The present invention discloses a thin film transistor and a process for forming thereof by a high anisotropy etching process. The composite body is formed from a porous material from a carbon-containing matrix, into which carbon fibers are embedded, this matrix is thickened by fluid infiltration of Si, which is essentially converted by reaction with carbon to SiC. More preferably, the preclean step comprises maintaining the supercritical carbon dioxide, the chelating agent, and an acid in contact with the substrate. The invention provides for improving cognitive function and performance in healthy individuals, and in individuals suffering from a disease or disorder in which mental status is compromised.