Al2O3 peaks observed even for the untreated sample may originate from the surface oxidation of Al film at ambient condition. Figure 4 XRD patterns of a 90-nm-thick Al film on Si substrate before and after annealing. Samples annealed for 9 h at 550°C. Figure 5 shows the variation of sheet resistance against annealing time for a MM-102 concentration 40-nm-thick Al film on Si substrate. For comparison, the sheet resistances of an untreated and a 9-h annealed 90-nm-thick Al films are also plotted. The distribution of sheet resistances at each data MK-0457 point was less than 3% around the average value, leading to the overlap of

error bars with the symbols representing the average. The sheet resistance of the sample increases by approximately

25 times after 3 h annealing at 550°C. This is an indicator that spontaneous granulation has significantly progressed and the initial Al film was substantially consumed in the middle of the process (see the particles of a variety of sizes in Figure 2b). Although the sheet resistance GSK1120212 cost of the sample is determined by the combined effects of particles and residual film, it is reasonable to think that the residual film is a dominant player due to the small size of the particles. Raising the annealing time further, the sheet resistance slightly increases, then almost saturates at about 260 Ω/sq, which corresponds to a 27-fold increase from the initial value. The slight increase of the sheet resistance may be caused by the further granulation and Al-Si alloying. The sheet resistances of a 40-nm-thick and a 90-nm-thick Al films after 9 h annealing are close to each other, reflecting that microparticle formation accompanying Al film consumption has maturely taken

place in both samples. The resistivity (ρ) of the untreated Al films was (3.8 to 4.1) × 10−7 Ω m when calculated using a simple relation, ρ = R s × t, where R s and t are the sheet resistance and the thickness of the film, respectively. This calculated value is more than an order of magnitude larger than the literature value [(2.65 to 2.82) × 10−8 Ω m] [16, 26], MRIP which is attributable to the presence of Al2O3 layer on the surface of Al films. The surface-oxidized microparticles of Al-Si alloys and the channel network structures of the surface-oxidized Al films are expected to cooperatively suppress the thermal conduction through the heterogeneous systems, resulting in the improved thermoelectric performance. Figure 5 Sheet resistance of a 40-nm-thick Al film on Si substrate as a function of annealing time. Annealing temperature was fixed at 550°C. The sheet resistance rapidly increases after 3 h annealing and then almost saturates. For comparison, sheet resistances of a 90-nm-thick Al film before and after 9 h annealing are also plotted.