MBE growth and advanced characterization of large-scale van der Waals heterostructures

• Applicant: Dr. Joao Marcelo Jordao Lopes
• Subject Area: Experimental Condensed Matter Physics ; Synthesis and Properties of Functional Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545820811

The concept of van der Waals (vdW) heterostructure have emerged as a promising way to design new two-dimensional (2D) metamaterials with new hybrid properties. Stacking different 2D crystals promotes synergistic effects that generate unprecedented new functionalities. Up to date, a large variety of exotic properties have been investigated in vdW heterostructures assembled by stacking exfoliated flakes. A technological lock for their realistic integration into applications lies in their limited size and production compatibility. Any industrial application will require a scalable approach to the vdW assembly. Thus, the large-scale realization of single-crystalline vdW heterostructures is a crucial step towards their ultimate applications. In 2D-CHARM, we will develop the direct synthesis of large-scale and highly crystalline vdW heterostructures using molecular beam epitaxy (MBE). They will be composed of the 2D insulator hexagonal boron nitride (hBN) and 2D ferroelectric materials (2D-FEs, either SnSe or In2Se3). Such 2D-FEs/hBN heterostructures are very promising building blocks for different applications including ultra-compact non-volatile ferroelectric memories and artificial multiferroics. The growth development will be strongly supported by the advanced characterization providing a complete structural information. Our analytical approach will range from the millimeter down to the atomic scale, using state-of-the-art techniques based on scanning transmission electron microscopy (STEM). In particular, four-dimensional (4D)-STEM will be used to obtain full-sets of structural information, which will be combined with results from other conventional techniques including X-ray diffraction. Moreover, 4D-STEM allows phase retrieval methods giving access to atomic distortion together with local electrostatic field at the atomic scale. Hence, employing atomic resolution 4D-STEM on the 2D-FEs/hBN heterostructures will enable unveiling the relationship between the precise structural properties and related local polarizations explored by piezo-response force microscopy and Kelvin probe force microscopy in configurations that can be directly integrated into device structures. The final goal of this project is to realize a large-scale and high quality vdW stacking of 2D-FEs/hBN by MBE growth. For this, we will address three ambitious challenges: i) growth of high-quality and large-scale hBN multilayers; ii) controlled growth of 2D FEs on the synthesized hBN; iii) fundamental understanding of the properties of 2D FEs/hBN heterostructures. In the project, we will assemble the complementary expertise of the partners, which are essential to achieve the objectives. In particular, an efficient feedback between MBE growth and advanced characterization will boost the development of large-scale hBN and 2D FEs by MBE.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Co-Investigators: Privatdozent Dr. Michael Hanke; Dr. Jonas Laehnemann
• Cooperation Partners: Dr. Matthieu Jamet; Dr. Hanako Okuno