All-Materials-Inclusive Flash Spark Plasma Sintering.

A new flash (ultra-rapid) spark plasma sintering method applicable to various materials systems, regardless of their electrical resistivity, is developed. A number of powders ranging from metals to electrically insulative ceramics have been successfully densified resulting in homogeneous microstructures within sintering times of 8-35 s. A finite element simulation reveals that the developed method, providing an extraordinary fast and homogeneous heating concentrated in the sample's volume and punches, is applicable to all the different samples tested. The utilized uniquely controllable flash phenomenon is enabled by the combination of the electric current concentration around the sample and the confinement of the heat generated in this area by the lateral thermal contact resistance. The presented new method allows: extending flash sintering to nearly all materials, controlling sample shape by an added graphite die, and an energy efficient mass production of small and intermediate size objects. This approach represents also a potential venue for future investigations of flash sintering of complex shapes.

Nanopatterning of thin polymer films by controlled dewetting on a topographic pre-pattern.

We develop a non-lithographic method for fabricating ordered micro/nanostructures of polymer thin films based on controlled dewetting of the films on topographically pre-patterned substrates with a large area. An ordered nanopattern of polystyrene (PS) is accomplished by thermal treatment of a thin PS film above its Tg spin coated on a topographically patterned substrate. We investigate the influence of pattern geometry on the final morphology of the dewetted polymer films using both mesa and indent patterned substrates. The controlled dewetting, initiated preferentially at the edges of individual pre-patterned mesas, in particular gives rise to spherical cap domains located at the center of the mesas. The domains are much smaller than the individual mesas as a consequence of the significant pattern reduction to nearly 300%. The arrays of 70 nm PS nano-sphere caps are obtained from arrays of 200 nm square pre-patterned mesas. Our method is also applicable for other polymers such as a poly(4-vinyl pyridine) (P4VP) containing Rhodamine 6G (Rh6G) dye on a pre-patterned PS substrate and successfully produced highly fluorescent stable nanopatterned films.