NOVELTY - Preparing a substrate surface structured with thermally stable metal alloy nanoparticles comprises: providing a micellar solution of amphiphilic molecules in a suitable solvent; loading the micelles of the micellar solution with metal ions of a first metal salt; loading the micelles of the micellar solution with metal ions of at least one second metal salt; depositing the metal ion-loaded micellar solution onto a substrate surface to form a film comprising an ordered array of domains; and co-reducing the metal ions contained in the deposited domains of the film.    USE - The method is useful for preparing a substrate surface structured with thermally stable metal alloy nanoparticles, where the substrate surface is useful as a catalyst, in particular a catalyst for catalyzing the oxidation of CO to CO2 or the formation of water by reacting hydrogen and oxygen, and where the catalyst is a catalyst for treating/decontaminating car exhaust emissions or a catalyst for fuel cells (all claimed).    ADVANTAGE - The method is environment friendly and produces highly efficient substrate surface structured with thermally stable metal alloy nanoparticles.    DETAILED DESCRIPTION - Preparing a substrate surface structured with thermally stable metal alloy nanoparticles comprises: providing a micellar solution of amphiphilic molecules in a suitable solvent; loading the micelles of the micellar solution with metal ions of a first metal salt; loading the micelles of the micellar solution with metal ions of at least one second metal salt; depositing the metal ion-loaded micellar solution onto a substrate surface to form a film comprising an ordered array of domains; and co-reducing the metal ions contained in the deposited domains of the film by way of a plasma treatment to form an ordered array of nanoparticles consisting of an alloy of the metals used for loading the micelles on the substrate surface. INDEPENDENT CLAIMS are:    (1) a substrate surface comprising an array of thermally stable metal alloy nanoparticles obtainable with the method above;    (2) use of the substrate surface as a catalyst, in particular a catalyst for catalyzing the oxidation of carbon monoxide (CO) to carbon dioxide (CO2) or the formation of water by reacting hydrogen and oxygen; and    (3) a method for nanostructuring a substrate surface which is a bead or particle having a diameter in the micrometer range, mesoporous material comprising particles or aggregates of particles, or a fibrous material, such as a fiber mesh, comprising: (a) providing a micellar solution of amphiphilic molecules such as an organic diblock or multiblock copolymer in a suitable solvent and loading the micelles of the micellar solution with metal ions of at least one metal salt; (b) contacting the metal ion-loaded micellar solution with the beads, particles, mesoporous material or fibers by pressing the metal ion-loaded micellar solution through a layer of the beads, particles, mesoporous material or fibers which is provided on a porous support without adhering to the support and subsequently drying the beads, particles, mesoporous material or fibers, where a film, in particular a polymer film, comprising an ordered array of domains, in particular polymer domains, is formed on the surface of the beads, particles, mesoporous material or fibers; (c) reducing the metal ions contained in the deposited domains of the film, preferably by way of a plasma treatment to form an ordered array of nanoparticles on the bead, microparticle, mesoporous material or fiber substrate surface.