substrate

in thin films
Also contains definition of: subphase in thin films
https://doi.org/10.1351/goldbook.S06084
The terms substrate and subphase refer to a condensed phase that physically supports a @[email protected] or layer. The term substrate should be used with care in the light of the existing double meaning of the term substrate in @[email protected] science and technology, on the one hand, and in biochemistry, on the other. The term subphase applies, mainly, to a liquid phase underlying an adsorption layer or a floating @[email protected]
Source:
PAC, 1994, 66, 1667. (Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)) on page 1671 [Terms] [Paper]