An apparatus/method may comprise, a multi-layer reflecting coating forming an EUV reflective surface which may comprise an inter-diffusion barrier layer which may comprise a carbide selected from the group ZrC and NbC or a boride selected from the group ZrB2 and NbB2 or a disilicide selected from the group ZrSi2 and NbSi2 or a nitride selected from the group BN, ZrN, NbN, BN, ScN and Si3N4. The apparatus and method may comprise an EUV light source collector which may comprise a collecting mirror which may comprise a normal angle of incidence multi-layer reflecting coating; an inter-diffusion barrier layer comprising a material selected from the group comprising a carbide selected from the group ZrC and NbC, or a boride selected from the group ZrB2 and NbB2 or a disilicide selected from the group ZrSi2 and NbSi2 a nitride selected from the group BN, ZrN, NbN, BN, ScN and Si3N4.