Search

The structure–property relationship at interfaces is difficult to probe for thermoelectric materials with a complex interfacial microstructure. Designing thermoelectric materials with a simple, structurally‐uniform interface provides a facile way to understand how these interfaces influence the transport properties. Here, we synthesized Bi2−xSbxTe3 (x = 0, 0.1, 0.2, 0.4) nanoflakes using a hydrothermal method, and prepared Bi2−xSbxTe3 thin films with predominantly (0001) interfaces by stacking the nanoflakes through spin coating. The influence of the annealing temperature and Sb content on the (0001) interface structure was systematically investigated at atomic scale using aberration‐corrected scanning transmission electron microscopy. Annealing and Sb doping facilitate atom diffusion and migration between adjacent nanoflakes along the (0001) interface. As such it enhances interfacial connectivity and improves the electrical transport properties. Interfac reactions create new interfaces that increase the scattering and the Seebeck coefficient. Due to the simultaneous optimization of electrical conductivity and Seebeck coefficient, the maximum power factor of the Bi1.8Sb0.2Te3 nanoflake films reaches 1.72 mW m−1 K−2, which is 43% higher than that of a pure Bi2Te3 thin film. [ABSTRACT FROM AUTHOR]

The High Target Utilisation Sputtering technique (HiTUS) is of interest for industrial processes, including in roll‐to‐roll manufacturing. This study marks the first application of HiTUS to thermoelectric materials, exemplified by bismuth telluride. The HiTUS technique separates the sputtering power into the plasma power and the target power, with additional kinetic energy in the sputtering particles from the applied electrical field, thus enabling a much wider sputter parameter space to modify the film performance. This study investigates how plasma power, target power, and substrate bias in HiTUS intricately influence crystal orientation/size, elemental composition, surface morphology, and other film properties. These factors subsequently affect carrier density/mobility, and consequently the thermoelectric performance of the bismuth telluride film. These deposited films reach a power factor of 6.5 × 10−4 W m−1 K−2 with a figure of merit ≈0.14 at room temperature, the highest value for room‐temperature sputtered un‐doped bismuth telluride. Subsequent post‐deposition annealing significantly enhances the crystallinity of the film (highly polycrystalline), further improving the power factor to 23.5 × 10−4 W m−1 K‐2, with a figure of merit ≈0.45 at room temperature. The excellent performance of the HiTUS fabricated thermoelectric film opens opportunities for the large‐area manufacture of thin‐film thermoelectric materials and devices. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) films, which are normally fabricated by MicroElectroMechanical‐Systems (MEMS) technology, are crucial for the development of micro‐TE devices (e.g., Peltier coolers for hot‐spot cooling, TE generators). However, achieving a significant TE property (e.g., high power factor) of TE films and a low‐cost fabrication process is challenging. A novel fabrication technique named PowderMEMS to fabricate high‐performance, low‐cost TE films, and micro‐patterns is presented in this article. The TE film is based on agglomeration of micro‐sized N‐type Bi2Te2.5Se0.5(BTS) powders with stoichiometric composition by the molten binder bismuth (Bi). The influence of the key process parameters (e.g., the weight ratio between the TE powder and the binder, the hot‐pressing duration, and pressure) on the TE performance is investigated. The TE film exhibits a maximum power factor of 1.7 mW m−1K−2 at room temperature, which is the highest value reported so far for the state‐of‐the‐art TE thick film (thickness > 10 μm). Besides, the PowderMEMS‐based TE films are successfully patterned to the micro‐pillar array, which opens up a new MEMS‐compatible approach for manufacturing micro‐TE devices. [ABSTRACT FROM AUTHOR]

It has been reported that introducing Ag interlayer at the Cu/Bi 2 Te 3 interface can achieve ultra-low electrical contact resistivity. However, there is no consensus on the influence of Ag diffusion induced by Ag interlayer on electrical contact. Thus, the impact of Ag diffusion on electrical contact conductivity for Cu/Ag/Bi 2 Te 3 multilayers was investigated. The generation of interfacial compounds induced by Ag diffusion was analyzed and the contact resistivity was measured in Cu/Ag/Bi 2 Te 3 multilayers with different Ag interlayer thickness before and after annealing. It was found that Ag diffusion induced interfacial compounds Cu 4 Ag 3 Te 4 at the Cu/Ag interface before annealing, which could decrease contact resistivity to 3.728×10−12 Ω∙m2. After annealing, the relative amount of Cu 4 Ag 3 Te 4 at the Cu/Ag interface slightly decreased, and the Ag 2 Te was found to appear at the Ag/Bi 2 Te 3 interface, which could further decrease contact resistivity to 3.187×10−12 Ω∙m2. With Ag interlayer thickness increasing from 50 nm to 300 nm, the contact resistivity decreased from 3.726×10−10 Ω∙m2 to 3.728×10−12 Ω∙m2 before annealing because the relative amount of Cu 4 Ag 3 Te 4 increased about 5 times, after annealing the contact resistivity further decreased by 10.27∼41.7 % because the relative amount of Ag 2 Te increased about 1.1 times. In addition, we had optimized the ultra-low contact resistivity test method by redesigning the structure of test samples and modifying the formula of contact resistivity to eliminate two errors. One is caused by Cu electrode short-circuit resistance due to the test current being short-circuited by the middle electrode between two test electrodes. The other is caused by the increased electrical resistance of Bi 2 Te 3 thin film due to Te atom volatilization after annealing. The results showed that the errors of the test results were reduced by at least 21.50 %. Our work provides guidance for further optimizing electrical contact of thin-film thermoelectric devices. [Display omitted] • The influence of Ag diffusion on contact resistivity is investigated. • The variation of contact resistivity with Ag interlayer thickness is studied. • Interfacial compounds induced by Ag diffusion is semi-quantitatively analyzed. • Ultra-low contact resistivity test method is optimized by eliminating two errors. [ABSTRACT FROM AUTHOR]

In this work, we investigated the thermoelectric properties of SnSe (Tin Selenide) thin films onto SiO 2 /Si-wafer substrates as prepared by RF (radio frequency) magnetron sputtering technique. The sputtering conditions used base pressure below 5.5 10−4 Pa and working pressure at 0.93 Pa within the Ar atmosphere as a flow rate fixed 40 sccm. The RF sputtering power was applied at 80 W and sputtering time for 30 min. After thin film deposition, as-deposited thin films were annealed by the vacuum annealing method at 300–450 °C. The crystal structure, morphology and film thickness, and atomic composition of SnSe thin film were carried out by X-ray diffraction (XRD), the field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques, respectively. The thermoelectric properties (electrical resistivity; ρ) and Seebeck coefficient; S) were measured by the ZEM-3 method to calculate the power factor (PF) value. The results showed that the as-deposited thin films had improved the crystallography of SnSe from amorphous to crystalline phases after thin films were annealed at a temperature range of 300–400 °C. At room temperature, the maximum power factor of 0.35 mW m˗1 K˗2 (ρ = 202 mΩ m and S = 165 μV K˗1) could be found to estimate the dimensionless Figure of Merit (ZT) values around 0.44 for annealing thin film sample at 400 °C. • RF magnetron sputtering fabricated SnSe thin films onto SiO 2 /Si-wafer substrates. • Amorphous SnSe thin film could be changed to crystalline through thermal annealing at 300–400 °C. • The annealing thin film sample at 400 °C showed the PF max of 0.35 mW m˗1 K˗2 to be estimated the ZT value of around 0.44. [ABSTRACT FROM AUTHOR]

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Thermoelectric thin films are of great interest for self-powering Internet of Things (IoT) nodes via energy harvesting. Heusler-type Fe 2 VAl attracts some attention for room-temperature thermoelectric applications. However, the large overall thermal conductivity leads to a poor performance that restricts the current investigations. Herein, we report a comprehensive study of structural, thermoelectric, and magnetic properties of Fe 2 V 0.9 Ti 0.1 Al thin films on quartz substrate, grown by magnetron sputtering. It is found that high-temperature annealing is more effective than the long-time annealing at the low temperatures to stabilize the L 2 1 type structure of Fe 2 VAl, leading to a much larger Seebeck coefficient and slightly higher thermal conductivity. More importantly, the significant off-stoichiometry phenomenon, namely Fe-rich composition, contributes to n-type conduction of thin films. Both the picosecond and nanosecond time-domain thermoreflectance techniques were employed to successfully measure the thin-film thermal conductivities, merely one-third of bulk material, demonstrating the effectiveness of utilizing nanostructuring to reduce the thermal conductivity of Fe 2 VAl. Moreover, magnetic susceptibility measurements reveal that thin films are ferromagnets, while the bulk sample is characterized by paramagnetism. Our finding sheds new light on the composition-structure-property relationship of Fe 2 VAl thin films for future related applications. Image, graphical abstract The significant off-stoichiometry of Ti doped Fe 2 VAl films in the L2 1 type structure grown on quartz substrate leads to the unexpected n-type conduction and strong ferromagetism, which are may be helpful for thermoelectric, magnetoelectronic, and also spintronic applications. [ABSTRACT FROM AUTHOR]

Amorphization using impurity doping is a promising approach to improve the thermoelectric properties of tin-doped indium oxide (ITO) thin films. However, an abnormal phenomenon has been observed where an excessive concentration of doped atoms increases the lattice thermal conductivity (κl). To elucidate this paradox, we propose two hypotheses: (1) metal hydroxide formation due to the low bond enthalpy energy of O and metal atoms and (2) localized vibration due to excessive impurity doping. To verify these hypotheses, we doped ZnO and CeO2, which have low and high bond enthalpies with oxygen, respectively, into the ITO thin film. Regardless of the bond enthalpy energy, the κl values of the two thin films increased due to excessive doping. Fourier transform infrared spectroscopy was conducted to determine the metal hydroxide formation. There was no significant difference in wave absorbance originating from the OH stretching vibration. Therefore, the increase in κl due to the excessive doping was due to the formation of localized regions in the thin film. These results could be valuable for various applications using other transparent conductive oxides and guide the control of the properties of thin films.

Nanostructured Bi 2 Te 3 thin films were electrodeposited in the electrolyte of TeO 2 and Bi(NO 3) 3 ·5H 2 O without any additive. Electrochemical tests proved that Bi3+ was reduced to Bi firstly, which induce the reduction of HTeO 2 + to fulfill the co-position. The stoichiometric ratio of Bi 2 Te 3 was controlled by the adjustment of depositing duration under suitable deposition potential. The EIS results illustrated that the rate of stable growth of the films was determined by the applied potential. The nucleation of Bi 2 Te 3 was a progressive process, during which all the nuclei formed uniformly. The subsequent stable growth of the Bi 2 Te 3 thin films was controlled by Nernst diffusion process at a suitable depositing rate. The uniform nucleation and growth caused the ideal (110) texture. The hydrogen evolution reaction and the over growth was avoided, so that the compact rice-like nanostructure could be obtained. The Bi 2 Te 3 thin films were controlled to a state of stoichiometry composition, single phase structure, compact rice-like nano-morphology and (110) texture. Their electrical conductivity reached as high as 1.240 × 105 S·m−1, which caused the maximum PF of 5.234 × 10−4 W·m−1·K2. This facile synthetic approach is promising for the preparation of nanostructured Bi 2 Te 3 thin films as the thermoelectric materials. Display Omitted • Bi 2 Te 3 thermoelectric films were electrodeposited without additive. • The electrodeposition mechanism of Bi 2 Te 3 film was revealed to guide the deposition. • The composition and ideal nanostructure of the film were successfully controlled. • The film with ideal composition, morphology and texture reached largest known PF. [ABSTRACT FROM AUTHOR]

Bismuth telluride (Bi2Te3) thin films have been deposited onto polyimide sheet substrates by direct-current (DC) magnetron sputtering at different powers and their microstructure, composition, and electrical and thermoelectrical properties studied. The experimental results indicated that the sputtering power was the key parameter determining their thermoelectric properties. X-ray diffraction analysis confirmed the highly (015) preferred orientation of the films. The Te content and grain size depended on the sputtering power. The power factor of Bi2Te3 deposited by DC sputtering at power of 60 W was comparable to that obtained for highly (00l) Bi2Te3 thin film. [ABSTRACT FROM AUTHOR]

Graphic abstract Highlights • Ag added Ge 2 Sb 2 Te 5 (GST) thin films were successfully Ag 8 GeTe 6 phase formation mixed GST. • Microstructural of Ag added GST thin films were controlled in cubic structure. • Thermoelectric properties were discussed based on the Ag:GST composition variation. Abstract Ag-added Ge 2 Sb 2 Te 5 thin films were prepared by a pulsed-DC co-magnetron sputtering process using Ge 2 Sb 2 Te 5 and Ag targets. The effect of variation in Ag content through variable power on Ag target was studied on the microstructural and thermoelectric properties of as-deposited and fast annealed thin films at 400 °C in a vacuum. It is found that Ag addition induces enhancement in conductivity. When the power on Ag target is exceeded to a critical power, Ag 8 GeTe 6 phase formation occurs mixed with Ge 2 Sb 2 Te 5 cubic structure which limits the thermoelectric performance. Best conditions provide the films having a lowest electrical resistivity as 0.98 × 10−4 Ω cm and the maximum power factor as 5.83 × 10−3 W m−1 K−2. [ABSTRACT FROM AUTHOR]

Thermoelectric thin film/substrate structures have many practical applications such as in heat recovery systems. The general problem of thermally induced delamination between a thermoelectric thin film and a substrate is investigated. The temperature varies along the length direction but is constant along the thickness direction of the film. Analytical solutions of the temperature field in the film and the stress intensity factors (SIFs) at the delamination crack tips are obtained. The combined heat convection and heat radiation between the film surfaces and the surrounding medium (i.e., the air) are taken into account. Numerical results show that the SIFs sharply increase as the tips of the delamination crack approach the ends of the film. The combined heat convection and heat radiation can increase or decrease the SIFs. The mechanism for the delamination propagation in the thermoelectric film/substrate system is examined. The critical (permissible) temperature difference across the film governing the delamination propagation is identified. [ABSTRACT FROM AUTHOR]

Thermoelectric thin films are of great interest to microelectronic devices and miniaturized temperature sensors. In this article, we have studied the influence of film thickness on the electrical and thermoelectric properties of Mg-doped CuCrO 2 delafossite material (CuCrO 2 :Mg), a delafossite-type oxide. For this purpose, a serie of CuCr 0.97 Mg 0.03 O 2 thin films with various thicknesses (25, 50, 100, 200, 300, 400 and 600 nm) have been deposited by Radio Frequency (RF) magnetron sputtering. The as-deposited films were annealed at 550 °C under vacuum to obtain well crystallized delafossite phase. Grazing incidence X-ray diffraction patterns indicated that samples had pure delafossite structure. The atomic force microscope observations revealed the increase of the grain size with increasing thickness. The electrical and thermoelectric properties are characterized in temperature ranging from 40 to 220 °C and they were thickness dependent. The thickness dependency of the Seebeck coefficient was not expected and indicated that the carrier density changes with thickness below 100 nm. The variation of the film resistivity below 100 nm thickness was explained by both the change of the carrier density and the potential barrier addition due to small grain size. Using the electrical conductivity, the polaron activation energy (E σp  = 0.131 eV for 100 nm thick sample) was determined and its variation indicated that the stress/strain effect in the film with increasing thickness impacts the mobility. Moreover, the unexpected increase of the resistivity between 400 and 600 nm was also explained by the micro-cracks formation. The electrical and thermoelectric measurements showed a degenerated hopping semi-conductor behavior for the whole thicknesses. The highest electrical conductivity (1.7 S·cm −1 at 40 °C) was obtained for 100 nm thick film which presented a Seebeck coefficient of +307 µV·K −1 at 40 °C. We report maximum power factor of 16 µW·m −1 ·K −2 at 40 °C for the optimum thickness of 100 nm, which reached 59 µW·m −1 ·K −2 at 200 °C. The above results were explained in terms of microstructure and stress/strain effect. [ABSTRACT FROM AUTHOR]

Sb 2 Te 3 -based thermoelectric thin film is a competitive candidate for preparing thermoelectric thin film devices, which power the wearable electronic devices and chip-sensor of internet-of-things. In this work, a directed thermal diffusion reaction method was applied to synthesize p -type Sb 2 Te 3 thin films synthesis at polyimide flexible substrate with self-assembled growth. A high power factor of 1.94 mWm−1K−2 with excellent flexibility which is very competitive among similar Sb 2 Te 3 based materials by the control of synthesis condition, especially the chemical composition. Meanwhile, the performance of thermoelectric thin film device is limited by contact resistance. Thus the more systematic study of contact resistance, including choice of electrode material for the device was investigated. The results indicate that Mo/Sb 2 Te 3 have the lowest contact resistivity compared with Al/Sb 2 Te 3 and Ni/Sb 2 Te 3. In addition, the fabricated flexible device with Mo electrode has outstanding thermal stability. [Display omitted] • A novel directed thermal diffusion reaction method was applied for p -type Sb 2 Te 3 thin films. • Sb 2 Te 3 thin film controlled by synthesis condition can achieve a high power factor. • The fabricated flexible device with Mo electrode has a low contact resistance and a high output power. • This Sb 2 Te 3 thin film device possesses excellent flexibility. [ABSTRACT FROM AUTHOR]

In this report, Bi-doped antimony zinc thin films were prepared on BK7 glass substrates by using direct magnetron co-sputtering technique. Bi was doped at the halfway point of deposition, and the doping contents were 2 at.%, 4 at.%, and 6 at.%, respectively. We present the micro-structural and room-temperature thermoelectric properties of Bi-doped Zn-Sb thin films in this paper. The maximum value of the Seebeck coefficient was found to be 300 μV/K with a Bi content of 6 at.%. This is one of the highest values of the Seebeck coefficient for Zn-Sb thin films deposited by direct magnetron co-sputtering. Carrier concentration is obtained from Hall effect measurements, which provided insights into the transport mechanisms that affected electrical conductivity and Seebeck coefficient. It is significant to doping Bi, which enhances the power factor to an optimal value of 0. 26 mW/mK and the optimal ZT value to 0.086 with the Bi content of 4 at.% at room-temperature. [ABSTRACT FROM AUTHOR]

Cu doped ZnSb based thin films were deposited by direct current magnetron co-sputtering. X-ray diffraction results show that the un-doped thin film reveals a single ZnSb phase and it transforms to Zn 4 Sb 3 phase after Cu doped. The material with Zn 4 Sb 3 phase which belongs to R-3c space group crystal will lead to lower thermal conductivity. The Hall effect measurement shows that the samples are P-type semiconductors. The electrical conductivity increasers after Cu doped due to the increase of carrier concentration and the improvement in crystallinity. Though the Seebeck coefficient decreases after Cu doped, the ZT value increases from 0.11 to 0.43 with higher electrical conductivity and lower thermal conductivity at room-temperature. The temperature-dependent of ZT value is estimated to be ∼1.35 for the thin film with Zn 4 Sb 3 phase by using the bulk lattice thermal conductivity together with the thin film electrical thermal conductivity. [ABSTRACT FROM AUTHOR]

In filled CoSb 3 thin films with various In content were prepared on flexible substrates by multi-step co-sputtering method, which provided a promising way to prepare low-cost and high performance thin films. The influence of In content on the microstructure and thermoelectric properties of the CoSb 3 based thin films are systematically investigated. The thin film transforms from P -type to N -type with the increasing of In content. Both of the electrical conductivity and the Seebeck coefficient of the thin films increase after In filled. The thermal conductivity of the In filled thin film significantly decreases and the ZT value of the In-filled thin films are much higher than that of the unfilled thin film. It can be observed that the In filled thin films are single CoSb 3 phase and the grain size increases after In filled. The average grain size of all the thin films are less than 50 nm, indicates the thin films are nano-particles structure. [ABSTRACT FROM AUTHOR]

In this study, AZO thin films prepared by direct current reactive magnetron sputtering using a Zn-Al alloy target and In with varied content were doped through the prefabricated layer doping method in order to optimize their thermoelectric properties. The effects of In content on the room temperature microstructure and thermoelectric properties of the AZO thin films were investigated. It was found that the absolute value of the Seebeck coefficient of the thin films increases stably after In doping and reaches 153 μV·K when the In content is 0.71%. Though the electrical conductivity of In-doped thin films is smaller than those of the un-doped films, the power factor of the thin films shows a significant increase after In doping with a maximum value of 2.22 × 10 W·m·K, which is several times that of the un-doped films.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Antimonide cobalt thin films were deposited on BK7 glass substrates at various substrate temperatures by ion beam sputtering deposition with a fan-shape target. The influence of deposition temperature on the microstructure and thermoelectric properties of antimonide cobalt thin films were systematically investigated. It is found that the Seebeck coefficient of the thin film increases at first and then decreases with the increasing deposition temperature. The Seebeck coefficient of the sample deposited at 250 °C has maximum value and increases stably when the measuring temperature increased from room-temperature to 600 K. The electrical conductivity of the thin film increases significantly to 5.6 × 10 4 S cm −1 when the deposition temperature was 450 °C and then decreases greatly when the temperature increased to 500 °C and 550 °C. The behavior of electrical conductivity of the sample deposited at 250 °C changes from metallic to semiconducting after the measuring temperature exceeded 540 K. The power factor of antimonide cobalt thin film deposited at 250 °C has a maximum value of 0.93 × 10 −4 W m −1 K −2 at room-temperature and then increases to 3.5 × 10 −4 W m −1 K −2 when the measuring temperature was 540 K. [ABSTRACT FROM AUTHOR]

Highlights: [•] Zn-Sb thin film thermoelectric property enhanced via phase optimization. [•] The carrier concentration is suitable for obtaining high-quality sample. [•] Zn-Sb thin film with mixed ZnSb and Zn4Sb3 phase has highest power factor. [ABSTRACT FROM AUTHOR]

Highlights: [•] AZO thin films were deposited using the cost-effective and flexible design Zn–Al target. [•] AZO thin film has better thermoelectric properties at higher temperature. [•] The thermoelectric properties of AZO thin films enhance after changing the Al content. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stoichiometric Bi2Te3 films were obtained by controlling the target power. [•] The microstructure of Bi2Te3 thin films was affected by annealing temperature. [•] Annealing temperature affected various properties of Bi2Te3 thin films. [•] High thermoelectric properties was obtained at the annealing temperature of 300°C. [ABSTRACT FROM AUTHOR]

Abstract: Bismuth–tellium (Bi–Te) thin films were fabricated using radiofrequency (RF)-magnetron co-sputtering with various deposition conditions to improve their thermoelectric properties. The deposition conditions controlled were the working pressure and substrate temperature. The films were analyzed in terms of their crystalline structure, surface morphology, composition, Seebeck coefficient, and electrical properties. The Seebeck coefficient and electrical resistivity were measured at room temperature. The Te content and grain size decreased with increased deposition pressure and the thermoelectric performance was excellent at 0.4Pa. The thin films with the best thermoelectric performance had a Bi2Te3 crystal structure and were formed at a deposition pressure of 0.4Pa and a substrate temperature of 473K. [Copyright &y& Elsevier]

Antimony and tellurium were deposited on BK7 glass using direct-current magnetron and radiofrequency magnetron cosputtering. Antimony telluride thermoelectric thin films were synthesized with a heated substrate. The effects of substrate temperature on the structure, surface morphology, and thermoelectric properties of the thin films were investigated. X-ray diffraction patterns revealed that the thin films were well crystallized. c-Axis preferred orientation was observed in thin films deposited above 250°C. Scanning electron microscopy images showed hexagonal crystallites and crystal grains of around 500 nm in thin film fabricated at 250°C. Energy-dispersive spectroscopy indicated that a temperature of 250°C resulted in stoichiometric SbTe. SbTe thin film deposited at room temperature exhibited the maximum Seebeck coefficient of 190 μV/K and the lowest power factor (PF), S σ, of 8.75 × 10 W/mK. When the substrate temperature was 250°C, the PF increased to its highest value of 3.26 × 10 W/mK. The electrical conductivity and Seebeck coefficient of the thin film were 2.66 × 10 S/m and 113 μV/K, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Bismuth–telluride-based materials have excellent room-temperature thermoelectric properties. In this study, the composition of Bi–Te thin films deposited by RF-magnetron sputtering was systematically varied across a single wafer. X-ray diffraction, field emission-scanning electron microscopy (FE-SEM, JEOL, JSM-7000F) and energy dispersive X-ray spectroscopy (EDS) were then used to investigate the thermoelectric properties of the Bi–Te films as a function of the Te fraction. The Te content of the films ranged from 38% to 81%, and their microstructure and crystal structure varied depending on the Te content. The Seebeck coefficients of the Bi–Te thin films were in the range −10 to 153μV/K, and the maximum power factor of the films was 3.7×10−4 W/K2 m, without post annealing. [Copyright &y& Elsevier]

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Bi and Te on cold rolled silver substrate have been performed. The voltammetric analysis of underpotential shift demonstrates that the initial Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fitted UPD dynamics mechanism. A thin film of bismuth telluride was formed by alternately depositing Te and Bi via an automated flow deposition system. X-ray diffraction indicated the deposits of Bi2Te3. Energy Dispersive X-ray Detector quantitative analysis gave a 2: 3 stoichiometric ratio of Bi to Te, which was consistent with X-ray Diffraction results. Electron probe microanalysis of the deposits showed a network structure that results from the surface defects of the cold rolled Ag substrate and the lattice mismatch between substrate and deposit. [ABSTRACT FROM AUTHOR]

Abstract: Thermoelectric bismuth telluride (Bi2Te3) films were prepared by co-sputtering of bismuth and tellurium targets and changes in their characteristic properties after rapid thermal annealing were investigated. Films with four different compositions were elaborated by adjusting the powers for each target. Rapid thermal treatments in range of 300–400°C were carried out during 10min under reductive atmosphere (flowing Ar gas with 10% H2). Electrical transport properties of the films were determined by Hall effect measurements. As increasing the annealing temperature, carrier concentrations of the films were decreased while their mobility increased. These changes were clearly observed for the films close to the stoichiometric composition. Seebeck coefficients of all samples have negative values, indicating the prepared films have n-type conduction, and their magnitude was increased after the thermal treatment. Rapid thermal annealing was found to be very effective in improving the thermoelectric properties of Bi2Te3 thin films. Recrystallization of Bi2Te3 phase has caused the enhancement of thermoelectric properties, along with the decrease of the carrier concentration. Maximum of Seebeck coefficient and corresponding power factor were obtained for the stoichiometric film annealed at 400°C (about −128μV/K and 9×10−4 W/K2 m, respectively). At further higher temperatures, mound defects were observed on surface due to the evaporation of Te elements and consequent disruption of film''s structure. [Copyright &y& Elsevier]

Abstract: Thermoelectric bismuth telluride thin films were prepared on SiO2/Si substrates by radio-frequency (RF) magnetron sputtering. Co-sputtering method with Bi and Te targets was adopted to control films'' composition. Bi x Te y thin films were elaborated at various deposition temperatures with fixed RF powers, which yielded the stoichiometric Bi2Te3 film deposition without intentional substrate heating. The effects of deposition temperature on surface morphology, crystallinity and electrical transport properties were investigated. Hexagonal crystallites were clearly visible at the surface of films deposited above 290 °C. Change of dominant phase from rhombohedral Bi2Te3 to hexagonal BiTe was confirmed with X-ray diffraction analyses. Seebeck coefficients of all samples have negative value, indicating the prepared Bi x Te y films are n-type conduction. Optimum of Seebeck coefficient and power factor were obtained at the deposition temperature of 225 °C (about −55 μV/K and 3×10−4 W/K2·m, respectively). Deterioration of thermoelectric properties at higher temperature could be explained with Te deficiency and resultant BiTe phase evolution due to the evaporation of Te elements from the film surface. [Copyright &y& Elsevier]

Abstract: Bismuth thin films were prepared on glass substrates with RF magnetron sputtering and the effects of deposition temperature on surface morphology and their electrical transport properties were investigated. Grain growth of bismuth and the coalescence of grains were observed above 393K with field emission secondary electron microscopy. Continuous thin films could not be obtained above 448K because of the segregation of grains. Hall effect measurements showed that substrate heating yields the decrease of carrier density and the increase of mobility in exponential ways until 403K. Resistivity of sputter deposited bismuth films has its minimum (about 0.7×10−3 Ωcm) in range of 403–433K. Annealing of bismuth films deposited at room temperature was carried out in a radiation furnace with flowing hydrogen gas. The change of resistivity was not significant due to the cancellation of the decrease of carrier density and the increase of mobility. However, the abrupt change of electrical properties of film annealed above 523K was observed, which is caused by the oxidation of bismuth layer. [Copyright &y& Elsevier]

Amorphization using impurity doping is a promising approach to improve the thermoelectric properties of tin-doped indium oxide (ITO) thin films. However, an abnormal phenomenon has been observed where an excessive concentration of doped atoms increases the lattice thermal conductivity ( κ l ). To elucidate this paradox, we propose two hypotheses: (1) metal hydroxide formation due to the low bond enthalpy energy of O and metal atoms and (2) localized vibration due to excessive impurity doping. To verify these hypotheses, we doped ZnO and CeO 2, which have low and high bond enthalpies with oxygen, respectively, into the ITO thin film. Regardless of the bond enthalpy energy, the κ l values of the two thin films increased due to excessive doping. Fourier transform infrared spectroscopy was conducted to determine the metal hydroxide formation. There was no significant difference in wave absorbance originating from the OH stretching vibration. Therefore, the increase in κ l due to the excessive doping was due to the formation of localized regions in the thin film. These results could be valuable for various applications using other transparent conductive oxides and guide the control of the properties of thin films.

In recent years, organic/inorganic hybrids capture wide attention due to their advantages in endowing composites with both high Seebeck coefficient and low thermal conductivity originating from inorganics and polymer, respectively. However, simply blending tend to weaken this advantage, resulting in lower thermoelectric performance than that of single organics or inorganics. Here we propose a polar organic solvents aided layer-by-layer (OS-LbL) technique to prepare high performance nanocomposite films comprising poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and Sb 2 Te 3 nanocomposites. Polar organic solvents not only promote the dispersion of Sb 2 Te 3 nanoplates but also post-treat the PEDOT:PSS layer at the hetero-junction interface, successfully increasing the electrical conductivity and thermopower at the same time. Besides, the organic/inorganic interface inducing by OS-LbL promotes a low thermal conductivity of 0.0522 Wm−1K−1. As a result, a maximum ZT value up to 0.10 at room temperature. The results show that using OS-LbL method to combine PEDOT:PSS with Sb 2 Te 3 nanoplates is a promising pathway to achieve polymer-based, high-performance thermoelectric applications. [ABSTRACT FROM AUTHOR]

Ionic liquid (IL) post-treatment for thin films of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is employed for the simultaneous enhancement of Seebeck coefficients and electrical conductivities. Through systematic variation of the ILs, by changing the anions while keeping the cation unchanged, changes in thermoelectric, spectroscopic, and morphological properties are investigated by means of UV-vis spectroscopy and grazing-incidence wide-angle X-ray scattering (GIWAXS) as a function of the IL concentration. The simultaneous enhancement in the two important thermoelectric properties is ascribed to the binary nature of the ILs, which complements that of PEDOT:PSS. The anions of the ILs primarily interact with the positively charged, conducting PEDOT, while the cations interact with negatively charged insulating PSS. Therefore, post-treatment with ILs allows for primary and secondary doping of PEDOT:PSS at the same time. Differences in the obtained Seebeck coefficients for the investigated ILs are ascribed to the chemical properties of the anions. Additionally, the choice of the latter has implications on the morphology of the treated PEDOT:PSS films regarding average π-π-stacking distances of PEDOT chains, PEDOT-to-PSS ratios, and edge-on-to-face-on ratios, influencing charge transport properties macroscopically. A morphological model is presented, highlighting the influence of each IL in comparison with pristine PEDOT:PSS films.

The zinc antimonide compound ZnxSby is one of the most efficient thermoelectric materials known at high temperatures due to its exceptional low thermal conductivity. For this reason, it continues to be the focus of active research, especially regarding its glass-like atomic structure. However, before practical use in actual surroundings, such as near a vehicle manifold, it is imperative to analyze the thermal reliability of these materials. Herein, we present the thermal cycling behavior of ZnxSby thin films in nitrogen (N2) purged or ambient atmosphere. ZnxSby thin films were prepared by cosputtering and reached a power factor of 1.39 mW m(-1) K(-2) at 321 °C. We found maximum power factor values gradually decreased in N2 atmosphere due to increasing resistivity with repeated cycling, whereas the specimen in air kept its performance. X-ray diffraction and electron microscopy observations revealed that fluidity of Zn atoms leads to nanoprecipitates, porous morphologies, and even growth of a coating layer or fiber structures on the surface of ZnxSby after repetitive heating and cooling cycles. With this in mind, our results indicate that proper encapsulation of the ZnxSby surface would reduce these unwanted side reactions and the resulting degradation of thermoelectric performance.