Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

 
 
Session Overview
Session
MS-98: 2D type crystals and their heterostructures
Time:
Saturday, 21/Aug/2021:
2:45pm - 5:10pm

Session Chair: Matteo Bosi
Session Chair: Adela Rodríguez-Romero
Location: Club C

50 1st floor

Invited: Eli Sutter (USA)Xinliang Feng (Germany)


Session Abstract

Low dimensional materials (graphene, transition metal dichalcogenides, black phosphorus, boron nitride, etc) are getting more and more and more attention thanks to their exceptional physical and mechanical characteristics. Recently, the possibility to combine 2D materials to form lateral and vertical Van der Waals heterostructures permitted to investigate new properties and applications for this class of materials. The scope of this microsymposium will be to cover the crystallographic, structural, optical and physical properties of all the type of 2D crystals, their heterostructures and their possible applications.


Introduction
Presentations
2:45pm - 2:50pm

Introduction to session

Matteo Bosi, Adela Rodríguez-Romero



2:50pm - 3:20pm

1D Nanowires of 2D Layered Materials: A New Frontier in Nanomaterials

Eli Sutter, Peter Sutter

University of Nebraska-Lincoln, Lincoln, United States of America

Semiconductor nanowires have mostly been synthesized from conventional three dimensional (3D) crystalline materials. Layered crystals, in which covalently bonded sheets are held together by weaker van der Waals forces, have emerged as a class of materials with extraordinary properties not found in 3D crystals. Shaping layered materials into nanowires could open up new, tunable structural, optoelectronic, and electronic transport/device characteristics.

Here, we discuss the realization of this vision, namely the synthesis and emerging properties of van der Waals nanowires of layered crystals, formed by combining the concepts of vapor-liquid-solid (VLS) growth and van der Waals epitaxy. We demonstrate the possibility of forming nanowires of germanium (II) sulfide (GeS), a 2D/layered chalcogenide semiconductorwith anisotropic structure [1], by a VLS process [2]. High-quality van der Waals nanowires crystallize with layering along the wire axis and show bright, size dependent band-edge luminescence [3], [4]. A strong propensity for forming screw dislocations, often found for layered crystals [4], introduces extraordinary properties without analogues in 3D-crystalline nanowires. Eshelby twist, induced by a torque on the ends of a cylindrical solid due to the stress field of an axial dislocation, causes a chiral structure of the layered nanowires and leads to spontaneous, size-tunable twist moiré patterns between the van der Waals layers along the wires. Using tailored growth protocols complex structures can be obtained that are impossible to realize in planar van der Waals stacks, including homojunctions between twisted (dislocated) and ordinary layered (dislocation-free) segments as well as continuously variable Eshelby twist translating into a seamless progression of helical moiré patterns [5]. Combined electron diffraction and local (nanometer-scale) optoelectronic measurements using cathodoluminescence and electron-energy loss spectroscopy show the correlation between the interlayer twist and locally excited light emission/optical absorption that is due to progressive changes in the lattice orientation and in the interlayer moiré registry along the nanowires. These findings demonstrate an avenue for the scalable fabrication of van der Waals structures with defined twist angles for the emerging field of twistronics, in which interlayer moiré patterns are realized along a helical path on a nanowire instead of a planar interface.

References

[1] E. Sutter, B. Zhang, M. Sun, P. Sutter, ACS Nano 13, 9352 (2019).

[2] E. Sutter, P. Sutter, ACS Applied Nano Materials 1, 1042 (2018).

[3] P. Sutter, C. Argyropoulos, E. Sutter, Nano Letters 18, 4576 (2018).

[4] P. Sutter, S. Wimer, E. Sutter, Nature 570, 354 (2019).

[5] P. Sutter, J.-C. Idrobo, and E. Sutter, Adv. Funct. Mater. 31, 2006412 (2021).



3:20pm - 3:50pm

Advances in organic 2D crystals

Xinliang Feng

Technische Universitaet Dresden, Dresden, Germany

Over the last decade, the discovery of graphene has triggered a new paradigm of two-dimensional (2D) crystal materials. They are characterized by a periodic network structure and topographical thickness at the atomic/molecular level, enabling the investigation of fundamental exotic physical and chemical properties down to a single-layer nanosheet. Thereby, robust technologies and industrial applications, ranging from electronics and optoelectronics to energy storage, energy conversion, membranes, sensors, and biomedicine, have been inspired by the discovery and exploration of such new materials.

In contrast to the tremendous efforts dedicated to the exploration of graphene and inorganic 2D crystals such as metal dichalcogenides, boron nitride, black phosphorus, metal oxides, and nitrides, there has been much less development in organic 2D crystalline materials, including the bottom-up organic/polymer synthesis of graphene nanoribbons, 2D metal-organic frameworks, 2D polymers/supramolecular polymers, as well as the supramolecular approach to 2D organic nanostructures. One of the central chemical challenges is to realize a controlled polymerization in two distinct dimensions under thermodynamic/kinetic control in solution and at the surface/interface. In this talk, we will present our recent efforts in bottom-up synthetic approaches towards novel organic 2D crystals with structural control at the atomic/molecular level and beyond. We will introduce a surfactant-monolayer assisted interfacial synthesis (SMAIS) method that is highly efficient to promote supramolecular assembly of precursor monomers on the water surface and subsequent 2D polymerization in a controlled manner. 2D conjugated polymers and coordination polymers belong to such materials classes. The unique structures with possible tailoring of conjugated building blocks and conjugation lengths, tunable pore sizes and thicknesses, as well as impressive electronic structures, make them highly promising for a range of applications in electronics and spintronics. Other application potential of organic 2D crystals, such as in membranes, will also be discussed.



3:50pm - 4:10pm

Crystal growth and characterisation of organic-inorganic lead-free 2D double perovskite for application in radiation sensin

Valeria Murgulov1, Catherine Schweinle2, Michael Daub1,2, Harald Hillebrecht1,2, Michael Fiederle1

1Freiburg Materials Research Center FMF, Albert-Ludwigs-Universität Freiburg, Germany; 2Institute of Inorganic and Analytical Chemistry, Faculty of Chemistry and Pharmacy, Albert-Ludwigs-Universität Freiburg, Germany

Single crystals of lead-free organic-inorganic 2D (BA)2CsAgBiBr7 with double perovskite structure (monoclinic, P21/m) exhibit a significant potential for X-ray sensing [1]. This stems from their heavy elements constituting the perovskite octahedral network that is in an alternating arrangement with the barrier layer of organic BA+ cations, consequently producing desirable electrical properties. In this study, several yellow-coloured single crystals of (BA)2CsAgBiBr7 were grown from a low-temperature solution [2]. All crystals are characterised by growth/dissolution features and defects (Figure 1). The phase purity and crystallinity of all samples have been verified from the powder XRD data. High ordering of Ag+ and Bi3+ octahedra cations is apparent from the XRD patterns for single crystals, which depict peaks arising from the {001} plane.

Results from electrical characterisation of the single crystals of (BA)2CsAgBiBr7 reveal high resistivity (1011 Wcm) and low density of trap states (1011-1012 cm-3), which are comparable to those published in literature [1]. This implies that the samples synthesised in this study also satisfy requirements for radiation sensors.

Figure 1. The top crystal surface of the sample (BA)2CsAgBiBr7_Exp1 (top right corner, 4 x 4 x 0.75 mm3) is characterised by irregular growth /dissolution features (image on the left made in reflected light, 100 mm scale bar) and defects such as twinning planes at 90o (image on the right made in transmitted light).

[1] Xu, Z., Liu, X., Li, Y., Liu, X., Yang, T., Ji, C., Han, S., Xu, Y., Luo, J., & Sun, Z. (2019). Angew. Chem. Int. Ed. 58, 15757. [2] Connor, B. A., Leppert, L., Smith, M. D., Neaton, J.B., & Karunadasa, H. I. (2018). J. Am. Chem. Soc. 140, 5235.



4:10pm - 4:30pm

Determination of stress, cracks and defects density in crystals after wafer-bonding processes: a novel HRXRD – X-ray micro CT conjoint analytical approach

Aurelio Borzì1, Robert Zboray1, Simone Dolabella1,2, Alex Dommann1, Antonia Neels1,2

1Center for X-ray Analytics, Empa, Ueberlandstrasse 129, Dubendorf, Switzerland; 2Department of Chemistry, University of Fribourg, Avenue de l'Europe 20, 1700 Fribourg, Switzerland

Functional devices such as sensors, actuators or micro-electromechanical systems (MEMS) are obtained through a large variety of microfabrication processes, many of whom affect the structure and microstructure of materials because of the introduction of stress, strain, crystalline defects and volume-cracks. The materials degradation originated by these effects may translate into a lack of performance and reliability of the final devices. Indeed, in the frame of the microfabrication industry, controlling the structure of materials at the micrometer and nanometer scale represents a fundamental objective toward the optimization of the microfabrication process itself and achievement of improved devices' performance and lifetime.

In this work, we studied the influence of an innovative wafer bonding process, namely Impulse Current Bonding (ICB), in principle enabling low-temperature bonding between a wide class of materials, on the degradation of SCSi, SC-sapphire and borosilicate glass structures and crystallinity. A comprehensive frame of the microstructural deterioration at different size scales is obtained by a correlative approach between high-resolution X-ray diffraction (HRXRD) and X-ray micro-computed tomography (CT). In particular, micro CT revealed the formation of large cracks with thickness in the order of tens of microns generated to release the high stress at the bonding interface. In parallel, strain and tilt affecting the SCSi crystallinity due to the presence of defects at the nanoscale dimension are revealed by HRXRD methods, such as the mapping of the reciprocal space (RSM), radial scans (i.e., 2θ/θ) and angular scans (i.e., ω-scans or rocking curves) of symmetrical and asymmetrical reflections. The residual stress after the bonding process is also calculated from the in-plane and out-of-plane X-ray strain. The effectiveness and strength of the bonding are also assessed by our approach and compared to the conventional wafer bonding technologies, i.e., the anodic bonding.

We aim to present here a unique approach to the evaluation of the structural and crystalline degradation of materials involved in wafer bonding microfabrication processes. The combination of X-ray micro CT with HRXRD enables a holistic evaluation of the bonding between SCSi, sapphire and borosilicate glass wafers achieved exploiting an innovative low-temperature process, namely ICB. This allows the correlation between the micrometer scale and volumetric defect detection (voids and cracks) with atomic-level strain and defect analysis.



4:30pm - 4:50pm

Crystallography online by the Bilbao Crystallographic Server: new computer tools for the study of layer and multi-layer materials

Gemma de la Flor1, Emre Tasci2, Luis Elcoro3, Gotzon Madriaga3, Juan Manuel Perez-Mato3, Yuri E. Kitaev4, Robert Evarestov5, Mois I. Aroyo3

1Institute of Applied Geosciences, Karlsruhe Institute of Technology, Karlsruhe, Germany; 2Department of Physics Engineering, Hacettepe University, Ankara, Turkey; 3Departamento de Física de la Materia Condensada, Universidad del País Vasco UPV/EHU, Leioa, Spain; 4Laboratory of Quantum-size Heterostructures, Ioffe Institute, Saint Petersburg, Russia; 5Institute of Chemistry, Saint Petersburg State University, Saint Petersburg, Russia

The interest in layered and multi-layered materials such as graphene and van der Waals crystals, e.g. the transition metal dichalcogenide crystal family, is constantly growing owing to their interesting properties and possible technological applications. The symmetry of single monolayers can be described by the so-called layer groups, which are three-dimensional crystallographic groups with two-dimensional translations. Due to the arising interest in these type of materials, new programs dedicated to the study of materials with layer and multilayer symmetry have been developed and implemented in the Bilbao Crystallographic Server (www.cryst.ehu.es) [1,2]. The server is in constant improvement and development, offering free of charge tools to study an increasingly number of crystallographic systems which now also includes the ones with layer symmetry.

The section dedicated to Subperiodic groups in the Bilbao Crystallographic Server gives access to the layer groups databases which contains the basic crystallographic information of the 80 layer groups (generators, general positions, Wyckoff positions and maximal subgroups) [3] and the Brillouin zone and k-vectors tables that form the background and classification of the irreducible representations of layer groups which can also be calculated with one of the programs available in the server. More sophisticated programs to identify the layer symmetry of periodic sections and to describe the electronic structure and surface states of crystals [4] are also available. The symmetry relations between the localized state (atomic displacements) and extended states (phonon, electrons) over the entire Brillouin zone can also be calculated. The utility of the available applications will be demonstrated by illustrative examples.