Structures and stability of Al<Subscript><Emphasis Type="Bold">7</Emphasis></Subscript>C and Al<Subscript><Emphasis Type="Bold">7</Emphasis></Subscript>N clusters

We report results of the atomic and electronic structures of Al₇C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is found to be the one in which carbon atom occupies an interstitial position in Al₇ cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al₇C^- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al₇C^- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al₇N which has the same number of valence electrons as in Al₇C^- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al₇N)₂ to study interaction between magic clusters. Received 28 July 2001     

Carbide precipitates in solution-quenched PH13-8 Mo stainless steel: A small-angle neutron scattering investigation

This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel. From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical particle model with a locked aspect ratio.     

Electronic properties of model quantum-dot structures in zero and finite magnetic fields

We have computed electronic structures and total energies of circularly confined two-dimensional quantum dots and their lateral dimers in zero and finite uniform external magnetic fields using different theoretical schemes: the spin-density-functional theory (SDFT), the current-and-spin-density-functional theory (CSDFT), and the variational quantum Monte Carlo (VMC) method. The SDFT and CSDFT calculations employ a recently-developed, symmetry-unrestricted real-space algorithm allowing solutions which break the spin symmetry. Results obtained for a six-electron dot in the weak confinement limit and in zero magnetic field as well as in a moderate confinement and in finite magnetic fields enable us to draw conclusions about the reliability of the more approximative SDFT and CSDFT schemes in comparison with the VMC method. The same is true for results obtained for the two-electron quantum dot dimer as a function of inter-dot distance. The structure and role of the symmetry-breaking solutions appearing in the SDFT and CSDFT calculations for the above systems are discussed. Received 16 October 2001 and Received in final form 17 January 2002     

Photo-induced evolution of copper sheets from cluster molecules and its application to photolithographic copper patterning

UV photoexcitation of (t-butylethynyl copper)₂₄ cluster films induces segregation of the crystals into metallic and organic phases and leads to evolve the metallic sheets sandwiched by organic polymers. The growth of the metallic crystals in the plane of the photo-electromagnetic field is attributed due to plasmon-plasmon interaction among nanoparticles embedded in dielectric polymer matrices. The surface enhanced photochemical reaction of residual cluster molecules on the photon incident direction is expected to take an important role for joining the metal particles to produce a metallic sheet. We can apply this phenomenon for photolithographic copper pattern generation on a flexible base plate.     

Thermal conductance for single wall carbon nanotubes

We report a theoretical analysis of the phonon thermal conductance, κ(T), for single wall carbon nanotubes (SWCN). In a range of low temperatues up to 100 K, κ(T) of perfect SWCN is found to increase with temperature, approximately, in a parabolic fashion. This is qualitatively consistent with recent experimental measurements where the tube-tube interactions are negligibly weak. When the carbon-carbon bond length is slightly varied, κ(T) is found to be qualitatively unaltered which implies that the anharmonic effect does not change the qualitative behavior of κ(T). Received 12 June 2001     

A comparative study on the interaction between tin(II) porphyrin and selected group 8B metals for potential application as reduction catalysts

We study the interaction between tin(II) porphyrin (SnPor) with platinum and non-precious Group 8B metals (iron, cobalt and nickel) by density functional theory and discuss the electronic properties of the resulting products. We also model the interaction of the resulting compounds with water where applicable. Our studies indicate that, SnPor-Ni possesses electronic properties similar to SnPor-Pt, suggesting that it may possess similar photocatalytic properties for reduction reactions, such as converting water to hydrogen gas.     

微纳米加工技术在纳米物理与器件研究中的应用

物质在纳米尺度下可能呈现出与体材料不同的物理特件，这正是纳米科技发展的基础之一。要想探索在纳米尺度下材料物埋性质的变化规律及可能的应用领域，离不开相应的技术手段，微纳米加工技术作为当今高技术发展的重要技术领域之一，是实现功能人工纳米结构与器件微纳米化的基础。本文根据几个不同的应用领域，介绍了微纳米加工技术在纳米物理与器件研究领域的应用。     

Reinforcement effect of MAA on nano‐CaCo3‐filled EPDM vulcanizates and possible mechanism

Methacrylic acid (MAA) was used as in situ surface modifier to improve the interface interaction between nano‐CaCO₃ particle and ethylene–propylene–diene monomer (EPDM) matrix, and hence the mechanical properties of nano‐CaCO₃‐filled EPDM vulcanizates. The results showed that the incorporation of MAA improved the filler–matrix interaction, which was proved by Fourier transformation infrared spectrometer (FTIR), Kraus equation, crosslink density determination, and scanning electron microscope (SEM). The formation of carboxylate and the participation of MAA in the crosslinking of EPDM indicated the strong filler–matrix interaction from the aspect of chemical reaction. The results of Kraus equation showed that the presence of MAA enhanced the reinforcement extent of nano‐CaCO₃ on EPDM vulcanizates. Crosslink density determination proved the formation of the ionic crosslinks in EPDM vulcanizates with the existence of MAA. The filler particles on tensile fracture were embedded in the matrix and could not be observed obviously, indicating that a strong interfacial interaction between the filler and the matrix had been achieved with the incorporation of MAA. Meanwhile, the presence of MAA remarkably increased the modulus and tensile strength of the vulcanizates, without negative effect on the high elongation at break. Furthermore, the ionic bond was thought to be formed only on filler surface because of the absolute deficiency of MAA, which resulted in the possible structure where filler particles were considered as crosslink points. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1226–1236, 2006     

Structure control within poly(amidoamine) dendrimers: size, shape and regio-chemical mimicry of globular proteins

This work describes the syntheses of a new poly(amidoamine) (PAMAM) dendrimer family possessing a disulfide function (cystamine) in its core. Traditional redox-chemistry associated with the disulfide core in these dendrimer structures, provides a versatile strategy for designing unique sizes, shapes and controlling the regio-disposition of chemical groups on the surface of these dendrimers. Various single site, sulfhydryl functionalized dendron reactants may be generated in situ, under standard reducing conditions (i.e. dithiothreitol (DTT)). Facile control of size, shape and chemical functionality placement involves covalent hybridization of these single point, sulfhydryl reactive dendron components. This is accomplished by re-oxidation in the presence of air, to yield generation/surface chemistry differentiated cross-over products which may be isolated by preparative thin layer or column chromatography. Differentiated cystamine core dendrimers derived from combination and permutation of lower generation (i.e. Gen.=0-3) sulfhydryl functionalized dendrons possessing amino, hydroxyl, acetamido or dansyl surface groups, were synthesized and isolated. They were characterized by a variety of methods including; ¹³C NMR, capillary electrophoresis (CE), gel electrophoresis (PAGE), thin layer chromatography (TLC) and electrospray (ES) or matrix assisted laser desorption ionization (MALDI-TOF) mass spectrometry. This general strategy has broad implications for the systematic size, shape and regio-chemical control of a wide range of dendritic nanostructures, many of which may be designed to mimic the sizes, shapes and regio specific chemo-domains observed for globular proteins.     

纳米尺度分散的TiO2光催化降解甲醛的机理

纳米TiO2具有小尺寸效应,表面效应和宏观量子隧道效应等[1],广泛用于防水处理、空气净化、抗菌防霉等方面。本文对其能带结构及其消除甲醛的性能及机理进行分析。1　纳米TiO2光催化剂1 1　制备与表征以四氯化钛为主要原料,氨水、醇类化合物、盐酸等为主要反应助剂,采用亚稳态氯化法制备工艺,用相应的溶胶反应形成溶胶液体,低于100℃加热该液体,除去多余的水分,得到溶胶-凝胶体。过滤所得溶胶-凝胶体,并用蒸馏水反复洗涤数次,使其pH呈中性。将洗涤后的溶胶-凝胶体进行真空干燥,得到白色微粉,1000℃高温煅烧,将煅烧后得到的纳米TiO2基…