Item comprising an organic-inorganic layer with a low refractive index

A process for the manufacture of an article, comprising at least the following steps:

• supplying an article comprising a substrate having at least one main surface;
• depositing, on said main surface of the substrate, a layer L of a material M having a refractive index ranging from 1.38 to 1.47 at a wavelength of 632.8 nm;
• and
• recovering the article, wherein said layer L has been obtained by deposition, by co-evaporation, of at least two precursors:
• one metallic compound A chosen from alkaline-earth metal fluorides;
• and
• at least one organosilicon compound B, the deposition of the organosilicon compound B, in gaseous form, being carried out in the presence of an ion bombardment so as to obtain the material M,
• wherein the process comprises the step of depositing, on said main surface of the substrate, a multilayer interference coating, wherein the layer L constitutes at least one layer of said multilayer interference coating,
• wherein a thin organic-inorganic layer having a thickness of 1 to 20 nm is deposited on this layer L, wherein the thin organic-inorganic layer is a low-index layer which is the external layer of the multilayer interference coating, this organic-inorganic layer being obtained by deposition of an organosilicon compound or a mixture of organosilicon compounds in gaseous form, in the presence of an ion bombardment and in the absence of a mineral precursor, and
• wherein the organosilicon compound B comprises at least one divalent group of formula:
• wherein each R′1 to R′4 is independently vinyl, aryl, hydroxyl, or a hydrolysable group, or wherein compound B corresponds to formula:
• wherein each R′5, R′6, R′7 and R′8 is independently hydroxyl or a hydrolysable OR group, wherein R is an alkyl group.