Search results for "film."
showing 10 items of 4451 documents
Low vacuum photo electron emitting thin films
2009
Impact ionisation is a standard procedure to ionise gaseous or vaporisable substances in organic mass spectrometry. In this work, a "softer" ionisation is introduced which seems to be an alternative ion source for reducing collision between substance molecules and the hot internal walls of the box. Through collision mainly found in impact ionisation sources, fragments are built especially from thermally sensitive substances falsifying the spectra. We present here photoelectron emitting materials for the soft ionisation using semiconducting compounds, galliumn nitride (GaN), and a representative of the borides, lanthanum hexaboride (LaB 6 ). They are evaluated by photoelectron spectroscopic …
Soret emission from water-soluble porphyrin thin films: effect on the electroluminescence response
2009
The emission properties of TSPP [tetrakis(4-sulfonatophenyl) porphyrin] and TMPyP [tetrakis(4-methylpyridyl) porphyrin] in thin films, prepared both by the Langmuir–Blodgett technique and the spin-coating method, have been investigated. Surprisingly, in most of the samples analyzed, the emission spectra do not show the usual two bands typical of porphyrins (in the region 650–750 nm), and depend strongly on the excitation energy. The origin of a new emission band detected at ∼480–500 nm is discussed in terms of the nature of the porphyrin aggregates. Moreover, we demonstrate that the presence or absence of this band in the fluorescence spectrum is directly related to the generation of electr…
Amorphous TiO2 in LP-OMCVD TiNxOy thin films revealed by XPS
2001
Abstract TiN(O)–TiO 2 thin films were prepared on Si(1 0 0) by the low pressure organo metallic chemical vapor deposition (LP-OMCVD) method, using ammonia and titanium isopropoxide as precursors. In order to complete previous characterizations, an Ar + bombardment/XPS coupled study was carried out. This method is based on the fact that the behavior of a compound towards an ion bombardment is a function of its composition. In particular, Ar + bombardment of TiO 2 (whatever its form) leads to a preferential sputtering of oxygen atoms with subsequent reduction of titanium and formation of Ti 3+ and Ti 2+ easily detectable by XPS from a significant broadening of the Ti 2p lines. In the opposite…
Ellipsometric study of the physisorption of benzene on graphite
1987
The optical thickness of benzene on the (001) surface of a graphite single crystal has been studied by ellipsometry. Ellipsometric adsorption isotherms have been measured in the temperature range from 180 to 290 K. The maximum thickness of the adsorbed benzene film is constant in this temperature range and compares favourably with the value expected for one monolayer of molecules lying flat on the surface.
Evaluation of Thin Film Microextraction for trace elemental analysis of liquid samples using LIBS detection
2021
An analytical methodology based in the combination of Thin Film Microextraction with Laser-induced Breakdown Spectroscopy (TFME-LIBS) was investigated, for the first time, for detection of Cu, Cr, Ni and Pb in aqueous solutions. In this methodology, the analytes were extracted in a thin film of adsorbent material deposited on a solid support, which was introduced in the sample to analyse. After extraction, the analytes retained in the adsorbent were analysed by LIBS. In order to obtain adsorbent films useful for the microextraction step, two different experimental procedures for film generation, denoted as Drop Casting Deposition and Mould Deposition, were evaluated. In both cases, graphene…
Thermodynamic Study of Small Hydrophobic Ions at the Water–Lipid Interface
2001
Abstract The thermodynamics of binding of two small hydrophobic ions such as norharman and tryptophan to neutral and negatively charged small unilamellar vesicles was investigated at pH 7.4 using fluorescence spectroscopy. Vesicles were formed at room temperature from dimyristoyl phosphatidylcholine (DMPC) or DMPC/dimyristoylphosphatidic acid and DMPC/dimyristoylphosphatidylglycerol. The changes in fluorescence properties were used to obtain association isotherms at variable membrane surface negative charge and at different ionic strengths. The binding of both ions was found to be quantitatively enhanced as the percentage of negative phospholipid increases in the membrane. Also, a decrease …
Graphene and ionic liquids new gel paste electrodes for caffeic acid quantification
2015
Abstract Graphene/ionic liquids nanocomposite gels were synthesized by an electrochemical etching approach and fully characterized under a morphological and structural point of view. For this purpose, several analytical techniques were applied, as HR-TEM/EDX (High Resolution-Transmission Electron Microscopy/Energy Dispersive X-Ray Analysis); FE-SEM/EDX (Field Emission-Scanning Electron Microscopy/Energy Dispersive X-Ray Analysis); XPS (X-Ray Photoelectron Spectroscopy); FT-IR (Fourier Transform-Infrared Spectroscopy) and electrochemical techniques. After the characterization study, nanocomposite-gel paste electrodes were assembled, exhibiting a selective and specific detection toward the ca…
Application of a Novel Refinement Method for Accurate Determination of Chemical Diffusion Coefficients in Electroactive Materials by Potential Step T…
2005
We describe application of a novel refinement method for an accurate determination of the chemical diffusion coefficient, D, and the generalized kinetic parameter, A, from experimental potentiostatic intermittent titration technique (PITT) data suited for a variety of electrochemically doped electroactive polymers and inorganic intercalation host materials. The proposed, simple, two-step refinement procedure, based on earlier derived analytical expressions for the PITT response, is exemplified by the analysis of chronoamperometric responses to small-amplitude potential perturbation for p- and n-doped poly(fluorenone-bithiophene) (PFDOBT-HH) thin film electrode. The initial p-doping and the …
New n-type molecular semiconductor–doped insulator (MSDI) heterojunctions combining a triphenodioxazine (TPDO) and the lutetium bisphthalocyanine (Lu…
2018
International audience; Molecular semiconductor–doped insulator (MSDI) heterojunctions were designed using a new family of sublayers, namely triphenodioxazines (TPDO). The device obtained by combining the tetracyano triphenodioxazine bearing two triisopropylsilylethynyl moieties as a sublayer with the lutetium bisphthalocyanine (LuPc2) as a top layer showed a nonlinear current–voltage characteristic independent of the sign of the polarization, which is the signature of MSDI heterojunctions. Thus, a TPDO was used in a chemical sensor for the first time. Despite LuPc2 being the only material exposed to the atmosphere, the positive response of the device under ammonia revealed the key role pla…
Structure and properties of GaNxOy films grown by nitridation of GaAs (100) substrates
2004
GaAs (100) substrates have been heat-treated in a metal-organic chemical vapor deposition reactor under flows of NH 3 and an oxygen organo-metallic precursor at temperatures between 650°C and 750°C. Yellowish films formed at the surface of all the samples. Gallium, nitrogen and oxygen were detected by EDX analysis of the films. The oxygen content was estimated in the range of at 5-10 at% depending on the heat-treatment temperature. X-ray diffraction and HRTEM results indicate that the structure of the films corresponds to the hexagonal wurtzite phase of GaN with an expanded unit cell. Raman spectra show hands corresponding to the Raman active GaN modes as well as disorder-activated broad ba…