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Technical University of Munich
Technical University of Munich

Research topics

Two- and One-dimensional Semiconductors

SnIP-related One-dimensional semiconductors

Within a DFG funded project we’ll synthesize low-dimensional semiconducting materials with double-helical SnIP structure, delaminate them to nano-fibers and characterize them afterwards. Nanofibers or 1D-semiconductors like that will be tested afterwards concerning their potential usage as solar cells, sensors or field-effect transistors. Enlarging the SnIP structure family with SnIP homologues will enable us to derive structure-correlations for new inorganic, double-helix compounds. In sum, we are searching for ultra-thin, inorganic and chiral counterparts to the well-established double-helix compounds in biology and polymer science.

Funding: DFG Ni1095/8-1; e-conversion Cluster of Excellence - EXC 2089/1 - 390776260

Selected Publications:

  • Flexible and ultra-soft inorganic 1D semiconductor and heterostructure systems based on SnIP
    Claudia Ott,Felix Reiter, Maximilian Baumgartner, Markus Pielmeier, Anna Vogel, Patrick Walke, Stefan Burger, Michael Ehrenreich, Gregor Kieslich, Dominik Daisenberger, Jeff Armstrong, Thakur Ujwal Kumare, Pawan Kumar, Shunda Chen, Davide Donadio, Lisa S. Walter, R. Thomas Weitz, Karthik Shankar and Tom Nilges
    Advanced Functional Materials (2019), im Druck.

  • Inorganic SnIP-type double helices in main group chemistry
    Maximilian Baumgartner, Richard Weihrich, Tom Nilges
    Chem. Eur. J. 23 (2017), 6452-6457

  • Inorganic double helices in semiconducting SnIP
    Daniela Pfister, Konrad Schäfer, Claudia Ott, Birgit Gerke, Rainer Pöttgen, Oliver Janka, Maximilian Baumgartner, Anastasia Efimova, Andrea Hohmann, Peer Schmidt, Sabarinathan Venkatachalam, Leo van Wüllen, Ulrich Schürmann, Lorenz Kienle, Viola Duppel, Eric Parzinger, Bastian Miller, Jonathan Becker, Alexander Holleitner, Richard Weihrich, Tom Nilges
    Adv. Mater 28 (2016), 9783–9791

 

One-dimensional Hybrid Semiconductor Materials

Organic polymers, few-layer two-dimensional compounds like C3N4/graphene, or TiO2 are used as hosts to accommodate low-dimensional main group semiconductors and to create organic-inorganic or inorganic-inorganic hybrid materials. Examples are few-layer two-dimensional phosphorus and arsenic-based compounds which are examined and field effect transistors, gas sensors, and light detectors. One dimensional semiconductors, embedded in such hybrids are able to effectively from heterojunctions for charge generation and separation purposes enabling water splitting.

Funding: International Research and Training Group (IRTG 2020) ATUMS

Selected Publications:

  • Flexible and ultra-soft inorganic 1D semiconductor and heterostructure systems based on SnIP
    Claudia Ott,Felix Reiter, Maximilian Baumgartner, Markus Pielmeier, Anna Vogel, Patrick Walke, Stefan Burger, Michael Ehrenreich, Gregor Kieslich, Dominik Daisenberger, Jeff Armstrong, Thakur Ujwal Kumare, Pawan Kumar, Shunda Chen, Davide Donadio, Lisa S. Walter, R. Thomas Weitz, Karthik Shankar and Tom Nilges
    Advanced Functional Materials (2019), im Druck

  • Synthesis, Characterization, and Device Application of Antimony-Substituted Violet Phosphorus – A Layered Material
    Franziska Baumer, Yuqiang Ma, Chenfei Shen, Anyi Zhang, Liang Chen, Yihang Liu, Daniela Pfister, Tom Nilges, Chongwu Zhou
    ACS Nano 11(4) (2017), 4105-4113

  • Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties
    B. Liu, M. Köpf, A. A. Abbas, X. Wang, Q. Guo, Y. Jia, F. Xia, R. Weihrich, F. Bachhuber, F. Pielnhofer, H. Wang, R. Dhall, S. B. Cronin, M. Ge, X. Fang, T. Nilges, C. Zhou
    Adv. Mater. 27 (2015), 4423-4429

 

Phosphorene and Phosphorus-Arsenic-based Two-dimensional Materials

 

Phosphorene and As1-xPx based two-dimensional materials are fabricated from black phosphorus and bulk-As1-xPx the element allotropes by mechanical and soft-chemical approaches. The electronic structure is modulated upon delamination to few-layer down to one-layer sheets, and band gaps are accessible from 0.15 to 1.5 eV by this approach. Due to the prominent electronic features these few-layer materials are used to create field effect transistors, sensors and light detectors (vis and IR region).

Funding: e-conversion Cluster of Excellence - EXC 2089/1 - 390776260; BaCaTec

Selected Publications:

  • Room-temperature high detectivity mid-infrared photodetectors based on black arsenic phosphorus
    Mingsheng Long, Anyuan Gao, Peng Wang, Hui Xia, Claudia Ott, Chen Pan, Yajun Fu, Erfu Liu, Xiaoshuang Chen, Wei Lu, Tom Nilges, Jianbin Xu, Xiaomu Wang, Weida Hu, Feng Miao
    Science Adv. 3 (2017), e1700589

  • Black Phosphorus Field-Effect Transistors with Work Function Tunable Contacts
    Yuqiang Ma, Chenfei Shen, Anyi Zhang, Liang Chen, Yihang Liu, Jihan Chen, Qingzhou Liu, Zhen Li, Moh. R. Amer, Tom Nilges, Ahmad N. Abbas. Chongwu Zhou
    ACS Nano 11 (7) (2017), 7126-7133

  • Black Phosphorus Gas Sensors
    Ahmad N. Abbas, Bilu Liu, Liang Chen, Yuqiang Ma, Sen Cong, Noppadol Aroonyadet, Marianne Köpf, Tom Nilges, Chongwu Zhou
    ACS Nano 9 (2015), 5618-5624

 

 

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Polyphosphides

 

Our goal is to discover new semiconducting transition metal - main group polyphoshides. Variations in the polyphosphide substructure from 0 dimensional molecular units, polymeric 1 dimensional strands and 2 dimensional layers can be stabilized combining group 11 and group 14/15 elements. New building units like M3Sn heteroclusters (M = Au) and the first inorganic material with covalent Sb-P interactions have been prepared by main group halide mineralization reactions at elevated temperatures. One key finding is the new and effective route to black phosphorus which makes this allotrope (review article) now available for large scale applications. Due to their physical properties these polyphosphides are potential candidates for electrochemical applications.

Funding: DFG; State of Bavaria

Selected Publications:

 

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Solid State Batteries and Ion Conductors

Electrospinning of hybrid polymer-based materials

Electrospinning is used as powerful tool to synthesize hybrid organic-inorganic polymer membranes. Such hybrid materials can be applied in battery science as separator membranes, in semiconductor science as host-guest material for sensors and flexible devices and to align compounds for orientation sensitive experiments. For solid electrolytes we combine polar and non-polar organic polymers like polyethylene oxide, polymethylyl metacrylate, polyvinylidine fluoride with conductive salts and additives to homogenous and heterogeneous polymer blends. Such blends are electrospun to mirometer- thick fiber membranes, capable to conduct mobile ions in a reversible and fast fashion. Target materials are Lithium, Sodium and Magnesium conducting membranes which are stable against alkaline and alkaline earth element electrodes.

Selected Publications:

  • Electrospun Li(TFSI)@Polyethylene Oxide Membranes as Solid Electrolytes
    Patrick Walke, Katharina M. Freitag, Holger Kirchhain, Matthias Kaiser, Leo van Wüllen, Tom Nilges
    Z. Anorg. Allg. Chem., 644 (2018), 1863–1874

  • Elektrospun-Sodiumtetrafluoroborate-Polyethylene Oxide Membranes for Solvent-free Sodium Ion Transport in Solid State Sodium Ion Batteries
    K. M. Freitag, P. Walke, T. Nilges, H. Kirchhain, R. J. Spranger, L. van Wüllen
    Journal of Power Sources 378 (2018), 610-617

  • Enhancement of Li ion conductivity by electrospun polymer fibers and direct fabrication of solvent-free separator membranes for Li ion batteries
    Katharina M. Freitag, Holger Kirchhain, Leo van Wüllen, Tom Nilges
    Inorg. Chem. 56 (4) (2017), 2100–2107

Li, Na, Mg, Cu and Ag solid ion conductors

Our main focus is the synthesis, characterization and optimization of alkaline, alkaline earth and late transition metal solid ion conductors. After the discovery of new solid electrolytes we investigate the structure property relations, determine the structures of the polymorphic phases by the aid of crystallography and group-subgroup relations and examine their potential usage for liquid-based and solid state batteries. Half-cells are fabricated and tested for their electrochemical properties and performance and material optimization is added based on these results. Up to date we introduces super ion conductors with ion conductivities up to 10-2 S cm-1 and activation barriers for ion hopping smaller than 0.15 eV (Li+).

Selected Publications:

  • Influence of Copper on the Capacity of Phosphorus-Anodes in Sodium-Ion-Batteries
    Claudia Ott, Annabelle Degg, Patrick Walke, Felix Reiter, Tom Nilges
    Journal of Solid State Chemistry Volume 270, (2019), 636-641

  • Recent progress and developments in lithium cobalt phosphate chemistry - Syntheses, polymorphism and properties -
    Jennifer Ludwig, Tom Nilges
    Journal of Power Sources 382 (2018), 101-115

  • Particle size-controllable microwave-assisted solvothermal synthesis of the high-voltage cathode material LiCoPO4 using water/ethylene glycol solvent blends
    Jennifer Ludwig, Dominik Haering, Marca M. Doeff, Tom Nilges
    Solid State Sci. 67 (2017), 100-109

  • Morphology-controlled microwave-assisted solvothermal synthesis of high-performance LiCoPO4 as a high-voltage cathode material for Li-ion batteries
    Jennifer Ludwig, Cyril Marino, Dominik Haering, Christoph Stinner, Hubert A. Gasteiger, Tom Nilges
    J. Power Sources 342 (2017), 214-223
  • Low-activated Li-Ion Mobility and Metal to Semiconductor Transition in CdP2@Li Phases
    Nadine Eckstein, Ilona Krüger, Frederik Bachhuber, Richard Weihrich, Jose E. Barquera-Lozada, Leo van Wüllen, Tom Nilges
    J. Mater. Chem. A (2015), 3, 6484-649

  • Puzzling out the origin of the electrochemical activity of black P as negative electrode material with lithium for Lithium-ion batteries
    Marian Cristian Stan, Jan von Zamory, Stefano Passerini, Tom Nilges, Martin Winter
    J. Mater. Chem. A, 2013,1, 5293-5300

Funding: State of Bavaria; Munich School of Engineering; e-conversion Cluster of Excellence - EXC 2089/1 - 390776260

 

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Polymorphism, Phase Transitions, and Element Allotropes

Polymorphism is a common feature in solid state ionics. It is of fundamental interest to learn something about the formation, the stability and the kinetics of phases and their phase transitions. In cooperation with Prof Dr. P. Schmidt, BTU Cottbus - Senftenberg, and Prof. Dr. R. Weihrich, University Augsburg, we create a bottom up approach with the aid of new synthesis strategies, the modulation of phase formation and growth. Thermodynamics and kinetics of crystal formation and crystal growth are investigated. We focus on reactions via the gas phase and try to explain the formation and growth of such systems.

In the past few years we discovered ways to fabricate phosphorus and arsenic allotropes, like fibrous and black phosphorous in high purity, quality and also phase selective. These allotropes are nowadays used as starting materials for 2D materials like phosphorene or arsenene. We were able to use this knowledge to fabricate field effect transistors, sensors and light detectors (vis and IR region, see also Two and one-dimensional semiconductor section).

Funding: DFG, State of Bavaria

Selected Publications:

 

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Recycling processes for Rare Earth Element capturing

MiKa project

Within the MiKa project we develop and launch a recycling process for rare earth elements from solid materials (waste and recycling materials) by a combination of inorganic chemistry and biotechnology. Rare earth elements are separated from the starting materials by mild elution processes capable to pre separate them in different rare earth element containing solutions. These solutions are purified separating toxic heavy element ions and transferred into a micro algea separation process (in cooperation with Prof. Brück, TUM). By selective biosorption the rare earth elements will be concentrated and purified.

Funding: State of Bavaria, Bavarian State Ministry of the Environment and Consumer Protection

 

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Thermoelectrics and Energy Materials

Thermoelectric materials

The discovery of the new class of coinage metal polychalcogenide halides uncovered a new set of materials with promising properties. An extremely low thermal diffusivity in combination with high mobility and redox activity of structure units in the solid state are common features of this compounds. A linear and mobile chalcogen chain is responsible for a reversible switching of the electric properties from a p-conducting via a n-conducting state back to p-conduction by a simple change of temperature in one compound. Such a reversible redox-reaction (formation and breaking of covalently-bonded Te dumbells) within the chalcogenide substructure can have a certain impact in data storage applications due to its local resistivity switch in the sub-nano regime. The high mobility of the coinage metal and the polychalcogenide substructure lead to a highly efficient scattering of phonons and therefore an extremely low thermal diffusivity and thermal conductivity. Some compounds reach the thermal conductivity of nanostructured materials and superlattices known to be the best available thermoelectrics at the moment. Our activities are focused on the optimization of the thermoelectric properties to challenge the problems in energy production in the future. There are still major aspects in terms of the efficiency and the stability of thermoelectrics, especially in bulk samples without nano-structuring which need to be solved soon.

Selected Publications:

  • Phase Segregation of Polymorphic Solid Ion Conducting Cu7PSe6 during Thermoelectric Experiments
    Franziska Baumer, Tom Nilges
    Z. Anorg. Allg. Chem. 644 (2018), 1519–1524

  • A chemical, high-temperature way to Ag1.9Te via quasi-topotactic reaction of stuetzite-type Ag1.54Te – Structural and thermoelectrical properties
    Franziska Baumer, Tom Nilges
    Inorg. Chem. 56 (2017), 13930–13937

  • A Conceptional Approach to Materials for Resistivity Switching and Thermoelectrics
    Oliver Osters, Melanie Bawohl, Jean-Louis Bobet, Bernard Chevalier, Rodolphe Decourt, Tom Nilges
    Solid State Science 13 (2011), 944-947

 

Materials for water splitting

Semiconductors with a suitable bandgap are useful candidates for light harvesting and photo-electrochemical processes. Due to our activities in low dimensional semiconductor materials we are able to fabricate materials for water splitting processes. In the past we discovered Co-based phosphates by hydrothermal processed which contain Co in various oxidation states and comparable anions than the prominent Co-Pi catalyst for effective water splitting. Recently, we started to investigate inorganic-inorganic and organic inorganic hybrid materials like semiconductor@C3N4, semiconductor@carbon nanotube, semiconductor@TiO2, or semiconductor@polymer materials in photocatalytic processes. Due to an effective heterojunction formation between these two components effective charge separation takes place and current densities in water splitting experiments were improved significantly.

Selected publication:

  • Vapor growth of binary and ternary phosphorus-based semiconductors into TiO2 nanotube arrays and application in visible light driven water splitting
    Ebru Üzer, Pawan Kumar, Ryan Kisslinger, Piyush Kar, Karthik Shankar, Tom Nilges, (2019), eingereicht.

  • Vapor growth of semiconducting P allotropes into TiO2 nanotube arrays for photo-electrocatalytic water splitting applications
    Ebru Üzer, Pawan Kumar, Ryan Kisslinger, Piyush Kar, Karthik Shankar, Tom Nilges, (2019), eingereicht.

  • Co11Li[(OH)5O][(PO3OH)(PO4)5], a Lithium-Stabilized, Mixed-Valent Cobalt (II, III) Hydroxide Phosphate Framework
    Jennifer Ludwig, Stephan Geprägs, Dennis Nordlund, Marca M. Doeff, Tom Nilges
    Inorg. Chem. 56 (2017), 10950-10961

Funding: State of Bavaria, Munich School of Engineering

 

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 Non-harmonic refinement of crystal structures

In the scientific field of structure determination based on X-ray or neutron diffraction the refinement of atomic positions using a non harmonic approach is a method to examine systems showing high dynamic or static disorder. Disorder is a major aspect in the field of solid state ionics and is directly connected to ion dynamics and transport phenomena in solid electrolytes. Based on the potential of this method, like the calculation of joint probability density functions (jpdf) and one particle potentials (opp), we try to get a better insight in the structural features of materials and their physical properties. Directly connected to this method is the 3D - visualisation and analysis of the jpdf data using modern visualization programs.

 

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