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• Low-Temperature, Highly Efficient Growth of Carbon Nanotubes on Functional Materials by an Oxidative Dehydrogenation Reaction
  Posted by Jin Won Seo
  A. Magrez, J.W. Seo, R. Smajda, B. Korbely, J.C. Andresen, M. Mionic, S. Casimirius and Laszlo Forro
  In many applications like photovoltaics, fuel cells, batteries, or interconnects in integrated circuits carbon nanotubes (CNTs) have the role of charge transport electrodes. The building of such devices requires an in situ growth of CNTs at temperatures where the structure or chemical composition of the functional materials is unaltered. We report that in a chemical vapor deposition process involving an oxidative dehydrogenation reaction of C2H2 with CO2 growth temperatures below 400 °C are achieved. Furthermore, the growth can be performed on versatile materials ranging from metals through oxides to organic materials.
  
  
  

• Structural and electrical properties of fully strained (In,Ga)As field effect transistors with in situ deposited gate stacks
  Posted by Jean-Pierre Locquet
  C. Marchiori, E. Kiewra, J. Fompeyrine, C. Gerl, C. Rossel, M. Richter, J.-P. Locquet, T. Smets, M. Sousa, C. Andersson, and D. J. Webb
  Metal-oxide-semiconductor field-effect transistors 􏰃MOSFETs􏰂 were fabricated with amorphous Al2O3 and HfO2 / SiOx – Si gate stacks, grown by molecular beam deposition. As and In oxides were observed at the Al2O3/In0.17Ga0.83As interface, whereas no oxides were detected on the Si-passivated In0.17Ga0.83As surface after HfO2 deposition. Traces of As were found in both gate stacks. Si-passivated MOSFETs, with a drain current of 2.8 mA / mm at Vg − Vt = 2.0 V , Vd =1.0 V, Ion/Ioff=1E7, and inverse subthreshold slope of 98–120 mV/decade, show superior performance with respect to devices without Si interlayer.
  
  
  

• Transition from turbulent to nearly laminar vortex flow in superconductors with periodic pinning
  Posted by Victor Moshchalkov
  J. Gutierrez, A. V. Silhanek, J. Van de Vondel, W. Gillijns, and V. V. Moshchalkov
  We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex flow transition which manifests itself as a negative differential resistivity.
  
  
  

• Self-organized mode-locking effect in superconductor/ferromagnet hybrids
  Posted by Victor Moshchalkov
  J. Van de Vondel, A. V. Silhanek, V. Metlushko, P. Vavassori, B. Ilic, and V. V. Moshchalkov
  The vortex dynamics in a low-temperature superconductor deposited on top of a rectangular array of micrometer size permalloy triangles is investigated experimentally. We demonstrate the spontaneous formation of two separated rows of vortices and antivortices along each line of connected triangles. The existence of a clear flux-flow regime at zero external field supports this interpretation. Strikingly, the presence of vortex-antivortex rows gives rise to a self-organized synchronized motion of vortices which manifests itself as field independent Shapiro steps in the current-voltage characteristics.
  
  
  

• Type-1.5 Superconductivity
  Posted by Victor Moshchalkov
  Victor Moshchalkov, Mariela Menghini, T. Nishio, Q. H. Chen, A.V. Silhanek, V. H. Dao, L. F. Chibotaru, N. D. Zhigadlo, and J. Karpinski
  We demonstrate the existence of a novel superconducting state in high quality two-component MgB2 single crystalline superconductors where a unique combination of both type-1 and type-2 superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances.
  
  
  

• Symmetry-Induced Giant Vortex State in a Superconducting Film with a Fivefold Penrose Array of Magnetic Pinning Centers
  Posted by Victor Moshchalkov
  R. B. G. Kramer, A.V. Silhanek, J. Van de Vondel, B. Raes, and V.V. Moshchalkov
  A direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained by mapping the local field distribution with a scanning Hall probe microscope. Strikingly, for H = 1.6H1, interstitial and pinned vortices arrange themselves in ringlike structures (‘‘vortex corrals’’) which favor the formation of a giant vortex state at their center.
  
  
  

• Formation of stripelike flux patterns obtained by freezing kinematic vortices
  Posted by Victor Moshchalkov
  A.V. Silhanek, M.V. Milosevic, R. B. G. Kramer, G. R. Berdiyorov, J. Van de Vondel, R. F. Luccas, T. Puig, F. M. Peeters, and V.V. Moshchalkov
  We visualize the formation of flux rivers resulting from a short-range attractive interaction between vortices. This dynamically induced vortex-vortex attraction results from the migration of quasiparticles out of the vortex core (kinematic vortices).
  
  
  

• Controlled Positioning of Carbon Nanotubes by Dielectrophoresis: Insights into the Solvent and Substrate Role
  Posted by Jin Won Seo
  M. Duchamp, K. Lee, B. Dwir, J.W. Seo, E. Kapon, L. Forro and A. Magrez
  We demonstrate the ability to precisely control the deposition of a defined number of carbon nanotubes (CNTs) from solution onto microfabricated electrodes using dielectrophoresis. The solvation shell around the CNTs, exhibiting a high dielectric constant which is possibly larger than the intrinsic dielectric constant of CNTs, is found to play a crucial role in electrophoretic processes. Substrate resistivity is also very important: The spatial repartition of the electric field between the substrate and the microelectrodes leads to deviations from the precise location of the CNTs. A recipe is given for the dielectrophoresis of CNTs which can be extended to other nanowires or nanotubes.
  
  
  

• Second-order nonlinear optical properties of fluorescent proteins for second-harmonic imaging
  Posted by Koen Clays
  Evelien De Meulenaere, Stijn Spaepen, Jos Vanderleyden, Centre of Microbial and Plant Genetics, K.U.Leuven; Marc de Wergifosse, Edith Botek, Benoît Champagne, Laboratoire de Chimie Théorique Appliquée, FUNDP, Namur; Inge Asselberghs, Koen Clays, Department of Chemistry, K.U.Leuven
  The second-order nonlinear optical properties of three fluorescent proteins (FPs) (green, EGFP; yellow, EYFP; and red, DsRed) have been experimentally determined by frequency-resolved femtosecond hyper-Rayleigh scattering. As expected, DsRed, with its lower-energy bandgap between ground and excited state, exhibits the largest intrinsic hyperpolarizability. The anomalously low first hyperpolarizability for the yellow variant has been rationalized in terms of the centrosymmetrical arrangement between the phenolic Tyr203 (Tyr = tyrosine) residue and the chromophoric Tyr66 moiety, leaving as the only effective non-centrosymmetric chromophore for second-order nonlinear effects only the small imidazolinone moiety. The experimental findings are corroborated by high-level computational results and suggest molecular engineering pathways to produce a full rainbow of FPs with enhanced nonlinear optical properties
  
  
  

• Fiber optic SPR biosensing of DNA hybridization and DNA–protein interactions
  Posted by Jeroen Lammertyn
  Jeroen Pollet, Filip Delport, Kris P.F. Janssen,Karolien Jans, Guido Maes,Helge Pfeiffer, Martine Wevers,Jeroen Lammertyn
  In this paper we present a fiber optic surface plasmon resonance (SPR) sensor as a reusable, cost-effective and label free biosensor for measuring DNA hybridization and DNA–protein interactions. This is the first paper that combines the concept of a fiber-based SPR system with DNA aptamer bioreceptors. The fibers were sputtered with a 50 nm gold layer which was then covered with a protein repulsive self-assembled monolayer of mixed polyethylene glycol (PEG). Streptavidin was attached to the PEG's carboxyl groups to serve as a versatile binding element for biotinylated ssDNA. The ssDNA coated SPR fibers were first evaluated as a nucleic acid biosensor through a DNA–DNA hybridization assay for a random 37-mer ssDNA. This single stranded DNA showed a 15 nucleotides overlap with the receptor ssDNA on the SPR fiber. A linear calibration curve was observed in 0.5–5 μM range. A negative control test did not reveal any significant non-specific binding, and the biosensor was easily regenerated. In a second assay the fiber optic SPR biosensor was functionalized with ssDNA aptamers against human immunoglobulin E. Limits of detection (2 nM) and quantification (6 nM) in the low nanomolar range were observed. The presented biosensor was not only useful for DNA and protein quantification purposes, but also to reveal the binding kinetics occurring at the sensor surface. The dissociation constant between aptamer and hIgE was equal to 30.9 ± 2.9 nM. The observed kinetics fully comply with most data from the literature and were also confirmed by own control measurements.
  
  
  
  
  

• Direct room-temperature synthesis of methyl-functionalized Ti-MCM-41 nanoparticles and their catalytic performance in epoxidation
  Posted by Paolo Pescarmona
  Kaifeng Lin, Paolo P. Pescarmonaa, Kristof Houthoofd, Duoduo Liang, Gustaaf Van Tendeloob, Pierre A. Jacobs
  Methyl-functionalized Ti-MCM-41 nanoparticles with a size of 80 to 160 nm (Me-Ti-MCM-41 NP) were directly prepared via a dilute solution route by the co-condensation of tetraethoxysilane and methylalkoxysilanes in sodium hydroxide medium at room temperature. The characterization results showed the existence of ordered hexagonal mesoporous structure and tetrahedral Ti species in the nanoparticles. In the epoxidation of cyclohexene with tert-butyl hydroperoxide and aqueous H2O2, Me-Ti-MCM-41 NP samples displayed higher turnover frequencies (TOFs) for cyclohexene and initial reaction rates compared to Ti-MCM-41 and methyl-functionalized Ti-MCM-41 with normal particle size and to non-functionalized Ti-MCM-41 nanoparticles. Simultaneously, a higher selectivity for cyclohexene epoxide was observed in the case of aqueous H2O2, suggesting that the hydrolysis of cyclohexene epoxide with water is reduced on Me-Ti-MCM-41 NP samples. The improved catalytic behavior of Me-Ti-MCM-41 NP is discussed both in terms of the nanosize and methylation of the surface of the catalyst particles. The regeneration of Me-Ti-MCM-41 NP with tert-butyl hydroperoxide solution was evaluated via washing and calcination approaches.
  
  
  
  
  

• Synthesis and catalytic activity of Ti-MCM-41 nanoparticles
  Posted by Paolo Pescarmona
  Kaifeng Lin, Paolo P. Pescarmona, Hans Vandepitte, Duoduo Liang, Gustaaf Van Tendeloo, Pierre A. Jacobs
  Ti-MCM-41 nanoparticles 80–160 nm in diameter (Ti-MCM-41 NP) were successfully prepared by a dilute solution route in sodium hydroxide medium at ambient temperature. Ti-MCM-41 NP were characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, SEM, TEM, FT-IR, and UV–vis spectroscopy. The characterization results showed the existence of highly ordered hexagonal mesoporous structure and tetrahedral Ti species in Ti-MCM-41 NP. In the epoxidation of cyclohexene with aqueous H2O2, Ti-MCM-41 NP displayed higher conversion and initial reaction rate than a Ti-MCM-41 sample with normal particle size (Ti-MCM-41 LP). Diffusion of the reactants was accelerated and the accessibility to the catalytic Ti species was enhanced in the shorter channels in Ti-MCM-41 NP samples. Ti-MCM-41 NP showed much higher selectivity for cyclohexene oxide compared with Ti-MCM-41 LP, suggesting reduced hydrolysis of cyclohexene oxide with water in the former case. The increased selectivity for cyclohexene oxide can be attributed to the lower concentration of residual surface silanols in Ti-MCM-41 NP and the shorter residence time of epoxide in the shorter mesoporous channels. Ti-MCM-41 NP also appears to be a suitable catalyst in the epoxidation of a bulky substrate, like cholesterol, with tert-butyl hydroperoxide.
  
  
  
  
  

• Fabrication of 3D photonic crystals of ellipsoids: convective self-assembly in a magnetic field
  Posted by Koen Clays
  Tao Ding, Kai Song, Chen-ho Tung and Koen Clays: Advanced Materials, Vol. 21, p. 1936 (2009)
  We have fabricated 3D photonic crystals composed of ellipsoidal particles employing a convective assembly method in the applied magnetic field. The assembled ellipsoids represent a good order with both positional and orientational ordering. As a result, the assembled ellipsoidal superlattice showed strong structural color which is related to the sizes of the ellipsoids. The measured reflection spectra are in accordance with the theoretical simulation. The symmetry of the ellipsoids is lower than that of the spheres, which may break the degeneracy at the W- and U-point of the photonic band structure. Furthermore, this study also provides insight to the self-assembly of submicrometer-sized ellipsoidal particles
  
  
  

• Nano-engineering at two length scales: <20 nm for superparamagnetism, >200 nm for photonic bandgap properties, resulting in Faraday rotation in photonic crystals
  Posted by Koen Clays
  Wim Libaers, Branko Kolaric, Renaud A.L. Vallée, John Wong, Jelle Wouters, Ventsislav K. Valev, Thierry Verbiest and Koen Clays: Colloids and Surfaces A, Vol. 339, p. 13 (2009)
  We have developed a successful strategy towards colloidal photonic crystals with combined optical and magnetic properties derived from nanoscale engineering of these two properties at different length scale. Superparamagnetic properties were imparted by the synthesis of small (< 20 nm) magnetic maghemite nanoparticles. Optical bandgap properties were induced by the convective self-assembly of large (>200 nm) transparent monodisperse silica nanospheres. Insertion of the small magnetic particles after the fabrication of the photonic crystal ensures retention of the photonic bandgap upon imparting magnetic functionality. Comparative Faraday rotation measurements confirm the effect of the magnetic particles in a photonic crystal towards enhancing and tuning magnetic interactions in photonic crystals.
  
  
  

• Better materials for nonlinear optical imaging of cells
  Posted by Koen Clays
  Koen Clays (K.U.Leuven) in collaboration with Harry L. Anderson, University of Oxford, UK: Journal of the American Chemical Society, Vol. 131, p. 2758 (2009)
  Better dyes for COMBINED second-harmonic generation (SHG) AND two-photon fluorescence (TPF) microscopy imaging are reported. TPF results in enhanced spatial resolution, SHG provides additional structural information, both as a result of the nonlinear optical interaction. The dye is based on the highly polarizable porphyrin moiety. This important result was also highlighted in Nature, News and Views, by Prof. Therien, expert in porphyrin chemistry and photophysics, see http://www.nature.com/nature/journal/v458/n7239/full/458716b.html
  
  
  

• Exploiting Particle Shape in Solid Stabilized Emulsions
  Posted by Jan Vermant
  Madivala, Basavaraj; Steven Vandenbril, Fransaer, Jan; Vermant, Jan Soft Matter, 5, 1717-1727 2009)
  Pickering–Ramsden emulsions and other forms of particle stabilized soft materials have received quite some attention recently because of the relative ease of formulation and the possibility to create novel materials. There is, however, a clear need for approaches that are versatile and efficient. In the present work the effect of aspect ratio of particles on the stability of both water-in-oil and oil-in-water emulsions is investigated experimentally. Two types of non-spherical particles are used. Hydrophobic prolate ellipsoids with aspect ratios ranging from 1 to 9 are obtained by stretching polystyrene latex particles. Hydrophilic spindle type hematite particles have been synthesized with aspect ratios ranging from 1 to 6. A strong dependence of emulsion stability on the aspect ratio of the particles is observed. Optical as well as cryogenic scanning electron microscopy are used to visualize the droplet morphology and particulate structure and reveal fairly densely packed monolayers of ellipsoids, consistent with the mechanism of limited coalescence. Yet stable emulsions are only obtained for particles with a sufficient aspect ratio. Surface rheology on planar monolayers demonstrates the pronounced effect of aspect ratio on the surface moduli. The magnitude of the interfacial viscoelastic properties is shown to strongly depend on the aspect ratio at a given surface coverage. This is most probably due to an increased effective coverage and the occurrence of strong attractive shape induced capillary interactions. The dependence of the surface rheological properties on the aspect ratio of the particles rationalizes the observed emulsion stability as the surface rheological properties play a role in the coalescence process. The results demonstrate that interfaces with controlled surface rheology, as obtained by using shape induced capillary forces and packing effects, can be used for the rational design of Pickering emulsions and other types of high interface materials.
  
  
  

• Anisotropy of non-aqueous layered silicate suspensions subjected to shear flow.
  Posted by Jan Vermant
  Mobuchon C M.C. Heuzey, Carreau P.J. , Reddy Naveen K., Vermant J Journal of Rheology, 53(3) 517-538 2009).
  Nonaqueous layered silicate suspensions have a complex rheological behavior due to the presence of a microstructure on multiple length scales, which is sensitive to flow and flow history. In the present work, the flow-induced orientation and anisotropy of the nonequilibrium metastable structures in nonaqueous layered silicate suspensions has been studied using a combination of light scattering, scattering dichroism, and advanced rheometric measurements, including two dimensional small amplitude oscillatory shear (2D-SAOS) flow experiments. The nature of the structures during flow was mainly studied by means of small angle light scattering patterns. Linear dichroism measurements in the vorticity and velocity gradient directions were used to assess the microstructural anisotropy. The changes observed in the vorticity plane developed in the same range of shear rate as the shear-thinning behavior of the suspensions. Scattering dichroism was used to demonstrate that the flow-induced anisotropy was locked in upon cessation of flow. To verify that this also leads to an anisotropy of the rheological properties, the linear viscoelastic moduli were measured using (2D-SAOS) experiments. This new technique proved to be particularly sensitive to the anisotropic nature of the metastable microstructure of organoclay suspensions. Both the flow-induced orientation and larger scale microstructural rearrangements are shown to contribute to the transient rheological response of the nonaqueous layered silicate suspensions. ©2009 The Society of Rheology
  
  
  

• Self-assembly and rheology of ellipsoidal particles at interfaces
  Posted by Jan Vermant
  Madivala, Basavaraj; Fransaer, Jan; Vermant, Jan Langmuir, 25 (5), pp 2718-2728 (2009)
  Colloidal particles confined at liquid interfaces have important applications, for example in the stabilization of emulsions and foams. Also the self-assembly of particles at interfaces offers potential for novel applications and structured particle films. As the colloidal interactions of colloidal particles at interfaces differ from those in bulk, colloidal microstructures can be achieved at an interface which cannot be produced in bulk. In the present work the particle shape, surface charge, and wetting properties are varied, and the resulting self-assembly of particles at a fluid interface is studied. Model monodisperse micrometer-sized ellipsoidal particles were prepared by a mechanical stretching method. These particles were chosen to be well-suited for investigation by optical microscopy. When deposited at an interface between two fluids, shape-induced capillary interactions compete with the electrostatic repulsion. Changing the surface charge and the position at the interface can be used to manipulate the experimentally observed self-assembly process. The initial microstructure of charged ellipsoids at a decane−water interface consists of individual ellipsoids coexisting with linear chains of ellipsoids, connected at their tips. The aggregation behavior in these monolayers was investigated by optical microscopy combined with quantitative image analysis and a dominant tip−tip aggregation was observed. Microstructural information was quantified by calculating the pair-distribution and orientation-distribution functions, as a function of time. Compared to particles at an oil−water interface, particles of the same surface chemistry and charge at an air−water interface seem to have weaker electrostatic interactions, and they also have a different equilibrium position at the interface. The latter leads to differences in the capillary forces. The subsequent change in the balance between electrostatic and capillary forces gave rise to very dense networks having as a typical building block ellipsoids connected at their tips in triangular or flower-like configuration. These networks were very stable and did not evolve in time. The resulting monolayers responded elastically and buckled under compression. Furthermore, the mechanical properties of these monolayers, as measured by surface shear rheology, showed that the monolayer of ellipsoids exhibit a substantial surface modulus even at low surface coverage and can be used to create more elastic monolayers compared to aggregate networks of spheres of the same size and surface properties.
  
  
  

• Reversible gelation of rod-like viruses grafted with thermoresponsive polymers
  Posted by Jan Vermant
  Zhenkun Zhang,; Naveen K. Reddy, Naveen; Pavlik M. Lettinga, Jan Vermant, Eric Grelet Langmuir, 25 (4), pp 2432-2442 (2009)
  The synthesis and selected macroscopic properties of a new model system consisting of poly(N-isopropylacrylamide) (PNIPAM)-coated rod-like fd virus particles are presented. The sticky rod-like colloids can be used to study effect of particle shape on gelation transition, the structure and viscoelasticity of isotropic and nematic gels, and to make both open isotropic as well as ordered nematic particle networks. This model system of rod-like colloids, for which the strength of attraction between the particles is tunable, is obtained by chemically grafting highly monodisperse rod-like fd virus particles with thermoresponsive polymers, e.g. PNIPAM. At room temperature, suspensions of the resulting hybrid PNIPAM-fd are fluid sols which are in isotropic or liquid crystalline phases, depending on the particle concentration and ionic strength. During heating/cooling, the suspensions change reversibly between sol and gel state near a critical temperature of 32 °C, close to the lower critical solution temperature of free PNIPAM. The so-called nematic gel, which exhibits a cholesteric feature, can therefore be easily obtained. The gelation behavior of PNIPAM-fd system and the structure of the nematic gel have been characterized by rheology, optical microscopy and small-angle X-ray scattering.
  
  
  

• Mechanical and electronic properties of vanadium oxide nanotubes
  Posted by Jin Won Seo
  B. Sipos, M. Duchamp, A. Magrez, L. Forró, N. Barišić, A. Kis, J. W. Seo, F. Bieri, F. Krumeich, R. Nesper, and G. R. Patzke
  Vanadium oxide nanotubes with a diameter of 20–100 nm and an aspect ratio of 50–100 were synthesized by hydrothermal method. Young’s modulus of 20–80 GPa was obtained by bending measurements of individual nanotubes using an atomic force microscope. Electrical resistivity and thermopower measurements on a large assembly of nanotubes determined the characteristic energies required to put a charge into a polaronic site (∆Eg=0.20 eV) and to extract and propagate the polaron between neighboring sites (∆Ep=0.09 eV).
  
  
  

• Adsorption of molecular oxygen on the reconstructed β2(2 × 4)-GaAs(0 0 1) surface: A first-principles study
  Posted by Michel Houssa
  M. Scarrozza, G. Pourtois, M. Houssa, M. Caymax, M. Meuris, M.M. Heyns, and A. Stesmans
  In this work, first-principles modeling techniques are used to investigate the mechanism(s) of adsorption of molecular oxygen on the GaAs(0 0 1)-(2 × 4) surface. The reaction of adsorption was modeled using ab-initio molecular dynamics at constant temperature for two thermal regimes, i.e. 300 K and 680 K, respectively. The resulting adsorbate configurations were relaxed using density functional theory and the adsorption energies were subsequently computed. Our results suggest a dominant mechanism of adsorption described by molecular dissociation, followed by oxygen insertion in the Ga–As bonds, bridging Ga–O–As chemical bonds. The electronic properties of the clean reconstructed GaAs(001) surface and the ones obtained after O2 adsorption were computed. It is found that for the most stable adsorbate configuration, where oxygen is incorporated in a Ga–O–As unit, the associated density of electronic states is free of defect levels within the GaAs band gap region.
  
  
  
  
  

• First-principles study of the structural and electronic properties of (100)Ge/Ge(M)O2 interfaces (M=Al, La, or Hf)
  Posted by Michel Houssa
  M. Houssa, G. Pourtois, M. Caymax, M. Meuris, and M.M. Heyns
  The structural and electronic properties of (100)Ge/Ge(M)O2 interfaces, with M=Al, La, or Hf, are investigated using density functional theory. When a Ge atom is substituted by a Hf atom in the GeOx (suboxide) interfacial layer, a Ge–Hf bond is formed due to the fivefold coordination of Hf in the GeOx matrix. The formation of this bond gives rise to a defect level in the upper part of the Ge energy band gap. On the other hand, the incorporation of Al or La in the interfacial layer results only in the formation of Al–O–Ge or La–O–Ge bonds at/near the interface due to the fourfold coordination of these metals in the GeOx matrix. This gives rise to a surface-state free Ge energy band gap. These findings highlight the advantage of lower coordinated metal oxides that tend to form germanate layers in contact with Ge for their potential use as gate stacks in high performance metal-oxide-semiconductor field effect transistors.
  
  
  

• Ge dangling bonds at the (100)Ge/GeO2 interface and the viscoelastic properties of GeO2
  Posted by Michel Houssa
  M. Houssa, G. Pourtois, M. Caymax, M. Meuris, M.M. Heyns, V.V. Afanas’ev and A. Stesmans
  The electronic energy band structure of a (100)Ge/GeO2 interface with a Ge3Ge● center (Ge dangling bond) is calculated using density functional theory. The defect level associated with this dangling bond is found to lie near the middle of the Ge band-gap. Consequently, the Ge dangling bond at this interface should be paramagnetic when the Fermi level is near mid-gap, and it should thus be observed by electron spin resonance (ESR), which appears to be in contradiction with the results reported in V.V. Afanas’ev, Y.G. Fedorenko, and A. Stesmans, Appl. Phys. Lett. 87, 032107 (2005). We point out that the density of Ge3Ge● centers at the (100)Ge/GeO2 interface is possibly at/below ESR detection limit, due to the viscoelastic properties of GeO2, owing for a better stress relaxation at/near the interface, compared to its silicon counterpart.
  
  
  

• Modeling and optimization of a multi-enzyme electrokinetically driven multiplexed microchip for simultaneous detection of sugars
  Posted by Jeroen Lammertyn
  Yegermal Tesfaw Atalay, Pieter Verboven, Steven Vermeir, Nicolas Vergauwe, Bart Nicolaï and Jeroen Lammertyn
  A model-based methodology was developed to optimize microfluidic chips for the simultaneous enzymatic quantification of sucrose, d-glucose and d-fructose in a single microfluidic channel with an integrated optical detection system. The assays were based on measuring the change in concentration of the reaction product NADH, which is stoichiometrically related to the concentration of those components via cascade of specific enzymatic reactions. A reduced order mathematical model that combines species transport, enzyme reaction, and electrokinetic bulk flow was developed to describe the operation of the microfluidic device. Using this model, the device was optimized to minimize sensor response time and maximize signal output by manipulating the process conditions such as sample and reagent volume and flow rate. According to this simulation study, all sugars were quantified within 2.5 min in the optimized microchip. A parallel implementation of the assays can further improve the throughput. In addition, the amount of consumed reagents was drastically reduced compared to microplate format assays. The methodology is generic and can easily be adapted to other enzymatic microfluidic chips.
  
  
  
  

• Three-Dimensional Gas Exchange Pathways in Pome Fruit Characterized by Synchrotron X-Ray Computed Tomography
  Posted by Jeroen Lammertyn
  Pieter Verboven, Greet Kerckhofs, Hibru Kelemu Mebatsion, Quang Tri Ho, Kristiaan Temst, Martine Wevers, Peter Cloetens and Bart M. Nicolaï
  Our understanding of the gas exchange mechanisms in plant organs critically depends on insights in the three-dimensional (3-D) structural arrangement of cells and voids. Using synchrotron radiation x-ray tomography, we obtained for the first time high-contrast 3-D absorption images of in vivo fruit tissues of high moisture content at 1.4-µm resolution and 3-D phase contrast images of cell assemblies at a resolution as low as 0.7 µm, enabling visualization of individual cell morphology, cell walls, and entire void networks that were previously unknown. Intercellular spaces were always clear of water. The apple (Malus domestica) cortex contains considerably larger parenchyma cells and voids than pear (Pyrus communis) parenchyma. Voids in apple often are larger than the surrounding cells and some cells are not connected to void spaces. The main voids in apple stretch hundreds of micrometers but are disconnected. Voids in pear cortex tissue are always smaller than parenchyma cells, but each cell is surrounded by a tight and continuous network of voids, except near brachyssclereid groups. Vascular and dermal tissues were also measured. The visualized network architecture was consistent over different picking dates and shelf life. The differences in void fraction (5.1% for pear cortex and 23.0% for apple cortex) and in gas network architecture helps explain the ability of tissues to facilitate or impede gas exchange. Structural changes and anisotropy of tissues may eventually lead to physiological disorders. A combined tomography and internal gas analysis during growth are needed to make progress on the understanding of void formation in fruit.
  
  
  

• Magnetic field assisted nanoparticle dispersion
  Posted by Johan Martens
  B. Stuyven, Q. Chen, W. Van de Moortel, H. Lipkens, B.Caerts, A. Aerts, L. Giebeler, B. Van Eerdenbrugh, P. Augustijns. G. Van den Mooter, J. Van Humbeeck, J. Vanacken, V. Moshchalkov, J. Vermant en J. A. Martens
  Magnetohydrodynamic nanoparticle dispersion is an energy efficient method to deaggregate nanoparticles, combining hydrodynamic forces of turbulent flow with Lorentz forces generated by a magnetic field.
  
  
  
  
  

• Flow-induced conformational changes in gelatin structure and colloidal (and nanoparticle) stabilization
  Posted by Jan Vermant
  Akbulut M, Reddy NK, Bechtloff B, Sebastian Koltzenburg, Jan Vermant, and Robert K. Prud’homme
  LANGMUIR 24: 9636-9641 (2008)
  
  Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the surface, but moreover, flow can induce changes in the conformation of macromolecules in solution by providing sufficient stresses to perturb the segmental distribution function. However, there are few studies where the effect of flow on macromolecules has been shown to alter the structure of macromolecules adsorbed on surfaces. We have studied how the local energy dissipation alters the adsorption of gelatin onto polystyrene nanoparticles (r = 85 nm). The change in the nature of the adsorbed layer is manifest in the change in the ability of the nanoparticles to resist aggregation. Circular dichroism spectroscopy was used to assess conformational changes in gelatin, and dynamic light scattering was used to assess the colloid stability. Experiments were conducted in a vortex jet mixer where energy density and mixing times have been quantified; mixing of the gelatin and unstable nanoparticles occurs on the order of milliseconds. The adsorption of the gelatin provides steric stabilization to the nanoparticles. We found that the stability of the gelatin-adsorbed nanoparticles increased with increasing mixing velocities: when the mixing velocities were changed from 0.9 to 550 m/s, the radius of the nanoclusters (aggregates) formed 12 h after the mixing decreased from 2620 to 600 nm. Increasing temperature also gave rise to similar trends in the stability behavior with increasing temperature, leading to increasing colloid stability. Linear flow birefringence studies also suggested that the velocity fields in the mixer are sufficiently strong to produce conformational changes in the gelatin. These results suggest that the energy dissipation produced by mixing can activate conformational changes in gelatin to alter its adsorption on the surfaces of nanoparticles. Understanding how such conformational changes in gelatin can be driven by local fluid mechanics and how these changes are related to the adsorption behavior of gelatin is very important both industrially and scientifically.
  
  
  
  

• Particle-stabilized polymer blends
  Posted by Jan Vermant
  Vermant J, Vandebril S, Dewitte C, P. Moldenaers
  RHEOLOGICA ACTA, 47: 835-839 (2008)
  
  The effect of low-volume fractions of nanoparticles on the morphological processes and the rheological properties of immiscible blends are dis cussed. For blends of poly-isobutylene and poly-dimethylsiloxane stabilized by silica particles, particles help to suppress coalescence. Yet, particle bridging of different droplets has also been reported and leads to a slow build up of a gel-like structure, which could interfere with the morphology evolution under flow. We first investigated the importance of this effect under relevant conditions. To further assess the relative importance of the different processes in technically relevant polymer-polymer blends, the effect of carbon black particles on morphological processes-coalescence and break-up-in polyamide and ethylene-ethylene-metylacrylate copolymers will be studied using rheological methods. It will be shown that particles affect coalescence and break-up, suggesting that the effect of particles is linked to their effect on interfacial dynamics.
  
  
  

• Paramagnetic point defects in (100)Si/LaAlO3 structures: Nature and stability of the interface
  Posted by Andre Stesmans
  K. Clemer, A. Stesmans, V.V. Afanas'ev, L.F. Edge and D.G. Schlom
  The atomic nature of the interface in (100)Si/LaAlO3 structures with nanometer-thin amorphous LaAlO3 layers of high dielectric constant (K), deposited directly on clean (100)Si by molecular beam deposition at similar to 100 degrees C, was assessed through probing of paramagnetic point defects. On the as-grown samples K-band electron spin resonance indicated the absence of a Si/SiO2-type interface in terms of the archetypal Si-dangling bond-type Si/SiO2 interface defects (P-bO, P-b1). With no P-b-type defects observed, this state is found to persist during subsequent annealing (1 atm N-2 or 5% O-2 in N-2 ambient) up to the temperature T-an similar to 800 degrees C, referring to a thermally stable abrupt Si/LaAlO3 interface, quite in contrast with other high-K metal oxide/Si structures. However, in the range T-an similar to 800-860 degrees C a Si/SiO2-type interface starts forming as evidenced by the appearance of P-b0 defects and, with some delay in T-an, the EX center-a SiO2 associated defect, attesting to significant structural/compositional modification. The peaking of the defect density versus T-an curves indicates the SiOx nature of the interlayer to break up again upon annealing at T-an >= 930 degrees C, possibly related to crystallization and/or degrading silicate formation. No specific LaAlO3-specific point defects could be traced.
  
  
  

• Electronic structure of GeO2-passivated interfaces of (100)Ge with Al2O3 and HfO2
  Posted by Andre Stesmans
  V. V. Afanas'ev, A. Stesmans, A. Delabie, F. Bellenger, M. Houssa and M. Meuris
  Analysis of internal photoemission and photoconductivity in Ge/thermal germanium oxide/high-dielectric constant oxide (HfO2,Al2O3) structures reveals that the bandgap of the germanium oxide interlayer is significantly lower (4.3 +/- 0.2 eV) than that of stiochiometric GeO2 (5.4-5.9 eV). As a result, the conduction and valence band offsets at the interface appear to be insufficient to block electron and hole injection leading to significant charge trapping in the GeOx/high-kappa oxide stack. Formation of a hydroxyl-rich Ge oxide phase is suggested to be responsible for the modification of the oxide properties.
  
  
  

• P-associated defects in the high-kappa insulators HfO2 and ZrO2 revealed by electron spin resonance
  Posted by Andre Stesmans
  A. Stesmans, K. Clemer and V. V. Afanas'ev
  We report on the observation by electron spin resonance of P-related point defects in nanometer-thick HfO2 films on (100)Si after annealing in the range 500-900 degrees C and in ZrO2 powder - two oxides prominent in current high-kappa insulator research. Based on the principal g matrices and hyperfine tensors inferred from consistent X-, K-, and Q-band spectra simulations and comparison with established P-associated defects in silica, both centers appear similar in nature and are assigned to a P-2-type defect - a P substituting a Hf or Zr atom. Both centers were observed in the monoclinic phase of the high-kappa oxides, with the unpaired electron strongly localized on the P atom. Within the concern about dopant penetration out of Si into the high-kappa layers on top, identification of the dopant-associated defects in the latter appears crucial to which the present basic results provide fundamental access. The centers may operate as detrimental charge trapping sites.
  
  
  

• Primary Si-29 hyperfine structure of E
  Posted by Andre Stesmans
  A. Stesmans, K. Clemer and V.V. Afanas'ev
  Point defects in fumed similar to 7- nm- sized fumed silica nanoparticles have been studied by X-, K-, and Q- band electron spin resonance ( ESR ) following 10- eV irradiation. The E' defects are monitored as a function of post manufacture heat treatment with the sample brought into contact with " bulk" Si/ SiO2 entities at elevated temperatures in vacuum ( T-an= 1005 - 1205 degrees C ), i. e., the presence of an Si/ SiO2 interface. This results in a drastic increase in E' defect density with increasing T-an, enabling us to resolve the primary Si-29 hyperfine ( hf ) structure of the E' centers located in the core region of the nanoparticles. Detailed analysis of the observed hf spectra reveals several items pointing to a modification of the specific network structure of the core region of the nanoparticles. An increased hf splitting of 438 +/- 2 G is observed compared to bulk silica ( 418 +/- 2 G ) indicating that the core part E' centers exhibit a more pyramidal defect structure. Moreover, the increased primary hf splitting indicates that the core of the fumed silica particles is densified, possibly associated with the presence of more low- membered rings in the nm- sized silica network.
  
  
  

• Classification and control of the origin of photoluminescence from Si nanocrystals
  Posted by Andre Stesmans
  S. Godefroo, M. Hayne, M. Jivanescu, A. Stesmans, M. Zacharias, O. I. Lebedev, G. Van Tendeloo and V.V. Moshchalkov
  Silicon dominates the electronics industry, but its poor optical properties mean that III-V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons (do they arise from highly localized defect states or quantum confinement effects?) has been the subject of intense debate ever since. Attention has subsequently shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained. Here we show, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals. Moreover, we show that it is possible to control the origin of the photoluminescence in a single sample: passivation with hydrogen removes the defects, resulting in photoluminescence from quantum-confined states, but subsequent ultraviolet illumination reintroduces the defects, making them the origin of the light again.
  
  
  

• Confinement of surface state electrons in self-organized Co islands on Au(111)
  Posted by Peter Lievens
  Koen Schouteden, Erwin Lijnen, Ewald Janssens, Arnout Ceulemans, Liviu F Chibotaru, Peter Lievens and Chris Van Haesendonck
  We report on detailed low temperature scanning tunneling spectroscopy measurements performed on nanoscale Co islands on Au(111) films. At low coverages, Co islands self-organize in arrays of mono- and bilayer nanoscale structures that often have an hexagonal shape. The process of self-organization is induced by the Au(111) 'herringbone' reconstruction. By means of mapping of the local density of states with lock-in detection, electron standing wave patterns are resolved on top of the atomically flat Co islands. The surface state electrons are observed to be strongly confined laterally inside the Co nanosized islands, with their wavefunctions reflecting the symmetry of the islands. To complement the experimental work, particle-in-a-box calculations were performed. The calculations are based on a newly developed variational method that can be applied to '2D boxes' of arbitrary polygonal shape. The experimental patterns are found to fit nicely to the calculated wavefunctions for a box having a symmetry corresponding to the experimental island symmetry. The small size of the Co islands under study (down to 7.7 nm2) is observed to induce a strong discretization of the energy levels, with very large energy separations between the eigenstates up to several 100 meV. The observed standing wave patterns are identified either as individual eigenstates or as a 'mixture' of two or more energetically close-lying eigenstates of the cobalt island. Additionally, the Co surface state appears not to be limited to mono- and bilayer islands, but this state remains observable for multilayered islands up to five monolayers of Co.
  
  
  

• Tuning the Geometric Structure by Doping Silicon Clusters
  Posted by Peter Lievens
  Philipp Gruene, André Fielicke, Gerard Meijer, Ewald Janssens, Vu Thi Ngan, Minh Tho Nguyen, and Peter Lievens
  Herein we present the vibrational spectra of the small cationic copper- and vanadium-doped silicon clusters SinCu+ and SinV+ (n=6–8). Copper- and vanadium-doped silicon clusters show the same critical size for the transition from endohedral to exohedral structures, which has been rationalized by the similar atomic radii of the dopants.[9] It is thus interestingto investigate whether doping with these two atoms will generate clusters with the same geometric structure.
  
  
  

• Stability and dissociation pathways of doped AunX+ clusters (X = Y, Er, Nb)
  Posted by Peter Lievens
  Nele Veldeman, Ewald Janssens, Klavs Hansen, Jorg De Haeck, Roger E. Silverans and Peter Lievens
  Size dependent stabilities, fragmentation pathways and dissociation energies of a series of gas phase cationic doped gold clusters, AunX+ (3 n 20; X = Y, Er and Nb), and pure Aun+ clusters were investigated in photofragmentation experiments. Size dependent stability patterns were obtained and the branching between monomer and dimer evaporation was studied. For bare gold, the competing neutral monomer and dimer evaporation channels were found to be in agreement with earlier studies. For doped clusters, monomer evaporation is the most likely fragmentation channel with the exception of Au18Y+ and Au20Y+ for which gold dimer evaporation is also observed. Relations between the evaporative activation energies and both the experimental abundances and the fragment yield were derived based on unimolecular rate constants. The dissociation energies from this analysis show an odd–even staggering and enhanced stabilities for certain cluster sizes, in agreement with simple electronic shell model predictions.
  
  
  

• Optical property changes in low-k films upon ultraviolet-assisted curing
  Posted by Johan Martens
  S. Eslava, G. Eymery, P. Marsik, F. Iacopi, C. Kirschhock, K. Maex, J. Martens, M. Baklanov
  Ultraviolet-assisted curing (UV curing) has been applied recently to enhance the mechanical properties of low-k films. Knowledge about which UV energies are most effective is still limited and the consequences of applying the UV-curing process to integrated stacks in on-chip interconnects are unknown. To clarify these open questions, we investigated the optical properties of a SiCOH low-k layer by purged UV spectroscopic ellipsometry in the energy region 2-9 eV. The complex refractive index of the low-k film shows an absorption edge with a superimposed absorption band at 6.4 eV that vanishes upon UV-assisted curing. A comparison with Fourier transform infrared transmission demonstrates that the absorption at 6.4 eV must be attributed to the organic porogens, which also influence the absorption edge. Further analysis reveals the redshift of the absorption edge of silica-based low-k films with the presence of carbon species. The measured optical properties permit simulation of the standing wave pattern of light within the films in differently configured stacks.
  
  
  

• Tunability of pore diameter and particle size of amorphous microporous silica for diffusive controlled release of drug compounds
  Posted by Johan Martens
  C. Aerts, E.Verraedt, R. Mellaerts, A. Depla, P. Augustijns, J. Van Humbeeck, G. Van den Mooter, J. Martens
  Amorphous microporous silica (AMS) materials with variation in microporosity were prepared using an acidcatalyzed sol-gel procedure departing from tetraethylorthosilicate. The silicas were fined to specific particle sizes by crushing and sieving. AMS materials were loaded with 10 wt% ibuprofen either by uptake of molten ibuprofen or by adsorption of ibuprofen from a methylene chloride solution. DSC analysis of ibuprofenloaded AMS confirmed the molecular dispersion of ibuprofen on the silica material. In vitro ibuprofen release from AMS carrier was investigated in simulated intestinal fluid and in a dissolution medium simulating the gastrointestinal tract with simulated gastric fluid followed by simulated intestinal fluid. The release of ibuprofen molecules from the AMS silica carrier is governed by diffusion. The diffusivity of ibuprofen in the investigated series of AMS samples was in the range 10(-14)-10(-11) m(2) s(-1). By adapting the porosity and particle size of AMS, the release could be evenly spread over periods from 3 to 100 h. This flexibility of AMS opens perspectives for designing tailor-made controlled release formulations.
  
  
  

• Characterization of a Molecular Sieve Coating Using Ellipsometric Porosimetry
  Posted by Johan Martens
  S. Eslava, M. Baklanov, C. Kirschhock, F. Iacopi, S. Aldea, K. Maex and J. Martens
  Ellipsometric porosimetry was used to determine the adsorption isotherms of toluene, methanol, and water on b-oriented Silicalite-1 coatings with a thickness of less than ca. 250 nm and to obtain adsorption kinetics. The adsorption isotherms are of sufficient quality to reveal several aspects of the pore structure such as the adsorbate capacity and the adsorbate/framework affinity. The use of a combination of different molecular probes in ellipsometric porosimetry to elucidate the molecular accessibility of Silicalite-1 pores is demonstrated. It is shown that ellipsometric porosimetry is an appropriate technique for probing the influence of aging of the Silicalite-1 coating and of planarization polishing on the porosity, pore accessibility, and adsorbate/framework affinity.
  
  
  

• Solidification of emulsified polymer solutions via phase inversion (SEPPI): A generic way to prepare polymers with controlled porosity
  Posted by Johan Martens
  P. Vandezande, L. Gevers, J. Vermant, J. Martens, PA Jacobs, I. Vankelecom
  Porous polymeric structures with controlled porosity were prepared using a new approach involving solidification of emulsified polymer solutions via phase inversion (SEPPI). The new method starts from a polymeric emulsion for which the presence of nanosized particles or surfactants is crucial. Subsequent solidification of such emulsion is realized by simple contact with a polymer nonsolvent. The resulting solids exhibit spherical pores for which the emulsion droplets act as template. The preparation method allows easy control over pore morphology by tuning a number of easily accessible parameters, mainly at the level of the emulsion itself. A wide variety of polymers, including biocompatible and biodegradable polymers, can thus be turned into porous materials. Two typical applications in controlled release and solvent resistant nanofiltration are presented, illustrating the real practical utility of the presented method. Compared with the commonly used methods to prepare porous polymers, the presented method has a large potential since it (1) is applicable to a wide range of different polymers, (2) shows simply accessible flexibility in structural properties, such as porosity, pore size, pore interconnectivity, and pore wall functionality, (3) involves no chemical reaction in the polymer hardening process, and (4) allows creation of porous materials with an asymmetric structure.
  
  
  

• The use of liquid crystals as electrorheological fluids in microsystems: model and measurements
  Posted by Dominiek Reynaerts
  M. De Volder, K. Yoshida, S. Yokota and D. Reynaerts
  Fluids with controllable flow properties have gained considerable interest in the past few years. Some of these fluids such as magnetorheologic fluids are now widely applied to active dampers and valves. Although these fluids show promising properties for microsystems, their applicability is limited to the microscale since particles suspended in these fluids tend to obstruct microchannels. This paper investigates the applicability of electrorheologic liquid crystals (LCs) in microsystems. Since LCs do not contain suspended particles, they show intrinsic advantages over classic rheologic fluids in micro-applications. This paper presents a novel physical model that describes the static and the dynamic behaviour of electrorheologic LCs. The developed model is validated by comparing simulations and measurements performed on a rectangular microchannel. This assessment shows that the model presented in this paper is able to simulate both static and dynamic properties accurately. Therefore, this model is useful for the understanding, simulation and optimization of devices using LCs as electrorheological fluid. In addition, measurements performed in this paper reveal remarkable properties of LCs, such as high bandwidths and high changes in flow resistance.
  
  
  

• A fast, high stiffness and high-resolution piezoelectric motor with integrated bearing and driving functionality
  Posted by Dominiek Reynaerts
  H. Van Brussel, W. Van de Vijver, M. De Volder, S. Devos and D. Reynaerts
  With growing requirements on the precision of production machines, as expressed by the Taniguchi curves, the need arises for novel actuators that are able to combine high stiffness and high position resolution with high drive speeds. In this paper two novel integrated linear actuation systems with high active stiffness and with the unique ability to provide simultaneously high-resolution slow motion and lower-resolution high-speed motion, based on piezotechnology, are presented.
  Potential applications are stages for novel high-precision abrasive machining (e.g. ultraprecision grinding), lithography (e.g. extreme-UV wafer steppers), positioning devices working in vacuum (e.g. scanning electron microscopy).
  
  
  

• A PDMS lipseal for hydraulic and pneumatic microactuators
  Posted by Dominiek Reynaerts
  M. De Volder, F. Ceyssens, D. Reynaerts and R. Puers
  Recent publications show that hydraulic and pneumatic microactuators offer superior power and force densities at the microscale. The main technological barrier for the development of these actuators is the lack of microseal technologies. These seals must prevent the driving fluid leaking to the outside world without introducing friction. This paper presents a method to fabricate miniature lipseals in batch quantities. A simulation method for the design of these seals is developed and validated experimentally. Hydraulic and pneumatic actuators comprising lipseals have been fabricated and tested. These prototype actuators have an outside diameter of 1.5 mm, and were able to generate forces of 1.2 N at a supply pressure of 1.6 MPa.
  
  
  

• Nominal and effective dosimetry of silica nanoparticles in cytotoxicity assays
  Posted by Jin Won Seo
  D. Lison, L.C.J. Thomassen, V. Rabolli, L. Gonzalez, D. Napierska, J.W. Seo, M. Kirsch-Volders, P. Hoet, C.E.A. Kirschhock, J. Martens
  Because of their small size and large specific surface area (SA), insoluble nanoparticles are almost not affected by the gravitational force and are generally formulated in stable suspensions or sols. This raises, however, a potential difficulty in in vitro assay systems in which cells adhering to the bottom of a culture vessel may not be exposed to the majority of nanoparticles in suspension. J. G. Teeguarden et al., 2007, Toxicol. Sci. 95, 300–312 have recently addressed this issue theoretically, emphasizing the need to characterize the effective dose (mass or number or SA dose of particles that affect the cells) which, according to their model based on sedimentation and gravitation forces, might only represent a very small fraction of the nominal dose. We hypothesized, in contrast, that because of convection forces that usually develop in sols, the majority of the particles may reach the target cells and exert their potential toxicity. To address this issue, we exposed three different cell lines (A549 epithelial cells, EAHY926 endothelial cells, and J774 monocyte-macrophages) to a monodisperse suspension of Stöber silica nanoparticles (SNP) in three different laboratories. Four different end points (lacticodehydrogenase [LDH] release, LDH cell content, tetrazolium salt (MTT), and crystal violet staining) were used to assess the cell response to nanoparticles. We found, in all cell lines and for all end points, that the cellular response was determined by the total mass/number/SA of particles as well as their concentration. Practically, for a given volume of dispersion, both parameters are of course intimately interdependent. We conclude that the nominal dose remains the most appropriate metric for in vitro toxicity testing of insoluble SNP dispersed in aqueous medium. This observation has important bearings on the experimental design and the interpretation of in vitro toxicological studies with nanoparticles.
  
  
  

• Emerging solvent-induced homochirality upon confinement of achiral molecules against a solid surface
  Posted by Steven De Feyter
  N. Katsonis, H. Xu, R. M. Haak, T. Kudernac, Z. Tomovic, S. George, M. Van der Auweraer, A. P. H. J. Schenning, E. W. Meijer, B. L. Feringa, S. De Feyter
  Angew. Chem. Int. Ed., 2008, 47, 4997-5001. We show how solvent-induced homochirality emerges in self-assembled monolayers of achiral molecules, at the liquid-solid interface, by means of scanning tunneling microscopy. The chirality of the solvent directs the macroscopic chirality of the monolayer. The dynamics of the monolayer structure evolving towards homochirality are probed by time-dependent measurements.
  
  
  

• One building block, two different supramolecular surface-confined patterns: concentration in control at the liquid-solid interface
  Posted by Steven De Feyter
  S. Lei, K. Tahara, F. C. De Schryver, M. Van der Auweraer, Y. Tobe, S. De Feyter
  Angew. Chem. Int. Ed., 2008, 47, 2964-2968. The 2D pattern formed by physisorbed dehydrobenzoannulene molecules on a graphite surface depends on their concentrationin solution. The concentration dependence is directly related to the difference in stability between the linear and the honeycomb polymorphs and their respective molecular densities.
  
  
  

• Quantification of the number of DNA molecules on a nanoparticle with single molecule confocal microscopy
  Posted by Jeroen Lammertyn
  F. Delport, J. Hotta, A. Deres, J. Pollet, B. Sels, J. Hofkens, J. Lammertyn
  The development of nanomaterials has been a driving force for many innovative applications in biosensor technology and bio-electronics. Among these nanomaterials, nanoparticles functionalized with biopolymers such as proteins and DNA, are of great interest in the field of life sciences for their diagnostic properties. In this paper we present a method to count and control the number of DNA molecules immobilized at the surface of a single silica nanoparticle of 300nm. Hereto, small DNA primers of 15 bases, labelled with a fluorescent Atto-dye were bound to silica nanoparticles applying EDC/NHS chemistry. First, the average number of DNA molecules per nanoparticle was calculated from fluorescent spectroscopy bulk measurements on a batch of nanoparticles and in the reaction mixture before and after the immobilisation process. Second, individual nanoparticles were isolated and with single molecule confocal microscopy and total internal reflection microscopy, the number of fluorescent DNA molecules was counted. Single molecule detection techniques allow quantification from 1 to 10 fluorescent molecules on a single nanoparticle. A good correspondence was observed between the single molecule detection experiments on individual nanoparticles and the results from the fluorescence bulk measurements.
  
  
  

• Microplate Differential Calorimetric Biosensor for Ascorbic Acid Analysis in Food and Pharmaceuticals
  Posted by Jeroen Lammertyn
  S. Vermeir,B.M. Nicolaï, P. Verboven, P. Van Gerwen, B. Baeten, L. Hoflack, V. Vulsteke,J. Lammertyn
  In this paper we report on the development of a label-free low-volume high-throughput microplate calorimetric biosensor for fast ascorbic acid quantification in food and pharmaceutical products. The sensor is based on microplate differential calorimetry (MiDiCal) technology in which the heat generation, due to the exothermic reaction between ascorbic acid and ascorbate oxidase, is differentially monitored between two neighboring wells of an IC-built wafer. A severe discrepancy is found between expected and observed sensor readings. To investigate the underlying mechanisms of these findings a mathematical model, taking into account the biochemical reactions and diffusion properties of oxygen, ascorbic acid, and ascorbate oxidase, is developed. This model shows that oxygen depletion in the microliter reaction volumes, immediately after injection of sample (ascorbic acid) into the well, causes the enzymatic reaction to slow down. Validation experiments on fruit juice samples, food supplements, and a pain reliever supplemented with ascorbic acid reveal that the designed method correlates well with HPLC reference measurements. The main advantages of the presented biosensor are the low analysis cost due to the low amounts of enzyme and reagents required and the possibility to integrate the device in fully automated laboratory analysis systems for high-throughput screening and analysis.
  
  
  

• Design optimization of an enzymatic assay in an electrokinetically-driven microfluidic device
  Posted by Jeroen Lammertyn
  Y.T. Atalay, P. Verboven, S. Vermeir, N. Vergauwe, F. Delport, B. M. Nicolaı, J. Lammertyn
  Microfluidic systems are increasingly popular for rapid and cheap determinations of enzyme assays and other biochemical analysis. In this study reduced order models (ROM) were developed for the optimization of enzymatic assays performed in a microchip. The model enzyme assay used was b-galactosidase (b-Gal) that catalyzes the conversion of Resorufin b-D-galactopyranoside (RBG) to a fluorescent product as previously reported by Hadd et al. (Anal Chem 69(17): 3407–3412, 1997). The assay was implemented in a microfluidic device as a continuous flow system controlled electrokinetically and with a fluorescence detection device. The results from ROM agreed well with both computational fluid dynamic (CFD) simulations and experimental values. While the CFD model allowed for assessment of local transport phenomena, the CPU time was significantly reduced by the ROM approach. The operational parameters of the assay were optimized using the validated ROM to significantly reduce the amount of reagents consumed and the total biochip assay time. After optimization the analysis time was reduced from 20 to 5.25 min which resulted in 50% reduction in reagent consumption.
  
  
  

• The Cu7Sc Cluster is a Stable s-Aromatic Seven-Membered Ring
  Posted by Peter Lievens
  Tibor Höltzl, Ewald Janssens, Nele Veldeman, Tamás Veszprémi, Peter Lievens, Minh Tho Nguyen
  Density functional theory calculations demonstrate that the global minimum of the Cu7Sc potential energy surface is a seven-membered ring of copper atoms with scandium in its center, yielding a planar D7h structure. Nucleus-independent chemical shifts [NICS(1)zz and NICS(2)zz] show that this cluster has aromatic character, which is consistent with the number of 4s electrons of copper and scandium plus the 3d electrons of scandium satisfying Hückels rule. According to a canonical MO decomposition of NICS(1)zz and NICS(2)zz, the MOs consisting of the 4s atomic orbitals are mainly responsible for the aromatic behavior of the cluster. The electron localizability indicator (ELI-D) and its canonical MO decomposition (partial ELI-D) suggest that a localized basin is formed in Cu7Sc by the copper atoms whereas the two circular localized domains are situated below and above the ring. The planar Cu7Sc cluster can thus be considered as a -aromatic species. These findings agree with the phenomenological shell model.
  
  
  

• Hydrogen-Induced Ostwald Ripening at Room Temperature in a Pd Nanocluster Film
  Posted by Margriet Van Bael
  M. Di Vece, D. Grandjean, M.J. Van Bael, C.P. Romero, X. Wang, S. Decoster, A. Vantomme, and P. Lievens
  The structural and morphological changes occurring in an ensemble of vapor deposited palladium nanoclusters have been studied after several hydrogenation cycles with x-ray diffraction, extended x-ray absorption fine structure spectroscopy, Rutherford backscattering spectrometry, and STM. Initial hydrogenation increased the cluster size, a result that is attributed to hydrogen-induced Ostwald ripening. This phenomenon originates from the higher mobility of palladium atoms resulting from the low sublimation energy of the palladium hydride as compared to that of the palladium metal. The universality of this phenomenon makes it important for the application of future nanostructured hydrogen storage materials.
  
  
  

• Direct Measurements of the Effects of Salt and Surfactant on Interaction Forces between Colloidal Particles at Water-Oil Interfaces.
  Posted by Jan Vermant
  Bum Jun Park, John P. Pantina, Eric M. Furst, Martin Oettel, Sven Reynaert, and Jan Vermant Langmuir (24) pp 1686 - 1694; DOI: 10.1021/la7008804 (2008)
  The forces between colloidal particles at a decane-water interface, in the presence of low concentrations of a monovalent salt (NaCl) and the surfactant sodium dodecyl sulfate (SDS) in the aqueous subphase, have been studied using laser tweezers. In the absence of electrolyte and surfactant, particle interactions exhibit a long-range repulsion, yet the variation of the interaction for different particle pairs is found to be considerable. Averaging over several particle pairs was hence found to be necessary to obtain a reliable assessment of the effects of salt and surfactant. It has previously been suggested that the repulsion is consistent with electrostatic interactions between a small number of dissociated charges in the oil phase, leading to a decay with distance to the power -4 and an absence of any effect of electrolyte concentration. However, the present work demonstrates that increasing the electrolyte concentration does yield, on average, a reduction of the magnitude of the interaction force with electrolyte concentration. This implies that charges on the water side also contribute significantly to the electrostatic interactions. An increase in the concentration of SDS leads to a similar decrease of the interaction force. Moreover, the repulsion at fixed SDS concentrations decreases over longer times. Finally, measurements of three-body interactions provide insight into the anisotropic nature of the interactions. The unique time-dependent and anisotropic interactions between particles at the oil-water interface allow tailoring of the aggregation kinetics and structure of the suspension structure.
  
  
  
  
  

• Antiferromagnetic LaFeO3 thin films and their effect on exchange bias
  Posted by Jean-Pierre Locquet
  JW Seo, EE Fullerton, F. Nolting, A Scholl, J Fompeyrine and JP Locquet
  LaFeO3 in antiferromagnet with a very high Neel temperature (740K) and is a model system to study the magnetic coupling between antiferromagnets and adjacent ferromagnets. In this review paper the growth, structural and magnetic properties of LaFeO3 thin films and their exchange coupling with different ferromagnetic layers are reported.
  
  
  

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  (Phys.org) —Northwestern University researchers have developed a new method for delivering molecules into single, targeted cells through temporary holes in the cell surface. The technique could find applications in drug delivery, cell therapy, and related biological fields.

• Radioactive nanoparticles target cancer cells
  

  Cancers of all types become most deadly when they metastasize and spread tumors throughout the body. Once cancer has reached this stage, it becomes very difficult for doctors to locate and treat the numerous tumors that can develop. Now, researchers at the University of Missouri have found a way to create radioactive nanoparticles that target lymphoma tumor cells wherever they may be in the body. Michael Lewis, an associate professor of oncology in the MU College of Veterinary Medicine, says being able to target secondary tumors is vital to successfully treating patients with progressive cancers.

• Scientists uncover how grapefruits provide a secret weapon in medical drug delivery
  

  (Phys.org) —Grapefruits have long been known for their health benefits, and the subtropical fruit may revolutionize how medical therapies like anti-cancer drugs are delivered to specific tumor cells. University of Louisville researchers have uncovered how to create nanoparticles using natural lipids derived from grapefruit, and have discovered how to use them as drug delivery vehicles. UofL scientists Huang-Ge Zhang, D.V.M., Ph.D., Qilong Wang, Ph.D., and their team today (May 21, 2013), published their findings in Nature Communications.

• Tailoring optical processors: Arranging nanoparticles in geometric patterns allows for control of light with light
  

  Rice University scientists have unveiled a robust new method for arranging metal nanoparticles in geometric patterns that can act as optical processors that transform incoming light signals into output of a different color. The breakthrough by a team of theoretical and applied physicists and engineers at Rice's Laboratory for Nanophotonics (LANP) is described this week in the Proceedings of the National Academy of Sciences.

• How gold nanoparticles can help fight ovarian cancer
  

  Positively charged gold nanoparticles are usually toxic to cells, but cancer cells somehow manage to avoid nanoparticle toxicity. Mayo Clinic researchers found out why, and determined how to make the nanoparticles effective against ovarian cancer cells. The discovery is detailed in the current online issue of the Journal of Biological Chemistry.

• Researchers perform fastest measurements ever made of ion channel proteins
  

  The miniaturization of electronics continues to create unprecedented capabilities in computer and communications applications, enabling handheld wireless devices with tremendous computing performance operating on battery power. This same miniaturization of electronic systems is also creating new opportunities in biotechnology and biophysics.

• Researchers develop method to inkjet print highly conductive, bendable layers of graphene
  

  (Phys.org) —Imagine a bendable tablet computer or an electronic newspaper that could fold to fit in a pocket.

• Advance in nanotech gene sequencing technique
  

  (Phys.org) —The allure of personalized medicine has made new, more efficient ways of sequencing genes a top research priority. One promising technique involves reading DNA bases using changes in electrical current as they are threaded through a nanoscopic hole.

• Faster, stronger, lighter: New technique advances carbon-fiber composites
  

  These days, aerospace engineering is all about the light stuff: building airplanes with lighter wings, fuselage and landing gear in an effort to reduce fuel costs.

• Engineers' nanoantennas improve infrared sensing
  

  (Phys.org) —A team of University of Pennsylvania engineers has used a pattern of nanoantennas to develop a new way of turning infrared light into mechanical action, opening the door to more sensitive infrared cameras and more compact chemical-analysis techniques.

• Kinks and curves at the nanoscale
  

  One of the basic principles of nanotechnology is that when you make things extremely small—one nanometer is about five atoms wide, 100,000 times smaller than the diameter of a human hair—they are going to become more perfect.

• How nanotechnology could keep your heart healthy
  

  Since the heart is such a delicate and critical organ, clinicians usually opt not to intervene with the dead cells that remain after a heart attack or cardiac disease. "But we think that all heart attacks deserve some kind of treatment because it puts so much stress on the rest of the heart," said Thomas Webster, professor and chair of the Department of Chemical Engineering. Even a square centimeter of dead heart tissue can put significant strain on the rest of the heart, which has to pick up the slack, he said.

• Research improves dry lubricant used in machinery and biomedical devices
  

  Nearly everyone is familiar with the polytetrafluoroethylene (PTFE), otherwise known as Teflon, the brand name used by the chemical company DuPont. Famous for being "non-sticky" and water repellent, PTFE is a dry lubricant used on machine components everywhere, from kitchen tools and engine cylinders to space and biomedical applications.

• Stacking 2-D materials produces surprising results
  

  (Phys.org) —Graphene has dazzled scientists, ever since its discovery more than a decade ago, with its unequalled electronic properties, its strength and its light weight. But one long-sought goal has proved elusive: how to engineer into graphene a property called a band gap, which would be necessary to use the material to make transistors and other electronic devices.

• Graphene-boron mix shows promise for lithium-ion batteries
  

  Frustration led to revelation when Rice University scientists determined how graphene might be made useful for high-capacity batteries.

• Researchers report first fully integrated artificial photosynthesis nanosystem
  

  (Phys.org) —In the wake of the sobering news that atmospheric carbon dioxide is now at its highest level in at least three million years, an important advance in the race to develop carbon-neutral renewable energy sources has been achieved. Scientists with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have reported the first fully integrated nanosystem for artificial photosynthesis. While "artificial leaf" is the popular term for such a system, the key to this success was an "artificial forest."

• DNA-guided assembly yields novel ribbon-like nanostructures
  

  (Phys.org) —Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have discovered that DNA "linker" strands coax nano-sized rods to line up in way unlike any other spontaneous arrangement of rod-shaped objects. The arrangement-with the rods forming "rungs" on ladder-like ribbons linked by multiple DNA strands-results from the collective interactions of the flexible DNA tethers and may be unique to the nanoscale. The research, described in a paper published online in ACS Nano, a journal of the American Chemical Society, could result in the fabrication of new nanostructured materials with desired properties.

• Snake's ultra-black spots may aid high-tech quest
  

  Scientists have identified nanostructures in the ultra-black skin markings of an African viper which they said Thursday could inspire the quest to create the ultimate light-absorbing material.

• Carbon in a twirl: The science behind a self-assembled nano-carbon helix
  

  Nanotechnology draws on the fabrication of nanostructures. Scientists have now succeeded in growing a unique carbon structure at the nanoscale that resembles a tiny twirled mustache. Their method might lead the way to the formation of more complex nano-networks. Researchers of the Electronic Properties of Materials Group at the Faculty of Physics (University of Vienna) and their international collaborators have published their results in the new open-access journal of the Nature Publishing group, Scientific Reports.

• Moth-inspired nanostructures take the color out of thin films
  

  Inspired by the structure of moth eyes, researchers at North Carolina State University have developed nanostructures that limit reflection at the interfaces where two thin films meet, suppressing the "thin-film interference" phenomenon commonly observed in nature. This can potentially improve the efficiency of thin-film solar cells and other optoelectronic devices.

• Nanotechnology could help fight diabetes: Injectable nanogel can monitor blood-sugar levels, secrete insulin when needed
  

  Injectable nanoparticles developed at MIT may someday eliminate the need for patients with Type 1 diabetes to constantly monitor their blood-sugar levels and inject themselves with insulin.

• Ultraresponsive magnetic nanoscavengers for next generation water purification
  

  (Phys.org) —Among its many talents, silver is an antibiotic. Titanium dioxide is known to glom on to certain heavy metals and pollutants. Yet other materials do the same for salt. In recent years, environmental engineers have sought to disinfect, depollute, and desalinate contaminated water using nanoscale particles of these active materials. Engineers call them nanoscavengers. The hitch from a technical standpoint is that it is nearly impossible to reclaim the nanoscavengers once in the water.

• 40-year-old prediction confirmed: First direct proof of Hofstadter butterfly fractal observed in moire superlattices
  

  A team of researchers from Columbia University, City University of New York, the University of Central Florida (UCF), and Tohoku University and the National Institute for Materials Science in Japan, have directly observed a rare quantum effect that produces a repeating butterfly-shaped energy spectrum, confirming the longstanding prediction of this quantum fractal energy structure, called Hofstadter's butterfly. The study, which focused on moiré-patterned graphene, is published in the May 15, 2013, Advance Online Publication (AOP) of Nature.