Self-assembly of Mo<Subscript> 6</Subscript>S<Subscript> 8</Subscript> clusters on the Au(111) surface

The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo₆S₈ on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact. It experiences a strong, mostly non-ionic attraction to the surface at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room temperature. The analysis of the electronic structure reveals a negligible electron transfer and S-Au hybridised states, which indicate that the cluster-surface interaction is dominated by S-Au bonds, with minor contributions from the Mo atom in the surface vicinity. All results indicate that Mo₆S₈ clusters on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within nano-devices. Therefore, a classical potential model was developed on the basis of the DFT data, which allows to study larger cluster assemblies on the Au(111).     

Electronic and geometric structures of MoxSy and WxSy (x =1, 2, 4; y =1–12) clusters

Electronic and geometric structures of M_xS_y (M = W, Mo; x=1,2,4;y=1–12) clusters have been studied using density functional theory calculations, and compared to experimental photoelectron spectra. For the metal atoms, an uptake of up to six sulfur atoms has been observed, which can be explained by the bonding of S₃ ^- chains. A structural difference to the corresponding oxides is the preference of bridging sites for S, which might be the origin of the differences between the structures of bulk MO₃ and MS₂. For x=1,2 the HOMO–LUMO gaps vary irregularly. For x=4, a large HOMO–LUMO gap has been found for y=6,7, and 8 and the W₄S₆ and Mo₄S₆ clusters have been found to be magic with an extraordinarily high stability. PACS 73.22.-f; 61.46.+w     

All-electron scalar relativistic calculation on the interaction between nitric monoxide and small gold cluster

An all-electron scalar relativistic calculation on Au _n NO (n = 1–10) clusters has been performed by using density functional theory with the generalized gradient approximation at the PW91 level. The small gold cluster would like to bond with nitric and the nitric monoxide molecule prefers to occupy the on-top and single fold coordination site. The Au _n structures in all Au _n NO clusters are only distorted slightly and still keep the planar structures. With the bend of Au-N-O bond, the structures of Au _n NO clusters evolve from the 2D structure to 3D structure. The most favorable adsorption between small gold cluster and nitric monoxide molecule takes place in the case that nitric monoxide molecule is adsorbed onto an odd-numbered pure Au _n cluster and becomes odd-numbered Au _n NO cluster with even number of valence electrons. The scalar relativistic effect strengthens the Au–Au, Au–N interaction and weakens the N–O interaction, appearing as the shorter Au–Au, Au–N bond-length and the longer N–O bond-length. The differences between our work and previous work are believed to be the reflection of the scalar relativistic effect.     

Dissociation pathways of doubly and triply charged gold clusters

Collision induced dissociation is applied to study the fragmentation channels of multiply charged gold clusters, Au N2⁺, size N= 7 –35, and Au> _N3+}, N = 19–35, stored in an ion cyclotron resonance (Penning) trap. The main dissociation pathways are neutral monomer evaporation, Au> _NZ+to Au> _N-1Z+} + Au, for the larger and fission into a charged trimer plus the remaining cluster, Au> _NZ+to{}Au> _N-3(Z-1)+} +{}Au> ₃₊}, for the smaller clusters. In the intermediate cluster size region an odd–even alternation of the two competing decay pathways is observed. In addition, for some specific cluster sizes there are indications of neutral dimer evaporation, Au> _NZ+to{}Au> _N-2Z++Au> ₂}, and of extremely asymmetric fission of the form Au> _NZ+to Au> _N-1(Z-1)+} + Au⁺. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structures,stabilities and adsorption mechanisms of nitrogen adsorbed on Mon (n = 1–8) clusters

Configurations, stabilities and adsorption mechanisms of ground-state Mo_nN and Mo_nN₂ (n?=?1–8) clusters are calculated by using the density functional method within the PBE level. Evidently, N atoms tend to approach more Mo atoms. Doping with two N impurity prefers to occupy symmetrical position of the host Mo_n (n?=?1–8) cluster except for Mo₂N₂ clusters. Mo₄N, Mo₆N, Mo₂N₂, Mo₄N₂ and Mo₆N₂ clusters have higher structural stabilities than their neighbors by the second derivative of total binding energy. Mo₂N, Mo₄N and Mo₇N, Mo₂N₂, Mo₅N₂ and Mo₇N₂ clusters have higher kinetic reactivity than their neighbors by the HOMO–LUMO gaps. The adsorption capacity of a N atom to Mo₄ cluster is stronger than the other Mo–N clusters.     

Electronic properties of Chevrel phases by positron angular correlation

A comparative study of the Chevrel phases Mo₆S₈, Mo₆Se₈, PbMo₆S₈ and Cu_1.8Mo₆S₈ is made by the positron angular correlation technique at room temperature. Electronic properties like the number of conduction electrons per cluster, the density of states at the Fermi level, the electron effective masses and the Fermi velocities are obtained within the framework of the free electron model. The results are discussed in terms of available theoretical and other experimental data.     

NiFe/Mo多层膜界面的电子显微学研究

用高分辨电子显微学方法研究了Ni₈₀Fe₂₀/Mo磁性多层膜，结果表明：(1)多层膜的结晶状态，随Mo非磁性层厚度而变化.当Mo层厚度为0.7nm时，多层膜基本为非晶；当Mo层厚度大于1.6nm时，Mo层和NiFe层内分别结晶为体心立方和面心立方多晶，层内晶粒尺寸为2—6nm.(2)在Mo层厚度为1.6和2.1nm的多层膜中，NiFe层和Mo层之间存在两种取向关系：(110)_Mo∥(111)_NiFe,［111］_关键词：     

Theoretical study of small Mo clusters and molecular nitrogen adsorption on Mo clusters

This paper studies the small molybdenum clusters of Mo_n (n=2--8) and their adsorption of N₂ molecule by using the density functional theory (DFT) with the generalized gradient approximation. The optimized structures of Mo_n clusters show the onset of a structural transition from a close-packed structure towards a body-centred cubic structure occurred at n=7. An analysis of adsorption energies suggests that the Mo₂ is of high inertness and Mo₆ cluster is of high activity against the adsorption of N₂. Calculated results indicate that the N₂ molecule prefers end-on mode by forming a linear or quasi-linear structure Mo--N--N, and the adsorption of nitrogen on molybdenum clusters is molecular adsorption with slightly elongated N--N bond. The electron density of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the partial density of states of representative cluster are also used to characterize the adsorption properties of N₂ on the sized Mo_n clusters.     

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Infrared (IR) spectroscopy of chemisorbed C₆₀ on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm^-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C₆₀/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest to be the frustrated translational mode of the adsorbed molecules. Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction coefficient of the C₆₀ molecules, which results in rather small values (∼2×10⁹ s^-1 for Ag and Au, and ∼1.6×10⁹ s^-1for Cu), consistent with a marked metallic character of the adsorbed molecules. Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C₆₀ deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due to strong electron–phonon coupling with induced surface states. Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002     

Structures and electronic properties of Mo2nNn（n=1-5）:a density functional study

The lowest-energy structures and the electronic properties of Mo2nNn(n=1-5) clusters have been studied by using the density functional theory(DFT) simulating package DMol 3 in the generalized gradient approximation(GGA).The resulting equilibrium geometries show that the lowest-energy structures are dominated by central cores which correspond to the ground states of Mo n(n = 2,4,6,8,10) clusters and nitrogen atoms which surround these cores.The average binding energy,the adiabatic electron affinity(AEA),the vertical electron affinity(VEA),the adiabatic ionization potential(AIP) and the vertical ionization potential(VIP) of Mo2nNn(n=1-5) clusters have been estimated.The HOMO-LUMO gaps reveal that the clusters have strong chemical activities.An analysis of Mulliken charge distribution shows that charge-transfer moves from Mo atoms to N atoms and increases with cluster size.     

The effect of Ti on the wetting of CaF<Subscript>2</Subscript> substrate by In–Ti and Ga–Ti alloys. Ab-initio consideration

CaF₂ is a thermodynamically stable, non-reactive compound, displaying a relatively high contact angle with pure liquid metal melts. A remarkable decrease of this contact angle takes place when small amounts of Ti are added to liquid In (a decrease from 125 to 20°) or to liquid Ga (from 118 to 60°). Thermodynamic analysis indicates that this feature cannot be attributed to chemical reactions between the substrate and the melt. It was suggested that the reason for this behavior may be a preferential titanium adsorption from the liquid In–Ti or Ga–Ti solution at the substrate surface. In order to understand the nature of the In–Ti or Ga–Ti bonding in the vicinity of the CaF₂ surface, the adsorption energy of 0.5 monolayer of In and Ga was computed for three different surface conditions: (i) clean CaF₂(111), (ii) CaF₂(111) with In or Ga adatoms, and (iii) CaF₂(111) with Ti adatoms. The differences in adsorption energies for these configurations are related to the electron charge redistribution in the vicinity of the interface, and to the density of states of the electronic subsystems. It was found that the adsorption energy of In or Ga increases due to the lateral interactions with the adatoms. According to the analysis, a strong lateral interaction exists between Ti adatoms and Me, while relatively weak interaction exists between Me and Me adatoms. The difference of the lateral interactions was considered in order to explain the improvement of the wetting of CaF₂ substrate by Ti alloying of In and Ga.     

The configuration and electronic state of SO3 adsorbed on Au surface

We evaluated the adsorption of SO₃ molecule on Au (1 1 1) surface using first principles calculation by a slab model with a periodic boundary condition. We find that there are six stable adsorption configurations on an Au surface, where the SO₃ molecule is adsorbed above the three-fold fcc and hcp hollow sites and on the atop site. In two of these configurations, S and two O atoms are bound to the Au atoms, the next two configurations have all the three O atoms bound to the Au surface atoms, and the last two configurations have the S atom bound to an Au surface atom on the atop site and O atoms situated above the hollow sites. In these configurations, the electronic structures of SO₃ on the Au surface show that molecular orbitals of SO₃ and those of the Au surface are hybridized in the active metal d-band region, that the localized molecular orbitals in SO₃ are stabilized, and that charge is transferred from Au to S 3p by SO₃ adsorption on the Au surface though there is little other interaction of the S and O (bound to Au) component with Au. Moreover, the bond between the S and O atoms bound to Au is weakened due to SO₃ adsorption on the Au surface due to the charge polarization of the O-Au bond. This interaction is likely to encourage the S-O bond to break.     

Theoretical and experimental investigations of photophysics of the nile red molecule and its protonated structures

Results of quantum-chemical studies of the nile red (NR) molecule and its protonated structures by the INDO/S method are presented. It is demonstrated that the best agreement between the calculated and experimental data is obtained for the flat molecule in the ground electron state. Energies of the strongest singlet and triplet electronic states, molecular nature of these states, transition oscillator force, dipole moments in the ground and excited states, electron density distribution around atoms and molecular fragments in the S₀ and S₁ states, and rate constants of radiative, internal, and intercombination conversion are presented for the NR molecule and its protonated structures. The most probable NR protonation centers are analyzed using the molecular electrostatic potential (MESP) method. It is established that the reaction of proton addition to the NR molecule proceeds at the cyclic nitrogen atom. As demonstrated the results of quantum-chemical calculations, low fluorescent properties of the protonated NR structures (with a quantum yield of 4%) are due to a high rate of the S₁ – T₄ intercombination conversion.     

Estimating the adsorption energy of element 113 on a gold surface

We report first-principle based studies of element 113 (E113) interactions with gold aimed primarily at estimating the adsorption energy in thermochromatographic experiments. The electronic structure of E113-Au _n systems was treated within the accurate shape-consistent small core relativistic pseudopotential framework at the level of non-collinear relativistic density functional theory (RDFT) with specially optimised Gaussian basis sets. We used gold clusters with up to 58 atoms to simulate the adsorption site on the stable Au(111) surface. Stabilization of the E113-Au _n binding energy and the net Bader charge of E113 and the neighboring Au atoms with respect to n indicated the cluster size used was appropriate. The resulting adsorption energy estimates lie within the 1.0–1.2 eV range, substantially lower than previously reported values.     

First principles study on electronic properties and occupancy sites of molybdenum doped into LiFePO4

The electronic properties of Mo-doped LiFePO₄ and occupancy sites of Mo are investigated by employing the density functional theory plane-wave pseudopotential method. The calculated results show that Mo doping at Fe site has lower formation energy, which implies that Mo dopants prefer to occupy Fe sites within the LiFePO₄ lattice. Furthermore, the LiFe_1?3/12Mo_1/12PO₄ has wider lithium ion migration channels than Li_1?6/12Mo_1/12FePO₄. For the case of LiFe_1?3/12Mo_1/12PO₄, the calculated narrow band gap (0.18 eV) indicates that the electronic conductivity of LiFePO₄ could be enhanced by doping Mo at the Fe sites. The density of states and charge densities of LiFe_1?3/12Mo_1/12PO₄ demonstrate that the Mo-4d states and MoO bonding play important roles in band gap reduction of LiFe_1?3/12Mo_1/12PO₄.     

The surface structures growth’s features caused by Ge adsorption on the Au(111) surface

The initial stage of the adsorption of Ge on an Au(111) surface was investigated. The growth and stability of the structures formed at the surface were studied by ultrahigh-vacuum low-temperature scanning tunneling microscopy and analyzed using density functional theory. It was established that the adsorption of single Ge atoms at the Au(111) surface at room temperature leads to the substitution of Au atoms by Ge atoms in the first surface layer. An increasing of surface coverage up to 0.2–0.4 monolayers results in the growth of an amorphous binary layer composed of intermixed Au and Ge atoms. It was shown that the annealing of the binary layer at a temperature of T _s ? 500 K, as well as the adsorption of Ge on the Au(111) surface heated to T _s ? 500 K for coverages up to 1 monolayer lead to a structural transition and the formation of an Au–Ge alloy at least in the first two surface layers. Based on experimental and theoretical data, it was shown that the formation of single-layer germanene on the Au(111) surface for coverages ≤1 monolayer in the temperature range of T _s = 297–500 K is impossible.     

Chevrel相MxMo6S8化合物电荷转移和Mo原子上4d轨道能级的分裂

本文用配位场方法导出了Chevrel相M_xMo₆S₈化合物中M和Mo₆S₈原子簇间电荷转移和Mo原子上4d轨道能级分裂的解析关系。结合PbMo₆S₈的反射光谱,求得Mo₆S₈原子簇至Pb的电子转移数为1.18,和以前一般文献上认为的两个电子从Pb转移至Mo₆S₈不同。Mo₆上的4d电子数为18.8。 关键词：     

Mechanisms for long-range forces in the “three atoms+electron” system

The Born-Oppenheimer approximation is used to obtain an equation for the effective interaction of three atoms bound by a single electron. For low binding energies long-range forces arise between the atoms in an “electron + atom pair” that lead to bound states when the size of the three-atom cluster is several tens of angstroms. A system made up of alkali metal atoms is considered as an example. Zh. éksp. Teor. Fiz. 111, 1229–1235 (April 1997)     

Synthesis of composite gold/tin-oxide nanoparticles by nano-soldering

Composite Au–SnO₂ nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO₂ NPs. The multi-step process involves synthesis of pure Au and SnO₂ NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation laser heating of mixed solution of Au colloidal and SnO₂ colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO₂ NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated particles were observed on further laser heating. UV–vis spectra of Au–SnO₂ nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au NPs. The negative binding energy shift of Au 4f_7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO₂ between gold and tin oxide and formation of soldered nanocomposite.