Articles and Theses – 2021

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2021

Articles | Theses

Articles

Hans C. Hendrikse, Stivell Hémon-Charles, Lukas Helmbrecht, Eliane P. van Dam, Eric C. Garnett, Willem L. Noorduin, Shaping tin nanocomposites through transient local conversion reactions, Crystals Growth & Design, 2021, 21, 8, 4500-4505.

Affiliations
o AMOLF, Science Park 104, Amsterdam, 1098XG The Netherlands.
o École Polytechnique l’Université de Nantes, 44035 Nantes, France.
o Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1090 GD Amsterdam, The Netherlands.

Shape-preserving conversion offers a promising strategy to transform self-assembled structures into advanced functional components with customizable composition and shape. Specifically, the assembly of barium carbonate nanocrystals and amorphous silica nanocomposites (BaCO3/SiO2) offers a plethora of programmable threedimensional (3D) microscopic geometries, and the nanocrystals can subsequently be converted into functional chemical compositions, while preserving the original 3D geometry. Despite this progress, the scope of these conversion reactions has been limited by the requirement to form carbonate salts. Here, we overcome this limitation using a single-step cation/anion exchange that is driven by the temporal pH change at the converting nanocomposite. We demonstrate the proof of principle by converting BaCO3/SiO2 nanocomposites into tin-containing nanocomposites, a metal without a stable carbonate. We find that BaCO3/SiO2 nanocomposites convert in a single step into hydroromarchite nanocomposites (Sn3(OH)2O2/SiO2) with excellent preservation of the 3D geometry and fine features. We explore the versatility and tunability of these Sn3(OH)2O2/SiO2 nanocomposites as a precursor for functional compositions by developing shape-preserving conversion routes to two desirable compositions: tin perovskites (CH3NH3SnX3, with X = I or Br) with tunable photoluminescence (PL) and cassiterite (SnO2)—a widely used transparent conductor. Ultimately, these findings may enable integration of functional chemical
compositions into advanced morphologies for next-generation optoelectronic devices

Hans C. Hendrikse, Alejo Aguirre, Arno van der Weijden, Anne S. Meeussen, Fernanda Neira D’Angelo, Willem L. Noorduin, Rational design of bioinspired nanocomposites with tunable catalytic activity, Crystals Growth & Design, 2021, 21, 8, 4299–4304.

Affiliations
o AMOLF, Science Park 104, Amsterdam, 1098XG The Netherlands.
o Laboratory of Chemical Reactor Engineering, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
o Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands.
o Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1090 GD Amsterdam, The Netherlands.

Biological assembly processes offer inspiration for ordering building blocks across multiple length scales into advanced functional materials. Such bioinspired strategies are attractive for assembling supported catalysts, where shaping and structuring across length scales are essential for their performance but still remain tremendously difficult to achieve. Here, we present a simple bioinspired route toward supported catalysts with tunable activity and selectivity. We coprecipitate shape-controlled nanocomposites with large specific surface areas of barium carbonate nanocrystals that are uniformly embedded in a silica support. Subsequently, we exchange the barium carbonate to cobalt while preserving the nanoscopic layout and microscopic shape, and demonstrate their catalytic performances in the Fischer–Tropsch synthesis as a case study. Control over the crystal size between 10 and 17 nm offers tunable activity and selectivity for shorter (C5–C11) and longer (C20+) hydrocarbons, respectively. Hence, these results open simple, versatile, and scalable routes to tunable and highly reactive bioinspired catalysts.

I. Baglai, S.W. van Dongen, M. Leeman, R.M. Kellogg, B. Kaptein, W.L. Noorduin, Counteracting Enantiospecific Behavior of Tailor-Made Additives During Chiral Symmetry Breaking: Growth Inhibition versus Solid-Solution Formation, Israel Journal Chemistry, 2021, 61, 1–6.

G. Grimaldi, D. Anthony, L. Helmbrecht, A. van der Weijden, S. van Dongen, I. Schuringa, J. Borchert, E. Alarcón-Lladó, A. Rao, W. L. Noorduin, B. Ehrler, Microstructuring of 2D perovskites via ion-exchange fabrication, Applied Physics Letters, 2021, 119, 223102

M.H. Bistervels, M. Kamp, H. Schoenmakers, A.M. Brouwer, W.L. Noorduin, Light-controlled nucleation and shaping of self-assembling nanocomposites, Advanced Materials, 2021, 1-7, 2107843

A.V. Mader, L. Helmbrecht, W.L. Noorduin, Multi-layered Barium and Strontium Carbonate Structures Induced by the Small Organic Dye Acid Orange 7, Crystal Growth & Design, 2021, 21, 6349–6356.

J. Jung, R.L.M. Op het Veld, R. Benoist, O.A.H. van der Molen, C. Manders, M.A. Verheijen, E.P.A.M. Bakkers, Universal Platform for Scalable Semiconductor-Superconductor Nanowire Networks, Advanced Functional Materials, 2021, 31, 2103062.

E. M. T. Fadaly, A. Marzegalli, Y. Ren; L. Sun; A. Dijkstra, D. De Matteis, E. Scalise; A. Sarikov; M. De Luca, R. Rurali, J.E.M. Haverkort, S. Botti, L. Miglio, E. P. A. M. Bakkers, M.A. Verheijen, Unveiling Planar Defects in Hexagonal Group IV Materials. Nano Letters 21(2021), No. 8, 3619-3625.

Roberto Bergamaschini, Rianne C. Plantenga, Marco Albani, Emilio Scalise, Yizhen Ren, Håkon Ikaros T. Hauge, Sebastian Kölling, Francesco Montalenti, Erik P.A.M. Bakkers, Marcel A. Verheijen, Leo Miglio, Prismatic Ge-rich inclusions in the hexagonal SiGe shell of GaP-Si-SiGe nanowires by controlled faceting, Nanoscale, 2021, 13, 9436-9445

K. Arts, H. Thepass, M.A. Verheijen, R.L. Puurunen, W.M.M. Kessels, H.C.M. Knoops, Impact of Ions on Film Conformality and Crystallinity during Plasma-Assisted Atomic Layer Deposition of TiO2, Chemistry of Materials, 2021, 33, 13, 5002-5009

Hanglong Wu, Teng Li, Sai P. Maddala, Zafeiris J. Khalil, Rick R. M. Joosten, Brahim Mezari, Emiel J. M. Hensen, Gijsbertus de With, Heiner Friedrich, Jeroen A. van Bokhoven, Joseph P. Patterson, Studying Reaction Mechanisms in Solution Using a Distributed Electron Microscopy Method, ACS Nano 2021, 15, 10296−10308.

Mark M.J. van Rijt, Sjoerd W. Nooteboom, Arno van der Weijden, Willem L. Noorduin, Gijsbertus de With, Stability-limited ion-exchange of calcium with zinc in biomimetic hydroxyapatite, Materials & Design, 2021, 207, 109846.

Giulia Mirabello, Matthew GoodSmith, Paul H. H. Bomans, Linus Stegbauer, Derk Joester, Gijsbertus de With, Iron phosphate mediated magnetite synthesis: a bioinspired approach, Chem. Sci., 2021, 12, 9458.

Bernette M. Oosterlaken, Mark M. J. van Rijt, Rick R. M. Joosten, Paul H. H. Bomans, Heiner Friedric, and Gijsbertus de With, Time-Resolved Cryo-TEM Study on the Formation of Iron Hydroxides in a Collagen Matrix, ACS Biomater. Sci. Eng. 2021, 7, 3123−3131

Xufeng Xu, Baohu Wu, Helmut Cölfen, Gijsbertus de With, Assembly Control at a Low Péclet Number in Ultracentrifugation for Uniformly Sized Nanoparticles, J. Phys. Chem. C 2021, 125, 8752−8758.

J. J. Devogelaer, M. D. Charpentier, A. Tijink, V. Dupray, G. Coquerel, K. Johnston, H. Meekes, P. Tinnemans, E. Vlieg, J. H. ter Horst, R. de Gelder. Cocrystals of praziquantel: Discovery by networkbased link prediction, Cryst. Growth & Des., 21 (2021) 3428-3437.

R. Aninat, F.J. van den Bruele, J.J. Schermer, P. Tinnemans, J. Emmelkamp, E. Vlieg, M. van der Vleuten, H. Linden, M. Theelen, In-situ XRD study on the selenisation parameters driving Ga/In interdiffusion in Cu(In,Ga)Se2 in a versatile, industrially-relevant selenisation furnace, Solar Energy 230 (2021) 1085-1094.

T. Lerdwiriyanupap, G. Belletti, P. Tinnemans, H. Meekes, F. Rutjes, E. Vlieg, A. Flood, Combining diastereomeric resolution and Viedma ripening using a racemic resolving agent, Eur. J. Org. Chem., 2021 (2021), 5975–5980.

F. Ibis, T. Wang Yu, F. Marques Penha, D. Ganguly, M. A. Nuhu, A. E. D. M. van der Heijden, H. J. M. Kramer and H. B. Eral, Nucleation kinetics of calcium oxalate monohydrate as a function of pH, magnesium, and osteopontin concentra-tion quantified with droplet microfluidics, Biomicrofluidics, 2021, 15, 064103.

Lukas Helmbrecht, Moritz H. Futscher, Loreta A. Muscarella, Bruno Ehrler, Willem L. Noorduin, Ion Exchange Lithography: Localized Ion Exchange Reactions for Spatial Patterning of Perovskite Semiconductors and Insulators, Advanced Materials, 2021, 33, 20, 2005291.

Affiliations
o AMOLF, Science Park 104, Amsterdam, 1098XG The Netherlands.
o Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1090 GD Amsterdam, The Netherlands.

Patterning materials with different properties in a single film is a fundamental challenge and essential for the development of next-generation (opto)electronic functional components. This work introduces the concept of ion exchange lithography and demonstrates spatially controlled patterning of electrically insulating films and semiconductors with tunable optoelectronic properties. In ion exchange lithography, a reactive nanoparticle “canvas” is locally converted by printing ion exchange “inks.” To demonstrate the proof of principle, a canvas of insulating nanoporous lead carbonate is spatioselectively converted into semiconducting lead halide perovskites by contact printing an ion exchange precursor ink of methylammonium and formamidinium halides. By selecting the composition of the ink, the photoluminescence wavelength of the perovskite semiconductors is tunable over the entire visible spectrum. A broad palette of conversion inks can be applied on the reactive film by printing with customizable stamp designs, spray-painting with stencils, and painting with a brush to inscribe well-defined patterns with tunable optoelectronic properties in the same canvas. Moreover, the optoelectronic properties of the converted canvas are exploited to fabricate a green light-emitting diode (LED), demonstrating the functionality potential of ion exchange lithography.

Hao Su, Paul H. H. Bomans, Heiner Friedrich, Yifei Xu, Nico Sommerdijk, Crystallization via Oriented Attachment of Nanoclusters with Short-Range Order in Solution, J. Phys. Chem. C, 2021, 125, 1, 1143−1149.

Affiliations
o Laboratory of Materials and Interface Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
o Centre for Multiscale Electron Microscopy, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
o Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
o Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
o School of Chemistry, University of Leeds, Woodhouse Lane, LS2 9JT, Leeds, U.K.
o Department of Biochemistry, Radboud Institute of Molecular Life Sciences, Radboud University Medical Center, Geert Grooteplein 6525 GA Nijmegen, The Netherlands.

Many mineral crystallization processes in aqueous solutions involve formation of nanoclusters with short-range order. Their transformation into crystalline products is not well understood. Here we investigate the formation of long-range crystalline order within networks of cobalt-based nanoclusters. High-resolution cryogenic transmission electron microscopy (cryoTEM) together with NMR and FTIR spectroscopies shows the formation of 0.8 nm sized (Co)(NH3)5CO3 complexes at the initial stage. By ligand exchange, those complexes become bridged by CO3 2−/OH− ligands and form ∼2 nm sized clusters, which subsequently aggregate into sheetlike networks due to the structural heterogeneity of the clusters. By further ligand change and adjustment in cluster orientations, longrange order is established, which leads to the nucleation of ammonium cobalt kambaldaite nanocrystals. Our observations demonstrate that nanoclusters with short-range order can form crystals via an oriented-attachment pathway, which provides new insights into multistep crystallization processes.

Mark M. J. van Rijt, Bernette M. Oosterlaken, Heiner Friedrich and Gijsbertus de With, Controlled titration-based ZnO formation, CrystEngComm, 2021, 23, 3340–3348.

Affiliations
o Laboratory of Physical Chemistry, Centre for Multiscale Electron Microscopy, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P. O. Box 513, Eindhoven, 5600 MB, The Netherlands.

Hexamethylenetetramine (HMTA) is commonly used as a base releasing agent for the synthesis of ZnO under mild aqueous conditions. HMTA hydrolysis leads to gradual formation of a base during the reaction. Use of HMTA, however, does have limitations: HMTA hydrolysis yields both formaldehyde and ammonia, it provides no direct control over the ammonia addition rate or the total amount of ammonia added during the reaction, it results in a limited applicable pH range and it dictates the accessible reaction temperatures. To overcome these restrictions, this work presents a direct base titration strategy for ZnO synthesis in which a continuous base addition rate is maintained. Using this highly flexible strategy, wurtzite ZnO can be synthesized at a pH >5.5 using either KOH or
ammonia as a base source at various addition rates and reaction pH values. In situ pH measurements suggest a similar reaction mechanism to HMTA-based synthesis, independent of the varied conditions. The type and concentration of the base used for titration affect the reaction product, with ammonia showing evidence of capping behaviour. Optimizing this strategy, we are able to influence and direct the crystal shape and significantly increase the product yield to 74% compared to the 13% obtained by the reference HMTA reaction.

Sevgi Polat, Huseyin Burak Eral, Effect of L-alanyl-glycine dipeptide on calcium oxalate crystallization in artificial urine, Journal of Crystal Growth, 2021, 566–567, 126176.

Affiliations
o Department of Chemical Engineering, Faculty of Engineering, Marmara University, 34722 İstanbul, Turkey.
o Van’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science Utrecht University, 3584 CH Utrecht, the Netherlands.
o Process & Energy Laboratory, Delft University of Technology, 2628 CB Delft, the Netherlands.

Pathological crystallization of calcium oxalate (CaOx), the most common constituent of kidney stones, has attracted much attention due to recent surge in reported natural and synthetic additives effectively inhibiting its nucleation and growth. The aim of this study is to investigate the effect of L-alanyl–glycine (Ala–Gly), a dipeptide commonly found in human urine, on CaOx crystallization and its phase transformation in the presence of an artificial urine media. The nucleated CaOx crystals are characterized by XRD, FTIR, SEM, and dynamic light scattering in terms of changes in their crystalline form, morphology, and size. XRD and FTIR results revealed that Ala–Gly inhibited the formation of the thermodynamically most stable phase of CaOx, calcium oxalate monohydrate
(COM) crystals. SEM images revealed that hexagonal plate-shaped COM crystals are transformed into the smaller tetragonal bipyramidal calcium oxalate dihydrate (COD) crystals with increasing additive concentrations. At 125 ppm Ala–Gly concentration more pronounced aggregation of CaOx crystals is observed accompanied with higher negative zeta potential value of −27.1 ± 2.9 mV. Moreover, the phase transformation from COM to COD is also confirmed through thermogravimetric analysis. Consequently, these results suggest that Ala–Gly has a profound effect on preventing the formation of COM crystals and helping to stabilize the COD crystals, a CaOx phase that is reported to have a lower tendency to stick to kidney cells thus decreasing the risk of stone formation.

Frederico Marques Penha, Ashwin Gopalan, Jochem Christoffel Meijlink, Fatma Ibis, Huseyin Burak Eral, Selective Crystallization of D-Mannitol Polymorphs Using Surfactant Self-Assembly, Cryst. Growth Des., 2021, 21, 7, 3928–3935.

Affiliations
o Department of Chemical Engineering, KTH Royal Institute of Technology, Teknikringen 42, SE100-44 Stockholm, Sweden.
o Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands.

Selective crystallization of polymorphs is highly sought after in industrial practice. Yet, state-of-the-art techniques either use laboriously engineered solid surfaces or strenuously prepared heteronucleants. We propose an approach where surfactants in solution self-assemble effortlessly into mesoscopic structures dictating the polymorphic outcome of the target solute. Sodium dodecyl sulfate (SDS) surfactant is used as a tailored additive to crystallize different polymorphic forms of a model active pharmaceutical ingredient, d-mannitol. Different mesoscopic phases of SDS template particular polymorphs: packed monolayers, micelles, and crystals favored the β, α, and δ forms of d-mannitol, respectively. A synergistic effect of topological templating and molecular interactions is proposed as the rationale behind the observed selective crystallization of polymorphs. This crystal engineering technique suggests that surfactant self-assemblies can be used as tailored templates for polymorphic control.

Jason Jung, Roy L. M. Op het Veld, Rik Benoist, Orson A. H. van der Molen, Carlo Manders, Marcel A. Verheijen, Erik P. A. M. Bakkers, Universal Platform for Scalable Semiconductor- Superconductor Nanowire Networks, Adv. Funct. Mater. 2021, 2103062.

Affiliation
o Department of Applied Physics, Eindhoven University of Technology, Eindhoven, MB 5600, The Netherlands.

Semiconductor-superconductor hybrids are commonly used in research on topological quantum computation. Traditionally, top-down approaches involving dry or wet etching are used to define the device geometry. These often aggressive processes risk causing damage to material surfaces, giving rise to scattering sites particularly problematic for quantum applications. Here, a method that maintains the flexibility and scalability of selective area grown nanowire networks while omitting the necessity of etching to create hybrid segments is proposed. Instead, it takes advantage of directional growth methods and uses bottom-up grown indium phosphide (InP) structures as shadowing objects to obtain selective metal deposition. The ability to lithographically define the position and area of these objects and to grow a predefined height ensures precise control of the shadowed region. The approach by growing indium antimonide nanowire networks with well defined aluminium and lead (Pb) islands is demonstrated. Cross-section cuts of the nanowires reveal a sharp, oxide-free interface between semiconductor and superconductor. By growing InP structures on both sides of in-plane nanowires, a combination of platinum and Pb can independently be shadow deposited, enabling a scalable and reproducible in situ device fabrication. The semiconductor-superconductor nanostructures resulting from this approach are at the forefront of material development for Majorana based experiments.

Elham M. T. Fadaly, Anna Marzegalli, Yizhen Ren, Lin Sun, Alain Dijkstra, Diego de Matteis, Emilio Scalise, Andrey Sarikov, Marta De Luca, Riccardo Rurali, Ilaria Zardo, Jos E. M. Haverkort, Silvana Botti, Leo Miglio, Erik P. A. M. Bakkers, Marcel A.Verheijen, Unveiling Planar Defects in Hexagonal Group IV Materials, Nano Lett., 2021, 21, 8, 3619−3625.

Affiliations:
o Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, the Netherlands.
o Dipartimento di Fisica, Politecnico di Milano, via Anzani 42, 22100 Como, Italy.
o L-NESS and Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via R. Cozzi 55, I-20125 Milano, Italy.
o Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
o Departement Physik, Universität Basel, Klingelbergstr. 82, 4056 Basel, Switzerland.
o Lashkarev Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 45 Nauki avenue, 03028 Kyiv, Ukraine.
o Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus UAB, 08193 Bellaterra, Spain.
o Eurofins Materials Science Netherlands BV, High Tech Campus 11, 5656 AE Eindhoven.

Recently synthesized hexagonal group IV materials are a promising platform to realize efficient light emission that is closely integrated with electronics. A high crystal quality is essential to assess the intrinsic electronic and optical properties of these materials unaffected by structural defects. Here, we identify a previously unknown partial planar defect in materials with a type I3 basal stacking fault and investigate its structural and electronic properties. Electron microscopy and atomistic modeling are used to reconstruct and visualize this stacking fault and its terminating dislocations in the crystal. From band structure calculations coupled to photoluminescence measurements, we conclude that the I3 defect does not create states within the hex-Ge and hex-Si band gap. Therefore, the defect is not detrimental to the optoelectronic properties of the hex-SiGe materials family. Finally, highlighting the properties of this defect can be of great interest to the community of hex-III-Ns, where this defect is also present.

Theses

Mark M.J. van Rijt, Connecting ZnO to Organic Templates
PhD defense: 8 June 2021, Eindhoven University of Technology, Eindhoven

Promotor: Prof. Dr. G. de With
Co-promotor: Dr. H. Friedrich

In materials science there is a continuous strive to obtain materials with enhanced properties without introducing unwanted limitations. Inspiration for these materials can be found in nature, where the extraordinary control of biological processes results in excellent material properties, for example the impressive mechanical properties of bone, the surprising magnetic particles in magnetotactic bacteria and the beautiful iridescent colors of nacre shells. Many of these natural materials possess these properties due to a hybrid composition containing both organic and inorganic (mineral) phases. While nature has limited its choice to a few minerals, mainly silica, phosphates and carbonates, this is not the case for man-made materials. Therefore, by understanding and emulating the formation of natural materials with non-naturally incorporated minerals, a near endless range of new materials should be obtainable. An excellent candidate for this is the well-known metal oxide zinc oxide (ZnO). Its mostcommon polymorph wurtzite ZnO has a wide range of relevant physical properties making it a material of interest for a multitude of technological applications including piezo-electrics, photocatalysis and solar cells. Mineralization of organic templates with ZnO should therefore allow for the expression and control over a wide range of material properties.

Ghada Badawy, InSb Nanowire Heterostructures for Topological Quantum Computing
PhD defense: 8 July 2021, Eindhoven University of Technology, Eindhoven

Promoter: prof. dr. Erik Bakkers
Co-promotor: dr. Marcel A. Verheijen

Quantum computing promises to solve certain problems that seemed unsolvable with classical computers. A fundamental challenge, however, is the volatility of information in their building blocks—qubits. Topological quantum computing is considered superior to conventional quantum computing because of the way it stores information. Specifically, a topological quantum computer represents information using quasiparticle excitations known as Majorana fermions. The swapping of these quasiparticles in a material encodes the information such that information is encoded nonlocally, protecting it from local sources of noise and decoherence. Among the various platforms that are expected to host Majorana fermions, semiconducting nanowires are considered key contenders.
This thesis details the bottom-up growth of indium antimonide (InSb) nanowires and related heterostructures intended as building blocks for the envisioned Majorana-based topological quantum computing circuits. Majorana quasiparticles are predicted to emerge in semiconducting nanowires with strong spin-orbit
interaction coupled to a superconductor. The fragility of these quasiparticles demands materials and nanostructures free of any disorder—defects in the nanowire or a rough interface with the superconductor. Another important parameter is the coupling strength between the nanowire and the superconductor which has thus far been largely neglected. The experiments in this thesis improve the InSb nanowires by reducing the impurity levels in them and demonstrate a novel growth method, that allows them to reach lengths that were previously considered unattainable. These nanowires are further refined by including an epitaxial cadmium telluride (CdTe) shell that protects the InSb surface from the surrounding, undesirable electrostatic environment. The growth of an InSb nanostructure, termed a nanoflake, is detailed and is used to selectively deposit the superconductor on the InSb nanowires. To address the coupling strength between the nanowire and the superconductor, we introduce a control knob—the thickness of the same CdTe shell—to modulate the coupling.

Elham M. T. Fadaly, Epitaxy of Hexagonal SiGe Alloys for Light Emission
PhD defense: 16 April 2021, Eindhoven University of Technology, Eindhoven

Promotor: Prof. E.P.A.M. Bakkers
Co-promotor: Dr. J.E.M. Haverkort, Dr. M.A. Verheijen

Silicon germanium (SiGe) alloys in the hexagonal structure have been theoretically predicted to exhibit a direct band gap nature, i.e., efficient light emission, in the infrared wavelength range 3.5-1.8 μm. This wavelength range is of technological interest for the optical telecommunications window, which is the basis for fast communication. The fundamental bottleneck is that Si, Ge, and their binary alloys exist naturally in the optically inactive cubic structure. On the other hand, it is extremely challenging to achieve the hexagonal structure in this class of materials. In this thesis, Fadaly has developed high-quality hexagonal Si-based alloys in big volumes, which proved to be capable of emitting light efficiently and having excellent optoelectronic properties. The nanowire geometry offers a unique platform for realizing new crystal structures that are inaccessible except under extreme conditions. She has demonstrated that by changing the arrangement of the atoms of the natural cubic Si structure to the promising hexagonal one. She used hexagonal nanowire templates to transfer the crystal structure to SiGe in a core-shell geometry by utilizing the crystal transfer technique. The high quality crystals reported in this work has enabled the emission wavelength’s tunability over a broad range while preserving the superior optical properties by controlling the Si with Ge alloy composition. The Hex-SiGe emission yield is similar to that of direct-bandgap group-III–V semiconductors, the current state-of-the-art laser materials. The finding of this work could potentially lead to the development of the first silicon-based laser or mid-infrared light detectors, both of which would
be compatible with the current silicon technology. These lasers could be deployed in several applications such as telecommunications, LiDAR, a radar with laser for self-driving cars, and chemical sensors for medical diagnosis or measuring air and food quality.

Jan_Joris Devogelaer, Co-crystal prediction using network science and machine learning
PhD defense: 17 September 2021, Radboud Universiteit, Nijmegen

Promotor: Prof. dr. Elias Vlieg
Co-promotors: Dr. René de Gelder and Dr. Hugo Meekes

Co-crystallization, the phenomenon where two or more distinct solid compounds form a single crystalline material, has enjoyed a resurgence of interest over the past two decades. The ability to tune physicochemical properties of an underperforming compound, such as the aqueous solubility or hydration stability of a pharmaceutical, together with opportunities regarding controlling polymorphism and chiral separation, have played major roles in its increased popularity. Theoretical tools such as Etter’s graph sets and Desiraju’s supramolecular synthons have laid the foundation for the current understanding of co-crystal structures in terms of intermolecular interactions. Other decisive factors beyond matching complementary functional groups, however, have stayed relatively unclear. Crystallographic databases such as the Cambridge Structural Database (CSD) contain an abundance of information on co-crystalline systems. Guidelines for the effective design of co-crystals could possibly be unraveled from its content given the right set of tools. The objectives of this thesis are therefore to gain an enhanced understanding of co-crystal formation and to use this to predict new co-crystals using data derived from the CSD. The approaches used to achieve this goal are network science and machine learning.

Giuseppe Belletti, Solid state deracemization –Viedma ripening versus temperature cycling
PhD defense: 27 October 2021, Radboud Universiteit, Nijmegen

Promotor: Prof. dr. Elias Vlieg and Prof. dr. Floris P.J.T. Rutjes
Co-promotor: Dr. Hugo Meekes

Viedma ripening and temperature cycling are known as robust and effective deracemization techniques that use the solid state of chiral compounds. Due to the strict prerequisites, i.e. conglomerate formation and solution racemization, their field of application is a limited range of chiral molecules. Different approaches were used over the past decade to expand the scope of both processes, with the majority focusing on Viedma ripening. In this thesis we study a number of methods to extend the applicability of both processes. In addition, we investigate the consequences of combining Viedma ripening and temperature cycling on the same chiral system. Finally, we introduce a new mechanism that could describe temperature cycling, which is still under debate. The compound used in many studies reported in this thesis is NMPA, which was also the first organic compound used to prove the efficacy of Viedma ripening on a chiral substrate. Much information has been collected over the course of the years on NMPA, therefore making it an ideal model compound.

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