To provide a filmy structure of a nanometer size having a phase-separated structure effective for the case where a compound can be formed between two kinds of materials. A structure constituted by a first member containing a compound between an element A except both Si and Ge and Si.sub.nGe.sub.1-n (where 0.ltoreq.n.ltoreq.1) and a second member containing one of the element A and Si.sub.nGe.sub.1-n (where 0.ltoreq.n.ltoreq.1), in which one of the first member and the second member is a columnar member, formed on a substrate, whose side face is surrounded by the other member, the ratio Dl/Ds of an average diameter Dl in the major axis direction to an average diameter Ds in the minor axis direction of a transverse sectional shape of the columnar member is less than 5, and the element A is one of Li, Na, Mg, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Cs, Ba, La, Hf, Ta, W, Re, Os, Ir, Pt, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and B.