Formation of aligned periodic patterns during the crystallization of organic semiconductor thin films.

Self-organizing patterns with micrometre-scale features are promising for the large-area fabrication of photonic devices and scattering layers in optoelectronics. Pattern formation would ideally occur in the active semiconductor to avoid the need for further processing steps. Here, we report an approach to form periodic patterns in single layers of organic semiconductors by a simple annealing process. When heated, a crystallization front propagates across the film, producing a sinusoidal surface structure with wavelengths comparable to that of near-infrared light. These surface features initially form in the amorphous region within a micrometre of the crystal growth front, probably due to competition between crystal growth and surface mass transport. The pattern wavelength can be tuned from 800 nm to 2,400 nm by varying the film thickness and annealing temperature, and millimetre-scale domain sizes are obtained. This phenomenon could be exploited for the self-assembly of microstructured organic optoelectronic devices.

Vanadium oxide-carbon nanotube composite electrodes for energy storage by supercritical fluid deposition: experiment design and device performance.

Vanadium pentoxide (V2O5) deposited on porous multiwalled carbon nanotube (MWCNT) buckypaper using supercritical fluid CO2(scCO2) deposition shows excellent performance for electrochemical capacitors. However, the low weight loading of V2O5 is one of the main problems. In this paper, design of experiments and response surface methods were employed to explore strategies for improving the active material loading by increasing the organo-vanadium precursor adsorption. A second-order response surface model was fitted to the designed experiments to predict the loading of the vanadium precursors onto carbon nanotube buckypaper as a function of time, temperature and pressure of CO2, buckypaper functionalization, precursor type, initial precursor mass and stir speed. Operation conditions were identified by employing a model that led to a precursor loading of 19.33%, an increase of 72.28% over the initial screening design. CNTs-V2O5 composite electrodes fabricated from deposited samples using the optimized conditions demonstrated outstanding electrochemical performance (947.1 F g(-1) of V2O5 at a high scan rate 100 mV s(-1)). The model also predicted operation conditions under which light precursor aggregation took place. The V2O5 from aggregated precursor still possessed considerable specific capacitance (311 F g(-1) of V2O5 at a scan rate 100 mV s(-1)), and the significantly higher V2O5 loading (∼81%) contributed to an increase in overall electrode capacitance.

In situ immobilization of palladium nanoparticles in microfluidic reactors and assessment of their catalytic activity.

We report on the synthesis and characterization of catalytic palladium nanoparticles (Pd NPs) and their immobilization in microfluidic reactors fabricated from polydimethylsiloxane (PDMS). The Pd NPs were stabilized with D-biotin or 3-aminopropyltrimethoxysilane (APTMS) to promote immobilization inside the microfluidic reactors. The NPs were homogeneous with narrow size distributions between 2 and 4 nm, and were characterized by transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and x-ray diffraction (XRD). Biotinylated Pd NPs were immobilized on APTMS-modified PDMS and glass surfaces through the formation of covalent amide bonds between activated biotin and surface amino groups. By contrast, APTMS-stabilized Pd NPs were immobilized directly onto PDMS and glass surfaces rich in hydroxyl groups. Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS) results showed successful attachment of both types of Pd NPs on glass and PDMS surfaces. Both types of Pd NPs were then immobilized in situ in sealed PDMS microfluidic reactors after similar surface modification. The effectiveness of immobilization in the microfluidic reactors was evaluated by hydrogenation of 6-bromo-1-hexene at room temperature and one atmosphere of hydrogen pressure. An average first-run conversion of 85% and selectivity of 100% were achieved in approximately 18 min of reaction time. Control experiments showed that no hydrogenation occurred in the absence of the nanocatalysts. This system has the potential to provide a reliable tool for efficient and high throughput evaluation of catalytic NPs, along with assessment of intrinsic kinetics.