High mobility n-channel single-crystal field-effect transistors based on 5,7,12,14-tetrachloro-6,13-diazapentacene

Heteroaromatic oligomer 5,7,12,14-tetrachloro-6,13-diazapentacene (TCDAP) was characterized and assessed as n-channel material in field-effect transistor applications. A single-crystal transistor based on TCDAP as the channel material exhibits a very high electron mobility of 3.39 cm(2) V(-1) s(-1) and an on/off ratio of ～1.08 × 10(4) respectively.     

Synergistic enhanced photocatalytic and photothermal activity of Au@TiO2 nanopellets against human epithelial carcinoma cells

The photocatalytic and plasmonic photothermal cancer cell-killing activity of the metallic Au-capped TiO(2) (Au@TiO(2)) composite colloidal nanopellets has been investigated on HeLa cells under UV-visible (350-600 nm) light irradiation. The Au@TiO(2) composite nanopellets with the uniform Au-capped TiO(2) structure were successfully synthesized by simple reduction of HAuCl(4) on the surface of TiO(2) nanoparticles. The morphological structure and surface properties of Au@TiO(2) were characterized by using UV-visible absorption spectroscopy, TEM, SEM, XPS, EDX and XRD analyses. The formation of hydroxyl radicals (˙OH) was confirmed by photoluminescence (PL) spectra. The photocatalytic and photothermal cell-killing activity of the Au@TiO(2) nanopellets was found to vary with the molar ratio of Au to TiO(2). The direct involvement of the metal particles in mediating the electron transfer from the photoexcited TiO(2) under the band gap excitation is considered to carry out the efficient photocatalytic reaction on the cells. The plasmonic absorption spectra of Au@TiO(2) suspensions were also measured for the evaluation of photothermal cell killing. The charge separation, the interfacial charge-transfer and photothermal activity promoted the photocatalytic-photothermal cancer-cell killing more than TiO(2) alone. The cytotoxic effect of Au@TiO(2) nanopellets with low concentration of gold (TiO(2) : Au molar ratio > 1 : 1) was found to be 100%, whereas that of the commercial TiO(2) (P25) was ca. 50%. The comparative study of the cell viability using Au alone and TiO(2) alone revealed that the synergistic effect of photocatalytic hydroxyl radical formation and Au-plasmonic photothermal heat generation plays a vital role in the cancer cell killing. A plausible mechanism was also proposed for photocatalytic cancer cell killing based on the obtained results.     

Bioactive isocoumarins from a terrestrial Streptomyces sp. ANK302

Four isocoumarins have been isolated from the terrestrial Streptomyces sp. ANK302, namely 6,8-dimethoxy-3-methylisocoumarin (1), 6,8-dihydroxy-3-methylisocoumarin (2), 6,8-dihydroxy-7-methoxy-3-methylisocoumarin (3), and 6,7,8-trimethoxy-3-methylisocoumarin (4). Compound 1 is a new naturally-occurring isocoumarin, and 2 was isolated as a new bacterial product. The structures 1-4 were deduced from high resolution mass, 1D and 2D NMR spectra and by comparison with related compounds from the literature. Compound 2 showed a strong zoosporicidal activity at a concentration of 5 microg/mL against a phytopathogenic oomycete, Plasmopara viticola, and 1 was active against     

Electrically conducting film of silver sub-micron particles as mechanical and electrical interfaces for transfer printed micro- and nano-pillar devices

In this paper we report a novel application of electrically conductive film (ECF) of Ag sub-micron particles that includes both isotropic and anisotropic film technologies in providing simultaneous electrical contact and mechanical anchor between fracture transfer-printed (1-D) single crystal semiconductor micro- and nano-pillars and a carrier substrate. We assembled silver sub-micron particles (AgSP) monolayers with varying particle diameters and investigated their optical and electrical characteristics prior to their incorporation into thermoplastic polymers. It was found that transfer-printing of the Si micropillar arrays, into electrically conductive thermoplastic receiver substrates, made of films of AgSP/PMMA blends atop metallic substrates could be effectively achieved to yield electrically interfaced 1-D Si micropillar arrays with retention of their orientation and integrity according to the SEM images. The carrier substrate can potentially be reused to generate additional Si micropillar arrays that can be similarly harvested.     

Fabrication of Rh based solid-solution bimetallic alloy nanoparticles with fully-tunable composition through femtosecond laser irradiation in aqueous solution

Many late transition binary alloy nanoparticles (NPs) have been fabricated through a wide variety of techniques. Various steps are involved in the fabrication of such NPs. Here, we used a simple and green route to fabricate solid-solution Rh–Pd and Rh–Pt bimetallic alloy NPs through femtosecond laser irradiation in a solution without any chemicals like reducing agents. X-ray diffraction (XRD) peaks of NPs obtained in the solutions with different ratios of Rh–Pd and Rh–Pt ions monotonically varied from the position of pure Rh to those of Pd and to Pt which respectively indicated that these NPs were alloy. Composition of fabricated NPs was fully tuned over the entire range of Rh_1?x –Pd _x , and Rh_1?x –Pt _x with varying the mixing ratio of metal ions in the solution. Studies of Rh–Pd and Rh–Pt solid-solution system suggest that the alloy formation occurs through the nucleation of Rh and then followed by the diffusion of Rh, Pd and Rh, Pt to form a homogeneous alloy. The variety of average size of the alloy NPs for different compositions could be attributed to different reduction rate and surface energies of metal ions. Our result implies that femtosecond laser irradiation in aqueous solution is one of the potential methodologies to form multimetallic solid-solution alloy NPs with fully tunable composition.     

Issues on nanoimprint lithography with a single-layer resist structure

We summarize our key developments in nanoimprint lithography (NIL) that employs a single layer resist lift-off process: lowering of the imprint temperature (for thermal imprint) and pressure, achieving uniform resist thickness and low residual resist layer thickness in the trenches, and eliminating metal ‘rabbit ears’ for the single-layer lift-off. In thermal NIL, our requirements for lower operating temperature and pressure motivated us to develop an alternative resist that is a viscous fluid at room temperature and cures at a lower temperature of 70 °C than the operating temperature of the conventional thermal NIL (≈200 °C). For UV NIL, we devised a method to dispense the resist onto a hydrophobic mold and use the hydrophilic substrate surface to spread the resist via surface wetting to engineer a continuous and uniform film. We also explored the use of Si(110) substrates as molds to produce features with perfectly vertical side walls, and the use of aqua regia to directly etch away rabbit ears. PACS 86.65.+h; 81.16.Nd; 81.16.Rf     

Ultra-smooth platinum surfaces for nanoscale devices fabricated using chemical mechanical polishing

A technique involving two steps of chemical mechanical polishing (CMP) has been developed to produce ultra-smooth metal surfaces with an RMS roughness better than 0.1 nm. A figure of merit termed degree of smoothness (DOS) is proposed for the purpose of quantifying the extent of smoothness of a polished metal surface. A post CMP metal slurry cleaning solution was used for cleaning Pt slurry for the first time and by applying special techniques, a very high quality clean surface was attained. Applications of the polished Pt electrodes in interfacing molecular switching devices with self-assembled monolayers of molecules have been found to dramatically improve the packing and orientation of the molecular monolayer with a huge improvement in the molecular electronics device yields. These smooth metal surfaces may open doors for new opportunities in future nanoscale devices. PACS 81.05.Bx; 81.16.Rf; 81.65.Ps     

The Morrison rule in the ABFST multiperipheral model

The validity and consistency of the Morrison rule for the process ππ→πA₂ is considered at asymptotic energy in the context of the ABFST multiperipheral model. The Morrison rule turns out to be inconsistent with the model.     

PrimaryE2 transitions observed following neutron capture for the mass region 144≦A≦180

Values or upper limits for the radiative widths of 12 primaryE2 transitions observed in thermal neutron capture for nuclei with 144≦A≦180 are presented. The results are compared with the predictions of the Axel-Brink hypothesis using the systematics of the isoscalar and isovector quadrupole resonances. The strengths are on the average lower than expected. Analysis of previously reported average resonance data results in the same conclusion.     

Computer simulation of Fresnel diffraction from rectangular apertures and obstacles using the Fresnel integrals approach

In this paper, we describe a new computer simulation technique of generating Fresnel diffraction images from rectangular apertures of arbitrary dimensions by using Fresnel integrals instead of the more common fast Fourier transform methods. The simulation can be performed in almost any PC using the software MATLAB. Diffraction images can be generated for any wavelength of light and for any aperture–screen and aperture-source distances. Images for rectangular obstacles can also be simulated. Details of the algorithm and program are presented, as well as the interesting insights than can be gained from using the program. Finally, it is shown that the simulated images reduce to the simple Fraunhofer diffraction patterns for certain limiting situations.