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2022 Spring Meeting

Energy materials


2D materials for energy storage: batteries, super capacitor, solar cells, thermoelectric

Fifty years ago, it was forecast that our modern society would be supported and operated mainly by three elements of technology; i.e. materials, energy and information. Rapid rise in the research and development of new materials has not only largely improved our modern life but also controls further expansions of the other two technologies. The research of materials, such as more efficient batteries and light chemical energy conversion materials, is urgently required. Our symposium will be one such attempt in the field of energy research with focus on 2D materials.


The growth of the human population coupled with the simultaneous improvement of living conditions is resulting in a rapidly rising global energy demand, and the negative effects on the environment in the form of pollution and global warming are becoming ever more apparent. Therefore, it is of utmost importance to take action now and concentrate on an active search for alternatives to our current fossil fuel based economy. The general consensus is that only renewable energies could provide a long-term sustainable source of energy. One needs, however, to consider that if fossil fuel is taken out of the picture, one requires an adequate substitute energy carrier for mobile applications (cars, planes, etc.). Our symposium will focus on 2D materials that have attracted the focus of the scientific community in the vast field of energy materials. The applications of such materials will be having a broad view in the area of solar cell, Battery, super capacitor, thermoelectric, spintronics, photo catalysis, and fuel cells. Scientists doing their research in all the above area will be a getting a common platform to showcase their latest findings, which all will be attached through a common string named Energy.

For example, the driving force behind the solar hydrogen generation is the green environment with enormous resources of clean fuels. Semiconducting materials emerge as the prominent media that assist water splitting into oxygen and hydrogen with the help of sunlight. The proposal of symposium on 2D materials aims to integrate cutting edge computational aided systematic and high throughput investigation and newly synthesized 2D materials for the enhanced water dissociation activity of the recently synthesized semiconducting materials MX2 (where M= Transition metal & X=S, Se, Te) and hydrogenated silicone, stanine, phosphorene & MXene from band edge alignment concept. Rapid advancement of exfoliation and synthetic techniques immensely motivates the proposal on 2D materials to explore these exotic single layered materials. The outcome of the symposium can be useful from the perspective of an oil-free economy that replaces the fossil fuel consumption with sustainable energy. The results will be automatically connected to the various activities in the materials science communities, including the ongoing feedback between theory and experiment in energy harvesting for vivid industrial applications.

Hot topics to be covered by the symposium:

The following topics both in the field of Theory and Experiments will be covered in our Symposium “2D Materials for Energy Storage ”

  • Two-dimensional (2D) materials for energy production and storage
  • MXene for energy storage and Photocatalyis
  • 2D based materials for solar cells
  • 2D materials for enhance battery performance
  • 2D Materials for super Capacitor Technology
  • 2D Materials for Thermoelectrics
  • 2D Materials for Spintronics



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Authors : Natarajan, S. K. (1), Luy, J.-.N. (1), Schneider, J. (1), Arcisauskaite, V. (1) & Martinez, U.* (1).
Affiliations : (1) Synopsys QuantumATK, Fruebjergvej 3, 2100 Copenhagen, Denmark * lead presenter

Resume : Application of 2D materials is at the core of continuous down-scaling and performance improvements of various technologies ranging from nanoelectronic, energy storage to thermoelectric and sensing devices. Design, performance and reliability of these devices strongly depend on thermal properties of 2D materials. In this respect, atomistic simulations of thermal properties represent an invaluable tool that can be used to support the R&D of these advanced technologies. Thermal transport simulations of large structures, including multilayer heterostructures combining different 2D materials, can be computationally very demanding or even unmanageable if performed using ab initio (DFT) molecular dynamics (MD), whereas computationally cheaper conventional Force Fields for 2D materials are very scarce and take a long time to be developed. Particularly, they can be cumbersome to generate for 2D material heterostructures. In this talk, we will show that this can be overcome by using machine learning (ML) based force fields which are 10x-1000x more efficient compared to DFT based simulations. We will present how accurate ML force fields, Moment Tensor Potentials (MTPs) [1] with the reverse non-equilibrium MD (RNEMD) method in the QuantumATK software package for atomistic simulations [2,3] developed by Synopsys are used to simulate thermal transport and thermal conductivity of large-scale (~ 100 nm long, ~100000 atoms) 2D material structures. We will also introduce the automated machine learning force field MTP training and simulation workflow in QuantumATK and show how MTPs for 2D materials are trained on DFT data, such as energies, forces and stresses, of reference structures. Finally, we will demonstrate a good agreement of results obtained with MTPs and DFT and experiments. References 1) A. V. Shapeev. ‘Moment tensor potentials: a class of systematically improvable interatomic potentials’ Multiscale Modeling & Simulation 14, 1153 (2016). 2) S. Smidstrup et al. ‘QuantumATK: An integrated platform of electronic and atomic-scale modelling tools’ Journal of Physics: Condensed Matter 32, 015901 (2019). 3)

Authors : Mohamed BEN RABHA
Affiliations : LaNSER, CRTEn

Resume : The purpose of the present work was to study the impact of polycrystalline substrate thickness on solar cells performances. The thickness of a cell is a pertinent parameter during the manufacture of a solar cell since the penetration depth directly impacts the efficiency of solar cells. This work is geared towards the reduction of the substrate thickness to increase efficiency of PV cells using low cost material. Indeed, it has been shown that the production of solar cells with buried metal contacts improves carrier collection by: (i) increasing the collection surface, (ii) reducing the contact resistance and (iii) passivation of grain boundaries; this resulted in a significant decrease in leakage current and improved spectral response. It has been demonstrated that all these factors may lead to improved energy efficiency of low-grade metal made PV cell from 7% to nearly 12 % for a cell treated with buried contacts SP.

Authors : Konstantina A. Papadopoulou(1), David Parfitt(1), Alexander Chroneos(2,3), and Stavros-Richard G. Christopoulos(1)
Affiliations : (1)Faculty of Engineering, Environment and Computing, Coventry University, Priory Street, Coventry CV1 5FB, United Kingdom (2)Department of Materials, Imperial College London, London SW7 2BP, United Kingdom (3)Department of Electrical and Computer Engineering, University of Thessaly, 38221 Volos, Greece

Resume : After obtaining Ti3C2 MXene structures terminated with O, S, Se, F, Cl, and Br, we calculate the energy barrier for Li-ion diffusion on the surface of each MXene, being the first to report on the Li-ion diffusivity in Cl and Br terminated Ti3C2. We find that the Ti3C2Cl2 MXene has the lowest diffusion barrier, substituting the Ti3C2S2 reported in the literature so far. In addition, a study on the adsorption energies indicates that the top binding position is the most stable adsorption position for the Li-ion. Furthermore, it is shown that the adsorption energy depends on the electronegativity of the termination atoms, as well as the distance between the terminations, the Li, and the surface Ti-atoms. Finally, we show that the bond valence sum method provides an indication of the transition state of the Li-ion and can serve as a comparison tool for the diffusion barriers of different structures

Authors : Chiranjit Roy, Somnath Bhattacharyya
Affiliations : Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036

Resume : Recently, 2D materials MXene gained significant attention in various research fields due to their unique properties like chemical diversity, hydrophilicity, 2D morphology, metallic conductivity, etc. In spite of the promising properties of MXenes, these materials are not gaining momentum in various applications because of their poor chemical or oxidation stability. A few reported literatures stated that organic solvents with low temperature storage could prevent the oxidation of MXene flakes due to the presence of less number of dissolved oxygen molecules in the solvents. Till now, mostly investigated material regarding oxidation stability is Ti3C2Tx MXene only due to its high capacitance and excellent high metallic conductivity. In this regard, Ti2CTx MXene also delivers comparable electrical and electrochemical properties like the previous one, but it is getting less attention due to lack of knowledge about their suitable storage medium for prolonged period without oxidation/ degradation. To address this issue, this paper reports the best suitable medium for preventing or delaying the degradation or oxidation of Ti2CTx MXene. Herein, Ti2CTx MXene was dispersed in different solvents for duration of 3 months at ambient and freezing conditions and characterized thereafter using XRD, Raman spectroscopy, SEM, TEM and XPS. The results suggest that the best suitable mediums to store Ti2CTx MXene for 3 months are IPA or DMSO at -20°C or in water at -80°C.

Authors : M. Bondarenko, P. Silenko, Yu. Solonin, A. Ragulya, N. Gubareni, M. Zahornyi, O. Khyzhun, N. Yarova
Affiliations : Frantsevich Institute for Problems of Materials Science of NASU, Krzhyzhanovsky St. 3, 03142 Kiev, Ukraine

Resume : The development of new photocatalytic systems such as a photocatalytic TiO2-based system associated with graphitic carbon nitride (g-C3N4) for effectively obtaining of hydrogen through photocatalytic water splitting is one of the most promising areas of renewable energy. For efficient light utilization, the fabrication of g-C3N4/TiO2 composite material has attracted much attention. However, both pristine g-C3N4 and g-C3N4/TiO2 composite exhibits photoactivity in blue region of visible spectrum only. It is found that the doping of carbon nitride by oxygen significantly improves its photocatalytic properties. Therefore, to improve the photocatalytic activity of semiconductor photocatalyst, the coupling O-doped g-C3N4 (O-g-C3N4) with anatase TiO2 is a good strategy. New composite material O-g-C3N4/TiO2 was synthesized by gas phase method under the special reactionary conditions of the pyrolysis of melamine. Deposition of O-g-C3N4 (~5% O) on the anatase nanopowder particles is confirmed by XRD, IR, XPS, SEM, EDX methods. It is found by UV-Vis-DRS method, that O-g-C3N4/TiO2 photosensitivity is observed in the significant part of the visible light region and the band gaps of product is determined to be less than 2.38 eV. Constructing heterojunction structures of TiO2 and O-g-C3N4 may be used as a cost-effective way to avoid the drawbacks of each component and realize a synergic effect for boosting the photocatalytic activity of material for energy applications.

10:30 DISCUSSION    
10:45 BREAK    
Authors : Juliana M. Morbec
Affiliations : School of Chemical and Physical Sciences, Keele University, UK

Resume : Combining two-dimensional (2D) materials with organic materials can be very attractive for applications that require flexibility and where size and weight are important parameters to be considered, such as in wearable, portable and mobile applications. Organic materials usually exhibit excellent optical absorption efficiency and photo- and temperature-induced conformational changes, while 2D materials often show relatively high carrier mobility, superior mechanical flexibility, and tunable electronic and optical properties. Combining both systems can stabilize the organic materials and lead to heterostructures with both high carrier mobility and high optical absorption efficiency, which is promising for solar energy conversion. In this work we investigate, by means of density-functional-theory calculations, heterostructures composed of organic molecules (for example, pentacene, tetracene and azulene) and transition metal dichalcogenides (TMD) for application in photovoltaic devices. We examine the interaction between the molecules and monolayer TMDs as well as the band alignment of the heterostructures, considering effects of the molecular coverage and dielectric screening. Acknowledgement: This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 406901005.

Authors : Denys I. Miakota1, Ganesh Ghimire1, Rajesh Ulaganathan1, Raymond R. Unocic2, Sara Engberg1, Fabian Bertoldo3, David Geohegan2, Kristian S. Thygesen3, and Stela Canulescu1
Affiliations : 1 Department of Photonics Engineering, Technical University of Denmark, DK-4000 Roskilde, Denmark 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States; 3 CAMD and Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark

Resume : Rapid development of photovoltaic power industry has pushed an active search for new materials for photovoltaics and photodetection, where heterostructures with an efficient charge-carrier separation are of particular interest. Emerging van der Waals heterostructures (vdWHs) based on two-dimensional (2D) transition metal dichalcogenides (TMDs) constitute a promising platform for novel electronic and optical devices, such as ultra-thin film solar cells or photodetectors [1], [2].. Single layers of TMDs, such as MoS2, WS2, MoSe2 and WSe2 are direct bandgap semiconductors, which can effectively absorb and emit light at visible and near infrared wavelengths (with photon energies between 1 and 2 eV) [3]. Moreover, 2D TMDs with various bandgaps can be used as building blocks in vertical vdWHs forming novel vdW systems with extraordinary broad absorption across a wide range of the solar spectrum. Pioneer results on vdWHs were demonstrated using physical crystal stacking. However, vertical stacking of 2D TMDs layers in a 3D architecture is not favorable for large-scale applications and direct growth methods must be further investigated. Here, we present a two-step growth process: (1) oxide bilayer films obtained by pulsed laser deposition (PLD) and (2) sulfurized in a tube furnace at high-temperature in a sulfur-rich environment for TMDs heterostructure synthesis. We show that native oxygen vacancies in the PLD-grown precursors serve as niches for sulfur atoms and facilitate MoS2 and WS2 lateral crystal growth. First, we explore how the two-step synthesis process of oxides with variable concentration of oxygen vacancies can be applied for vdWHs growth. Second, these results serve as a potential step to facilitate integration of dissimilar 2D TMDs layers. Lastly, we investigate the use of PLD for the direct growth of quasi-continuous thin films of MoSe2 and WSe2 with two-step grown MoS2 and/or WS2 layers to merge sulfides and selenides in a vdWHs. Thus, our study suggests a way towards fabrication of vdWHs without using individual layer transfer. Potential results of this study are formation of high quality crystals with a good photoluminescence (PL) and strong Raman signals from individual layers. Overlaid, MoS2 and WS2, or MoSe2 and MoS2 form a heterostructure, and display contributions to the Raman spectra from both layers, but significantly quenched PL signal. This may be a promising sign of an effective charge carrier separation within the heterostructure created. The synthesis of heterostructures was examined by XPS, Raman spectroscopy, PL, AFM, SEM, optical microscopy, and TEM. [1] M. K. S. Bin Rafiq et al., Sci. Rep., vol. 10, no. 1, pp. 1–11, 2020. [2] M. Zhong et al., 2D Mater., vol. 5, no. 3, 2018. [3] S. J. Liang, B. Cheng, X. Cui, and F. Miao,Adv. Mater., vol. 32, no. 27, pp. 1–27, 2020

Authors : Surbhi Priya, Debabrata Mandal, Trilok Singh, Amreesh Chandra
Affiliations : Research Scholar; Research Scholar; Professor; Professor

Resume : Time Dependent Exfoliation of Bulk MoS2 for Electrochemical Studies-Ranging from Supercapacitors to Na-Ion Batteries Surbhi Priya1*, Debabrata Mandal2, Trilok Singh2 and Amreesh Chandra1,2# 1School of Energy Science & Engineering, 2School of Nano-Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur-721302, West Bengal, India Email: *, ABSTRACT: Transition-metal dichalcogenides (TMDs) such as MX2 (M = Mo, W, Nb, Ta, etc. and X = S, Se, etc.) are becoming useful for energy storage applications. Among these, molybdenum disulfide (MoS2), has emerged as a promising candidatedue to its exceptional electrical, physicochemical, and mechanical properties. Bulk MoS2 has a layered crystal structure consisting of stacked S-Mo-S monolayers separated by approximately 0.62 nm interlayer spacing, with strong covalent Mo-S bonds and weak Van der Waals forces between adjacent monolayers. Due to their high specific surface area and flexibility, mono or layered MoS2 nanosheets have superior electrochemical properties than bulk MoS2. In this work we present a simple single-step ultrasonic exfoliation technique for producing layered MoS2 nanosheets from bulk MoS2 powder. The two major concerns of chemical exfoliation i.e. usage of highly flammable chemicals and yield production have been eliminated in this process. Using LiBr and toluene for exfoliation, almost 70% yield was achieved. Various physiochemical characterizations were performed for both non-ultrasonicated and ultrasonicated MoS2. In case of ultrasonicated sample, studies were performed on the basis of time, i.e. the sample was collected after every hour of exfoliation for up to 3 hours. The peak broadening of the XRD profiles confirmed successful exfoliation, suggesting formation of nanosized layered structure from the bulk MoS2. The electrochemical investigations were carried out in 3-electrode configuration. The specific capacitance for pristine MoS2, 1, 2 and 3 h exfoliated samples were calculated to be 96, 110, 140 and 200 F g-1, respectively, at 1 A g-1 current density. An enhancement of about 110% from bulk to 3 h exfoliated sample was observed. Further, the effect of electrolyte on the electrochemical activity of MoS2 was analysed. In acidic electrolyte (1 M H2SO4) much higher specific capacitance (200 F g-1) was obtained compared to the alkaline (90 F g-1 in 1 M KOH) and neutral ones (50 F g-1 in 1 M Na2SO4). Moreover, the Na and Li-ion battery performance of MoS2 as anode material was investigated. The results exhibit high rate capability and excellent cycling stability, thus establishing the advantages of MoS2 as next generation high-end energy storage material.

Authors : Rebekah A. Wells, Charles R. Lhermitte, Marina C. Caretti, Kevin Sivula
Affiliations : Ecole Polytechnique Federal de Lausanne (LIMNO); Los Alamos National Laboratory; EPFL (LIMNO); EPFL (LIMNO)

Resume : The exceptional semiconducting properties of two-dimensional transition metal dichalcogenides (2D-TMDs) makes them suitable for a range of optoelectronic applications including photodetectors, solar cells, and photoelectrodes (ex. Solar H2 production). Not only does this class of materials provide a range of tunable optoelectronic properties, but their fabrication as large-area thin films paves the way towards ultrathin, flexible solar energy conversion devices. A key challenge in commercializing these TMD-based devices, however, is the scalable production.[1] Our group has addressed several aspects of this issue (including exfoliation, thin film fabrication, and defect mitigation) all while maintaining solution-processable methods suitable for large- device fabrication. In this presentation we describe our recent work advancing the processes at each step of the thin-film formation process. We present a novel powder-based electrochemical intercalation technique yielding 2D nanosheet dispersions with superior optoelectronic properties compared to conventional solution processing methods (ex. ultrasonication) and demonstrate high photon-to-chemical energy conversion efficiencies in MoS2. Next, we show the importance of process parameters in the formation of nanosheet thin films using a liquid-liquid interfacial self-assembly (LLISA) technique to increase nanoflake-substrate contact and maximize charge extraction.[2] In particular we highlight our results employing WSe2 for solar water reduction.[2] We further advance this method towards continuous roll-to-roll deposition of TMD-based thin films demonstrating reproducible printing of 100mm wide TMD flake films on plastic substrates at 10 mm s-1 with nanoflake loadings of 35 mg m-2.[3] Importantly we show that these large-scale films of semiconducting TMDs are robust and capable of solar-to-chemical energy conversion comparable to that of their batch-scale counterparts. Finally, we address the effects of processing conditions on TMD nanoflake quality and resulting photoelectrochemical device performance. While choosing the correct exfoliation methods can assist in avoiding unnecessary nanoflake damage, we discuss defect mitigation strategies to overcome inescapable imperfections and drastically improve the solar energy conversion ability of TMD nanoflake thin films.[4] In particular, we achieve state-of-the-are performance for solution-processed WSe2 nanoflake films for solar H2 production with 1 sun photocurrent densities over 4 mA cm-2.[4] References: [1] Yu, X.; Sivula, K. ACS Energy Lett. 2016, 1 (1), 315–322. [2] Yu, X.; Prévot, M. S.; Guijarro, N.; Sivula, K. Nat. Commun. 2015, 6, 7596. [3] Wells, R. A.; Johnson, H.; Lhermitte, C. R.; Kinge, S.; Sivula, K. ACS Appl. Nano Mater. 2019, 2 (12), 7705–7712. [4] Yu, X.; Guijarro, N.; Johnson, M.; Sivula, K. Nano Lett. 2018, 18 (1), 215–222.

12:00 DISCUSSION    
12:15 LUNCH BREAK    
Authors : Carlos Macías 1,2 , Antonella Cavanna 2 , Ali Madouri 2 , Laurent Travers 2, Jean-Christophe Harmand 2, Stéphane Collin 1,2 , Andrea Cattoni 1,2 , Amaury Delamarre 1,2.
Affiliations : 1 Institut Photovoltaïque d'Île-de-France (IPVF), 18 Bd Thomas Gobert, 91120 Palaiseau, France. 2 Centre de Nanosciences et de Nanotechnologies (C2N), CNRS, Université Paris-Saclay, 10 Bd Thomas Gobert, 91120 Palaiseau, France.

Resume : Epitaxy on two-dimensional Van der Waals crystals has attracted attention during the last years due to the possibility of synthetizing releasable semiconductor membranes on reusable substrates, and as a new pathway for the integration of 2D and 3D materials in multilayer stacks for next generation functional devices. In particular, the so-called remote epitaxy [1] on graphene-covered substrates is attractive for the fabrication of III-V epilayers for photovoltaic applications, as it may allow substrate reuse after growth, and therefore drastically reduce the cost of the currently most efficient solar cells, overcoming the limitations of mature transfer-recycle techniques. To synthetize transferrable layers in this way, large-area graphene grown on foreign substrates needs to be transferred to the target substrate with a high surface coverage, thickness uniformity, cleanliness, and no degradation of the underlying substrate surface. Despite the numerous research efforts carried out in the last years to improve transfer processes, the introduction of organic and metallic residues, wrinkles, and mechanical damage with the commonly used wet-transfer methods still hinders its use for many potential applications. In this contribution, we develop a dry transfer method of epitaxial graphene grown on Ge(110) by chemical vapor deposition to obtain substrates suitable for remote epitaxy. We avoid organic residues by using mechanical exfoliation with a strained nickel layer [2], where the accumulated strain energy is optimized controlling the deposited thickness. A high transfer yield and a clean 2D-3D interface are enabled by vacuum transfer and aircushion pressing of the graphene/metal stack on the target substrate. These improvements enabled the reproducible large-scale (~1 cm²) transfer to Si/SiO2 and GaAs without degradation of the graphene as shown by the Raman defect-related bands, negligible introduction of unintentional doping, a transfer yield exceeding 99 % and an optical transmission close to the theoretical value expected for pristine single-layer graphene. The surface chemistry was analyzed by X-ray photoelectron spectroscopy, that revealed a lower level of interface oxidation and C-O contamination in dry-transferred graphene as compared to wet-transferred graphene, while Ni oxides were found to be the main impurity in the former. Here, we will present our improved polymer-free transfer method and an extensive structural, chemical, and morphological characterization of transferred samples. We will discuss the challenges arising in each step of the process, from the graphene synthesis to the selective etching of the carrier layer. Finally, we will present our preliminary results on the molecular beam epitaxy growth and lift-off of GaAs on graphene-covered substrates, focusing on the effect of the graphene transfer method used, the introduced impurities and the interface quality. References: 1. Y. Kim et al., Nature, vol. 544, no. 7650, pp. 340–343, Apr. 2017. 2. J. Kim et al., Science, vol. 342, Issue 6160, pp. 833-836, 2013.

Authors : Patrick D. Lomenzo, Thomas Mikolajick, Uwe Schroeder
Affiliations : Patrick D. Lomenzo Nanoelectronic Materials Laboratory (NaMLab) gGmbH, 01187 Dresden, Germany; Thomas Mikolajick Nanoelectronic Materials Laboratory (NaMLab) gGmbH, 01187 Dresden, Germany Chair of Nanoelectronic Materials, TU Dresden, 01187 Dresden, Germany; Uwe Schroeder Nanoelectronic Materials Laboratory (NaMLab) gGmbH, 01187 Dresden, Germany;

Resume : Solid state supercapacitors are intrinsically capable of sustaining substantially higher voltages, faster charging/discharging rates, higher temperatures, and much greater lifetimes than electrochemical double layer capacitors. However, the relatively smaller capacitance of solid-state supercapacitors using nonlinear dielectrics impedes their adoption as an auxiliary energy storage medium in energy technologies. Nonetheless, advances in the properties of dielectrics offer a promising route to enhance the energy storage density of solid-state supercapacitors. An emergent class of antiferroelectrics originating from reversible field-induced phase transitions in the HfO2 and ZrO2 material system are particularly extraordinary due to the facile fabrication of 3-dimensional capacitor structures, nanoscale size, lead-free chemistry, and the adjustable properties of the phase transition with composition. Whereas linear dielectrics store energy through the reversible displacement of the electronic cloud and ionic moments with an applied electric field, reversible field-induced phase transitions amplify electric charge storage through the conversion of the internal crystalline structure of the dielectric. A major leap forward in the supercapacitor performance of antiferroelectric ZrO2 capacitors is achieved by using a built-in electric field to simultaneously enhance both energy storage density and efficiency. The enhancement of the energy storage in 8 nm thick ZrO2-based thin films is achieved by exploiting the workfunction difference of RuOx and TiN electrodes. By replacing the top TiN electrode with RuOx in a capacitor where ZrO2 is grown by atomic layer deposition on a bottom TiN electrode, the energy storage density of ZrO2 was increased from 59.1 to 63 J cm-3 with a simultaneous increase in efficiency from 67.7 % to 84.1 % at room temperature. The workfunction engineered ZrO2 capacitors display superior cycling and maximum voltage performance compared to conventional symmetric antiferroelectric supercapacitors with TiN electrodes. A maximum energy storage density of 94 J cm-3 with 75 % efficiency up to 1E7 cycles at room temperature is demonstrated with workfunction engineered ZrO2 supercapacitors, which represents a 50% increase in the energy storage density for the HfO2 and ZrO2 material system. The reliability and performance of the ZrO2 supercapacitors are assessed up to 125 °C. The improvement in energy storage density and concurrent increase in efficiency by workfunction engineering is not only major advance for HfO2 and ZrO2-based thin films, but is an extremely promising method to enhance the energy storage for all nanoscale antiferroelectric supercapacitors.

Authors : Fabrizio Moro, Xue Liu, Andrés Granados del Águila and Marco Fanciulli
Affiliations : Fabrizio Moro and Marco Fanciulli Department of Materials Science, University of Milano-Bicocca, Milano 20125, Italy; Xue Liu Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China; Andrés Granados del Águila Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore.

Resume : The recent discovery of magnetism within the family of exfoliable van der Waals (vdW) compounds has attracted considerable interest for both fundamental research and technological applications.[1] However, current vdW ferromagnetic semiconductors are limited by their extreme sensitivity to air, poor charge transport properties and weak super-exchange interactions leading to very low magnetic ordering temperatures. Among the family of 2D magnetic semiconductors, CrSBr has recently gained attention because of its relatively high bulk interlayer ferromagnetism and intralayer antiferromagnetic order with Néel Temperature, TN ~ 132 K.[2] Furthermore, theoretical studies show that monolayers of CrSBr might have even higher ferromagnetic ordering temperature whereas semiconducting transport properties, large negative magnetoresistance, stability under ambient conditions, and gate-tunable magnetic ordering have been experimentally observed.[3] Here we report the angular and temperature dependent electron spin resonance (ESR) properties of bulk CrSBr.[4] In-plane and out-of-plane angular dependent ESR studies show room temperature magnetic anisotropy with the easy and hard axis of the magnetization along the crystallographic b and c axis, respectively. Interestingly, the ESR linewidth reveals a non trivial angular dependence for rotations of the CrSBr crystal in the c-b plane suggesting the coexistence of a 2-fold and a 4-fold symmetries whereas only a 2-fold symmetry is observed for rotations in the a-b plane. Finally, ESR temperature dependent studies performed by cooling the CrSBr crystal with the external magnetic field, B parallel to b and c crystallographic directions, show a shift of the resonance line to lower and higher magnetic fields respectively, thus unambiguously demonstrating the in plane ferromagnetic order and the antiferromagnetic order in between the layers. A minimum of the linewidth in the temperature dependence provides information on the magnetic order temperature[5] with transitions occurring in the ranges 190 - 220 K and 240 - 270 K for the FM and AF order, respectively. In conclusion, our ESR studies on CrSBr crystals show interesting magnetic resonance properties for spintronic applications: the existence of a magnetic anisotropy at room temperature, the onset of ferromagnetic and antiferromagnetic resonances at high temperatures and a complex magnetization dynamics as inferred from the analysis of the ESR linewidth. References: [1] N. P. Wilson et a. Nature Materials 20, 1657–1662 (2021) [2] E. J. Telford Adv. Mater. 32, 2003240 (2020) [3] Y. Guo, et al. Nanoscale 10,18036. (2018) [4] F. Moro et al. in preparation [5] M. Farle Rep. Prog. Phys. 61, 755–826 (1998).

Authors : Subrat Rout, Prabhanjan Pradhan and Biplab K. Patra*(corresponding author) (corresponding author)
Affiliations : Materials Chemistry Department, CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, 751013, India

Resume : Organometallic-Metal halide perovskites (OMHP) have received great attention in the recent years due to their potential use as materials in optoelectronics and ferroelectrics. Perovskites are materials having general formula ABX3 where A is a monovalent cation like Cs, formamidinum (FA), and methyl ammonium (MA), B is a bivalent cation like lead (Pb) or tin (Sn) and X is halogen (X = Cl, Br and I). By replacing traditional A site cations with organometallic cations, the chemical stability and optoelectronic properties can be enhanced. Till date researchers have explored nitrogen (ammonium) based organometallic metal halide perovskites. Phosphorus atom resides close to the nitrogen atom and both have a similar covalent character, while their differences in atomic radius, mass, and electron structure may open interesting variables within either chemical or physical properties. Recently Han-Yue Zhang et. al. reported phosphanium based 2D perovskite system which showed enhanced ferroelctric properties. The material showed enhanced dielectric coefficient in the ferroelectric perovskites. Here we report a new two-dimensional phosphonium cation based lead halide perovskite 2D material which has been synthesized by ligand-assisted solvent evaporation method at 260 degree centigrade for 1.5 hr using a capillary self-assembly set up. These two-dimensional materials form layered sheet like structures in micrometre regime. With increasing annealing time from 1.5 hrs to 2 hrs., the micro-sheets are found to be converted into coin shaped structures having enhanced surface smoothness. The XRD of both the structures are well matching with each other indicating no phase change during annealing process. The synthesized material is air stable and is showing an absorption edge nearly 600 nm corresponding to a band gap of approximately 2 eV which would be an excellent candidate for both ferroelectric and optoelectronic applications.

Authors : G. Di Mari (1,2), G. Mineo (1,2), G. Malandrino (3), G. Franzò (2), S. Mirabella (1,2), E. Bruno (1,2)
Affiliations : (1) Dipartimento di Fisica e Astronomia “E. Majorana”, Università degli Studi di Catania, Via S. Sofia 64, I-95123, Catania, Italy; (2) CNR-IMM, Via S. Sofia 64, I-95123, Catania, Italy; (3) Dipartimento di Scienze Chimiche, Università degli Studi di Catania, INSTM UdR Catania, Viale A. Doria 6, I-95125, Catania, Italy

Resume : Transition metal oxides (TMO) lead to an innovative direction for the development of materials for electrochemical energy storage due to their excellent stability. Zinc oxide (ZnO), a primary TMO, represents a green choice due to its abundance and biocompatibility. Surface modification and structural design represent the most traveled ways to improve the conductivity of zinc oxides-based electrodes. Indeed, nanostructures with many different shapes have been produced by both sophisticated and costly techniques as well as by means of cheap methods [1]. Here we focus on a cost-effective mass production of nanostars by means of Chemical Bath Deposition (CBD) in aqueous solution. Nanostars appear as 2D self-assembled bundles of crystalline ZnO nanostrips (sized 1oo up to 1000 nm), with clear hexagonal symmetry on the assembly plane (building 6-point stars). These novel nanostructures are deeply characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), Photoluminescence spectroscopy (PL) and electrochemical measurements (e.g CV, GCD), in order to evidence their structural, morphological, optical and electrical properties. The different preparative parameters, such as concentrations, thermal annealing and reaction time (growth kinetic) were deeply investigated. Specifically, with the kinetic nanostars with different arm lengths (range 80 nm up to 12 µm) have been obtained. We then tested and optimized the stars with different dimension as capacitors for Energy Storage applications. [1] Najib, S., Bakan, F., Abdullayeva, N., Bahariqushchi, R., Kasap, S., Franzò, G., Sankir, M., Sankir, N.D., Mirabella, S. and Erdem, E., 2020. Nanoscale, 2020, DOI: 10.1039/D0NR03921G

Authors : Martina Romio, Yuri Surace, Damian M. Cupid
Affiliations : Battery Technologies, Center for Low-emission transport, AIT Austrian Institute of Technology GmbH Giefinggasse 4, 1210 Vienna, Austria

Resume : Magnesium-ion batteries (MIBs) are considered as promising alternatives to lithium-ion technologies due to the di-valent character of the Mg2+ cations, the high theoretical volumetric capacity of magnesium (3833 mA h cm¬-3 for the Mg-anode), as well as its low toxicity, natural abundance and safety (dendrite-free).1 However, the development of MIBs is hindered by the slow solid-state diffusion of Mg2+ ions into the cathode lattice, which leads to relatively low practical capacities, irreversible capacity losses and poor cyclic stability. Phosphate-based compounds are considered as suitable candidate electrode materials for multi-valent ion batteries due to their open three-dimensional frameworks, structural stability, and thermochemical safety under oxidising conditions.2,3 Therefore, in this work, the NASICON-based Mg0.5Ti2(PO4)2 (MTP) compound was synthesised by the solid-state method and investigated as a potential electrode active material for MIBs. However, in order to improve the slow kinetics of the Mg2+ insertion-extraction process via reducing the total diffusion distances of the Mg2+ ions during charge and discharge, nano-sized MTP-powders were prepared via ball milling the macro-sized MTP powder at different rotation speeds. All powders were subjected to comprehensive physico-chemical characterisation techniques (XRD, SEM and IR) to determine their phase purities as well as the changes in particle morphologies after milling. Furthermore, the electrochemical behaviour of MTP with Mg2+ ions was investigated using post-mortem analysis (XRD, IR, SEM and XPS), aiming to establish the nature of the charge storage reaction mechanism and quantify the influence of particle size on electrochemical performance. A second challenge in the development of MIBs is the formation of cationic insulating layers on the surface of the Mg anode when electrolytes prepared by mixing ionic salts (i.e. Mg(ClO4)2) and aprotic organic solvents are used. This leads to the passivation of the Mg-anode and poor performance of the overall cell. In order to address this problem, activated carbon (AC) was used as the counter electrode when using Mg(ClO4)2 in acetonitrile as the electrolyte. The electrochemical characterisation data showed an exponential drop in the discharge and charge capacities of MTP upon cycling which varied only slightly with particle size. This suggests that other factors such as the intrinsic electronic and ionic conductivities of MTP may play more critical roles in the electrochemical performance of the material. References 1. H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci., 2013, 6, 2265–2279; 2. P. Canepa, G. Sai Gautam, D. C. Hannah, R. Malik, M. Liu, K. G. Gallagher, K. A. Persson, G. Ceder, Chem. Rev., 2017, 117, 4287–4341; 3. B. Kang, G. Ceder, Nature, 2009, 458, 190.

Authors : Chengning Yao1, Benji Fenech Salerno1, Callon Peate1, Felice Torrisi1
Affiliations : 1 Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, Wood Lane, London W12 0BZ, the United Kingdom

Resume : Printable dielectric inks with desired dielectric properties are in high demand to enable high-performance printed electronics[1]. Two-dimensional (2D) materials based printed electronics have been demonstrated to outperform standard printed electronics, promising high-mobility devices[2] for printed integrated circuits[3]. Hexanol boron nitride (h-BN) is a highly suitable dielectric material for electronics based on 2D materials, because of its low atomic roughness, coupled with a wide band gap of 5.6 eV and a high in-plane dielectric constant of 6.8[4]. 2D h-BN nanosheets with single- and few-layer flakes (SFLF) can be obtained by liquid phase exfoliation (LPE)[5] from bulk h-BN powders. This method is a cost-effective technique with a prospect for mass production[6]. Here we report an optimized dielectric inks based on h-BN and BiOCl. Inks are produced by probe sonication and purified by centrifugation. Raman spectroscopy and Atomic Force Microscopy of the ink indicated the successful exfoliation of few-layer thick h-BN flakes. The lateral size and the thickness of the h-BN flakes in the inks both follow a log-normal distribution, which were peaked at 352 nm and 6.6 nm, respectively. A typical thickness of a LPE BiOCl flake is 5 nm. A metal-insulator-metal parallel plate capacitor configuration is designed to investigate the dielectric properties. Results showed that, compared to traditional polymer-based dielectric materials, capacitor performance using our dielectric inks is improved, revealing a dielectric constant of up to 9.68 based on h-BN, and 23.91 based on BiOCl. Increasing h-BN weight ratio against the polymers or adding high-κ dielectric additives could futher improve the dielectric constant and lower the leakage current density in electroncis. The work is beneficial to ultrathin printable electronics development with cost-effective dielectric inks, enabling wearable devices. References 1. F. Torrisi and T. Carey, Nano Today, 2018, 23, 73-96. 2. T. Carey, S. Cacovich, G. Divitini, J. Ren, A. Mansouri, J. M. Kim, C. Wang, C. Ducati, R. Sordan and F. Torrisi, Nature communications, 2017, 8, 1-11. 3. T. Carey, A. Arbab, L. Anzi, H. Bristow, F. Hui, S. Bohm, G. Wyatt‐Moon, A. Flewitt, A. Wadsworth and N. Gasparini, Advanced Electronic Materials, 2021, 2100112. 4. Y. Y. Illarionov, T. Knobloch, M. Jech, M. Lanza, D. Akinwande, M. I. Vexler, T. Mueller, M. C. Lemme, G. Fiori and F. Schwierz, Nature Communications, 2020, 11, 1-15. 5. V. Nicolosi, M. Chhowalla, M. G. Kanatzidis, M. S. Strano and J. N. Coleman, Science, 2013, 340. 6. J. N. Coleman, M. Lotya, A. O’Neill, S. D. Bergin, P. J. King, U. Khan, K. Young, A. Gaucher, S. De and R. J. Smith, Science, 2011, 331, 568-571.

Authors : Gardella, M.*(1), Ferrando, G. (1), Barelli, M. (1), Chowdhury, D. (1), Giordano, M.C. (1), Buatier de Mongeot, F. (1)
Affiliations : (1) Dip. di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy

Resume : The development of clean light harvesting platforms and technologies is crucial in view of the urgent energy and environmental global challenges. The use of ultra-thin 2D-TMD semiconductor layers such as MoS2 show great promise in photonics, but they suffer from poor photon absorption and the fabrication is typically constrained to micrometer-scale devices. New approaches enabling large area photon harvesting applications in such ultra-thin devices are thus intensively searched. In this work we propose a novel method based on Laser Intereference Lithography combined with physical deposition to fabricate large area MoS2 nanorippled layers extending over cm2 areas [1]. We then demonstrate enhanced photochemical reactivity and photobleaching of highly polluting methylene blue molecules promoted by this ultra-thin platform. We investigate this effect by tailoring the spectral overlap between the molecule absorption band and the guided mode anomalies supported by the nanotextured 2D-TMD film. These results are promising in view of engineering and optimization of light harvesting platforms for waste water treatment, dye molecules sensing devices and a broad range of other light harvesting applications. [1] ACS Appl. Mater. Interfaces 2021, 13, 13508−13516

Authors : Krishnendu Maji,[a] Pierric Lemoine,[b]* Adèle Renaud,[b] Bin Zhang,[c,d] Xiaoyuan Zhou,[c,d] Virginia Carnevali,[e] Christophe Candolfi,[f] Bernard Raveau,[a], Rabih Al Rahal Al Orabi,[e] Marco Fornari,[e],* Paz Vaqueiro,[g] Mathieu Pasturel,[b] Carmelo Prestipino,[b] Emmanuel Guilmeau[a]*
Affiliations : [a] CRISMAT, CNRS, Normandie Univ, ENSICAEN, UNICAEN, 14000 Caen, France [b] Univ Rennes, ISCR – UMR 6226, CNRS, F-35000 Rennes, France [c] College of Physics and Institute of Advanced Interdisciplinary Studies, Chongqing University, Chongqing 401331, China [d] Analytical and Testing Center of Chongqing University, Chongqing 401331, China [e] Department of Physics and Science of Advanced Materials Program, Central Michigan University, Mt. Pleasant, MI 48859, USA [f] Institut Jean Lamour, UMR 7198 CNRS – Université de Lorraine, 2 allée André Guinier-Campus ARTEM, BP 50840, 54011 Nancy Cedex, France [g] Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6DX, United Kingdom

Resume : Understanding the mechanism that connects heat transport with crystal structures and order/disorder phenomena is crucial to develop materials with ultralow thermal conductivity (κ), for thermoelectric and thermal barrier applications, and requires the study of highly pure materials. We synthesized the n-type sulfide CuPbBi5S9 with an ultralow κ value of 0.6–0.4 W m–1 K–1 in the temperature range 300–700 K. In contrast to prior studies, we show that this synthetic sulfide does not exhibit the ordered gladite mineral structure but instead forms a copper-deficient disordered aikinite structure with partial Pb replacement by Bi, according to the chemical formula Cu1/3□2/3Pb1/3Bi5/3S3. By combining experiments and lattice dynamics calculations, we elucidated that the ultralow κ value of this compound is due to very low energy optical modes associated with Pb and Bi ions and, to a smaller extent, Cu. This vibrational complexity at low energy hints at substantial anharmonic effects that contribute to enhance phonon scattering. Importantly, we show that this aikinite-type sulfide, despite being a poor semiconductor, is a potential matrix for designing novel, efficient n-type thermoelectric compounds with ultralow κ values. A drastic improvement in the carrier concentration and thermoelectric figure of merit have been obtained upon Cl for S and Bi for Pb substitution. The Cu1–x□xPb1–xBi1+xS3 series provides a new, interesting structural prototype for engineering n-type thermoelectric sulfides by controlling disorder and optimizing doping.

16:15 DISCUSSION    
16:30 BREAK    
Authors : Wenlei Xu[1], Yaolin Xu[2], Veronika Grzimek[2], Thorsten Schultz[3], Yan Lu[2], Norbert Koch[3], Nicola Pinna[1]
Affiliations : [1] Institut für Chemie and IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany [2] Department of Electrochemical Energy Storage, Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany [3] Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein Str. 15, 12489 Berlin, Germany

Resume : Exploring the influence of dimension of electrode materials on electrochemical behavior is of great significance to the development of rechargeable batteries. Herein, three titanium niobium oxide (TiNb2O7) nanostructures with different dimensions (1D, 2D, and 3D) were successfully designed based on a facile solvothermal method. The dimension effect on the performance evolution for lithium-ion batteries (LIBs) were studied in detail. Comprehensive characterizations proved that 2D TiNb2O7 (TNO-2D) shows a superior electronic conductivity and a large Li+-ion diffusion coefficient, resulting in great electrochemical properties. Operando and ex-situ X-ray diffraction measurements reveal the robust structure stability and high reversibility of TNO-2D. Moreover, after coating with carbon, TNO-2D achieves excellent rate capability (205 mAh g-1 at 50 C) and superior long-term cycling stability (87% after 1000 cycles at 5 C). This work provides insights into the rational design of electrode materials for accelerated charge transport and hence enhanced fast-charging capability, pushing forward the development of high-power rechargeable batteries for the future energy storage.

Authors : Richard Appiah-Ntiamoah, Hern Kim
Affiliations : Myongji University, Department of Energy Science and Technology, Environmental Waste Recycle Institute, Republic of Korea

Resume : Electrospun 1-D supercapacitor electrode materials which are based on FeOx/carbon nanofibers are typically synthesized using indirect carbothermal reduction (IDCR), which entails pre-oxidation of the polymer and Fe-salt nanofiber in air followed carbonization under inert atmosphere. This synthesis method has become the gold-standard because it stabilizes the polymer and Fe-salt, produces a high yield, and flexible binder-free electrode materials. However, it often generates aggregated FeOx nanoparticles with a large size, low crystallinity, and low transport kinetics which result in limited FeOx-pseudocapacitive reactions. Therefore, the much-coveted high theoretical capacitance of FeOx (i.e., 2299 F/g for Fe3O4 and 3625 F/g for Fe2O3) has so far not been achieved. In this study, we investigate how direct-carbothermal reduction (DCR) coupled with zinc doping (i.e., DCR-ZD) can mitigate the aforementioned limitations and improve energy storage performance. By DCR we mean the absence of a pre-oxidation step. Our results show that under DCR, early precipitation of Zn-salt in the form of ZnO is highly favored over FeOx, which exerts a physical confinement effect on FeOx and limit its migration and aggregation. This leads to the formation of uniformly dispersed ultra-small FeOx nanoparticle with high crystallinity. The micropores and mesopores created by the subsequent sublimation of ZnO(s) in the form of ZnO0(g) expose large areas of FeOx to high concentrations of polymer-derived CO(g) which catalyzes its carbothermal reduction into Fe3C nanoparticles. An added benefit of the porous structure is better electrolyte penetration to the Fe-sites. The dominant Fe3-C phase generates multiple pseudocapacitive redox reactions (i.e., Fe0/Fe2+, Fe2+/Fe3+, and Fe0/Fe3+) compared to the single one (i.e., Fe2+/Fe3+) by FeOx. Consequently, the specific capacitance of DCR-ZD-derived 1-D Fe3C/carbon is ~5X greater than that of IDCR-derived 1-D FeOx/carbon, at 1 Ag-1. More importantly, the DCR-ZD-derived 1-D Fe3C/carbon achieves ~25% of the theoretical capacitance of FeOx compared to just ~19.6% reported in literature. Therefore, DCR-ZD may prove to be a game-changer in the quest to synthesis high-performing iron-based supercapacitors for practical applications.

Authors : E. Black, J. Morbec
Affiliations : School of Chemical and Physical Sciences, Keele University, UK

Resume : Two-dimensional transition metal dichalcogenides (TMDCs) are considered encouraging materials for photovoltaic applications, with differing electronic and optical properties from their bulk counterparts. Pentacene is an organic compound with high exciton mobility, and complimentary electronic properties to TMDCs. Here are investigated systems of adsorbed pentacene on to monolayers of Group-VI dichalcogenides; MoS2, MoSe2, WS2 and WSe2, for photovoltaic applications. Using ab initio methods within density functional theory, optimized atomic positions were calculated and energetically favourable adsorption sites of pentacene were determined. These sites were further investigated with a varying concentration of adsorbed pentacene, with the aim of investigating how molecule-molecule interactions affect the interaction between molecule and substrate. The electronic properties of the favourable systems were then probed and the charge balance of the systems analysed. *This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)– 406901005

Authors : Nikolay Minev (1)*, Krastyo Buchkov (1,2), Rosen Todorov (1), Vladimira Videva (1,3), Mariya Stefanova (1), Hristosko Dikov (4), Deyan Dimov (1), Ivalina Avramova (5), Dimitre Dimitrov (1,2) and Vera Marinova (1)
Affiliations : 1 Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, Sofia, Bulgaria 2 Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria 3 Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria; 4 Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, Sofia, Bulgaria 5 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria

Resume : Recently, two-dimensional (2D) transition metal dichalcogenides (TMDCs) open a great innovation potential for direct integration with silicon (Si) technology, due to their outstanding chemical, physical, electronic and optical properties. Among them, platinum diselenide (PtSe2) is new addition to the 2D family. Due to its layer dependent transition between semiconductor and semimetal and interesting optical/electronic properties it is of significant interest for applications in electronics, spintronics, sensors, catalysis, etc [1, 2]. Here, we report the synthesis details of PtSe2 layers by thermally assisted selenization of pre-deposited Pt films using Chemical Vapour Deposition (CVD) method. The Pt layers were pre-deposited as thin films using Magnetron Sputtering technique on Silicone, quartz, and glass substrates. The existence of 2D PtSe2 was confirmed using X-ray photoelectron spectroscopy (XPS) and Raman analysis. UV-VIS-NIR spectroscopy and ellipsometry spectroscopy were used to investigate the optical properties and to determine the thickness of synthesized 2D PtSe2 layers. In addition, the measured current-voltage characteristics indicates Ohmic behaviour as well as intensity dependent photoconductivity. All the studied properties reveal great potential of PtSe2 to design varieties of heterostructures for future nanoelectronic and optoelectronic structures and devices. Acknowledgments This research was funded by Bulgarian Science Fund under the project numbers DFNI КП-06-ДO 02/2 and DFNI КП-06-ДO 02/3 in the frames of M-ERA program project “Functional 2D materials and heterostructures for hybrid spintronic-memristive devices“ N. M and V. M. acknowledge the financial support by the European Regional Development Fund within the Operational Programme ‘Science and Education for Smart Growth 2014–2020’ under the Project CoE ‘National Center of Mechatronics and Clean Technologies’ BG05M2OP001-1.001-0008-C01. References: [1] Chanyoung Yim, Kangho Lee,Niall McEvoy, Maria O’Brien,Sarah Riazimehr, Nina C. Berner, Conor P. Cullen, Jani Kotakoski, Jannik C. Meyer, Max C. Lemme, and Georg S. Duesberg “High-Performance Hybrid Electronic Devices from Layered PtSe2 Films Grown at Low Temperature” ACS Nano, 10, 9550−9558 (2016)] [2] Li-Syuan Lu, Guan-Hao Chen, Hui-Yu Cheng, Chih-Piao Chuu, Kuan-Cheng Lu, Chia-Hao Chen, Ming-Yen Lu, Tzu-Hung Chuang, Der-Hsin Wei, Wei-Chen Chueh, Wen-Bin Jian, Ming-Yang Li, Yu-Ming Chang, Lain-Jong Li, and Wen-Hao

Authors : Irnik Dionisiev*, I.D.(1), Nikolay Minev, N.M.(1), Vladimira Videva, V.V.(1), Krastyo Buchkov, K.B.(1,2), Vera Marinova, V.M.(1), Hristosko Dikov, H.D.(3), Tsvetanka Babeva, T.B.(1), Velichka Strijkova, V.S.(1), Dimitre Dimitrov, D.D.(1,2)
Affiliations : (1) Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, Bulgaria; (2) Institute of Solid State Physics, Bulgarian Academy of Sciences, Bulgaria; (3) Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, Bulgaria;

Resume : Semiconducting transition metal dichalcogenides (TMDs) are of great interest as absorbers for flexible high-specific-power photovoltaics due to their ultrahigh optical absorption coefficients, desirable band gaps and intrinsic self-passivated surfaces. Tungsten diselenide (WSe2), a semiconducting transition metal dichalcogenide, further shows great potential as active material in optoelectronic devices due to its ambipolarity and direct bandgap in its single-layer form. Recently [1,2], WSe2 have been further exploited to realize electrically tunable PN junctions, demonstrating its potential for digital electronics and solar cell applications. The present study is focused on WSe2 continuous layers synthesized on large area by using thermally assisted conversion (TAC) method of pre-deposited by magnetron sputtering tungsten (W) layers with defined thickness. The obtained WSe2 films on different substrates were characterized by AFM (Atomic force microscopy), Raman spectroscopy and XPS (X-ray photoelectron spectroscopy). Films thickness dependent optical properties were studied toward photovoltaic and photodetector applications. References: [1]Junli Du, et al. “Gate-Controlled Polarity-Reversible Photodiodes with Ambipolar 2D Semiconductors” Advanced Functional Materials, 31 (8) 2007559 (2021) [2]Ricardo Frisenda, et al. “Atomically thin p–n junctions based on two-dimensional materials” Chemical Society Reviews, 47, 3339 (2018) Acknowledgements: This research was funded by Bulgarian Science Fund under the project numbers DFNI КП-06-ДO 02/2 and DFNI КП-06-ДO 02/3 in the frames of M-ERA program project “Functional 2D materials and heterostructures for hybrid spintronic-memristive devices“ V. M. and D. D. acknowledge the financial support by the European Regional Development Fund within the Operational Programme ‘Science and Education for Smart Growth 2014–2020’ under the Project CoE ‘National Center of Mechatronics and Clean Technologies’ BG05M2OP001-1.001-0008-C01. Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science under contract D01-284/17.12.2019 was used for AFM measurements.

Authors : María J. Ramirez-Peral 1 2 3, Jesús Díaz-Sánchez 1, Arturo Galindo 3 4, I. Salazar-Beitia 4, H. van der Meulen 2 5, Miguel Crespillo 6, Carmen Morant 2 4, Enrique Vasco 3 and Celia Polop 1 2 7.
Affiliations : 1 Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Spain; 2 Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, Spain; 3 Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Spain; 4 Departamento de Física Aplicada, Universidad Autónoma de Madrid, Madrid, Spain; 5 Departamento de Física de Materiales, Universidad Autónoma de Madrid, Spain; 6 Centro de Micro-Análisis de Materiales, Universidad Autónoma de Madrid, Madrid, Spain; 7 Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, Spain;

Resume : One of the greatest challenges we face as a society is fighting climate change without negatively affecting the quality of life of the population. In this line, it is essential to improve the efficiency in the production and storage of renewable energy, as well as the autonomy of devices and machinery powered by electricity. At this point, it is essential to improve Li-ion batteries (LIBs), which are a key technology for clean, efficient transport and sustainable development, and therefore play a fundamental role in the transition towards a future zero-emissions society. Within the framework of the "StressLIC" Consortium granted by M-Era.Net (EU), we have set up a facility of Pulsed Laser Deposition (PLD) — Multibeam Optical Stress Sensor (MOSS) to deposit and characterize in situ Li-ion components to be used in all-thin film solid state Li-ion battery (SSLB). We present here a comprehensive study on the coexistence of phases in LiCoO2 (LCO) thin films deposited by PLD. LCO, which was the first cathode (CAT) commercialized by Sony in 1991 and later replaced due to its poor thermal stability, has regained prominence in the development of "zero strain" composite CATs for SSLBs, since LCO is the only CAT with a negative chemical coefficient of expansion, and thus a basic mix component to prevent CAT breathing during charge-discharge cycles. Polycrystalline LCO thin films are deposited on Si(100), without and with diffusion barrier of thermal SiO2, in order to study the chemical phases that arise as a result of the Li diffusion towards Si(100). The films are analyzed in terms of: (i) composition by Raman spectroscopy (RS), Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD); (ii) microstructure by scanning electron (SEM) and atomic force microscopies (AFM); and (iii) Li stoichiometry by impedance spectroscopy (IS). RS and IS reveal LCO grows stoichiometry in the Li rich regions, while within Li-poor regions, Co oxides are formed. RS and RBS interpret the Co oxides as Co3O4 and CoO2. SEM shows that films exhibit a columnar compact microstructure. The results point to a heterogeneously nucleation of LCO grains whose coarsening is ruled by short-range Li diffusion. The LCO deposition on SiO2/Si gives rise to higher LCO/Co-oxide ratios and thicker films as expected. However, the fact that Co oxides are still formed on SiO2/Si from the evaporation of stoichiometry target indicates that there are other sources of Li loss in addition to diffusion towards Si bulk, probably, losses in the evaporation plume and/or Li reevaporation under PLD conditions. From the compilation of all these results, we propose a thermodynamic model of LCO growth by physical vapor deposition.

Authors : Maciej Tobis*(1), Elzbieta Frackowiak(1) * lead presenter
Affiliations : (1) Poznan University of Technology, Institute of Chemistry and Technical Electrochemistry, 60 – 965 Poznań, Berdychowo 4, Poland

Resume : Electrochemical capacitors (ECs) are important high-power energy storage devices that gained significant attention for the potential applications in electric vehicles and portable or complex electronics. Different types of carbon-based materials, e.g., activated carbon or carbon fibers are mainly used as electrode materials thanks to relatively high capacitance as well as long cyclability and tunable porous texture. In comparison to other electrode materials such as metal polyoxometalates, conducting polymers, or transition metal dichalcogenides (TMDs), they possess relatively small capacitance mostly due to the lack of redox reactions. Among different materials, TMDs are highly promising due to the large variety of compounds, two-dimensional character, and presence of exposed active sites. TMDs can be represented by the MX2 formula, where M is a metal atom (Mo, W, V, Re, etc.) and X is a chalcogen atom (S, Se, or Te). TMDs consist of three atomic layers, where metal atoms are sandwiched between the chalcogen atoms and are connected with strong covalent bonds. The most commonly studied electrode material in ECs, among TMDs family, is molybdenum disulfide (MoS2). It possess two-dimensional layered structure, developed specific surface area and crystallography dependent conductivity. Carbons are often employed as structural supports for the deposition of TMD layered structures. Finally, they positively affect the composite conductivity as well as overall electrochemical performance. Modification of carbon surface with benzoquinone-hydroquinone compounds is already known to enhance specific capacitance due to exploring fast reversible redox reactions. However, the impact of the surface modification of carbon before hydrothermal synthesis of TMD/carbon composites on their electrochemical performance was never evaluated before. In this study, several MoS2 composites were prepared with different carbon materials such as carbon nanotubes or modified soot. Prior the reaction, surface of the carbon materials were modified with benzoquinone/hydroquinone species. Various structural and textural properties were evaluated by nitrogen sorption/desorption at 77K, X-Ray diffraction, Raman spectroscopy and scanning electron microscopy. Two- and three-electrode symmetric and asymmetric cells were employed for testing prepared materials. The electrochemical performance of the assembled cells was studied by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Cells were tested with sulphate based electrolytes. Acknowledgments: The authors would like to acknowledge the National Science Centre, Poland, for the financial support in the framework of the project 2018/31/B/ST4/01852. M.T. would like to thank the National Science Centre for the financial support within the project Preludium 20 2021/41/N/ST5/01364.

Authors : Cuenca, J.A.*(1), Thomas, E.L.H.(1), Williams, O.A.(1), Singh, R.P.(2), Mandal, S.(1)
Affiliations : (1) School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, Wales, UK (2) Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal, 462066, India

Resume : Semiconducting transition metal dichalcogenides (TMD) have shown potential for a wide range of electronic and optical applications. TMD’s can be fabricated using laser ablation, chemical vapour deposition and intercalation reactions. However after fabrication, fast and easy identification of the produced nanolayers poses a significant challenge for scalability of the process. Several approaches exist for the identification of TMDs including optical microscopy, Raman spectroscopy and atomic force microscopy; the former of which offers the easiest and fastest method. Optical identification of TMD nanolayers and flakes requires a measurable optical contrast between the drop-casted or as-grown nanolayers and the substrate material. This quantity is simply dependent upon the refractive indices and the thicknesses of the material. Thus, optical contrast can be altered by changing the substrates. In this work, we have used a simple finite element modelling method to investigate the optical contrast of various TMDs including molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and molybdenum ditelluride (MoTe2) on various substrates. In particular, this work examines the optical contrast between TMDs and thin (~200 nm) diamond films that are either intrinsic or boron doped. We demonstrate differences in reflectance by using these different substrates.

Authors : ?. Me?kinis, R. Gudaitis, S. Jankauskas*, A. Guobien?, M. Andrulevi?ius, A. Vasiliauskas
Affiliations : Institute of Materials Science of Kaunas University of Technology, K. Bar?ausko 59, Kaunas, Lithuania

Resume : Graphene is at the top of considerable interest due to the giant electron and hole mobility, flexibility, optical transparency, chemical inertness. One of the main limitations of stopping graphene's broader application in semiconductor device technology is a complex graphene transfer procedure. In this case, graphene is synthesized on the catalytic Cu or Ni foils. Afterward, follows the long process of the graphene transfer onto the targeted semiconductor or dielectric substrates. During that process, graphene can be contaminated by different adsorbents. Wrinkles or ripples can be formed on graphene. Thus, control of the graphene layer or graphene-semiconductor contact properties is complicated. Recently there was shown that direct synthesis of graphene on semiconducting or dielectric substrates is possible. However, the development of this technology is the very beginning. In the present research, graphene layers were directly synthesized by microwave plasma-enhanced chemical vapor deposition, ICP plasma beam source, and reactive magnetron sputtering on the flat and textured semiconducting monocrystalline Si(100) substrates. The films' structure was investigated by multiwavelength Raman scattering spectroscopy, atomic force microscopy, Kelvin probe microscopy, scanning electron microscopy. The composition was investigated by X-ray photoelectron spectroscopy. Graphene/Si(100) Schottky diodes were fabricated. Effects of the deposition conditions on the structure of the graphene layers were studied. The influence of the methane and hydrogen gas flow ratio, pressure, plasma power, and deposition time was considered. Nitrogen, fluorine, and boron-doped graphene were synthesized. There were revealed that both vertical graphene flakes and planar graphene layers could be synthesized by setting appropriate deposition conditions. Current-voltage characteristics, and photovoltaic and photoelectric properties of the graphene/Si diodes, were investigated. The relation between photovoltaic properties, graphene structure, and doping was found.

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Authors : Samy Brahimi, Samir Lounis
Affiliations : Laboratoire de Physique et Chimie Quantique, Université Mouloud Mammeri Tizi-Ouzou, B.P.No.17 RP, 15000 Tizi-Ouzou, Algeria; Peter Gruenberg Institut and Institute for Advanced Simulation, Forschungszentrum Juelich, 52425 Juelich & JARA, Germany

Resume : The CoPt binary alloy is an interesting material in point of view of tech- nological applications. The high perpendicular magnetic anisotropy energy (MAE) displayed by its tetragonal L10 structure [1, 2, 3], allows him to be a good candidate for ultra high density storage devices. The impact of reduced dimensionality and defects like anti-sites and stacking faults, and the effect of ad-atoms and vacancies on the MAE of CoPt thin films, are investigated from first principles with the VASP code [4, 5]. By studying the two types of terminations, either Co terminated films or Pt terminated films, we show the pertinent role of chemical nature of surface in terms of magnitude of MAE. The Pt termination displays an enormous MAE which can be 1000 % larger than the one of Co termination [6]. The stacking faults and anti-sites reduce drastically the MAE in reference to the Pt termina- tion [6]. Besides of extended defects and anti-sites, we consider the case of ad-atoms and vacancies. The Co and Fe single ad-atoms are supported by Pt terminated thin film while the Pt ad-atom is deposited on Co terminated film. Single Co and Pt vacancies on the surface layer are investigated. We found that the Fe ad-atom and Pt vacancy induce an in-plane MAE which is large enough to switch the surface MAE to point from out of plane to in plane [7]. We manage to connect our results on the MAE to the location of the different virtual bound states and to the orbital moment anisotropy. Keywords : magnetic anisotropy energy, thin films, L10 CoPt alloy, virtual bound states, orbital moment anisotropy. References [1] Weller D and Moser A 1999 IEEE Trans. Magn. 35 4423 [2] Perez A, Dupuis V, Tuaillon-Combes J, Bardotti L, Prével B, Bernstein E, Mélinon P, Favre L, Hannour A and Lamet M 2005 Adv. Eng. Mater. 7 475 [3] Zemen J, Masek J, Kucera J, Mol J A, Motloch P and Jungwirth T 2014 J. Magn. Magn. Mater. 356 87 [4] Kresse G and Furthmueller J 1996 Phys. Rev. B 54 11169 [5] Kresse G and Joubert D 1999 Phys. Rev. B 59 1758 [6] Brahimi S, Bouzar H and Lounis S 2016 J. Phys.: Condens. Matter 28 496002 [7] Brahimi S, Bouzar H and Lounis S 2019 J. Phys.: Condens. Matter 31 435803

Authors : Guillermo A. Ferrero, Gustav Åvall, Youhyun Son, Knut Janßen, Katherine Mazzio and Philipp Adelhelm
Affiliations : Humboldt Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, 12489 Berlin, Germany

Resume : The development of high-performance energy storage devices has recently attracted much attention for applications such as electrical vehicles, grid storage and portable devices. In this sense, sodium-ion batteries (SIBs) has appeared as an alternative to traditional lithium-ion batteries as a result of the availability, lower environmental impact and reduced cost of the battery due to the typical SIB chemistry. Even though graphite is a well-established and highly commercialized anode material, its application in SIBs suffers from several drawbacks, such as the practical impossibility of using traditional carbonates-based electrolytes due to unfavorable thermodynamic behavior – resulting in low specific capacities. Despite this, certain solvents (such as ethers) allow the use of graphite in SIBs through the formation of ternary graphite intercalation compounds by a co-intercalation reaction, showing excellent cyclability and kinetics. However, its capacity at 100-150 mAh g-1 is still low compare to other anode materials, in addition to showing large volume expansion. Transition metal dichalcogenides (TMDs) have emerged as promising anode materials owing to their low cost, high electric conductivity, good thermal stability and environmental friendliness. Among them, titanium sulphide (TiS2), with a two-dimensional framework, exhibits several advantages such as a high conductivity (compare to other metal oxides), a larger interlayer distance (0.569 nm) compared to graphite (0.335 nm) and high stability. Several papers have reported on the use of TiS2 as an anode material for SIBs, and observed that the voltage profiles and electrochemical behaviour of the system is highly dependent on the choice of electrolyte, yet this has seldomly been explicitly stated, nor the cause of the electrolyte dependence investigated. Here, we demonstrate that depending on the electrolyte employed, an electrochemical co-intercalation reaction, similar to those reported with graphite as active material can also occur. Galvanostatic charge-discharge experiments were first performed to assess differences between different electrolytes (linear ethers, cyclic ethers and carbonates). Here, differences were found on the voltage profiles among the linear ethers and the rest of the solvents employed. By using in-situ and ex-situ techniques, a huge expansion on the TiS2 layers was found when diglyme was the solvent used. It was concluded here that co-intercalation of the solvent with sodium was the mechanism that occurs. On the contrary, when a cyclic ether and/or a mixture of carbonates were used, a lower expansion of the layered structure occurred and remained constant during the cycling. Dilatometry experiments were used to confirmed these mechanisms. Thus, with this technique, it is possible to monitor the variation on the thickness of the electrode during cycling, i.e. operando. In this sense, a greater expansion was observed when diglyme was used as the solvent electrolyte. Finally, DFT was used to study the solvents investigated, and their interaction with the sodium cation. It was found that among the solvents, diglyme produced by far the smallest and most stable solvation shells, making them prime candidates for co-intercalation studies. Comparing the size and stability of the solvation shell, with the interlayer binding energy of TiS2, we found it was energetically favorable to expand the lattice and allow a solvation shell into the host structure, compared to forming a bare ion.

Authors : Nassima KANA, Bernard Humbert, Thomas DEVIC and Bernard LESTRIEZ
Affiliations : Université de Nantes, CNRS, Institut des Matériaux Jean Rouxel, IMN, F-44000 Nantes, France

Resume : Among all potential active materials for the anodes of Li-ion batteries, silicon is considered as one of the most promising candidate because of its high specific and volumetric capacities, about 3600 mAh.g-1 and 2200 respectively,1 as well as its low operation voltage (0.4 versus Li/Li+), abundant resources (the second largest in the earth’s crust), and environmental benignity (non-toxic). However, during the lithiation (formation of LixSi, x ~ 3.75) the silicon undergoes an expansion of about 280% of its initial volume2 which induces numerous damages to the electrode. The silicon micrometer particles tend to be pulverized when the size of the particles are upper than 150 nm.3 However, nanosizing the materials leads to more electrolyte degradation due to a higher specific surface developed and requires more binder and eventually more conducting additive in the electrode formulation. The pulverized Si particles are scattered and become electrically isolated and the adhesion of the Si electrode to the current collector are also damaged by these volume variations4. This effects drastically reduces the electrochemical performance and lifetime of the Si electrode. As a result, these challenges have seriously restricted the commercialization of Si anodes in high energy LIBs.5 To deal with these problems many researches are developing advanced binders. This later has a crucial role since it reinforces the mechanical strength of the electrode and thus helps to preserve the electrode architecture upon cycling against the large Si volume change.6 It is generally accepted that binders of very high molar masses (polymers) are necessary to allow cycling of silicon-based electrodes, as they favor the formation of more robust molecular bridges and therefore are a priori more capable of maintaining particle-to-particle contacts and therefore cohesion in the electrode. Quite surprisingly, we have discovered that it is possible to obtain good cyclability of silicon-based electrodes by using an organic binder of low molar mass (molecule). This calls into question the understanding of the mechanism by which the binder operates in silicon-based electrodes. This low molecular weight binder is a natural polyphenol, namely tannic acid. Here we will highlight that Silicon-based composite electrodes of high areal capacity (~7 when prepared with tannic acid as small binder show a stable cycling like the one obtained with one state-of-the-art binder such as carboxymethyl cellulose. We will report in-depth characterization of the interactions between tannic acid and the silicon particles surface as well as of the rheological behavior of the electrode slurries and the electrodes properties and electrochemical performances.  

10:30 DISCUSSION    
10:45 BREAK    
Authors : Guemiza, H.*, Pham-Truong, T.N., Vidal, F., Plesse, C., Aubert, P-H.
Affiliations : CY Cergy Paris Université, LPPI, F-95000 Cergy

Resume : Nowadays, flexible energy storage is gaining a lot of attention in many potential applications for soft and wearable electronics. In these fields, supercapacitors are one of the most promising technology, owing to their simple structure, their power and energy densities complementary to batteries specifications, and their long cycling life and stability [1]. The development of safe and high-performance flexible supercapacitors is especially attractive to power small, portable electronics, and more recently wearable devices like light-emitting diodes and flexible screens. Generally, the most widely used active materials of supercapacitors are carbon, conducting polymers, metal oxides etc. Among these, carbon materials such as activated carbon, carbon nanotubes (CNTs) and reduced graphene oxide (rGO) have been intensely investigated as electrode materials due to their favorable electronic conductivity, low cost, high chemical stability, and high specific surface area to accommodate the accessibility of a large number of ions at the electrode/electrolyte interface [2]. However, the re-stacking and bundling of these materials causes significant losses of electrochemically accessible surface area and thus, reduces their storage performance [2]. To tackle this key issue, we describe the elaboration of high-performing composites by combining rGO and poly(ionic liquid) (PIL). PIL are a sub-class of polyelectrolytes, providing both the mechanical properties of polymers and the ionic conducting properties of their ionic liquid-like ionic centers [3]. By intercalating imidazolium-based PILs, with cationic or anionic macromolecular chain, within the rGO sheets, restacking of rGO sheets is prevented and liquid-free soft electrodes are developed. Optimization is performed in order to get high specific capacitance without compromising the ionic performances inside the bulk electrode. Hence, the replacement of liquid electrolytes by quasi solid ones are one of the upcoming challenges in the near future especially for safety reasons. [1] D.W. Wang, F. Li, J. Zhao, W. Ren, Z.G. Chen, J. Tan, Z.S. Wu, I. Gentle, G.Q. Lu, H.M. Cheng, Fabrication of graphene/polyaniline composite paper via in situ anodic electropolymerization for high-performance flexible electrode, ACS Nano. 3 (2009) 1745–1752. [2] C. He, S. Sun, H. Peng, C.P. Tsui, D. Shi, X. Xie, Y. Yang, Poly(ionic liquid)-assisted reduction of graphene oxide to achieve high-performance composite electrodes, Compos. Part B Eng. 106 (2016) 81–87. [3] Y. Li, R. Liu, Q. Wang, Q. Tang, F. Liu, J. Jia, Poly(ionic liquids)/reduced graphene oxide miniemulsion polymers as effective support for immobilization of Ag nanoparticles and its amperometric sensing of l-cysteine, J. Iran. Chem. Soc. 16 (2019) 201–207.

Authors : Maytal Caspary Toroker
Affiliations : Department of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa 3600003, Israel

Resume : Hydrogen production through water splitting has attracted great interest in recent years due to its potential of generating energy without causing pollution. One of the best candidates for water splitting is nickel oxyhydroxide with iron content (Ni 1− x FexOOH) that has excellent efficiency at alkaline conditions and is now studied widely. But pure NiOOH has poor efficiency unless doped with Fe and Co. We explore the influence of co-doping on the efficiency of NiOOH in the process of water oxidation by using Density Functional Theory +U (DFT+U). We also test the effect of strain on catalytic efficiency by modeling water oxidation on expanded and contracted surfaces of NiFeCoOOH. We find that several doping locations of Co have a similar result as if NiFeOOH had no Co content. Iron is responsible for the high activity at the Fe active site due to the low energy required for charge extraction. Yet, the valence band edge includes Fe, Co and Ni states hybridized which allows better charge extraction during deprotonation. The valence band edge position is higher upon Co-doping, which should allow better hole transport toward the surface. Hence, the presence of Ni and Co atoms surrounding the active site is vital for better efficiency. Moreover, we found that applying strain does not improve the efficiency and therefore a substrate with minimal mismatch should be used for NiFeCoOOH electrocatalysis.

Authors : Amir Pakdel, Takao Mori
Affiliations : Department of Mechanical, Manufacturing & Biomedical Engineering, Trinity College Dublin, The University of Dublin, D02PN40 Dublin, IRELAND; National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044 JAPAN

Resume : Nanoengineering of thermoelectric materials is an effective approach to decouple their electronic and thermal transport properties, hence enhancing their thermoelectric efficiency. Nanoengineering strategies can significantly reduce the thermal conductivity through the corporation of different phonon scattering mechanisms, while the electrical conductivity may not be affected considerably. Here, we compare the effect of three nanoengineering approaches on the structural, electrical, and thermal properties of a layered chalcogenide alloy, Bi0.5Sb1.5Te3; (a) nano-hybridization of the alloy by adding Sb2O3 nanoparticles, (b) severe plastic deformation via high-pressure torsion, and (c) grain refinement by sonication of Bi0.5Sb1.5Te3 before sintering [1,2]. It is shown that among these methods, severe plastic deformation induces ultrafine grains and a high density of dislocations, resulting in a large reduction of the total thermal conductivity (32.8%) and a moderate decline in the electrical conductivity of (15.7%) at 300 K. A notable decrease in the lattice thermal conductivity (56.8% at 300 K) is attributed to midfrequency phonon scattering by the dislocations together with low and high frequency scatterings through grain boundaries and point defects, respectively. References: [1] Advanced Engineering Materials, 2021 (24) 2100955. [2] Journal of Materials Chemistry A, 2018 (6) 21341.

12:00 DISCUSSION    
Authors : Zhen Li*, Patrizio Graziosi, and Neophytos Neophytou
Affiliations : School of Engineering, University of Warwick, Coventry, CV4 7AL, UK Consiglio Nazionale delle Ricerche ? Istituto per lo Studio dei Materiali Nanostrutturati, CNR ? ISMN, via Gobetti 101, 40129, Bologna, Italy

Resume : Two-dimensional (2D) materials such as graphene, black phosphorus (BP), transition metal dichalcogenides (e.g. WS2, MoS2, MoSe2, MoTe2, etc.), group IVA-VA compounds (e.g. SnSe, GeSe, SnS, etc.), boron nitiride, MXenes (e.g Ti4N3), and Xenes (e.g. black phosphorene, silicene, germanene, stanine, tellurene, etc.), have attracted significant attention due to their exceptional electronic properties and the possibility of 2D electronic devices. They have also attracted attention as potential thermoelectric (TE) materials due to their low dimensional nature which could allow improvements in the Seebeck coefficient and power factor. Due to their flexible and stretchable nature, they are prime candidates of flexible energy harvesters to enable flexible electronics, sensors, and empower the internet of things (IoT), among others. In this work, using theory and simulation we investigate general thermoelectric performance features of two-dimensional (2D) transition metal dichalcogenides (TMDCs). We use the Boltzmann Transport Equation (BTE) and investigate their thermoelectric power factor as a function of their bandgap and their spin orbit coupling. We show that there exists an optimal value for the power factor as the bandgap is reduced as a consequence of the bands becoming more linear, which benefits the electronic conductivity. For even lower bandgaps, however, the power factor is reduced because bipolar effects gradually diminish the Seebeck coefficient. We show that for a specific bandgap, spin splitting can also help to tune the bandgap and band linearity towards more optimal directions, which improves the power factor even further. Our results, and specifically the illustration of the competition between band linearity (at small bandgaps) and large Seebeck (at large bandgaps) can offer design guidelines, useful in identifying potentially high thermoelectric performance within the myriad of 2D material candidates. We further present a method to extract electronic transport properties using full band ab initio approaches, which will allow more quantitative exploration of 2D thermoelectrics.

Authors : Hasnae Chfii, Amal Bouich, Lahoucine Atourki, Bérnabe Mari, Mohamed Abdlefdil,
Affiliations : Laboratory MANAPSE, University Mohammed V, Rabat, Morocco Institut de Disseny i Fabricació, Universitat Politècnica,València, Spain

Resume : Abstract In this work, The CuCoO2 delafossite powders were successfully prepared by hydrothermal by optimizing different conditions such as annealed Temperature (100 – 150 – 200 – 250 °C), Annealed time from 24hours, two days, and 3days with optimal pH fixed. The powder prepared with annealed temperature at100 °C for 24 hours showed an excellent crystallinity with higher intensity of the peak characteristic which posited at 2θ=37,7 ºC, low impurities phases, and fewer defects with a suitable bandgap around 3,2 eV compared to the other powders prepared, this comparison was based according to the following analysis x-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and the properties by Photoluminescence (PL) and UV-visible spectroscopy. Furthermore, the CuCoO2 delafossite thin film was deposited at FTO by spin coating technique then analyzed in order to be used as Hole Transparent Layer (HTL) in Perovskite Solar Cell (PSC). Keywords Perovskite, Thin-film, Delafossite, HTL, Hydrothermal synthesis, Spin coating.

Authors : Salvatore Timpa, Mehrdad Rahimi, Jacko Rastikian, Stéphan Suffit, François Mallet, Philippe Lafarge, Clément Barraud, and Maria Luisa Della Rocca
Affiliations : Salvatore Timpa, Mehrdad Rahimi, Jacko Rastikian, Stéphan Suffit, Philippe Lafarge, Clément Barraud affiliated to Laboratoire Matériaux et Phénomènes Quantiques, Université de Paris, CNRS-UMR7162, 75013 Paris, France François Mallet affiliated Laboratoire Matériaux et Phénomènes Quantiques, Université de Paris, CNRS-UMR7162, 75013 Paris, France and Sorbonne Université, UFR925, 75005 Paris, France

Resume : Research on new thermoelectric (TE) devices and materials to improve energy conversion is highly demanded in nanoelectronics. Energy conversion of TE nanogenerators is ruled by the TE effect, the phenomenon occurring when a temperature difference through a material creates an electrical voltage. The TE efficiency ZT, depending on the Seebeck coefficient (S), the electrical conductivity (sigma), the thermal conductivity (k) and the temperature (T), is the relevant parameter that researchers struggle to improve. Values of ZT >> 1 are typically sought for a TE material to be exploitable in applications. The discovery of 2D materials has open new routes of investigation, high ZT values have been predicted in graphene nanostructure1 and transition metal dicalcogenides (TMD) have revealed high Seebeck coefficients. I will present our recent contribution in engineering new devices based on 2D materials improving thermoelectric (TE) performances, particularly considering the on-substrate configuration, actually the most appropriate for applications. In particular, we have focused on the thermoelectric properties of tungsten diselenide (WSe2), which has revealed so far promising results among the transition metal dichalcogenides (TMD) family. Indeed, WSe2 owns a particularly low thermal conductivity (1-2 W/mK at room temperature), making it appealing for TE applications. We have investigated the electric and thermoelectric properties of hBN/WSe2 heterostructures, where the hBN (hexagonal boron nitride) layer acts simultaneously as a dielectric spacer that decouples the TMD from the SiO2 substrate and efficiently couples the TMD to a local gate. Our investigation reveals that, depending on the used metal to contact, high values of Seebeck coefficient S up to 180 μV/K can be attained in hBN/WSe2 based devices, revealing the importance of the electronic properties at the electrode/2D material interface for enhanced device performances6. Furthermore, we have focused onto the complex question of correctly measuring the physical parameters defining the TE performances in actual devices based on supported low dimensional materials. We have recently proposed the use of the Joule self-heating method, already applied to evaluate the thermal conductivity of supported metallic nanowires, to the case of multilayer graphene nanowires. Graphene is used as a test-bed 2D material for the easiness of its manipulation for device fabrication. We found out that, by using a thick and rough SiO2 oxide layer, thermal losses can be considerably reduced and an effective reduction of the graphene thermal conductivity can be attained, with values as low as 40 W/m K, renewing its interest for TE applications.


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Symposium organizers
Manickam MINAKSHIMurdoch University

School of Engineering and Information - Technology, Murdoch, WA 6150, Australia
Priya VASHISHTAUniversity of Southern California

Dept. of Physics & Astronomy, Los Angeles, CA 90089-0242, USA
Rajeev AHUJA (Main Organizer)Department of Physics and Astronomy, Uppsala University

Box-516 SE-75120 Uppsala, Sweden