An article including a substrate having at least one main surface coated with a layer A having a refractive index lower than or equal to 1.50, said layer A being obtained by deposition of activated species issued from at least one compound C in gaseous form, containing in its structure at least one Si-fluoroalkyl group, at least one carbon atom, at least one hydrogen atom and optionally at least one nitrogen atom and/or at least one oxygen atom, the deposition of said layer A being carried out by applying a bombardment with an ion beam to layer A while layer A is being formed, and said layer A being formed in the absence of inorganic precursor compounds. Application to the preparation of interferential coatings.