Dynamics of the processes of electron-hole recombination and capture of charge carriers in anatase doped with boron, carbon, or nitrogen

The first-principles investigation of the processes of nonradiative recombination of electron-hole pairs and binding of excited charge carriers with impurity atoms in anatase doped with boron, carbon, or nitrogen has been carried out using the perturbation theory method. The perturbation is provided by a dynamically screened electron-electron interaction potential calculated in the random phase approximation. It has been shown that the most probable processes occurring upon doping with boron and carbon are exchange processes in which electrons are bound with the impurity atom, whereas the most probable processes observed upon doping with nitrogen are exchange processes in which holes are bound with the impurity atom. These processes occur within a time interval of shorter than 2 fs. The next in probability are the processes of energy losses by unbound electrons and holes due to the generation of phonons. For the case of nitrogen doping, the time of this process is estimated at approximately 300 fs. For excitons formed in this case, the luminescence photon energy and the binding energy of electrons or holes with the impurity atom are estimated. The agreement between the calculated data and the results of experiments on the photocatalysis proceeding on the surface of N-doped anatase is discussed.     

A study of nitric oxide adsorbed on nickel oxide,cobalt oxide,and graphite by X-ray photoelectron spectroscopy

The nitrogen 1s binding energy of nitric oxide adsorbed on nickel oxide, cobalt oxide and graphite was measured at several temperatures by X-ray photoelectron spectroscopy. For the oxides, a temperature dependent range of binding energies was observed, but for graphite the nitrogen 1s binding energy was independent of temperature. The values obtained suggest that significant back donation of electrons occurs from the oxides to the adsorbed nitric oxides, but no back donation occurs from graphite to adsorbed nitric oxide. However, adsorption did not cause changes in the binding energy of substrate core electrons. It is believed that unless the mean free path of electrons is short, the total photoelectron signal will not reveal changes in binding energy of electrons from substrate atoms at the surface.     

Interaction between impurity nitrogen and tungsten: a first-principles investigation

We investigate the stability, diffusion, and impurity concentration of nitrogen in intrinsic tungsten single crystal employing a first-principles method, and find that a single nitrogen atom is energetically favourable for sitting at the octahedral interstitial site. A nitrogen atom prefers to diffuse between the two nearest neighboring octahedral interstitial sites with a diffusion barrier of 0.72 eV. The diffusion coefficient is determined as a function of temperature and expressed as D(N)=1.66×10^-7exp (-0.72/kT). The solubility of nitrogen is estimated in intrinsic tungsten in terms of Sieverts' law. The concentration of the nitrogen impurity is found to be 4.82×10^-16 Å^-3 at a temperature of 600 K and a pressure of 1 Pa. A single nitrogen atom can easily sit in an off-vacancy-centre position close to the octahedral interstitial site. There exists a strong attraction between nitrogen and a vacancy with a large binding energy of 1.40 eV. We believe that these results can provide a good reference for the understanding of the behaviour of nitrogen in intrinsic tungsten.     

Basicity of trifluoromethylsulfonylformamidines. DFT and FTIR study and NBO analysis

The effect of the electron–acceptor substituent CF₃SO₂ at the imine nitrogen atom on the basicity and the electron distribution in N,N‐alkylformamidines ( 1 , 2 , 3 , 4 , 5 ) was studied experimentally by the FTIR spectroscopy and theoretically at the DFT (B3LYP/6‐311+G(d,p)) level of theory, including the natural bond orbital (NBO) analysis. The calculated proton affinities of the imine nitrogen atom and the sulfonyl oxygen (PA_N′ and PA_O) depend on the atomic charges, the C?N′ and N′―S bond polarity and on the energy of interaction of the amine nitrogen and the oxygen lone pairs with antibonding π* and σ*‐orbitals. The basicity of the imine nitrogen atom is increased with the increase of the electron‐donating power of the substituent at the amine nitrogen atom due to stronger interaction n_N → π*_C?N′, but is decreased for the electron‐withdrawing groups MeSO₂ and CF₃SO₂ at the imine nitrogen atom in spite of the increase of this conjugation. Protonation of ( 1 , 2 , 3 , 4 , 5 ) in CH₂Cl₂ solution in the presence of CF₃SO₃H occurs at the imine nitrogen atom, while the formation of hydrogen bonds with 4‐fluorophenol takes place at the sulfonyl oxygen atom, whose basicity is lower than that of N,N′‐dimethylmethanesulfonamide but higher than of N,N′‐dimethyltrifluoromethanesulfonamide. Copyright © 2015 John Wiley & Sons, Ltd.     

Confinement of atoms with Robin’s condition: Spontaneous symmetry breaking

The properties of the ground state of the hydrogen atom in a spherical vacuum cavity with general boundary “not going out” conditions (i.e., when the probability current through the boundary vanishes) are studied. It is shown that in contrast to the confinement of an atom by a potential barrier, in this case depending on the parameters of the cavity, the atom could be in stable equilibrium at the center of the cavity or shift towards its periphery: spontaneous breaking of spherical symmetry occurs. The phase diagram of the shift and the dependence of the shift value and the binding energy of the ground state of the atom on the cavity parameters are presented. At the same time, the deformation properties of the electron wave function (WF) for an asymmetric distortion are so nontrivial that a non-zero shift occurs even when an electron is repulsed from the cavity boundary.     

The interaction of nitrogen with vacancies in molybdenum

The recovery of a nitrogen bombarded molybdenum single crystal is studied with thermal helium desorption spectrometry (THDS). A new recovery stage at T = 900 K is found, which is ascribed to the dissociation of nitrogen occupied monovacancies (NV). The dissociation is a first order process with activation energy E^D = 2.55 ± 0.05 eV; the binding energy of a nitrogen atom to a vacancy is estimated to be 1.35 ± 0.05 eV.     

Adsorption of N2 and N2O on Ni(7 5 5) surface: ab initio periodic density functional study

Adsorption of N₂ and N₂O at various sites on Ni(7 5 5) has been investigated by density functional theory (DFT) method (periodic DMol³). Several possible adsorption structures (attaching the nitrogen atom to the surface, or lying parallel) are found for both molecules. There is a clear binding energy preference of N₂ and N₂O for step sites in contrast to the case of CO. It is revealed that the decomposition of N₂O occurs exclusively near the step, but not on the terrace. Two decomposition channels can be considered; dissociative adsorption and spontaneous decomposition during TPD ramp. Three possible candidates for the precursor of the spontaneous decomposition of N₂O during TPD ramp are discussed.     

Energies of electrons bound to nitrogen pairs in GaP

The binding energies of electrons bound to nitrogen pairs in GaP are evaluated by use of the effective mass theory with a suitable model potential. The variational procedure yields (i) satisfactory agreement with previous experimental values for nitrogen pairs and (ii) no bound state for the isolated nitrogen atom. Our results suggest the electron to be bound in a potential with strain-like contributions which approaches earlier ideas of Allen.     

X-ray photoelectron spectra of palladium—ylide complexes. Bond character in dichlorobis(1,1-dimethyl-1-p-nitrobenzylamine-2-acetimide-N)palladium(II)

Dichlorobis(1,1-dimethyl-1-p-nitrobenzylamine-2-acetimide-N) palladium(II) and dichlorobis(1,1-dimethyl-1-benzylamine-2-acetimide-N)palladium(II) were newly synthesized and the X-ray photoelectron spectra of the complexes were investigated.The values of the nitrogen 1s binding energy of these complexes and related compounds show that there is a net electron transfer from the nitrogen atom to the palladium atom in the complexes.     

E.S.R. spectrum of 3,5-lutidine anion and comments on nitrogen hyperfine couplings

The E.S.R. spectrum of the 3,5-lutidine anion has been observed. The methyl groups prevent the dimerization which occurs for pyridine. From the observed splitting constants and those of the pyrazine negative ion an estimate is made of the relative contribution to the nitrogen hyperfine splitting of the π-orbital spin densities on the nitrogen atom and on the adjacent carbon atoms.     

Ar adsorptions on Al (111) and Ir (111) surfaces: a first-principles study

We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites, i.e., top, bridge, fcc- and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew, Burke and Ernzerhof functions. The geometric structures, the binding energies, the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces, the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated. Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2 × 2) structure. The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML. For the Ar adsorption on Ir (111) surface at the same coverage, the most favourable site is the hcp-hollow site, with a corresponding binding energy of 0.493 eV. The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s, 3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital. For Ar adsorption on Ir (111) surface, the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.     

First-principles study of plasmons in doped graphene nanostructures

The operating frequencies of surface plasmons in pristine graphene lie in the terahertz and infrared spectral range,which limits their utilization. Here, the high-frequency plasmons in doped graphene nanostructures are studied by the timedependent density functional theory. The doping atoms include boron, nitrogen, aluminum, silicon, phosphorus, and sulfur atoms. The influences of the position and concentration of nitrogen dopants on the collective stimulation are investigated,and the effects of different types of doping atoms on the plasmonic stimulation are discussed. For different positions of nitrogen dopants, it is found that a higher degree of symmetry destruction is correlated with weaker optical absorption. In contrast, a higher concentration of nitrogen dopants is not correlated with a stronger absorption. Regarding different doping atoms, atoms similar to carbon atom in size, such as boron atom and nitrogen atom, result in less spectral attenuation. In systems with other doping atoms, the absorption is significantly weakened compared with the absorption of the pristine graphene nanostructure. Plasmon energy resonance dots of doped graphene lie in the visible and ultraviolet spectral range.The doped graphene nanostructure presents a promising material for nanoscaled plasmonic devices with effective absorption in the visible and ultraviolet range.     

The reaction of nitrous oxide with rhodium

A clean rhodium filament at room temperature is highly reactive towards nitrous oxide. The oxygen atom of the N₂O molecule is adsorbed with a sticking probability of 0.45 whilst the nitrogen atoms appear in the gas phase as molecular nitrogen. The room temperature uptake of oxygen is about 5 × 10¹⁴ atom cm^?2 and is independent of nitrous oxide pressure in the range 3.5 × 10^?8 to 1.1 × 10^?6 torr. The adsorption curve is of typical form with an initial region of essentially constant sticking probability. For the first 80% of adsorption at room temperature the shape is satisfactorily accounted for if molecules are able to visit 4–5 adsorption sites whilst held in a weakly-bonded precursor state.     

He+2团簇的形成机理与结合能计算

当He+离子与He原子相互作用时, 由于一个电子往返运动于两核之间形成单电子键, 从而使He+与He结合成为具有较强键能的He+2.根据此形成机理, 采用简单的变分波函数, 计算了He+2基态的能量曲线.结果显示,当核间距为1.74 a 0时, 能量有一极小值-0.090 14 a.u.(以He++He能量为零起始计算).从而得到He+ 2离子结合能为0.090 14 a.u., 这与实验结果0.090 96 a.u.符合得相当好, 比有的理论计算值更接近实验结果.     

Electronic structure of non-stoichiometric zirconium nitrides ZrNx

The electronic structures of zirconium nitrides, ZrN_x, have been investigated by X-ray photoelectron spectroscopy over the entire composition range of the rocksalt structure (0.5 ? x ? 1). The valence region spectrum of nearly stoichiometric ZrN is consistent with APW band structure calculation. When removing a nitrogen atom the valence band spectra exhibit an intensity increase of the d conduction band, due in part to the filling of a new created defect state at around 2 eV binding energy.     

Fine-structure quenching and multiplet distortion in a screened Coulomb atom

Theoretical results presented in this paper reflect that the relativistic fine-structure due to the mass-velocity, spin-orbit and Darwin terms is sensitive to the screening strength parameter in an exponential screened Coulomb hydrogen atom, that is sometimes used to model a plasma-embedded atom. With stronger screening the fine-structure correction undergoes a gradual suppression in magnitude, but contributes to the total binding energy in an increasing proportion, indicating that the relativistic contribution to binding may become quite significant in the ultra-low binding regime under large screening strength. In the presence of screening the l-independence of the fine-structure correction as predicted by the Dirac theory progressively disappears, and a departure from the Z⁴-scaling law of the correction occurs along the H-isoelectronic sequence of ions - both the effects become accentuated with growing screening strength. In conjunction with screening-induced removal of the Coulomb degeneracy of non-relativistic levels, these result in a deformed multiplet structure for the screened Coulomb atom. Received 31 May 1999 and Received in final form 20 September 1999     

The adsorption and stability of sulfur containing amino acids on Cu{5 3 1}

The adsorption of l-cysteine and l-methionine amino acids on a chiral Cu{5 3 1} surface was investigated with high resolution X-ray photoelectron spectroscopy (XPS) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) Spectroscopy using synchrotron radiation. XPS shows that at 300 K l-cysteine adsorbs through two oxygen, a nitrogen and a sulfur atom, in a four point ‘quadrangular footprint’, whereas l-methionine adsorbs through only two oxygen and a nitrogen atom in a ‘triangular footprint’. NEXAFS was used to clarify the adsorption geometry of both molecules, which suggests a binding orientation to the top layer and second layer atoms in two different orientations associated with adsorption sites on {1 1 0} and {3 1 1} microfacets of the Cu{5 3 1} surface.     

EPR study of free radicals in γ-irradiated thiazide compounds

The aim of this paper was to identify the type of radicals formed by γ-irradiation in powdered chlorothiazide (CTZ), hydrochlorothiazide (HCTZ), althiazide (ATZ) and trichloromethiazide (TCTZ) on the basis of analysis of their electron paramagnetic resonance spectra with enhanced resolution. In TCTZ, HCTZ and ATZ the radical was formed by abstraction of a hydrogen atom from the carbon atom C-3, and in the case of CTZ by addition of a hydrogen atom to the nitrogen atom N-4. The hyperfine structure is found. The electron densities at nitrogen atom positions in the N-C-N group in HCTZ, ATZ and TCTZ depend on a single 3-position substitution and are in line with their diuretic potency.     

Periodic lattice distortions in epitaxial films of Fe(110) on W(110)

The epitaxial growth of Fe(110) on W(110) at 500 K is analyzed using LEED and AES. Frank-van der Merwe growth is established by AES. According to LEED, pseudomorphism occurs up to θ = 1.64, where every W atom of two topmost W layers is just covered by exactly one Fe atom. For 2?θ?9, characteristic reflection-multiplets are observed, symmetric about the basic Fe(110) reflections, which are interpreted in terms of periodic lattice distortions. The latter are caused by interaction with the misfitting W substrate.     

K-shell x-ray spectroscopy of atomic nitrogen

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64±0.02 eV was determined for the K-shell binding energy.