Computational investigation of CO adsorbed on Au<Subscript>x</Subscript>, Ag<Subscript>x</Subscript> and (AuAg)<Subscript>x</Subscript> nanoclusters (x = 1 − 5, 147) and monometallic Au and Ag low-energy surfaces

Density functional theory calculations have been performed to investigate the use of CO as a probe molecule for the determination of the structure and composition of Au, Ag and AuAg nanoparticles. For very small nanoclusters (x = 1 ? 5), the CO vibrational frequencies can be directly correlated to CO adsorption strength, whereas larger 147-atom nanoparticles show a strong energetic preference for CO adsorption at a vertex position but the highest wavenumbers are for the bridge positions. We also studied CO adsorption on Au and Ag (100) and (111) surfaces, for a 1 monolayer coverage, which proves to be energetically favourable on atop only and bridge positions for Au (100) and atop for Ag (100); vibrational frequencies of the CO molecules red-shift to lower wavenumbers as a result of increased metal coordination. We conclude that CO vibrational frequencies cannot be solely relied upon in order to obtain accurate compositional analysis, but we do propose that elemental rearrangement in the core@shell nanoclusters, from Ag@Au (or Au@Ag) to an alloy, would result in a shift in the CO vibrational frequencies that indicate changes in the surface composition.     

Intermediate phases in [111]- and [001]-oriented PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>–29PbTiO<Subscript>3</Subscript> single crystals

Phase transformations in [111]- and [001]-oriented PbMg_1/3Nb_2/3O₃–29PbTiO₃ single crystals have been studied using dielectric and optical measurements before and after applying an electric field. It is shown that the subsequence of phase transitions rhombohedral (R)—tetragonal (T)—cubic (C) phases is observed in nonpolarized samples of both orientations as temperature increases. In the [111]-oriented crystal, an additional intermediate monoclinic phase (it is possible, M _a ) is induced after preliminary polarization at room temperature and the R–M _a –T–C phase transitions are observed on heating. In the [001]-oriented crystal, after its polarization, the monoclinic phase forms instead of the rhombohedral phase even at room temperature and the M _a –T–C transitions occur on heating. The results are discussed from the point of view of the existence polar nanoregions with different local symmetries in a glasslike matrix.     

Atomistic simulation of sodium–gadolinium molybdate of stoichiometric (Na<Subscript>1/2</Subscript>Gd<Subscript>1/2</Subscript>MoO<Subscript>4</Subscript>) and cation-deficient (Na<Subscript>2/7</Subscript>Gd<Subscript>4/7</Subscript>MoO<Subscript>4</Subscript>) compositions

Crystals of sodium–gadolinium molybdates of two compositions: stoichiometric (Na_1/2Gd_1/2MoO₄) and cation-deficient (Na_2/7Gd_4/7MoO₄) composition in which 1/7 of the corresponding cation positions are not occupied are simulated by the method of interatomic potentials. For cation-deficient crystals, two kinds of cation position distribution are considered: the statistical distribution of sodium, gadolinium, and unoccupied cation positions in the I4₁/a structure and their partial ordering in the I space group. As a result of the simulation, structural characteristics of sodium–gadolinium molybdates agreeing well with the known experimental data are obtained. In addition, a number of important elastic and thermodynamic properties of these compounds are predicted. The results obtained in the partial-occupancy approximation and by constructing a 7 × 2 × 2 supercell are compared. The local structure of sodium–gadolinium molybdates are analyzed in detail. The influence of the deviation from the stoichiometry as well as cation ordering on the properties of these crystals is discussed.     

Laser and electrical current induced phase transformation of In<Subscript>2</Subscript>Se<Subscript>3</Subscript> semiconductor thin film on Si(111)

Phase transformation of thin film (∼30 nm)In₂Se₃/Si(111) (amorphous→crystalline) was performed by resistive annealing and the reverse transformation (crystalline→amorphous) was performed by nanosecond laser annealing. As an intrinsic-vacancy, binary chalcogenide semiconductor, In₂Se₃ is of interest for non-volatile phase-change memory. Amorphous In _x Se _y was deposited at room temperature on Si(111) after pre-deposition of a crystalline In₂Se₃ buffer layer (0.64 nm). Upon resistive annealing to 380°C, the film was transformed into a γ-In₂Se₃ single crystal with its {0001} planes parallel to the Si(111) substrate and parallel to Si , as evidenced by scanning tunneling microscopy, low energy electron diffraction, and X-ray diffraction. Laser annealing with 20-ns pulses (0.1 millijoules/pulse, fluence≤50 mJ/cm²) re-amorphized the region exposed to the laser beam, as observed with photoemission electron microscopy (PEEM). The amorphous phase in PEEM appears dark, likely due to abundant defect levels inhibiting electron emission from the amorphous In _x Se _y film.     

Synthesis of magnetic core–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Au nanoparticle for biomolecule immobilization and detection

The production of monodispersed magnetic nanoparticles with appropriate surface modification has attracted increasing attention in biomedical applications including drug delivery, separation, and purification of biomolecules from the matrices. In the present study, we report rapid and room temperature reaction synthesis of gold-coated iron nanoparticles in aqueous solution using the borohydride reduction of HAuCl₄ under sonication for the first time. The resulting nanoparticles were characterized with transmission electron microscopy (TEM), electron spectroscopy for chemical analysis (ESCA), ultraviolet visible spectroscopy (UV–Vis), and X-ray diffraction (XRD). Surface charges and magnetic properties of the nanoparticles were also examined. The pattern of Fe₃O₄ nanoparticles is face centered cubic with an average diameter of 9.5 nm and the initial reduction of gold on the surface of Fe₃O₄ particles exhibits uniform Fe₃O₄–Au nanoparticles with an average diameter of 12.5 nm. The saturation magnetization values for the uncoated and gold-coated Fe₃O₄ nanoparticles were found to be 30 and 4.5 emu/g, respectively, at 300 K. The progression of binding events between boronic acid terminated ligand shell and fructose based on the covalent bonding interaction was measured by absorbance spectral changes. Immunomagnetic separation was also performed at different E. coli concentration to evaluate capturing efficiency of resulting nanoparticles. Immunomagnetic separation percentages were varied in a range of 52.1 and 21.9% depend on the initial bacteria counts.     

Si<Subscript>x</Subscript>Ge<Subscript>1-x</Subscript> ultrahigh-vacuum chemical vapor deposition on Si(111)(7×7) from GeH<Subscript>4</Subscript>/Si<Subscript>2</Subscript>H<Subscript>6</Subscript> mixtures

We report the results of a study on ultrahigh-vacuum chemical vapor deposition of Si_xGe_1-x layers on Si(111)(7×7) with GeH₄ and Si₂H₆ mixtures. Using combined scanning tunneling microscopy and X-ray photoelectron spectroscopy, structural properties, the growth kinetics and the composition of the deposited alloys are analyzed as a function of the growth temperature for two different GeH₄:Si₂H₆ mixture ratios. The mutual influence of the precursors is shown by comparing the structures formed during deposition and the sticking coefficients of Si₂H₆ and GeH₄ with results obtained from exposure of Si(111) to the pure gases. Received: 28 July 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-731/502-5452, E-mail: hubert.rauscher@chemie.uni-ulm.de     

Defect formation in Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>/Ge(111) epitaxial heterostructures

Selective chemical etching and transmission electron microscopy are used to study the defect formation in Ge_1?xSi_x/Ge(111) epitaxial heterostructures at 0.01<x<0.35. As the Si content in the solid solution (SS) increases, the dislocation densities in the epitaxial layer, at the interface, and in the near-interface region in the substrate are found to vary nonmonotonically. The difference in the depth distribution of dislocations observed in the heterostructures in three different SS composition ranges is caused by the effect of the SS composition on the kinetics of misfit-stress relaxation, in particular, on the intensity of misfit-dislocation generation and multiplication. It is found that, in the heterostructures grown by hydride epitaxy at 600°C, misfit-dislocation multiplication through a modified Frank-Read mechanism occurs only in the range 0.03<x<0.20. The results obtained are explained in the context of the effect of silicon-rich microprecipitates, which form during the spinodal decomposition of the SS, on dislocation generation and motion in the epitaxial layer. A mechanism is proposed for misfit-dislocation generation by heterogeneous sources in the epitaxial layer; the mechanism is based on the generation of interstitial dislocation loops near microprecipitates.     

Scanning tunneling microscopy/spectroscopy study of adsorption of C<Subscript>60</Subscript>F<Subscript>36</Subscript> molecules on the 7 × 7-Si(111) surface

Spatially resolved images of an individual C₆₀F₃₆ fluorofullerene molecules on Si(111)-7 × 7 surface have been obtained by means of scanning tunneling microscopy/spectroscopy (STM/STS). The presence of isomers with different symmetry (T, C ₃, C ₁) has been revealed in STM investigation of initial adsorption stage of C₆₀F₃₆ on silicon surface Si(111)-(7 × 7). The adsorbed fluorofullerene molecule can occupy any adsorption site of silicon surface (corner site, faulted half, unfaulted half) that indicates for strong molecule-substrate interaction. The HOMO-LUMO gap of the adsorbed C₆₀F₃₆ molecules have been estimated from current image tunneling spectroscopy (CITS) and z(V) with engaged feedback measurements. The value of HOMO-LUMO gap observed experimentally was 3 eV. The C₆₀F₃₆ molecules adsorption on Si(111)-(7 × 7) surface was stable and kept equilibrium configuration during several hours.     

Crossing of the πd<Subscript>5/2</Subscript> and πg<Subscript>7/2</Subscript> orbitals in the <Subscript>51</Subscript>Sb isotopes

Self-consistent calculations using the D1S Gogny force have been performed in order to study the mechanism involved in the crossing of the πd _5/2 and πg _7/2 orbitals in the Sb isotopes. This inversion is well predicted by the HFB + blocking calculations with spherical symmetry performed for the odd-A Sb isotopes. In addition, several HFB and HF calculations have been performed for even-even nuclei of the five neighbouring isotopic chains (Z = 46 to 54, from the proton dripline to N = 82). The results obtained for the binding energies of the two proton orbitals indicate that the radii of the systems play an important role in the crossing, even though some particular πν interactions also give a contribution. The spin-orbit interaction, which is known to be concentrated mainly at the nuclear surface, is proposed to be the main responsible of the crossing.     

Preparation and application of core–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/polythiophene nanoparticles

The Fe₃O₄/polythiophene nanoparticles, possessing core–shell structure, were prepared by two-step method. In the first step, the Fe₃O₄ particles were synthesized via co-precipitation of FeCl₃ and FeSO₄, using the NH₃·H₂O and N₂H₄·H₂O as precipitant system. In the second step, the thiophene adsorbed and polymerized on the surface of the Fe₃O₄ in the solvent of chloroform. Raman, FTIR, EDS, XRD, TEM, Zeta potential measurement and TG-SDTA were employed to characterize the composition and structure of the products. The results showed that the Fe₃O₄/polythiophene nanoparticles were successfully synthesized with good dispersion and stable core–shell structure, provided with average particle size of approximately 20 nm, in which the diameter of Fe₃O₄ core was approximately 14 nm and the thickness of polythiophene shell was approximately 3–4 nm. Then, the nanoparticles were added into alkyd varnish to prepare a composite coating. The neutral salt spray test, paraffin control test and mechanical test were carried out to identify the properties of the composite coating. It was found that the composite coating had good performances of anticorrosion and paraffin controlling when the mass fraction of the nanoparticles was 0.8–1 wt% in alkyd varnish. As a multifunctional material, the Fe₃O₄/polythiophene nanoparticles can be used in the internal coating of pipeline and have great potential application in crude oil pipeline transportation.     

Synthesis and magnetic properties of CdS/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> hierarchical nanostructures

CdS/α-Fe₂O₃ hierarchical nanostructures, where the CdS nanorods grow irregularly on the side surface of α-Fe₂O₃ nanorods, were synthesized via a three-step process. The diameters and lengths of CdS nanorods can be tuned by changing the ethylenediamine (EDA) and Cd ion concentrations. The magnetic investigations by superconducting quantum interference device indicate that the hierarchical nanostructures have an Morin transition at lower temperature (230 K) than that of the single bulk α-Fe₂O₃ materials (263 K). Importantly, the hierarchical nanostructures exhibit weakly ferromagnetic characteristics at 300 K. A sharp peak assigned to the surface trap induced emission are observed in room temperature PL spectra. Combining with the optoelectronic properties of CdS, the CdS/α-Fe₂O₃ hierarchical nanostructures may be used as multi-functional materials for optoelectronic and magnetic devices. Supported by the National Natural Science Foundation of China (Grant Nos. 50772025 and 50872159), the Ministry of Science and Technology of China (Grant No. 2008DFR20420), the China Postdoctoral Science Foundation (Grant Nos. 20060400042 and 200801044), the Natural Science Foundation of Heilongjiang Province, China (Grant No. F200828), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070217002), and the Innovation Foundation of Harbin City (Grant No. RC2006QN017016)     

Synthesis and characterization of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>–Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> magnetoelectric composites with dielectric and magnetic properties

Composite structures consisting of (001)-oriented SrTiO₃ (STO)/La_0.7Sr_0.3MnO₃ (LSMO) films of 30 nm thickness, grown on an (001) Pb(Mg_1/3Nb_2/3)TiO₃– 28 mol.% PbTiO₃ piezoelectric relaxor-ferroelectric single-crystalline wafer were investigated by means of Wide-Angle X-ray Diffraction (WAXRD) in situ under influence of a d.c. electric field with strength E up to ±18 kV/cm. The WAXRD measurements of the films and substrate reflection profiles resulted in a determination of the strain s in the films and the substrate separately. The strained state of the STO/LSMO films is effectively controlled by a huge converse piezoelectric effect of the PMN-PT substrate. The coefficients of coupling between electric-field-induced out-of-plane strain in the films and in the substrate for the composite system STO/LSMO/PMN-PT are obtained.     

入射能量对Au/Au(111)薄膜生长影响的分子动力学模拟

利用分子动力学模拟了Au原子在Au(111)表面低能沉积的动力学过程.采用嵌入原子方法的原子间相互作用势,通过对沉积层原子结构的分析和薄膜表面粗糙度、层覆盖率的计算,研究了沉积粒子能量对薄膜质量的影响及其机制.结果表明:当入射能量Ein25 eV时,沉积层和基体表层均呈现规则的单晶面心立方(111)表面的排列,沉积原子仅注入到基体最表面两层,随着入射能量的增加,薄膜表面粗糙度降低,薄膜越趋于层状生长,入射能量的增加有利于薄膜的成核和致密化;当Ein 25 eV时,沉积层表面原子结构出现了较为明显的晶界,沉积原子注入到基体表面第三层及以下,随着入射能量的增加,薄膜表面粗糙度增加,沉积层和基体表层原子排列越不规则,载能沉积会降低基体内部的稳定性,导致基体和薄膜内部缺陷的产生,降低薄膜质量.此外,当基体内部某层沉积原子数约等于该层总原子数的一半时,沉积原子将能穿过该层进入到基体内部更深层.     

Features of the structure and properties of β-FeSi<Subscript>2</Subscript> nanofilms and a β-FeSi<Subscript>2</Subscript>/Si interface

The electronic, geometric, and magnetic structure of nanofilms of the β phase of iron disilicide FeSi₂ with the (001), (100), and (010) surfaces have been simulated through density functional calculations. A substantial reconstruction of the (001) surface terminated with silicon atoms has been observed, which was accompanied by an increase in the surface symmetry and appearance of “squares” of silicon atoms. Analysis of the electron density of states (DOS) and spin DOS projected on the contributions of layers of atoms (LSDOS) indicates that all plates have metallic properties. The main contribution near the Fermi level comes from the surface iron layers and it decreases rapidly with an increase in the distance from the surface of the plate. Analysis of the calculated effective magnetic moments of atoms shows that the surface layers in the plates have a significant magnetic moment, in particular, iron layers on the (001) surface (1.89 μ_B/atom). The moments of atoms decrease rapidly with an increase in their distance from the surface. The electron and geometric regions of a (001)Si/FeSi₂ interface have been studied. Analysis of the LSDOS shows that the surface conducting state mainly determined by the contribution from the near-surface silicide layers is implemented in this region. The possibility of the formation of the perfect and sharp Si/FeSi₂ interface has been demonstrated.     

Preparation and magnetic and electrical properties of EuBaMn<Subscript>2</Subscript>O<Subscript>6−δ</Subscript> (δ=0,1)

The EuBaMn₂O₆ composition prepared in air at T=1500°C is shown to be a cubic perovskite exhibiting spin-glass properties below T_f=40 K. The reduced composition, EuBaMn₂O₅, crystallizes in a perovskite-like, YBaCuFeO₅-type layered structure with a tetragonal unit cell. EuBaMn₂O₅ with crystallographically ordered Eu³⁺ and Ba²⁺ ions is a ferromagnet with T_N=160 K. The anomalous behavior of the paramagnetic susceptibility is assumed to be due to a partial ordering of the Mn²⁺ and Mn³⁺ ions. EuBaMn₂O₅ oxidized in air at 900°C to EuBaMn₂O₆ has a magnetic ordering temperature T_M=260 K, near which the magnetoresistance reaches a peak value. X-ray diffraction measurements show the long-range order in the Eu³⁺ and Ba²⁺ ion arrangement to persist in the oxidized EuBaMn₂O₆ sample.     

Synthesis and characterization of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>·LiMn<Subscript>0.33</Subscript>Fe<Subscript>0.67</Subscript>PO<Subscript>4</Subscript>/C cathode materials

A new polyanionic cathode material, Li₃V₂(PO₄)₃·LiMn_0.33Fe_0.67PO₄/C for lithium-ion batteries, was synthesized using a sol-gel method and with N,N-dimethyl formamide as a dispersion agent. The analysis of electron transmission spectroscopy and X-ray diffraction revealed that the composite contained two phases. The material has high crystallinity with a grain size of 20–50 nm. The valence states of Mn, V, and Fe in the composite were analyzed by X-ray photoelectron spectroscopy. The electrochemical kinetics in Li₃V₂(PO₄)₃ is effectively enhanced by the incorporation of LiMnPO₄ and LiFePO₄, via structure modification and reduced Li diffusion length. The Li₃V₂(PO₄)₃·LiMn_0.33Fe_0.67PO₄/C materials displayed high rate capacity and steady cycle performance with discharge capacity remained 148 mAh g^?1 after 50 cycles at the rate of 0.2C. In particular, the composite exhibited excellent reversible capacities, with the values of 157, 134, 120, 102, and 94 mAh g^?1 at charge/discharge 0.2, 0.5, 1, 2, and 5C rates, respectively.     

Preparation and characterization of LiNi<Subscript>0.495</Subscript>M<Subscript>0.01</Subscript>Mn<Subscript>0.495</Subscript>O<Subscript>2</Subscript> (M = Zn,Co, and Y) for lithium ion batteries

Layered structured LiNi_0.5Mn_0.5O₂ and LiNi_0.495M_0.01Mn_0.495O₂ (M = Zn, Co, and Y) compounds were prepared by PVP (poly(vinyl pyrrolidone))-assisted sol-gel method, and their structural, morphological, vibrational, transport, and electrochemical properties were characterized by XRD, SEM, FTIR, Raman, AC impedance, and galvanostatic charge and discharge analysis. XRD patterns reveal that doping does not change the crystal structure of the LiNi_0.5Mn_0.5O₂ compound. SEM images show that the average size of the particle is in sub-micron ranges. The AC impedance studies shows an electrical conductivity of ～2.5 × 10^?7 S/cm for the parent compound. The introduction of Zn/Co/Y at equivalent sites increased the electrical conductivity by one order ～10^?6 S/cm. The compound LiNi_0.495Co_0.01Mn_0.495O₂ shows the highest electrical conductivity of 2.85 × 10^?6 S/cm and delivers a specific discharge capacity of 110 mAh/g at the end of the 25th cycle in the voltage window of 2.5–4.4 V for a current density of 30 mA/g.     

Piezĭlectric and elastic properties of Sr<Subscript>3</Subscript>NbGa<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>14</Subscript> (SNGS) single crystals

The elastic, piezoelectric, and dielectric constants of new piezoelectric single crystals Sr₃NbGa₃Si₂O₁₄ (SNGS) are measured. The elastic moduli C ₁₁ and C ₆₆ and the piezoelectric coefficient e ₁₁ are determined over a wide temperature range. It is demonstrated that the piezoelectric activity of the crystal is retained up to the highest temperatures (900°C).     

Hydrogen bond and exchange interaction in the (CuSO<Subscript>4</Subscript>)(en)·2H<Subscript>2</Subscript>O and (CuSO<Subscript>4</Subscript>)(en)·2D<Subscript>2</Subscript>O organometallic compounds

The influence of the replacement of hydrogen with deuterium in molecules of water of crystallization in the structure of the (CuSO₄)(en) · 2H₂O and (CuSO₄)(en)·2D₂O organometallic compound molecules on exchange interaction between copper ions was studied. The X-ray structural data and the data on angular anisotropy of the effective g-factor of Cu²⁺ ions in both compounds show that distortions of the initial structure caused by deuteration are minimum. A comparative analysis of the width of the exchange coupled EPR lines of the two compounds is indicative of a decrease in the exchange parameter in the deuterated sample, which substantiates the participation of H-bonds in exchange interactions in the systems studied.     

A first principles study of the adsorption and dissociation of CO<Subscript>2</Subscript> on the δ-Pu (111) surface

A complete understanding of the nature of the 5f electrons has been and continues to be a major scientific problem in condensed matter physics. Bulk and surface electronic structure studies of the actinides as also atomic and molecular adsorptions on the actinide surfaces provide a path towards this understanding. In this work, ab initio calculations within the framework of density functional theory have been used to study the adsorption of molecular CO₂ and the corresponding partially dissociated (CO + O) and completely dissociated (C + O + O) products on the δ-Pu (111) surface. The completely dissociated C + O + O configurations exhibit the strongest binding with the surface (7.92 eV), followed by partially dissociated products CO + O (5.08 eV), with molecular CO₂ adsorption having the lowest binding energies (2.35 eV). For all initial vertically upright orientations, the CO₂ molecule physisorbs or do not bind to the surface and the geometry and orientation do not change. For all initial flat lying orientations chemisorption occurs, with the final state corresponding to a bent CO₂ molecule with bond angles of 117°–130° and the elongation of the CO bond. For CO + O co-adsorption, the stable configurations corresponded to CO dipole moment orientations of 100°–172° with respect to the surface normal and the elongation of the CO bond. The most stable chemisorption cases correspond to anomalously large rumpling of the top Pu layer. The interactions of the CO₂ and CO with the Pu surface have been analyzed using the energy density of states and difference charge density distributions. The nature and the behavior of the 5f electrons have also been discussed in detail in the context of this study.