Synthesis of Nucleobase‐Functionalized Carbon Nanotubes and Their Hybridization with Single‐Stranded DNA

For the first time ssDNA (25‐aptamer of mixed dA, dT, dG, and dC) was wrapped around functionalized single‐walled carbon nanotubes (SWCNTs), whose external surfaces were attached to multiple triazole‐(ethylene glycol)‐dA ligands. This method of hybridization involved the formation of hydrogen bonds between dT of ssDNA and dA of functionalized SWCNTs. It deviates from the reported π–π stacking between the nucleobases of DNA and the external sidewalls of nanotubes. The structural properties of the functionalized SWCNTs and its ssDNA complex were characterized by spectroscopic (including CD and Raman), thermogravimetric, and microscopic (TEM) methods. The results thus obtained establish a new platform of DNA delivery by use of nanotubes as a new vehicle with great potential in biomedical applications and drug development.     

A facile route to regular and nonregular dot arrays by integrating nanoimprint lithography with sphere‐forming block copolymer directed self‐assembly

Nanoimprint lithography is used to create large‐area two‐dimensional prepatterns with tunable topographic heights in a resist layer. The resist prepatterns are applied to direct the self‐assembly of sphere‐forming polystyrene‐block‐polydimethylsiloxane block copolymers so as to form sparse nonregular nanodot arrays with flexible pattern layouts from high‐topography prepattern or dense regular nanodot arrays with a multiplicative pattern density from low‐topography prepattern. By precisely controlling the topographic height in substrate prepatterns, the origin of directed self‐assembly of block copolymer spheres using low‐topography prepattern is found to be topographic contrast. High‐fidelity pattern transfer from spherical block copolymer nanotemplates to functional materials indicates a promising route to ultrahigh density nanodevices. Bit‐patterned media over 1 teradot/in on a 2.5‐inch disk are fabricated, thus presenting future magnetic data storage media with great areal density growth potential. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 361–367     

A novel method of supporting gold nanoparticles on MWCNTs： Synchrotron X-ray reduction

Gold nanoparticles decorating the surface of multiwalled carbon nanotubes （MWCNTs） are prepared by photochemical reduction. The gold clusters form different interesting geometrical faceted shapes in accordance to time duration of synchrotron X-ray irradiation. The shape of nanogold could be spherical, rod-like, or triangular. Carbon nanotubes serve as optimal templates for the heterogeneous nucleation of gold nanocrystals. These nanocrystal structures are characterized by transmission electron microscope （TEM） and element analysis by energy dispersive spectroscopy （EDS）. 2007 Chinese Society of Particuology and Institute of Process Engineering,Chinese Academy of Sciences. Published by Elsevier B.V.     

Growth and characterization of DyP/GaAs and DyAs/GaAs-based heterostructures and superlattices

Details of the structural and electrical properties of epitaxial DyP/GaAs and DyAs/GaAs is reported. DyP is lattice matched to GaAs, with a room temperature mismatch of less than 0.01%. DyAs, on the other hand, has a mismatch of nearly 2.4%. Both DyP and DyAs have been grown by solid source MBE using custom designed group V thermal cracker cells and group III high-temperature effusion cells. High-quality DyP and DyAs epilayers, as determined by XRD, TEM, and AFM analysis, were obtained for growth temperatures ranging from 500°C to 600°C with growth rates between 0.5 and 0.7 μm/h. The DyP epilayers are n-type with measured electron concentrations of the order of 3×10²⁰ to 4×10²⁰ cm⁻³, with room temperature mobilities of 250–300 cm²/V s, and with a barrier height of 0.75 eV to GaAs. The DyAs epilayers are also n-type with concentration of 1×10²¹ to 2×10²¹ cm⁻³, with mobilities between 25 and 40 cm²/V s. DyP is stable in air with no apparent oxidation taking place, even after months of ambient exposure to untreated air.     

High‐temperature synthesis of Rb2MnP2S6 in molten salt medium

Transparent yellow plates of rubidium manganese hexa­thio­diphosphate, Rb₂MnP₂S₆, were synthesized in molten RbBr. The compound is isotypic to other compounds of the type A₂MP₂Q₆ (A = K, Rb, Cs; M = Mn, Fe; Q = S, Se). Its structure can be viewed as columns of face‐sharing S₆ polyhedra parallel to the a axis, interconnected by Rb⁺. The S₆ polyhedra are centered alternately by Mn (in octahedral coordination) and P₂ units (in trigonal antiprisms). The Mn atom and P₂S₆ group lie on centers of symmetry.     

A compact synchrotron‐based transmission X‐ray microscope

A compact transmission X‐ray microscope has been designed and implemented based on a cylindrical symmetry around the optical axis that sharply limits the instabilities due to thermal mechanical drift. Identical compact multi‐axis closed‐loop actuation modules drive different optical components. The design is modular and simplifies the change of individual parts, e.g. the use of different magnification and focusing devices. This compact instrument can be easily transported between laboratory and synchrotron facilities and quickly put into operation. An automated alignment mechanism simplifies the assembly of different modules after transportation. After describing the design details, the results of the first tests are presented.     

Roles of interface and oxide trap density in the kinked current behavior of Al/SiO2/Si(p) structures with ultra-thin oxides

A clear current kinked phenomenon was observed in Al/SiO₂/Si(p) structures with nanoscale (<2.5 nm) SiO₂ in a forward biased region. It was found that the kinked points are dependent on oxide thickness and are not the same as flat-band voltages. A model regarding the oxide voltage dropping efficiency with the consideration of interface trap density ( $D_{\mathrm{it}}$ ) and effective charge number density ( $Q_{\mathrm{eff}}/q$ ) was proposed for the observation. It is noted that the kinked point is severely affected by the oxide quality and uniformity. However, Al/SiO₂/Si(n) structures in a forward biased region do not exhibit this current kinked phenomenon because the dropping behavior of oxide is absolutely different from Al/SiO₂/Si(p) structures.     

Design consideration of monolithic millimeter-wave barrier varactor diode frequency multiplier arrays

A new device structure for highly efficient frequency tripling in the millimeter and submillimeter wavelength regions is presented. The Barrier-Intrinsic-N⁺ (BIN) diode structure [1,2] is modified for highly efficient millimeter- and submillimeter-wave frequency tripling device to be employed into the monolithic back-to-back diode frequency tripler array. The modified BIN diode structures have series resistances of a few ohms and cut-off frequencies in the terahertz range. The modified BIN diode structures have weaker C-V nonlinearities than the BIN diode structure does, however, the modified BIN structures have much higher intrinsic cut-off frequencies than does the BIN counterpart. The C-V nonlinearity, capacitance ratio, breakdown voltage, series resistance and cut-off frequency of this new device structure will be discussed in this paper. In addition, the calculated high-frequency performance of this device using a large-signal nonlinear circuit model will be presented in this paper. The operation and performance of the monolithic diode-grid frequency tripler arrays employing large numbers of the modified BIN diodes will also be discussed in this paper.