Presence Of Residual Oxygen Research Articles

Riboflavin‐Catalyzed Photoinduced Atom Transfer Radical Polymerization

AbstractThe photoATRP of methyl acrylate (MA) is investigated using riboflavin (RF) and CuBr2/Me6TREN as a dual catalyst system under green LED irradiation (λ ≈ 525 nm). Both RF and CuBr2/Me6TREN enhanced oxygen tolerance, enabling effective ATRP in the presence of residual oxygen. High molar mass polymers (up to Mn ≈ 129 000 g·mol−1) with low dispersity (Đ ≤ 1.16) are prepared, and chain‐end fidelity is confirmed through successful chain extension. The molecular masses of the obtained polymer increased linearly with conversion and showed high initiation efficiency. Mechanistic studies by laser flash photolysis reveal that the predominant activator generation mechanism is reductive quenching of RF by Me6TREN (83%, under [CuBr2]/[Me6TREN] = 1/3 condition), supported by polymerization kinetics and thermodynamic calculations.

Fabrication of Platinum Nanoparticles with Different Morphologies by Thermal Dewetting in the Presence of Residual Oxygen and Their Optical Properties

Fabrication of Platinum Nanoparticles with Different Morphologies by Thermal Dewetting in the Presence of Residual Oxygen and Their Optical Properties

A solid-state electrochemical device for studying thermodynamic properties of non-stoichiometric oxides: Application to UO2+x

We report attempts at determining the evolution of the oxygen activity in hyper-stoichiometric uranium dioxide for very low values of deviation from stoichiometry, using a solid-state electrochemical device. To this end, solid-state oxidation cycles coupled with oxygen activity measurements are carried out on a dense polycrystalline uranium oxide sample. We thus follow the evolution of the oxygen activity in the material as it oxidises or reduces, for temperatures ranging from 1093 to 1273 K. The data are subsequently analysed using an oxygen point defect model and equilibrium constants, corresponding to the various supposed point defect equilibria, are determined. We show that the model faithfully reproduces the trends observed in the experimental data. A more detailed analysis of the equilibrium constants obtained enables us to identify more precisely the limitations of the experimental method. In particular, we highlight the fact that the presence of residual oxygen in the device prevents us from determining the desired physical quantities for stoichiometry deviations less than 10−3. Ways of circumventing these difficulties which would further allow us to determine point defect diffusion coefficients are outlined.

Memory properties and short-range order in silicon oxynitride-based memristors

Silicon oxynitride films of various compositions were grown by the plasma-enhanced chemical deposition method using a setup with remote plasma and an inductive excitation from a gas mixture of 10% monosilane (diluted with argon) and nitrogen in the presence of residual oxygen in working gas mixtures. The high-frequency generator power (13.56 MHz) was varied in the range of 50–150 W. The samples composition was studied using x-ray photoelectron spectroscopy. A comparison of the experimental Si 2p photoelectron spectrum with the calculation showed that, at a low generator power (50 W), the short-range order in silicon oxynitride films is better described by the “random mixture” model. As the generator power is increased (100 W and higher), the excess silicon content in a silicon oxynitride film is decreased, and the short-range order is better described by the “random bonding” model. On metal–insulator–semiconductor-structures based on the silicon oxynitride films obtained, measurements of current–voltage characteristics were carried out, and the resistive switching of the obtained structures is studied in the present contribution. It is found that, in films in which the short-range order is described by the random bonding model, a stable switching in the bipolar regime is observed.

Composition and optical properties of amorphous plasma-chemical silicon oxynitride of variable composition a-SiO-=SUB=-x-=/SUB=-N-=SUB=-y-=/SUB=- : H

The a-SiOxNy : H films of various compositions were obtained by plasma chemical deposition from a gas mixture of 10% monosilane (diluted with argon) and nitrogen in the presence of residual oxygen in the working gas mixture. The nitrogen flow rate varied in the range from 4 to 6 cm3/min, the power of the high-frequency generator (13.56 MHz) varied in the range of 50-150 Watts. The electronic structure and optical properties of the films were studied using X-ray photoelectron spectroscopy, vibrational spectroscopy, transmission and reflection spectroscopy, and spectral ellipsometry. It is shown that, as the generator power decreases, the content of excess silicon in the films increases and amorphous silicon nanoclusters appear. As the generator power increases, the oxygen concentration in the films decreases. Apparently, this is due to the greater dissociation of molecular nitrogen with an increase in the power of the plasma discharge and an increase in the concentration of active nitrogen. Thus, it is possible to control the composition of aa-SiOxNy : H films not only by changing the nitrogen flow, but also by varying the generator power. Keywords: silicon oxynitride, plasma-chemical deposition, stoichiometric composition, Si nanoclusters.

Состав и оптические свойства аморфного плазмохимического оксинитрида кремния переменного состава a-SiO-=SUB=-x-=/SUB=-N-=SUB=-y-=/SUB=- : H

The SiOxNy:H films of various compositions were obtained by plasma chemical deposition from a gas mixture of 10% monosilane (diluted with argon) and nitrogen in the presence of residual oxygen in the working gas mixture. The nitrogen flow rate varied in the range from 4 to 6 cm3/min, the power of the high-frequency generator (13.56 MHz) varied in the range of 50-150 Watts. The electronic structure and optical properties of the films were studied using X-ray photoelectron spectroscopy, vibrational spectroscopy, transmission and reflection spectroscopy, and spectral ellipsometry. It is shown that, as the generator power decreases, the content of excess silicon in the films increases and amorphous silicon nanoclusters appear. As the generator power increases, the oxygen concentration in the films decreases. Apparently, this is due to the greater dissociation of molecular nitrogen with an increase in the power of the plasma discharge and an increase in the concentration of active nitrogen. Thus, it is possible to control the composition of a SiOxNy:H films not only by changing the nitrogen flow, but also by varying the generator power.

Evaluation of N doped rGO-ZnO-CoPc(COOH)8 nanocomposite in cyanide degradation and its bactericidal activities

In the present study, an attempt has been made to design a solar light driven N-rGO-ZnO- CoPc(COOH)8 nanocomposite for the degradation of cyanide. The morphological and structural characterization of the synthesized nanocomposite was performed by XRD, FT-IR, XPS, UV–vis DRS, FESEM, TEM, EDS, PL spectra and BET surface area. The results revealed that almost 91% degradation and 86% toxicity removal occurred at 25 mgL−1 of initial cyanide concentration by the N-rGO-ZnO-CoPc(COOH)8 nanocomposite under illumination of solar light within 120 min. Analysis of free radicals reveals that the generation of OH. radicals was the predominant species in the photocatalytic degradation process. The cyanide degradation follows pseudo-first order kinetics. The estimated apparent rate constant (Kapp) of the above nanocomposite was 3 times higher than that of the ZnO photocatalyst alone together with a very good recycle activities. This might be due to the application of metallpthalocyanine photosensitizer CoPc(COOH)8 which enhances the rate of visible light absorption efficiency and activates the higher band gap ZnO photocatalyst under visible light. In addition, the presence of residual oxygen in N-rGO also promotes nucleation and anchor sites for interfacial contact between ZnO and N-rGO for effective charge transfer. Further, the N-rGO-ZnO-CoPc(COOH)8 photocatalytic system showed significant antibacterial activities against mixed culture systems. Therefore, the N-rGO-ZnO-CoPc(COOH)8 nanocomposite may be an alternative solar light driven photocatalyst system for the removal of cyanide from the wastewater along with its strong disinfectant activities.

Effects of Residual Oxygen in the Degradation of the Performance of Organic Bulk Heterojunction Solar Cells: Stability, Role of the Encapsulation

We have shown in our first articles [1] [2] that even after encapsulation, the first rapid phase of degradation mechanism observed has been attributed to oxidation of interfaces and an alteration of the charges collection process. A second phase slower is induced by the oxidation of the active film, namely a decrease in the absorption and a degradation of the charge transport process. We revealed that another decrease in power conversion efficiency which has been induced by a possible interfacial passivation occurred at the organic/cathode interface, owing to the presence of residual oxygen, moisture and other impurities. This is in reality the real cause of the first rapid phase of degradation mechanism observed.

Synthesis of Ge and Si nanoparticles by spark discharge

The production of airborne nanoparticles by multi gap spark discharge generators is shown to be feasible for semiconductors on the example of erosion germanium and silicon electrodes in inert atmosphere. Pure silicon and germanium crystalline nanoparticles with the mean diameter less than 15 nm combined in submicron agglomerates were obtained. Since the presence of residual oxygen in the setup partially oxidized silicon nanoparticles and core-shell germanium structures with pure Ge core and oxidized shell were also observed in the samples. This continuous nanoparticles production technique enables direct impaction of prepared nanoparticles onto a liquid or substrate for applications in the fields of electronics, biomedicine and energetics.

Research into resource-saving molybdenum-containing alloying additive, obtained by the metallization of oxide concentrate

We established that the phase composition of oxide molybdenum concentrate is re presented mainly by MoO3, as well as МоО2, WO3, Mo2C and associated ore impurities of Al2O3, CaO, SiO2 and MgO. We found non-uniform microstructure in the form of plates, granules of round shape, and thread-like formations. It was determined that phase composition of metallized molybdenum concentrate, obtained by carbon-thermal technique, is mostly composed of metal Mo with the presence of MoC and Mo2C. Unrestored component is represented by the oxy-carbide compound (Mo, O, C) and the lower molybdenum oxide MoO2. We noted fragmented presence of Mo8O23. Spongy microstructure revealed areas where the molybdenum oxide restoration products dominate. The presence of residual oxygen confirms the existence, along with metal Mo, of unrestored oxide or oxy-carbide compounds. The residual oxygen could also be contained in the oxide compounds of Si, Al, Ca, Mg, K, Na as associated ore impurities. This is confirmed by discovery of the specified elements in the examined areas. The detected phases and compounds do not display significant susceptibility to sublimation. High restorative ability, due to the excess of carbon in the form of carbides, provides the post-restoration of oxide component in the liquid metal in the process of alloying, as well as protection against secondary oxidation

Fabrication and Photocurrent Generation Properties of Insoluble Hierarchical Polythiophene Thin Films Prepared by Sequential Electrochemical Polymerization

Abstract Insoluble hierarchical polybithiophene/poly(ethylenedioxythiophene) thin films with a double-layered structure were prepared on an indium tin oxide transparent electrode by sequential electrochemical polymerization. The formation of the hierarchical structure was supported by the transmission absorption spectra and Raman scattering spectra of the double-layered polythiophene thin films. In the presence of residual oxygen as an electron acceptor, light irradiation on the polythiophene-modified electrodes generated stable cathodic photocurrents. A broad peak at approximately 440 nm corresponding to the absorption of neutral polythiophene was observed in the incident photon to current conversion efficiency profile of the polybithiophene/poly(ethylenedioxythiophene)-modified electrode. The photocurrent density of the polybithiophene/poly(ethylenedioxythiophene)-modified electrode was higher than that of the poly(ethylenedioxythiophene)-modified electrode.

The influence of impurity and isotopic composition of single-crystal germanium on optical transmission in the range of 520–1000 cm−1

The optical properties of pure and doped germanium single crystals of natural isotopic composition and isotopically pure 70Ge and 74Ge single crystals have been investigated. The influence of dopants and the presence of residual oxygen in germanium on the position and shape of phonon absorption peaks and on the attenuation coefficients for these peaks in the spectral range of 520–1000 cm−1 is experimentally revealed. The decrease in the frequency of peaks in phonon absorption bands with an increase in the mass number of germanium isotopes is analyzed.

Bonding to bleached enamel treated with 10% sodium bicarbonate: a one-year follow-up

Objective. This article is a brief review about in vitro proposals to overcome the low bond strength values to bleached dental surfaces through a one-year follow-up case report of the immediate replacement of composite resin restorations after enamel bleaching. Clinical considerations. The presence of residual oxygen after bleaching may be responsible for inhibiting the polymerization of the monomers present in the adhesive systems, leading to the failure of the restorative procedure. The use of antioxidants, especially the 10% sodium bicarbonate solution (SB), could be a fast and practical alternative to improve the bond strength of these restorations. In office bleaching with hydrogen peroxide 35% (Lase Peroxide Sense, DMC, Ribeirão Preto, SP, BRA) was performed followed by the removal of the unsatisfactory restorations. Then, the BS was applied and the new adhesive restorations were placed. After one year, the clinical performance of the restorations were successful, showing no signs of failure nor infiltration. Conclusions. The use of the 10% sodium bicarbonate in bleached enamel seems to be a viable alternative for clinical practice.

Erbium Silicide Growth in the Presence of Residual Oxygen

The chemical changes of Ti/Er/n-Si(100) stacks evaporated in high vacuum and grown ex situ by rapid thermal annealing were scrutinized. The emphasis was laid on the evolution with the annealing temperature of (i) the Er-Si solid-state reaction and (ii) the penetration of oxygen into Ti and its subsequent interaction with Er. For that sake, three categories of specimens were analyzed: as-deposited, annealed at 300°C, and annealed at 600°C. It was found that the presence of residual oxygen into the annealing atmosphere resulted in a substantial oxidation of the Er film surface, irrespective of the annealing temperature. However, the part of the Er film in intimate contact with the Si bulk formed a silicide (amorphous at 300°C and crystalline at 600°C) invariably free of oxygen, as testified by x-ray photoelectron spectroscopy depth profiling and Schottky barrier height extraction of 0.3 eV at 600°C. This proves that, even if Er is highly sensitive to oxygen contamination, the formation of low Schottky barrier Er silicide contacts on n-Si is quite robust. Finally, the production of stripped oxygen-free Er silicide was demonstrated after process optimization.

Growth of InN Nanocrystalline Films by Activated Reactive Evaporation

InN films are grown on silicon and glass substrates by radio frequency (rf) activated reactive evaporation. High purity indium (99.99) is evaporated by resistive heating in the presence of nitrogen plasma. X-ray diffraction shows that the film deposited at low rf plasma powers (< or =100 W) are indium rich and further increase in the rf power formation of InN take place. The average crystallite size was found varying from 8 nm to 20 nm as the power increases from 200 to 400 W. The diffraction pattern shows the polycrystalline nature of InN films. The band gap obtained from the transmission spectra show an increase in the band gap with the increase in rf power which can be attributed to variation of nitrogen: indium stoichiometry. The Raman spectra shows wurtzite nature of the film and the photoluminescence measurements show a weak peak around 1.81 eV for the film grown at 400 W. Plasma diagnostics has been carried out in order to understand the role of active species in the process. The large shift in the band gap is attributed to Moss-Burstein shift and presence of residual oxygen in the film.

Formation of epitaxial gold nanoislands on (100) silicon

Coherent gold nanoislands were prepared directly on (100)-oriented Si substrates by a physical methodology, consisting of the thermal evaporation of a very thin Au film $(t\ensuremath{\sim}2\text{ }\text{nm})$ and its successive annealing in the temperature range $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}lTl814\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. We found that at annealing temperature of $814\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and in the presence of residual oxygen during the annealing process, epitaxial monocrystalline gold nanoislands embedded in the Si lattice are formed. The crystallographic orientation and epitaxial relationship between the Au nanoislands and the Si lattice are well defined. In contrast, at lower annealing temperatures, namely at $350\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and $626\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, the nanoislands are randomly oriented without epitaxial relationships. The morphology, orientation, and crystalline structure of Au nanoislands were investigated by scanning and high-resolution transmission electron microscopy and grazing-incidence x-ray diffraction. A model of the epitaxial Au nanoisland formation on (100)Si is presented in which the Si-atom out-diffusion and the formation of a liquid Au-Si droplet during the annealing process (increasing temperature) and the Si redeposition and oxidation (i.e., ${\text{SiO}}_{x}$ complex formation and removing of the excess Si in the gold islands) during the cooling process (decreasing temperature) play a fundamental role.

Dissolution and migration of platinum after long-term operation of a polymer electrolyte fuel cell under various conditions

The distribution patterns of Pt crystals that have moved from electrodes to the membrane phase of membrane electrode assembly (MEA) are monitored using transmission electron microscopy (TEM) after long-term operation (>1000 h) of a polymer electrolyte membrane fuel cell (PEMFC) at various operating and feed conditions. The dissolution of cathode Pt and subsequent migration to the membrane is readily observed when residual oxygen concentrations inside the cathode are kept high under low current density conditions. Dissolution of anodic Pt can also be observed under constant-current operation when hydrogen feed is kept low to induce a hydrogen shortage on the Pt surface. It is postulated that the Pt at the both electrodes is dissolved by chemical oxidation to PtO in the presence of residual oxygen. The Pt ions that are dissolved in water migrate to the membrane phase and undergo repeated oxidation/dissolution and reduction/deposition by crossover of oxygen and hydrogen, respectively. As a result, the distribution patterns and crystal sizes of the migrated Pt are strongly dependent on the relative concentrations of the crossover oxygen and hydrogen. The final position of the deposited Pt band is located at the point where crossover oxygen becomes depleted, typically between 1 and 10 μm from the cathode–membrane interface. Higher concentrations of oxygen and hydrogen in the membrane yield sharper and narrower Pt bands with large Pt aggregates, whereas lower concentrations yield wider distribution bands with smaller Pt crystals.

기판 온도 변화에 따른 AlN 박막 성장에 잔류 산소가 미치는 영향

Aluminum nitride (AlN) thin films have been deposited on Au electrodes by using reactive RF magnetron sputtering method in a gas mixture of Ar and <TEX>$N_2$</TEX> at different substrate temperature. It was found that substrate temperature was varied in the range up to <TEX>$400^{\circ}C$</TEX>, highly c-axis oriented film can be obtained at <TEX>$300^{\circ}C$</TEX> with full width at half maximum (FWHM) <TEX>$3.1^{\circ}$</TEX>. Increase in surface roughness from 3.8 nm to 5.9 nm found to be associated with increase in grain size, with substrate temperature; however, the AlN film fabricated at <TEX>$400^{\circ}C$</TEX> exhibited a granular type of structure with non-uniform grains. The Al 2p and N 1s peak in the X-ray photoelectron spectroscopy (XPS) spectrum confirmed the formation of Al-N bonds. The XPS spectrum also indicated the presence of oxynitrides and oxides, resulting from the presence of residual oxygen in the vacuum chamber. It is concluded that the AlN film deposited at substrate temperature of <TEX>$300^{\circ}C$</TEX> exhibited the most desirable properties for the application of high-frequency surface acoustic devices.

RAFT Polymerization of Methyl 6-O-Methacryloyl-α-d-glucoside in Homogeneous Aqueous Medium. A Detailed Kinetic Study at the Low Molecular Weight Limit of the Process

We report a detailed kinetic study of the RAFT polymerization of methyl 6-O-methacryloyl-α-d-glucoside (a methacrylic ester-type glycomonomer) with the chain transfer agent (CTA) (4-cyanopentanoic acid)-4-dithiobenzoate and initiator 4,4‘-azobis(4-cyanopentanoic acid) in homogeneous aqueous media. The influence of temperature, initiator and CTA concentration, molar mass of the CTA radical leaving group, and the presence of residual oxygen on the polymerization kinetics were investigated in comparison with corresponding conventional free radical polymerizations (i.e., with no CTA present). RAFT processes were characterized by an initial non-steady-state period, the length of which depended inversely on the radical flux in the system, and were found to proceed at a significantly slower rate than the corresponding conventional free radical polymerizations. Also, attainment of the steady-state coincided with complete consumption of the initial CTA. The use of a macromolecular CTA reduced the length of the non-steady-state period but, interestingly, did not eliminate it, and the duration of this period was still shown to depend inversely on the initial CTA to initiator ratio. To our knowledge, this is the first time that a non-steady-state period has been observed in a RAFT polymerization initiated by a macromolecular CTA. Finally, the results of this investigation were used as a guide for the preparation of a series of well-defined living glyco-oligomers (DPn = 15−66, PDI = 1.05−1.12) in high yield.

Resonance Raman spectroscopic study of polypyrrole in CuZSM‐5

AbstractRaman spectroscopy was employed to study the polymerization of pyrrole over a selection of copper‐exhanged ZSM‐5 zeolites. No polymerization occurred on catalysts of low copper content, which suggested that a critical concentration of copper(II) cations was required for reaction. On ZSM‐5 materials with low Si/Al ratios, bands were detected which were characteristic of partially oxidized polypyrrole and monomeric pyrrole. The polymer was degraded in the presence of residual oxygen. It was shown that the polymer incorporated both aromatic‐ and quinoidal‐type structures. Further, resonance Raman spectroscopy suggested that the charge carrier present in the oxidized polymer was associated with the quinoid arrangement.