NOVELTY - Method for fabricating hollow spheres comprises: (a) providing a homogeneous precursor solution comprising a first solvent and one or more anhydrous precursor species; (b) forming aerosol droplets having a first size distribution using the homogeneous precursor solution in an anhydrous carrier gas; (c) transporting the aerosol droplets through an aerosol reactor comprising a reactant to form many hollow spheres; and (d) controlling size and thickness of the hollow spheres.    USE - The method is useful for fabricating hollow spheres and nanofoams (claimed), where the nanofoams are useful: for power storage, spintronic applications, medical imaging, low-dielectric constant dielectrics, high performance catalysts for fuel cells, petrochemical processes, and the reduction of emissions of nitrogen oxides from internal combustion engines and coal-fired power plants.    ADVANTAGE - The method is a general, low-temperature, low cost, template free, nondestructive fabrication method for the metal oxide nanostructures. The nanofoams provided by the method, increase the sensitivity of the biomedical detectors; and enhance heat transfer of jet-turbine blades while decreasing their weight.    DETAILED DESCRIPTION - Method for fabricating hollow spheres comprises: (a) providing a homogeneous precursor solution comprising a first solvent and one or more anhydrous precursor species; (b) forming aerosol droplets having a first size distribution using the homogeneous precursor solution in an anhydrous carrier gas; (c) transporting the aerosol droplets through an aerosol reactor comprising a reactant to form many hollow spheres, where each of the hollow spheres is formed by one or more chemical reactions occurring at a surface of the aerosol droplet; and (d) controlling size and thickness of the hollow spheres by the precursor solution concentration, aerosol droplet size, temperature, residence time of the aerosol droplets in the aerosol reactor, and/or the reactant distribution in the aerosol reactor. An INDEPENDENT CLAIM is included for a method for fabricating nanofoam comprising step (a), (b) and (c), where one or more chemical reactions occurs at a surface of the aerosol droplet to form partially consolidated hollow sphere; and aggregating partially consolidated hollow spheres to form nanofoam.