Toughness and toughening mechanisms of porous thin films

Porous materials are referred to those containing pores, cavities, channels, and interstices. According to the pore size d, porous systems are generally classified using the standard specified by International Union of Pure and Applied Chemistry (IUPAC): microporous (d 50 nm) [1]. In recent years, there has been a rapid growth in the research of porous materials owing to their exceptional physical properties, with potential applications as adsorbents, catalysts, and catalyst supports. Combined with the advantages brought by thin-film structure, porous thin films are attracting increased attention. Typical porous thin films include porous low dielectric constant films [2,3], nanoporous thinfilm glasses [4], highly ordered TiO2 nanotube array thin films [5–7], meso- and macroporous SiO2 thin films [8], as shown in Figure 4.1.