Abstract: A 1,2-dioxetane derivative of the formula (I): wherein Ar is an aryl group which may have an alkyl group, an aryl group, a halogen atom, an alkoxyl group, a carboxyl group, a formyl group, an alkyl ester, an aryl ester, an alkylketone, an arylketone or a hetero ring bonded thereto, X is a substituent capable of labeling an organic compound or a biological molecule, or an ester, Y is a hydrogen atom, an acyl group or a group of the formula —Si(R4R5R6) (wherein each of R4, R5 and R6 which are independent of one another, is an alkyl group or an aryl group), Z is an alkyl group, an aryl group, an oxygen atom, a sulfur atom, a carbonyl group, —(CO)—O—, —O—(CO)—, —NH—, —NH—CO—, —CO—NH—, —OSi(R7R8)— (wherein each of R7 and R8 which are independent of each other, is an alkyl group or aryl group) or a group of the formula —(R9R10)SiO— (wherein each of R9 and R10 which are independent of e

Abstract: An X-ray mirror having its layer structure in the sequence of: a substrate having the surface roughness (R.sub.max) of 1,000 .ANG. or below; an intermediate layer of high molecular weight material formed on this substrate and having a surface roughness (R.sub.max) of 100 .ANG. or below; and a thin film formed on this intermediate layer, the X-ray mirror being produced by the process steps of: providing a substrate having a surface roughness (R.sub.max) of 1,000 .ANG. or below; forming on this substrate an intermediate layer of a high molecular weight material by spin-coating with a surface roughness (R.sub.max) of 100 .ANG. or below; and finally forming a thin film on this intermediate layer.