Adsorbed Oxygen Atoms Research Articles

Influence of energy accommodation on a robust spacecraft rendezvous maneuver using differential aerodynamic forces

Differential aerodynamic forces are a promising propellant-less option to control satellite formation flight. To this day, satellite lift is the most frequently neglected and, as a consequence, the methodology of differential lift only poorly studied. This is because the adsorption of atomic oxygen on the satellite’s surfaces in Very Low Earth Orbit induces diffuse reflection and high levels of energy accommodation, both of which results in the low lift coefficients experienced in-orbit so far. Analysis has shown that surface materials which promote specular or quasi-specular reflections are able to strongly increase the magnitude of the available differential lift forces. An influence of advanced surface materials on respective maneuver sequences, however, has not yet been analyzed at all. In addition, the robustness of the differential lift-based controller proposed up to now is questionable and not able to cope with the occurring uncertainties and dynamic variations. This paper aims to address these two research gaps. To do so, a robust control approach based on Lyapunov principles developed by Perez and Bevilacqua for the differential drag-based control of the in-plane relative motion is used in a subsequent second control phase to control the out-of-plane relative motion via differential lift. In a successive second step, the influence of different levels of energy accommodation on the full rendezvous maneuver sequence is analyzed. The results show that even a modest reduction in energy accommodation strongly reduces the maneuver times as well as the resulting orbital decay. In all analyzed cases, the proposed control approach led to a successful rendezvous.

Influence of fluorine and oxygen atom adsorption on electronic structure of InSb(111) surface

The projector augmented-wave method was applied for investigation of oxygen and fluorine atom adsorption on the InSb(111) surface depending on its termination. It was shown that oxygen adsorption leads to appearance of additional surface states in the fundamental gap in case of the In-terminated surface while the density of surface states decreases for the Sb-terminated surface. Fluorine co-adsorption results in partial or complete removal of the surface state and an unpinning of the Fermi level. The increase of fluorine concentration leads to considerable changes of the near-surface-layer structure due to the penetration of both electronegative adsorbates (O and F) into the substrate.

Cerium Doped Pt/TiO2 for Catalytic Oxidation of Low Concentration Formaldehyde at Room Temperature

Formaldehyde is a carcinogenic and teratogenic toxic gas. With the extensive use of a variety of building materials, indoor formaldehyde has seriously threatened human health and environment. The catalytic oxidation is considered the most promising method for the removal of formaldehyde from air. In this work, we report a Pt/TiO2 catalyst with Ce modification, and investigate its activity of catalytic oxidation of low concentration formaldehyde at room temperature. The experimental results show that the trace formaldehyde (20 mg/m3) could be completely degraded at 55 min by using Pt–Ce/TiO2 catalyst. In view of multiple characterizations, such as BET, XRD, TEM, STEM, XPS and CO adsorption, it is indicated that the modification of Ce can effectively improve the dispersion of Pt particles in the surface and reduction of Pt particle size from 2.9 to 2.2 nm. Moreover, XPS results show that the Ce in the catalyst could enhance the binding energies of Pt, provide abundant oxygen vacancies, and could increase the ratio of adsorbed oxygen atoms to lattice oxygen atoms, which is conducive to the adsorption of oxygen, leading to the improvement of catalytic activity.

Barrier mechanism of nitrogen-doped graphene against atomic oxygen irradiation

Nitrogen-doped graphene (NG) exhibited a good activity as an electrocatalyst of oxygen reduction reaction while there was no experimental example to investigate the catalytic ability and barrier performance of the NG to atomic oxygen (AO). Here we explored the effect of AO on the structure and barrier properties of pristine graphene (PG) and NG coated Cu foils. AO with high energy and strong oxidizing capacity reacts with graphene and then the graphitic structures are broken down into smaller parts, leading to the oxidation of underlying Cu. Miraculously, AO irradiation causes little damage of NG films and the oxidation degree of NG coated Cu is significantly reduced than that of PG coated. Density functional theory calculations show NG can catalyze the bonding of adsorbed oxygen atom with a second oxygen atom to form O2. And eventually, O2 molecule moves away from the NG surface and the damage of NG film is slow down.

Microstructures, magnetic, and dielectric properties of Ba‐doped BiFeO3 nanoparticles synthesized via molten salt route

AbstractAs the paradigm of magnetoelectric multiferroic materials, BiFeO3 (BFO) has potential applications in spintronics, memory devices, sensors, and actuators. However, its large leakage current and small magnetism at room temperature restrict its practical applications. It is demonstrated that the substitutions of Bi by alkali earth elements at A‐site of BFO can significantly reduce the leakage current and enhance the remanent magnetization of BFO. In this work, Ba‐doped BFO nanoparticles Bi1‐xBaxFeO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized via molten salt route. X‐ray diffraction patterns revealed that with increasing the Ba‐doped content the formation of the impurity phase was depressed and the rhombohedral distortions of these nanoparticles were suppressed, as confirmed by Raman spectra. X‐ray photoelectron spectroscopy measurements reveal that the Fe element in the nanoparticles exists in the dual valence states of Fe3+ and Fe2+, and two kinds of oxygen atoms (lattice oxygen atoms and the adsorbed oxygen atoms) exist in the nanoparticles. With increasing the Ba‐doped content, the content ratios of Fe3+ to Fe2+ ions were generally increased, whereas the oxygen vacancy concentrations were decreased. The average particle sizes of the Ba‐doped BFO nanoparticles were decreased as compared with that of nondoped BFO nanoparticles. In contrast, the room temperature magnetization of the Ba‐doped BFO nanoparticles was greatly enhanced by Ba‐substitution, as confirmed by the M‐H loops. At room temperature, the remanent magnetization and coercive field of the Bi0.8Ba0.2FeO3 nanoparticles were 0.51 emu/g and 1130 Oe, respectively. Furthermore, the leakage current density was reduced by one order of magnitude at x = 0.2 and the dielectric properties are also improved by Ba‐substitution. The improvements on the remanent magnetization, leakage current density as well as dielectric properties of the Ba‐doped BFO nanoparticles make them promising candidates for spintronics and dielectric energy storages.

Modeling of sensor properties for reducing gases and charge distribution in nanostructured oxides: A comparison of theory with experimental data

The theory is developed of sensory response to reducing gases of nanostructured semiconductor oxides such as In2O3 with large concentration of electrons in the conduction band. The charge distribution in nanoparticles is determined by the functional relationship between the density of negative and positive charges inside the nanoparticles and electrons on the surface. The capture of conduction electrons by adsorbed oxygen atoms causes redistribution of electrons in the nanoparticles, thereby decreasing the near-surface electron density and the conductivity of the system. Thus, there is a functional relationship between negative charge on the surface and charge structure inside the nanoparticle, which has to be considered. The conditions for the association-dissociation reactions of oxygen molecules on the surface also change. On adsorption of a reducing gas, the O− ions react with the gas molecules and the electrons are released into the volume of the nanoparticles. The conductivity of the system thereby increases, which constitutes the sensory effect. The radial distributions of the conduction electrons and electrostatic potential in a nanoparticle are here calculated as a function of the hydrogen concentration in the ambient air. A kinetic scheme is developed of chemical reactions corresponding to the above sensory mechanism, and the associated equations are solved. As a result, the theoretical functional relationships of sensitivity to temperature and hydrogen concentration are established. The theoretical results are in good agreement with the experimental data.

Electrochemical studies of 2-aminopyridine on nanocrystalline Zn[sbnd]Ni alloy electrodeposition

Nanocrystalline alloy exhibit superior characteristics that are not typically found in conventional coating and its formation is usually induced by additives. However, the influence mechanism of additives on the electrodeposition process was rare to be investigated, especially in the molecular scale. In this study, nanocrystalline ZnNi alloy was electrodeposited from the bath containing 2-aminopyridine as a novel additive and the influence mechanism of 2-aminopyridine in contrast with triethylenetetramine, vanillin and coumarin on electrodeposition of nanocrystalline ZnNi alloy was studied by the combined theoretical and experimental studies. It is found that intermediate Znad+ can catalyze the reduction of Zn2+ and Ni2+. The electrodeposition mechanism of ZnNi alloy is unchanged both without and with 2-aminopyridine, however an increased overpotential is observed with 2-aminopyridine, which is related to its strong adsorption on electrode surface. Triethylenetetramine increase the ZnNi deposition overpotential by complexing with metal ions. Vanillin and coumarin is achieved mainly by their spot adsorption of oxygen atoms on electrode surface. While synergistic surface adsorption of the amine group and adsorption ring plane in 2-aminopyridine maximizes the ZnNi deposition overpotential, leading to the formation of nanocrystalline ZnNi alloy.

Adsorption of hydrogen and oxygen on graphdiyne and its BN analog sheets: A density functional theory study

In this paper, the structural and electronic properties of atomic oxygen and hydrogen adsorption on graphdiyne (GDY) and its BN analog (BNdiyne) has been studied by the first-principles calculations. The calculated results show that the most stable adsorption positions of atomic hydrogen (oxygen) for GDY and BNdiyne monolayer are the top site (T2) and the hollow site (H2), respectively. The strong interaction (chemisorption) between atomic hydrogen and the monolayers leads to a decrease of 0.1 eV in the band gap of GDY, while an increase of 0.15 eV in BNdiyne. The shallow impurity energy level introduced by oxygen enhances the conductivity of GDY which could be indicated from the non-zero transmission coefficient at zero bias as well. In addition, a tiny magnetic has occurred in the oxygenated GDY while it has not occurred in the hydrogenated GDY which is different from the graphyne.

Theory of Sensitivity of Nanoscale-Structured Layers of Metal Oxides to Reducing Gases

A theory of sensor response on reducing gases of nanoscale-structured semiconducting oxides with the high concentration of conduction-band electrons has been developed (modeled on In2O3). The distribution of charges in nanoparticles is determined by the functional relationship of the density of negative and positive charges in nanoparticles and electrons on their surface. The capture of conduction electrons by adsorbed oxygen atoms causes electron redistribution in nanoparticles, such that the near-surface density of electrons and the conductivity of the system decrease. In this case, the conditions of the association and dissociation of oxygen molecules on the surface also change. During the adsorption of reducing gases (H2, CO), atomic oxygen ions react with them and electrons are released that enter bulk nanoparticles. The conductivity of the system increases, which corresponds to the sensor effect. A kinetic scheme of chemical reactions, which corresponds to the that described above, has been plotted and corresponding equations were solved. As a result, theoretical dependences of the sensitivity of sensor on the temperature and pressure of hydrogen were found, which agree well with experimental curves at qualitative and quantitative level.

Femtosecond Laser-Induced Recombinative O + O = O2 Reaction on Single Crystal Pd(100) Surface Requires Thermal Assistance

The process of recombinative desorption of molecular oxygen (O-adsorbed + O-adsorbed = O-2,O-gas) from the Pd(100) single crystal surface, under femtosecond laser irradiation, has been investigated with the help of pre- and postradiation temperature-programmed desorption (TPD) measurements. This femtosecond optical pulse-induced surface chemistry is found to depend strongly on the initial surface temperature. The threshold temperature is observed to be 400 K, above which this reaction remains active for the absorbed fluence of 2.86 mJ/cm(2). Furthermore, the desorption-yield is observed to be linear with respect to the absorbed fluence. We explain our observations with the help of combined two-temperature model simulation and density functional theory-based computations. A two-step mechanism for the femtosecond optical pulse-induced recombinative desorption of molecular oxygen is evident: the first step involves the hot electron-mediated activation of the oxygen atoms and the second step involves the thermal activation (phonon-mediated) of the oxygen atoms leading to the recombination of oxygen atoms to form molecular oxygen which immediately desorbs from the Pd(100) surface. This is the first report on the femtosecond optical pulse-induced recombinative surface chemistry of adsorbed oxygen atoms on the Pd single crystal surface.

Monatomic oxygen adsorption on halogen-substituted monovacant graphene

Doping of graphene-based materials with heteroatoms relies on the disruption of existing charge densities found on pristine graphene. Even though it is known that this phenomenon helps catalyze oxygen reduction reaction (ORR), there are only a few theoretical studies regarding the use of halogen as dopants despite their high electronegativity differences with carbon. Using density functional theory calculations, this work explores the low-concentration halogenation of monovacant graphene as well as the adsorption of oxygen atom onto resulting halogen-based substrates (X = F, Cl, Br, I). In general, formation of doped graphene and the subsequent adsorption of monatomic oxygen is more favored in non-coplanar systems than in their coplanar counterparts. In addition, F-based systems exhibited the most favorable energetics for monoatomic adsorption and electronic properties among the four substrates. Electronegativity also plays a key role on the destruction and formation of molecular structures during the adsorption of monatomic oxygen. Further work with adsorption of O2 on these substrates is warranted to elucidate their potential to catalyze ORR.

Enabling selective aerobic oxidation of alcohols to aldehydes by hot electrons in quantum-sized Rh nanocubes

Selective aerobic oxidation of primary alcohols to aldehydes at low temperature and ambient condition is essential for many value-increasing industrial processes, although the low oxidizing power of the ambient oxygen represents the major challenge to widely implement this important reaction. Herein, we report that the oxidizing power of oxygen adsorbed on quantum-sized Rh nanocubes is significantly enhanced upon photo-illumination to accelerate the oxidation reaction with a selectivity of 100%. Light absorption in the Rh nanocubes anchored on large silica spheres leads to efficient generation of hot electrons in the Rh nanocubes, which are injected into the O–O bonds adsorbed on Rh surface to cleave them into adsorbed oxygen atoms with a much higher oxidizing power. The silica (SiOx) spheres enhance both the light absorption power and colloidal stability of the small Rh nanocubes, making the Rh/SiOx hybrid particles as a unique photocatalyst to readily promote the selective aerobic oxidation of alcohols to aldehydes.

Theoretical study of acetate decomposition on Au(111) surface: Oxygen-assisted γ-CH activation mechanism

Inspired by the recent experimental results that the oxygen atoms adsorbed on Au(111) surface have a great influence on the mechanism and path of the decomposition of acetate(ACS Catal, 2014, 4(9): 3281−3288), the density functional theory was performed to simulate the decomposition of acetate on Au(111) surface with and without oxygen atom. The present calculation resents show that the pre-adsorbed oxygen atoms on Au(111) surface can activate the γ-CH bond of acetate and reduce the activation energy of the reaction, then finally get the product of carbon dioxide and formaldehyde. While without adsorbed oxygen atoms, acetate on Au(111) surface breaks down into carbon dioxide and methyl through C-C bond cleavage. In addition, the decomposition of acetate on Ag(111) surface with pre-adsorbed oxygen atoms has also been simulated and that of Au(111), and it was found that the oxygen atoms on Ag(111) assist γ-CH bond activation more efficiently due to its more negatively charged. The present study highlights the importance of oxygen-assisted γ-CH bond activation for oxygen-containing molecular on Au(111) and provide a new route for the synthesis of ester.

Effect of Oxygen on the Quantum, Magnetic, and Thermodynamic Properties of Co Nanowires on the Reconstructed Anisotropic (1 × 2)/Au(110) and (1 × 2)/Pt(110) Surfaces: Ab Initio Approach

Ab initio theoretical study of the quantum magnetic properties of Co nanowires on the pure and oxygen-reconstructed (1 × 2)/Au(110) and (1 × 2)/Pt(110) surfaces is performed. Their structures and electronic configurations are calculated using the electron density functional theory. High values of magnetic moment and magnetic anisotropy energies of Co atoms are found on both pure and oxygen-reconstructed (1 × 2)/Au(110) and (1 × 2)/Pt(110) surfaces. The adsorption of oxygen atoms on the (1 × 2)/Au(110) substrate is shown to affect the structural arrangement of Co nanowire atoms on this substrate and to increase the magnetic anisotropy energy (by 1.91 meV per nanowire atom). The adsorption of oxygen on the Pt(110) substrate substantially decreases the magnetic anisotropy energy of the Co nanowire on it (by 5.98 meV per atom). The origin of these changes is revealed by analyzing the local densities of states of the d electrons of nanowire atoms. The temperature ranges of the states with the lowest free surface energy are determined using the atomistic thermodynamics methods. These data and the available experimental data are used to predict the possibility of observing the structures under study in experiments.

Vibration-induced structures in scanning tunneling microscope light emission spectra of Ni(110)-(2 × 1) O

We obtained scanning tunneling microscopy (STM) light emission spectra of a Ni(110)-(2 × 1) O surface. A mosaic of nanoscale bright and dark domains was observed in the STM image. When the tip was fixed over the dark domain, stepwise structures were observed at 100 and 150 meV below the quantum cutoff in the STM light emission spectra. These energies were consistent with the reported vibrational energies of oxygen atoms adsorbed on the Ni(110)-(2 × 1) O surface, and indicated the expected isotope shifts between 16 O and 18O. Therefore, these stepwise structures are induced by the vibrations of adsorbed oxygen atoms. The 100-meV mode corresponded to the vibration polarized parallel to the surface. A theory describing the coupling between the STM light emission and vibration polarized parallel to the surface is proposed. We conclude that the oxygen atoms cover the dark domain and bare Ni atoms correspond to the bright domain. When the exposure level of oxygen was approximately 1/10 of that for Ni(110)-(2 × 1) O, bright-imaged nanostructures were observed in the terrace where bare Ni atoms are exposed. The step structure caused by the vibrations of adsorbed oxygen was observed in the STM light emission spectra of the bright-imaged nanostructures, showing that these structures are covered by oxygen atoms. In other words, the isolated nanostructures covered by oxygen atoms are imaged not as dark, but as bright, unlike in the case of Ni(110)-(2 × 1) O observed by STM.

Influence of AlN(0001) Surface Reconstructions on the Wettability of an Al/AlN System: A First-Principle Study.

A successful application of a hot dip coating process that coats aluminum (Al) on aluminum nitride (AlN) ceramics, revealed that Al had a perfect wettability to the ceramics under specific circumstances, which was different from previous reports. In order to elucidate the mechanism that controlled the supernormal wetting phenomenon during the dip coating, a first-principle calculation of an Al(111)/AlN(0001) interface, based on the density functional theory (DFT), was employed. The wettability of the Al melt on the AlN(0001) surface, as well as the effect that the surface reconstruction of AlN and the oxygen adsorption had on Al for the adhesion and the wettability of the Al/AlN system, were studied. The results revealed that a LCM (laterally contracted monolayer) reconstruction could improve the adhesion and wettability of the system. Oxygen adsorption on the free surface of Al decreased the contact angle, because the adsorption reduced of the surface tension of Al. A prefect wetting was obtained only after some of the oxygen atoms adsorbed on the free surface of Al. The supernormal wetting phenomenon came from the surface reconstruction of the AlN and the adsorption of oxygen atoms on the Al melt surface.

First-principles study of adsorption and diffusion of oxygen on surfaces of TiN, ZrN and HfN

Using first-principles calculations based on density functional theory, we systematically study the adsorption and diffusion behaviors of single oxygen (O) atom on the (0 0 1) surfaces of TiN, ZrN and HfN nitride coatings. The top of N site (top(N)) is the most energetic favorable site for O atom and followed by the hollow site for all the three nitrides. O atom tends to diffuse on the (0 0 1) surfaces of the nitrides from the top of transition metal top(TM) sites to a neighboring top(TM) sites by avoiding N sites. The adsorption of O on ZrN and HfN is more stable than that on TiN. Our findings could explain the experimental phenomenon that the oxide thickness of TiN is smaller than that of ZrN under the same oxidation conditions.

Contactless electroreflectance study of the surface potential barrier in n-type and p-type InAlAs van Hoof structures lattice matched to InP

N-type and p-type In0.52Al0.48As van Hoof structures with various thicknesses of undoped In0.52Al0.48As layer (30, 60, 90, and 120 nm) were grown using metal–organic vapor phase epitaxy on InP substrates and studied per their contactless electroreflectance (CER) at room temperature. InAlAs bandgap related CER resonance followed by a strong Franz–Keldysh oscillation (FKO) of various period was observed clearly in both structures. The period of this oscillation decreased with decreasing thickness of the undoped In0.52Al0.48As layer, and was slightly narrower for p-type structures. The FKO period analysis indicates that the Fermi level is pinned 0.73 ± 0.02 eV below the conduction band at In0.52Al0.48As surface. This pinning was attributed to surface reconstruction combined with the adsorption of oxygen and carbon atoms (in consequence of air exposure) which were detected on the In0.52Al0.48As surface by x-ray photoelectron spectroscopy. Also, CER measurements repeated one year after the sample growth show that the process of InAlAs oxidation in laboratory ambient conditions is negligible, and thus that this alloy can be used as a protective cap layer in InP-based heterostructures.

Hydrogen evolution reaction and electronic structure calculation of two dimensional bismuth and its alloys

We present a systematic ab initio study of atomic hydrogen and oxygen adsorption on bismuthene monolayer and its alloys with arsenic and antimony through electronic structure calculations based on density functional theory within generalized gradient approximation. We systematically investigated the preferable adsorption site for hydrogen and oxygen atom on 2D Bi, BiAs and BiSb. It was found that the hydrogen atom prefers top site of bismuth atom and oxygen atom prefers to reside in the hexagonal ring of these 2D bismuth alloys. The free energy calculated from the individual adsorption energy for each monolayer subsequently guides us to predict the best suitable catalyst among the considered 2D monolayers. The 2D BiSb serves better for hydrogen evolution reaction (HER) with hydrogen adsorption energy as −1.384 eV while 2D BiAs is suitable for oxygen evolution reaction (OER) with oxygen adsorption energy as −1.092 eV. We further investigated the effects of the adsorbate atom on the electronic properties of 2D Bi, BiAs and BiSb. The adsorption of oxygen on 2D BiAs and BiSb was shown to reduce the bulk band gap by 40.56 and 67.79% respectively which will be advantageous for the observation of Quantum Spin Hall effect at ambient conditions.

Detection of 2,4-dinitrotoluene by graphene oxide: first principles study

The surface of graphene oxide (GO) with different oxidation level is widely used in gas sensing applications. Otherwise, detection of 2,4-dinitrotoluene (DNT) have been extensively attend as a high explosive and environmental sources by various methods. Atomic level modelling are widely employed to explain the sensing mechanism at a microscopic level. The present work is an attempt to apply density functional theory (DFT) to investigate the structural and electronic properties of GO and adsorption of oxygen atom and hydroxyl on graphene surface. The focus is on the adsorption mechanisms of DNT molecule on the GO monolayer surface to detect DNT molecule. The calculated adsorption energy of DNT molecule on the GO surface indicates physisorption mechanism with −0.7 eV adsorption energy. Moreover, basis-set superposition errors correction based on off site orbitals consideration leads to −0.4 eV adsorption energy which it is more in the physisorption regime. Consequently, the results could shed more light to design and fabrication an efficient DNT sensor based on GO layers.