Correlations in 11B NMR spectra of dihalo derivatives of bis(1,2-dicarbollyl)cobalt(III)

In the ¹¹B NMR spectra of dihalo derivatives of bis(dicarbollyl)cobalt(III), we have identified a correlation between the ¹¹B NMR chemical shifts of substituted boron atoms and boron atoms found in other positions on the carborane skeleton. We have observed an increased shielding effect for fluorine atoms (compared with other halogens), manifested in an upfield shift of the ¹¹B NMR signals for antipodal and trans boron atoms. For the fluorine-containing compound Bu₄N⁺ [8,8′-F₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻, we propose the following sequence of electron density transfer: B(8) → {B(6) and B(10)} → B(4, 7). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 547–549 (cont.), July–August, 2006.     

The effect of C atom concentration on the electronic properties of boron carbonitride alloy nanotube in zig-zag form

Electronic properties of single-walled boron nitride nanotube in zig-zag form are numerically investigated by replacing B atoms with C atoms. Using a tight-binding Hamiltonian, the methods based on Green’s function theory, Landauer formalism and Dyson equation, the electronic density of states and electronic conductance in boron nitride nanotube and boron carbonitride nanotube are calculated. Our calculations indicate that in a boron nitride nanotube, the localized states associated with C impurities appear as the concentration of C atoms increases. The boron carbonitride nanotube thus behaves like a semiconductor. Also, by increasing the C atom concentration, the voltage in the first step on the I–V characteristics decreases, whereas the corresponding current increases.     

Effect of laser fluence on the deposition and hardnessof boron carbide thin films

We deposited amorphous thin films of boron carbide by pulsed laser deposition using a B₄C target at room temperature. As the laser fluence increased from 1 to 3 J/cm², the number of 0.25–5 μm particulates embedded in the films decreased, and the B/C atomic ratio of the films increased from 1.8 to 3.2. The arrival of melt droplets, atoms, and small molecular species depending on laser fluence appeared to be involved in the film formation. In addition, with increasing fluence the nanoindentation hardness of the films increased from 14 to 32 GPa. We believe that the dominant factor in the observed increase in the films’ hardness is the arrival of highly energetic ions and atoms that results in the formation of denser films. Received: 23 March 2001 / Accepted: 1 July 2001 / Published online: 2 October 2001     

Investigations on the Diffusion of Boron in SiGe Mixed Crystals

By studying the quadrupolar interaction of ¹²B in silicon–germanium mixed crystals with the β-NMR method, the boron–germanium pair was identified and the saturation amplitudes for boron in differently composed crystals were measured. The relative saturation amplitudes agree with statistical predictions. At low temperatures boron is preferentially implanted into stable interstitial sites. These sites are converted into substitutional sites by diffusion processes which take advantage of reorientation jumps.     

Modeling the atomic and electronic structure of diamond nanocrystals containing [NV]<Superscript>−</Superscript> centers by the density functional method

We have used the density functional method to model the atomic and electronic structure of diamond nanocrystals passivated by hydrogen atoms and either not containing defects or containing a single [NV]⁻ center. We have shown that in all cases, after relaxation the nanocrystals are formed as diamond-like structures. We have studied the features of the electronic structure of the nanocrystals. We have analyzed in detail the mechanism for the formation of energy levels in the bandgap due to [NV]⁻ centers. We have established that the optical absorption and fluorescence spectra for the [NV]⁻ centers are mainly associated with transitions of electrons between the highest occupied β orbitals (projection of the electron spin equal to +1/2) and lower unoccupied α orbitals (projection of the electron spin equal to −1/2). The results on the localization and energy position of the states in the bandgap match data obtained for the [NV]⁻ center in bulk diamond. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 86–92, January–February, 2007.     

Experimental evidence for molecular ultrafast dissociation in O<Subscript>2</Subscript> clusters

Resonant Auger spectra of O₂ clusters excited at the O1s edge are reported. After excitation to the repulsive 1s^-13σ^* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular ultrafast dissociation processes within the clusters or on their surface.     

Hydrogenation of p-chloronitrobenzene on Ni–B Nanometal Catalysts

A series of Ni–B catalysts were prepared by mixing nickel acetate in 50% ethanol/water or methanol/water solution. The solution of sodium borohydride (1 M) in excess amount to nickel was then added dropwise into the mixture to ensure full reduction of nickel cations. The mol ratio of boron to nickel in mother solution was 3 to 1. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, electronic states of surface atoms and catalytic activities of the Ni–B catalysts were studied. Ranel nickel catalyst was included for comparison. These catalysts were characterized by N₂ sorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid phase hydrogenation of p-chloronitrobenzene. All of the catalysts prepared in this study had nanosized particles. The preparation condition has significant influence on the particle size and surface compositions of the catalyst. The Ni–B catalyst was passivated by boron; therefore it was more stable than Raney nickel and did not catch fire after exposure to air. The catalysts prepared under N₂ flow could suppress the oxidation of Ni by the dissolved oxygen in water and had metallic state of nickel. The catalyst prepared with vigorous stirring at 25°C under N₂ stream yielded the smallest particles and resulted in the highest activity. It was much more active than the Raney nickel catalyst. The reaction condition also has pronounced effect on the hydrogenation activity. Using methanol as the reaction solvent increased p-chloronitrobenzene conversion to a large extent, compared to that using ethanol as the reaction medium. The selectivity of main product (p-chloroaniline) was greater than 99% on all of the Ni–B catalysts.     

Density-functional study of Si<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 10–15) clusters

Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the structural and electronic properties of Si _n C _n (n = 10–15) clusters. We find that the Si _n C _n clusters prefer cagelike structures. An extensive isomer search shows that the lowest-energy arrangements are those in which the silicon atoms and the carbon atoms form two distinct subunits. It is found that the carbon atoms favor to form fullerene-like structure due to the sp ²-like bond. The silicon atoms are trying to cope with an unfavorable sp ² environment, but distorted tetrahedra still show up somewhere of the cagelike structures. On the basis of the lowest-energy geometries obtained, the binding energy, HOMO–LUMO gap, Mulliken charge, ionization potential and electron affinity of the clusters have been computed and analyzed. An electronic charge transfer from the Si-populated to the C-populated regions is observed.     

X-ray spectra induced in highly charged 40Arq+ interacting with Au surface

By use of optical spectrum technology, the spectra of X-ray induced by highly charged ⁴⁰Ar ^q+ ions interacting with Au surface have been studied. The results show that the argon Kα X-ray were emitted from the hollow atoms formed below the surface. There is a process of multi-electron exciting in neutralization of the Ar¹⁶⁺ion, with electronic configuration 1s² in its ground state below the solid surface. The yield of the projectile Kα X-ray is related to its initial electronic configuration, and the yield of the target X-ray is related to the projectile kinetic energy.     

X-ray photoelectron spectroscopy study of the electronic structure of La<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3+δ</Subscript> solid solutions

The electronic structure of La_1–x Ga _x MnO_3+δ. solid solutions is studied by X-ray photoelectron spectroscopy (XPS). The valence state of the manganese is estimated by various methods: by analyzing the difference in the binding energies of the Mn2p_3/2 and O1s electronic levels, analyzing exchange splitting in the spectrum of Mn3s, and from the dependence of the binding energy of the XPS spectrum of Mn2p_3/2 on the calcium concentration. The state of oxidation of the manganese in the compositions containing calcium lies between Mn³⁺ and Mn⁴⁺. The efficacies of these methods are compared. A correlation is found between the type of crystalline structure of La_1–x Ga _x MnO_3+δ. (0 ≤ x < 1) and the binding energy of the Mn2p_3/2 peak. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 419–427, May–June, 2009.     

Photoluminescence and multiphonon resonant Raman scattering in Ni-and Co-doped Zn1−x MnxTe crystals

Low-temperature photoluminescence, exciton reflection, and multiphonon resonant Raman scattering spectra of Ni-and Co-doped Zn_1−x Mn_xTe crystals were investigated. Intense emission occurs in a broad spectral region (1100–17 000 cm⁻¹) in the crystals containing Ni atoms. It is caused by intracenter transitions involving Mn²⁺ ions and transitions between the conduction band and a level of the doubly charged acceptor. The features of the exciton photoluminescence and multiphonon resonant Raman scattering involving longitudinal-optical (LO) phonons at various temperatures are investigated. The insignificant efficiency of the localization of excitons on potential fluctuations in the Zn_1−x Mn_xTe:Co crystals is established. A temperature-induced increase in the intensity of the 5LO multiphonon resonant Raman scattering line due to the approach of the conditions for resonance between this line and the ground exciton state is observed in these crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 616–621 (April 1998)     

The characteristic X-ray spectra of free atoms of metals

The article presents the results of a study of characteristic X-ray spectra of free atoms by means of a new simple technique. A pulsed electron beam was used for evaporation and to create inner-shell vacancies in free atoms of metals. The spectra were obtained with the help of an X-ray monochromator which allowed precise comparison between the free-atoms spectra and corresponding solid-state spectra. The shifts of the peaks were measured and found to be in the range Δλ/λ≈10⁻⁵–10⁻⁴. The K-, L- and M-series spectra were studied. A number of the free-atoms spectra revealed structure which was not resolved in the solid-state spectra and which is of interest for atomic structure calculation applications. This electron beam technique for the investigation of X-ray characteristic spectra of free atoms can be used for the refinement of X-ray wavelength standards.     

Structures,stabilities and electronic properties of boron-doped silicon clusters B3Sin (n=1–17) and their anions

The structures, stabilities and electronic properties of neutral and anionic B₃Si_n (n?=?1–17) clusters have been systemically investigated on the basis of density functional theory at the B3LYP/6-311?+?G(d) level and CALYPSO structure prediction method. The structural searches show that three boron atoms tend to form B₃ triangle encapsulated into Si_n cages with the increasing number of silicon atoms. Most of the lowest energy structures can be derived by using the squashed pentagonal bipyramid structure of B₃Si₄ and B₃Si₄^? as the major building unit. The relative stabilities are studied based on the calculated binding energies, second-order difference of energies and HOMO–LUMO gaps of the lowest energy structures. In addition, Hirshfeld, natural population analysis, Bader approaches and natural electronic configuration are performed to explore the charge transfer. At last, molecular orbital, magnetic properties, IR, Raman and UV–vis spectra are also, respectively, analysed for providing strong support for essential theoretical and experimental research.     

Bose-Einstein condensation of rubidium atoms

A setup for preparing the Bose-Einstein condensate of rubidium atoms has been built. The condensate consists of 10⁵–10^{6 87}Rb atoms in the hyperfine state F _g = 2 of the ground electronic state. Three key indications of condensation—a sharp increase in the phase-space density of atoms, the threshold emergence of two fractions in the cloud, and anisotropic expansion of the condensate—have been observed.     

First-principles calculations of BC4N nanostructures: stability and electronic structure

In this work, we apply first-principles methods to investigate the stability and electronic structure of BC₄N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 Å, or cut and bent to form nanocones, with 60^° and 120^° disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B–N and C–C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D ² law. The results show that the 60^° disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene.     

Observation of the Molecular Quenching of μp(2S) Atoms

Kinetic energy distributions of muonic hydrogen atoms μp(1S) have been obtained by means of a time-of-flight technique for hydrogen gas pressures between 4 and 64 hPa. A high energy component of ∼900 eV observed in the data is interpreted as the signature of long-lived μp(2S) atoms, which are quenched in a non-radiative process leading to the observed high energy: the collision of a thermalized μp(2S) atom with a hydrogen molecule H₂ results in the resonant formation of a {[(ppμ)⁺]^*pee}^* molecule. Then the (ppμ)⁺ complex undergoes Coulomb de-excitation and the ∼1.9 keV excitation energy is shared between a μp(1S) atom and one proton. The preliminary analysis of the time spectra gives a long-lived μp(2S) population of ∼1% of all stopped muons, and a quenching rate of ∼4⋅10¹¹ s⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photoionization spectra of silver atoms adsorbed on the surface of a ZnS single crystal

We have used photostimulated flash luminescence to study deep electronic states arising when silver ions Ag⁺ are deposited under high vacuum onto the surface of a ZnS single crystal, followed by creation of the conditions for neutralization of the silver ions. The flux density of the silver ion beam was 10⁷ cm⁻²·sec⁻¹. We have observed the appearance of two types of deep electronic states with photoionization energies 1.60 eV and 1.80 eV, arising after depositing the silver ions onto the surface of the ZnS single crystal. We have hypothesized that there may be two different preferred sites for adsorption of silver atoms on the zinc sulfide surface. The corresponding photoionization spectra of the adsorbed silver atoms have maxima at 775 nm and 690 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 335–338, May–June, 2006.     

Recent Result of Muon Catalyzed t–t Fusion at RIKEN-RAL

We have measured X-rays and neutrons associated with the muon catalyzed t–t fusion process at the RIKEN-RAL Muon facility. In the X-ray measurement, we observed K_α and K_β X-rays originating from the muon sticking process in muon catalyzed t–t fusion, and obtained the K_α X-ray yield and the K_β/K_α intensity ratio. An average recoil energy of the (μ⁻α) atoms in a solid T₂ medium was determined from the observed Doppler broadening width of the K_α X-ray line. The obtained t–t fusion neutron has shown an exponential time spectrum with a single component and a continuous energy spectrum with a maximum energy of 9 MeV. We have determined the t–t fusion neutron yield, the t–t fusion cycling rate and the muon sticking probability from the neutron data. The obtained maximum neutron energy is a very peculiar value from the view point of the reaction Q value (11.33 MeV) with the three-particle decay mode at the exit channel: t + t → α + n + n + Q. The obtained neutron energy distribution was analyzed by a simple model with two neutron energy components; reasonable agreement has been obtained, suggesting a strong (n–α) correlation in the exit channel of the t–t muon catalyzed fusion reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Azobenzene-functionalized alkanethiols in self-assembled monolayers on gold

Self-assembled monolayers (SAMs) of 4-trifluoromethyl-azobenzene-4′-methyleneoxy-alkanethiols (CF₃– C₆H₄–N=N–C₆H₄–O–(CH₂) _n –SH on (111)-oriented poly-crystalline gold films on mica were examined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The spectra are analyzed with the help of density-functional-theory calculations of the isolated molecule. Only one doublet is detected in the sulphur 2p spectra of the investigated SAMs, consistent with a thiolate bond of the molecule to the gold surface. The C 1s XP spectra and the corresponding XAS π ^* resonance exhibit a rich structure which is assigned to the carbon atoms in the different chemical surroundings. Comparing XPS binding energies of the azobenzene moiety and calculated initial-state shifts reveals comparable screening of all C 1s core holes. While the carbon 1s XPS binding energy lies below the π ^*-resonance excitation-energy, the reversed order is found comparing core ionization and neutral core excitation of the nitrogen 1s core-hole of the azo group. This surprising difference in core-hole binding energies is interpreted as site-dependent polarization screening and charge transfer among the densely packed aromatic moieties. We propose that a quenching of the optical excitation within the molecular layer is thus one major reason for the low trans to cis photo-isomerization rate of azobenzene in aromatic-aliphatic SAMs.     

The electronic and structural properties of BN and BP nano-cages interacting with OCN: A DFT study

The adsorption of OCN⁻ (cyanato anion) on boron nitride (B₁₂N₁₂ and B₁₆N₁₆) and boron phosphide nano-cages (B₁₂P₁₂ and B₁₆P₁₆) in terms of energetic, geometric, and electronic properties are studied using density functional theory calculations. Our study results indicated that the first OCN⁻ strongly prefers to be adsorbed from its N atom upon B atoms of the nano-cages than the O atoms of OCN⁻. These findings have been rationalized using frontier molecular orbitals and total electron density plots. The energy gap of the B₁₂P₁₂ is significantly reduced upon the adsorption of OCN⁻ compared to B₁₂N₁₂, thus leading to the increase in electrical conductance of nano-cage.