Biomedical subjects

Daihua Zhang

Publications and source records attributed to Daihua Zhang.

4 recordsLinked to original sources

PubMed2006

Transparent, conductive, and flexible carbon nanotube films and their application in organic light-emitting diodes.

We have carried out comparative studies on transparent conductive thin films made with two kinds of commercial carbon nanotubes: HiPCO and arc-discharge nanotubes. These films have been further exploited as hole-injection electrodes for organic light-emitting diodes (OLEDs) on both rigid glass and flexible substrates. Our experiments reveal that films based on arc-discharge nanotubes are overwhelmingly better than HiPCO-nanotube-based films in all of the critical aspects, including surface roughness, sheet resistance, and transparency. Further improvement in arc-discharge nanotube films has been achieved by using PEDOT passivation for better surface smoothness and using SOCl2 doping for lower sheet resistance. The optimized films show a typical sheet resistance of approximately 160 Omega/ square at 87% transparency and have been used successfully to make OLEDs with high stabilities and long lifetimes.

Elasticity↗

PubMed2005

Efficient synthesis and electronic studies of core-shell nanowires based on colossal magnetoresistive manganites.

We report our recent study on the pulsed laser deposition process in the synthesis of colossal magnetoresistive MgO/LaCaMnO3 and MgO/LaSrMnO3 core-shell nanowires. A highly efficient process has been developed by depositing an epitaxial layer of manganite onto randomly oriented MgO nanowires grown on SiO2/Si substrates. In addition, in-depth studies revealed that the sample-target distance played a critical role in determining the core-shell nanowire quality. The MgO/LaCaMnO3 and MgO/LaSrMnO3 nanowires opened up the unique opportunity to explore a number of intriguing physical properties at the nanoscale. Remarkable metal-insulator phase transitions and pronounced colossal magnetoresistance have been observed in both LaCaMnO3 and LaSrMnO3 nanostructures.

Journal Article↗

PubMed2005

Single crystalline magnetite nanotubes.

We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core-shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be approximately 4 x 10-2 Omega cm at room temperature. Magnetoresistance of approximately 1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.

Ferrosoferric Oxide↗

PubMed2004

charge storage behavior of nanowire transistors functionalized with bis(terpyridine)-Fe(II) molecules: dependence on molecular structure.

We studied the influence of three bis(terpyridine)-Fe(II) molecules-(X-tpy)2FeCl2 (X = H (1), SAc (2), and 4-phenyl-SAc (3)-on charge storage of a nanowire transistor. The molecules were assembled on the surface of an indium oxide nanowire that forms the conduction channel of the transistor. We found that the charge storage characteristics of such a device strongly depends on the structure of the terpyridine ligand: both retention time (tau) and threshold voltage shift (DeltaVth) increased in the order of 1 < 2 < 3, with tau of 200 s, 12 h, and 287 h and DeltaVth at 4.8, 12, and 28 V, respectively. Furthermore, when we placed the devices with molecules 1 and 3 in a vacuum and recorded the I-Vg curves in a two-day period, we observed higher hysteresis stability for device with molecule 3. For example, DeltaVth was reduced from 4.8 to 1.7 V for the device with molecule 1, while there was no reduction in DeltaVth for the device with molecule 2. These results suggest that thiolate headgroup and/or longer ligand length raises the charge tunneling barrier and results in longer charge retention and wider, more stable memory window. This work demonstrates the potential of chemical synthesis toward tailored device characteristics.

Journal Article↗