Modification of Hexatriacontane by O2–N2 Microwave Post-Discharges

Etch rates of hexatriacontane (HTC) as high as ~10 mg s⁻¹ m⁻² in late O₂ post-discharge are obtained at 333 K where no significant UV nor VUV irradiation occurs. Introducing N₂ in the gas mixture helps control the ratio of O/O₂ densities, which is shown to play a key role in the functionalization or etching of the HTC. The oxygen atoms are required for any further modification of the HTC because they initiate the formation of the radical chains by abstraction of one hydrogen. O(³P) atoms do not contribute directly to break the alkane chain close to room temperature but they can functionalise it. O₂ is the important reactive species for the etching because of the role played by the peroxide groups on the scission of the hydrocarbon chains.     

Interaction Mechanisms Between Ar–O<Subscript>2</Subscript> Post-Discharge and Stearic Acid I: Behaviour of Thin Films

We study the interaction of thick films (~4 mm) of stearic acid (SA), a C₁₈ alkane skeleton with an acid function, with late Ar–O₂ post-discharge. Contrary to what is observed with thin films of SA (~2–3 μm) which are efficiently etched (part I), only functionalization is observed over the first 2 h of treatment with a plasma source operated in the continuous mode, whatever the temperature. The heat released by surface reactions affects non-linearly the temperature of the substrate. Pulsing the source at a frequency ranging from 0.1 to 1 kHz slows down the functionalization process but does not allow any etching of the material. On the contrary, the SA can be etched as thick films by pulsing the oxygen flow rate at a frequency below 50 mHz. By pulsing the reactive gas, the time averaged value of the [O]/[O₂] ratio is decreased, limiting the functionalization processes due to oxygen atoms, and the mean temperature is lowered, decreasing the diffusion length of O₂ (and/or possibly O₂*) species in the SA which are responsible for the scission of C–C bonds of radicals.     

2-d data collection in high pressure powder diffraction studies-applications to semiconductors

Abstract

Using angle-dispersive diffraction techniques and synchrotron radiation, we have made a detailed re-examination of the high-pressure behaviour of a number of core II-VI, III-V and group IV semiconductors. Despite much previous work on these materials, the good resolution afforded by angle-dispersive techniques, and the high-sensitivity of the image-plate area detector have yielded many new results which reveal that the accepted structural systematics have to be modified quite substantially. In this paper, we summarise the newly emerging structural systematics, and use the results to show how access to full 2-d powder patterns has proved essential in determining correct crystal structures.     

Recognition and Sensing of Creatinine

Current methods for creatinine quantification suffer from significant drawbacks when aiming to combine accuracy, simplicity, and affordability. Here, an unprecedented synthetic receptor, an aryl‐substituted calix[4]pyrrole with a monophosphonate bridge, is reported that displays remarkable affinity for creatinine and the creatininium cation. The receptor works by including the guest in its deep and polar aromatic cavity and establishing directional interactions in three dimensions. When incorporated into a suitable polymeric membrane, this molecule acts as an ionophore. A highly sensitive and selective potentiometric sensor suitable for the determination of creatinine levels in biological fluids, such as urine or plasma, in an accurate, fast, simple, and cost‐effective way has thus been developed.     

Strong asymmetric hydrogen bonding in 2‐(oxamoylamino)ethylammonium oxamate–oxamic acid (1/1)

The title compound, C₄H₁₀N₃O₂⁺·C₂H₂NO₃⁻·C₂H₃NO₃, contains at least 11 distinct hydrogen‐bond interactions showing a great variety of bond strengths. The shortest and strongest hydrogen bond [O...O = 2.5004 (12) Å] is found between the uncharged oxamic acid molecule and the oxamate monoanion. The grouping formed by such a strong hydrogen bond can thus be considered as a hydrogen bis(oxamate) monoanion. It lacks crystallographic symmetry and the two oxamate groups have different conformations, showing an asymmetric hydrogen‐bond interaction. Significantly, the asymmetry allows us to draw a direct comparison of site basicity for the two inequivalent carboxylate O atoms in the planar oxamate anion. The constituent molecular ions of (I) form ribbons, where all amide and carboxylate groups are coplanar. Graph‐set analysis of the hydrogen‐bonded networks reveals the R²₂(10) and R²₂(9) homodromic nets as important structure‐directing motifs, which appear to be a common feature of many oxamate‐containing compounds.     

Emission spectroscopy detection of N2 active species in plasma nitriding process

The present paper is a review of recent works related to the optical emission spectroscopy applied to the determination of ground state densities of N atoms in Ar-N₂ flowing post-discharges. The effect of small quantities of H₂ in the Ar-N₂ discharge on N atom densities within the post-discharge has been analysed. The authors demonstrate that optical emission of Na impurity may be applied to the determination of the vibrational temperature of N₂(X,v) states at the temperatures usual for nitriding of metals in Ar-N₂ post-discharge. From the diagnostic of Ar-N₂ post-discharges, it is clearly specified that nitriding of iron base alloys in a flowing post-discharge reactor is originating in N atoms, especially when a few H₂ molecules are admixed into the Ar-N₂ discharge. Finally, correlation between the N-atom density and the thickness of the iron nitrided layers when H₂ is introduced into the Ar-N₂ discharge are given. Dedicated to Prof. Jan Janča on the occasion of his 60^th birthday.     

Determination of fifteen priority phenolic compounds in environmental samples from Andalusia (Spain) by liquid chromatography–mass spectrometry

This work describes the optimisation of a method to determinate fifteen phenolic compounds in waters, sediments and biota (green marine algae) by liquid chromatography coupled to mass spectrometry (LC-MS) with atmospheric pressure chemical ionisation (APCI) in the negative mode. The LC separations of the studied compounds and their MS parameters were optimised in order to improve selectivity and sensitivity. Separation was carried out with a C₁₈ column using methanol and 0.005% acid acetic as mobile phase in gradient mode. The molecular ion was selected for the quantitation in selective ion monitoring (SIM) mode. A solid-phase extraction (SPE) method was applied in order to preconcentrate the target analytes from water samples. However, extraction of the compounds from sediment and biota samples was carried out by liquid–solid extraction with methanol/water after studying the influence of other organic solvents. In addition, a clean-up step by SPE with HLB Oasis cartridges was necessary for sediments and biota. The proposed analytical methodology was validated in the target environmental matrices by the analysis of spiked blank matrix samples. Detection limits were 10–50 ng L^–1 for water, 1–5 g kg^–1 for sediments and 2.5–5 g kg^–1 for biota samples. Good recoveries and precision values were obtained for all matrices. This methodology has been successfully applied to the analysis of incurred water, sediment and biota samples from Andalusia (Spain).     

All-optical square-pulse generation and multiplication at 1.5 mum by use of a novel class of fiber Bragg gratings

A new class of linearly chirped fiber Bragg gratings, suitable for all-fiber optical multiplication and reshaping of picosecond pulse trains, is proposed and experimentally demonstrated. Repetition-rate multiplication, based on the temporal Talbot effect, is achieved by accurate control of the grating chirp, and a suitable design of the index-modulation depth profile allows for simultaneous square-pulse shaping. A 50-ps squarelike optical pulse train at 10-GHz repetition rate is obtained, starting from a 2.5-GHz Gaussian pulse train emitted by a mode-locked Er-Yb laser.     

Oxygen plasma functionalization of poly(p-phenilene sulphide)

Surface effects during plasma activation of poly(p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100 W. The electron density and temperature were measured with a double Langmuir probe and were 4 × 10¹⁵ m⁻³ and 3 eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4 × 10²¹ m⁻³. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7 × 10⁻³ N/m or/and increased to 7 × 10⁻² N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20 at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.