NOVELTY - Nanocomposite structure (200) comprises: a core (201) comprising a nanoparticle or a group of nanoparticles; and a distribution of isolated or islands of nanoparticles (202A-202E) smaller in size than the core, where the isolated or islands of nanoparticles are attached to the surface of the core, and the islands of nanoparticles are free of organic ligands.    USE - The nanocomposite structure is useful: for chemical production (e.g. oxidation of carbon monoxide to carbon dioxide); as catalysts (e.g. anode and cathode catalyst) in electrochemical cells e.g. fuel cells; and in nonlinear optics, plasmonic devices, fluorescence markers for biology and medical applications, or as energy absorbers for treatment of cancer.    ADVANTAGE - The nanocomposite structure: is free of organic layers and thermally stable; has increased surface area; and exhibits improved catalytic activity.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for producing nanoparticles-on-nanoparticles, comprising: either aerosolizing powders of a first composition of a micrometer size, ablating the aerosolized powders to generate nanoparticles of the first composition, aerosolizing powders of micrometer sized particles of a second composition, mixing the nanoparticles of the first composition with the aerosolized powders of the second composition, and ablating the mixture in such a manner as to generate nanoparticles of the second composition, which are formed on the surface of the nanoparticles of the first composition in such a manner as to form nanoparticles-on-nanoparticles comprising nanoparticles of the second composition on the surface of a core of nanoparticles of the first composition, where the nanoparticles of the second composition are smaller in size than the core of nanoparticles; or aerosolizing a mixture of powders of oxide of a micrometer size and a metal or metal alloy micrometer sized particles, and ablating the aerosolized mixture to generate nanoparticles of oxide and nanoparticles of metal or metal alloy, where nanoparticles of the metal and metal alloy are formed on the surface of the nanoparticles of oxide in such a manner as to form nanoparticles-on-nanoparticles comprising a distribution of individual metallic nanoparticles or islands of metallic nanoparticles on the surface of the core of the oxide nanoparticles.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the nanocomposite structure.    Nanocomposite structure (200)    Core (201)    Isolated or islands of nanoparticles (i.e. metallic nanoparticles) (202A-202E)