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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 (Formula presented.) (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 (Formula presented.) 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.

Demonstration of a robust, tellurium-free thermoelectric module for near-room-temperature applications with a high conversion efficiency of 8.5% and a maximum cooling of 72 K.

This work develops an efficient, environmentally friendly and cost-effective thermoelectric module for mid-temperature waste heat recovery by using n-type Se-doped Mg3(Bi,Sb)2 and p-type CoSb3-based skutterudite.

The incorporation of carbon nanotubes (CNTs) within polymer hosts offers a great platform for the development of advanced thermoelectric (TE) composite materials. Over the years, several CNT/polymer composite formulations have been investigated on an effort to maximize the TE performance. Meanwhile, several studies focused on the decay dynamics of the charged excitons within CNTs itself and therefrom derived structures, aiming to investigate the lifetimes and the corresponding recombination processes of free charge carriers. The latter physical phenomena play a crucial role in the performance of various types of energy converting and scavenging materials. Nevertheless, up to this date, there is no systematic study on the combination of TE parameters and the critical charge carrier dynamics within CNT-containing TE polymer composites. Herein, a variety of composites with single and hybrid CNT fillers based on polycarbonate (PC) and polyether ether ketone (PEEK) polymer matrices were prepared by melt-mixing in the small scale. At the same loading, the addition of single fillers in PC results in higher Seebeck coefficients and similar conductivities when compared to the use of hybrid-filler systems. In contrast, with hybrid-filler systems in PEEK composites, higher power factors could be reached than in single-filler composites. Moreover, the PC-based composites are studied using ultrafast laser time-resolved transient absorption spectroscopy, for the investigation of the exciton lifetimes and the physical origins of free charge carrier transport within the TE films. The findings of this study reveal interesting links between the TE parameters and the obtained charge carrier dynamics. Namely, it is found that the Seebeck coefficient of the composites relates directly to the exciton lifetimes, whereas the volume conductivity is independent of the exciton lifetimes and is determined mainly by the average number and the mobility of the free charged electrons at the higher energy states.

Solid-state thermoelectric (TE) technology is a promising approach to harvest low-grade waste heat (573 K) and converts it to useful electricity in industrial and civilian settings. After decades of efforts in improving the figure-of-merit (zT) of TE materials, the development of advanced modules has started springing up in recent years. Although high-performance modules have been largely reported based on the successful material improvement, it remains less investigated how and whether the module-level designs can further increase the conversion efficiency. Herein, following the recent demonstration of a tellurium (Te)-free TE generator, an increase is demonstrated in the efficiency by reducing both the electrical and thermal energy losses through simply optimizing geometric factors of filling factor and leg-pair numbers. These module-level optimizations enable a record conversion efficiency of 8.2% under a ∆T ≈ 260 K, thus fulfilling 90% of the theoretical efficiency of the materials and solidly exceeding the Bi

Nanograined Bi2Te3 offers a large surface-to-volume ratio, making it an interesting material to employ the high mobility surface states for devices. We present THz spectroscopic measurements to reveal the role of the surface carriers.

We present experimental and theoretical results on electronic structure and thermoelectric properties (electrical resistivity and Seebeck coefficient) of Co1−xMxSi (M=Fe, Ni) compounds. Cobalt monosilicide, CoSi, is a recent candidate to the family of materials with topologically non-trivial electronic structure. Moreover, the compound has been considered as a promising thermoelectric material. According to literature data the maximum experimental thermoelectric efficiency parameter ZT of CoSi is close to 0.2. The combination of the unique electronic structure, promising thermoelectric properties and phase stability in a broad temperature range makes CoSi suitable to study the effect of topological states, both bulk and surface (Fermi arcs), on thermoelectric properties. We measured thermoelectric properties (Seebeck coefficient and electrical resistivity) of Co1−xMxSi from 4 K to 800 K. Electronic structure of the compounds was calculated using density functional theory as implemented in VASP software package. Possible connections of the observed peculiarities in the thermoelectric properties with topological features in the electronic structure of the compounds are discussed

Recently we reported on a unique, chip based measurement platform for the complete characterization of the in-plane thermoelectric properties of thin film samples. For the validation of the platform, good thermoelectric materials with a low thermal conductivity and large Seebeck coefficient have already been characterized. In order to check the capability of the platform, with regard to new material classes and applications, we performed measurements of the electrical conductivity σ, thermal conductivity λ and Seebeck coefficient S of two 100 nm Au and Ti thin film samples with considerably larger thermal and electrical transport values. The measured thermoelectric properties of both films show clear size effects, with a remarkably reduced electrical and thermal conductivity as well as Seebeck coefficient, compared to the bulk material, respectively. The Lorenz number of the thin films, which are calculated from the measured electrical and thermal conductivities, are equal to the bulk value, predicted by the Wiedemann–Franz law.

Microthermoelectric modules are of potential use in fields such as energy harvesting, thermal management, thermal imaging and high-spatial-resolution temperature sensing. In particular, microthermoelectric coolers (µ-TECs)—in which the application of an electric current cools the device—can be used to manage heat locally in microelectronic circuits. However, a cost-effective µ-TEC device that is compatible with the modern semiconductor fabrication industry has not yet been developed. Furthermore, the device performance of µ-TECs in terms of transient responses, cycling reliability and cooling stability has not been adequately assessed. Here we report the fabrication of µ-TECs that offer a rapid response time of 1 ms, reliability of up to 10 million cycles and a cooling stability of more than 1 month at constant electric current. The high cooling reliability and stability of our µ-TEC module can be attributed to a design of free-standing top contacts between the thermoelectric legs and metallic bridges, which reduces the thermomechanical stress in the devices. A free-standing top contact design reduces the thermomechanical stress in microthermoelectric coolers, resulting in improved reliability and cooling stability.

The synthesis of phase‐pure ternary solutions of tetradymite‐type materials (BixSb1−x)2Te3 (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy‐dispersive X‐ray spectroscopy (EDX), powder X‐ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties ‐ Seebeck coefficient as well as electrical and thermal conductivity ‐ is demonstrated.

Silicon waste (SW), a byproduct from the photovoltaic industry, can be a prospective and environmentally friendly source for silicon in the field of thermoelectric (TE) materials. While thermoelectricity is not as sensitive toward impurities as other semiconductor applications, the impurities within the SW still impede the enhancement of the thermoelectric figure of merit, zT. Besides, the high thermal conductivity of silicon limits its applications as a TE material. In this work, we employ traditionally metallurgical methods in industry reducing the impurities in SW to an extremely low level in an environmentally friendly and economical way, and then the thermal conductivity of purified silicon is greatly reduced due to the implementation of multiscale phonon scattering without degrading the power factor seriously. Benefiting from these strategies, from 323 to 1123 K, for the sample made from purified silicon waste, the average zT, relevant for engineering application, is increased to 0.32, higher than that of the state-of-the-art n-type Ge-free bulk silicon materials made from commercially available silicon, but the total cost of our samples is negligible.

3D topological insulators (TI) host surface carriers with extremely high mobility. However, their transport properties are typically dominated by bulk carriers that outnumber the surface carriers by orders of magnitude. A strategy is herein presented to overcome the problem of bulk carrier domination by using 3D TI nanoparticles, which are compacted by hot pressing to macroscopic nanograined bulk samples. Bi2 Te3 nanoparticles well known for their excellent thermoelectric and 3D TI properties serve as the model system. As key enabler for this approach, a specific synthesis is applied that creates nanoparticles with a low level of impurities and surface contamination. The compacted nanograined bulk contains a high number of interfaces and grain boundaries. Here it is shown that these samples exhibit metallic-like electrical transport properties and a distinct weak antilocalization. A downward trend in the electrical resistivity at temperatures below 5 K is attributed to an increase in the coherence length by applying the Hikami-Larkin-Nagaoka model. THz time-domain spectroscopy reveals a dominance of the surface transport at low frequencies with a mobility of above 103 cm2 V-1 s-1 even at room temperature. These findings clearly demonstrate that nanograined bulk Bi2 Te3 features surface carrier properties that are of importance for technical applications. © 2021 The Authors. Small published by Wiley-VCH GmbH.

The synthesis of phase‐pure ternary solutions of tetradymite‐type materials (BixSb1−x)2Te3 (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy‐dispersive X‐ray spectroscopy (EDX), powder X‐ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties ‐ Seebeck coefficient as well as electrical and thermal conductivity ‐ is demonstrated., Tetradymite‐type ternary (BixSb1‐x)2Te3 (x=0.25, 0.5, 0.75) nanoparticles were synthesized in an ionic‐liquid approach. The effect of thermal annealing on the chemical composition and morphology of the nanoparticles as well as their transport properties prior and after annealing is reported.

Successful optimization of the thermoelectric (TE) performance of materials, described by the figure of merit zT, is a key enabler for its application in energy harvesting or Peltier cooling devices. While the zT value of bulk materials is accessible by a variety of commercial measurement setups, precise determination of the zT value for thin and thick films remains a great challenge. This is particularly relevant for films synthesized by electrochemical deposition, where the TE material is deposited onto an electrically conductive seed layer causing an in-plane short circuit. Therefore, a platform for full in-plane zT characterization of electrochemically deposited TE materials is developed, eliminating the impact of the electrically conducting seed layer. The characterization is done using a suspended TE material within a transport device which was prepared by photolithography in combination with chemical etching steps. An analytical model to determine the thermal conductivity is developed and the results verified using finite element simulations. Taken together, the full in-plane zT characterization provides an inevitable milestone for material optimization under realistic conditions in TE devices. �� 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We present theoretical and experimental results on electronic structure and thermoelectric properties of cobalt monosilicide (CoSi) and of Co1−x M x Si diluted alloys (M = Fe and Ni) at temperatures from 2 K to 800 K. CoSi crystallizes into a non-centrosymmetric cubic B20 structure, which suggests the possibility of a topologically non-trivial electronic structure. We show that the electronic structure of CoSi exhibits linear band crossings in close vicinity to Fermi energy, confirming the possibility of non-trivial topology. The proximity of the linear-dispersion bands to Fermi energy implies their important contribution to the electronic transport. Calculation of thermopower of CoSi, using ab initio band structure and the constant relaxation time approximation, is carried out. It reveals that many body corrections to the electronic spectrum are important in order to obtain qualitative agreement of theoretical and experimental temperature dependences of thermopower. Phonon dispersion and lattice thermal conductivity are calculated. The phonons give a major contribution to the thermal conductivity of the compound below room temperature.

An analytical study has been performed on the measurement capabilities of a 100-nm thin suspended membrane setup for the in-plane thermal conductivity measurements of thin film samples using the 3ω measurement technique, utilizing a COSMOL Multiphysics simulation. The maximum measurement range under observance of given boundary conditions has been studied. Three different exemplary sample materials, with a thickness from the nanometer to the micrometer range and a thermal conductivity from 0.4 W/mK up to 100 W/mK have been investigated as showcase studies. The results of the simulations have been compared to a previously published evaluation model, in order to determine the deviation between both and thereby the measurement limit. As thermal transport properties are temperature dependent, all calculations refer to constant room temperature conditions.

Integrating transparent solar-harvesting systems into windows can provide renewable on-site energy supply without altering building aesthetics or imposing further design constraints. Transparent photovoltaics have shown great potential, but the increased transparency comes at the expense of reduced power-conversion efficiency. Here, a new technology that overcomes this limitation by combining solar-thermal-electric conversion with a material's wavelength-selective absorption is presented. A wavelength-selective film consisting of Cs0.33WO3 and resin facilitates high visible-light transmittance (up to 88%) and outstanding ultraviolet and infrared absorbance, thereby converting absorbed light into heat without sacrificing transparency. A prototype that couples the film with thermoelectric power generation produces an extraordinary output voltage of approximate to 4 V within an area of 0.01 m(2) exposed to sunshine. Further optimization design and experimental verification demonstrate high conversion efficiency comparable to state-of-the-art transparent photovoltaics, enriching the library of on-site energy-saving and transparent power generation.

We study the low-temperature electrical and thermal conductivity of CoSi and Co 1−xMxSi alloys (M = Fe, Ni; x ≤ 0.06). Measurements show that the low-temperature electrical conductivity of Co1−xFexSi alloys decreases at x > 0.01 by an order of magnitude compared with that of pure CoSi. It was expected that both the lattice and electronic contributions to thermal conductivity would decrease in the alloys. However, our experimental results revealed that at temperatures below 20 K, the thermal conductivity of Fe- and Ni-containing alloys is several times larger than that of pure CoSi. We discuss possible mechanisms of the thermal conductivity enhancement. The most probable one is the dominant scattering of phonons by charge carriers. We propose a simple theoretical model that takes into account the complex semimetallic electronic structure of CoSi with nonequivalent charge carrier pockets. This model explains well the increase of the lattice thermal conductivity with increasing disorder and the linear temperature dependence of thermal conductivity in the Co1−xFexSi alloys below 20 K.

The MCoSb-based (M = Hf, Zr) half-Heusler compounds were recognized as a promising p-type thermoelectric (TE) material for more than 2 decades although the base compound is intrinsically n-type. Here we investigate the TE properties of Ni-substituted n-type MCoSb. The anomalous changes of carrier concentration and lattice thermal conductivity with higher amount of Ni indicate the presence of atomic disorder. Peak power factor of ∼33 μW cm−1 K−2 and peak ZT of 0.6 are obtained in ZrCo0.9Ni0.1Sb. Further substitute Zr by Hf suppresses the lattice thermal conductivity and yields a peak ZT exceeding 1 in the composition Zr0.5Hf0.5Co0.9Ni0.1Sb at 1073 K. Thus the MCoSb compounds possess promising TE properties by both n- and p-type doping, which is unique among the half-Heusler based TE materials.

Single-crystalline, ternary n -type Bi 2 Te 3−y Se y nanowires are grown by potential-pulsed electrochemical deposition with 45 nm, 70 nm and 195 nm nominal diameters. Electrical conductivity and thermopower of the nanowires are measured. TEM analysis proves that the nanowires grow along the [110] direction with the c-axis perpendicular to the nanowire axis and yield diameters of 70–80 nm (nominally 45 nm, #1), 85–100 nm (70 nm, #2) and 265–325 nm (195 nm, #3). This yields electronic transport along the basal plane of the Bi 2 Te 3 crystal structure. Chemical composition of the nanowires is measured by TEM-EDX spectroscopy. These nanowires show exciting electronic properties, like Shubnikov-de-Haas oscillations at low temperatures, summarized in another paper. All nanowires investigated are oxygen contaminated but single crystalline, precipitates are only observed in #3 nanowire. The stoichiometry offset and fluctuations of #2 nanowire are significantly larger compared to #1 and #3 nanowires. The thermopower correlates with these structural data, the smallest thermopower is found for #2 nanowire and a similar, larger thermopower is found for #1 and #3 nanowires. For #1 and #2 nanowires dislocation densities of about 7.8 × 10 10 cm −2 and 1.0 × 10 11 cm −2 are observed, respectively, wherein dislocations lie parallel to the growth direction. While for #3 nanowire, a dislocation density of 1.2 × 10 10 cm −2 is observed and dislocations are oriented perpendicular to the growth direction. This reduces the heat conductivity of the #3 nanowire due to phonon scattering on the strain field of dislocations.

The characterization of nanostructured samples with at least one restricted dimension like thin films or nanowires is challenging but important to understand their structure and transport mechanism and to improve current industrial products and production processes. We report on the development of a chip-based platform to simultaneously measure the in-plane electrical and thermal conductivity, the Seebeck coefficient as well as the Hall constant of a thin film in the temperature range from 120 K up to 450 K and in a magnetic field of up to 1 T. Due to the design of the setup, time consuming preparation steps can be omitted and a nearly simultaneous measurement of the sample properties is achieved. Typical errors caused by different sample compositions, varying sample geometries, and different heat profiles are avoided with the presented measurement method. As a showcase study displaying the validity and accuracy of our system, we present measurements of the thermoelectric properties of a 110 nm Bi87Sb13 thin film in the temperature range from 120 K up to 450 K.

Considerable efforts have been devoted to enhancing thermoelectric performance, by employing phonon scattering from nanostructural architecture, and material design using phonon-glass and electron-crystal concepts. The nanostructural approach helps to lower thermal conductivity but has limited effect on the power factor. Here, we demonstrate selective charge Anderson localization as a route to maximize the Seebeck coefficient while simultaneously preserving high electrical conductivity and lowering the lattice thermal conductivity. We confirm the viability of interface potential modification in an n-type Bi-doped PbTe/Ag

Three-dimensional (3D) assemblies of nanostructures are gaining more and more attention during the recent years as promising systems to increase the integration density in microelectronic devices. Here we present the fabrication of large areas of 3D nanowire networks (NWNWs) of antimony for thermoelectric applications by electrodeposition in etched ion-track membranes. The synthesis parameters have been investigated and optimized to achieve mechanically stable and free-standing NWNWs without a supporting matrix. A cross-plane method for the complete steady state thermoelectric characterization of an embedded nanowire assembly (NWA) is also introduced, which enables the measurements of Seebeck-coefficient, cross-plane thermal conductivity, and electrical resistance of the NWA, and can also be applied to thin films. First results of the thermoelectric properties of Sb NWA are presented.

To investigate the physical properties of Bi nanowires and to explore their possible implementation in thermoelectric devices, it is essential to understand their chemical and thermal stability in air both at room and moderate temperatures. In this work, we study the influence of low temperature annealing processes on the morphology and composition of the wires by scanning and transmission electron microscopy and by Raman spectroscopy, revealing the formation of a metal oxide phase. This oxidation process initiates an increase of the nanowires surface roughness at low annealing temperatures, while clear protuberances are formed at 250 °C. Difficulties to electrically contact single Bi nanowires, as well as the high resistance values measured and reported by other groups, are attributed to this oxidation process, which constitutes a clear challenge for the reliable characterization of Bi nanowires and the investigation of their performance.

The electrical resistivity and thermopower of cobalt monosilicide (CoSi) and dilute alloys of CoSi with iron at temperatures from 2 to 370 K are experimentally investigated. CoSi is a semimetal and considered to be a promising thermoelectric material. It crystallizes into the cubic structure without an inversion center. This feature suggests the existence of topologically nontrivial electronic states and makes CoSi a candidate for the Weyl semimetal class. The main goal of the study is to find experimental confirmation of this assignment. It is shown that the experimental temperature dependences of the electrical resistivity and thermopower of CoSi and Co1–xFexSi (x = 0.04) at low temperatures cannot be interpreted within the standard theory of conductivity in metals and may be related to topological features of the electronic structure of this compound.

The characterization of nanostructured samples with at least one restricted dimension like thin films or nanowires is challenging, but important to understand their structure and transport mechanism, and to improve current industrial products and production processes. We report on the 2nd generation of a measurement chip, which allows for a simplified sample preparation process, and the measurement of samples deposited from the liquid phase using techniques like spin coating and drop casting. The new design enables us to apply much higher temperature gradients for the Seebeck coefficient measurement in a shorter time, without influencing the sample holder's temperature distribution. Furthermore, a two membrane correction method for the 3ω thermal conductivity measurement will be presented, which takes the heat loss due to radiation into account and increases the accuracy of the measurement results significantly. Errors caused by different sample compositions, varying sample geometries, and different heat profiles are avoided with the presented measurement method. As a showcase study displaying the validity and accuracy of our platform, we present temperature-dependent measurements of the thermoelectric properties of an 84 nm Bi

GENERAL PRINCIPLES AND THEORETICAL CONSIDERATIONS Transverse Thermoelectric Effects and Their Application H. J. Goldsmid Thermoelectric Induction in Power Generation: Prospects and Proposals L. I. Anatychuk Thermoelectric Devices as Heat Engines: Alternative Thermodynamic Cycles L. E. Bell Functionally Graded Thermoelectric Generator and Cooler Elements E. Muller, K. Zabrocki, C. Goupil, G. Jeffrey Snyder, and W. Seifert Thermodynamics and Phase Transformations in Thermoelectric Materials: Applications to the Development of New Materials Jean-Claude Tedenac First Principles Calculations of Electron Transport Properties in Disordered Thermoelectrics Janusz Tobola and Laurent Chaput New Thermoelectric Materials with Precisely Determined Electronic Structure and Phonon Dispersion Tsunehiro Takeuchi 8 Entropy Flow in Interactive Semiconductor/Metal Nanoensembles Dieter M. Gruen Ab Initio-Based Band Engineering and Rational Design of Thermoelectric Materials Jiong Yang, Xun Shi, Wenqing Zhang, Lidong Chen, and Jihui Yang Band Structure Guidelines for Higher Figure-of-Merit: Analytic Band Generation and Energy Filtering Espen Flage-Larsen and Ole Martin Lovvik Introduction to Modeling Thermoelectric Transport at High Temperatures Andrew F. May and G. Jeffrey Snyder The Effect of Resonant Energy Levels on the Thermoelectric Power and Thermoelectric Power Factor Joseph P. Heremans Graphene-Like Exfoliated Quasi-2D Thermoelectric Crystals Alexander A. Balandin 14 The Bottom-Up Approach to Bulk Thermoelectric Materials with Nanoscale Domains Anuja Datta, Adrian Popescu, Lilia Woods, and George S. Nolas Surface and Interface Effects on Thermoelectric Behavior in Crystalline Nanowires Frederic Sansoz MATERIALS PREPARATION AND MEASUREMENT High-Performance Nanostructured Thermoelectric Materials Prepared by Melt Spinning and Spark Plasma Sintering Xinfeng Tang, Wenjie Xie, Han Li, Baoli Du, Qingjie Zhang, Terry M. Tritt, and Ctirad Uher Fabrication Routes for Nanostructured TE Material Architectures Muhammet S. Toprak, Shanghua Li, and Mamoun Muhammed Preparation and Thermoelectric Properties of Iron Disilicide Yukihiro Isoda and Haruhiko Udono The Deposition of Bi2Te3 and Sb2Te3 Thermoelectric Thin Films by Thermal Coevaporation and Applications in Energy Harvesting L. M. Goncalves Thermoelectric Materials, Measurements, and Opportunities for Energy Harvesting Patrick J. Taylor Thermal and Thermoelectric Characterization of Individual Nanostructures and Thin Films Li Shi Microchips and Methods for the Characterization of Thermoelectric Transport Properties of Nanostructures Friedemann VOlklein, Daniel Huzel, Heiko Reith, and Matthias Schmitt Neutron Scattering Investigations of Thermoelectric Materials Mogens Christensen

International audience; Segmented magnetic nanowires are a promising route for the development of three dimensional data storage techniques. Such devices require a control of the coercive field and the coupling mechanisms between individual magnetic elements. In our study, we investigate electrodeposited nanomagnets within host templates using vibrating sample magnetometry and observe a strong dependence between nanowire length and coercive field (25 nm to 5 µm) and diameter (25 nm to 45 nm). A transition from a magnetization reversal through coherent rotation to domain wall propagation is observed at an aspect ratio of approximately 2. Our results are further reinforced via micromagnetic simulations and angle dependent hysteresis loops. The found behavior is exploited to create nanowires consisting of a fixed and a free segment in a spin-valve like structure. The wires are released from the membrane and electrically contacted, displaying a giant magnetoresistance effect that is attributed to individual switching of the coupled nanomagnets. We develop a simple analytical model to describe the observed switching phenomena and to predict stable and unstable regimes in coupled nanomagnets of certain geometries.

In the version of this Article originally published, in the Methods section ‘Analytical calculation and FEM simulation’ the first equation was incorrect and has now been replaced. In addition, in the section ‘Conclusions’, the packing density mistakenly read ‘5,000 leg pairs per cm2’ and has now been corrected to read ‘5,500 leg pairs per cm2’.

The characterization of the thermal properties of thin film materials is important both for understanding of their structure and conduction mechanisms and for their technical applications. Thermal conductivity and diffusivity are crucial parameters for the design of integrated devices, thermal microsensors and actuators. Reliable system simulation and design optimization of such devices is based on the accurate determination of thermophysical properties. It is therefore highly desirable to acquire such data. Usually, thermal properties of thin films differ considerably from the bulk values, since the parasitic surface effects are much stronger due to the smaller dimensions and aspect ratios. The measurement of these properties is sophisticated and associated with various problems. We report on steady-state and transient methods for the characterization of in-plane and cross-plane film properties by using microelectrothermal chips.

Weyl semimetals are often considered the 3D-analogon of graphene or topological insulators. The evaluation of quantum oscillations in these systems remains challenging because there are often multiple conduction bands. We observe de Haas-van Alphen oscillations with several frequencies in a single crystal of the Weyl semimetal niobium phosphide. For each fundamental crystal axis, we can fit the raw data to a superposition of sinusoidal functions, which enables us to calculate the characteristic parameters of all individual bulk conduction bands using Fourier transform with an analysis of the temperature and magnetic field-dependent oscillation amplitude decay. Our experimental results indicate that the band structure consists of Dirac bands with low cyclotron mass, a non-trivial Berry phase and parabolic bands with a higher effective mass and trivial Berry phase.

Solid state refrigeration is of great interest due to its potential application in electronic and optoelectronic systems. Nowadays, macroscopic thermoelectric coolers are part of such systems and their cooling performance and reliability are well proven. However, the feasibility of microstructuring such kind of devices by means of photolithographic techniques, opens the possibility of integration on a chip for better local thermal management. Together with previous facts, electrodeposition processes are well known to be low cost, highly scalable and compatible with lithographic techniques. In this work we report on the fabrication of BiTe-based Micro-Thermoelectric Coolers by means of a mixed process flow involving photolithography and electrodeposition techniques. Materials and geometry of the device have been chosen to optimise the cooling performance on an integrated photonic system.