Quantum Hall effect in twisted bilayer graphene

We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling.     

Vertical growth of Ge nanowires from biotemplated Au nanoparticle catalysts

Semiconductor nanowires are being actively investigated because of their unique physical properties and potential applications in nanoelectronics and optoelectronic devices. However, current hurdles for device integration include the lack of control over the orientation, location, and packing density of nanowires. This communication presents for the first time the use of a unique, bottom-up approach for the catalyzed growth of semiconductor nanowires via biological templating. High-density, vertically oriented growth of Ge nanowires with monodispersed diameters and spacings was achieved through patterning of very small sized (5-20 nm) Au nanoparticles using bacterial surface-layer proteins as a template. We envision the applicability of this biotemplating approach to a variety of nanowires and substrate materials.     

Functional PEG-modified thin films for biological detection

We report a general procedure to prepare functional organic thin films for biological assays on oxide surfaces. Silica surfaces were functionalized by self-assembly of an amine-terminated silane film using both vapor- and solution-phase deposition of 3'-aminopropylmethyldiethoxysilane (APMDES). We found that vapor-phase deposition of APMDES under reduced pressure produced the highest quality monolayer films with uniform surface coverage, as determined by atomic force microscopy (AFM), ellipsometry, and contact angle measurements. The amine-terminated films were chemically modified with a mixture of carboxylic acid-terminated poly(ethylene glycol) (PEG) chains of varying functionality. A fraction of the PEG chains (0.1-10 mol %) terminated in biotin, which produced a surface with an affinity toward streptavidin. When used in pseudo-sandwich assays on waveguide platforms for the detection of Bacillus anthracis protective antigen (PA), these functional PEG surfaces significantly reduced nonspecific binding to the waveguide surface while allowing for highly specific binding. Detection of PA was used to validate these films for sensing applications in both buffer and complex media. Ultimately, these results represent a step toward the realization of a robust, reusable, and autonomous biosensor.     

Kinetic Study of the Thermopolymerization of Furfuryl Methacrylate (FM) by Mathematical Modeling, 2–Moments of Molecular Size Distribution of the Primary Chains in the Networks

The formation kinetics and structure of three‐dimensional networks in free radical polymerization of FM thermally initiated at high temperature are studied by analysis of zero and first‐order moments of molecular size distribution of primary chains (MSDPC) in the networks. Zero‐order moment values of MSDPC reveal that the system elapses as a living radical polymerization. Also, by means of the analysis of these moments and the first‐order ones of MSDPC, the sigmoidal shape of polymerization kinetic curves can be explained. On the other hand, the results of average crosslink density obtained using moment values of MSDPC suggest that this parameter does not change with polymerization temperature.