Advanced Electron Microscopy Division

The mission of the European Research Council (ERC) funded Advanced Electron Microscopy (AEM) Division at TU Darmstadt is to establish atomic-scale structure-property correlations in functional materials and devices. Based on our expertise in aberration-corrected scanning transmission electron microscopy for atomic-resolution imaging and analysis in Materials Science, we aim to develop and apply state-of-the-art in situ/operando (S)TEM for stimuli-based studies ( i.e. temperature, electrical biasing, gas and cooling). A further direction will be the implementation and application of 4D-STEM. We have also a strong interest in big data analysis for EM. The group has a broad international collaborations network in Science and Industry.

Our group is located in the research field M+M (Matter and Materials) of the TU Darmstadt.

Prof. Molina-Luna is Head of the In Situ Microstructural Analytics Lab (InSituLab) of the Center for Reliability Analytics (CRA), TU Darmstadt

Picture: Rahel Welsen

Head of the Division

Prof. Dr. Leopoldo Molina-Luna Tel. +49 6151 16-20180 Fax. +49 6151 16-20185 Peter-Grünberg-Straße 2 D- 64287 Darmstadt Raum: L2|01 52

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Latest news

July 12, 2024

First TU researcher with four ERC grants

Machine learning for electron microscopy: Leopoldo Molina-Luna receives EU funding

July 16, 2024

We congratulate Robert Winkler on his successful doctoral examination

June 26, 2024

Thanks to the MISTI Funds for Promoting Exchange

June 27, 2024

Best Oral Presentation Awards at MRS Spring 2024

Best Oral Presentation Awards at MRS Spring 2024 for Robert Winkler and Tianshu Jiang

March 19, 2024

Cover art for Nano Letters

About the Cover

February 23, 2024

Weld-free mounting of lamellae for electrical biasing operando TEM

Weld-free mounting of lamellae for electrical biasing operando TEM

February 07, 2024

Texture Transfer in Dielectric Layers via Nanocrystalline Networks: Insights from in Situ 4D-STEM

Texture Transfer in Dielectric Layers via Nanocrystalline Networks: Insights from in Situ 4D-STEM

December 20, 2023

Article featured in Communications Engineering:

Operando two-terminal devices inside a transmission electron microscope

December 20, 2023

The first MerlinEM User Meeting

The first MerlinEM User Meeting

March 01, 2024

Harald Rose Prize for Dr. Alexander Zintler

Award for outstanding doctoral thesis in the field of electron microscopy

Current Highlights

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Ongoing Projects

EU Projects: - FOXON - STARE

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Opening of the iJRL Memristor Technology and NCKU-TUDa Workshop on Memristor Technology -from material to energy efficient computing

Prof. Molina-Luna was part of the TUDa delegation to Taiwan and delivered a talk at the NCKU-TUDa Workshop.

The iJRL „Memristor Technology“ pursues the goal to progress on relevant aspects of the fundamentals, technology and exploitation of memristive devices. It addresses the materials properties and defect structure of several kinds of memristor realizations based on oxide, magnetic and ferroelectric materials. From the application side, it covers several novel computing schemes using memristors to increase energy efficiency, including field programmable gate arrays (FPGAs), neuromorphic computation and processing-in-memory. From the analysis and modelling side, a unique selling point is to encompass all relevant scales from density functional theory, multi-phase and compact modelling as well as circuit design. The experimental analysis correlates advanced transmission electron microscopy (TEM) methods with physical models used for compact simulation of model device and array behavior. Thereby, the iJRL establishes a methodology from innovative materials to single devices and arrays up to the circuit level that can be transferred to novel emerging materials in this fast-developing field also for interested partners in the field of electronic material and semiconductor industry.

Quantum Detectors and NanoMEGAS seminar with Technische Universität Darmstadt (Advanced Electron Microscopy Division)

Tuesday 28th February 2023 at 4pm – 6pm

Quantum Detectors and NanoMEGAS would like to invite you to a seminar and a live demonstration of the MerlinEM and NanoMEGAS DigiSTAR precession hardware showcasing 4D STEM and precession in association with Technische Universität Darmstadt (TU Darmstadt).

This event will see talks from all three institutions, Quantum Detectors, NanoMEGAS and TU Darmstadt. Prof. Dr. Leopoldo Molina-Luna's group will give a live demonstration of their JEOL ARM-200F showing the capabilities of the MerlinEM alongside the NanoMEGAS DigiSTAR precession hardware. You will also be granted VIP behind-the-scenes access to view the TU Darmstadt lab and the JEOL ARM-200F.

This will run alongside those attending the Microscopy Conference in Darmstadt and as a virtual event in case you cannot make it to Darmstadt. Quantum Detectors will also be exhibiting at MC Darmstadt 2023.

We hope to see you there. Sign up below!

Sign up link: https://forms.gle/DLvF2onJV49WmiVG8

Poster Prize for Physical Sciences at the Princeton-Nature 2nd Frontiers in Electron Microscopy for Physical and Life Sciences Conference 2022

This certificate is in recognition of the poster prize awarded to Leopoldo Molina-Luna at the 2nd Frontiers in Electron Microscopy for Physical and Life Sciences Princeton-Nature conference, held Sept 28-30 2022. In recognition of a flash talk and poster presentation of his lab’s work, Leopoldo was provided with a 1 year subscription to Nature, the international journal of science.

OPERANDO TWO-TERMINAL DEVICES INSIDE A TRANSMISSION ELECTRON MICROSCOPE

Oscar Recalde-Benitez1, Tianshu Jiang1, Robert Winkler1, Alexander Zintler1, Yating Ruan2, Esmaeil Adabifiroozjaei1, Alexey Arzumanov2, Tijn van Omme3, William A. Hubbard4,5 Yevheniy Pivak3, Hector H. Perez-Garza3, B. C. Regan 4,5, Philipp Komissinskiy2, Lambert Alff2 and Leopoldo Molina-Luna1*

1. Advanced Electron Microscopy Division, Department of Materials- and Earth Science, Technical University of Darmstadt, Darmstadt, Hessen, Germany.

2. Advanced Thin Film Technology Division, Department of Materials- and Earth Science,Technical University of Darmstadt, Darmstadt, Hessen, Germany.

3. DENSsolutions, Delft, Netherlands.

4. NanoElectronic Imaging, Inc., Los Angeles, CA, USA.

5. University of California, Los Angeles and the California NanoSystems Institute, Los Angeles, USA.

Our Recent Publications

Controlling the Formation of Conductive Pathways in Memristive Devices (Adv. Sci. 33/2022)

Memristive Devices Sketch of oxygen vacancy segregation toward a specific grain boundary in a hafnia (Hf) based memristor. The orange pillars correspond to atomic positions of Hf calculated based on transmission electron microscopy imaging. The water symbolizes oxygen vacancies attracted (through a waterfall) to the grain boundary region (canyon), which will then form the speedway (Autobahn) of the filamentary conductive current. More details can be found in article number 2201806 by Leopoldo Molina-Luna, Lambert Alff, and co-workers.

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Structural and Electrical Response of Emerging Memories Exposed to Heavy Ion Radiation

Hafnium oxide- and GeSbTe-based functional layers are promising candidates in material systems for emerging memory technologies. They are also discussed as contenders for radiation-harsh environment applications. Testing the resilience against ion radiation is of high importance to identify materials that are feasible for future applications of emerging memory technologies like oxide-based, ferroelectric, and phase-change random-access memory. Induced changes of the crystalline and microscopic structure have to be considered as they are directly related to the memory states and failure mechanisms of the emerging memory technologies. Therefore, we present heavy ion irradiation-induced effects in emerging memories based on different memory materials, in particular, HfO2-, HfZrO2-, as well as GeSbTe-based thin films. This study reveals that the initial crystallinity, composition, and microstructure of the memory materials have a fundamental influence on their interaction with Au swift heavy ions. With this, we provide a test protocol for irradiation experiments of hafnium oxide- and GeSbTe-based emerging memories, combining structural investigations by X-ray diffraction on a macroscopic, scanning transmission electron microscopy on a microscopic scale, and electrical characterization of real devices. Such fundamental studies can be also of importance for future applications, considering the transition of digital to analog memories with a multitude of resistance states.

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Controlling the Formation of Conductive Pathways in Memristive Devices

Resistive random-access memories are promising candidates for novel computer architectures such as in-memory computing, multilevel data storage, and neuromorphics. Their working principle is based on electrically stimulated materials changes that allow access to two (digital), multiple (multilevel), or quasi-continuous (analog) resistive states. However, the stochastic nature of forming and switching the conductive pathway involves complex atomistic defect configurations resulting in considerable variability. This paper reveals that the intricate interplay of 0D and 2D defects can be engineered to achieve reproducible and controlled low-voltage formation of conducting filaments. The author find that the orientation of grain boundaries in polycrystalline HfOx is directly related to the required forming voltage of the conducting filaments, unravelling a neglected origin of variability. Based on the realistic atomic structure of grain boundaries obtained from ultra-high resolution imaging combined with first-principles calculations including local strain, this paper shows how oxygen vacancy segregation energies and the associated electronic states in the vicinity of the Fermi level govern the formation of conductive pathways in memristive devices. These findings are applicable to non-amorphous valence change filamentary type memristive device. The results demonstrate that a fundamental atomistic understanding of defect chemistry is pivotal to design memristors as key element of future electronics.

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Enhanced Conductivity and Microstructure in Highly Textured TiN1–x/c-Al2O3 Thin Films

Titanium nitride thin films are used as an electrode material in superconducting (SC) applications and in oxide electronics. By controlling the defect density in the TiN thin film, the electrical properties of the film can achieve low resistivities and a high critical temperature (Tc) close to bulk values. Generally, low defect densities are achieved by stoichiometric growth and a low grain boundary density. Due to the low lattice mismatch of 0.7%, the best performing TiN layers are grown epitaxially on MgO substrates. Here, we report for the first time a Tc of 4.9 K for ultrathin (23 nm), highly textured (111), and stoichiometric TiN films grown on 8.75% lattice mismatch c-cut Al2O3 (sapphire) substrates. We demonstrate that with the increasing nitrogen deficiency, the (111) lattice constant increases, which is accompanied by a decrease in Tc. For highly N deficient TiN thin films, no superconductivity could be observed. In addition, a dissociation of grain boundaries (GBs) by the emission of stacking faults could be observed, indicating a combination of two sources for electron scattering defects in the system: (a) volume defects created by nitrogen deficiency and (b) defects created by the presence of GBs. For all samples, the average grain boundary distance is kept constant by a miscut of the c-cut sapphire substrate, which allows us to distinguish the effect of nitrogen deficiency and grain boundary density. These properties and surface roughness govern the electrical performance of the films and influence the compatibility as an electrode material in the respective application. This study aims to provide detailed and scale-bridging insights into the structural and microstructural response to nitrogen deficiency in the c-Al2O3/TiN system, as it is a promising candidate for applications in state-of-the-art systems such as oxide electronic thin film stacks or SC applications.

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Birth of a grain boundary: In situ TEM Observation of the Microstructure Evolution in HfO2 Based Memristors

ACOM orientation + index mapping of a TiN/HfO2/Pt Metal-Insulator-Metal stack shows no contrast for HfO2 in the a) pristine device due to no preferred orientation (amorphous) and grain boundaries in HfO2 interconnecting the metals in the b) in situ annealed device. The formation of a grain boundary was monitored in situ by using TEM c-h): at 160°C crystallization starts with two grains at the edges of the image growing towards each other perpendicular to the layer interfaces and fully merge after 90 minutes. The white hatched line is a guide to the eye to illustrate grain borders. Scale bar is 10 and 5 nm in b) and h) respectively. TEM images were colored with the split black/blue red/white LUT.

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Epitaxy Induced Highly Ordered Sm2Co17–SmCo5 Nanoscale Thin-Film Magnets

Utilizing the molecular beam epitaxy technique, a nanoscale thin-film magnet of c-axis-oriented Sm2Co17 and SmCo5 phases is stabilized. While typically in the prototype Sm(Co, Fe, Cu, Zr)7.5–8 pinning-type magnets, an ordered nanocomposite is formed by complex thermal treatments, here, a one-step approach to induce controlled phase separation in a binary Sm–Co system is shown. …..

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Forming-Free Grain Boundary

05 August 2019, Advanced Electronic Materials

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Neuromorphic Computing: Tailoring the Switching Dynamics in Yttrium Oxide‐Based RRAM Devices by Oxygen Engineering

For neuromorphic computing that mimics the human brain, digital memory has to turn analogue. A key scientific question is how to teach materials to adopt synaptic plasticity. Using the novel technique of oxygen engineering on yttrium oxide shows that this particular material is a prominent candidate to allow for controlling and fine‐tuning switching dynamics.

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In Situ Transmission Electron Microscopy Analysis of Thermally Decaying Polycrystalline Platinum Nanowires

ACS Nano 2020, 14, 9, 11309–11318

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