Influences of substrate types and heat treatment conditions on structural and thermoelectric properties of nanocrystalline Bi2Te3 thin films formed by DC magnetron sputtering
“…4 , we investigated the degree of alignment in the integrated nanoplate films using the Lotgering factor, F , which was calculated using Eq. ( 1 ) 41 – 43 : Figure 3 XRD patterns of the nanocomposite films obtained for various SWCNT-ethanol solutions. Figure 4 Lotgering factor of the nanocomposite films obtained for various SWCNT-ethanol solutions.…”
Single-wall carbon nanotubes (SWCNTs) and Bi2Te3 nanoplates are very promising thermoelectric materials for energy harvesting. When these two materials are combined, the resulting nanocomposites exhibit high thermoelectric performance and excellent flexibility. However, simple mixing of these materials is not effective in realizing high performance. Therefore, we fabricated integrated nanocomposites by adding SWCNTs during solvothermal synthesis for the crystallization of Bi2Te3 nanoplates and prepared flexible integrated nanocomposite films by drop-casting. The integrated nanocomposite films exhibited high electrical conductivity and an n-type Seebeck coefficient owing to the low contact resistance between the nanoplates and SWCNTs. The maximum power factor was 1.38 μW/(cm K2), which was 23 times higher than that of a simple nanocomposite film formed by mixing SWCNTs during drop-casting, but excluding solvothermal synthesis. Moreover, the integrated nanocomposite films maintained their thermoelectric properties through 500 bending cycles.
“…4 , we investigated the degree of alignment in the integrated nanoplate films using the Lotgering factor, F , which was calculated using Eq. ( 1 ) 41 – 43 : Figure 3 XRD patterns of the nanocomposite films obtained for various SWCNT-ethanol solutions. Figure 4 Lotgering factor of the nanocomposite films obtained for various SWCNT-ethanol solutions.…”
Single-wall carbon nanotubes (SWCNTs) and Bi2Te3 nanoplates are very promising thermoelectric materials for energy harvesting. When these two materials are combined, the resulting nanocomposites exhibit high thermoelectric performance and excellent flexibility. However, simple mixing of these materials is not effective in realizing high performance. Therefore, we fabricated integrated nanocomposites by adding SWCNTs during solvothermal synthesis for the crystallization of Bi2Te3 nanoplates and prepared flexible integrated nanocomposite films by drop-casting. The integrated nanocomposite films exhibited high electrical conductivity and an n-type Seebeck coefficient owing to the low contact resistance between the nanoplates and SWCNTs. The maximum power factor was 1.38 μW/(cm K2), which was 23 times higher than that of a simple nanocomposite film formed by mixing SWCNTs during drop-casting, but excluding solvothermal synthesis. Moreover, the integrated nanocomposite films maintained their thermoelectric properties through 500 bending cycles.
“…There are a few measurement methods in obtaining the thermal conductivities of thin films in the in-plane direction. Here, we calculated the in-plane total thermal conductivity, κ, of the films, which was sum of the electronic and lattice thermal conductivities based on the previous report [30]. The electronic thermal conductivity was acquired from the experimentally measured electrical conductivity combined with the Wiedemann-Franz law.…”
Section: Methodsmentioning
confidence: 99%
“…However, a possible mechanism can be explained based on the theory of recovery and recrystallization of plastically deformed metals [56]. The as-deposited Bi 2 Te 3 thin films obtain relatively high lattice strain [30], which is a similar trend in plastically deformed metals. According to the above-mentioned theory, firstly, a recovery occurs at lower temperature, and subsequently, recrystallization occurs at higher temperature.…”
Section: Structural Characteristics Of the Bi 2 Te 3 Thin Filmsmentioning
confidence: 99%
“…Among these, sputtering can deposit thin films with high adhesion on various substrates. However, sputtering frequently causes deviations in the composition of the alloyed thin films when the substrate is heated during deposition [30]. To decrease the composition deviation and enhance the thermoelectric characteristics of thin films, post processing treatments, such as heat treatment, laser annealing, and homogeneous electronbeam irradiation, are widely utilized [31][32][33][34][35].…”
Section: Introductionmentioning
confidence: 99%
“…Figure6shows the calculated thermal transport characteristics of the Bi2Te3 thin films in the in-plane direction formed under different temperature increase rates during heat treatment. The detailed calculation procedure is presented in the previous report[30]. The electronic thermal conductivity, κe, is derived from the experimentally measured electrical conductivities using the Wiedemann-Franz law, given by κe = LσT.…”
Thin film thermoelectric generators are expected to be applied as power supplies for various Internet of Thing devices owing to their small size and flexible structure. However, the primary challenges of thin film thermoelectric generators are to improve their thermoelectric performance and reduce their manufacturing cost. Hence, Bi2Te3 thin films were deposited using direct current magnetron sputtering, followed by heat treatment at 573 K with different temperature increase rates ranging from 4 to 16 K/min. The in-plane Seebeck coefficient and electrical conductivity were measured at approximately 293 K. The in-plane thermal conductivity was calculated using the models to determine the power factor (PF) and dimensionless figure of merit (ZT). The temperature increase rate clearly affected the atomic composition, crystal orientation, and lattice strains, but not the crystallite size. The PF and dimensionless ZT increased as the temperature increase rate increased. The highest PF of 17.5 µW/(cm·K2) and ZT of 0.48 were achieved at a temperature increase rate of 16 K/min, while the unannealed thin film exhibited the lowest PF of 0.7 µW/(cm·K2) and ZT of 0.05. Therefore, this study demonstrated a method to enhance the thermoelectric performance of Bi2Te3 thin films by heat treatment at the appropriate temperature increase rate.
Water‐floating carbon nanotube thermoelectric generators (CNT‐TEGs) can effectively power Internet of Things (IoT) applications. CNT‐TEGs produce electricity by floating on water to generate a temperature gradient in the CNT films, where water pumping via capillary action causes evaporation‐induced cooling in selected areas. However, the amount of electricity required for target applications needs to be increased. Therefore, the wettability of CNT films is controlled via various treatments to increase water evaporation and temperature difference in the films. The contact angle of the water droplet on the film surface related to the wettability decreases upon atmospheric‐pressure plasma jet irradiation and increases upon waterproof spray treatment. Intermediate wettability is obtained by combining the two aforementioned treatments. Under the environmental conditions of light irradiation (1 kW m−2) and wind (3 m s−1) at a water temperature of 20 °C, the CNT‐TEGs with the combined treatment exhibit a highest output voltage of 3.9 mV, which is 30% larger than that of the pristine CNT‐TEG. At a water temperature of 60 °C, a highest output voltage of 13.1 mV is achieved in the pristine CNT‐TEG. The performance enhancement of CNT‐TEGs by controlling the wettability of CNT films under various environmental conditions can facilitate advancements in IoT technology.
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