The invention relates to a master substrate, a method for making a high density relief structure, and optical discs replicated with the high-density relief structure, the master substrate comprising a substrate layer (10) and a recording stack deposited on the substrate layer, the recording stack comprising:—an information layer (12),—an interface layer (11) sandwiched between said information layer and the substrate , forming marks and spaces representing an encoded data pattern, wherein said recording material is an alloy comprising at least two materials of the group of materials containing Ge, Sb, Te, In, Se, Bi, Ag, Ga, Sn, Pb, As. A very high-density relief structure is achieved.