Reaction Of Oxygen Atoms Research Articles

Micro-grooving into thick CVD diamond films via hollow-cathode oxygen plasma etching

Hollow-cathode oxygen plasma etching was proposed as a promising means to make micro-texturing into CVD diamond coatings. Oxygen ions and electrons were confined in the hollow-cathode to have higher ion and electron densities in the order of 1017 to 1018m−3 in the inside of hollow-cathode. Quantitative plasma diagnosis proved that direct reaction of oxygen atom or radicals with carbon in the diamond coating should drive the reactive ion etching (RIE) process. A diamond-coated WC (Co) disc specimen was employed to describe the RIE-behavior with aid of stainless steel mask with the line width of 100μm. Surface depth profile measurement as well as the Raman spectroscopy demonstrated that a micro-groove was precisely etched into the diamond film as a sharp-edged profile.

Theoretical Investigation of the Radical–Radical Reaction of O(3P) + C2H3 and Comparison with Gas-Phase Crossed-Beam Experiments

Herein, we present an ab initio study of the prototypal radical-radical reactions of ground-state atomic oxygen [O((3)P)] with the vinyl (C2H3) radical using density functional theory and a complete basis set model. Two distinctive pathways on the lowest doublet potential energy surfaces (PESs) were predicted to be in competition: addition and abstraction. The barrierless addition of O((3)P) to the hydrocarbon radicals leads to energy-rich intermediate formation followed by subsequent isomerization and decomposition to yield various products: CH2CO (ketene) + H, CO + CH3, C2HOH (acetylenol) + H, (3,1)CCHOH + H, H2O + C2H, (3,1)CH2 + HCO, H2CO (formaldehyde) + CH, C2H2 (acetylene) + OH, and (3,1)CCH2 + OH. The competing but minor H-atom abstraction mechanisms produce C2H2 + OH and (1,3)CCH2 + OH. The optimized structures of the reactants, products, intermediates, and transition states and the reaction mechanisms were obtained on the lowest doublet PESs. The major pathway was predicted to be the formation of CH2CO + H through the low-barrier, single-step cleavages of the addition intermediates. The Levine-Bernstein prior method, statistical surprisal approach, and microcanonical Rice-Ramsperger-Kassel-Marcus theory were applied to deduce the energy distributions of H atoms and OH products and quantitative rate constants. On the basis of the statistical theory and the population analysis, the predicted energy distributions were compared to the kinetic energy release of H and the preferential population of the Π(A') component of OH products reported in recent gas-phase crossed-beam investigations (Park, M. J.; Jang, S. C.; Choi, J. H. J. Chem. Phys. 2012, 137, 204311), and their kinetic and dynamic characteristics were discussed.

Synthesis of Core/Shell CuO-Zno Nanoparticles and Their Second-Harmonic Generation Performance / Kodols/Čaula Cuo-Zno Nanodaļiņu Sintēze Un To Spēja Ģenerēt Otrās Harmonikas Signālu

Abstract The present paper presents the method for obtaining core/shell CuO-ZnO nanoparticles and nanocoatings by using a commercially available vacuum coating system. Initially generated Cu-Zn core/shell nanoparticles have been oxidised with a highly reactive atomic oxygen beam. Second-harmonic generation has been observed in the obtained samples. The dependence of second- harmonic intensity on the wavelength of the exciting radiation is shown in the paper.

Surface reactions and structural evolution of organosilicate glass under Ar plasma bombardment

Ab initio molecular dynamics (AIMD) simulations with a variable time step setup were used to investigate collision reactions, collision cascades and subsequent structural changes of organosilicate glass (OSG) low-k dielectric surfaces under Ar plasma bombardment with kinetic energies up to 100eV. Reactions that result in carbon loss and glass network structure changes during plasma treatment were carefully examined, since carbon loss increases the dielectric constant of the low-k dielectrics and the susceptibility to water attack, thus adversely affecting the performance of these dielectric materials in microelectronic devices. Results from AIMD based collision cascade simulations have provided mechanistic understanding of collision reactions during plasma bombardment. It was found that Si–CH3 bond scission and CH3 abstraction reactions are the primary methods of carbon loss. Two distinct mechanisms were identified for CH3 removal from 100eV plasma bombardment, one due to direct momentum transfer from the high-energy incident Ar atom to a Si–O bond on the OSG surface, and the other due to generation of highly reactive atomic oxygen radicals during collision cascades. Atomic oxygen radicals generated during cascades were found to occur at a rate of 1–3 per 100eV Ar impact with radical kinetic energies ranging from 2.2 to 42.6eV, well above the minimum energy of 0.1eV for Si–CH3 bond breakage. Both reaction mechanisms were examined through atomic charge analysis and the results indicated that the Ar atom ionizes when it impacts the OSG surface, causing temporary charge transfer from the Ar atom to the Si–O bond and playing a role in CH3 removal. The cascading atomic oxygen radicals and the ionization of the Ar atom during the Si–CH3 bond scission and CH3 removal demonstrate the secondary effects of Ar bombardment which must be considered during plasma etching of low-k dielectrics.

ChemInform Abstract: Vacancy‐Mediated Processes in the Oxidation of CO on PdO(101)

AbstractReview: 21 refs.

Vacancy-Mediated Processes in the Oxidation of CO on PdO(101).

Metal oxide films can form on late transition-metal catalysts under sufficiently oxygen-rich conditions, and typically cause significant changes in the catalytic performance of these materials. Several investigations using sensitive in situ surface characterization techniques reveal that the CO oxidation activity of Pd and other late transition-metal catalysts increases abruptly under conditions at which metal oxide structures begin to develop. Findings such as these provide strong motivation for developing atomic-scale descriptions of oxidation catalysis over oxide films of the late transition-metals. Surface oxygen vacancies can play a central role in mediating oxidation catalysis promoted by metal oxides. In general, adsorbed reactants abstract oxygen atoms from the lattice of the oxide surface, thereby creating oxygen vacancies, while gaseous O2 replenishes the reactive surface oxygen atoms and eliminates oxygen vacancies. Oxygen vacancies also represent a distinct type of surface site on which the binding and reactivity of adsorbed species can differ compared with sites on the pristine oxide surface. Detailed characterization of vacancy-mediated rate processes is thus essential for developing reliable mechanistic descriptions of oxidation catalysis over reducible metal oxide films. Careful measurements performed in ultrahigh vacuum (UHV) using well-defined oxide surfaces in combination with molecular simulations afford the capability to isolate and characterize such reaction steps, and thus provide information that is needed for developing mechanistic models of oxidation catalysis over metal oxides. In this Account, we discuss vacancy-mediated processes that are involved in the oxidation of CO on the PdO(101) surface as determined from UHV surface science experiments and density functional theory (DFT) calculations. These studies show that CO binds strongly on Pd atoms that are located next to surface oxygen vacancies, and diffuses rapidly to these sites during reduction of the oxide surface by CO. The enhanced binding also raises the energy barriers for desorption and oxidation of CO, but the difference in these barriers remains nearly identical to that for CO adsorbed on the pristine PdO(101) surface. These recent studies also show that oxygen from the subsurface efficiently eliminates surface oxygen vacancies during CO oxidation at temperatures as low as 400 K, and thereby reveal a facile pathway by which PdO(101) surface domains can be maintained during oxide reduction.

Study of Surface Reaction and Gas Phase Chemistries in High Density C4F8/O2/Ar and C4F8/O2/Ar/CH2F2Plasma for Contact Hole Etching

In this study, the characterizations of oxide contact hole etching are investigated with C₄F₈/O₂/Ar and CH₂F₂/C₄F₈/O₂/ Ar plasma. As the percent composition of C₄F₈ in a C₄F₈/O₂/Ar mixture increases, the amount of polymer deposited on the etched surface also increases because the C_xF_y polymer layer retards the reaction of oxygen atoms with PR. Adding CH₂F₂ into the C₄F₈/O₂/Ar plasma increases the etch rate of the oxide and the selectivity of oxide to PR. The profile of contact holes was close to 90°, and no visible residue was seen in the SEM image at a C₄F₈/(C₄F₈+O₂) ratio of 58%. The changes of chemical composition in the chamber were analyzed using optical emission spectroscopy, and the chemical reaction on the etched surface was investigated using X-ray photoelectron spectroscopy.

Reaction dynamics of oxygen atoms with unsaturated hydrocarbons from crossed molecular beam studies: primary products, branching ratios and role of intersystem crossing

We review the progress made in the understanding of the dynamics of the reactions of ground state oxygen atoms, O(3P), with unsaturated hydrocarbons (acetylene, ethylene, allene, propyne and propene) which are of great relevance, besides from a fundamental point of view, in combustion chemistry and of interest also in atmosphere- and astro-chemistry. Advances in this area have been made possible by an improved crossed molecular beams (CMBs) instrument with rotating mass spectrometric detection and time-of-flight analysis which features product detection by low-energy electron soft-ionisation for increased sensitivity and universal detection power. This apparatus offers the capability of identifying virtually all primary reaction channels, characterising the dynamics, and determining the branching ratios (BRs) for these polyatomic multichannel nonadiabatic reactions. The reactive scattering results are rationalised with the assistance of theoretical information from other laboratories on the stationary points and product energetics of the relevant ab initio potential energy surfaces (PESs). For the simpler prototypical systems, such as O(3P) + ethylene, detailed comparisons with synergic state-of-the-art quasiclassical trajectory surface-hopping calculations on full dimensional ab initio coupled triplet and singlet PESs have recently been possible. For more complex systems, such as O(3P) + propene, comparisons with the results of synergic statistical calculations of BRs on ab initio coupled triplet and singlet PESs, have also been carried out very recently. The combined experimental/theoretical approach has allowed for a better understanding of the mechanism of these reactions. And overall has deepened considerably our understanding of chemical reactivity; in addition, these studies provide an important bridge between CMBs dynamics and thermal kinetics as well as valuable information for improving combustion and astrochemistry models.

Reactivity of triacetone triperoxide and diacetone diperoxide: Insights from nuclear Fukui function

Triacetone triperoxide (TATP) is more sensitive than diacetone diperoxide (DADP) in the solid-state explosion. To explain this reactivity difference, we analyzed the electronic structures and properties of the crystals of both compounds by using Ab initio method to calculate the structures of their individual molecules as well as their lattice structures and particularly calculating Nuclear Fukui function to gain insight into the sensitivity of the initial, rate-determining step of their decomposition. Our results indicate that TATP and DADP crystal structures exhibit significantly different electronic properties. Most notably, the electronic structure of the TATP crystal shows asymmetry among its reactive oxygen atoms as supported by magnitudes of their nuclear Fukui functions. The greater explosion sensitivity of crystalline TATP may be attributed to the properties of its electronic structure. The electronic calculations provided valuable insight into the decomposition sensitivity difference between TATP and DADP crystals.

Oxygen defects in phosphorene.

Surface reactions with oxygen are a fundamental cause of the degradation of phosphorene. Using first-principles calculations, we show that for each oxygen atom adsorbed onto phosphorene there is an energy release of about 2eV. Although the most stable oxygen adsorbed forms are electrically inactive and lead only to minor distortions of the lattice, there are low energy metastable forms which introduce deep donor and/or acceptor levels in the gap. We also propose a mechanism for phosphorene oxidation involving reactive dangling oxygen atoms and we suggest that dangling oxygen atoms increase the hydrophilicity of phosphorene.

Matrix-isolation studies on the radiation-induced chemistry in H₂O/CO₂ systems: reactions of oxygen atoms and formation of HOCO radical.

The radiation-induced transformations occurring upon X-ray irradiation of solid CO2/H2O/Ng systems (Ng = Ar, Kr, Xe) at 8-10 K and subsequent annealing up to 45 K were studied by Fourier transform infrared spectroscopy. The infrared (IR) spectra of deposited matrices revealed the presence of isolated monomers, dimers, and intermolecular H2O···CO2 complexes. Irradiation resulted in effective decomposition of matrix-isolated carbon dioxide and water yielding CO molecules and OH radicals, respectively. Annealing of the irradiated samples led to formation of O3, HO2, and a number of xenon hydrides of HXeY type (in the case of xenon matrices). The formation of these species was used for monitoring of the postirradiation thermally induced chemical reactions involving O and H atoms generated by radiolysis. It was shown that the radiolysis of CO2 in noble-gas matrices produced high yields of stabilized oxygen atoms. In all cases, the temperatures at which O atoms become mobile and react are lower than those of H atoms. Dynamics and reactivity of oxygen atoms was found to be independent of the precursor nature. In addition, the formation of HOCO radicals was observed in all the noble-gas matrices at remarkably low temperatures. The IR spectra of HOCO and DOCO were first characterized in krypton and xenon matrices. It was concluded that the formation of HOCO was mainly due to the radiation-induced evolution of the weakly bound H2O···CO2 complexes. This result indicates the significance of weak intermolecular interactions in the radiation-induced chemical processes in inert low-temperature media.

Covalent grafting of phenylphosphonate on calcium niobate platelets

HypothesisThis work explores covalent grafting of phenylphosphonate (PPA) onto exfoliated, protonated calcium niobate (HCN), a Dion-Jacobson layered perovskite. The specific hypothesis is that PPA can be readily grafted onto the face surfaces of exfoliated HCN, which has reactive apical oxygen atoms. ExperimentsPrevious research has established the conditions required for full exfoliation of HCN in aqueous solutions of tetrabutylammonium hydroxide (TBAOH), denoted as TBACN. This work first explores the effect of reflux conditions on the dispersion state of TBACN suspensions, and then investigates PPA grafting onto both non-exfoliated HCN and exfoliated TBACN dispersed in deionized (DI) water, TBA solution, and various alcohols. The products are characterized by a variety of techniques including light scattering to assess the TBACN dispersion state, 31P MAS NMR to confirm PPA grafting, and XPS to estimate PPA grafted amounts. FindingsThe results confirm the grafting of PPA on HCN and TBACN, quantify the extent of PPA grafting, and identify various grafting modes (mono-, bi-, and tridentate). All of these aspects are found to be dependent on the layered materials’ exfoliation state, suspension processing conditions, and solvent composition. The results are rationalized in terms of a plausible mechanism of the grafting process.

Interaction of epitaxial silicene with overlayers formed by exposure to Al atoms and O2 molecules.

As silicene is not chemically inert, the study and exploitation of its electronic properties outside of ultrahigh vacuum environments require the use of insulating capping layers. In order to understand if aluminum oxide might be a suitable encapsulation material, we used high-resolution synchrotron photoelectron spectroscopy to study the interactions of Al atoms and O2 molecules, as well as the combination of both, with epitaxial silicene on thin ZrB2(0001) films grown on Si(111). The deposition of Al atoms onto silicene, up to the coverage of about 0.4 Al per Si atoms, has little effect on the chemical state of the Si atoms. The silicene-terminated surface is also hardly affected by exposure to O2 gas, up to a dose of 4500 L. In contrast, when Al-covered silicene is exposed to the same dose, a large fraction of the Si atoms becomes oxidized. This is attributed to dissociative chemisorption of O2 molecules by Al atoms at the surface, producing reactive atomic oxygen species that cause the oxidation. It is concluded that aluminum oxide overlayers prepared in this fashion are not suitable for encapsulation since they do not prevent but actually enhance the degradation of silicene.

Reactions of atomic oxygen with the chlorate ion and the perchlorate ion

The reactions of the chlorate ion with atomic oxygen formed under photolysis of the nitrate ion introduced to potassium chlorate crystal by co-crystallization were studied by optical and infrared absorption spectroscopy. The perchlorate ion was found to form in solids as product of addition reaction of singlet atomic oxygen, formed under dissociation of the peroxynitrite ion – the product of isomerization of the excited nitrate ion. Triplet atomic oxygen does not react with the chlorate ion. The atomic oxygen formed under photolysis of the nitrate ion introduced to potassium perchlorate crystal by co-crystallization does not react with the perchlorate ion.

Plasma-catalytic oxidation of acetone in annular porous monolithic ceramic-supported catalysts

Oxidative decomposition of acetone over multichannel monolithic ceramic-supported catalysts combined with non-thermal plasma was investigated. Plasma was generated inside the porous ceramic by applying an alternating current (AC) voltage to the coaxial electrodes. The tandem plasma-catalytic reactor consisted of two ceramic-supported catalysts containing zinc oxide (ZnO) and/or manganese oxide (MnO2), in which the first supported catalyst was exposed to the plasma discharge and the second one was placed in the post-plasma region. Several sets of catalyst arrangements such as MnO2-loaded monolith followed by bare monolith, ZnO-loaded monolith followed by bare monolith, ZnO-loaded monolith followed by MnO2-loaded monolith and two consecutive MnO2-loaded monoliths with different Mn contents were examined in relation to the acetone decomposition and the byproducts formation. More than 90% of acetone was decomposed at a specific input energy (SIE) of about 1.0 kJ L−1 with the catalyst arrangement of MnO2 (0.1% Mn) followed by MnO2 (5.0% Mn), while the decomposition efficiency obtained with two consecutive bare monoliths was about 66% at the same SIE. The use of ZnO in the plasma discharge region did not largely improve the acetone decomposition efficiency. Wherever it is placed either in the plasma discharge region or in the post-plasma region, MnO2 catalyst substantially promoted the acetone decomposition, obviously due to the dissociation of ozone into far more reactive oxygen atoms available for oxidizing acetone molecules.

Effect of Nitrous Oxide High Pressure Annealing on the Performance of Low Temperature, Soluble-Based IZO Transistors

The effects of oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and nitrous oxygen (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O) high pressure annealing (HPA) on soluble indium-zinc oxide (IZO) thin-film transistors (TFTs) were compared. The N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O HPA treatment produced superior device performance compared with the O2 HPA treatment. The N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O HPA-treated device exhibited a reasonable μSAT, low SS, Vth, and high ION/OFF ratio of 1.0 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, 0.09 V/decade, 1.4 V, and 2.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , respectively, even at a temperature as low as 200 °C. This improvement was attributed to the supply of reactive oxygen atoms from N2O molecules, leading to the reduction of oxygen vacancies, and a decrease in the impurity concentration of the resulting soluble IZO film.

Diffusion and Reactions of Photoinduced Interstitial Oxygen Atoms in Amorphous SiO2 Impregnated with 18O-Labeled Interstitial Oxygen Molecules

Both diffusion and reactions of interstitial oxygen atoms (O0) in amorphous SiO2 (a-SiO2) were examined using oxygen-excess a-SiO2 containing 18O-labeled interstitial oxygen molecules (O2) and exposed to F2 laser light (hν = 7.9 eV). Both the F2 laser photolysis of interstitial O2 at 77 K and subsequent heat treatment at ≳200 °C give rise to oxygen exchange between residual interstitial O2 and oxygen atoms in the a-SiO2 network, and these temperatures are far lower than the temperature at which conventional thermal network-interstitial oxygen exchange in unirradiated a-SiO2 occurs (≳700 °C). However, at the initial stage of the low-temperature F2 laser photolysis, an efficient formation of interstitial ozone molecules (quantum yield ≳0.06) via nearly exchange-free diffusion of photogenerated interstitial O0 is observed, and this reaction predominates over the network-interstitial oxygen exchange.

Computational Studies on O(3P) +CHF2 Reaction Mechanism

The reaction of oxygen atom with difluoric methyl radical has been studied using DFT method at 6-311++g** level. All the geometries, vibration frequencies and energies of different stationary points are calculated by B3LYP/6-311++G** and the results agree with the experimental values. The relationship and the changes among them can confirm the mechanism of the reaction and the process of electron transfer. Through the analysis, the major reaction channel and the minor reaction channel are confirmed.

Atomic oxygen diffusion on and desorption from amorphous silicate surfaces

Surface reactions involving atomic oxygen have attracted much attention in astrophysics and astrochemistry, but two of the most fundamental surface processes, desorption and diffusion, are not well understood. We studied diffusion and desorption of atomic oxygen on or from amorphous silicate surfaces under simulated interstellar conditions using a radio-frequency dissociated oxygen beam. Temperature programmed desorption (TPD) experiments were performed to study the formation of ozone from reaction of atomic and molecular oxygen deposited on the surface of a silicate. It is found that atomic oxygen begins to diffuse significantly between 40 K and 50 K. A rate equation model was used to study the surface kinetics involved in ozone formation experiments. The value of atomic oxygen desorption energy has been determined to be 152 ± 20 meV (1764 ± 232 K). The newly found atomic oxygen desorption energy, which is much higher than the well-accepted value, might explain the discrepancy in abundance of molecular oxygen in space between observations and chemical models.

Characterization of polymer materials exposed at the Mir orbital space station

The results of studies of polyimide and fluoropolymer films after a prolonged exposure at the Mir orbital space station are reported. The weight loss of external polyimide films was ∼40–60%; the weight of FEP-100A fluoropolymer films remained unchanged, and the weight of F-4MB films increased by ∼50%. The external and internal surfaces of polyimide films were hydrophilized. The external surface of a polyimide film acquired anisotropic properties, which manifested themselves as the shape anisotropy of liquid drops, the surface tension and the work of adhesion, the light scattering circular diagrams, and in the formation of spatially oriented fractal structures. The appearance of anisotropic properties is a consequence of the arrangement of a film on the station surface at an angle to the flow of atomic oxygen. The possible reactions of fast and scattered oxygen atoms, which are responsible for the chemical and structural transformations of polyimide, are discussed.