperoxid wurden Graphitfasern erfolgreich mit PreuĂisch Blau (PB) modifiziert. Bei den Messungen an diesen Elektroden wurde ein linearer Zusammenhang zwischen der geflossenen Ladung und der zugegebenen nanomolaren Menge an H2O2 gefunden. Die PB-Abscheidung wurde zuvor an Gold-Dickschichtelektroden untersucht. Perspektivisch soll das System zur Messung von H2O2 in feuchter Raumluft und im Atemkondensat dienen