NOVELTY - Two substances chosen from material (a-c) are used as precursors. The precursor is placed on front portion of reaction furnace. A semiconductor or insulator single-crystalline substrate is placed on rear portion of reaction furnace. The precursor and substrate are heat-treated under inert atmosphere. Thus, binary alloy single-crystalline metal nanostructure is fabricated.    USE - Method for fabricating binary alloy single-crystalline metal nanostructure such as palladium-gold single-crystalline metal nanowire, cobalt-silver single-crystalline metal nanowire, silver-tellurium single-crystalline metal nanowire, and bismuth-tellurium single-crystalline metal nanobelt used for semiconductor applications, hydrogen gas sensors for highly sensitive fuel cell, nano-sized magnetic sensors, and magnetic devices.    ADVANTAGE - The method simply provides binary alloy single-crystalline metal nanostructure, in high yield without using catalyst. The nanowire and nanobelt having high quality, excellent morphology and uniform size are produced in complete single-crystalline condition without defects and coagulation on single-crystalline substrate.    DETAILED DESCRIPTION - Two substances chosen from material (a-c) are used as precursors. The precursor is placed on front portion of reaction furnace. A semiconductor or insulator single-crystalline substrate is placed on rear portion of reaction furnace. The precursor and substrate are heat-treated under inert atmosphere. Thus, binary alloy single-crystalline metal nanostructure is fabricated. The binary alloy of nanostructure includes material (a) containing metal oxides, metal substances or metal halides of a metal, material (b) containing metal oxides, metal substances or metal halides of another metal, and/or material (c) containing binary alloy substances. The metal halide of material (a and b) is metal fluoride, metal chloride, metal bromide, or metal iodide. The metal oxide of material (a and b) is silver oxide, gold oxide, cobalt oxide, palladium oxide, or tellurium oxide. The metal substance of material (a and b) is silver, gold, cobalt, palladium, or tellurium. The metal halide material (a and b) is silver halide, gold halide, cobalt halide, palladium halide, or tellurium halide. The binary alloy substances of material (c) is palladium and gold alloy, cobalt and sliver alloy, silver and tellurium alloy, or bismuth and tellurium alloy. A palladium-gold single-crystalline metal nanowire is of formula: PdxAu1-x, where x is 0.01-0.99, cobalt-silver single-crystalline metal nanowire is of formula: CoyAg1-y, where y is 0.01-0.5, silver-tellurium single-crystalline metal nanowire (Ag2Te), and bismuth-tellurium single-crystalline metal nanobelt (Bi1Te1) are fabricated. An INDEPENDENT CLAIM is included for binary alloy nanostructure.