Scientific publications

Different kinds of ZnO nanowires were synthesized by vapor-solid and vapor-liquid-solid methods via a chemical vapor transport and condensation process. The samples were characterized by scanning electron microscopy, X-ray diffraction (XRD) and photoluminescence analyses. The control on the growth morphologies can be achieved by the source materials and by using a thin gold layer as a catalyst. 15-80 nm nanowires were obtained and XRD patterns show two different growth directions. High intensity green light from photoluminescence spectroscopy was observed which shows that the experimental results could be useful for light-emitting materials and other optoelectronic device applications.

Using direct oxidation of Zn powder as a source material, zinc oxide comb and saw structures were fabricated by vapor phase transport and condensation. X-ray diffraction pattern showed that the samples had a wurtzite crystal structure. Different structures such as comb-like nano- and microstructures and saw-like structures have been studied by scanning electron microscopy. ZnO comb-like nanostructures with an average size of 15–20 nm and 50 nm were observed, as well as comb-like and saw-like microstructures. Photoluminescence (PL) spectra of these ZnO samples at room temperature were discussed. PL spectra showed strong UV and green emissions that indicate their possible application in optoelectronic devices. Also, the I–V behavior of a single nanowire was investigated. Approximately linear current versus voltage was observed for this nanowire, which showed good ohmic contacts to structure.

In this work, Cu(In,Ga)Se2 (CIGS) nanoparticles were synthesized using a wet chemical method. The method is based on a non-vacuum thermal process that does not use selenization. The effects of temperature, source materials, and growth conditions on the phase and particle size were investigated. X-ray diffraction results confirm the formation of a tetragonal CIGS structure as the main phase with the purity more than 99% obtained by energy-dispersive X-ray spectroscopy (EDX). The morphology and size of the samples were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using these methods, 20-80 nm particles were obtained. Through measurements of the absorption spectra of CIGS nanoparticles, the band gap of the synthesized material was determined to be about 1.44 eV, which corresponds to an acceptable wavelength region for absorber layers in solar cells.

We exploit the strong optical anisotropy of metal nanorods to measure their mobility in a complex fluid. Gold rods in hot agarose solutions cause dynamic, depolarized scattering with an exponentially decaying autocorrelation. As the solution cools down, its decay constant increases. At a certain temperature, the autocorrelation drastically changes its shape and the dynamic contrast drops. We show that, at this temperature, the gelling liquid confines the rods and dampens their motion almost entirely. Depolarized scattering proves to be extraordinarily sensitive to the transition from Brownian to confined motion. We calculate true mobilities for the particles using Pusey and van Megen's correction of the Siegert relation for nonergodic systems. Multipoint measurements show that the rods are immobilized throughout the gel.

Crystalline and amorphous materials composed of the same atoms exhibit strikingly different properties. Likewise, the behavior of materials composed of mesoscale particles depends on the arrangement of their constituent particles. Here, we demonstrate control over particle arrangement during agglomeration. We obtain disordered and ordered agglomerates of the same alkyl thiol-coated gold nanoparticles depending on temperature and solvent. We find that ordered agglomeration occurs exclusively above the melting temperature of the ligand shells. Many-particle simulations show that the contact mechanics of the ligand shells dominate the order-disorder transition: Purely spherical particle-particle interactions yield order, whereas localized "stiction" between the ligand shells leads to disorder. This indicates that the "stickiness" and the packing of the agglomerates can be switched by the state of the ligand shells. It suggests that contact mechanics govern ordering in a wide range of nanoparticles.

Noble gas and metal atoms form minimum-energy clusters. Here, we present analogous agglomerates of gold nanoparticles formed in oil-in-water emulsions. We exclude interfacial templating and nucleation-and-growth as formation mechanisms of these supraparticles. Similar to atomic clusters, the supraparticles form when a mobile precursor state can reconfigure until the nanoparticles' interactions with each other and with the liquid-liquid interface are maximized. This formation mechanism is in striking contrast to that previously reported for microparticle clusters.

In this paper the inhibitive performance of cerium molybdate nanowires prepared by a novel methodology is reported. The methodology is based on a low-temperature, controlled-rate mixing process. Structurally, cerium molybdate nanowires were found to be amorphous-like materials whose inhibiting action towards aluminium alloy 2024-T3 was demonstrated by DC polarization and electrochemical impedance spectroscopy (EIS), corroborated by microstructural surface analysis of the metallic substrate. The observed inhibiting action is attributed to the higher solubility of the cerium molybdate nanomaterials with respect to crystalline sodium cerium molybdate obtained at room temperature.

The design of synthetic biology-inspired control devices enabling entire mammalian cells to receive, process and transfer metabolic information and so communicate with each other via synthetic multichannel networks may provide new insight into the organization of multicellular organisms and future clinical interventions. Here we describe communication networks that orchestrate behavior in individual mammalian cells in response to cell-to-cell metabolic signals. We engineered sender, processor and receiver cells that interact with each other in ways that resemble natural intercellular communication networks such as multistep information processing cascades, feed-forward-based signaling loops, and two-way communication. The engineered two-way communication devices mimicking natural control systems in the development of vertebrate extremities and vasculature was used to program temporal permeability in vascular endothelial cell layers. These synthetic multicellular communication systems may inspire future therapies or tissue engineering strategies. © 2012 Nature America, Inc. All rights reserved.

The Cu(i)-catalyzed cycloaddition of terminal azides and alkynes (click chemistry) represents a highly specific reaction for the functionalization of biomolecules with chemical moieties such as dyes or polymer matrices. In this study we evaluate the use of bicinchoninic acid (BCA) as a ligand for Cu(i) under physiological reaction conditions. We demonstrate that the BCA-Cu(i)-complex represents an efficient catalyst for the conjugation of fluorophores or biotin to alkyne- or azide-functionalized proteins resulting in increased or at least equal reaction yields compared to commonly used catalysts like Cu(i) in complex with TBTA (tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl] amine) or BPAA (bathophenanthroline disulfonic acid). The stabilization of Cu(i) with BCA represents a new strategy for achieving highly efficient bioconjugation reactions under physiological conditions in many application fields. © 2012 The Royal Society of Chemistry.