In situ thermal annealing was used for the first time to observe directly that Au nanoparticles, which were originally fully embedded in the near-surface region of TiO(2), can be tailored into hemispheres exposed at the surface at elevated temperature. Precise control of the size of the Au hemispheres was achieved by subsequent low-energy ion sputtering. This method can be used to control the structure and size of a wide variety of nanoparticles in a matrix where surface structure and particle size are required to obtain specific material properties.