Showing papers by "Wen-Chang Chen published in 2006"

Morphological Transformation and Photophysical Properties of Rod‐Coil Poly[2,7‐(9,9‐dihexylfluorene)]‐block‐poly(acrylic acid) in Solution

Abstract: The synthesis, morphology, and photophysical properties of PF-b-PAA with different coil lengths in dilute solutions of dichloromethane/methanol are reported. A tape-like lamellar morphology is observed at a short coil length of PF-b-PAA. As the coil length increases, a large compound micelle, sphere, or vesicle is observed with different methanol contents because of the enhancement of the PAA swelling with methanol and the interfacial tension between the PF core and the PAA corona. Upon further increase of the coil length, an inverted morphology of a sphere or rod with a PF corona and PAA core is first observed but the core/corona is then reversed at a high methanol content as a result of the enhanced solubility of PAA. The morphological transformation leads to a significant variation in optical absorption or fluorescence characteristics because of the possible H-aggregate formation.

A New Class of High Tg and Organosoluble Aromatic Poly(amine−1,3,4-oxadiazole)s Containing Donor and Acceptor Moieties for Blue-Light-Emitting Materials

Abstract: A new naphthylamine-derived aromatic dicarboxylic acid, 1-[N,N-di(4-carboxyphenyl)amino]naphthalene (2), was successfully synthesized by the sodium hydride-mediated condensation of 1-aminonaphthalene with 4-fluorobenzonitrile, followed by the alkaline hydrolysis of the intermediate dicyano compound 1. Four poly(amine−hydrazide)s were prepared from the polycondensation reactions of the dicarboxylic acid 2 and 4,4‘-dicarboxytriphenylamine (2‘) with terephthalic dihydrazide (TPH) and isophthalic dihydrazide (IPH), respectively, via the Yamazaki phosphorylation reaction. The poly(amine−hydrazide)s were readily soluble in many common organic solvents and could be solution cast into transparent and flexible films with good mechanical properties. These hydrazide polymers had glass-transition temperatures (Tg) in the range of 182−230 °C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the range of 300−400 °C. The resulting poly(amine−1,3,4-oxadiazole)s had useful levels of ther...

Amperometric glucose biosensor based on screen-printed carbon electrodes mediated with hexacyanoferrate- : chitosan oligomers mixture

Abstract: A glucose oxidase (GOD) biosensor has been described based on screen-printed carbon electrodes (SPCEs) with hexacyanoferrate(III) (i.e. ferricyanide, Ferri) used as an electron transfer mediator. Mixing with chitosan oligomers (COs), a Ferri–COs mixture was drop-coated onto the surface of SPCEs, and GOD was then layered on, forming a GOD/Ferri–COs glucose biosensor. Thus, a disposable and low-cost biosensor can be fabricated easily, simply and rapidly. The characteristics of the sensor were studied by cyclic voltammetry, chronopotentiometry and amperometry. Sensors without GOD layering-on showed a quasi-reversible reaction of the redox couple (Ferri/ferrocyanide), and a significant enhancement of the sensor response signal could be obtained in the presence of COs. In addition, effects of GOD loading, COs concentration, solution pH and applied potential on the response of the glucose biosensor were also investigated. At an applied potential of 0.3 V, the biosensor exhibited a relatively fast response (response time was less than 20 s), low detection limit (ca. 1.38 mM), good reproducibility and high sensitivity (ca. 0.677 μA mM−1) with a wide linear range up to 33.3 mM of glucose.

New Fluorene-Acceptor Random Copolymers: Towards Pure White Light Emission from a Single Polymer

Abstract: Two kinds of fluorene-acceptor copolymers containing three emitting segments have been synthesized and explored as the emissive layer in white-light-emitting devices (WLEDs). The light-emitting copolymers PFQTP and PFBTTP either contain blue-emitting (9,9-dihexyl-fluorene, F), greenemitting (quinoxalire Q) (or yellowemitting (2,1,3-benzothiadiazole, BT)), and red-emitting (thieno[3,4-b]-pyrazine, TP) units in the backbone. The energy-transfer processes between the emitting units are investigated by their absorption, photoluminescence, time-resolved photoluminescence, and electroluminescence. The experimental results suggest that only a relatively small faction of the acceptor moiety incorporated into the fluorene can achieve white light emission through energy transfer. The energy transfer from BT to TP is more efficient that that of Q to TP because of the degree of spectroscopic overlap between absorption and luminescence. The electroluminescent device with PFBTTP1 (0.1% of BT and 0.25% of TP) as an emissive layer exhibits the Commission Intemationale de L'Eclairage (CIE) 1931 coordinates of (0.33, 0.34), a luminance of 1 870 cd·m -2 under the condition of maximum luminance yield of 1.92 ed·A -1 , and without signifleant variation with driving voltages. The present study suggests that the single polymers based on three flucrene-acceptor segments could be potentially used for pure-white-light-emitting diodes.

New environmentally responsive fluorescent N-isopropylacrylamide copolymer and its application to DNA sensing

Abstract: We report two novel multifunctional copolymers consisting of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAA) segment and a fluorescent fluorene-containing acrylic polymer segment with pH responsiveness and/or DNA-sensing ability. The functional acrylic monomer with a fluorene dimer side group substituted with amino units was synthesized first. Then, it was copolymerized with N-isopropyl-acrylamide to result in a new water-soluble, fluorescent PNIPAA copolymer (P1). The fluorescent properties of P1 under neutral and acidic conditions did not change with the temperature. However, significant variation was observed under basic conditions. The protonation of the amino moiety at a low pH improved the solubility and prevented aggregation for fluorescence quenching, but not under the basic conditions. Although aggregation of the fluorene units was significant at room temperature under basic conditions, the aggregation was resolved at a temperature above the lower critical solution temperature. These findings indicated the pH- and temperature-responsive characteristics of P1. Moreover, after the amino groups were quaternized, the obtained polymer could be used as a biosensor because the fluorescence intensity was quenched with the addition of DNA. This study demonstrates that multifunctional materials with pH- and temperature-sensing characteristics and biological molecules could be realized by the incorporation of a functional fluorene-containing moiety with PNIPAA.

The Properties and Preparation of Chitosan/Silica Hybrids Using Sol-Gel Process

Abstract: Chitosan/silica hybrids (Chitosan/SiO2) using a sol-gel process were prepared at a wide range of in situ silica content from 0% to 100%. This work was undertaken to investigate the thermal properties, optical, adsorption, and biodegradability properties of this type of hybrid. Fourier transform infrared (FTIR) spectra were recorded to depict the interfacial interaction. Thermogravimetric analysis was used to determine the actual silica content forming in the hybrids and to evaluate the enhanced heat resistance of hybrids resulting from silica. Crystallography was illustrated using an X-ray diffractometer. Fracture surface was revealed through a scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) to probe the dispersion degree of SiO2, which in turn confirmed the results of optical property on the formation of nanocomposites. To prevent the dissolution of chitosan and silica in the acid and alkaline solution, respectively, all prepared hybrids are capable of chelating Cu (II) as well as F...

Theoretical Electronic Structure and Properties of Alternating Fluorene–Acceptor Conjugated Copolymers and Their Model Compounds

Abstract: The theoretical geometries and electronic properties of fluorene (F) based alternating donor–acceptor conjugated copolymers and their model compounds were studied by the density function theory (DFT) at the B3LYP level with 6–31G or 6–31G** basis set. The acceptors investigated in this study include thiazole (TZ), thiadiazole (TD), thienopyrazine (TP), thienothiadiazole (TT), thiadiazolothienopyrazine (TTP), quinoxaline (Q), benzothiadiazole (BT), pyrazinoquinoxaline (PQ), thiadiazoloquinoxaline (TQ), and benzobisthiathiadiazole (BB). The torsional angle, bridge bond length, bond length alternation, and intramolecular charge transfer were simulated and correlated with the electronic properties, i.e., HOMO, LUMO level, and band gap. The geometries of fluorene-based donor–acceptor alternating copolymers and their model compounds are significantly affected by the structure of acceptors, particularly the ring size on the backbone. The electronic properties of the polymers and their model compounds are well correlated with the acceptor strength, coplanarity of the backbone, and intramolecular charge transfer. The theoretical study suggests that the electronic properties of alternating fluorene–acceptor conjugated copolymers could be tuned by the geometries or acceptor strength. Hence, these proposed copolymers could have potential applications as light-emitting diodes (LEDs), transparent conductor, or photovoltaic devices.

Development of Thin-Junction Detector

Abstract: Two methods to produce a thin-junction sensor are reported here. The first method consists of a regular boron implantation with energies of 2 keV (dose of 1 times 1015/cm2) and 5 keV (dose of 1 times 1014/cm2) into silicon directly, and 10 keV (1 X 1014/cm2), 45 keV (1 times 1015/cm2) into Si through a thin oxide layer (500 A and 1000 A respectively) to form a junction. An aluminum layer was coated in the same vacuum system after back-sputtering to remove oxide on top of the implanted silicon substrate. This method may have the following advantages: 1) it may improve the soft X-ray radiation hardness of the device because there is no oxide layer on the junction; 2) it substantially attenuates the incident visible light; and 3) it allows detection of low energy X-ray down to 300 eV. The second method consists of a low energy of 2 keV and dose of 1 times 1015/cm2 boron implantation into the bare silicon followed by laser annealing that activates boron with minimal diffusion, to retain the ultra thin-junction. The laser annealing method was compared with control wafers. Two of the control wafers were implanted by boron with the same energy and dose as that of the laser annealed wafer. One of them was annealed using high temperature of 1000degC and time of 30 minutes thermal annealing. The other was annealed using our regular annealing temperature of 700degC and with longer annealing time of 17 hours. The remaining control wafer was implanted by boron with higher energy of 45 keV and dose of 1 times 1015/cm2 (our standard boron implantation energy and dose) and annealed using regular (700degC, 30 min) thermal annealing.

Development of New 3d Si Detectors at BNL and CNM

Abstract: New 3d Si detector structures have been proposed by BNL at the end of 2005. Different from the traditional planar Si detector technology, 3d detector technology places p+ and n+ electrodes vertically through the entire detector thickness, thus involves 3-demensional processing. Our new 3d structures have a number of new feature either in configuration and/or in processing: 1) electrodes are etched not all the way through the detector thickness to ensure a simple, true one-sided processing; 2) single electrode columns (p+ or n+) are etched and doped, with the other type of columns (n+ or p+) planar implanted; and 3) stripixel electrode configuration can be arranged to get 2d position sensitive strip-like detectors with single-sided processing. The processing of the first prototype detectors batch of the new 3d detectors with single column (n+ column on p-type substrate) has begun. n+ columns have been etched by CNM of Barcelona, and BNL has just finished the remaining planar processing. Electrical test results on the test stripixel structures as well as on the stripixel detectors are good. Processing and device simulations have been made on these new 3d Si detectors.

Edgeless silicon pad detectors

Abstract: We report measurements in a high-energy pion beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors diced through their contact implants. A large surface current on such an edge prevents the normal reverse biasing of the device, but the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at low temperature. The depth of the dead layer at the diced edge is measured to be (12.5±8 stat. .±6 syst. ) μm.

A Novel 2-D Position Sensitive Silicon Detector With Micron Resolution for Heavy Ion Tracking

Abstract: A new 2-D position sensitive silicon detector for tracking of energetic heavy ions is under development in a program to study the radiation effect within a single human cell. The detector is based on a concept of interleaved pixel electrodes arranged in a projective 2-D strip readout (stripixel). A fine position resolution in the sub-micron range can be achieved by determining the centroid of the charge collected on pixel electrodes with a granularity in the range of 10 mum. Beam test results with 1 GeV/n Fe ions have demonstrated an rms position resolution of about 0.5 mum with a 30 mum pixel pitch