Postdeposition growth of a uniquely nanostructured organic film by vacuum annealing

Abstract

The organic red pigment N,N-di(3,5-xylyl)perylene-3,4:9,10bis(dicarboximide) is easily vacuum deposited at ambient substrate temperatures to form ordinary looking smooth films. When subsequently annealed in vacuo between ∼160 and 220 °C, an initially 1000 Å uniformly thick film transforms to an extremely dense, random array of discrete, crystalline whiskers, uniformly oriented with their long axes normal to the substrate. Whisker growth occurs at zero supersaturation ratio (no incident flux) and all film material is conserved. Whisker cross sectional dimensions are ∼27×55 nm, lengths 1–1.5 μm, and areal number densities ∼50 per square micron. The high-aspect-ratio whiskers grow purely by surface diffusion to minimum energy binding sites believed to be emergent screw dislocations on the whisker tips, while the uniform cross sectional shapes reflect the ratio of surface free energies of the bounding crystal faces. The transformation has been followed in situ with reflection absorption IR spectroscopy as a function of time and temperature to obtain a dimensionless growth parameter. The surface self-diffusion coefficient and surface entropy to free energy ratio are extracted. The pigment whiskers are readily sputter or vapor-coated to provide conformally coated nanostructure-sized features with metal and semiconductor properties. Vapor coating and annealing of the original pigment films can be done reproducibly in large areas and offer a novel alternative approach to plasma etching and photolithography for producing nanostructured surfaces with new properties.

Electrochemical and Microstructural Evaluation of Aged Nanostructured Thin Film Fuel Cell Electrocatalyst

“…[5][6][7] For comparison with dispersed-catalyst baseline MEAs, commercial Gore 5720 products (0.2/0.3 mg Pt /cm 2 Pt/C with Gore-select R 18-μm PFSA membranes) from Gore Chemical were used. Multiple pairs of Pt and CoMn layers were deposited on annealed PR149 substrates using two targets, Pt and Co 9 Mn.…”

“…The highly dispersed nature of the catalyst allows good utilization of the precious metal. [5][6][7] The ∼0.5 μm long support whiskers are electrically non-conductive, thereby greatly reducing their susceptibility to electro-oxidative corrosion. 1,2 On the other hand, the oxygen reduction reaction (ORR) activity per surface area of Pt, i.e., the specific activity, also decreases with reduced particle size.…”

Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells

“…Table shows a comparison of the performance of MEAs prepared with novel architectures, as mentioned below. − NSTF has been utilized in the cathode catalyst layer to attain high MEA performance, as shown in Figure . The NSTF was first developed as an ORR catalyst by Debe et al , It consists of Pt or Pt alloy covered organic whiskers on a microstructured substrate prepared without the use of an ionomer and carbon support (Figure a). , These NSTFs including Pt, PtNi, PtNiFe, and PtCoMn-based catalysts showed superior catalytic activity when compared to a commercial Pt/C. It has a 20–30 times thinner catalyst layer due to the absence of the carbon support and higher surface area owing to its novel structure compared to the conventional catalyst layer.…”

An Empirical Model for the Flooding Behavior of Ultra-thin PEM Fuel Cell Electrodes

“…For the 3 rd -generation sample, the cathode catalyst was NSTF-PtCoMn at a 0.2 mg-Pt/cm 2 loading. The catalyst coated membrane (CCM) for these results had Pt coated nanostructure thin film catalysts on both the anode and cathode of a 30 micron thick, cast Nafion® 1000 equivalent weight membrane (for three of the MEA's) or a 30 micron thick ~ 850EW 3M ionomer (11).…”