Single molecular observation of penta- and hexagonic assembly of bisporphyrin on a gold surface

Artificial light-harvesting antennae of coordination-organized macrocyclic porphyrin pentamer and hexamer are visualized by high resolution scanning tunneling microscopy (HRSTM) on a gold surface.     

Recent development of self-interaction-free time-dependent density-functional theory for nonperturbative treatment of atomic and molecular multiphoton processes in intense laser fields

In this paper, we present a short account of some recent developments of self-interaction-free density-functional theory (DFT) and time-dependent density-functional theory (TDDFT) for accurate and efficient treatment of the electronic structure, and time-dependent quantum dynamics of many-electron atomic and molecular systems. The conventional DFT calculations using approximate and explicit exchange-correlation energy functional contain spurious self-interaction energy and improper long-range asymptotic potential, preventing reliable treatment of the excited, resonance, and continuum states. We survey some recent developments of DFT/TDDFT with optimized effective potential (OEP) and self-interaction correction (SIC) for both atomic and molecular systems for overcoming some of the above mentioned difficulties. These DFT (TDDFT)/OEP-SIC approaches allow the use of orbital-independent single-particle local potential which is self-interaction free. In addition we discuss several numerical techniques recently developed for efficient and high-precision treatment of the self-interaction-free DFT/TDDFT equations. The usefulness of these procedures is illustrated by a few case studies of atomic, molecular, and condensed matter processes of current interests, including (a) autoionizing resonances, (b) relativistic OEP-SIC treatment of atomic structure (Z=2-106), (c) shell-filling electronic structure in quantum dots, (d) atomic and molecular processes in intense laser fields, including multiphoton ionization, and very-high-order harmonic generation, etc. For the time-dependent processes, an alternative Floquet formulation of TDDFT is introduced for time-independent treatment of multiphoton processes in intense periodic or quasiperiodic fields. We conclude this paper with some open questions and perspectives of TDDFT.     

Study of Aluminum–Oxygen Binary Systems: Determination of Partial Interatomic Distances

This paper reports on an Auger-electron study of the oxidation of the perfect surface of polycrystalline Al in residual gas atmosphere at a partial pressure of oxygen of 10 ^-10 torr. Under supervacuum conditions, layer-by-layer oxidation of the aluminum surface takes place along with stabilization of the chemical composition of the oxide film. Oxygen can penetrate into the oxidation region not only by deposition from the residual atmosphere but also by other mechanisms. After the chemical composition of the oxide film was stabilized, its local atomic structure was studied by Al and O K-edge extended electron energy loss fine structure (EELFS) spectroscopy. The estimated partial interatomic distances for Al–Al, Al–O, O–Al, and O–O atomic pairs permitted us to conclude that an oxide-like phase is formed in the subsurface layers of aluminum oxidized under supervacuum conditions and to construct a model of the local atomic structure of this oxide-like phase.     

Structure and oxidation at quasicrystal surfaces

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f vs. 5f surfaces), and with bulk composition (e.g. i-Al–Pd–Mn vs. i-Al–Cu–Fe). We have also compared our results for the quasicrystals with results for crystalline approximants and other related crystalline phases. Our main conclusions are that, under specific conditions of sputter-annealing, the bulk atomic and electronic structures of the clean quasicrystal propagate to the surface. Also, the oxidation chemistry is dominated by that of the primary constituent, aluminum.     

Electronic structure investigations of quasicrystals

We present a review of the determination of density of states (DOS) of quasicrystals using valence band photoemission spectroscopy. The absence of fine or spiky structure in the angle-integrated DOS of quasicrystals suggests the possibility of delocalized electronic states. These were confirmed with angle-resolved photoemission studies, which clearly establish the presence of dispersing features attributed to momentum-dependent bandstructure. Such dispersing states are observed not only for deeper-lying sp states, but also for d-derived bands near the Fermi level. Data from three different high symmetry surfaces of decagonal Al–Ni–Co, an ideal model system, are presented. We find that only a few dominant reciprocal lattice vectors are sufficient to describe the quasiperiodic potential, and the implications for electronic properties are discussed.     

Measurement of hyperfine structures and isotope shifts in 4f5d6s and 4f6s6p of Sm I

We report the first observation of hyperfine structures (HFSs) and isotope shifts (ISs) of Sm I in the range of 540–560 nm using an atomic beam resonance–fluorescence technique. The least square fitting was used to determine hyperfine constants in 4f⁵5d6s² and 4f⁶6s6p of atomic samarium (Sm I). The isotope shifts of 18 transition lines were also determined and analyzed by the King plot.     

Resonant states of the hydrogen atom in strong magnetic fields

Resonant states of atomic hydrogen in strong magnetic fields have been computed by semiclassical methods. Eigenvalues are obtained by using an adiabatic separation of variables and standard WKB methods; these are confirmed by semiclassical quantization of numerically computed quasiperiodic trajectories. Large numbers of resonant states are found at B = 10 kT for L_z values above 20.     

Sorption–Atomic Absorption Determination of Trace Elements in Natural Waters Using Simultaneous Atomization of a Solid Concentrate and Suspended Matter

A sorption–atomic absorption technique with dynamic preconcentration on DETATA adsorbents in a microcolumn crucible followed by the direct atomization of a solid matrix (concentrate + suspended matter) was used to determine the total dissolved and suspended Cd, Pb, and Tl (El_dis+ El_susp) in natural waters. The detection limits were 1–3 ng/L for Cd and 5–30 ng/L for Pb and Tl. The results of the sorption–filtration atomic absorption determination of the total dissolved and suspended elements can provide extra information for the speciation analysis of waters.     

Atomic charge distribution in 4-isopropylphenol molecule derived from atomic polar tensors

On the basis of the calculated atomic polar tensors the generalized atomic polar tensor charges have been calculated for 4-isopropylphenol (4-IP) and related compounds: benzene, quinone, phenol and p-nitroaniline (p-NA). The second order Möller–Plesset perturbation method and Huzinaga–Dunning's double valence ζ basis set supplemented by d polarisation function on heavy atoms and p on hydrogen atoms (D95V^**) have been used. Analysis of the atomic charges has been done. It is found that the phenyl rings of the 4-IP and p-NA molecules have an intermediate structure between the aromatic ring and the quinoid one.     

X-ray diffraction study of the structure of Al-Co melts

The structure of Al-Co melts with 0 at.%, 10 at.%, 18 at.%, 23.5 at.%, 26 at.%, 80.7 at.%, and 100 at.% Co has been studied by X-ray diffraction. Inverse Monte Carlo simulation using the experimental curves of the structural factor was employed to reconstruct the models of melts, analyzed by the Voronoi-Delaunay technique. The dependence of parameters that define short-and longer range ordering of atoms is nonmonotonous in the range 85–74 at.% Al and is extremal in the vicinity of a melt with 76.5 at.% Al. In the stated range of concentrations, the cobalt atoms basically lie at distances of ≈4.2 Å in the pentagonal rings of icosahedral type polytetrahedral clusters. Therefore one can speak about correlation in the character of atomic ordering in melts and corresponding periodic and quasiperiodic phases.     

Characterization and electrical behavior of polyaniline–poly-N-isopropylacrylamide-co-acrylic acid/alumina aqueous dispersions in the presence of dodecyl benzenesulfonic acid

Polymer composites containing polyaniline–poly-N-isopropylacrylamide-co-acrylic acid/alumina (PANI–PNA/Al₂O₃) were synthesized by chemical polymerization of aniline in an aqueous solution containing dispersed PNA/Al₂O₃ in the presence of dodecylbenzene sulfonic acid (DBSA) using different wt% of Al₂O₃ (5%, 10%, 20%, and 30%). The structure and morphology of the polymer matrix were identified by scanning electron microscope (SEM) and atomic force microscope (AFM). Thermal stability and an amended crystallinity were reasserted by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD), respectively. Chemical interaction of Al₂O₃ and PANI was characterized by XPS. The enhancement of the electrical conductivity in the temperature range 293–483 K shows a semiconducting behavior with a negative temperature coefficient of resistivity (TCR). In addition, the conductivity data are characterized by three different regions with small changing jerks with increasing temperature.     

Elastic scattering of low-energy electrons by N2 including the effect of target electronic correlation

A procedure to use configuration-interaction (CI) target wave-functions in the electron–molecule collision theory is applied to study the elastic e⁻–N₂ scattering in the (5–20) eV incident energy range. Correlated static and exchange contributions to the interaction potential are presented. Two different atomic basis sets are used. Differential cross sections (DCS) obtained by using Hartree–Fock or CI wave-functions are presented and compared. In the CI case, single and double, and single, double and triple excitations are considered. The effect of electron correlation is analyzed in all the cases. The continuum wave-functions were obtained via the Schwinger variational iterative method. The influence on the DCS of both the size of the atomic basis set and the inclusion of higher-order excitations in the CI calculation is discussed.     

Sol-Gel Synthesis and Structure of Borosilicon Oxycarbide Glasses

Existing sol-gel polymerisation/pyrolysis routes employing two separate boron containing metal alkoxide precursors have been applied to form multi-component silicon oxycarbide glasses based on a borosilicon oxycarbide (B–Si–O–C) system. 29Si, and 11B magic angle spinning nuclear magnetic resonance (MAS-NMR) was used to characterize the atomic structure of the gels, glasses and glass ceramics. Structural changes such as glass formation and crystal nucleation were identified by X-ray diffraction (XRD). Transmission electron microscopy (TEM) provided images of crystal nucleation and growth.     

Nonlinear electrical dipolar switching at single molecular scale

At the single molecular scale (less than 2 Å × 2 Å × 9.8 Å), the nonlinear electrical dipolar switching behavior from crystalline two-monolayer polyvinylidene fluoride films was measured using a scanning tunneling microscope (STM). The atomic structure of the polymer chain was clearly imaged by the STM. The nonlinear switching behavior at the single molecular scale appears as the hysteresis in the tunneling current–voltage relationship with switching onset voltage of 0.19 V/monomer. The nonlinear dipolar switching behavior at the single molecular scale has many potential applications including single molecular scale switching devices and re-writable non-volatile memories.     

Benzoxazolylacrolein derivatives as ligands for extraction atomic absorption analysis

The extraction of chelate and ion-association complexes formed by various metal ions and two new organic reagents (derivatives of benzoxazolylacrolein) has been investigated in order to evaluate the possibilities for analytical application. The composition of the extracted species and their conditional extraction constants are given. Two simple extraction procedures for flame atomic absorption analysis of high purity lead salts have been developed. The proposed methods permit determination of (a) 1 × 10^–5% Co, Fe and Ni and 5 × 10^–6% Cu and Zn and (b) 1 × 10^–5% Pd and 5 × 10^–6% Ag and Au, with relative standard deviations in the range 4–8%.     

Determination of platinum by atomic absorption spectrometry with chromatographic preconcentration from aqueous solutions

The conditions for determining platinum by electrothermal atomic absorption spectrometry after its extraction-chromatographic preconcentration and separation from iron(III) and copper(II) were selected. A procedure was developed that allows 0.01–0.1 mg/L platinum to be determined with a relative standard deviation of 5–7 % in the presence of 1000-fold amounts of Fe(III) and Cu(II).Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 41–44.Original Russian Text Copyright © 2005 by Moskvin, Yakimova, Alekseeva.     

First-principles study of a new type nanojunction: Finite length carbon chain inserted into half of a carbon nanotube

Based on first-principles calculations, we investigate the structure and electronic properties of a carbon atomic chain in finite length inserted into half of a single walled carbon nanotube (SWCNT), which we called half chain@SWCNT or more generally HCS. Comparing the optimized structure of HCS with that of the same chiral indices SWCNT and all carbon chain inserted SWCNT, we find that the geometry of the tube in HCS is slightly altered due to the weakly interacting between the inserted chain and the outer tube wall of HCS. Our calculation of band structure indicates that the armchair (5, 5) HCS exhibits metallic character, which is as that of (5, 5) SWCNT and all carbon chain inserted (5, 5) SWCNT. The zigzag (8, 0) and (9, 0) HCSs have small change in the energy gap compared to the corresponding pristine ones. Due to the downshift of conduction bands originating from the carbon chain, the calculation of band structure shows that chiral (6, 4) HCS is a semiconductor system with a small band gap of 0.94 eV, less than 1.125 eV in pristine SWCNT. The studied HCSs with unique structure and electronic property may construct a new generation nanoscale junctions without the usual heptagon–pentagon defect pair considerations.     

<113>_(c)晶带轴下Ba(B′_(1/3)B″_(2/3))O_(3)钙钛矿B位1∶2有序结构的透射电镜表征

提出了通过透射电子显微镜表征Ba(B′_(1/3)B″_(2/3))O 3钙钛矿(B′=Zn^(2+)、Mg^(2+)、Co^(2+)或Ni^(2+),B″=Ta^(5+)或Nb^(5+))B位1∶2有序结构时可采用的一个新的晶带轴(<113>c),并首次研究了<113>c带轴下有序钙钛矿的原子架构.在<113>c晶带轴下,选区电子衍射(SAED)中的±1/3{112}型超晶格斑点揭示了钙钛矿的1∶2有序结构.对应的高分辨电子衍射(HRTEM)图像清楚地显示了有序畴的大小和原子结构.高分辨图像中的成分衬度与原子结构非常匹配,进一步证实了沿<113>c带轴下的1∶2有序结构.     

Mechanical activation of aluminum: 2. Size,shape, and structure of particles

The structure of active Al/C composite prepared by the mechanochemical method from aluminum and graphite powders (10–30 wt % C) is studied by scanning and transmission electron microscopies, atomic force microscopy, local elemental analysis, X-ray diffraction, as well as by adsorption and sedimentation measurements. It is established that the particles of chemically active Al/C composite represent porous plate-like aggregates with a mean size smaller than 2.5–5 m and composed of nanocrystalline aluminum blocks with a size of 15–60 nm distributed in a loose amorphous carbon. Single aluminum particles with a size of up to 10 nm are also observed; however, their weight fraction is small.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 819–828.Original Russian Text Copyright © 2004 by Streletskii, Pivkina, Kolbanev, Borunova, Leipunskii, Pshechenkov, Lomaeva, Polunina, Frolov, Butyagin.     

In situ electrochemical and AFM study of thalidomide–DNA interaction

The interaction of thalidomide (TD) with double-stranded DNA (dsDNA) was studied using atomic force microscopy (AFM) at highly oriented pyrolytic graphite (HOPG), differential pulse voltammetry (DPV) at glassy carbon electrodes (GCE), UV–Vis and electrophoresis. After incubation of dsDNA with different concentrations of TD, the AFM images show the formation of thin and incomplete TD–DNA network films with a number of embedded molecular aggregates and regions of uncovered HOPG. Both the TD–dsDNA aggregates and network thickness directly depended on the TD concentration and incubation time. The voltammetric data also showed that the modifications caused by TD to the DNA double helical structure are time-dependent. In agreement with AFM, DPV, UV–Vis and electrophoresis results, a model is proposed for the TD–DNA interaction, considering that TD intercalates into the dsDNA, causing defects in the dsDNA secondary structure and DNA double helix unwinding. Moreover, both AFM and DPV show that condensation is caused to DNA by TD and occurs until 24 h of incubation, as well as DNA oxidative damage, detected electrochemically by the appearance of the 8-oxoGua and/or 2,8 oxoAde oxidation peak.