Understanding electron transport in metal-molecule-metal (MMM) junctions is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity in a MMM junction include the nature of metal-molecule contacts and the electronic structure of the molecular backbone. We have studied the electronic transport property and the valence electronic structure on rigid, conjugated oligoacenes of increasing length with either thiol (-S) or isocyanide (-CN) linkers using conducting probe atomic force microscopy (CP-AFM) and ultraviolet photoelectron spectroscopy (UPS). We find that for these conjugated systems the Au-CN contact is more resistive than Au-S. The difference in contact resistance correlates with UPS measurements that show the highest-occupied molecular orbital (HOMO) of the isocyanide series is lower in energy (relative to the Fermi level of Au) than the HOMO of the thiol series, indicating the presence of a higher tunneling barrier at the contact for the isocyanide-linked molecules. By contrast, the difference in the HOMO positions for the two series of molecules does not appear to affect the length dependence of the junction resistance (i.e., the beta value = 0.5 A-1).

The development of new gate dielectric materials that offer both low-temperature processability and high capacitance is an important goal for organic electronics in order to facilitate the fabrication of low-voltage circuitry on plastic substrates. [1][2][3][4] Marks, Facchetti, and colleagues, for example, have recently demonstrated that ultra-thin (∼10 nm) crosslinked polymer blend films [5,6] and self-assembled siloxane layers [7] can be used as gate insulators in organic thin-film transistors (OTFTs), providing turn-on potentials of a few volts with gate leakage current densities < 10 -8 A cm -2 . Likewise, Berggren and colleagues have demonstrated polyelectrolyte proton conductors as solution-processable, high-capacitance gate dielectrics for low-voltage OTFT operation. [8,9] In an alternative strategy, we and others have shown that a solid state polymer electrolyte consisting of a Li salt (LiClO 4 or Li bis(trifluoromethylsulfonyl)imide (LiTFSI)) dissolved in poly(ethylene oxide) (PEO) can also serve as a high-capacitance gate insulator in OTFTs. [10][11][12][13][14][15][16][17][18][19][20][21] The specific capacitance for LiClO 4 /PEO is exceptionally large (>10 lF cm -2 ), providing both low-voltage operation and very high ON-currents for OTFTs. Low voltage, LiClO 4 /PEO gated transistors based on polythiophene, [10] poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), [11] pentacene, [12] perylene diimides, [13] and organic single crystals [14][15][16] have been demonstrated.However, the switching speed of these devices is determined by the polarization response time of the LiClO 4 /PEO, and not by the carrier mobility in the semiconductor channel, as is usually the case. [22] The slow polarization response of LiClO 4 / PEO limits transistor switching speed to a few hertz at room temperature, which is a major disadvantage for applications.In order to decrease the polarization response time while maintaining a large specific capacitance, we have investigated ion gels (Fig. 1) as novel gate dielectric materials. Ion gels comprise a polymer network swollen with an ionic liquid. [23] In this work, we have gelled ionic liquids by self-assembly of a triblock copolymer, PS-PEO-PS (Fig. 1), where the polystyrene (PS) endblocks are insoluble in the ionic liquid. [24] The ion gels contain a modest amount of polymer (as little as 4 wt %) producing sufficient mechanical integrity without appreciable change in the ionic conductivity. The room-temperature ionic conductivity is more than 10 -3 S cm -1, much larger than in the PEO/LiClO 4 or PEO/LiTFSI systems (10 -5 S cm -1 at 25°C), which dramatically decreases the polarization response time. In this Communication, we demonstrate that high-capacitance (∼ 40 lF cm -2 ) ion gel-gated OTFTs (GEL-OTFTs) can operate at frequencies up to 1 kHz. This represents a nearly 1000-fold improvement over PEO-gated transistors and a 10-fold improvement over our initial report on ion gel-gated polymer TFTs.[25] Moreover, we have surveyed the behavior of gels made from thr...

Metal-oxide nanocrystals are expected to find useful applications in catalysis, energy storage, magnetic data storage, sensors, and ferrofluids. [1] In particular, colloidal metal-oxide nanocrystals are of great interest for technological applications owing to their unique size-dependent properties and excellent processability. Recent advances in the colloidal synthesis of metal oxides reveal that thermal decomposition of metal acetylacetonates, [2] metal cupferronates, [3] metal alkoxides, [4] and metal carbonyls [5] in complex organic solvent systems can lead to monodisperse metal oxide nanoparticles in certain cases.Manganese oxides are widely used as electrode materials, [6] catalysts, [7] and soft magnetic materials. [8] In spite of their important applications, there has been only one report on synthesis of monodisperse colloidal manganese-oxide nanoparticles.[3] Furthermore, a systematic study on the relationship between particle size and physical properties has never been conducted. Herein we report a simple, reliable synthesis of size-focused colloidal nanocrystals of two different manganese oxides, Mn 3 O 4 and MnO, from thermal decomposition of a single precursor [Mn(acac) 2 ] (acac = acetylacetonate) in oleylamine, as well as their unique size-dependent magnetic properties.A slurry of [Mn(acac) 2 ] (0.3 g) in oleylamine (7.6 g; 1:24 molar ratio) was heated at 180 8C for 9 h under an atmosphere of argon, and the resulting reaction mixture was cooled to room temperature to form a brown suspension. After centrifugation at 3000 rpm for 10 min, the supernatant was removed to afford a brown precipitate. Dichloromethane (10 mL) was added to the resulting brown precipitate to give a brown suspension, which was sonicated for 10 min to form a clear solution. Removal of the insoluble material, if any, by centrifugation and precipitation by adding ethanol (40 mL) produced a brown powder, which could be easily redispersed in various organic solvents such as hexane, toluene, and dichloromethane. The low-resolution transmission-electronmicroscope (TEM) image of the powder shows nearly monodisperse spherical nanoparticles of 10 nm in diameter as shown in Figure 1

A Au particle-on-wire system that can be used as a specific, sensitive, and multiplex DNA sensor is developed. A pattern formed by multiple Au nanowire sensors provides positional address and identification for each sensor. By using this system, multiplex sensing of target DNAs was possible in a quantitative manner with a detection limit of 10 pM. Target DNAs from reference bacteria and clinical isolates were successfully identified by this sensor system, enabling diagnostics for infectious diseases.KEYWORDS DNA, multiplex, pathogen, pattern, surface-enhanced Raman scattering M ultiplex, sensitive, and specific DNA detection is of great demand for various biological and biomedical studies including gene profiling, drug screening, and clinical diagnostics because it has a potential to provide the most information from a small sample volume at low cost.1 In this regard, simple, reliable, and highthroughput methods that allow detection of multiple DNAs in one assay have been developed by taking various sensing approaches such as the measurement of fluorescence, [1][2][3] surface plasmon resonance (SPR), 4 electric signals, 5 and mass changes.6 Among these DNA sensing methods, fluorescence-based assay is currently the most preferred technique for multiplex DNA detection.7 Surface-enhanced Raman scattering (SERS) has also been considered as an attractive method for label-free multiplex DNA detection because of its single molecule level sensitivity, 8-10 molecular specificity, 11 and insensitivity to quenching. 7,12 These distinct advantages have led to the development of a number of ingenious SERS sensing platforms. [13][14][15][16] However, achieving optimum reproducibility of SERS signals and detecting various target molecules with a very small sample volume in one assay still remain as challenging tasks for practical multiplex SERS sensors. It has been shown that hot spots at nanoscale gaps between a nanowire (NW) and nanoparticles (NPs) can become highly SERS-active. [17][18][19][20][21][22] We have recently reported a new biomolecule detection method that provides reproducible SERS signals by using nanoscale gaps between Au NW and NPs. 23Here we present a multiplex DNA detection method employing multiple Au particle-on-wire systems as a SERS sensing platform. The system operates by the self-assembly of Au NPs onto Au NW in the presence of target DNAs, providing reproducible SERS signals in proportion to the concentrations of target DNAs. Multiple pathogen DNAs could be successfully detected by employing this method, demonstrating that this multiplex SERS sensor can be used a convenient system for clinical diagnostic and biomolecular interaction studies.Raman signal can be dramatically enhanced by placing the signal carrying molecules in the interstices between the assembled nanostructures. [24][25][26][27][28][29] To fabricate a SERS-active nanostructure that can be turned on by biomolecular binding, we adopted an Au particle-on-wire structure constructed by self-assembly of Au NPs onto Au NW through DN...

Multi-walled carbon nanotubes (CNTs) can affect plant phenotype and the composition of soil microbiota. Tomato plants grown in soil supplemented with CNTs produce two times more flowers and fruit compared to plants grown in control soil. The effect of carbon nanotubes on microbial community of CNT-treated soil is determined by denaturing gradient gel electrophoresis and pyrosequencing analysis. Phylogenetic analysis indicates that Proteobacteria and Bacteroidetes are the most dominant groups in the microbial community of soil. The relative abundances of Bacteroidetes and Firmicutes are found to increase, whereas Proteobacteria and Verrucomicorbia decrease with increasing concentration of CNTs. The results of comparing diversity indices and species level phylotypes (OTUs) between samples showed that there is not a significant affect on bacterial diversity.

Fabricating well-defined and highly reproducible platforms for surface-enhanced Raman scattering (SERS) is very important in developing practical SERS sensors. We report a novel SERS platform composed of a single metallic nanowire (NW) on a metallic film. Optical excitation of this novel sandwich nanostructure provides a line of SERS hot spots (a SERS hot line) at the gap between the NW and the film. This single nanowire on a film (SNOF) architecture can be easily fabricated, and the position of hot spots can be conveniently located in situ by using an optical microscope during the SERS measurement. We show that high-quality SERS spectra from benzenethiol, brilliant cresyl blue, and single-stranded DNA can be obtained on a SNOF with reliable reproducibility, good time stability, and excellent sensitivity, and thus, SNOFs can potentially be employed as effective SERS sensors for label-free biomolecule detection. We also report detailed studies of polarization- and material-dependent SERS enhancement of the SNOF structure.

A stretchable polymer channel layer for organic field-effect transistors is obtained by spin-coating a blend solution of polythiophene and rubber polymer. A network of the polythiophene nanofibril bundles surface-embedded in the rubber matrix allows large stretchability of the polythiophene film layer.

We report the effects of the growth ambient on photoluminescence (PL) emission properties of ZnO films grown on Si (100) by rf magnetron sputtering. Upon increasing the O2/Ar+O2 ratio in the growing ambient, the visible emission in the room-temperature PL spectra was drastically suppressed without sacrificing the band-edge emission intensity in the ultraviolet region. This tendency is estimated to be due to the reduction of the oxygen vacancies and zinc interstitials in the film induced by the improvement of the film stoichiometry with respect to high oxygen content, indicating that the visible emission in ZnO originates from oxygen vacancy or zinc interstitial related defects. The violet emission peaked at about 401 nm (3.09 eV) was observed in the low-temperature PL spectra of the ZnO films grown under oxygen-rich conditions. This emission band was assigned to the electron transition from the bottom of the conduction band to the Zn vacancy level, positioned approximately 3.06 eV below the conduction band edge.