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Nanoripple structures spontaneously formed at room temperature during chemical and electrochemical deposition of metals, semiconductors, and alloys on gold and copper templates, patterned with nanocavities, have been studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Annealing the templates at approximately equal to 373 K also results in ripple formation. Both experimental results and modeling, including anisotropic surface diffusion, demonstrate that nanocavity size in the template determines the ripple wavelength and amplitude, prior to a final stage of coarsening. Therefore, an ordered array of "nanodefects" introduced in the substrate is able to guide the self-organization of these nanofeatures during their growth, creating the possibility for nanofabrication of parallel interconnections with adjustable periodicity. Ripples are robust nanostructures that can in turn be used as templates for the preparation of hybrid nanostructured surfaces with specific physical properties.
ACS Nano 2008 Dec 23
PMID:Spontaneous nanoripple formation on metallic templates. 1920 89

Photocurrent generation in nanostructured organic solar cells is simulated using a dynamical Monte Carlo model that includes the generation and transport properties of both excitons and free charges. Incorporating both optical and electrical properties, we study the influence of the heterojunction nanostructure (e.g., planar vs bulk junctions) on donor-acceptor organic solar cell efficiencies based on the archetype materials copper phthalocyanine (CuPc) and C(60). Structures considered are planar and planar-mixed heterojunctions, homogeneous and phase-separated donor-acceptor (DA) mixtures, idealized structures composed of DA pillars, and nanocrystalline DA networks. The thickness dependence of absorption, exciton diffusion, and carrier collection efficiencies is studied for different morphologies, yielding results similar to those experimentally observed. The influences of charge mobility and exciton diffusion length are studied, and optimal device thicknesses are proposed for various structures. Simulations show that, with currently available materials, nanocrystalline network solar cells optimize both exciton diffusion and carrier collection, thus providing for highly efficient solar energy conversion. Estimations of achievable energy conversion efficiencies are made for the various nanostructures based on current simulations used in conjunction with experimentally obtained fill factors and open-circuit voltages for conventional small molecular weight materials combinations.
ACS Nano 2008 May
PMID:Photocurrent generation in nanostructured organic solar cells. 1920

ZnO nanowires (NWs) are grown on a bulk copper half-transmission electron microscopy grid by chemical vapor deposition in a high temperature tube furnace. Photoluminescence (PL) microscopy revealed band gap emission at 380 nm and a more intense visible emission around 520 nm due to defect states in these NWs. High-resolution transmission electron microscopy shows that the ZnO NWs are single crystalline with hexagonal structure. Auger electron spectroscopy (AES) and energy dispersive X-ray spectroscopy reveal that copper atoms are present along the length of the NW. AES also found that the surface of the NWs is oxygen rich. The surface concentration of zinc increases moving from the tip toward the base of the NW while the concentration of oxygen decreases. The copper in this system not only remains at the tip of the growing NW but also acts as a dopant along the length of the NW, leading to a decrease in the intensity of the band gap PL of these NWs.
ACS Nano 2008 Feb
PMID:Analysis of copper incorporation into zinc oxide nanowires. 1920 39

The discovery of the metallopeptide Ni(Cysteine-Glycine-Cysteine)(2-), Ni(CGC)(2-), in the A-cluster active site of Acetyl CoA Synthase has prompted the synthesis of many small molecule models which employ M(N(2)S(2)) complexes as metalloligands. In vitro studies have shown that nickel incorporates into the N(2)S(2) binding pocket even when copper is in the enzyme growth medium, while copper is preferentially taken up in the proximal site, displacing the catalytically active nickel. (Darnault, C.; Volbeda, A.; Kim, E.J.; Legrand, P.; Vernede, X.; Lindahl, P.A.; Fontecilla-Camps, J.C. Nat. Struct. Biol. 2003, 10, 271-279.) The work herein has been designed to address the chemical viability of copper(II) within the tripeptide N(2)S(2) ligand set. To this end, a series of CuN(2)S(2)(2-) complexes, the resin-bound, O-Cu(CGC)(2-) (A) and free Cu(CGC)(2-) (B) complexes, as well as Cu(ema)(2-) (C) and Cu(emi)(2-) (D) dianions, have been characterized by UV-vis, electron paramagnetic resonance (EPR), and electrospray ionization mass spectrometry (ESI-MS) spectroscopies, cyclic voltammetry (CV), and, where appropriate, X-ray diffraction studies, and compared to the Ni(II) congeners. EPR spectroscopic results have indicated that, in frozen N,N-dimethylformamide (DMF) solution, the copper complexes are distorted square planar structures with nitrogen and sulfur donors. This is consistent with X-ray diffraction measurements which also show copper(II) in a distorted square planar environment that is bereft of CuN(2)S(2)(2-) intermolecular interactions. Density-functional theory (DFT) calculations resulted in optimized structures that are consistent with crystallographic data and indicated highest occupied molecular orbital (HOMO)-singly occupied molecular orbital (SOMO) gaps of 5.01 and 4.68 eV for C and D, respectively. Optimized structures of Ni(ema)(2-) and Ni(emi)(2-) share the same basic characteristics as the copper(II) congeners. Electrochemical characterization of C and D resulted in a reversible Cu(III/II) couple at -1.20 V and - 1.40 V, respectively. Reactivity studies with Rh(CO)(2)(+) show similar donor capabilities for complexes A-D. Analysis of A shows that transmetalation does not occur. From competitive metal uptake studies on immobilized tripeptide it is concluded that the N(2)S(2)(4-) ligating unit has a slight preference for Cu(2+) over Ni(2+) and that the biosynthetic pathway responsible for constructing the distal site of ACS must be selective for nickel insertion or copper exclusion, or both.
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PMID:Chemical issues addressing the construction of the distal Ni[cysteine-glycine-cysteine]2- site of acetyl CoA synthase: why not copper? 1925 85

Motivated by the discovery of the superatom states of C60 molecules, we investigate the factors that influence their energy and wave function hybridization into nearly free electron bands in molecular solids. As the n = 3 solutions of the radial Schrodinger equation of the central attractive potential consisting of the short-range C atom core and the long-range collective screening potentials, respectively, located on the icosahedral C60 molecule shell and within its hollow core, superatom states are distinguished by their atom-like orbitals corresponding to different orbital angular momentum states (l = 0, 1, 2,...). Because they are less tightly bound than the pi orbitals, that is, the n = 2 states, which are often exploited in the intermolecular electron transport in aromatic organic molecule semiconductors, superatom orbitals hybridize more extensively among aggregated molecules to form bands with nearly free electron dispersion. The prospect of exploiting the strong intermolecular coupling to achieve metal-like conduction in applications such as molecular electronics may be attained by lowering the energy of superatom states from 3.5 eV for single chemisorbed C60 molecules to below the Fermi level; therefore, we study how the superatom state energies depend on factors such as their aggregation into 1D-3D solids, cage size, and exo- and endohedral doping by metal atoms. We find, indeed, that if the ionization potential of endohedral atom, such as copper, is sufficiently large, superatom states can form the conduction band in the middle of the gap between the HOMO and LUMO of the parent C60 molecule. Through a plane-wave density functional theory study, we provide insights for a new paradigm for intermolecular electronic interaction beyond the conventional one among the sp(n) hybridized orbitals of the organic molecular solids that could lead to design of novel molecular materials and quantum structures with extraordinary optical and electronic properties.
ACS Nano 2009 Apr 28
PMID:The superatom states of fullerenes and their hybridization into the nearly free electron bands of fullerites. 1935 Nov 48

Low-temperature pyrolysis is a possible method for the disposal of wood waste treated with chromated copper arsenic (CCA). A mathematical model (heat and mass transfer) including chemical reactions of the thermal degradation of a particle of wood is presented. A spherical particle is heated by a convective nitrogen flow. The progress of the pyrolysis process is characterized by three main steps: (1) drying of the wet sample; (2) heating of the sample until ignition of pyrolysis reactions; (3) pyrolysis and subsequent production of char and volatiles. The mathematical model is based on the volume averaging concept and it uses Shafizadeh and Chin [F. Shafizadeh, P.S. Chin, Thermal deterioration of wood, wood technology: chemical aspects, ACS Symposium Series 43 (1977) 57-81] pyrolysis model to describe the reaction pathway. It is solved by the line method, taking time as the preferred variable. Our model predicts intra-particle profiles for several variables (temperature, moisture content, concentration of wood). Simulations are presented with a spherical particle of 1cm radius.
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PMID:Mathematical modelling of slow pyrolysis of a particle of treated wood waste. 1953 4

Development of materials and structures leading to lithium ion batteries with high energy and power density is a major requirement for catering to the power needs of present day electronic industry. Here, we report an in situ formation of a sandwiched structure involving single-walled carbon nanotube film, copper oxide, and copper during the direct synthesis of nanotube macrofilms over copper foils and their electrochemical performance in lithium ion batteries. The sandwiched structure showed a remarkably high reversible capacity of 220 mAh/g at a high cycling current of 18.6 A/g (50 C), leading to a significantly improved electrochemical performance which is extremely high compared to pure carbon nanotube and any other carbon based materials.
ACS Nano 2009 Aug 25
PMID:In-situ formation of sandwiched structures of nanotube/CuxOy/Cu composites for lithium battery applications. 1963 92

We demonstrated a novel method to produce core/shell composite nanowires (NWs) by self-scrolling carbon nanotubes (CNTs) onto copper NWs via forced-field-based molecular dynamic (MD) simulations. When large diameter CNTs are placed beside the copper NWs, the CNTs approach the NWs, collapse, and self-scroll onto the NWs, resulting in coaxial core/shell composite NWs. It is found that the van der Waals force plays an important role in the formation of the composite NWs. The expected outcome of this novel method is to determine various strategies on how to produce composite NWs. Coaxial core/shell composite NWs represent an important class of nanoscale building blocks with substantial potential for exploring new concepts and functional materials.
ACS Nano 2009 Aug 25
PMID:The core/shell composite nanowires produced by self-scrolling carbon nanotubes onto copper nanowires. 1965 86

Droplet-based microfluidic systems are an expansion of the lab on a chip concept toward flexible, reconfigurable setups based on the modification and analysis of individual droplets. Superhydrophobic surfaces are one suitable candidate for the realization of droplet-based microfluidic systems as the high mobility of aqueous liquids on such surfaces offers possibilities to use novel or more efficient approaches to droplet movement. Here, copper-based superhydrophobic surfaces were produced either by the etching of polycrystalline copper samples along the grain boundaries using etchants common in the microelectronics industry, by electrodeposition of copper films with subsequent nanowire decoration based on thermal oxidization, or by a combination of both. The surfaces could be easily hydrophobized with thiol-modified fluorocarbons, after which the produced surfaces showed a water contact angle as high as 171 degrees +/- 2 degrees . As copper was chosen as the base material, established patterning techniques adopted from printed circuit board fabrication could be used to fabricate macrostructures on the surfaces with the intention to confine the droplets and, thus, to reduce the system's sensitivity to tilting and vibrations. A simple droplet-based microfluidic chip with inlets, outlets, sample storage, and mixing areas was produced. Wire guidance, a relatively new actuation method applicable to aqueous liquids on superhydrophobic surfaces, was applied to move the droplets.
ACS Nano 2009 Sep 22
PMID:Easy route to superhydrophobic copper-based wire-guided droplet microfluidic systems. 1968 79

We present the fabrication and characterization of nanoscale electrical interconnect test structures constructed from aligned single-wall carbon nanotubes using a template-based fluidic assembly process. This CMOS-friendly process enables the formation of highly aligned parallel nanotube interconnect structures on SiO(2)/Si substrates of widths and lengths that are limited only by lithographical limits and, hence, can be easily integrated onto existing Si-based platforms. These structures can withstand current densities of approximately 10(7) A.cm(-2), comparable or better than copper at similar dimensions. Both the nanotube alignment and failure current density improve with decreasing structure width. In addition, we present a novel Pt nanocluster decoration method that drastically decreases the resistivity of the test structures. Ab initio density functional theory calculations indicate that the increase in conductivity of the nanotubes is caused by an increase in conduction channels close to their Fermi levels due to the platinum nanocluster decoration, with a possible conversion of the semiconducting single-wall carbon nanotubes into metallic ones. These results reflect a huge step toward the proposed replacement of copper-based interconnects with carbon nanotubes at gigascale integration levels.
ACS Nano 2009 Sep 22
PMID:Highly aligned scalable platinum-decorated single-wall carbon nanotube arrays for nanoscale electrical interconnects. 1972 14


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