Jong Jin Park

Selective dispersion of high purity semiconducting single-walled carbon nanotubes with regioregular poly(3-alkylthiophene)s

Conjugated polymers, such as polyfluorene and poly(phenylene vinylene), have been used to selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs), but these polymers have limited applications in transistors and solar cells. Regioregular poly(3-alkylthiophene)s (rr-P3ATs) are the most widely used materials for organic electronics and have been observed to wrap around SWNTs. However, no sorting of sc-SWNTs has been achieved before. Here we report the application of rr-P3ATs to sort sc-SWNTs. Through rational selection of polymers, solvent and temperature, we achieved highly selective dispersion of sc-SWNTs. Our approach enables direct film preparation after a simple centrifugation step. Using the sorted sc-SWNTs, we fabricate high-performance SWNT network transistors with observed charge-carrier mobility as high as 12 cm(2) V(-1) s(-1) and on/off ratio of >10(6). Our method offers a facile and a scalable route for separating sc-SWNTs and fabrication of electronic devices.

Porous PVDF As Effective Sonic Wave Driven Nanogenerators

Piezomaterials are known to display enhanced energy conversion efficiency at nanoscale due to geometrical effect and improved mechanical properties. Although piezoelectric nanowires have been the most widely and dominantly researched structure for this application, there only exist a limited number of piezomaterials that can be easily manufactured into nanowires, thus, developing effective and reliable means of preparing nanostructures from a wide variety of piezomaterials is essential for the advancement of self-powered nanotechnology. In this study, we present nanoporous arrays of polyvinylidene fluoride (PVDF), fabricated by a lithography-free, template-assisted preparation method, as an effective alternative to nanowires for robust piezoelectric nanogenerators. We further demonstrate that our porous PVDF nanogenerators produce the rectified power density of 0.17 mW/cm3 with the piezoelectric potential and the piezoelectric current enhanced to be 5.2 times and 6 times those from bulk PVDF film nanogenerators under the same sonic-input.

Ordered Zigzag Stripes of Polymer Gel/Metal Nanoparticle Composites for Highly Stretchable Conductive Electrodes

Stretchable electrodes have gained ever-increasing interest for a wide range of applications including smart clothing, [ 1 ] dielectric elastomer actuators (DEAs), [ 2 ] stretchable and rollable displays, [ 3 ] and fl exible electronics. [ 4 ] The required strain varies depending on the application. For example, a stretchable display needs about 10 to 30% strain, but more than 100% strain is desired for DEAs. Realization of stretchable electrodes has been explored with a number of different approaches. One of them is to generate the stretchable structures of metals. [ 5 ] Inplane S-shaped [ 6 ] or z-shaped [ 7 ] metal strips, or out-of-plane wavy geometry [ 8 ] can have a large net elongation. Although a large strain ( ≈ 60%) without electrical failure has been reported, fabrication of a fi ne-structured electrode is yet to be achieved. Another approach is to use a composite material made of an elastomer and conducting metal fi llers or carbon nanotubes. [ 9 ]

High performance foldable polymer thin film transistors with a side gate architecture

Foldable polymer thin film transistors gated by an ion gel dielectric were fabricated on a polymer substrate. Side gate structure was employed to simplify the fabrication process, which is a unique advantage of the transistors based on the ion gel dielectric. Utilizing the diffusion of crosslinkable oligomers in the P3HT thin films followed by UV gelation through a patterned mask, the ion gel made a strong bonding to the P3HT layer. Due to the deformable nature of the ion gel dielectric, the transistor arrays were electrically and mechanically stable at repeated folding events.

Failure Mode Investigation for Blue Polymer EL Device

We report the failure mode observed in polymer EL blue device. Such modes were analyzed by non-destructive and destructive ways. As a non-destructive way, investigation of mobility changes of hole and electron, measuring transient EL corresponding to life curve, had been done. We also observed compositional and morphological variation using TEM-EDX, STM, FT-IR, TOF-SIMS and reverse engineering method as a destructive way. Electron mobility has a higher dependency on life curve, which fact could be reflected on the formation of insoluble layer inside emitting layer on anode side. And such insoluble layer showed relatively ordered surface morphology, and might be a cross-linked layer through C-O-C bond cleavage process while EL operation. But, contrary to sulfur migration mechanism into insoluble layer insisted by CDT, we did confirm no obvious difference of sulfur composition between insoluble and emitting layers. Rather, theres some degree of Ba diffusion into emitting layer from decomposition of BaF 2 , but, which dose not have a major effect on device degradation.