Scalable bottom‐up assembly of suspended carbon nanotube and graphene devices by dielectrophoresis

Bottom‐up assembly by dielectrophoresis (DEP) has emerged in recent years as a viable alternative to conventional top–down fabrication of electronic devices from nanomaterials, particularly carbon nanotubes and graphene. Here, we demonstrate how this technique can be extended to fabricate devices containing carbon nanotubes and graphene suspended between two electrodes over a back‐gate electrode. The suspended device geometry is critical for the development of nano‐electromechanical devices and to extract maximum performance out of electronic and optoelectronic devices. This technique allows for parallel assembly of devices over large scale. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Poly(sodium styrene sulfonate)-b-poly(methyl methacrylate) diblock copolymers through direct atom transfer radical polymerization: Influence of hydrophilic–hydrophobic balance on self-organization in aqueous solution

A series of poly(sodium styrene sulfonate)-b-poly(methyl methacrylate), PSSNa-b-PMMA, amphiphilic diblock copolymers have been synthesized through atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in N,N-dimethylformamide/water mixtures, starting from a PSSNa macroinitiator. The kinetics of the polymerization was followed by ¹H NMR, while the chemical composition of the copolymers was verified by a variety of techniques, such as ¹H NMR, FTIR and TGA. The MMA content of the copolymers ranges from 0 up to 60 mol%, while the number–average molecular weight of the PSSNa macroinitiator was 9000 g/mol. The self-association of the diblock copolymers in aqueous solution was compared to the respective behavior of similar random P(SSNa-co-MMA) copolymers through optical density measurements, pyrene fluorescence probing, dynamic light scattering and surface tension measurements. It is shown that the diblock copolymers form micellar structures in water, characterized by an increasing hydrophobic character and a decreasing size as the length of the PMMA block increases. These micelle-like structures turn from surface inactive to surface active as the length of the PMMA block increases. Moreover, contrary to the MMA-rich random copolymers, the respective diblock copolymers form water insoluble polymer/surfactant complexes with cationic surfactants such as hexadecyltrimethyl ammonium bromide (HTAB), leading to materials with antimicrobial activity.     

Central Charge Extended Supersymmetric Structures for Fundamental Fermions Around Non-Abelian Vortices

Fermionic zero modes around non-abelian vortices are shown that they constitute two N = 2, d = 1 supersymmetric quantum mechanics algebras. These two algebras can be combined under certain circumstances to form a central charge extended N = 4 supersymmetric quantum algebra. We thoroughly discuss the implications of the existence of supersymmetric quantum mechanics algebras, in the quantum Hilbert space of the fermionic zero modes.     

Generalized entropic structures and non-generality of Jaynes’ Formalism

The extremization of an appropriate entropic functional may yield to the probability distribution functions maximizing the respective entropic structure. This procedure is known in Statistical Mechanics and Information Theory as Jaynes’ Formalism and has been up to now a standard methodology for deriving the aforementioned distributions. However, the results of this formalism do not always coincide with the ones obtained following different approaches. In this study we analyse these inconsistencies in detail and demonstrate that Jaynes’ formalism leads to correct results only for specific entropy definitions.     

Comparative study of electrostatic binding vs. complexation of Cu2+ ions with water‐soluble polymers containing styrene sulphonic acid and/or maleic acid units or their sodium salt forms

The interaction of Cu²⁺ ions with the homopolymer poly(styrene sulfonic acid) (PSSH), as well as with the copolymers of maleic acid (MAc) with styrene sulfonic acid (SSH) or vinyl acetate (VAc), was investigated in dilute aqueous solution through turbidimetry, potentiometry, viscometry, and spectrophotometry in the visible region. Cu²⁺ ions were introduced either through neutralization with Cu(OH)₂ of the acid form of the (co)polymers (PSSH, P(SSH‐co‐MAc) and P(VAc‐co‐MAc)) or through mixing of the sodium salt form of the (co)polymers (PSSNa, P(SSNa‐co‐MANa) and P(VAc‐co‐MANa)) with CuSO₄. Turbidimetry, potentiometry, and spectrophotometry revealed that the first carboxylic group of MAc or both carboxylate groups of MANa are involved in the complexation with Cu²⁺ ions when neutralization with Cu(OH)₂ or mixing with CuSO₄ are applied, respectively. The increased values of the reduced viscosity observed mainly at the first stages of neutralization of P(VAc‐co‐MAc) with Cu(OH)₂ indicate that interchain polymer‐Cu²⁺ complexation takes possibly place. Finally, the spectrophotometric behavior observed upon neutralization of P(SSH‐co‐MAc) with Cu(OH)₂ or mixing of P(SSNa‐co‐MANa) with CuSO₄ revealed that the strength of counterion binding by the sulfonate groups is, in fact, comparable with the complexation of Cu²⁺ ions with the carboxylate groups of MAc. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1149–1158, 2008     

De Sitter cosmic strings and supersymmetry

We study massive spinor fields in the geometry of a straight cosmic string in a de Sitter background. We find a hidden N = 2 supersymmetry in the fermionic solutions of the equations of motion. We connect the zero mode solutions to the heat-kernel regularized Witten index of the supersymmetric algebra.     

Plasmon‐enhanced Raman scattering by suspended carbon nanotubes

We report plasmon‐enhanced Raman scattering of the order of 10³ by a metallic carbon nanotube partially suspended inside a near‐field cavity. The tube is part of a small bundle, and is interfaced with an Au nanodisc dimer using a recently developed assembly scheme based on dielectrophoretic deposition. Spatially resolved Raman measurements with two excitation wavelengths and two orthogonal polarizations confirm that the enhancement arises from a 65 nm long suspended tube segment. We show that the orientation of the tube inside the cavity can be as effective for generating enhancement as placing the nanotube precisely in a plasmonic hotspot. Position and shape of the G‐peak show that the suspended part of the tube is free of strain and doped with a Fermi energy shift ≤40 meV. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Kaluza-Klein pistons with noncommutative extra dimensions

We calculate the scalar Casimir energy and Casimir force for an ℝ³ × N Kaluza-Klein piston setup in which the extra-dimensional space N contains a noncommutative two-dimensional sphere S _fz. We study the cases with T ^d ×S _fz and S _fz as the extra-dimensional spaces, where T ^d is the d-dimensional commutative torus, and examine the validity of the results and the regularization obtained in the piston setup in each case. We examine the Casimir energy with one-loop corrections for one piston chamber due to the self-interacting scalar field in the noncommutative geometry. We compute with some approximations. We compare the obtained results with the results of analogous computations for the Minkowski space-time M ^D . In conclusion, we discuss the stabilization of the extra-dimensional space in the piston setup.