bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Silicon-Based Nanocomposites for Thermoelectric High Temperature Waste Heat Recovery
Authors: Schierning Gabi , Wiggers Hartmut , Schmechel Roland 
Published: February 2020

Thermoelectric generators convert heat flows directly into useable electrical energy. In an appealing future scenario of application, waste heat could be partly recovered by thermoelectric generators. It is typically argued that the heat comes without additional costs. Hence, every contribution of a thermoelectric generator results in an increase of the over-all process efficiency.
A thermoelectric converter material with sufficient performance at competitive costs is hereby one precondition. A pragmatic way to optimize the thermoelectric performance of a material is the introduction of nanostructural elements into bulk materials. Hereby, the availability of high quality nanopowder fosters the development of novel thermoelectric materials: Materials which have per se an insufficient thermoelectric figure of merit can be optimized in a range that they become interesting substitute materials like nanocrystalline silicon or composites of nanocrystalline silicon and metal silicides.
High hot side temperatures require innovative device concepts. Some years ago, a thermoelectric generator concept was proposed, which uses a large area pn junction aligned in parallel to the temperature gradient. This device concept is especially designed for high hot side temperatures and large ΔTs of at least a few hundreds of degree C. All electrical and mechanical contacts on the pn junction device are on the cold side which is beneficial with respect to stability against degradation of the device. Using nanocrystalline silicon as thermoelectric converter material, we have shown that for temperature differences larger than 300°C, the pn junction device performs competitively with an ideal traditional device and outperforms this device if non-ideal contact resistances of a real device are included.
(Invited) Thermoelectric Materials and Modules for High Temperature Application
Authors: Funahashi Ryoji , Barbier Tristan 
Published: February 2020

Oxide materials are considered to be promising ones because of their durability against high temperature, low cost for producing etc. The misfit CoO2 compounds show high thermoelectric efficiency at high temperature in air. Thermoelectric modules using p-type Ca3Co4O9, one of the CoO2 compounds and n-type CaMnO3 have been produced. The maximum power density against area of the substrate of the module reaches 4.3 kW/m2 at 973 K of the heat source temperature. Cascade modules piled up the oxide and Bi2Te3 modules have been prepared. The maximum power density of 7.8 kW/m2 has been obtained at 1000 K of the heat source temperature. Testing of the cascade systems on industrial furnace and incinerators makes clear the next goals from viewpoints of efficiency and economy for the application of the waste heat recovery by thermoelectrics.
In order to improve thermoelectric conversion efficiency, new thermoelectric materials with higher ZT than the above oxides are indispensable. We are developing some new homologous oxides composed of Ba and Co. These layered oxides show low thermal conductivity.
A silicide material with a good n-type thermoelectric property has been discovered. This silicide possesses a composition of Mn3-xCrxSi4Al2 (x = 0-0.7) and hexagonal CrSi2 structure. The dimensionless thermoelectric figure of merit ZT reaches 0.21 at 773 K for a non Cr substituted sample at the Mn site and 0.30 at 573 K for a Cr substituted one with x = 0.3. Since oxide passive layer is formed on the surface, electrical resistivity measured at 873 K is constant for two days in air, which indicates good oxidation resistance in air of this material. Thermoelectric modules consisting of 64 pairs of legs have been fabricated using MnSi1.7 and Mn3Si4Al2 devices as p- and n-type legs, respectively. Output power reaches 9.4 W, which corresponds to 2.3 kW/m2 of power density against surface area of the substrate at the heat source temperature of 873 K in air. The Ni–B plating can improve the degradation of the output power for the silicide modules significantly at the heat source temperature of 773 K. Also, the Ni–B plating can decrease the contact resistance at the junctions. Mixing Pt or Pd into the Ag paste effectively improves the durability at the heat-source temperature of 773 K. The output power can be estimated to hold more than 85 % of the initial value after 10 years with current generation of 1A.
(Invited) Recent Advances on the Promising Thermoelectric Oxides Materials
Authors: Barbier Tristan , Funahashi Ryoji 
Published: February 2020

Because of their ability to convert heat into electricity through the Seebeck effect, there has been increasing interest, in the past few decades, in research into thermoelectric materials for applications in green energy harvesting. Indeed, several sectors, could take advantage of thermoelectric materials capacity to directly convert the waste-heat into electrical energy. These technologies could be available only if performing and cheap thermoelectric materials, operating at temperatures well beyond room temperature, are available.
Recently, the improved knowledge of the underlying physics of thermoelectric materials, together with advanced synthesis techniques, has led to the discovery of new material systems with ZT values higher than 2 at elevated temperatures [1-5]. However the generally complex and costly synthesis procedures, together with the expensive, toxic, and rare elements used, present serious impediments to large scale applications. In this context, work therefore continues to focus on the development of thermoelectric materials and processing methods that not only can exhibit high performance, but also possess the potential to be produced on a large scale.
In this context oxide materials appear as promising materials due to their wide range of electronic properties ranging from insulating to semiconducting and conducting [6]. Their electronic properties can be engineered by changing their morphology, doping and stoichiometry. Based on this trend, the relationship between the stacking sequence and the thermoelectric properties of the Ba-Co-O system will be discussed. Indeed, the wide range of polytypic structures associated to this system offers a great opportunity for designing an “optimal” structure.

[1] J. P. Heremans, V. Jovovic, E. S. Toberer, A. Saramat, K. Kurosaki, A. Charoenphakdee, S. Yamanaka, G. J. Snyder,
Science, 321 554–7 (2008).

[2] Y. Pei, A. Lalonde, S. Iwanaga, G. J. Snyder, Energy Environ.
Sci., 4 [6] 2085-2089 (2011).

[3] Y. Pei, X. Shi, A. Lalonde, H. Wang, L. Chen, G. J. Snyder, Nature, 473 [7345] 66–9 (2011).

[4].S. N. Girard, J. He, X. Zhou, D. Shoemaker, C. M. Jaworski, C. Uher, V. P. Dravid, J. P. Heremans, M. G. Kanatzidis, J. Am. Chem. Soc., 133 [41] 16588–16597 (2011).

[5] K. Biswas, J. He, I. D. Blum, C. Wu, T. P. Hogan, D. N. Seidman, V. P. Dravid, M. G. Kanatzidis, Nature, 490 414–418 (2012).

[6] W. E. Pickett, Rev Mod Phys, 61:433–512 (1989).
(Invited) Thin Film Thermoelectric Metal-Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity
Authors: Talin A. Alec , Erickson Kristopher , Léonard François , Stavila Vitalie , Foster Michael E. , Spataru Catalin , Jones Reese , Foley Brian , Hopkins Patrick , Allendorf Mark D 
Published: February 2020

Metal-organic frameworks (MOFs) are extended, crystalline compounds consisting of metal ions interconnected by organic ligands such as benzene carboxylates, forming a crystalline, nanoporous structure. The low atomic density and long, bridge-like bonding characteristic implies that MOFs should exhibit low thermal conductivity, which is an attractive feature for thermoelectric energy conversion. However, most MOFs are electrical insulators due to the non-conjugated character of the organic ligands and poor overlap between their pi orbitals and the valence orbitals of the metal ions. Recently, we discovered that infiltrating the pores of the copper-containing MOF Cu3(BTC)2 with redox-active guest molecules TCNQ (7,7,8,8-tetracyanoquinododimethane) increases the electrical conductivity of thin film devices by as much as seven orders of magnitude [1]. Density functional theory indicates that electrical conductivity results from a donor-bridge-acceptor geometry, in which TCNQ binds to two Cu(II) dimer units within the MOF pore. In this paper we report the first thermoelectric properties characterization of a MOF thin film which yield a positive Seebeck coefficient of ~400 uV/K, in qualitative agreement with DFT calculations which also indicate that holes should be the dominant charge carriers in TCNQ@Cu3(BTC)2. Finally, we present results of molecular dynamics simulations which indicate that the phonon thermal conductivity of Cu3(BTC)2 MOF is indeed low, thus further suggesting that conducting MOFs are promising materials for thermoelectric energy conversion [2].
[1] A. A. Talin, A. Centrone, M. E. Foster, V. Stavila, P. Haney, R. A. Kinney, V. Szalai, F. El Gabaly, H. P. Yoon, F. Léonard, M. D. Allendorf, Science
343, 66 (2014)
[2] K. J. Erickson , F. Léonard , V. Stavila , M. E. Foster, C. D. Spataru , R. E. Jones , B. M. Foley, P. E. Hopkins, M. D. Allendorf, and A. A. Talin, Adv. Mater. DOI: 10.1002/adma.201501078 (2015).
(Invited) Nano-Length-Scale Inorganic/Organic Hybridization for Thermoelectric Materials
Authors: Koumoto Kunihito , Wan Chunlei , Tian Ruoming , Yang Ronggui 
Published: February 2020

Thermoelectric materials have been mostly inorganics based on metals, alloys, and inorganic compounds for a long time, but recently we have witnessed a rapid growth of organics for near room-temperature applications. High TE performance of organic materials appear to be mainly due to their low thermal conductivity, and the guiding principle to get high ZT is to enhance the power factor of low-thermal-conductivity organics. This is completely opposite to that for exploiting inorganic TE materials which usually possess high power factor but high thermal conductivity. Accordingly, nano-length-scale hybridization (not a mere composite) of inorganic and organic compounds would be promising to realize high-power-factor and low-thermal-conductivity simultaneously to get high ZT.
We have recently found that TiS2-based inorganic/organic hybrid superlattices show a reasonable power factor and ultralow thermal conductivity; ZT=0.21~0.28 at 300~373 K in an ambient atmosphere1). It was also found that the polar molecules coexisting with organic cations in the van der Waals gap between TiS2 monolayers have dielectric screening effects to suppress the electrostatic attractive force between organic cations present in the gap and carrier electrons present in the TiS2 monolayers, and hence carrier mobility is enhanced while lattice thermal conductivity is lowered by increasing dielectric constant of polar molecules, which leads to enhanced ZT
2). Such hybrid superlattice materials are mechanically flexible, which would be beneficial for a variety of energy-harvesting applications.
Inorganic/organic hybridization should be a promising concept for the future TE materials design. There are an infinite number of combinations of inorganic and organic species. Nano-length-scale hybridization of the known compounds composed of non-rare and non-toxic elements must be cultivated to discover high-ZT materials.
1. C. L. Wan, K. Koumoto et al., Nature Mater. (2015). [DOI:10.1038/nmat4251]
2. C. L. Wan, K. Koumoto et al., submitted.
(Invited) Electrodeposited Micro Thermoelectric Module Design for Hybrid Semiconductor Laser Cooling on a Silicon Photonics Platform
Authors: Enright Ryan , Lei Shenghui , Mathews Ian , Cunningham Graeme , Frizzell Ronan , Shen Alexandre 
Published: February 2020

With the promise of highly integrated, high performance optoelectronic devices for communication applications, silicon photonics has emerged as a scalable solution to meet the demands for increased bandwidth in communication networks. An ultimate vision for silicon photonics realizes the integration of both electronic and photonic functionality in optoelectronic devices. However, while such level of integration has appeal, it introduces new thermal challenges alongside already existing ones; all of which have to be dealt with against the backdrop of the need for more compact, higher performance and energy efficient thermal solutions. In particular, the performance of active photonic devices, such as semiconductor lasers and optical amplifiers, are thermally sensitive; being required to operate at temperatures significantly lower than their electronic counterparts and often below the ambient temperature found in equipment racks. In traditional non-integrated optoelectronic packages, this thermal requirement has been dealt with by isolating temperature sensitive devices and cooling them using centimeter-scale thermoelectric modules. However, this solution is poorly suited to integrated optoelectronic devices sharing the same substrate and limits the minimum system size.
An alternative approach is to integrate thermoelectric temperature control at the device level to simultaneously provide targeted cooling for individual temperature sensitive devices and reduce the footprint of the thermal solution to enable full optoelectronic integration. Here we present the design of a micro thermoelectric cooler (μTEC) integrated around a hybrid laser, i.e., direct band-gap III-V material wafer-bonded to a silicon-on-insulator substrate, where the key fabrication step is the electrodeposition of p-doped (Bi1-xSbx)2Te3 and n-doped Bi2(TexSe1-x)3. We outline the processing requirements needed to ensure backend compatibility with silicon photonics fabrication. Starting with baseline experimental performance data for our hybrid laser technology and thermoelectric properties reported in the literature, we develop a multiphysics numerical model of the hybrid laser with integrated μTEC. We then assess our design in terms of system-level relevant operating temperatures and laser performance requirements. Our results suggest that electrodeposited μTECs can meet the thermal requirements of active photonics devices in silicon photonics under realistic operating conditions. We conclude by highlighting performance enhancements to be gained by improving electrodeposited material processing beyond the state-of-the-art.
(Invited) Reducing the Thermal Conductivity By Driving PbTe to a Phase Transition Via Strain and/or Alloying
Authors: Savic Ivana 
Published: February 2020

The efficient control of thermoelectric energy conversion processes is highly desirable as nearly 60% of the consumed energy is wasted as heat. Low thermal conductivity is one of the key factors leading to high thermoelectric efficiency of a material [1]. However, one of the major obstacles in the design of materials with low lattice thermal conductivity is the difficulty in efficiently scattering phonons across the entire frequency spectrum [2]. Using first principles calculations, we show that driving PbTe materials to the brink of a Peierls-like phase transition could be a powerful strategy to solve this problem. We illustrate this concept by applying tensile [001] strain to PbTe and its alloy with a chemically similar material in the rock-salt structure (e.g. PbSe), and by alloying PbTe with a related material in the rhombohedral, Peierls-distorted, structure (e.g. GeTe). This induces extremely soft optical modes, which increases acoustic-optical phonon coupling and decreases phonon lifetimes at all frequencies. We predict that PbTe, Pb(Se,Te) and (Pb,Ge)Te alloys tuned in the described manner could have substantially reduced lattice thermal conductivity compared to PbTe. The proposed concept may open new opportunities for the development of more efficient thermoelectric materials. This work was done in collaboration with Ronan Murphy, Eamonn Murray and Stephen Fahy.
[1] G. J. Snyder and E. S. Toberer, Nature Mater. 7, 105 (2008).
[2] K. Biswas et al. Nature 489, 414 (2012).
(Invited) Phonon Dispersion Engineering and Thermal Transport in Si Membranes
Authors: Alzina Francesc , Reparaz J. Sebastian , Graczykowski Bartlomiej , El Sachat Alexandros , Sledzinska Marianna , Chávez-Ángel Emigdio , Wagner Markus R , Shchepetov Andrey , Prunnila Mika , Ahopelto Jouni , Sotomayor Torres Clivia M 
Published: February 2020

Present silicon technology provides single crystal films and membranes with thicknesses on the order of 10 nm and below. Along the years, the thermal studies on such structures have shown a reduction of the thermal conductivity consistent with the decrease of the characteristic size. Although the lowering of thermal conductivity is detrimental for heat dissipation processes in nanoelectronic devices, it becomes advantageous to increase the figure of merit (ZT) of Si and turning it as a promising material for thermoelectric applications. It is widely accepted that, for submicrometer thicknesses and down to 20 nm, the reduction of the in-plane thermal conductivity is mainly determined by the shortening of the phonon mean free path due to the diffusive scattering of phonons at the boundaries. In this case an analytical model that adopts the phonon bulk properties and includes the boundary scattering by a conductivity reduction factor is shown to match the experimental trend of systematical reduction of the thermal conductivity as the thickness of the film or membrane decreases.
In this talk we will report on the modification of the phonon properties in Si membranes, such as the dispersion relation, and its dependence on the thickness. The thermal conductivity in Si results from the cumulative contribution of the transport of phonons with a broad range of wavevectors and mainly from long-wavevector phonons. Thus, heat transport at room temperature can be influenced by the reduction of the membrane thickness as the dispersion relation of the short-wave-phonons starts to be affected by emerging new vibrational modes arising from the boundary conditions at the membrane surface. Our measurements of the thermal conductivity in ultra-thin sub-20 nm Si membranes have demonstrated this extreme and, in fact, we have been able to disentangle the effects of phonon confinement from those related to surface morphology and chemical composition. Finally, we will discuss the prospects of employing the increased modification of phonon dispersion relation achieved in phononic crystals in controlling heat transport. While some applications require the existence of absolute band gaps, the approach to reduce the thermal conductivity is more linked to the decrease of phonon’s group velocity and phonon-phonon interactions in an extended range of frequencies.
(Invited) Tuning of Heat Transport across Thin Films of Polycristalline AlN via Multiscale Structural Defects
Authors: Jaramillo-Fernandez Juliana , Ordonez-Miranda Jose , Ollier Emmanuel , Sanatinia Reza , Kataria Himanshu , Chávez-Ángel Emigdio , Volz Sebastian , Sotomayor Torres Clivia M 
Published: February 2020

Thermal conductivity of the elemental components of device-like structures is of fundamental importance for enhancing the thermoelectrical efficiency. However, the accurate description and control of their thermal properties remain a difficult task due to multiscale defects, and the anisotropic and heterogeneous structures usually present in thin films fabricated by vapor deposition techniques. Experimental thermal characterization, accurate theoretical description and controlled modulation of the thermal properties of these materials are therefore desirable.
To accurately asset the thermal role of structural features which are present in mono- and nanocrystalline thin films, we are studying the size-dependent reduction of their effective thermal conductivity by optical and electrothermal techniques. We propose a physical and quantitative description of the reduction of the effective thermal conductivity with film thickness based on an electron microscope study, thickness-dependent 3ω measurements and a theoretical model. The latter takes into account the distribution of the grain geometry and considers the films as a serial assembly of three layers, composed of parallelepiped grains. These structural zones are namely: the near-interface, transition, and columnar region. We show that the resistances due to the interface with the substrate and to the near-interface and transition regions dominate the thermal conduction as the film thickness is scaled down; while for thick films, the effects of the increased mean free paths and intrinsic resistance resulting from the columnar region predominate. These transitions in the thermal transport mechanisms appear due to the relative size of each domain with respect to the total film thickness. In addition, optical techniques have been used to perform thermal measurements on epitaxially grown films. The main objective of these optical measurements is to identify differences in heat transport mechanisms between mono- and nanocrystalline systems, which are related to multiscale defects, such as dislocations and grain boundaries. Furthermore, recent studies of the thermal conductivity using Raman thermometry of III-V/Si structures will be reported, where the relative dimensions of opening in Si prior to the growth of the III-V layers has a marked impact in the value of the thermal conductivity, being larger for larger opening.
Self-Assemble Formation of Ge Dots on Si(100) via C/Ge/C/Si Structure
Authors: Itoh Yuhki , Kawashima Tomoyuki , Washio Katsuyoshi 
Published: February 2020

Self-assemble formation of Ge quantum dots on Si is one of the promising candidates to implement optical devices, such as laser diodes [1], photo detectors [2] and solar cells [3], on a Si ULSI platform. It has been reported that the usage of sub-monolayer (ML) carbon (C) gave a beneficial way to form Ge dots as a result of c(4×4) reconstruction on Si(100) [4]. In our previous studies, self-assemble formations of Ge dots by C mediation were investigated as follow. In the case of sequential deposition of C and Ge on Si (Ge/C1/Si structure) at low temperature and subsequent annealing, it was confirmed that Si-C bonds promoted to form Ge dots during solid phase epitaxy [5]. In the case of C2/Ge/Si structure, an incorporation of C atoms into Ge layer during annealing induced to decrease the bulk free energy due to the formation of Ge-C bonds in the nucleation process, and led to scale down dot size and increase dot density [6]. On the basis of these backgrounds, by combining both structures, Ge dot formation via C2/Ge/C1/Si structure was investigated in this study. This is because the formation of Si-C bonds at the Ge/Si interface and Ge-C bonds in Ge dots is expected to help to obtain small and high-density Ge dots. The samples were prepared by solid-source molecular beam epitaxy system. C2/Ge(7.5 ML)/C1/Si(100) structures by changing C1 and C2 coverage were formed at substrate temperature of 200°C and were annealed at 650°C in the MBE chamber. As a result, small (20 nm) and dense (1.7 × 1010 cm-2) Ge dots were obtained at C1 = 0.25 ML and C2 = 0.1 ML. This indicates that the C2/Ge/C1/Si structure, which enables to control the binding states of both Si-C and Ge-C bonds, is an effective way to form Ge quantum dots self-assembly. In the meeting, the influence of the relationship between C1 and C2, the dot formation mechanism related to C binding states, and the optimization of the C2/Ge/C1/Si structure will be presented in detail.
Acknowledgments
This study was partially supported by JSPS KAKENHI Grant Number 24246003 and 15H03554 and, JSPS Core-to-Core Program, A. Advanced Research Networks.
Reference
[1] F. Ross et al., Phys. Rev. Lett. 80 (1998) 984.
[2] G. Abstreiter et al., Semicond. Sci. Technol. 11 (1996) 1521.
[3] A. Alguno et al., Appl. Phys. Lett. 83 (2003) 1258.
[4] O. Leifeld et al., Mat. Sci. Eng. B 74 (2000) 222.
[5] S. Hatakeyama et al., Microelec. Eng. 125 (2014) 28.
[6] Y. Itoh et al., Materials Today Asia 2014 O2.2 (2014).