09:00 〜 09:15
▲ [13a-D62-1] Nanostructured zinc oxide thin films for thermoelectric applications
キーワード：ZnO, nanostructured thin films, thermoelectrics
Zinc oxide is n-type superconductor with wide direct band gap (3.3 eV) which has always been attracted much attention in the scientific community because of its versatile applications (optics, solar cells, electrodes, gas sensors, etc.). ZnO can be also regarded as low-cost, nontoxic, stable thermoelectric material for space applications, solar-thermal and electrical-energy production [1]. In order to improve the efficiency of the thermoelectric conversion, the adimensional figure of merit ZT = sS2×T/k (s = electric conductivity, S = Seebeck coefficient; T = temperature and k = thermal conductivity) must be increased.
Our results [1] on Al-doped (AZO) ZnO thin films demonstrated that k can be depressed - and consequently ZT be improved - thanks to phonon scattering by the natural defects like grain boundaries, dislocations, and so on. AZO films deposited by PLD (pulsed laser deposition) on several substrates (SrTiO3 (STO), Al2O3, silica) always shows lower values of k and higher values of ZT in comparison with the bulk of the same composition: kSTO = 6.5 W/m×K, kAl2O3 = 6.90 W/m×K and ksilica = 4.89 W/m×K at 300K while (ZT)STO = 0.03, (ZT)Al2O3 = 0.04 and (ZT)silica = 0.045 at 600K (Being kbulk = 34 W/m K at 300K and (ZT)bulk = 0.014 at 600K). These results can be explained in relation to morphologies and nanostructures of the ZnO films.
Nanoengineering approach by insertion of nanosized nanopores or nanoparticles as artificial defects for phononic scattering, to reduce the thermal conductivity has also been tried. Porous AZO films prepared on silica by Mist-Chemical Vapor Deposition (CVD) shown very low k at 300K: kporous = 2.64 W/m×K [2]. AZO-PMMA nanocomposite thin films prepared on silica by double-beam PLD method showed kAZO-PMMA = 4.1 W/m K at 300 K [3]. More recently, insertion of Al2O3 nanodots in AZO films has been tried by PLD, ablating a surface-modified AZO target with Al2O3 slice stuck on it [4]. Results of Al2O3-doped AZO films will be reported at the conference.
Our results [1] on Al-doped (AZO) ZnO thin films demonstrated that k can be depressed - and consequently ZT be improved - thanks to phonon scattering by the natural defects like grain boundaries, dislocations, and so on. AZO films deposited by PLD (pulsed laser deposition) on several substrates (SrTiO3 (STO), Al2O3, silica) always shows lower values of k and higher values of ZT in comparison with the bulk of the same composition: kSTO = 6.5 W/m×K, kAl2O3 = 6.90 W/m×K and ksilica = 4.89 W/m×K at 300K while (ZT)STO = 0.03, (ZT)Al2O3 = 0.04 and (ZT)silica = 0.045 at 600K (Being kbulk = 34 W/m K at 300K and (ZT)bulk = 0.014 at 600K). These results can be explained in relation to morphologies and nanostructures of the ZnO films.
Nanoengineering approach by insertion of nanosized nanopores or nanoparticles as artificial defects for phononic scattering, to reduce the thermal conductivity has also been tried. Porous AZO films prepared on silica by Mist-Chemical Vapor Deposition (CVD) shown very low k at 300K: kporous = 2.64 W/m×K [2]. AZO-PMMA nanocomposite thin films prepared on silica by double-beam PLD method showed kAZO-PMMA = 4.1 W/m K at 300 K [3]. More recently, insertion of Al2O3 nanodots in AZO films has been tried by PLD, ablating a surface-modified AZO target with Al2O3 slice stuck on it [4]. Results of Al2O3-doped AZO films will be reported at the conference.