(562d) Nanostructured Ultrathin Films Formed By Covalent Molecular Assembly In Supercritical Carbon Dioxide

Ultrathin organic films have been of great interest in recent years due to their potential use as boundary lubricants in several technological applications, such as information storage devices and micro-electro-mechanical systems (MEMS). In this work, the tribological properties of ultrathin films containing nanoparticles encapsulated in immobilized dendrimers are investigated. The films were formed by covalent molecular assembly in supercritical carbon dioxide and the nanoparticles were formed by reduction of precursors in either aqueous or supercritical media. We use fluorination as a means of capping the matrix to yield smaller nanoparticles and better tribological properties for the film-coated surface. Formation of nanoparticles are confirmed by XPS and TEM. We have shown that the introduction of metal particles after the additional fluorination step reduces the metal particle size and helps in improving tribological properties. While fluorination, presence of the dendrimer and presence of the nanoparticles contribute towards reducing the coefficient of friction (CoF), the size of the nanoparticle can be controlled by appropriate sequencing of the above processing steps, thereby leading to further decrease in the CoF. The effect is demonstrated for Au and extended to Fe nanoparticles.

Bimetallic nanoparticles are important materials because they often display properties that are quite different from those of the individual metal particles. We report the formation of Fe, Ni and Fe/Ni nanoparticles within a dendrimer-laden, ultrathin film matrix immobilized on a solid support and constructed by covalent layer-by-layer (LbL) assembly using supercritical carbon dioxide(SCCO2). Particle size and distribution, and composition were controlled by precursor composition and process conditions. Fe/Ni nanoparticle-containing films exhibited lower CoF than those containing the monometallic species, thereby suggesting that combination of nanoparticles can be used to derive greater benefits.

Finally, we demonstrate a general template-based method for formation of Pd and Pt nanoparticles within the immobilized dendrimer matrix using SCCO2 as the processing medium and their use in metal-insulator semiconductor (MIS) device fabrication to demonstrate the memory effect and retention capability for non-volatile memory (NVM) applications. Significant charge storage capability of the nanoparticle memory devices were demonstrated under low operation voltage, with sufficient retention times. This could be related to the good controllability of the size, distribution and density of the nanoparticles that can be achieved by the supercritical medium.