The thermal diffusivity of aluminum oxide (Al(2)O(3)) films and the thermal boundary resistance between Al(2)O(3) and molybdenum (Mo) films were investigated using 'rear heating/front detection (RF) type' picosecond and nanosecond thermoreflectance systems. Amorphous Al(2)O(3) films sandwiched between Mo films (Mo/Al(2)O(3)/Mo) were prepared on fused silica substrates by RF magnetron sputtering using Al(2)O(3) and Mo targets. The thicknesses of the Al(2)O(3) and Mo layers were 0.5-100 nm and 70 nm, respectively. The thermal diffusivity of the amorphous Al(2)O(3) films was found to be 9.5 x 10(-7) m(2)/s. The thermal boundary resistance between Al(2)O(3) and Mo was 1.5 x 10(-9) m(2)K/W, corresponding to the thermal resistance of a 4.2 nm thick Al(2)O(3) film or a 77 nm thick Mo film. However, the thermal diffusivity of the amorphous Al(2)O(3) film is approximately one twelfth that of bulk polycrystalline Al(2)O(3). This difference was attributed to the smaller mean free path of phonons in amorphous Al(2)O(3) due to its disordered structure. (C) 2009 Elsevier B.V. All rights reserved.