Development of intentional contamination in iron by bath for silicon wafers and evaluation of VPD-Bulk and LPD-Bulk for metallic contaminants analyses by ICPMS

International audienceThis paper offers a preliminary study for the analysis of metallic contamination on frontend patterned wafers obtained by two different techniques based on the etching of the whole patterns, LPD-Bulk and VPD-Bulk coupled with an ICPMS. To elaborate the analysis of patterned wafers, methods were first verified and optimised on reference Si wafers. Both techniques are complementary methods for the etching of wafers. LPD-Bulk enables a fast etching of several micrometres of Si but with less precision than VPD-Bulk, which is more adapted for the etching of layers thinner than1 micrometre. The intentional contamination in SC1 and H2O bath of monitoring wafers showed that contamination in H2O is better controlled due to the absence of chemical reactions, competition between oxidation and etching processes occurring during SC1. And diffusion of contaminants at the tested temperatures from 20°C to 80°C, does not occur. Heat treatment should be applied to allow the diffusion of metallic contaminants in the bulk of the wafers

Interfacial layer characterization in dental composite.

Nowadays, dental resins find increasing use by practitioners. However, photopolymerization of such resins is limited to a so-called 'depth of cure'. To face this problem, dentists superimpose resin layers of limited depth. This technique raises the problem of the quality of interlayer. This paper aims at screening different cases of adhesion at the interface. Shear strength of such interfacial layers is tested in shear mode in various conditions (with or without an oxygen-inhibited layer, or contaminated by saliva or water). Unexpectedly, the presence of an oxygen-inhibition on the first layer, as assessed using micro-Raman spectroscopy, induces higher shear strength. In this case, a cohesive break occurs while an adhesive one is observed in all the other cases

Volume contraction in photocured dental resins: the shrinkage-conversion relationship revisited.

Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values. OBJECTIVES: This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion. METHODS: Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry. RESULTS: An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements. SIGNIFICANCE: This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective

Volume contraction in photocured dental resins: the shrinkage-conversion relationship revisited.

Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values. OBJECTIVES: This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion. METHODS: Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry. RESULTS: An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements. SIGNIFICANCE: This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective

Identification of free radicals trapped in solid methacrylated resins

Photopolymerization of methacrylated dental resins at room temperature leads to the appearance of long-life free radicals because of system vitrification. These free radicals were observed by electronic paramagnetic resonance (EPR), and their characterization was undertaken by reference to the reactional mechanism, from the comparison with the model EPR signal and from theoretical simulation. Overlapping of two EPR signals assigned to two different kinds of radicals because of methacrylate end groups accounted for all the experimental and theoretical results. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1691-1699, 2003

Kinetic study of free radicals trapped in dental resins stored in different environments.

In this work, we used electron paramagnetic resonance to follow the decrease kinetics of free radicals trapped in an experimental resin (ER) and in a commercial composite (Charisma((R)) (Ch)) stored under different conditions (in air at 25 and 37 degrees C; in argon, oxygen and water at 25 degrees C). During the first day, the decay was fast (0-24h-rate of decay of allylic radical: 1700-1000a.u. for Ch, 1700-1500a.u. for ER) and the storage conditions had no influence on the kinetics. This phase was ascribed to a post-polymerization phenomenon. From 1day to 1month, the rate of decay depended on the storage environment. In argon, free radicals were quite stable (1day to 1month-rate of decay of allylic radical: 1200-1000a.u. for Ch, 1400-1200a.u. for ER). For the other storage environments, in ER, the rate of decay was higher in water than in oxygen and in air (1day to 1month-rate of decay of allyl radical: 1400a.u. to 100, 500 and 800a.u., respectively). In Ch, free radicals faded quicker than in ER, as undetectable levels were reached before 1month, which attests to the influence of fillers on radical decrease kinetics. Heating experiments were also performed, and free radical concentrations decreased faster at higher temperatures, especially above the glass transition temperature. In conclusion, ambient oxygen is mainly involved in the termination process of free radicals. Therefore, conditions influencing oxygen diffusion have an impact on radical kinetics as well

A physico-chemical explanation of the post-polymerization shrinkage in dental resins.

The main problem of a methacrylated dental resin's photopolymerization is the shrinkage phenomenon. This occurs, as expected, during light irradiation but also, unexpectedly, during about 24h after photopolymerization (i.e. during the so-called 'post-polymerization' stage). During this period, the conversion degree does not change significantly (no more initiation, very limited, if any, propagation reaction) but free radicals concentration decreases. OBJECTIVES: To better understand what happens during the 24h after the photopolymerization, a thermal study of these resins is investigated at first and an explanation is then discussed. METHODS: In this paper, the glass transition temperatures (T(g)) are measured at 0 and 24h by DMA. The post-shrinkage phenomenon is observed by TMA. Conversion degree (DC) is followed by Raman and free radical decay by ESR spectroscopy. RESULTS: T(g) increases significantly during post-polymerization (55-80 degrees C). The same samples were studied by TMA at room temperature and shrinkage is observed. The fact that the degree of conversion (DC) does not increase significantly and that the 'post-shrinkage' occurs at T<T(g) leads to the hypothesis that a physical phenomenon should occur which can, in turn, be responsible for a secondary chemical phenomenon (post-polymerization). SIGNIFICANCE: The proposed explanation is that, as photopolymerization of dental resins is very fast, a large excess of free volume is trapped in non-equilibrated samples. As they have no time to return to an equilibrium state, free volume should decrease below T(g) and samples do physically shrink during the first 24h. As a consequence, free radicals can come into 'contact' and undergo limited propagation but significant termination justifying the decrease in overall radical concentration

The impact of photocatalytic paint porosity on indoor NOx and HONO levels

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TiO2 nanoparticles coated with bio-inspired ligands for the safer-by-design development of photocatalytic paints

International audienceAddition of titanium dioxide nanoparticles (TiO2 NPs) in photocatalytic paints represents a promising alternative aiming to mineralize gaseous pollutants, such as volatile organic compounds (VOCs). However, the risks of release of nanoparticles to human health and the environmental impact have to be taken carefully into account for their development. To take into account these risks, we develop a new method of TiO2 NP synthesis. Here, we report the electrostatic stabilization in aqueous medium with pyrophosphate buffers of different pH ranges followed by coating with bio-inspired molecules (lysine, deferoxamine, dopamine) and polymers (polyacrylic acid, polyethylene glycol, polydopamine) of 4–5 nm spherical photocatalytic TiO2 NPs for the development of safer-by-design photocatalytic paint. Characterization of the so-formed TiO2 nanocomposites by dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the good grafting of the ligands on the TiO2 surface and an enhanced stability in water compared to the pristine TiO2 NPs. The photocatalytic activity of the TiO2 nanocomposites was investigated by following the degradation of methylene blue (MB) under irradiation. The results showed a modulation of the photocatalytic activity (decrease or increase of the MB degradation rate) as a function of the nature/binding strength of the bio-inspired coating on the oxide surface. Finally, the most promising nanocomposites were incorporated in paints on which preliminary chalking assays were performed after storage for one year in the dark or in interior daylight