The contact resistance between metals and semiconductors has become critical for the design of thin-film thermoelectric devices with their continuous miniaturization. Herein, we report a novel interface tuning method to regulate the contact resistance at the Bi2Te3–Cu interface, and three Bi2Te3 films with different oriented microstructures are obtained. The lowest contact resistivity (∼10–7 Ω cm2) is observed between highly (00l) oriented Bi2Te3 and Cu film, nearly an order of magnitude lower than other orientations. This significant decrease of contact resistivity is attributed to the denser film connections, lower lattice misfit, larger effective conducting contact area, and smaller width of the surface depletion region. Meanwhile, our results show that the reduction of contact resistance has little dependence on the interfacial diffusion based on the little change in contact resistivity after the introduction of an effective Ti barrier layer. Our work provides a new idea for the mitigation of contact resistivity in thin-film thermoelectric devices and also gives certain guidance for the size design of the next-level miniaturized devices.Keywords: contact area; contact resistance; Interface tuning; interfacial diffusion; oriented microstructure;

•Aluminum buffer layer is introduced to improve copper crystallinity and reduce thermal stress in the electrode films.•The prepared Al-Cu flexible conducting electrodes exhibit high electrical conductivity of 3.05 μΩ·cm.•Negligible changes of electrical resistivity for Al(0.86 μm)-Cu thin film is achieved at the bending radius more than 6 mm.•The crack evolution is effectively alleviated in Al(0.86 μm)-Cu thin film resulting from better energy recovery capacity.•The Al(0.86 μm)-Cu flexible thin-film electrode exhibits strong adhesive ability to 5B-level with polyimide substrate.Great demands for flexible conducting electrodes (FCEs) are promoted considering the rapid development of flexible electronics. Conventional thin-film FCE, however, has limits of low conductivity, poor mechanical reliability and requires complicated fabrication process due to the use of nanowires and nanoparticles. In this work, aluminum-copper bilayer FCEs were fabricated via facile thermal evaporation. Aluminum buffer layer is introduced to improve copper crystallinity and reduce internal thermal stress in the electrode films, resulting in enhanced electrical conductivity and reliability. The preparation condition and thickness of buffer layer (Al) has been optimized. The lowest electrical resistivity of 3.05 μΩ·cm was achieved for Al(0.86 μm)-Cu bilayer FCE, which is comparable to that of the bulk material (1.77 μΩ·cm). Additionally, the Al-Cu films exhibited excellent adhesion and flexibility under a bending radius of larger than 6 mm (ε = 1.82%) over 1000 cycles. And nanoindenter test was also conducted to describe the elastic characteristics of the flexible electrode and explain the mechanism of crack evolution. Meanwhile, superior reliability with negligible resistance changes was observed for Al-Cu FCEs after thermal shock tests.Download high-res image (243KB)Download full-size image

Advanced polymer-based dielectric composites are core materials in the electronics and power systems. Construction of core-shell architectures has been proved as a powerful strategy to dramatically enhance the dielectric and energy storage performances. Herein, core-shell structured amorphous SiO2 encapsulating Bi2S3 nanorods with varying shell thickness were employed as the fillers in poly(vinylidene fluoride) (PVDF) matrix, affording a Bi2S3@SiO2/PVDF nanocomposite. The dielectric behaviors of Bi2S3@SiO2/PVDF composites with varying SiO2 shell thickness as a function of filler loading in comparison with Bi2S3/PVDF were studied. Bi2S3@SiO2 core-shell structure dramatically suppressed the dielectric loss (<0.04) and decrease in conductivity yet maintaining high dielectric constant. Furthermore, adjusting Bi2S3@SiO2-PVDF interface by controlling the SiO2 shell thickness results in changing dielectric behaviors. The effects of SiO2 shell and the arising Bi2S3@SiO2 interface on the dielectric and electric properties were investigated via interfacial charge calculation based on Maxwell-Wagner-Sillars model. The role of semiconductor-insulator interfacial polarization in determining the dielectric behaviors of the composites were understood. Due to the greatly reduced dielectric loss, Bi2S3@SiO2/PVDF nanocomposites can withstand high electric field and the study on energy storage capacity and efficiency was realized in the polymer-based composite with conductive filler. This study demonstrates the robust effect of core-shell architecture in suppressing dielectric loss yet maintaining the high dielectric constant of the polymer-based composites, providing a promising route to achieve high-performance dielectrics.

•Microstructure of Sb2Te3 film was modulated by controlling sputtering pressure.•Low porosity and crystal orientation was obtained in flexible Sb2Te3 thin film.•Mechanism of crystal growth influenced by Ar pressure was discussed and presented.•The ZT value of Sb2Te3 film with (015) crystal orientation is markedly improved.Preparation of high performance flexible thermoelectric thin films would promote applications of flexible thermoelectric device. In this work, antimony telluride (Sb2Te3) thin films were directly deposited on polyimide substrate. The crystalline structures and morphologies of the thin films were analyzed, and the mechanism of crystal growth influenced by sputtering pressure was discussed. We also investigated the effects of microstructure on their thermoelectric properties, where Hall effect measurement was conducted to provide further insight into the enhancement of thermoelectric properties. The mean free path of the carrier was calculated on the basis of carrier concentration and mobility. Our results showed that with (015) crystal preferential orientation, the electrical conductivity and Seebeck coefficient of Sb2Te3 thin films were simultaneously increased, and a maximum power factor of 6.0 μW cm−1 K−2 was achieved, which was increased by 75% compared with the ordinary thin film. Meanwhile, due to the reduced lattice thermal conductivity and increased power factor, the estimated figure of merit (ZT) value was largely enhanced to 0.42.Download high-res image (117KB)Download full-size image

Design of layered structures in polymer-based dielectric composites would result in regionalized distribution of fillers which is important in determining the electrical properties of the composites. Here, BaTiO3/poly(vinylidene fluoride) (BT/PVDF, denominated as B) composite layer and pure PVDF (denominated as P) layer were stacked in five different sequences to investigate the influence of interfaces formed between adjacent layers in sandwich structure on the breakdown strength of composites. B/P/B film showed the highest breakdown strength, suggesting that breakdown strength could be simply enhanced via forming two hetero-interfaces by inserting a pure polymer layer in the composite with filler homogenously distributed. Thus; the dielectric behavior and energy storage capability of B/P/B sandwich-structured composites with various BT volume fractions were studied. The significantly improved dielectric polarization and breakdown strengths were observed in B/P/B sandwich structure, where the interfaces between adjacent layers play the crucial role. Maximum discharged energy density near breakdown field was achieved at ultralow BT loading of 1 vol%. The results highlight the benefit from structural design of multilayer composites towards high-performance pulsed power systems.

AbstractA robust surface geometrical structure not only enables a favorable practical application but also leads to a long-term reliability of superhydrophobic surfaces, and hence it is pivotal to find an effective route to improve the mechanical durability of superhydrophobic surfaces. This study reports a simple magnetron sputtering method to directly construct a robust rose petal-like copper surface with high water adhesion (petal effect). A stable surface micro/nanosphere topography combining with naturally low surface energy is spontaneously formed by the strain-induced-island growth of the copper films during the sputtering process. Further reduced surface energy by fluorosilane, the rose petal-like surface shows a high water contact angle (≈161.4°), effective adhesion force of ≈154 µN, and no-loss transportation critical droplet volume of ≈98 µL. In addition, as-prepared superhydrophobic surfaces exhibit superior mechanical stability according to the thermal shock (−40 °C/90 °C) for ≈500 cycles, water-impacting test for ≈6 h, and finger touch (≈20 times) as well as tape-peeling test (≈65 times) without losing superhydrophobicity. This work might provide a novel but simple way to directly and effectively fabricating robust superhydrophobic metallic surfaces for potential industrial applications, and can be easily extended to other metals and alloys.

Flexible electrode films play critical and fundamental roles in the successful development of flexible electronic devices. In this study, carbon nanotubes (CNTs) were implanted into silver (Ag) ink to enhance the electrical conductivity and the reliability of the printed Ag electrode films. The fabricated carbon nanotubes-enriched silver (Ag-CNTs) electrode films were printed on the polyimide substrates by a facile screen printing method and sintered at a relatively low temperature. The resistivity of Ag-CNTs films was decreased by 62.27% compared with the pure Ag film. Additionally, the Ag-CNTs films exhibited excellent flexibility under a bending radius of 4 mm (strain ε = 2.09%) over 1000 cycles. Furthermore, the Ag-CNTs film displayed unchangeable electrical conductivity together with a strong adhesion after an accelerated aging test with 500 thermal shock cycles. These improvements were attributed to the Ag-CNTs interconnected network structure, which can provide electronic transmission channels and prevent cracks from initiating and propagating.

•A thermoelectric harvester is proposed applied in extreme environment in space.•Paraffin/EG composite is optimized with enhanced thermal property and reliability.•Both simulation and experiment are used to evaluate the performance of harvester.•High-grade electrical energy is enhanced when using the paraffin/5 wt% EG composite.In this study, a thermoelectric energy harvesting device applied with extremely large temperature variation (from +100 °C to −50°C) for space application is presented using phase change material (PCM) for thermal control and storage. Aiming at developing a high-performance PCM to fill into the heat storage unit (HSU) of the device, the thermal conductivity, leakage and thermal reliability of paraffin-based composites with different loadings of expanded graphite (EG) were investigated. Results showed the form-stable paraffin/EG composite has enhanced thermal conductivity and maintainable latent heat storage capacity after repeated thermal cycling test. Furthermore, the prototype device of thermoelectric harvester was developed, where the proportion of EG in the PCM is key to balance the heat storage capacity and the heat transfer rate. Both simulation and experiment are used to evaluate the performance of the harvester. The experimental evidence verifies that the thermoelectric harvester with paraffin/5 wt% EG composite owns the largest total energy output and the most portion of high-grade electrical energy.Download high-res image (150KB)Download full-size image

•A facile one-step sputtering process is developed to construct sandwich-porous copper films.•The ratio of surface-energy to substrate-temperature determines the formation of the porous structure.•High conductivity and super-elastic property are achieved due to the introduction of nano pores in the copper films.•The crack-growth is effectively hindered resulting from high elastic recovery work of sandwich-porous copper films.Porous metal film has drawn plenty of attention due to the excellent reliability and potential of integration in current interconnects/electrodes technologies. However, the practical applications of porous metal film have been hampered by complex technique and poor electrical properties. Here, we report a one-step method to directly construct a unique sandwich-porous copper film combining with high mechanical and electrical performance by a simple sputtering process. Growth parameters, with emphases on substrate temperature and deposition time, are systematically investigated to provide direct experimental validation of the formation mechanism of the sandwich-porous films. Results demonstrate that by tuning a porous-factor (β) during the film deposition, it is possible to noticeably affect the surface topography, from columnar to porous and/or dense structure, and hence effectively control the formation of the sandwich-porous structure. Additionally, nanoindentation tests for the sandwich-porous films are also investigated, where high conductivity and super-elastic property are achieved due to the special microstructures with presence of nanoporous. This discovery may pave a facile and effective way to fabricate multifunctional porous metallic films for bottom-up fabrication schemes of next-generation devices in the microelectronics industry.Download high-res image (244KB)Download full-size image

With the growing global energy crisis, new methods of energy development and utilization have become the main solutions to energy issues. Solution based polymer thermoelectric (TE) generation technologies provide a low-cost and eco-friendly means of direct energy conversion from low-grade heat to electricity. By integrating high Seebeck coefficient tellurium nanorods with the conducting polymer polyaniline (PANI) to form PANI/Te hybrid films, well-matched nanoscale interfaces improve carrier transport properties yet keep the thermal conductivity at a rather low level of 0.2 W m−1 K−1. Therefore, the originally mutual restricted parameters (electrical conductivity, Seebeck coefficient and thermal conductivity) finally reach an increase in the ZT value. The maximum power factor of the PANI/Te (70 wt%) composite film reached 105 μW m−1 K−2 at room temperature and further reached up to 146 μW m−1 K−2 at 463 K, and the ZT value increased from 0.156 at room temperature to 0.223 at 390 K, which are the highest values reported so far for PANI based TE materials. A screen-printing process was employed to fabricate in-plane power generation devices based on the high-performance PANI/Te hybrid films. A prototype device with 10 legs of PANI/Te–Ag could provide a maximum output voltage and output power of 29.9 mV and 0.73 μW, respectively at temperature gradient 40 K. The results evidently demonstrate a promising and economic route for conducting polymers to be applied in low-grade energy conversion utilization.

•The thermal stability of the Cu thin film electrode was improved with the substrate bias voltage.•Resistivity evolution of the Cu thin film electrode was obtained under thermal shock test.•Bias Cu thin film electrode showed a better thermal shock resistance.•The interface bond strength of the Cu thin film was improved via the substrate bias voltage.The performance degradation of the thin-film electrodes has remained a challenge for the whole performance of micro-devices. Here, we introduce substrate bias voltage (SBV) in magnetron sputtering technique to improve the thermal stability and reliability of copper (Cu) electrode. The effects of the SBV on the stability and reliability of Cu film electrodes were investigated by scanning electron microscopy and thermal shock. Unstable electric performance is suppressed, and the interface bonding strength between the film and substrate is obviously improved by applying SBV. In addition, this work provides a facile way to achieve high reliability and thermal stability for Cu electrodes used in various thin-film devices.

Correction for ‘High thermoelectric performance of a defect in α-In2Se3-based solid solution upon substitution of Zn for In’ by Jiaolin Cui et al., J. Mater. Chem. C, 2015, 3, 9069–9075.

In this project, we have successfully manipulated the lattice defects in α-In2Se3-based solid solutions (In2−xZnxSe3) by appropriate substitution of Zn for In, via a non-equilibrium fabrication technology (NEFT) of materials. The manipulation of the defect centers involves reduction of the number of interstitial In atoms (Ini) and Se vacancies (VSe), and creation of a new antisite defect ZnIn as a donor. Through this technique, the lattice structure tends to be ordered, and also more stabilized than that of pure α-In2Se3. In the meantime, the carrier concentration (n) and mobility (μ) have increased by 1–2 orders of magnitude. As a consequence, the solid solution at x = 0.01 gives the highest TE figure of merit (ZT) of 1.23(±0.22) in the pressing direction at 916 K, which is about 4.7 times that of pure α-In2Se3 (ZT = 0.26). This achieved TE performance is mainly due to the remarkable improvement in the electrical conductivity from 0.53 × 103 (Ω−1 m−1) at x = 0 to 4.88 × 103 (Ω−1 m−1) at x = 0.01 at 916 K, in spite of the enhancement in the lattice thermal conductivity (κL) from 0.26 (W m−1 K−1) to 0.32 (W m−1 K−1).

The refrigeration capability of a thermoelectric device is dictated by interfacial effects and the figure of merit ZT, which govern the contact resistance and the Carnot efficiency for heat conversion. Here we report a controllable (110) oriented Bi0.5Sb1.5Te3 film grown on a Cu film electrode. The hierarchical Bi0.5Sb1.5Te3 film is composed of tens of cactus like flakes that have a (110) oriented backbone and abundant 50–80 nm branches in the (015) direction. The lattice mismatch of the (110) oriented Bi0.5Sb1.5Te3 to the Cu electrode is estimated to be approximately 2.4%, which implies a decreased interfacial dislocation density and formation of fewer interfacial defects leading to low contact resistance (1.0 × 10−9 Ω m2). The enhanced out plane ZT ≈ 0.73 is calculated from the in plane properties. Hence a maximum heat-flux pumping capability of 138 W cm−2 can be obtained for Tc = 400 K and the corresponding temperature difference is 6 K. Our work indicates that the control of the metal-semiconductor interfacial structure is an efficient approach to improve the refrigeration capability.

BaTiO3/poly(vinylidene fluoride) (BT/PVDF) composite material, a promising dielectric material for capacitor, has recently attracted much attention because of the promising dielectric performance and its abundant availability. Insufficient control of the hierarchal morphology of the blend has yielded a precipitous decline in breakdown strength at high BT nanoparticles volume fractions. Here, we demonstrate that breakdown strength and energy storage density can be increased up to higher value by creating uniform distribution of low content of BT nanoparticles in PVDF matrix. The dielectric properties of BT/PVDF nanocomposite were measured as a function of BT nanoparticles loading. The nanocomposite displayed a 150% increase in dielectric breakdown strength and energy density increased to more than triple that of the pure PVDF even at the 1 vol% BT nanoparticles loading. It was attributed to the uniform distribution of low content BT nanoparticles in PVDF matrix, which lead to superior dielectric breakdown strength and energy storage density than those of composites filled with high content of BT nanoparticles. Furthermore, the nanocomposites films with low content of fillers were more flexible and cost-effective. The finding based on this research provides a low-cost method to achieve high performance in capacitor.

The main challenge in the field of capacitors is how to reconcile the contradiction of lowering the dielectric loss while maintaining a high dielectric constant of polymer based composites. In this work, a novel two-phase ferroelectric polymer composite, consisting of semiconducting bismuth sulfide (Bi2S3) nanorods and a poly(vinylidene fluoride) (PVDF) matrix, was fabricated by a sequence of casting, hot-stretching and hot-pressing techniques. Orderly polymer composites based on PVDF assembled with parallel aligned Bi2S3 nanorods were realized in the composites after a hot-stretching-pressing process. It’s interesting to note that those orderly polymer composites exhibit excellent dielectric properties. Results show that the composites with oriented structure have high dielectric constant and unusual low dielectric loss. The parallel aligned Bi2S3 nanorods along the tensile-strain direction could be responsible for the improvement of dielectric properties of the composites. This study also provides an extremely useful method to reduce the dielectric loss of similar kinds of composites.

•Sb-doped Mg2Ge was synthesized by tantalum-tube melting followed by hot pressing.•The effect of Sb doping on thermoelectric properties was studied in 300–740 K.•Sb doping with sufficient Mg excess increased σ, leading to enhanced power factor.The Sb-doped Mg2Ge compounds were successfully synthesized by tantalum-tube weld melting method followed by hot pressing and the thermoelectric properties were examined. The effects of Sb doping on the electrical conductivity, Seebeck coefficient, and thermal conductivity have been investigated in the temperature range of 300–740 K. It was found that the Sb doping with sufficient Mg excess increased the electrical conductivity dramatically, leading to enhancement of the power factors. The thermal conductivity was also reduced upon Sb doping, mainly due to mass fluctuation scattering and strain field effects. Mg2.2Ge0.095Sb0.005 showed a maximum thermoelectric figure of merit of ≈0.2 at 740 K.

•Preferential growth transformation is obtained by a facile post-annealing process.•Preferential growth and transformation mechanisms have been discussed.•Electrical conductivity and Seebeck coefficient are enhanced synchronously.•The largest power factor of 48.2 μW/cm K2 in Bi0.5Sb1.5Te3 films is achieved.•Our study provides an effective way to improve the thermoelectric performance.Preferential growth transformation from (015) plane to (00l) plane of the bismuth antimony tellurium (Bi0.5Sb1.5Te3) film has been achieved through a facile post-annealing process with enhanced thermoelectric performance. The Bi0.5Sb1.5Te3 film with preferential growth of (015) crystal plane was obtained via dc magnetron sputtering, and the Stranski–Krastanov model has been used to explain its growth mechanism. Preferential growth transformation from (015) plane to (00l) plane occurred after a post-annealing process. The driving force of this phenomenon is the natural tendency to reduce the total interfacial energy of the system, and the migration and coalescence of atoms along the in-plane direction form the layered structure. Moreover, the carrier concentration of Bi0.5Sb1.5Te3 films is optimized to ~019/cm3 in the film with preferential growth of (00l) plan. Hence, a synchronous increase of electrical conductivity and Seebeck coefficient is obtained due to the greatly enhanced carrier mobility and optimized carrier concentration. Therefore, the Bi0.5Sb1.5Te3 film with the preferential growth of (00l) plane possesses power factor of 48.2 μW/cm K2 which is three times higher than that of the film with the preferential growth of (015) plane. Our study has provided a facile strategy to induce preferential growth transformation in Bi0.5Sb1.5Te3 films and meanwhile largely enhanced the thermoelectric performance.

A solar-driven hybrid generation system (HGS) in an integrated design is successfully fabricated, which consists of a silicon thin-film solar cell (STC), thermoelectric generators (TEGs) and a heat collector. STC absorbs parts of the solar energy and directly converts it into electric energy. The undesired waste heat from STC and parts of the solar energy are collected by the heat collector and conducted to TEG to produce thermoelectric conversion. The structure and the performance of HGS are discussed. A numerical simulation is also performed on TEG to obtain the distribution of heat flux using finite element method (FEM). The results show that the performances of TEG and STC are synchronously enhanced due to the integrated design. Especially the heat flux on the hot side of TEG integrated in HGS increases by more than tenfold. The total generated power of 393 mW is obtained in HGS, which is twice larger than that of single STC. The developed HGS is a promising power system which can effectively broaden the use of the solar spectrum and increase the power output in solar conversion.Highlights► A novel hybrid system with an integrated design has been proposed and fabricated. ► The performances of TEG and STC are both promoted due to integration. ► The heat flux on hot side of TEG increases by tenfold with the heat collector. ► The hybrid generation system broadens the use of solar spectrum.

Highly ordered one-dimensional CoFe2O4 nanowires array possesses unique properties due to the low-dimensional effect, which make it a wide range of potential applications. In this paper, ordered CoFe2O4 nanowires array was prepared by a modified sol–gel method using anodic aluminum oxide template. Microstructure analysis performed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and Raman spectra indicated the crystallization of pure CoFe2O4 phase. The nanowires were constituted by polycrystalline CoFe2O4 nanograins with an average size of 15 nm, which results in an increase of band gap as evidenced by photoluminescence spectra. Furthermore, we found that the CoFe2O4 nanowires were coated with amorphous Al2O3 forming a core–shell structure. The formation mechanism of this structure was discussed. The nanowires array preserved the good magnetic property of CoFe2O4 bulk material, showing the prospect for applications.Highlights► Ordered CoFe2O4 nanowires array was prepared by a modified sol–gel template method. ► The nanowires are composed of nanosized CoFe2O4 grains with around 15 nm. ► CoFe2O4 nanowires are coated with amorphous Al2O3 forming core–shell structure. ► The optical band gap of CoFe2O4 nanowires increases. ► The nanowires array preserves the good magnetic property of CoFe2O4 bulk material.

A novel three-phase composite, consisting of semiconductive bismuth sulfide (Bi2S3) nanorods and self-passivated aluminum flakes (AFs)1 embedded in a poly(vinylidene fluoride) (PVDF) matrix, was fabricated by simple but robust ball-milling and hot-pressing techniques. The dielectric properties of composites were studied before and after the addition of AFs as a function of Bi2S3 volume fraction and frequency. The Bi2S3 nanorods in PVDF matrix form a percolation path and increase the dielectric constant of the composite dramatically. And after adding the third phase AFs, a parallel structure forms during the hot-pressing progress. Parallel AFs in the PVDF matrix can largely reduce the leakage current due to the self-passivated insulating shell outside the AFs, thus an obvious reduction in the dielectric loss of the three-phase Bi2S3–AFs/PVDF composite is observed. Meanwhile, many microcapacitors formed with Al flakes as electrodes and Bi2S3/PVDF composite as the dielectric layer form, which makes an additional contribution to the high dielectric constant of the three-phase composite.Highlights► Aluminum flakes form a parallel structure in polymer matrix. ► The dielectric loss is largely lower after the addition of self-passivated AF. ► Parallel structure is helpful for composite to maintain a high dielectric constant.

The miniature thermoelectric cooler (TEC) is a promising device for microelectronics applications with high cooling performance and short response time. In this paper, a comprehensive numerical analysis focusing on the cooling performance and response time of the TEC is performed by finite element methods (FEMs). The effects of load current, geometric size, ratio of length to cross-sectional area and substrate's thermal resistance on the performance of the TEC are studied. The results show that the performance of TECs has been improved by reducing the TEC's size and ratio of length to cross-sectional area, resulting in a maximum cooling temperature difference of 88 °C, a cooling power density of 1000 W cm−2 and a short response time on the order of milliseconds. Furthermore, the substrate, which hinders the circulation of heat between the TEC and the atmosphere, also has a significant influence on the performance of the TEC.

•Highly oriented Bi2Te3 thin film is fabricated and integrated into device.•The layered Bi2Te3 film is beneficial for the improvement of thermoelectric properties.•2-μm-thick film device shows excellent power generation and cooling performance.•Introduction of such special layered film into device is a very promising approach.An approach for fabrication of planar devices integrating layered Bi2Te3 thin-films with different microscale thicknesses instead of bulk materials is reported. The films were prepared by the radio-frequency magnetron sputtering. The microstructure, composition, and thermoelectric (TE) properties of the thin-films were characterized using X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and a TE measurement system, respectively. The results show that the Bi2Te3 films with layered microstructure possess promising TE properties. The power generation and cooling performance of parallel micro-devices with n-type thermolegs were tested and found to be superior to those of bulk material devices. For a typical parallel device with 38 optimized 2-μm-thick legs, the output voltage, estimated maximum power and corresponding power density are up to 5.6 mV, 6.53 μW and 43 mW cm− 2, respectively, for a temperature difference of 81 K. The coefficient of performance (COPmax) of the device was also estimated. The minimum value of COPmax approaches 6.8 at ΔT = 3.2 K. The results prove that high performance of micro-device with low internal resistance can be realized by integrating special layered Bi2Te3 thin-films.

Layer-by-layer assembly of nanostructured Bi0.5Sb1.5Te3 thin films were prepared by a simple magnetron sputtering method. X-ray diffraction investigations revealed that all the thin films were well crystallized with preferred orientation along (00l) direction. Scanning electron microscopy images indicated that nanostructure of the condensed films was stacked by tens of parallel repeating layers. Meanwhile, the particular thicknesses of layers could be controlled in the range of 20–140 nm by adjusting the deposition time. The electrical conductivity and power factor were significantly increased compared with those of ordinary thin films, while the maximum power factor reached 53 μW cm−1 K−2 when the layer thickness was 40 nm. The multi-layered materials are promising candidates for miniaturized modules with their unique properties.

The effect of metal-semiconductor Zn-ZnO core–shell structure on dielectric properties of polyvinylidene fluoride (PVDF) composites was investigated. Zn-ZnO fillers were obtained by the heat-treatment of raw Zn particles under air. The enhanced dielectric constant of Zn-ZnO/PVDF composites results from the duplex interfacial polarizations induced by metal-semiconductor interface and semiconductor–insulator interface. The dielectric loss is still low because of the presence of ZnO semiconductor shell between Zn metal core and insulator PVDF matrix. Furthermore, the dielectric performance of as-prepared composites could be further optimized through adjusting the thickness of semiconductor shell.Keywords: dielectric constant; dielectric loss; metal-semiconductor interface; polymer composites; semiconductor shell;

Large-scale, well-aligned CdTe nanowire arrays with different crystallographic phases have been prepared simply by regulating the basic growth parameters of the sputtering method. Pure zinc blende phase nanowire arrays that propagate in the (111) direction are achieved using a high growth temperature coupled with a low deposition rate. Conversely, wurtzite phase nanowire arrays with growth in the (002) direction have also been prepared by using a lower growth temperature and higher deposition rate. A Gibbs free energy nucleation model is use to explain the formation of these different crystal phases under the growth conditions employed. The differences in crystal structure are shown to exhibit different energy bands, defects and carrier transport properties. The wurtzite phase, with a narrower band gap (1.64 eV), is found to have better photoelectric properties than those of the zinc blende phase.

Polyvinylidene fluoride (PVDF) composites filled by self-passivated zinc (Zn) particles were fabricated through a simple method of flocculation. The following measurement exhibits that the Zn/PVDF composite with filler volume fraction of 0.24 possesses the excellent dielectric properties, and the obtained dielectric constant and loss at 103 Hz were 52 and 0.05, respectively. It's considered that high dielectric constant is originated from the enhanced interfacial polarization, while the low loss is due mainly to the self-passivation layer of zinc carbonate hydroxide, which can serve as the insulating interface and reduce leakage current effectively through blocking the free transfer of charge carriers between adjacent Zn fillers. The developed polymer composites with favorable dielectric properties are potential for embedded capacitor applications.Highlights► Zn/PVDF composites with favorable dielectric properties were obtained. ► Dielectric constant was increased to 52 due to enhanced interface polarization. ► Dielectric loss was reduced to 0.05 due to the self-passivation layer of Zn filler. ► The developed polymer composites can be used as embedded capacitors.

An approach for fabrication of highly (0 0 l)-textured Sb2Te3 thin film with layered structure by the magnetron sputtering method is reported. The composition, microstructure, and thermoelectric properties of the thin films have been characterized and measured by x-ray diffraction, scanning electron microscopy with energy-dispersive x-ray spectroscopy, and a thermoelectric (TE) measurement system, respectively. The results show that well-oriented (0 0 l) Sb2Te3 thin film with layered structure is beneficial for improvement of thermoelectric properties, being a promising choice for planar TE devices. The power generation and cooling performance of a layered p-Sb2Te3 film device are superior to those of the ordinary thin-film device. For a typical parallel device with 38 layered Sb2Te3 film elements, the output voltage, maximum power, and corresponding power density are up to 10.3 mV, 11.1 μW, and 73 mW/cm2, respectively, for a temperature difference of 76 K. The device can produce a 6.1 K maximum temperature difference at current of 45 mA. The results prove that enhanced microdevice performance can be realized by integrating (0 0 l)-oriented Sb2Te3 thin films with a layered architecture.

This study describes a simple and low-cost method for fabricating novel 2–3-type composites composed of zinc flakes and polyvinylidene fluoride (PVDF) by direct wet ball-milling and hot-pressing of the mixture of raw zinc powders and PVDF powders in alcohol. It is interesting that zinc spherical powders can be changed into 2-dimensional zinc flakes in the ball-milling and parallel oriented in the polymer under the following hot-pressing process. The composites are demonstrated to have significantly higher dielectric constants than those of bulk zinc/PVDF composites, with quite low dielectric loss and good thermal stability. A mechanism of parallel-board microcapacitor is proposed to explain the relationship of microstructure and dielectric properties.

CdTe nanorod arrays have been directly grown on borosilicate glass as well as on Si (100), common glass, and FTO glass (SnO2) by magnetron sputtering deposition. The parallel and uniform CdTe nanorods with diameters of about 100 nm are self-assembly with (00l) orientation regardless of substrate. The formation of CdTe nanorod arrays is followed by the Stranski–Krastanov model and Gibbs free energy requirement. The CdTe nanorod arrays on different substrates similarly show broad absorption from ultraviolet light to visible light (300–800 nm), and the CdTe nanorod arrays also have a high short circuit photocurrent with excellent photoresponse. This study provide a simple strategy to grow CdTe nanorod arrays without the constraints introduced by the substrate and open new potential for CdTe nanorod arrays application in nanostructured solar energy conversion devices.

Oriented n-type bismuth telluride thin films with various layered nanostructures have been fabricated by radio-frequency (RF) magnetron sputtering. The crystal structures and microstructures of the films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The transport properties including carrier concentration, mobility, Seebeck coefficient and in-plane electrical conductivity were measured, which showed strong microstructure-dependent behaviors. The relationship between morphologies and transport properties of the films was explored. The optimal morphology and transport properties of films were obtained at the substrate temperature of 350 °C under the pressure of 1.0 Pa with oriented layered structure. Based on these results, a formation mechanism of these nanostructures is proposed and discussed. The interfaces and grain boundaries formed in these layered structures are beneficial to the reduction in thermal conductivity, which could result in potential TE films with high ZT value.

Highly (00l00l)-oriented pure Bi2Te3 films with in-plane layered grown columnar nanostructure have been fabricated by a simple magnetron co-sputtering method. Compared with ordinary Bi2Te3 film and bulk materials, the electrical conductivity and Seebeck coefficient of such films have been greatly increased simultaneously due to raised carrier mobility and electron scattering parameter, while the thermal conductivity has been decreased due to phonon scattering by grain boundaries between columnar grains and interfaces between each layers. The power factor has reached as large as 33.7 μW cm−1 K−2, and the out-of-plane thermal conductivity is reduced to 0.86 W m−1 K−1. Our results confirm that tailoring nanoscale structures inside thermoelectric films effectively enhances their performances.Highlights► Highly (00l00l)-oriented Bi2Te3 films with layered grown columnar nanostructure have been realized by magnetron co-sputtering. ► The electrical conductivity and Seebeck coefficient are simultaneously increased greatly while the thermal conductivity is decreased. ► Tailoring nanostructures inside thermoelectric films effectively enhances their performances.

Oriented thermoelectric (TE) p-Sb2Te3 and n-Bi2Te3 thin films with special nanostructures have been synthesized by a simple vacuum thermal evaporation technique. The composition and microstructure of the films were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), presenting a well preferential crystal growth with dense slender columnar grains grown perpendicular to the substrate, and energy dispersive X-ray spectrum (EDX) indicating the compositions distribution in the films. The electric transport properties, i.e., conductivity and Seebeck coefficient, and the thermal transportation of the oriented films show optimized properties. Prototype devices were built up by p and n elements in series and parallel circuits. The largest output power and cooling could be achieved in Sb2Te3 parallel device with Pmax = 6.51 μW at ΔT = 106 K, and cooling of 4.1 K at 2 V. The 24-pair p–n couples series device could output maximum voltage of 313 mV at ΔT = 102 K. The power generation and the cooling of the devices show times enhanced TE performances than those consisting of common films. The results proved that introducing nanostructures into films is an effective choice to obtain high-efficient micro TE device.

AbstractA novel two-phase composite system using polypropylene (PP) as matrix and semiconductor bismuth sulfide (Bi2S3) as filler, was prepared by a simple process. Surfactant KH550 was chosen to modify the interface between inorganic fillers and organic PP matrix. The variations of dielectric properties of the Bi2S3/PP composites with the volume fraction of Bi2S3, frequency and temperature were discussed. The results reveal a percolative behavior of the composites with the threshold of 0.08. The composite is demonstrated to have good dielectric properties. The thermal stability of dielectric property and high breakdown strength of the composites show their potential application in film capacitor.

A series of Bi2S3/LDPE composites, with low density polyethylene (LDPE) as matrix and bismuth sulfide as filler, are fabricated by a simple process. The microstructure, dielectric properties and tensile strength of the composites have been studied. The variation of dielectric properties of the Bi2S3/LDPE composites with the volume fraction of Bi2S3, frequency and temperature is discussed. The composites have significantly high dielectric constants and good thermal stability, with a quite low percolation threshold. The addition of low content of Bi2S3 significantly improves the dielectric constant of polymer matrix from 3 to above 60 at 100 Hz.

Bi2Te3–Te arrays with sheet–rod multiple heterostructure were obtained in large scale, using Te nanorod arrays as the in-situ templates under solvothermal process. The array is formed by the ordered Bi2Te3–Te rods where Bi2Te3 sheets distribute from the top face to the bottom face along the Te rod vertically. The microstructure of the heterostructure was studied through X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrical conductivity and Seebeck coefficient of the arrays were also studied. The course of reaction was monitored so as to propose a possible growth mechanism of such novel heterostructure. The key for the preparation of such heterostructure is to balance the velocity between the dissolution of Te rods and the formation of Bi2Te3 sheets. This synthetic approach could be promising to prepare self-assembled low-dimensional nanoarrays of metals and semiconductors with high yield.Graphical abstractBi2Te3–Te arrays with sheet–rod multiple heterostructure were obtained in a large scale using Te nanorod arrays as the in-situ templates under the solvothermal process.

Bi2Te3 thin films, composed of ordered nanowire arrays, have been successfully fabricated by a convenient physical vapor deposition method without using any template. The composition and microstructure of these films were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). The effects of deposition rate, substrate temperature, and deposition time on morphologies of Bi2Te3 films were investigated. The effects of morphology of film on the electrical conductivity and Seebeck coefficient were also studied. The results show that the nanowire arrays are composed of single-crystalline Bi2Te3 nanowires with diameters of about 18 nm. The nanowires are parallel to each other and uniformly distributed. The film of nanowire arrays shows good transport properties. The growth mechanism of such nanostructure was proposed.

Local-oriented single-crystalline ZnO nanowires have been synthesized in large scale by a simple microemulsion method in the presence of sulfonate-polystyrene (S-PS) and dodecyl benzene sulfonic acid sodium salt (DBS). The as-prepared product is characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), infrared (IR) spectra and photoluminescence (PL) spectrum. The nanowires exhibit a local congregation and preferentially grow along the [0 0 2] facet. FT-IR spectrum indicates that S-PS is adsorbed on the surface of ZnO nanowires. The PL spectrum shows evidently red-shifted ultraviolet (UV) emission.

The solid electrolyte Li0.5La0.5TiO3 (LLTO) with high lithium ion conductivity was prepared by the conventional solid-state reaction method, and those LLTO powders were mixed with inactive second phase (Al2O3, MgO, SiO2) to give composites. The microstructure and conductivity properties of the composite are investigated by using X-ray diffraction, scanning electron microscope and AC impedance method. Those prepared LLTO is cubic crystal with superstructure. All conductivities of LLTO-based composites decrease with the addition of Al2O3 or MgO, but the grain boundary conductivity increases with the addition of SiO2.

Single-crystal Bi2Te3–Te nanocomposites with heterostructure were synthesized using a two-step solvothermal process in the presence of ethylenediaminetetraacetic acid disodium salt. The first step is the formation of the Te nanorods and the second step is to grow the Bi2Te3 sheets off the Te rods surface to form the Bi2Te3–Te nanocomposites. The products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. We demonstrate a method of an epitaxial growth of Bi2Te3 nanosheets perpendicular to the axis of the central Te rod and a formation process of Bi2Te3–Te nanocomposites is also proposed.SEM image of an individual sheet-rod with EDX patterns (inset) taken from sheet and rod indicated by arrows.

Design of core–shell nanoarchitectures is powerful approach to obtain advanced high-k polymer nanocomposites. Core–shell nanoparticles with uniform amorphous Al2O3 shell layer encapsulating BaTiO3 (BT) particles were fabricated through an effective, facile and low-cost heterogeneous nucleation method. The dielectric behaviors of the polyvinylidene fluoride (PVDF) nanocomposite films were adjusted by varying BT@Al2O3 nanoparticles loadings. The effects of Al2O3 shell and the arising interfaces on the dielectric and electric properties in comparison with bare BT nanoparticles were studied. Due to the highly insulating Al2O3 shell with proper dielectric constant, the local electric field distribution around interfaces between polar BT nanoparticles and PVDF were greatly modified leading to obvious dielectric loss suppression yet maintaining high dielectric constant. The study provides a solution for obtaining high-k dielectric composite with low loss and high breakdown strength, which is highly desired in high power systems.

•Integrated thin-film TE device is designed for energy harvesting and light sensing.•Large and maintainable Seebeck coefficient is obtained in wide temperature range.•Fresnel lens is highly integrated with TE device for energy concentration.•The integrated TE device exhibits high voltage output and large responsivity.•The TE sensor has excellent environmental adaptation and wide detection range.In this study, we prepared a multi-functional thin-film thermoelectric device for small-scale energy harvesting and self-powered light sensing. A comprehensive optimization was conducted in terms of thermoelectric material, device, and system integration. The thermoelectric thin films in the device were prepared using the sputtering method together with a post-annealing process. A Fresnel lens was incorporated into the thin-film thermoelectric device for energy concentration. In addition, a simulation procedure was used to facilitate the optimization of the heat sink, which can provide fast heat dissipation and mechanical support for the thin-film thermoelectric device. The electricity generation and light sensing performance was then characterized under solar irradiation, followed by a feasibility study for sensor application. The results indicate that our thin-film thermoelectric device exhibits high voltage output and greatly enhanced responsivity. This work presents a significant progress toward an integrated design of an applicable and multifunctional thin-film thermoelectric sensor for detecting sunlight intensity.

Correction for ‘High thermoelectric performance of a defect in α-In2Se3-based solid solution upon substitution of Zn for In’ by Jiaolin Cui et al., J. Mater. Chem. C, 2015, 3, 9069–9075.

With the growing global energy crisis, new methods of energy development and utilization have become the main solutions to energy issues. Solution based polymer thermoelectric (TE) generation technologies provide a low-cost and eco-friendly means of direct energy conversion from low-grade heat to electricity. By integrating high Seebeck coefficient tellurium nanorods with the conducting polymer polyaniline (PANI) to form PANI/Te hybrid films, well-matched nanoscale interfaces improve carrier transport properties yet keep the thermal conductivity at a rather low level of 0.2 W m−1 K−1. Therefore, the originally mutual restricted parameters (electrical conductivity, Seebeck coefficient and thermal conductivity) finally reach an increase in the ZT value. The maximum power factor of the PANI/Te (70 wt%) composite film reached 105 μW m−1 K−2 at room temperature and further reached up to 146 μW m−1 K−2 at 463 K, and the ZT value increased from 0.156 at room temperature to 0.223 at 390 K, which are the highest values reported so far for PANI based TE materials. A screen-printing process was employed to fabricate in-plane power generation devices based on the high-performance PANI/Te hybrid films. A prototype device with 10 legs of PANI/Te–Ag could provide a maximum output voltage and output power of 29.9 mV and 0.73 μW, respectively at temperature gradient 40 K. The results evidently demonstrate a promising and economic route for conducting polymers to be applied in low-grade energy conversion utilization.

The refrigeration capability of a thermoelectric device is dictated by interfacial effects and the figure of merit ZT, which govern the contact resistance and the Carnot efficiency for heat conversion. Here we report a controllable (110) oriented Bi0.5Sb1.5Te3 film grown on a Cu film electrode. The hierarchical Bi0.5Sb1.5Te3 film is composed of tens of cactus like flakes that have a (110) oriented backbone and abundant 50–80 nm branches in the (015) direction. The lattice mismatch of the (110) oriented Bi0.5Sb1.5Te3 to the Cu electrode is estimated to be approximately 2.4%, which implies a decreased interfacial dislocation density and formation of fewer interfacial defects leading to low contact resistance (1.0 × 10−9 Ω m2). The enhanced out plane ZT ≈ 0.73 is calculated from the in plane properties. Hence a maximum heat-flux pumping capability of 138 W cm−2 can be obtained for Tc = 400 K and the corresponding temperature difference is 6 K. Our work indicates that the control of the metal-semiconductor interfacial structure is an efficient approach to improve the refrigeration capability.

In this project, we have successfully manipulated the lattice defects in α-In2Se3-based solid solutions (In2−xZnxSe3) by appropriate substitution of Zn for In, via a non-equilibrium fabrication technology (NEFT) of materials. The manipulation of the defect centers involves reduction of the number of interstitial In atoms (Ini) and Se vacancies (VSe), and creation of a new antisite defect ZnIn as a donor. Through this technique, the lattice structure tends to be ordered, and also more stabilized than that of pure α-In2Se3. In the meantime, the carrier concentration (n) and mobility (μ) have increased by 1–2 orders of magnitude. As a consequence, the solid solution at x = 0.01 gives the highest TE figure of merit (ZT) of 1.23(±0.22) in the pressing direction at 916 K, which is about 4.7 times that of pure α-In2Se3 (ZT = 0.26). This achieved TE performance is mainly due to the remarkable improvement in the electrical conductivity from 0.53 × 103 (Ω−1 m−1) at x = 0 to 4.88 × 103 (Ω−1 m−1) at x = 0.01 at 916 K, in spite of the enhancement in the lattice thermal conductivity (κL) from 0.26 (W m−1 K−1) to 0.32 (W m−1 K−1).