First virtual Bilateral Conference on Functional Materials (BiC-FM)

Direct measurement of THz plasmon propagation length in graphene

Belosevich V.V.^1,2, Fedorov G.E.¹

1 – Moscow Institute of Physics and Technology, Dolgoprudny, Russia

2 – Moscow State Pedagogical University, Moscow, Russia

vsevolod.belosevich@phystech.edu

Despite years of research, the concept of a terahertz (THz) gap cannot be considered completely obsolete. THz technologies are evolving but sources and detectors are still in need. In 1996 M.Dyakonov and M.Shur proposed [1] a method of rectifying THz radiation with High Electron Mobility Transistor (HEMT). In this configuration THz radiation is coupled between source and top-gate and DC signal occurs between source and drain. They have also proved this geometry of a device to be efficient for detecting terahertz radiation.

At the same time graphene appears to be one of the most promising materials in this field. Various graphene based THz detectors have been demonstrated [2,3]. Among all the ways to obtain graphene, chemical vapor deposition (CVD) is the simplest and cheapest one. There is a possibility for automatization of device fabrication based on this method that is not less important.

In this work we fabricated series of devices in Dyakonov-Shur configuration with different top-gate electrode position. We used CVD-grown graphene as a transport channel. In this configuration source and gate act as sleeves of bowtie antenna.

Figure 1: Schematic representation of the detector

The mechanism of THz radiation rectification and resulting DC voltage signal across the channel involves in particular nonlinearities and excitation of plasmons in graphene. Different top-gate positions allow us to estimate the length of plasmon propagation.

Acknowledgement.This work was supported by the Russian Foundation for Basic Research, grant 18-29-20116.

References:

[1] M. Dyakonov and M. Shur, IEEE Transactions on Electron Devices 43, 380 (1996)

[2] Mittendorff, Martin, et al, Applied Physics Letters 103.2 (2013)

[3] Castilla, Sebastián, et al, Nano letters 19.5 (2019)

Naphthyl – functionalized dendrimers can regulate surface properties of materials

Bondareva J.V.¹

1 – Skolkovo Institute of Science and Technology, Moscow, Russia

julia.bondareva@skolkovotech.ru

Control over synthetic macromolecules' peripheral functionalization constitutes a considerable perspective on future applications and challenging task for chemists. One of such exciting and promising macromolecules is a dendrimer. Dendrimers are a class of polybranched synthetic macromolecules characterized by high monodispersity, good biocompatibility, and multivalent surfaces. [1] Selective peripheral functionalization of dendritic macromolecules having a well-defined constitution and a perfect shape is of high importance. Dendrimer research is currently associated with numerous technological and biomedical applications such as coatings, films, and in vivo contrast agents in magnetic resonance imaging. [2]

Our approach is based on functionalized sulfonimide dendrimers capable of forming stable monomolecular films at the air-water interface (so-called Langmuir films [3]) with subsequent polymerization the compressed state. The principle of covalent stabilization of monolayers is the dimerization of beta-naphthyl groups, which make up the outer shell of dendrimers, under the influence of UV radiation. The main advantages of the selected approach are (i) simplicity of experimental setup for the monolayer production and characterization, (ii) obtained films can easily be transferred onto a variety of solid substrates (e.g., silicon wafers, copper grids, HOPG, etc.), (iii) the latter expands the number of analytical tools to characterize the dendrimer films (e.g., optical and DIC microscopy on metal grids, ellipsometry analysis on silicon wafers, AFM and STM studies on HOPG, etc.)

The scientific project assumes the collaboration with physics-oriented experimental teams for performing conformational analysis of dendrimer molecules in the liquid phase. In practice, these films are interesting for changing the properties of polar hydrophilic surfaces to the opposite – hydrophobic ones using minimal amounts of a substance.

References:

[1] F. Vögtle, G. Richardt, and N Werner, Dendrimer Chemistry: Concepts, Syntheses, Properties, Applications, John Wiley and Sons (2009).

[2] M. Fischer, F. Vögtle, Dendrimers: From Design to Application – A Progress Report. Angewandte Chemie – International Edition, 38 (7), 884–905 (1999).

[3] A. Ulman, An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self-Assembly, Academic Press, Inc., San Diego, (1991).

Visible light driven photocatalytic performance of Ag modified ZnO nanorod through effective charge carrier separation

Abinash Das^a, Mathan Kumar P^b, Muthuraaman Bhagavathiachari^b, Ranjith G. Nair^a1

Solar Energy Materials Research & Testing Laboratory (SMaRT lab), Department of Physics, National Institute of Technology Silchar, Silchar, Assam-788010 (India)

Department of Energy, School of Chemical Sciences, University of Madras, Guindy Campus, Chennai-600025 (India)

rgnair2007@gmail.com

Over the past few decades, a lot of interest has been generated among the researchers to use ZnO based photocatalyst for energy and environmental applications. However, most of the work suggests that the effectiveness of implementing bare ZnO is limited due to several inherent shortcomings of the photocatalyst. Considering the same, current study has shown that the modification of ZnO with silver (Ag) can significantly improve the visible light driven photocatalytic activity through suitable modification in physicochemical properties. Highly active silver modified ZnO has been prepared using modified hydrothermal method. The structural, morphological, elemental and optical properties were characterised using XRD, TEM, FESEM, EDS, FTIR, UV–Vis and photoluminescence (PL) spectroscopy. The visible light driven photocatalytic performance of Ag doped ZnO was studied for the degradation of methylene blue (MB), and it is found that silver modified ZnO shows approximately seven times higher performance in terms of rate constant than the pristine ZnO. The improved performance of Ag modified ZnO was further supported by the photoelectrochemical (PEC) study, indicating the reduced charge transfer resistance of Ag doped ZnO. The PEC study emphasizes on the role of Ag in obstructing the recombination pathway of photogenerated charge carriers.

Parametric modelling of electric percolation and conductivity of carbon nanotubes nanocomposite

N.A. Gudkov¹, S.V. Lomov¹, I.S. Akhatov¹, S.G. Abaimov¹

1. CREI Centre for Design Manufacturing and Materials, Skolkovo Institute of Science and Technology, Bolshoy blvd., 30, bld.1 Skolkovo, 121205 Moscow, Russian Federation

Nikita.Gudkov@skoltech.ru

Conductive polymers are widely used in different industry branches. Adding carbon nanotubes (CNT) is one of the most efficient ways to make a polymer conductive, because of high intrinsic conductivity of CNTs and their 1D nature, which provides nanocomposites with relatively low electric percolation thresholds. All these properties lead to low weight fraction of filler and therefore low weight of a nanocomposite. The present work aims at developing of a digital twin of a CNT nanocomposite, representing its electric conductivity.

To obtain conductivity of an infinite medium, a representative volume element (RVE) approach was utilized. The digital twin creation can be divided into three parts: geometry generator, connection finder, and conductivity calculator. Geometry generator builds a set of uniformly and isotropically distributed CNTs inside the RVE. The distribution of CNT lengths is assumed to be Weibull. The maximal curvature of the CNTs is controlled. The periodicity of the geometry is ensured: a CNT crossing one face returns back to the RVE at the opposite face. The new approach was implemented here to consider geometrical torsion of CNTs. This made the digital twin independent from the size of segments, by which CNT curves are approximated. Connection finder is based on the sub-region division to make algorithm check less possible pairs of segments, which speeds up the searching process. Periodic boundary conditions are used for current calculations; they are compared with uniform potential conditions commonly used in the literature, and it is shown that the latter significantly overestimate the RVE conductivity.

Sensitivity of the model to input geometry generation parameters is investigated. It is found that 5 µm size is the optimal RVE size for reasonable volume fractions of CNTs. All results are obtained for multi-walled CNTs with diameter 50 nm. Segment size 0.3 µm was chosen based on the calculation accuracy. For a CNT volume fraction of 2 %: changing mean length of CNTs from 2.5 µm to 5 µm increases conductivity more than 4 times; changing curvature from 0 to 3.46 µm-1 decreases conductivity 5 times; changing torsion from 0 to 3 µm-1 increases conductivity 6 times.

Influence of non-zero ballistic resistivity of CNTs is investigated. The results show that neglecting intrinsic resistivity causes error of 0.5 decimal order of magnitude.

Due to enormous difference in electrical conductivity between matrix and CNTs, nanocomposite percolation behavior can be described with Kolmogorov’s zero-one law. It means that an infinite medium has a jump in conductivity when volume fraction increases and goes through the percolation threshold. However, there is a finite-size effect, which depends on size of the RVE and smooths this jump. Conductivity of the nanocomposite near the percolation threshold is investigated and its scaling is found to follow the power-law and finite-size dependencies. We obtained percolation threshold equals 0.61 % volume fraction for our default configuration (see above). For 10 µm mean CNT length percolation threshold moves to 0.32 % Vf. For 2 times decreased curvature it moves to 0.54 % Vf, and for 2 times decreased torsion it moves to 0.7 % Vf. However, critical index seems to be nearly invariant with regard to geometric parameters. Its value changes in the range between 1.184 and 1.747.

Acknowledgements:

This work was supported by Skoltech NGP Program (Skoltech-MIT joint project). This work was pre-printed at https://arxiv.org/abs/2009.06013.

TiO₂ nanotubes and black TiO₂ nanotubes: application to solar electricity and hydrogen production

Hou X.L.¹, Lund P.D.¹

¹New Energy Technologies Group, Department of Applied Physics, School of Science, Aalto University, FI-00076 Aalto, Espoo Finland

Xuelan.hou@aalto.fi

TiO₂ nanomaterials have attracted much scientific and technological in recent years. TiO₂ nanomaterials can be used for direct splitting of water into H₂ and O₂ to generate hydrogen fuel [1] and also in Grätzel type solar cells for electricity.[2]

In order to create a high surface area of TiO₂ to achieve a maximum turn-over rate, various 1D and highly defined TiO₂ morphologies have been explored for the replacement of nanoparticle networks. Nanotubes can be grown by hydro/solvothermal or template methods, or even more large area fabricated application, by self-organizing anodic oxidation. The latter is not limited to TiO₂ nanotubes (TNTs)but to a full range of other functional oxide structures on various metals and binary and ternary alloys can be formed. [3] In order to absorb and utilize solar light as much as possible, excellent black TiO₂ are emerging, which have not only a suitable bandgap of 1.8 eV- 2.8 eV, but also has enhanced light absorption ability. [4, 5] The light absorption of black TiO₂ was broadened to NIR light (2 um)).

The presentation will focus on these highly ordered TNTsand discuss the most recent progress in synthesis and modification of black TNTs for solar cells and hydrogen production.

Acknowledgement.This work has been supported by the China Scholarship Council (CSC), No. 201706250038, and funded by the Academy of Finland Flagship Programme, Photonics Research and Innovation (PREIN), decision number: 320167.

References:

[1] Fujishima, A. and Honda, K., 1972. Electrochemical photolysis of water at a semiconductor electrode. nature, 238(5358), pp.37–38.

[2] O'Regan, B. and Grätzel, M., 1991. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO 2 films. nature, 353(6346), pp.737–740.

[3]Roy, P., Berger, S. and Schmuki, P., 2011. TiO2 nanotubes: synthesis andapplications. Angewandte Chemie International Edition, 50(13), pp.2904–2939.

[4] Chen, X., Liu, L., Peter, Y.Y. and Mao, S.S., 2011. Increasing solar absorption for photocatalysis with black hydrogenated titanium dioxide nanocrystals. Science, 331(6018), pp.746–750.

[5] Hou, X., Jiang, S. and Li, Y., 2019. A two-anode reduction technique to monitor the defect and dope the surface of TiO2 nanotube array as photo-anode for water splitting. Applied Catalysis B: Environmental, 258, p.117949.

Stable Doping of Carbon Nanotubes by V₂O₅ Using Fast Sol-Gel Method

Ilatovskii D.A.¹, Krasnikov D.V.¹, Goldt A.E.¹, Nasibulin A.G.^1,2

1 – Skolkovo Institute of Science and Technology, Moscow, Russia

2 – Aalto University, Espoo, Finland

Daniil.Ilatovskii@skoltech.ru

The promising tendency of the use of single-walled carbon nanotube (SWCNT) thin films is to apply them as a transparent conductor of new generation [1]. Despite the fact, that many materials have been tested for this purpose: metal oxide ceramics, conducting polymers, thin-film metals, metal microgrids, and nanowires, neither has replaced the only one industrial product – indium tin oxide (ITO). Nevertheless, ITO does not satisfy requirements for modern transparent conducting films (TCFs): mechanical flexibility for flexible electronics and high refractive index [2]. Moreover, availability of indium is limited [3], so its price continuously increases (near 300 USD per kg) and it is necessary to develop indium-free electrodes.

Vanadium pentoxide has a great potential as a doping agent for SWCNTs due to its nature: high work function (WF) of 7.0 eV giving doping effect and high stability to humidity, sun irradiation and inert gases [4].

In this work, we show for the first time fast, simple and cheap method for treatment of thin films based on SWCNTs by V₂O₅ using sol-gel method for synthesis, which provides effective and highly stable adsorption doping. We used optical and Raman spectroscopy, contact 4-probe measurement of conductivity, XPS, and TEM in order to characterize the obtained materials and to check their stability in time. According to this method, we obtained films with equivalent resistance less than R₉₀ = 100 Ohm/sq; which increased less than by 5 % after one month of ageing.

Acknowledgement.This work was supported by RFBR project № 20-33-90324.

References:

[1] Zhang, J. et al., Carbon, 98, (2016).

[2] Hofmann, A. I., Cloutet, E. & Hadziioannou, G., Advanced Electronic Materials, 4, (2018).

[3] Kumar, A. & Zhou, C., ACS Nano 4, 11–14 (2010).

[4] Beke S., Thin Solid Films, 519, (2011).

Electrochemical behaviour of thermally reduced graphite oxide in Li-ion batteries

Iurchenkova A.A.¹, Lobiak E.V.²,Fedorovskaya E.O^.1,2,3

1 – Novosibirsk State University, Laboratory of hybrid nanomaterials for electrochemical storage devices, Pirogova st. 1, Novosibirsk, 630090, Russia.

2 – Nikolaev Institute of Inorganic Chemistry, SB RAS, 3 Acad. Lavrentiev ave., 3., 630090, Novosibirsk, Russia.

3 – Research Group of Electrochemical Energy Conversion and Storage, Department of Chemistry, School of Chemical Engineering, Aalto University, P.O. Box 16100, FI-00076, Finland.

a.iurchenkova@g.nsu.ru

The popularity of Li-ion batteries as storage devises rapidly grow in recent years. It relates to their high energy and power density, long cycling life. Despite a large amount of research in the field of creating and improving materials for Li-ion batteries, many questions remain.

Our work is devoted to study the influence of the functional composition and morphology of reduced graphite oxide (RGO) on its characteristics as an anode material for Li-ion batteries. Graphite oxide synthesized by Hammers method was chosen as precursor for RGO synthesis. Firstly, graphite oxide (GO) was ultrasonicated in concentrated sulphuric acid, washed by distillate water and freeze dried. After that grey-brown powder of GO was thermally expanded in Ar atmosphere and then thermally treated at different temperatures (500 °C, 600 °C, 700 °C). Investigation of functional composition of obtained samples were carried out by Fourier-transformed infrared, X-ray photoelectron and Raman spectroscopic methods. Morphology of samples was investigated by scanning electron and high-resolution transmission electron microscopic methods. Electrochemical performance in Li-ion batteries was studied by charge-discharge method in two-electrode cell. RGO samples synthesized at different temperature were applied on copper foil and dried under the vacuum. The foil with active material was cut to electrodes and placed in a two-electrode coin-cell. Metallic Li and 1M LiPF6 in DMC/EC solution were used as counter electrode and electrolyte, respectively.

It is obtained that materials have epoxy, hydroxyl, carboxyl and carbonyl oxygen-containing groups (OCFG) on the surface. The amount of OCFG on the surface decreases and its defectiveness increases with an increase in the processing temperature of the material. Also, OCFG are removed from material’s surface in order: epoxy (250ºC), carboxyl (250–600 °C), hydroxyl (600–800 °C) and carbonyl (700-1000 °C). Maximal specific capacitance of samples reaches 400 mAhg^-1.

Acknowledgement.This work was supported by the Russian Federation President Fund, project № МК-712.2019.3.

Nonlinear optical absorption in lead halide perovskite thin films

Khudyakov D.V.¹, Ganin D.V.¹, Lyashedko A.D.³, Frolova L.A.^4,2, Troshin P.A.^4,2, Lobach A.S.²

1 – Physics Instrumentation Center of Prokhorov General Physics Institute of the RAS, Troitsk, Moscow, Russia

2 – Institute of Problems of Chemical Physics of the RAS, Chernogolovka, Russia

3 – Optosystems Ltd., Troitsk, Moscow, Russia

4 – Skolkovo Institute of Science and Technology, Moscow, Russia

dimakh65@gmail.com

Metal halide perovskites have attracted intensive attention primarily because of their excellent optical and electronic properties. Beyond the well-known properties of the perovskite materials, they also have recently been investigated as a potential media for nonlinear optical modulators [1,2]. In the present report, we employed the Z-scan technique to investigate the nonlinear optical response of CsPbI₂Br, MA_0.15FA_0.75Cs_0.1PbI_2.85Br_0.15 and MA_0.15FA_0.75Cs_0.1PbI₃ perovskite films (PF) with 45-350 nm thickness under irradiation of pulsed Yb-doped fiber laser (_p=400 fs, =1.064 μm) as the pump source. It was found that thin PF (45–65 nm) have stronger nonlinear absorption with large coefficient =261–928 cm/GW and lower saturation intensity (I_sat) compared with thick PF (250–350 nm) with smaller =47–55 cm/GW and higher I_sat. It was shown that I_sat of the nonlinear absorption in PF depends on the pump pulse duration and increases for shorter pulses.

Acknowledgement.This work of the IPCP RAS staff was carried out in the frame of the State task (registration number AAAA-A19-119032690060-9).

References:

[1] A.Ferrando, J.P.Martínez-Pastor, I.Suarez, J. Phys. Chem. Lett. 9, 5612 (2018)

[2] C.Redondo-Obispo, I.Suarez, S.J.Quesada et al., J. Phys. Chem. Lett. 11, 2188 (2020)

Li-ion batteries with negative electrodes made of reduced graphite oxide

Kobets A.A.¹, Fedorovskaya E.O.²

1 – Novosibirsk State University, Novosibirsk, Russia

2 – Research Group of Electrochemical Energy Conversion and Storage, Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, Aalto, Finland

a.a.kobets@mail.ru

Lithium ion batteries are the alternative energy sources with long life durability, high reversible power, long cyclic stability and high ecological safety. Carbon nanomaterials, transition metal oxides, electroactive polymers are the perspective electrode components of Li-ion batteries. This work is dedicated to investigation of nanostructure carbon materials with oxygen containing functional groups on the surface as negative electrodes in lithium-ion batteries.

Carbon materials are considered as suitable materials for negative electrode materials of Li-ion batteries due to their thermal and chemical properties, electrochemical stability, accessible surface, good reversibility of lithium ion intercalation/deintercalation. Functional groups on the surface of the carbon materials affect on the electrochemical behavior of the negative electrode, for example, increase the specific capacitance, stabilize the reversible capacitance, and improve the process of intercalation/deintercalation of lithium ions.

In this study, we used reduced graphite oxide (RGO), which has all the advantages of nanostructured carbon materials. RGO was obtained by heating graphite oxide in concentrated sulfuric acid. Graphite oxide was obtained by a modified Hammers method. Further, RGO was modified in a mixture of concentrated acids (1:1 HNO₃:H₂SO₄), in a 50 % alkali solution, in oxalic acid, and annealed in an argon atmosphere. The idea of work was to find correlation between functional composition and electrochemical processes during charge and discharge process. The morphology of all samples was investigated by SEM and TEM methods. The functional composition of these materials was also studied using FTIR, Raman and XPS spectroscopy. In addition, charge-discharge characteristics of lithium-ion batteries with electrodes prepared from the obtained samples were studied. All methods of modification lead to changes in morphology and functional composition that influence on electrochemical properties.

Acknowledgement.This work was financially support by the Grants Council of the President of the Russian Federation (grant MK 712.2019.3).