Atsuki Tomeda

Bio: Atsuki Tomeda is an academic researcher from Osaka University. The author has contributed to research in topics: Thermoelectric materials & Nanowire. The author has an hindex of 5, co-authored 7 publications receiving 112 citations.

Methodology of Thermoelectric Power Factor Enhancement by Controlling Nanowire Interface

Abstract: The simultaneous realization of low thermal conductivity and high thermoelectric power factor in materials has long been the goal for the social use of high-performance thermoelectric modules. Nanostructuring approaches have drawn considerable attention because of the success in reducing thermal conductivity. On the contrary, enhancement of the thermoelectric power factor, namely, the simultaneous increase of the Seebeck coefficient and electrical conductivity, has been difficult. We propose a method for the power factor enhancement by introducing coherent homoepitaxial interfaces with controlled dopant concentration, which enables the quasiballistic transmission of high-energy carriers. The wavenumber of the high-energy carriers is nearly conserved through the interfaces, resulting in simultaneous realization of a high Seebeck coefficient and relatively high electrical mobility. Here, we experimentally demonstrate the dopant-controlled epitaxial interface effect for the thermoelectric power factor enhanc...

[The 4th Thin Film and Surface Physics Division Award Speech] Methodology of thermoelectric power factor enhancement by controlling nanowire interface

Abstract: The simultaneous realization of low thermal conductivity and high thermoelectric power factor in materials has long been the goal for the social use of high-performance thermoelectric modules. Nanostructuring approaches have drawn considerable attention because of the success in reducing thermal conductivity. On the contrary, enhancement of the thermoelectric power factor, namely, the simultaneous increase of the Seebeck coefficient and electrical conductivity, has been difficult. We propose a method for the power factor enhancement by introducing coherent homoepitaxial interfaces with controlled dopant concentration, which enables the quasiballistic transmission of high-energy carriers. The wavenumber of the high-energy carriers is nearly conserved through the interfaces, resulting in simultaneous realization of a high Seebeck coefficient and relatively high electrical mobility. Here, we experimentally demonstrate the dopant-controlled epitaxial interface effect for the thermoelectric power factor enhancement using our \"embedded-ZnO nanowire structure\" having high-quality nanowire interfaces. This presents the methodology for substantial power factor enhancement by interface carrier scattering.

Carrier and phonon transport control by domain engineering for high-performance transparent thin film thermoelectric generator

Abstract: We develop transparent epitaxial SnO2 films with low thermal conductivity and high carrier mobility by domain engineering using the substrates with low symmetry: intentional control of the domain size and the defect density between crystal domains. The epitaxial SnO2 films on r-Al2O3 (a low symmetry substrate) exhibit a twice higher mobility than the epitaxial SnO2 films on c-Al2O3 (a high symmetry substrate), resulting in twice larger thermoelectric power factor in the SnO2 films on r-Al2O3. This mobility difference is likely attributed to the defect density between crystal domains. Furthermore, both samples exhibit almost the same thermal conductivities (∼5.1 ± 0.4 W m−1 K−1 for SnO2/r-Al2O3 sample and ∼5.5 ± 1.0 W m−1 K−1 for SnO2/c-Al2O3 sample), because their domain sizes are almost the same. The uni-leg type film thermoelectric power generator composed of the domain-engineered SnO2 film generates the maximum power density of ∼54 μW m−2 at the temperature difference of 20 K. This demonstrates that a transparent film thermoelectric power generator based on the domain engineering is promising to run some internet of things sensors in our human society.

Embedded-ZnO Nanowire Structure for High-Performance Transparent Thermoelectric Materials

Abstract: We present the structure of ZnO nanowires (NWs) embedded in ZnO films for high-performance transparent thermoelectric materials. The design concept is that the ZnO NWs exhibit high power factor and work as phonon scatterers to reduce the thermal conductivity. Here, we form an embedded-ZnO NWs structure on Si(111) substrates using physical vapor transport for ZnO NW formation and pulsed laser deposition for embedding NWs with ZnO. The NWs grew along the c-axis orientation vertically on the ZnO buffer/Si(111) substrates. Nanoscale voids near NWs were also observed in filling ZnO. The electrical measurements of films including NWs exhibited the reduction of electrical conductivity from that of bulk ZnO to a similar extent to the reduction in the case of ZnO films without NWs. This indicates that there was small electron scattering by ZnO NWs and the voids. However, considering that the mean free path of electron becomes lower by increasing carrier concentration, the electron scattering effect by nanostructuring can be found to be even weaker under the high doping condition compared with phonon scattering with large mean free path. Therefore, our study develops embedded-ZnO NWs structures promising for high-performance thermoelectric material with high electrical conductivity and low thermal conductivity.

Theory of enhancement of thermoelectric properties of materials with nanoinclusions.

Abstract: Based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons, we present a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. We show that the Seebeck coefficient can be significantly increased due to a strongly energy-dependent electronic scattering time. By including phonon scattering, we find that the enhancement of $ZT$ due to electron scattering is important for high doping, while at low doping it is primarily due to a decrease in the phonon thermal conductivity.

Methodology of Thermoelectric Power Factor Enhancement by Controlling Nanowire Interface

Abstract: The simultaneous realization of low thermal conductivity and high thermoelectric power factor in materials has long been the goal for the social use of high-performance thermoelectric modules. Nanostructuring approaches have drawn considerable attention because of the success in reducing thermal conductivity. On the contrary, enhancement of the thermoelectric power factor, namely, the simultaneous increase of the Seebeck coefficient and electrical conductivity, has been difficult. We propose a method for the power factor enhancement by introducing coherent homoepitaxial interfaces with controlled dopant concentration, which enables the quasiballistic transmission of high-energy carriers. The wavenumber of the high-energy carriers is nearly conserved through the interfaces, resulting in simultaneous realization of a high Seebeck coefficient and relatively high electrical mobility. Here, we experimentally demonstrate the dopant-controlled epitaxial interface effect for the thermoelectric power factor enhanc...

[The 4th Thin Film and Surface Physics Division Award Speech] Methodology of thermoelectric power factor enhancement by controlling nanowire interface

Abstract: The simultaneous realization of low thermal conductivity and high thermoelectric power factor in materials has long been the goal for the social use of high-performance thermoelectric modules. Nanostructuring approaches have drawn considerable attention because of the success in reducing thermal conductivity. On the contrary, enhancement of the thermoelectric power factor, namely, the simultaneous increase of the Seebeck coefficient and electrical conductivity, has been difficult. We propose a method for the power factor enhancement by introducing coherent homoepitaxial interfaces with controlled dopant concentration, which enables the quasiballistic transmission of high-energy carriers. The wavenumber of the high-energy carriers is nearly conserved through the interfaces, resulting in simultaneous realization of a high Seebeck coefficient and relatively high electrical mobility. Here, we experimentally demonstrate the dopant-controlled epitaxial interface effect for the thermoelectric power factor enhancement using our \"embedded-ZnO nanowire structure\" having high-quality nanowire interfaces. This presents the methodology for substantial power factor enhancement by interface carrier scattering.