In principle, layer transfer allows the combination of crystalline materials without thermodynamic, kinetic or geometric constraints (lattice mismatch, crystal symmetry, combination of different thermodynamic phases, (de-)wetting properties), limiting classical bulk crystal growth or thin film epitaxy. In this way, layer transfer could set a new paradigm in fabricating innovative crystalline heterostructures with tailor-made properties. In particular for 2D-crystals such as graphene, transition metal di-chalcogeneides (TMDC) or hexagonal boron nitride (hBN), it has been demonstrated that specific material properties could be achieved merely by particular way of stacking order and orientation of individual layers. Such artificial heterostructures can often only be realized via layer transfer and not via established crystal growth. Therefore, layer transfer has established itself as a new "bottom-up" method for the construction of novel "2D goes 3D" materials and represents a fundamentally new synthesis path of crystalline materials.

We see our strategic cooperation "Layer transfer for 2D heterolayers" as an integral part of the overarching efforts towards material sovereignty and we aim to make a significant contribution to the development of quantum materials in the Berlin area.

A successful cooperation is promised by the complementary expertise of the Layer Transfer working group of Dr. Martin and the AG HYD of Prof. List-Kratochvil, which offers natural synergy effects and an ideal basis for scientific exchange and the development of new research projects.

Leibniz-Institut für Kristallzüchtung (IKZ)
Coordination: Dr. Jens Martin
https://www.ikz-berlin.de/forschung-lehre/nanostrukturen-schichten/sektion-halbleiternanostrukturen#c1493

IRIS-Adlershof
Coordination: Dr. Sylke Blumstengel
Hybrid Devices Group, Institut für Physik, Institut für Chemie & IRIS Adlershof
http://www.hyd.iris-adlershof.de/

Dielectric oxide layers and 2D materials with their plethora of functional properties are in the focus of worldwide research to understand their physical properties on the atomic – scale and to engineer their functional characteristics for future device applications. However, the complexity of these materials systems in terms of synthesis, thin film deposition, characterization as well as device processing and integration steps often exceeds the capacities available at individual laboratories. Hence, IKZ and Jiaotong University in Xi´an decided to establish a joint lab and benefit from synergies in complementary research activities and student education. Online lectures, exchange of PhD students and international workshops will be undertaken to promote the common goals. Currently, research focuses on the development of lead-free ferro-/piezoelectric layers for green technology in application areas like sensing & energy harvesting e.g. for the future Internet of Things (IoT). Furthermore, the fundamental physics and processing steps of 2D materials are investigated with the perspective to engineer future functional 3D crystals through advanced layer-by-layer transfer processes.

Xi'an Jiaotong-Universität:
Head: Prof. Gang Niu
Prof. Gang Niu´s webpage:  http://gr.xjtu.edu.cn/web/gangniu
International School on Dielectics: http://esteie.xjtu.edu.cn/ 

IKZ:
Head: Dr. Jutta Schwarzkopf
Section: Nano Structures & Layers / Thin Oxide Films
Dr. Jens Martin
Section: Nano Structures & Layers / Thin Oxide Films / Topic: „2D goes 3D” by Layer Transfer

Electron microscopy is the most versatile technique to obtain correlated information on structural and physical properties of solids with high spatial resolution. Transmission electron microscopy and scanning transmission electron microscopy made tremendous methodological advances in the last years. Due to the possibility to realize abberation corrected lenses true atomic resolution can be obtained with a resolution to 0.05 nm and a precision in the pm range. Analytical methods now allow for atomic resolution chemical mapping and electron loss spectroscopy achieves energy resolution that competes with that achievable in synchrotrons. The development of fast cameras with single electron sensitivity and sample holders that allow to follow processes in situ under biasing, at high temperature and under ambient pressure.

JEMA joins latest equipment in structural and analytical electron microscopy. While IKZ provides an aberration corrected (S)TEM (FEI Titan 80-300) equipped with a fast CETA2 camera (up to 400 frames per second) and latest in-situ holders that allow for operation under biasing and heating (Protochips Fusion) and at various gas atmosphere up to atmospheric pressure and temperatures up to 1000°C, Humboldt-Universität provides its (S)TEM with energy dispersive spectroscopy and energy loss spectroscopy.

The Leibniz-Institut für Kristallzüchtung in addition to transmission electron microscopes provides two scanning electron microscopes among them a fully analytical Dual Beam microscope (FEI Nova 600) that allows for structuring samples by an ion beam, and preparing electron transparent lamella from selected areas of a sample and lifting them out for further analysis in the TEM. This microscope provides in addition energy dispersive and wavelength spectroscopy and electron backscatter diffraction. A second, latest generation SEM Thermo Fisher Apreo S with three in-lens detectors and a STEM detector is equipped with a He cooling stage and a Gatan Monarc CL system to study optical properties of semiconductors.

JEMA has been the first joint activity in the field of electron microscopy in Adlershof. A similar centre exists now between Helmholtz Zentrum Berlin und HU Berlin in the field of cryomicroscopy. Other joint labs are on the way, all of them offering complementary equipment, thus making the Campus Adlershof a true centre for electron microscopy in Berlin. 

The IKZ research group X-Ray Optics and DESY Nanolab operate a joint laserlab for time-resolved ultrafast spectroscopy at the IKZ-DESY Joint Lab. The setup is open for experimental characterization of IKZ materials and methods using various optical techniques. IN addition, the lab is used for preparation experiments for synchrotron beamtimes.

The goal of this collaboration is to achieve thin films of complex oxides with drastically improved electronic properties or that exhibit spectacular phenomena. Our approach is to target systems for study where appropriate substrates are needed to enhance properties or unleash novel phenomena in the overlying complex oxide film. The electronic properties and phenomena of interest include superconductivity, ferroelectricity, ferromagnetism, antiferromagnetism, piezoelectricity, pyroelectricity, multiferroicity, metal-insulator transitions, catalysis, electrical mobility, high spin polarization, thermoelectricity, non-linear optical, magnetoelectric, magneto-optic, and magnetothermal effects. Complex oxides are record holders for many of these behaviors. In many cases thin films with properties comparable to a desired complex oxide in bulk form have not been achieved because of the lack of an appropriate substrate, for example, when there are no commercial isostructural substrates with good lattice match.

This is the case for many perovskites, pyrochlores, magnetoplumbites and many other complex oxides, where there are no commercial substrates whatsoever with these structures. Our collaboration includes both types of substrate needs: more ideal substrates for the stable polymorph of complex oxides with stellar properties that have not been achieved in thin film form and substrates enabling the growth of metastable polymorphs of oxides. The latter approach was verified by a joint experiment published by Haeni et al. (2004) that ignited a fury of research in the strain-engineering of complex oxides.

Leibniz-Institut für Kristallzüchtung (IKZ):
Coordination: Dr. Christo Guguschev
Section: Oxides & Fluorides / Substrate Crystals for Advanced Functional Oxides

Cornell University:
Coordination: Prof. Darrell G. Schlom
Herbert Fisk Johnson Professor of Industrial Chemistry in the Department of Materials Science & Leibniz Chair at IKZ
Cornell Webpage: http://schlom.mse.cornell.edu/
Leibniz Chair: https://www.leibniz-gemeinschaft.de/ueber-uns/international/leibniz-chairs.html

J. H. Haeni, P. Irvin, W. Chang, R. Uecker, P. Reiche, Y. L. Li, S. Choudhury, W. Tian, M. E. Hawley, B. Craigo, A. K. Tagantsev, X. Q. Pan, S. K. Streiffer, L. Q. Chen, S. W. Kirchoefer, J. Levy & D. G. Schlom
Room-temperature ferroelectricity in strained SrTiO₃
Nature
DOI: https://doi.org/10.1038/nature02773

K.J. Choi, M.D. Biegalski, Y.L. Li, A. Sharan, J. Schubert, R. Uecker, P. Reiche, Y.B. Chen, X.Q. Pan, V. Gopalan, L.-Q. Chen, D.G. Schlom, and C.B. Eom
Enhancement of Ferroelectricity in Strained BaTiO₃ Thin Films
Science
DOI: https://doi.org/10.1126/science.1103218

J.H. Lee, L. Fang, E. Vlahos, X. Ke, Y.W. Jung, L.F. Kourkoutis, J-W. Kim, P.J. Ryan, T. Heeg, M. Roeckerath, V. Goian, M. Bernhagen, R. Uecker, P.C. Hammel, K.M. Rabe, S. Kamba, J. Schubert, J.W. Freeland, D.A. Muller, C.J. Fennie, P. Schiffer, V. Gopalan, E. Johnston-Halperin, and D.G. Schlom
A Strong Ferroelectric Ferromagnet Created by means of Spin-Lattice Coupling
Nature
DOI: https://doi.org/10.1038/nature10219

D. G. Schlom, L. Chen, C. J. Fennie, V. Gopalan, D. A. Muller, X. Pan, R. Ramesh and R. Uecker
Elastic strain engineering of ferroic oxides
MRS BULLETIN
DOI: https://doi.org/10.1557/mrs.2014.1

N.M. Dawley, E.J. Marksz, A.M. Hagerstrom, G.H. Olsen, M.E. Holtz, V. Goian, C. Kadlec, J. Zhang, X. Lu, J.A. Drisko, R. Uecker, S. Ganschow, C.J. Long, J.C. Booth, S. Kamba, C.J. Fennie, D.A. Muller, N.D. Orloff, and D.G. Schlom
Targeted Chemical Pressure Yields Tunable Millimetre-Wave Dielectric
Nature Materials
DOI: https://doi.org/10.1038/s41563-019-0564-4

C. Guguschev, D. Klimm, M. Brützam, T.M. Gesing, M. Gogolin, H. Paik, A. Dittmar, V.J. Fratello, D.G. Schlom
Single crystal growth and characterization of Ba₂ScNbO₆ – A novel substrate for BaSnO₃ films
DOI: https://doi.org/10.1016/j.jcrysgro.2019.125263

A patent application is ongoing (US reference number: 16/424,987)

This includes the deposition and characterization of single-crystalline, oxide layers with low defect density and defined electrical and structural properties tuned by doping and lattice strain. In order to achieve a high structural perfection of the layers, the section "Thin Oxide Films" uses the method of metal-organic vapor phase epitaxy (MOVPE), which is already the deposition method of choice in industry due to its scaling potential. In the application laboratory we are looking for synergies especially with regional academic and industrial partners.

At the IKZ, measurements are performed in particular with "Inductively Coupled Plasma Optical Emission Spectroscopy" (ICP-OES) and x-ray fluorescence analysis (XRF). Prior to the actual ICP-OES measurement, the materials to be measured must first be digested using a suitable method, which must be developed specifically for each material and impurity. Usually this involves grinding and microwave digestion in acidic or basic solution. XRF measurements are mainly used for the planar visualization of composition and impurities with a resolution of 25 µm. The core competence of IKZ is the measurement of oxidic (e.g. Ga₂O₃, REScO₃) and fluoridic (CaF, KTF) materials.

On request, the IKZ also offers measurement services for external customers for the materials mentioned above.

For structural and optical characterization, wafers or longitudinal sections with polished surfaces are typically produced and then etched or irradiated. For the production of the required surface quality, several laboratory polishing machines are available on which polishing can be carried out with different polishing agents using purely mechanical but also chemical-mechanical processes. For laser applications, 3D samples are also required for which exact angles of the sample surfaces to each other must be realized. In addition to precise sawing and polishing machines, x-ray and laser measuring devices are available for this purpose, with which the samples can be precisely aligned before processing.

On request, the IKZ also offers processing services for external customers for the materials mentioned above.

Thin films are often employed in devices in which large electric fields are present and where local defects can affect device performance drastically. Microscopically small contacts minimize the chances of device failure and provide good statistics. Another application of lithography is the electrical characterization of exfoliated 2D-crystals as they have only microscopic lateral dimensions. Due to the irregular shape of the crystals, contact patterns must be designed individually.

Hao Chen, Pinjia Zhou, Jiawei Liu, Jiabin Qiao, Barbaros Oezyilmaz, Jens Martin
Gate controlled valley polarizer in bilayer graphene
Nature Communications
DOI: 10.1038/s41467-020-15117-y