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Selected AbstractsSynthesis and Characterization of Carbazole-Based Dendrimers with Porphyrin CoresEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006Ting Hua Xu Abstract A series of novel dendritic carbazole-based porphyrins [T(Cz-Gn)Ps] have been synthesized by a combination of Ullmann coupling and Adler condensation reactions and their intramolecular energy-transfer properties have been studied by absorption and steady-state fluorescence spectroscopy. It has been found that the light-harvesting capabilities of T(Cz-Gn)Ps increase with increasing generation, but that the efficiency of the energy transfer decreases from T(Cz-G0)P to T(Cz-G2)P due to the Förster energy-transfer process. In addition, these dendritic macromolecules can emit intense red light with high fluorescence quantum yields and so may find applications in photonic devices. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Arborol-Functionalised Tetrathiafulvalene Derivatives: Synthesis and Thin-Film FormationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2003Thierry Le Gall Abstract The syntheses of a series of novel tetrathiafulvalene derivatives substituted with four side-chains terminating in hydrophilic amidoalcohol (arborol) groups are reported, for example the tetrathiafulvalene derivative 15. Some of these arborol derivatives formed thin films by spin-coating from methanol solution onto solid supports such as glass, ITO-coated glass and gold. The quality of the films improved markedly with an increasing number of alcohol substituents at the periphery of the molecule. Optical absorption spectroscopy showed that oxidative doping of these films could be achieved chemically and electrochemically. The observation of low-energy bands in the UV/Vis absorption spectra (,max = 820 nm tailing to ca. 1300 nm) and the moderate levels of conductivity (,rt , 10,4 S cm,1) in these doped films strongly suggest that a significant degree of supramolecular order is present, with ,-, stacking of the TTF cores. To the best of our knowledge this is the first time that semiconducting behaviour has been achieved in molecular arborol systems that possess an electroactive core unit. This work offers the prospect of using spin-coated films of TTF-arborols as semiconducting charge-transport layers in optoelectronic devices. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Fluorescent Nanostructures: Direct Laser Writing of Nanosized Oligofluorene Truxenes in UV-Transparent Photoresist Microstructures (Adv. Mater.ADVANCED MATERIALS, Issue 7 20097/2009) Fluorescent nanostructures within a transparent microstructure can be achieved via direct laser writing. On p. 781, Alexander Kuehne, Peter Skabara, Martin Dawson, Richard Pethrick, and co-workers report on a novel UV-transparent photoresist that incorporates star-shaped nanometer-sized oligofluorene truxenes. The method and materials will find applications in optical, electro-optical, and photonic devices. (Cover artwork by Leif Heuser). [source] Tuning of electron transport through molecular bridge systems: A study of shot noiseINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008Santanu K. Maiti Abstract We study electron transport characteristics through a single phenalenyl molecule attached with two nonsuperconducting electrodes by the use of Green's function technique. Parametric calculations are given based on the tight-binding model to characterize the electron transport through such molecular bridge system. It is observed that the electron transport properties are significantly influenced by (a) the interference effect and (b) the molecule-to-electrodes coupling strength. In this context we also describe the noise power of the current fluctuations that provides an important information about the electron correlation, which is obtained by calculating the Fano factor (F). The knowledge of this current fluctuations gives a key idea for fabrication of efficient molecular devices. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] An investigation into the swelling properties, dimensional changes, and gel layer evolution in chitosan tablets undergoing hydrationADVANCES IN POLYMER TECHNOLOGY, Issue 1 2009Manuel Efentakis Abstract The purpose of this research is to determine several characteristics of chitosan lactate in tablet form such as dimensional changes, gel evolution, swelling (liquid uptake), and erosion using an image analysis method. The examination of these characteristics will be helpful in the design of oral drug delivery systems with this polymer. It has been demonstrated that image analysis is a valuable technique, allowing the study of quantitative measurements of dimensional and core changes and gel evolution. The dimensional expansion changes of the chitosan lactate tablets were greater in water, and the crushing strength and the stirring effect affected these attributes to a limited extent. The fastest and greatest liquid uptake was observed in water, whereas the greatest erosion was observed in HCl. The thickness of the gel layer increased considerably with time up to the eighth hour, indicating the formation and development of a thick and durable gel, particularly in water. This is an essential characteristic for potential sustained drug release delivery. Consequently, this polymer appears to be a versatile material and a promising vehicle for the preparation of various oral sustained release medications and relevant devices. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:32,39, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20147 [source] Preparation and optical properties of an all-polymer light modulator using colored N -isopropylacrylamide gel particles in a gel-in-gel systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Hiroaki Tsutsui Abstract A novel all-polymer light modulator with a gel-in-gel system was developed. The gel-in-gel system was constructed with colored gel particles responsive to stimuli held independently in another stimuli-nonresponsive gel matrix. Well-known thermoresponsive N -isopropylacrylamide (NIPAM) gel particles containing a pigment were dispersed and fixed in an outer stimuli-nonresponsive gel matrix. When poly(vinyl alcohol),styrylpyridinium (PVA,SbQ) was used for the outer gel matrix, the light modulator showed excellent color-changing properties because the PVA,SbQ matrix was selectively formed around the NIPAM gel particles and the particles exhibited a large volume change in the matrix. The temperature when the outer gel matrix was formed affected the haze of the light modulator. When the outer gel matrix was formed in the swollen state of the NIPAM gels, the haze of a light modulator increased with heating. On the contrary, the haze of a light modulator prepared in the shrunken state of the NIPAM gels decreased with heating. The response time of the color change was less than 1 s. The gel-in-gel system made a very fast macroscopic color change, taking advantage of the fast response of the micrometer-sized gel particles. We believe that a light modulator with a gel-in-gel system may find various applications in optical devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2295,2303, 2007 [source] Access Platform Techniques for Transcatheter Aortic Valve ReplacementJOURNAL OF CARDIAC SURGERY, Issue 4 2010Jacques Kpodonu M.D. Aim of study: A large number of the high-risk patients with critical aortic stenosis referred for transcatheter valve implantation approach may not be candidates for the femoral approach due to peripheral vascular disease with the morbidity and mortality increased severalfold in patients who develop access related complications. Method & Results: A thorough knowledge and review of various alternate access site techniques and trouble shooting are therefore important and required by the implanting cardiac surgeons involved in transcatheter aortic valve therapy. Conclusion: The article review highlights the various percutaneous, hybrid, and surgical access techniques platforms available as well as options for implantation of these devices. (J Card Surg 2010;25:373-380) [source] Stereoscopic video images for telerobotic applicationsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 3 2005Manuel Ferre This article addresses the use of stereoscopic images in teleoperated tasks. Depth perception is a key point in the ability to skillfully manipulate in remote environments. Displaying three-dimensional images is a complex process but it is possible to design a teleoperation interface that displays stereoscopic images to assist in manipulation tasks. The appropriate interface for image viewing must be chosen and the stereoscopic video cameras must be calibrated so that the image disparity is natural for the observer. Attention is given to the calculation of stereoscopic image disparity, and suggestions are made as to the limits within which adequate stereoscopic image perception takes place. The authors have designed equipment for image visualization in teleoperated systems. These devices are described and their performance evaluated. Finally, an architecture for the transmission of stereoscopic video images via network is proposed, which in the future will substitute for current image processing devices. © 2005 Wiley Periodicals, Inc. [source] Binding properties of peptidic affinity ligands for plasmid DNA capture and detectionAICHE JOURNAL, Issue 2 2009Ying Han Abstract Peptides constructed from ,-helical subunits of the Lac repressor protein (LacI) were designed then tailored to achieve particular binding kinetics and dissociation constants for plasmid DNA purification and detection. Surface plasmon resonance was employed for quantification and characterization of the binding of double stranded Escherichia coli plasmid DNA (pUC19) via the lac operon (lacO) to "biomimics" of the DNA binding domain of LacI. Equilibrium dissociation constants (KD), association (ka), and dissociation rates (kd) for the interaction between a suite of peptide sequences and pUC19 were determined. KD values measured for the binding of pUC19 to the 47mer, 27mer, 16mer, and 14mer peptides were 8.8 ± 1.3 × 10,10 M, 7.2 ± 0.6 × 10,10 M, 4.5 ± 0.5 × 10,8 M, and 6.2 ± 0.9 × 10,6 M, respectively. These findings show that affinity peptides, composed of subunits from a naturally occurring operon,repressor interaction, can be designed to achieve binding characteristics suitable for affinity chromatography and biosensor devices. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Random poly(fluorenylene-vinylene)s containing 3,7-Dibenzothiophene-5,5-dioxide units: Synthesis, photophysical, and electroluminescence propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2009Roberto Grisorio Abstract The synthesis of new random poly(arylene-vinylene)s containing the electron withdrawing 3,7-dibenzothiophene-5,5-dioxide unit was achieved by the Suzuki,Heck cascade polymerization reaction. The properties of poly[9,9-bis(2-ethylhexyl)-2,7-fluorenylene-vinylene- co -3,7-dibenzothiophene-5,5-dioxide-vinylene] (50/50 mol/mol, P1) and poly[1,4-bis(2-ethylhexyloxy)-2,5-phenylene-vinylene- co -3,7-dibenzothiophene-5,5-dioxide-vinylene] (50/50 mol/mol, P2) were compared with those of terpolymers obtained by combining the fluorene, dibenzothiophene, and 1,4-bis(2-ethylexyloxy)benzene in 20/40/40 (P3), 50/25/25 (P4), and 80/10/10 (P5) molar ratios. The polymers were characterized by 1H NMR and IR, whereas their thermal properties were investigated by TGA and DSC. Polymers P1,5 are blue,green emitters in solution (,em between 481 and 521 nm) whereas a profound red shift observed in the solid state is emission (,em from 578 to 608 nm) that can be attributed both to the charge transfer stabilization exerted by the polar medium and to intermolecular interactions occurring in the solid state. Cyclic voltammetry permitted the evaluation of the ionization potentials and also revealed a quasi-reversible behavior in the reduction scans for the polymers (P1,4) containing the higher amounts of 3,7-dibenzothiophene-5,5-dioxide units. Electroluminescent devices with both ITO/PEDOT-PSS/P1,5/Ca/Al (Type I) and ITO/PEDOT-PSS/P1,5/Alq3/Ca/Al (Type II) configuration were fabricated showing a yellow to yellow,green emission. In the case of P4, a luminance of 1835 cd/m2 and an efficiency of 0.25 cd/A at 14 V were obtained for the Type II devices. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2093,2104, 2009 [source] Synthesis and characterization of a bis-(4-trifluoromethanesulfonyloxyphenyl)phenylamine monomer and its polymer for light-emitting applicationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2007Huseyin Zengin Abstract This study focuses on the preparation, polymerization, characterization, and optical properties of a new bis-(4-trifluoromethanesulfonyloxyphenyl)phenylamine monomer. This is the first nitrogen-containing monomer having nitrogen atoms as bridges between phenyl rings, and it was synthesized in three steps. The polymerization was carried out through the Ni(0)-catalyzed homocoupling reaction of the bis-(4-trifluoromethanesulfonyloxyphenyl)phenylamine compound. The resulting polymer, polybis(paraphenyl)phenylamine, emitted an intense blue color (where , = 415 nm) upon irradiation by ultraviolet light. The photoluminescence quantum yield was found to be 36% with a long excited-state lifetime of 3.3 ns. Electrical conductivity data for an HCl-doped film of the polymer were also examined. This novel polymer is of interest as an organic emitting material for electroluminescent devices. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1860,1867, 2007 [source] Perfluorocarbons: Life sciences and biomedical uses Dedicated to the memory of Professor Guy Ourisson, a true RENAISSANCE man.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2007Marie Pierre Krafft Abstract Perfluorocarbons are primarily characterized by outstanding chemical and biological inertness, and intense hydrophobic and lipophobic effects. The latter effects provide a powerful noncovalent, labile binding interaction that can promote selective self- assembly. Perfluoro compounds do not mimic nature, yet they can offer abiotic building blocks for the de novo design of functional biopolymers and alternative solutions to physiologically vital issues. They offer new tags useful for molecular recognition, selective sorting, and templated binding (e.g., selective peptide and nucleic acid pairing). They also stabilize membranes and provide micro- and nanocompartmented fluorous environments. Perfluorocarbons provide inert, apolar carrier fluids for lab-on-a-chip experiments and assays using microfluidic technologies. Low water solubility, combined with high vapor pressure, allows stabilization of injectable microbubbles that serve as contrast agents for diagnostic ultrasound imaging. High gas solubilities are the basis for an abiotic means for intravascular oxygen delivery. Other biomedical applications of fluorocarbons include lung surfactant replacement and ophthalmologic aids. Diverse colloids with fluorocarbon phases and/or shells are being investigated for molecular imaging using ultrasound or magnetic resonance, and for targeted drug delivery. Highly fluorinated polymers provide a range of inert materials (e.g., fluorosilicons, expanded polytetrafluoroethylene) for contact lenses, reconstructive surgery (e.g., vascular grafts), and other devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1185,1198, 2007. [source] Dendrimer complexes: Fine control of metal assembly in macromoleculesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2005Kimihisa Yamamoto Abstract New phenylazomethine dendrimers have been developed, with each dendrimer having a unique single structure. From ultraviolet,visible absorption spectra, we determined that stannous chloride added to dendritic polyphenylaz omethine (DPA) was assembled in a stepwise manner from the core shell to the periphery. The selective binding was achieved by the electron density gradient formed in the dendrimer, and it was confirmed by shell-selective imine reduction, transmission electron microscopy, and NMR measurements. The complex formation constants of the respective shells were estimated to be considerably different by a simulation analysis of ultraviolet,visible absorption spectra. The reversible assembly and release of iron into and out of the dendrimer were possible by electrochemical oxidation and reduction, respectively. DPA with a porphyrin at the core was found to function as an effective reduction catalyst of carbon dioxide. DPA with aryl amine at the core was demonstrated to function as a hole-transporting material in electroluminescent devices. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3719,3727, 2005 [source] Synthesis and properties of new ultraviolet,blue-emissive fluorene-based aromatic polyoxadiazoles with confinement moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2003Nam Choul Yang Abstract Three families of fluorene,oxadiazole-based polymers with confinement moieties have successfully been prepared by the two-step method for polyoxadiazole synthesis. These polymers show good solubility in common organic solvents, high thermal stability, and strong violet and blue photoluminescence in solution and as films, respectively. Their low-lying highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels originate from the electron deficiency of an oxadiazole moiety, and this suggests that they may be useful for blue-emitting and electron-transport/hole-blocking layers in electroluminescent devices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 674,683, 2003 [source] Postoperative monitoring of lower limb free flaps with the Cook,Swartz implantable Doppler probe: A clinical trialMICROSURGERY, Issue 5 2010B.Med.Sc., P.G.Dip.Surg.Anat., Ph.D., Warren M. Rozen M.B.B.S. Background: Free flaps to the lower limb have inherently high venous pressures, potentially impairing flap viability, which may lead to limb amputation if flap failure ensues. Adequate monitoring of flap perfusion is thus essential, with timely detection of flap compromise able to potentiate flap salvage. While clinical monitoring has been popularized, recent use of the implantable Doppler probe has been used with success in other free flap settings. Methods: A comparative study of 40 consecutive patients undergoing microvascular free flap reconstruction of lower limb defects was undertaken, with postoperative monitoring achieved with either clinical monitoring alone or the use of the Cook-Swartz implantable Doppler probe. Results: The use of the implantable Doppler probe was associated with salvage of 2/2 compromised flaps compared to salvage of 2/5 compromised flaps in the group undergoing clinical monitoring alone (salvage rate 100% vs. 40%, P = 0.28). While not statistically significant, this was a strong trend toward an improved flap salvage rate with the use of the implantable Doppler probe. There were no false positives or negatives in either group. One flap loss in the clinically monitored group resulted in limb amputation (the only amputation in the cohort). Conclusion: A trend toward early detection and salvage of flaps with anastomotic insufficiency was seen with the use of the Cook,Swartz implantable Doppler probe. These findings suggest a possible benefit of this technique as a stand-alone or adjunctive tool in the clinical monitoring of free flaps, with further investigation warranted into the broader application of these devices. © 2009 Wiley-Liss, Inc. Microsurgery 30:354,360, 2010. [source] An accurate scaling approach for small-signal modeling of high-power HBT devicesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2007Sami Bousnina Abstract This paper presents an accurate scaling approach for small-signal modeling of high-power multi-cell heterojunction bipolar transistors (HBTs). This approach is mainly based on the characterization of an elementary-cell device and a proper modeling of the metalwork structure surrounding the transistor intrinsic part. The determined elementary-cell small-signal model is then scaled up to generate the S-parameters of the multi-cell device. An experimental validation was performed on a single-cell and three-cells GaAsHBT devices and excellent agreement was obtained between measured and simulated S-parameters over frequency range 1,15 GHz. This modeling approach is particularly useful for on-wafer characterization and modeling of high power HBT devices. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2429,2434, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22765 [source] A modified HICUM model for GaInP/GaAs HBT devicesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2006S.-C. Tseng Abstract A compact physics-based transit-time model is established for the GaInP/GaAs HBT device. The VBIC model fails to describe the transit-time frequency versus bias (IC, VCE), especially at low- and medium-current regimes. Starting with the HICUM model, we introduce a new time constant to describe the transit-time frequency versus bias (IC, VCE) more precisely. This model has obvious advantages over the VBIC model for showing the relation of ft versus bias (IC, VCE) in the low and medium current regimes for GaInP/GaAs HBT devices. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 780,783, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21474 [source] Characterization of a planar self-complementary square-spiral antenna in the THz regionMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006E. R. Brown Abstract This paper describes a compact, self-complementary square-spiral antenna on a GaAs substrate with a broadside high-directivity (,29 dB) frequency-independent pattern when coupled through a silicon hyperhemisphere. The driving-point resistance undulates between ,100 and 300, from 200 GHz to 1 THz,much higher than the 72, value from Booker's modified formula, but quite beneficial for coupling to high-impedance broadband devices. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 524,529, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21398 [source] Introduction to the programming of deep brain stimulatorsMOVEMENT DISORDERS, Issue S3 2002Jens Volkmann MD Abstract The clinical success of deep brain stimulation (DBS) for treating Parkinson's disease, tremor, or dystonia critically depends on the quality of postoperative neurologic management. Movement disorder specialists becoming involved with this therapy need to acquire new skills to optimally adapt stimulation parameters and medication after implantation of a DBS system. In clinical practice, the infinite number of possible parameter settings in DBS can be reduced to few relevant combinations. In this article, the authors describe a general scheme of selecting stimulation parameters in DBS and provide clinical and neurophysiological arguments for such a standardized algorithm. They also describe noninvasive technical trouble shooting by using programming features of the commercially available neurostimulation devices. © 2002 Movement Disorder Society [source] Lead-free piezoelectric (Na0.5Bi0.5)0.94TiO3,Ba0.06TiO3 nanofiber by electrospinningPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 9 2009Y. Q. Chen Abstract Lead-free (Na0.5Bi0.5)0.94TiO3,Ba0.06TiO3 (NBT-BT6) nanofibers were synthesized by the sol,gel process and electrospinning, and a butterfly-shaped piezoelectric response was measured by scanning force microscopy. NBT-BT6 nanofibers with perovskite phase were formed, after being cleaned at 700 °C for 1 hour, and the diameters are in the range of 150 nm to 300 nm. The average value of the effective piezoelectric coefficient d33 is 102 pm/V. The high piezoelectricity may be attributed to the easiness for the electric field to tilt the polar vector of the domain and to the increase of the possible spontaneous polarization direction. There is a potential for the application of NBT-BT6 nanofibers in nanoscale piezoelectric devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Porous silicon/metal nanocomposite with tailored magnetic propertiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Petra Granitzer Abstract Porous silicon (PS) templates in the meso/macro porous regime with oriented pores clearly separated from each other and filled in a galvanic deposition process with various metals, especially ferromagnetic ones are magnetically investigated. The employment of different metals (e.g. Ni, Co, NiCo) together with the variation of the electrochemical deposition parameters modifies the structural characteristics of the PS/metal nanocomposite and thus leads to distinct magnetic properties of the hybrid system. Furthermore the use of different PS-templates which means a change of the pore-diameter and interpore spacing results also in various magnetic characteristics, especially influences on the magnetic interactions among the deposited metal nanostructures. Therefore the specimens show tailored magnetic properties like coercivity, squareness and magnetic anisotropy. The achieved nanocomposite merges electronic properties of a semiconductor with nanomagnetism and therefore opens the possibility of integrated spin-based electronic devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thin-film intermediate band photovoltaics: advanced concepts for chalcopyrite solar cellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009David Fuertes Marrón Abstract We have studied the potential of thin-film photovoltaic devices provided with an intermediate band (IB). Cu-containing chalcopyrites appear as promising candidates, with maximum theoretical efficiencies above 45% under ideal conditions. This figure has been re-evaluated by considering a number of non-idealities, like optical and current losses and nonradiative recombination that affect current chalcopyrite-based devices. Strategies for the practical implementation of IBs in chalcopyrite hosts will be discussed, including the incorporation of foreign impurities in the chalcopyrite structure at substitutional sites of the cation sublattice and the realisation of nanostructured devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transparent carbon nanotube field emission devices for display and lampPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007Yousuk Cho Abstract A new, simple method to fabricate transparent carbon nanotube field emission devices is developed. The highly graphitized, single wall carbon nanotubes (SWNTs) are attached to an Sn/ITO glass by the arc discharge method. Post-heat treatments of the sample below the deformation temperature of soda-lime glass form a Sn,SWNT composite, and the nanotubes form good mechanical adhesion and electrical contact with the substrates. When the composite is oxidized in air below 400 °C, the Sn particles change to a transparent oxide form. The emission current density of the heat-treated SWNT,Sn composite is about 1 mA/cm2 at an electric field of 3 V/,m. The emission current density of the SWNT,SnOx composite is similar. However, at a higher oxidation temperature, the emitter shows more stable emission property and longer life time. The transparency of the emitter can be useful in the design of emitter devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atomic study of molecular wires composed of thiophene oligomersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007P. Bai Abstract In this paper, we study the electron conductance of thiophene oligomers based molecular wires through atomic structures using the first principles method based on density functional theory and nonequilibrium Green's function. The molecular wires are built by sandwiching various thiophene oligomers between two metal electrodes via terminal groups at atomic levels. The effects of alkyl substituents on the thiophene oligomers are modelled by varying inter-ring angles of the oligomers. Thiophene dimers, tetramers and hexamers are used to studied thiophene size effects. The projected orbitals, energy gaps, transmission functions and current,voltage characteristics of the molecular wires are calculated and analyzed. Results show that the molecular wires with the planar structures of thiophene oligomers have larger electron transmission functions, hence better electronic conductance than those with twist structures. The conductance of molecular wires decreases when the chain length of the thiophene oligomer increases. The results can provide guidance for design of thiophene molecular electronic wires and other devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comparative study on unpassivated and passivated AlGaN/GaN HFETs and MOSHFETsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006G. Heidelberger Abstract In this comparative study we investigate AlGaN/GaN-based unpassivated and passivated HFETs and MOSHFETs with regards to DC-, RF-, and power-performance. For optimal comparability, all devices emanate from the same wafer consisting of a SiC-substrate, a 3 µm GaN- and a 30 nm Al0.28Ga0.72N-layer. Devices are processed simultaneously to a large extend. Passivated devices are coated with a 10 nm thick SiO2 -layer between the electrodes, MOSHFETs contain a 10 nm thick SiO2 -layer serving as gate-insulator underneath the gate and as conventional passivation-layer between the electrodes. Unpassivated devices serve as reference. We present empirical evidence that MOSHFETs outperform both the conventional and the passivated HFETs with respect to DC-, RF-, and power-performance, and we point out the different mechanisms responsible for the behaviour of the devices. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Si/SiO2 nanocomposite by CVD infiltration of porous SiO2PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2005G. Amato Abstract The aim of the present paper is to report first results on an innovative method for producing Si/SiO2 nanocomposites. Starting from a porous oxide structure, we infiltrated Si by Chemical Vapour Deposition of SiH4, under controlled conditions. In this way, we succeeded in infiltrating Si into the SiO2 template. Porous oxide is obtained by dry oxidation of mesoporous Si. By means of the electrochemical process used for producing porous Si, an interconnected pore structure is obtained. This allows for Si infiltration, giving rise, in principle, to an interconnected network of Si crystallites, in which electrical carriers are easily driven. Efficient charge injection in Si nanocrystals is of crucial importance for several applications, from electroluminescence to memory devices. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Charge carrier density dependence of the hole mobility in poly(p -phenylene vinylene)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2004C. Tanase Abstract The hole transport in various poly(p -phenylene vinylene) (PPV) derivatives has been investigated in field-effect transistors (FETs) and light-emitting diodes (LEDs) as a function of temperature and applied bias. The discrepancy between the experimental hole mobilities extracted from FETs and LEDs based on a single disordered polymeric semiconductor originates from the strong dependence of the hole mobility on the charge carrier density. The microscopic charge transport parameters are directly related to the chemical composition of the analysed polymers. By chemically modifying the PPV, the hole mobility in both FETs and LEDs can be changed by orders of magnitude. For highly disordered PPVs it is demonstrated that the exponential density of states (DOS), which is used to describe the charge transport in FETs, is a good approximation of the tail states of the Gaussian DOS, which describes the charge transport in LEDs. Increase of the directional order in the PPV film enhances the mobility but also induces a strong anisotropy in the charge transport, thereby obscuring a direct comparison between sandwich and field-effect devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication and analysis of polymer field-effect transistorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2004S. Scheinert Abstract Parameters of organic field-effect transistors (OFET) achieved in recent years are promising enough for R & D activities towards a commercial low-cost polymer electronics. In spite of the fast progress, preparations dominated by trial and error are concentrated essentially on higher mobility polymers and shorter channel patterning, and the analysis of measured data is based on oversimplified models. Here ways to professionalize the research on polymer field-effect transistors are discussed exploiting experience accumulated in microelectronics. First of all, designing the devices before fabricating and subsequently analyzing them requires appropriate modelling. Almost independently from the nature of the transport process, the device physics is basically described by the drift-diffusion model, combined with non-degenerate carrier statistics. Therefore, with a modified interpretation of the so-called effective density of states, existing simulation tools can be applied, except for special cases which are discussed. Analytical estimates are helpful already in designing devices, and applied to experimental data they yield input parameters for the numerical simulations. Preparations of OFET's and capacitors with poly(3-ocylthiophene) (P3OT), poly(3-dodecylthiophene) P3HT, Arylamino-poly-(phenylene-vinylene) (PPV), poly(2-methoxy, 5 ethyl (2, hexyloxy) paraphenylenevinylene) MEH-PPV, and pentacene from a soluble precursor are described, with silicon dioxide (SiO2) or poly(4-vinylphenol) (P4VP) as gate insulator, and with rather different channel length. We demonstrate the advantage of combining all steps from design/fabrication to analysis of the experimental data with analytical estimates and numerical simulation. Of special importance is the connection between mobility, transistor channel length, cut-off frequency and operation voltage, which was the starting point for the development of a low-cost fabrication of high-performance submicrometer OFET's by an underetching technique. Finally results of simulation studies are presented concerning the formation of inversion layers, the influence of a trap distribution (as in the a-Si model) and of different types of source/drain contacts on top and bottom contact OFET's, and short-channel effects in submicrometer devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bonding environment and electronic structure of Gd metallofullerene and Gd nanowire filled single-wall carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008T. Pichler Abstract Being single-walled carbon nanotubes, archetypical 1D systems with peculiar anisotropic electronic properties, it is possible to infer modifications in a controlled manner by filling their inner hollow space. One successful approach was proposed for Gd, which regards filling with metallofullerenes and a successful transformation into different novelmetal nanowires by a versatile nanochemical reaction. In this contribution we report on a combined high resolution photoemission and X-ray absorption study on Gd@C82 peapods and Gd nanowires. From a detailed analysis of the Gd 4d response and the valence band in photoemission we are able to elucidate the changes in the bonding environment and charge transfer in these 1D systems. We observe a clear modification of the low energy electronic properties of the SWCNT by the filling with Gd nanowires. Our findings provide important input to understand the interplay between charge transfer and hyridisation in the nanochemical processes in these hybrid systems and to elucidate their electronic transport properties regarding their application potential in nanoelectronic devices. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic superlattices and waveguides based on graphene: structures, properties and applicationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008Leonid A. Chernozatonskii Abstract The new class of quasi-2D superlattices based on graphene with periodically adsorbed hydrogen pairs was proposed. The ab initio DFT method was used for optimization of the atomic geometry and electronic structure of proposed structures. It was found that the superlattices band gap decreases nonmonotonically with distance between hydrogen pairs. Based on these results we hope that the graphene superlattices can be promising candidates for various nanotechnological applications especially as elements in nanoelectronic devices. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||