Template-free sol–gel preparation of nanoporous ORMOSIL films with adjustable refractive index

●An ORMOSIL film with adjustable refractive index from 1.21 to 1.10 was prepared.●The film was prepared at room temperature via template-free sol–gel method.●Heating the film, the refractive index of the film can be decreased to 1.07.●Heating the film, the thickness of the film will also be change.

A nanoporous organically modified silicate (ORMOSIL) film with adjustable refractive index from 1.21 to 1.10 was prepared at room temperature via a template-free sol–gel method, using tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as co-precursors and hexamethylisilazane (HMDS) as surface modifier. Heating the ORMOSIL film, the refractive index of the ORMOSIL film can be further decreased to as low as 1.07. This adjustable refractive index thin film can find potential application in optical and microelectronic fields.