Showing papers by "Yasuyuki Ishikawa published in 2013"
TL;DR: In this paper, a combined first-principles molecular dynamics/density functional theory study of the electrooxidation of ammonia is conducted to gain an atomic-level understanding of electrocatalytic processes at the Pt(100)/alkaline solution interface.
Abstract: A combined first-principles molecular dynamics/density functional theory study of the electrooxidation of ammonia is conducted to gain an atomic-level understanding of the electrocatalytic processes at the Pt(100)/alkaline solution interface and to probe the mechanistic details of ammonia electrooxidation on the metal surface. A systematic study of adsorption and relative stability of ammonia and the intermediate species on the Pt(100) surface as a function of potential is carried out and activation energy profiles for the mechanistic steps in the ammonia oxidation are presented. The reaction mechanism is potential dependent: the modeling study supports the Oswin and Salomon’s mechanism for moderate surface potentials (≥+0.5 V vs RHE), and the Gerischer and Maurer’s mechanism for lower potentials (<+0.5 V vs RHE). The high electrocatalytic activity of Pt(100) is ascribed to the facile dimerization of bridging nitrogen atoms to form molecular nitrogen, whereas low activity of Pt(111) and Pt(110) is imputed...
64 citations
TL;DR: In this paper, the formation and properties of the 2DEG at ZnO/Zn(Mg)O interfaces using first-principles calculations based on hybrid density functional theory were studied.
Abstract: The discovery of a high-mobility two-dimensional electron gas (2DEG) in wurtzite ZnO/Zn(Mg)O heterostructures is promising for applications due to the high mobility of the carriers. In this paper, we study the formation and properties of the 2DEG at ZnO/Zn(Mg)O interfaces using first-principles calculations based on hybrid density functional theory. The 2DEG arises from the polarization discontinuity at the interface between the two materials. The uncompensated bound charge at the interface gives rise to an electric field in the bulk of ZnO which confines free carriers close to the interface. We find that the type of the confined carriers is determined by the interface termination, while the amount of charge and the confinement width could be controlled by the Mg doping and the device dimensions.
35 citations
TL;DR: In this article, the influence of experimental conditions on the features of graphene-supported Pt, Ir, and Pt-Ir alloy nanoparticles was studied using transmission electron microscopy, and the performance of the finely dispersed catalysts toward ammonia oxidation was investigated using cyclic voltammetry.
Abstract: Graphene oxide nanosheets are used as a support to anchor metal ions and produce graphene–metal nanoparticle hybrids in a sol–gel method. The influence of experimental conditions on the features of graphene-supported Pt, Ir, and Pt-Ir alloy nanoparticles is studied using transmission electron microscopy. Good dispersion of metal nanoparticles on the graphene sheets are observed for the catalysts heat-treated under exposure to N2 gas. The existence of metal species with zero oxidation state in the prepared catalysts is evident from the X-ray photoelectron spectroscopy. The characteristic X-ray diffraction peaks of Pt are observed for the graphene-supported Pt and Pt-Ir catalysts. Electrochemical activity of the finely dispersed catalysts toward ammonia oxidation is investigated using cyclic voltammetry. The performance increased in the order Ir < Pt ≈ Pt-Ir.
33 citations
TL;DR: In this paper, an accurate theoretical energy level, lifetime, and transition probability calculation of core-excited Fe XVI was performed employing the relativistic multireference Moller-Plesset perturbation theory.
Abstract: Accurate theoretical energy level, lifetime, and transition probability calculations of core-excited Fe XVI were performed employing the relativistic Multireference Moller-Plesset perturbation theory. In these computations the term energies of the highly excited n ≤ 5 states arising from the configuration 1s 22sk 2pm 3l p nl' q , where k + m + p + q = 9, l ≤ 3 and p + q ≤ 2 are considered, including those of the autoionizing levels with a hole-state in the L-shell. All even and odd parity states of sodium-like iron ion were included for a total of 1784 levels. Comparison of the calculated L-shell transition wavelengths with those from laboratory measurements shows excellent agreement. Therefore, our calculation may be used to predict the wavelengths of as of yet unobserved Fe XVI, such as the second strongest 2p-3d Fe XVI line, which has not been directly observed in the laboratory and which blends with one of the prominent Fe XVII lines.
13 citations
TL;DR: In this paper, high-resolution measurements of the iron L-shell emission near 15 A using the EBIT-I electron beam ion trap at Livermore were made using the flexible atomic code augmented with transition energies produced by calculations based on the relativistic multi-reference Moller-Plesset perturbation theory, allowing them to identify multiple M-shell iron lines.
Abstract: We have made high-resolution measurements of the iron L-shell emission near 15 A using the EBIT-I electron beam ion trap at Livermore that exhibit L-shell transitions from autoionizing levels in Fe13+, Fe14+ and Fe15+ ions. The observed L-shell iron spectra were modeled using the flexible atomic code augmented with transition energies produced by calculations based on the relativistic multi-reference Moller–Plesset (MRMP) perturbation theory, allowing us to identify multiple M-shell iron lines. Our measured values for the Fe XV emission lines are in excellent agreement with a recent measurement using the BESSY-II synchrotron but the present measurements have somewhat higher accuracy. Our MRMP calculations are compared to earlier calculations using the many-body perturbation theory approach, and we find good agreement for some but not all transitions.
8 citations