Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric... more Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric in wearable devices. In this work, copper selenide films are achieved by a novel low-temperature technique, namely pulsed hybrid reactive magnetron sputtering (PHRMS). A brief introduction to the basic chemistry and physics involved during growth is included to explain its fundamentals. PHRMS is a single-step, room temperature (RT), fabrication process carried out in another ways conventional vacuum sputtering system. It does not require high-temperature post-annealing to obtain films with great thermoelectric performance. It is, therefore, compatible with polymeric substrates like Kapton tape. Several sets of films covering a large exploratory compositional range (from Cu/Se = 1 to 9) are deposited and their microstructure and thermoelectric properties are analyzed at RT. Power factors as high as 1.1 mW m−1 K−2 in the in-plane direction and thermal conductivities as low as κ = 0.8 ± 0.1 W m−1 K−1 in the out-of-plane direction have been obtained for β-Cu2Se films. Consequently, a figure of merit of 0.4 at RT can be estimated under the assumption that for this polycrystalline cubic phase no additional anisotropy in the thermoelectric properties is introduced by the planar configuration. Moreover, PHRMS is also industrially scalable and compatible with the in-line fabrication of other selenides.
In this work, we measure the thermal and thermoelectric properties of large-area Si 0.8 Ge 0.2 na... more In this work, we measure the thermal and thermoelectric properties of large-area Si 0.8 Ge 0.2 nano-meshed films fabricated by DC sputtering of Si 0.8 Ge 0.2 on highly ordered porous alumina matrices. The Si 0.8 Ge 0.2 film replicated the porous alumina structure resulting in nano-meshed films. Very good control of the nanomesh geometrical features (pore diameter, pitch, neck) was achieved through the alumina template, with pore diameters ranging from 294 ± 5nm down to 31 ± 4 nm. The method we developed is able to provide large areas of nano-meshes in a simple and reproducible way, being easily scalable for industrial applications. Most importantly, the thermal conductivity of the films was reduced as the diameter of the porous became smaller to values that varied from κ = 1.54 ± 0.27 W K −1 m −1 , down to the ultra-low κ = 0.55 ± 0.10 W K −1 m −1 value. The latter is well below the amorphous limit, while the Seebeck coefficient and electrical conductivity of the material were retained. These properties, together with our large area fabrication approach, can provide an important route towards achieving high conversion efficiency, large area, and high scalable thermoelectric materials.
— Aluminum nitride (AlN) thin films were grown in a N 2 atmosphere onto a Si/Si 3 N 4 substrate b... more — Aluminum nitride (AlN) thin films were grown in a N 2 atmosphere onto a Si/Si 3 N 4 substrate by pulsed laser ablation. We have varied the substrate temperature for the thin film growth, using X-ray reflectometry analysis, we have characterized the thickness and density of the thin layer and the interface roughness from the X-ray reflectivity profiles. Experimental data showed that the root-mean-square roughness was in the range of 0.3 nm. The X-ray photoelectron spectroscopy (XPS) was employed to characterize the chemical composition of the films. These measurements detected carbon and oxygen contamination at the surface. In the high-resolution XPS Al2p data, binding energies for Al–N and Al–O species were identified but no Al–Al species were present. In the N1s data, N–O species were not detected, but chemically bonded O was present in the films as Al–O species. Furthermore, the value of optical energy gap, E g was ∼5.3 (±0.1) eV. The composition varied with process conditions, and the nitrogen content decreased in AlN films processed above 500 °C.
Aluminum nitride films (AlN) were produced by Nd:YAG pulsed laser (PLD), with repetition rate of ... more Aluminum nitride films (AlN) were produced by Nd:YAG pulsed laser (PLD), with repetition rate of 10 Hz. The laser interaction on Al target under nitrogen gas atmosphere generates plasma which is produced at room temperature with variation in the pressure work from 0.39 Pa to 1.5 Pa thus producing different AlN films. In this sense the dependency of optical properties with the pressure of deposition was studied. The plasma generated at different pressures was characterized by optical emission spectroscopy (OES). Additionally ionic and atomic species from the emission spectra obtained were observed. The plume electronic temperature has been determined by assuming a local thermo-dynamic equilibrium of the emitting species. Finally the electronic temperature was calculated with Boltzmann plot from relative intensities of spectral lines. The morphology and composition of the films were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy analysis (XPS) and Raman Spectroscopy. The optical reflectance spectra and color coordinates of the films were obtained by optical spectral reflectometry technique in the range from 400 nm to 900 nm. A clear dependence in morphological properties and optical properties, as a function of the applied deposition pressure, was found in this work which offers a novel application in optoelectronic industry.
Si x Ge 1−x alloys are well-known thermoelectric materials with a high figure of merit at high te... more Si x Ge 1−x alloys are well-known thermoelectric materials with a high figure of merit at high temperatures. In this work, metal-induced crystallization (MIC) has been used to grow Si 0.8 Ge 0.2 films that present improved thermoelectric performance (zT=5.6×10 −4 at room temperature) —according to previously reported values on films—with a relatively large power factor (σ·S 2 =16 μW·m −1 ·K −2). More importantly, a reduction in the thermal conductivity at room temperature (κ=1.13±0.12 W·m −1 ·K −1) compared to other Si–Ge films (∼3 W·m −1 ·K −1) has been found. Whereas the usual crystallization of amorphous SiGe (a-SiGe) is achieved at high temperatures and for long times, which triggers dopant loss, MIC reduces the crystallization temperature and the heating time. The associated dopant loss is thus avoided, resulting in a nanostructuration of the film. Using this method, we obtained Si 0.8 Ge 0.2 films (grown by DC plasma sputtering) with appropriate compositional and structural properties. Different thermal treatments were tested in situ (by heating the sample inside the deposition chamber) and ex situ (annealed in an external furnace with controlled conditions). From the studies of the films by: x-ray diffraction (XRD), synchrotron radiation grazing incidence x-ray diffraction (SR-GIXRD), micro Raman, scanning electron microscopy (SEM), x-ray photoemission spectroscopy (XPS), Hall effect, Seebeck coefficient, electrical and thermal conductivity measurements, we observed that the in situ films at 500 °C presented the best zT values with no gold contamination. S Online supplementary data available from stacks.iop.org/NANO/27/175401/mmedia
Silicon and germanium present distinct and interesting transport properties. However, composites ... more Silicon and germanium present distinct and interesting transport properties. However, composites made of silicon-germanium (SiGe) have resulted in a breakthrough in terms of their transport properties. Currently, these alloys are used in different applications, such as microelectronic devices and integrated circuits, photovoltaic cells, and thermo-electric applications. With respect to thermoelectricity, in the last decades, Si 0.8 Ge 0.2 has attracted significant attention as an energy harvesting material, for powering space applications and other industrial applications. This chapter focuses on the recent advances and new approaches in silicon-germanium (Si 1−x Ge x) nanostructures for thermoelectric devices with high thermoelectric efficiency obtained through magnetron sputtering.
Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric... more Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric in wearable devices. In this work, copper selenide films are achieved by a novel low-temperature technique, namely pulsed hybrid reactive magnetron sputtering (PHRMS). A brief introduction to the basic chemistry and physics involved during growth is included to explain its fundamentals. PHRMS is a single-step, room temperature (RT), fabrication process carried out in another ways conventional vacuum sputtering system. It does not require high-temperature post-annealing to obtain films with great thermoelectric performance. It is, therefore, compatible with polymeric substrates like Kapton tape. Several sets of films covering a large exploratory compositional range (from Cu/Se = 1 to 9) are deposited and their microstructure and thermoelectric properties are analyzed at RT. Power factors as high as 1.1 mW m−1 K−2 in the in-plane direction and thermal conductivities as low as κ = 0.8 ± 0.1 W m−1 K−1 in the out-of-plane direction have been obtained for β-Cu2Se films. Consequently, a figure of merit of 0.4 at RT can be estimated under the assumption that for this polycrystalline cubic phase no additional anisotropy in the thermoelectric properties is introduced by the planar configuration. Moreover, PHRMS is also industrially scalable and compatible with the in-line fabrication of other selenides.
In this work, we measure the thermal and thermoelectric properties of large-area Si 0.8 Ge 0.2 na... more In this work, we measure the thermal and thermoelectric properties of large-area Si 0.8 Ge 0.2 nano-meshed films fabricated by DC sputtering of Si 0.8 Ge 0.2 on highly ordered porous alumina matrices. The Si 0.8 Ge 0.2 film replicated the porous alumina structure resulting in nano-meshed films. Very good control of the nanomesh geometrical features (pore diameter, pitch, neck) was achieved through the alumina template, with pore diameters ranging from 294 ± 5nm down to 31 ± 4 nm. The method we developed is able to provide large areas of nano-meshes in a simple and reproducible way, being easily scalable for industrial applications. Most importantly, the thermal conductivity of the films was reduced as the diameter of the porous became smaller to values that varied from κ = 1.54 ± 0.27 W K −1 m −1 , down to the ultra-low κ = 0.55 ± 0.10 W K −1 m −1 value. The latter is well below the amorphous limit, while the Seebeck coefficient and electrical conductivity of the material were retained. These properties, together with our large area fabrication approach, can provide an important route towards achieving high conversion efficiency, large area, and high scalable thermoelectric materials.
— Aluminum nitride (AlN) thin films were grown in a N 2 atmosphere onto a Si/Si 3 N 4 substrate b... more — Aluminum nitride (AlN) thin films were grown in a N 2 atmosphere onto a Si/Si 3 N 4 substrate by pulsed laser ablation. We have varied the substrate temperature for the thin film growth, using X-ray reflectometry analysis, we have characterized the thickness and density of the thin layer and the interface roughness from the X-ray reflectivity profiles. Experimental data showed that the root-mean-square roughness was in the range of 0.3 nm. The X-ray photoelectron spectroscopy (XPS) was employed to characterize the chemical composition of the films. These measurements detected carbon and oxygen contamination at the surface. In the high-resolution XPS Al2p data, binding energies for Al–N and Al–O species were identified but no Al–Al species were present. In the N1s data, N–O species were not detected, but chemically bonded O was present in the films as Al–O species. Furthermore, the value of optical energy gap, E g was ∼5.3 (±0.1) eV. The composition varied with process conditions, and the nitrogen content decreased in AlN films processed above 500 °C.
Aluminum nitride films (AlN) were produced by Nd:YAG pulsed laser (PLD), with repetition rate of ... more Aluminum nitride films (AlN) were produced by Nd:YAG pulsed laser (PLD), with repetition rate of 10 Hz. The laser interaction on Al target under nitrogen gas atmosphere generates plasma which is produced at room temperature with variation in the pressure work from 0.39 Pa to 1.5 Pa thus producing different AlN films. In this sense the dependency of optical properties with the pressure of deposition was studied. The plasma generated at different pressures was characterized by optical emission spectroscopy (OES). Additionally ionic and atomic species from the emission spectra obtained were observed. The plume electronic temperature has been determined by assuming a local thermo-dynamic equilibrium of the emitting species. Finally the electronic temperature was calculated with Boltzmann plot from relative intensities of spectral lines. The morphology and composition of the films were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy analysis (XPS) and Raman Spectroscopy. The optical reflectance spectra and color coordinates of the films were obtained by optical spectral reflectometry technique in the range from 400 nm to 900 nm. A clear dependence in morphological properties and optical properties, as a function of the applied deposition pressure, was found in this work which offers a novel application in optoelectronic industry.
Si x Ge 1−x alloys are well-known thermoelectric materials with a high figure of merit at high te... more Si x Ge 1−x alloys are well-known thermoelectric materials with a high figure of merit at high temperatures. In this work, metal-induced crystallization (MIC) has been used to grow Si 0.8 Ge 0.2 films that present improved thermoelectric performance (zT=5.6×10 −4 at room temperature) —according to previously reported values on films—with a relatively large power factor (σ·S 2 =16 μW·m −1 ·K −2). More importantly, a reduction in the thermal conductivity at room temperature (κ=1.13±0.12 W·m −1 ·K −1) compared to other Si–Ge films (∼3 W·m −1 ·K −1) has been found. Whereas the usual crystallization of amorphous SiGe (a-SiGe) is achieved at high temperatures and for long times, which triggers dopant loss, MIC reduces the crystallization temperature and the heating time. The associated dopant loss is thus avoided, resulting in a nanostructuration of the film. Using this method, we obtained Si 0.8 Ge 0.2 films (grown by DC plasma sputtering) with appropriate compositional and structural properties. Different thermal treatments were tested in situ (by heating the sample inside the deposition chamber) and ex situ (annealed in an external furnace with controlled conditions). From the studies of the films by: x-ray diffraction (XRD), synchrotron radiation grazing incidence x-ray diffraction (SR-GIXRD), micro Raman, scanning electron microscopy (SEM), x-ray photoemission spectroscopy (XPS), Hall effect, Seebeck coefficient, electrical and thermal conductivity measurements, we observed that the in situ films at 500 °C presented the best zT values with no gold contamination. S Online supplementary data available from stacks.iop.org/NANO/27/175401/mmedia
Silicon and germanium present distinct and interesting transport properties. However, composites ... more Silicon and germanium present distinct and interesting transport properties. However, composites made of silicon-germanium (SiGe) have resulted in a breakthrough in terms of their transport properties. Currently, these alloys are used in different applications, such as microelectronic devices and integrated circuits, photovoltaic cells, and thermo-electric applications. With respect to thermoelectricity, in the last decades, Si 0.8 Ge 0.2 has attracted significant attention as an energy harvesting material, for powering space applications and other industrial applications. This chapter focuses on the recent advances and new approaches in silicon-germanium (Si 1−x Ge x) nanostructures for thermoelectric devices with high thermoelectric efficiency obtained through magnetron sputtering.
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