bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Applications of Solid Electrolyte Membranes in Heterogeneous Catalysis. Electrochemical Reaction and Separation
Authors: Stoukides Michael , Vourros Anastasios , Vasileiou Eirini , Kyriakou Vasileios , Garagounis Ioannis
Published: February 2020

In addition to their applications in sensors, separators and solid oxide fuel cells, solid electrolytes have been used in the construction of solid state cell-reactors, in which catalytic reactions were studied. Depending on the reaction system, there was a variety of goals in these studies: a) to take advantage of the selective conduction of ions, b) improve the yield to the desired product and c) cogenerate electricity and value-added chemicals. Two examples of applications of solid state cell-reactors in heterogeneous catalysis are presented here, a) the production of ethylene and hydrogen from methane with simultaneous separation of hydrogen from the reaction mixture and b) the electrochemical synthesis of NH3.     

      The production of hydrogen with simultaneous conversion of methane to C2 hydrocarbons was studied in a solid state oxygen ion (O2-) conducting cell at temperatures between 700 oC and 850 oC. Methane, diluted in nitrogen was introduced over the anode (Ag) and steam, also diluted in nitrogen, was introduced over the cathode (Pt). When oxygen was electrochemically “pumped” from the cathode to the anode, steam was electrolyzed to produce gaseous H2 while CH4 was converted to C2H6, C2H4 and CO2. At the anode, C2yields exceeding 8% were obtained while an up to 65% conversion of steam was achieved at the cathode.

      The electrochemical synthesis of ammonia was studied in a proton conducting solid electrolyte cell. The BaZr0.7Ce0.2Y0.1O2.9 (BZCY72) proton conducting ceramic was used as the electrolyte with a Ni-BZCY72 cermet and a Pt film serving as cathodic and anodic electrodes, respectively. The reaction was studied at atmospheric pressure and at temperatures between 450 oC and 700 oC, under both, open- and closed-circuit conditions. A peculiar reaction rate enhancement was observed when the cell returned to open-circuit after operating under closed-circuit for a certain time. A possible explanation of this new phenomenon is that a fraction of protons electrochemically transported to the cathode, is "stored" in the Ni-BZCY72 electrode in the form of a highly reactive hydride which, upon current interruption, reacts with adsorbed N species to produce ammonia.
Water Purification in Porous Media Via Shock Electrodialysis
Authors: Schlumpberger Sven , Lu Nancy B. , Suss Matthew E , Bazant Martin Z.
Published: February 2020

In this project, we demonstrate experimentally and theoretically the feasibility of exploiting deionization shocks in porous media to perform water purification (“shock electrodialysis”, see figure 1). The basic idea of this new approach is to drive an over-limiting current (faster than diffusion) through a weakly charged porous medium sandwiched between two cation-exchange membranes, producing a sharp “shock” (a propagating wave of salt depletion driven by surface conduction [1,2]) in the salt concentration profile within the porous medium [3, 4]. Flowing through the porous medium allows for continuous deionized and brine streams, which can be separated at the outlet. We here will present our work towards the development of a shock electrodialysis device (see figure 2), which enables the desalination of arbitrary feedwater streams, and allows for continuous, fast flows through the device for high throughput desalination. Using this device, we were able to remove up to 99+% of ions from NaCl feed solutions of various concentrations (see figure 3 for data for one specific feed flowrate and concentration). In addition, in order to gain a thorough understanding of the phenomena underlying the system, we performed detailed simulations of the device (see figure 4). This simulation framework will be compared to experimental data and is also used to gain useful engineering insights which are useful in improving the prototypes that we are building. Overall, preliminary results show good desalination factors, reasonable efficiency, and unique separation capabilities, such as removal of particles and disinfection, which may find applications in compact water treatment and brine concentration.

[1] Mani, A.; Zangle, T.; Santiago, J.G. On the Propagation of Concentration Polarization from Microchannel-Nanochannel Interfaces Part I: Analytical Model and Characteristic Analysis. Langmuir 2009, 25 (6), 3898-3908

[2] Zangle, T.; Mani, A.; Santiago, J.G. On the Propagation of Concentration Polarization from Microchannel-Nanochannel Interfaces Part II: Numerical and Experimental Study. Langmuir 2009, 25 (6), 3909-3916

[3] Deng, D.; Dydek, E.V.; Han, J.; Schlumpberger, S.; Mani, A.; Zaltzman, B; Bazant, M. Z. Overlimiting Current and Shock Electrodialysis in Porous Media. Langmuir 2013, 29 (52), 16167-16177

[4] Deng, D.; Aouad, W.; Braff, W.A.; Schlumpberger, S.; Suss, M.E.; Bazant, M.Z. Water Purification by Shock Electrodialysis: Deionization, Filtration, Separation, and Disinfection. Desalination 2015, 357, 77-83

Figure 1
Porous Diamond Membrane Fabricated By Templated Growth for Electrochemical Separation Processes
Authors: Gao Fang , Giese Christian , Lewes-Malandrakis Georgia , Nebel Christoph E.
Published: February 2020

Boron-doped diamond has been applied as an outstanding electrode material for electrochemical applications. Using templated growth techniques, a variety of diamond nanostructures like diamond wires and diamond foams can be fabricated [1, 2]. Using quartz or glass fiber paper as growth templates, porous diamond membranes are fabricated [3]. Compared to polymer membranes or membranes based on sp2 carbons, diamond membranes can survive in aggressive media and high temperature conditions. Also, the ion selectivity can be controlled by surface terminations as well as the bias potential of the membrane. Therefore, this kind of membranes is very promising for the electrochemical separation processes such as desalination, pollutants concentration and protein separation. However, both the fabrication and application of diamond membranes are so far reported only in very limited cases.

In this paper, we report our recent progress with respect to the templated diamond growth using quartz fiber paper as the growth template. With optimized microwave CVD growth, nanocrystalline diamond film is fully coated onto the quartz fiber as has been confirmed via SEM. The growth conditions in terms of temperature, methane concentration and boron/carbon ratio are investigated in detail. The diamond quality is evaluated via Raman spectroscopy, and the boron concentration is determined via SIMS. The potential window of the diamond membrane is determined via cyclic voltammetry in an aqueous NaClO4 solution to be ~2.5 V. By applying potential to the membrane, ions will accumulate inside the membrane and change its porosity. As a result, the ion flux through the membrane can be well tuned. This ion selectivity can be used to separate charged molecules. As an example, 5-Carboxyfluorescein and substance P are separated by the diamond membrane under different biases. In a neutral solution, for example, negatively charged 5-caboxyfluorescein can penetrate a positively charged membrane, while the positively charged substance P cannot. Therefore, this membrane can potentially be used for separation processes in biochemical and biomedical applications. Finally, due to the robustness of diamond, the membrane can be cleaned via a high potential (+3 V vs Ag/AgCl) oxidation process in 2 M H2SO4. Metal deposits and organic contaminants are proved to be removable by this method. Therefore, this membrane is also suitable for applications like undersea activities where only simple in-situ maintenances are possible. 

[1] F. Gao, M.T. Wolfer, C.E. Nebel, Carbon, 80 (2014) 833-840.

[2] F. Gao, G. Lewes-Malandrakis, M.T. Wolfer, W. Müller-Sebert, P. Gentile, D. Aradilla, T. Schubert, C.E. Nebel, Diamond Relat. Mater., 51 (2015) 1-6.

[3] S. Ruffinatto, H.A. Girard, F. Becher, J.C. Arnault, D. Tromson, P. Bergonzo, Diamond Relat. Mater., 55 (2015) 123-130.
Hybrid Films Deposition for Nanochannel Membranes with Functional Surfaces
Authors: Kim Jeong Hwan , Lee Sung-Woong , Jung Sun-A , Yoon Jae-Sung , Yoo Yeong-Eun
Published: February 2020

Thin film deposition is one of the most significant issues in the fabrication of nano structures. Especially it is difficult to achieve conformal films on high-aspect ratio nanostructures, such as nanochannel membranes. Though there are various thin film deposition techniques, atomic layer deposition (ALD) has attracted due to its extreme surface conformality and excellent thickness controllability. Because ALD is a chemical gas phase thin film deposition method based on sequential and self-saturating surface reactions, it can be used for coating of nano structures with high-aspect ratio.

Sputtering process is one of the popular film deposition techniques due to its relative simplicity of process and fast deposition speed. However, film depositions by sputtering technique are less conformal compared to those by ALD, because of ions directionality sputtered by plasma. Therefore it is difficult to form films on the surfaces perpendicular to substrate by sputtering process.

However, if ALD and sputtering techniques are combined, hybrid thin films deposition which different films are deposited on selectively different surfaces (eg. surfaces perpendicular and parallel to substrate). In this poster, I will present the results of hybrid films deposition on nanochannel membranes with high-aspect ratio. For different functionalities (hydrophilicity and hydrophobicity) of surfaces, Al2O3 and Pt films were grown on nanochannel membranes. Al2O3 films deposition on the vertical surfaces (inner surfaces of nanochannels) was controlled precisely in nanometer scale by using ALD process. Pt films were formed on horizontal surfaces (outer surfaces of nanochannels) by using DC magnetron sputtering. In addition, I will also present the ionic seperation in NaCl solution using fabricated nanochannel membranes by hybrid deposition process and using electrcal bias on Pt films.
Spectroscopic Ellipsometry Characterization of Pd Thin Film Grown by Atomic Layer Deposition
Authors: Zhang Yihang , Zhou Xueqi , Cao Kun , Chen Xiuguo , Liu Shiyuan , Shan Bin , Chen Rong
Published: February 2020

Ultrathin noble metal films have attracted lots of attentions in fuel cell catalysts, hydrogen storage, emission control, etc. Among many synthesis methods, atomic layer deposition (ALD) is a powerful one to fabricate ultrathin films with great precision [1]. The measurement of such noble metal films is quite important to both understand the initial growth behavior and guide the film fabrication process. Spectroscopic ellipsometry (SE) is a fast and non-destructive thin film characterization technique with atomic sensitivity [2]. The initial growth of noble metals, however, is in island growth mode and bulk metal model could not correlate with such structures. Similar structures have been reported by the Maxwell-Garnett Effective medium approximation (MG-EMA) model to study the optical properties of Au, Ag thin films [3-4]. In this paper, we choose the MG-EMA model with General oscillator (GO) to study the size and volume fraction.

In this study, MG-EMA model has been chosen to study Pd ultrathin film grown on Si substrate, as well as its growth on self-assembled monolayers (SAMs) modified substrate respectively. The GO model with one Drude and two Lorentz oscillators is firstly applied to fix the optical constants of Pd. Compared with Pd bulk model, MG-EMA model with GO is more reliable to predict the film thickness verified by X-ray reflection test. The stable growth rate on Si substrate reveals our methods are feasible and is in accordance with the quartz crystal microbalance measurement. For Pd coverage, MG-EMA fitting result is similar with the statistical computation from scanning electron microscope when cycles of Pd ALD cycles are over 400, while large bias exists for cycles under 400, might be due to that air is not the proper filling medium between nanoparticles. Then we change the filling medium into SAMs as a comparison, better fitting performance is obtained. It is demonstrated that the filling medium between nanoparticles is important for the application of MG-EMA model.

References:

 

H. Feng, J. Lu, P. C. Stair, J. W. Elam. Catal. Lett, 141, 512-517(2011).

K. Vedam, Thin Solid Films, 313, 1-9(1998).

K. C. See, J. B. Spicer, J. Brupbacher, D. Zhang, T. G. Vargo, J. Phys. Chem. B, 109, 2693-2698(2005).

T. Ung, L. M. Liz-Marzán, P. Mulvaney, J. Phys. Chem. B, 105, 3441-3452(2001).
(Invited) A Rational Design for Batteries at Nanoscale by Atomic Layer Deposition
Authors: Liu Chanyuan , Gillette Eleanor , Chen Xinyi , Pearse Alexander J , Kozen Alexander C , Schroeder Marshall A , Gregorczyk Keith , Lee Sang Bok , Rubloff Gary W
Published: February 2020

A self-aligned nanostructured battery fully confined within a single nanopore presents a powerful platform to determine the rate performance and cyclability limits of nanostructured storage devices. Atomic layer deposition (ALD) has enabled us to create and evaluate such structures, comprised of nanotubular electrodes and electrolyte confined within anodic aluminum oxide (AAO) nanopores as “all-in-one” nanopore batteries.This nanopore battery displays exceptional power-energy performance and cyclability when tested as massively parallel devices (~2billion/cm2), each with ~1um3 volume (~1fL). [1]

The unprecedented thickness and conformality control of ALD and the highly self-aligned nanoporous structure of anodic aluminum oxide (AAO) are essential to enable fabrication of precision, self-aligned, regular nanopore batteries. To realize such structure, we began with fine tuning of ALD process conformality inside high aspect ratio (300:1) AAO nanopores. Ru/Pt metal is optimized to be 15µm deep at both sides of 50µm long AAO pores in order to provide fast electron transport to overlying V2O5 at both anode and cathode sides, while keeping them spatially and electrically isolated. Crystalline V2O5 was deposited as active storage material inside the metal nanotubes using O3 as the oxidant. Then the V2O5 was electrochemically prelithiated at one end to serve as anode while pristine V2O5 without Li at the other end served as cathode, enabling the battery to be cycled between 0.2V and 1.8V. Capacity retention of this full cell is 95% at 5C rate and 46% at 150C, with more than 1000 charge/discharge cycles. Further increase of full cell output potential is also demonstrated for SnO2 and TiO2 anodes in asymmetric full cells with V2O5cathodes. These results demonstrate the promise of ultrasmall, self-aligned/regular, densely packed nanobattery structures as a test bed to study ionics and electrodics at nanoscale with a variety of geometrical modifications and as a building block for high performance energy storage systems.

[1] Liu, C.; Gillette, E. I.; Chen, X.; Pearse, A. J.; Kozen, A. C.; Schroeder, M. A.; Gregorczyk, K. E.; Lee, S. B.; Rubloff, G. W., An all-in-one nanopore battery array. Nature Nanotechnology
2014,
9 (12), 1031-1039.
(Invited) Organic-Inorganic Hybrid Materials Formed By ALD Organometallic Infiltration into Polymers
Authors: Jur Jesse S , Akyildiz Halil Ibrahim
Published: February 2020

Atomic layer deposition on polymers has been demonstrated to yield infiltration of reactive vapors that react with the polymer to form hybrid organic-inorganic materials structures.  From this infiltration, new dosing schemes have been utilized to elicit controlled reaction and diffusion. Inspection of these materials has shown a unique set of characteristics, including the ability to fabricate optically active hybrid materials as a result of the formation of a bandgap. As an example process, we examined the ability to infiltrate trimethylaluminum into polyethylene terephthalate (PET) using elongated sequential exposures. As a consequence of PET-AlOx coordination complex formation within the PET polymer (in film and fiber form), semiconductor behavior is observed in modified material; hence a novel approach toward modifying the band structure of organic materials for optoelectronic and electronic applications.  Furthermore, the photoluminescence behavior of the modified PET is shown to increase up to 13 fold while internal quantum efficiency (IQE) values increased from ~4-5% up to ~25% in the UV spectrum.  Photocatalytic applications have been explored for these materials for their ability to reduce metal ions, such as Ag and Au, out of aqueous salt solutions during UVA light exposure.   As a result of this photoreduction process, patterned metallic structures are formed that are useful for flexible electronic and e-textile device systems.
Sulfate Adsorption onto and Desorption from Silicon Dioxide Films
Authors: Wu Bing , Raghavan Srini
Published: February 2020

Sulfuric acid, especially in a mixture with hydrogen peroxide, is a commonly used chemical in the surface preparation of silicon. Removal of adsorbed sulfate based contaminants by DI rinsing is an important step in processing steps using sulfuric acid. Fundamental information on the rate and extent of adsorption and desorption of sulfate on surfaces is very scarce.

This presentation will discuss sulfate adsorption onto and desorption from SiO2 surfaces using a quartz crystal microbalance with dissipation monitoring capability (QCM-D). The amount of adsorption of sulfate was estimated from frequency shifts of a SiO2 coated AT-cut quartz crystal. The quartz crystal, with a fundamental frequency of 5 MHz, consists of a quartz disk of 14mm diameter, and gold electrodes that are sputtered on both sides of the quartz disc. The SiO2 coating, 300 nm thick, was deposited by PVD onto the active side of quartz crystals.

Figure 1 shows a real time frequency recording of a SiO2 coated crystal exposed to flowing 0.2 M sodium sulfate solution. The frequency and dissipation change were measured for different harmonics of the fundamental crystal frequency at the same time. The divergent overtones and high dissipation factor indicated a “soft” adsorbed layer, rendering the Sauerbrey relation invalid for mass calculation from frequency changes. Hence, a viscoelastic model was used for conversion of frequency changes to mass changes. It can be seen the sulfate adsorption onto and desorption from SiO2 surface happens fairly quickly as marked in the figure. At 22 C, the rate constants of desorption are about 0.06 s-1 and 0.16–0.18 s-1 for flow rates of 0.2 ml/min and 1.0 ml/min respectively.

The adsorption isotherm of sulfate is shown in figure 2. The equilibrium adsorption increases linearly with sulfate concentration at the range of 0.1 M to 0.6 M.

Figure 1
(Invited) Advanced Nanostructured Thermoelectric Materials for Energy Conversion
Authors: Wu Yue
Published: February 2020

The rapid development of nanomaterials in the past decade has provided a possibility of directly converting waste heat back to electricity based on the thermoelectric Seebeck effect. In the past four years, we have developed a transformative approach to pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical entertainment in the manufacture/recycling. These nanostructured thermoelectric materials show a significantly enhanced performance compared to the bulk crystals based on the quantum confinement and minority carrier blocking.
(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).
Mechanical Properties of Li7La3Zr2O12 and Li0.33La0.57TiO3
Authors: Wolfenstine Jeffrey
Published: February 2020

Abstract

Many new types of high energy Li batteries may require a solid Li-ion conducting electrolyte. The major requirements for the solid Li-ion electrolyte are; high Li-ion conductivity, low electronic conductivity and good chemical/electrochemical stability. However, in many applications adequate mechanical properties are also relevant. For example, an electrolyte with a high shear modulus is required to prevent dendrite penetration when using a Li anode. At present information on the mechanical properties of two new promising solid Li-ion conductors; Li7La3Zr2O12 (LLZO) and Li0.33La0.57TiO3 (LLTO) is lacking. It is therefore the purpose of this talk to present some of the first information on the room temperature mechanical behavior of high density (>98% relative density) LLZO and LLTO. These include: hardness, elastic modulus, fracture strength, fracture toughness and thermal expansion. The results will compared to existing data for other solid Li-ion conductors and theoretical predictions. In addition, the methods to improve the mechanical behavior of LLZO and LLTO while retaining high ionic conductivity will be presented.
Recent Progress in the Fundamental Understanding of Garnet-Based Superionic Conductors and Fabrication of Solid-State Cells for Advanced Lithium Batteries
Authors: Thompson Travis , Johannes Michelle , Huq Ashfia , Allen Jan L. , Wolfenstine Jeff , Sharafi Asma , Sakamoto Jeff
Published: February 2020

In recent years, the push to move past conventional Li – ion battery technology has grown. Several advanced battery technologies and cell chemistries have been identified as promising candidates including i) solid-state batteries with Li metal anodes, ii) Li – S, and iii) flow batteries. Although an engineered solution using liquids may be possible for some of these options, a solid electrolyte is an enabling technology for each of these beyond Li – ion alternatives. Li7La3Zr2O12 (LLZO) with the cubic garnet structure is a promising solid electrolyte for advanced battery concepts such as solid state Li-ion batteries. Cubic LLZO is a fast ion conductor and is chemically and electrochemically stable between 0 and 6V vs. Li/Li+. This presentation will show recent advances 1) in the understanding of the conduction mechanism and 2) towards fabrication of solid-state device. First, neutron diffraction was used to successfully determine the Li site occupancy for a series of cubic LLZO compositions stabilized by Tantalum. Furthermore, the Li site occupancy has been related to the bulk ionic conductivity and activation energy as measured by Electrochemical Impedance Spectroscopy (EIS) with equivalent circuit modelling as a function of temperature. It was found that the maximum in the conductivity coincides with the cubic-to-tetragonal phase transition. The cubic-to-tetragonal transitional point also represents the maximum in octahedrally coordinated Li site occupancy and shortest Li-Li separation distances. Determination of the carrier concentration from results of the neutron diffraction and conductivity measurements support the earlier suggestion by Ohta et al. that not all the Li-ions are participating in conduction. Second, recent results towards bonding of electrodes to a cubic LLZO membrane will be presented. The ability to form electrochemically active solid/solid interfaces will allow for fundamental investigation of the charge transfer mechanism from one crystalline solid to another. Overall, the purpose of this work is to establish a fundamental knowledge base to assess the feasibility of large-format solid-state batteries.