Graphene & 2DM Singapore Summit 2019 - Phase Events · graphene for use in graphene development applications by leading corporations and institutions. Grafoid’s leading investment

ABSTRACTS BOOK

FOREWORD

On behalf of the Organising Committee we take great pleasure in welcoming you to Singapore for the first edition of the “Graphene & 2DM” International Summit (GS2). GS2 2019 will be a 2 days event that means to gather the key players of the Graphene Community and related sectors, in particular from Singapore. It aims to become an established event, attracting global participants, intent on sharing, exchanging and exploring new avenues of graphene-related scientific and commercial developments. This Summit will clarify the differentiating potential in all sectors where Singapore-graphene based industry is strong and could further gain in competitiveness and will develop proper incentives towards the achievement of Singapore-leadership in the fields of “graphene and 2DM” commercialization and “graphene and 2DM”-driven technology improvement. We truly hope that this event serves as an international platform for communication between science and business. We would like to thank all the sponsors, exhibitors, speakers and participants that join us this year. We are in particular indebted to the following companies for their financial support: Aixtron, Merck and Grafoid. One thing we have for granted: very few industries, one way or another, will escape from the influence of "Graphene and 2DM" and the impact on businesses is here to stay. Hope to see you again in the next edition of Graphene & 2DM Singapore.

ORGANISER

ORGANISING COMMITTEE Antonio H. Castro Neto (PHASE EVENTS, Singapore)

Antonio Correia (PHASE EVENTS, Singapore)

Konstantin Novoselov (PHASE EVENTS, Singapore)

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S P O N S O R S

GOLD SPONSOR__ AIXTRON is the global technology leader providing metalorganic chemical vapour deposition (MOCVD) equipment in high volume

manufacturing. The newly formed 2D materials team, located in the UK, has been formed with the objective of proving MOCVD as a viable candidate for large-scale manufacturing of 2D nanomaterial on standard semiconductor substrates.

More info: www.aixtron.com/en

SILVER SPONSOR__

The life science business of Merck brings together the world-class products and services, innovative capabilities. We provide scientists and engineers with best-in-class lab materials, technologies and services. With the 2015 combination of Merck Millipore and Sigma-Aldrich, we now have a broad portfolio of 300,000 products, an expanded global footprint and an industry-leading eCommerce platform - SigmaAldrich.com We are dedicated to making research and biotech production simpler, faster and safer.

BRONZE SPONSORS__ Founded in 2011, Grafoid Inc. is a graphene research, development and investment company that invests in,

manages and develops markets for processes that produce economically scalable graphene for use in graphene development applications by leading corporations and institutions. Grafoid’s leading investment produces application friendly, minimal-defect, high-energy density few layer graphene, utilizing a safe, non-destructive extraction process, leaving the lowest possible ecological footprint. The completely unique, proprietary process results in what Grafoid regards as a new global standard for economically scalable, high-purity graphene products — trademarked under the MesoGraf™ trade name — that can be tailored to both industrial and commercial applications.

More info: www.grafoid.com

Founded in 1987, Huawei is a leading global provider of information and communications technology (ICT) infrastructure and smart devices. We are committed to bringing digital to every

person, home and organization for a fully connected, intelligent world. We have nearly 188,000 employees, and we operate in more than 170 countries and regions, serving more than three billion people around the world. Huawei's end-to-end portfolio of products, solutions and services are both competitive and secure. Through open collaboration with ecosystem partners, we create lasting value for our customers, working to empower people, enrich home life, and inspire innovation in organizations of all shapes and sizes. At Huawei, innovation focuses on customer needs. We invest heavily in basic research, concentrating on technological breakthroughs that drive the world forward.

More info: www.huawei.com

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http://www.aixtron.com/en

http://www.grafoid.com/

EXHIBITORS

PARTNERS

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SPEAKERS LIST

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Rezal Khairi Ahmad (NanoMalaysia Berhad, Malaysia) Commercializing Graphene Applications in Malaysia

Invited Plenary -

Wei Li Ang (NTU, Singapore) Use of Graphene Oxide Nanocolloids as electrochemical labels for PCR detection of Genetically Modified Food

Poster

49 L. Antonio Benitez (ICN2, Spain) Tunable room-temperature spin galvanic (SGE) and spin Hall effects (SHE) in proximitized graphene

Oral

32 Milan Blaskovic (Centre for Advanced 2D Materials, Singapore) Temperature dependence of interaction between DNA and graphitic surfaces – modelling true nature of interactions

Oral

33 Lapo Bogani (University of Oxford, UK) Quantum control of molecular graphene

Oral 35 Francesco Bonaccorso (Bedimensional / IIT, Italy) Liquid phase production of 2D crystals for energy applications

Keynote 14 Alessandra Bonanni (Nanyang Technological University, Singapore) Nano-graphene oxide as electroactive label for the detection of biomolecules

Oral 36 Alexander Botin (Sklifosovsky Institute of Emergency Medicine, Russia) Polygraphene as Carbon Nanomatrix for Detoxication and Sterilization of Gaseous and Liquid Media for Air and Water Treatment

Oral

37 Vincent Bouchiat (Grapheal SAS, France) CVD Graphene monolayers for bioelectronics and wound care sensors

Invited Plenary 19

Antonio H Castro Neto (National University of Singapore, Singapore) Title to be defined

Plenary - Goki Eda (NUS, Singapore) Van der Waals heterostructure optoelectronics

Invited Plenary -

Vladimir Falko (National Graphene Institute, University of Manchester, UK) Moiré superlattices in TMD heterostructures

Keynote 15 Jean-Christophe Gabriel (NTU, Singapore) 2D nanosheet based lyotropic liquid crystals: from synthesis to structure and applications

Invited Parallel Session

26 Xiaorui Gao (National University of Singapore, Singapore) Significant Role of Al in Ternary Layered Double Hydroxides for Enhancing Electrochemical Performance of Flexible Asymmetric Supercapacitor

Oral

38 Slaven Garaj (NUS, Singapore) Title to be defined

Keynote - Kuan Eng Johnson Goh (A*STAR IMRE, Singapore) Developing 2D Semiconductors for Spin-valley Qubits

Invited Plenary 20

Roman Gorbachev (University of Manchester, UK) Novel methods and materials for 2D heterostructures

Invited Plenary 21

Magdalena Grzeszczyk (University of Warsaw, Poland) The effect of environment on optical properties of monolayer MoSe2

Poster 50 Junxiong Hu (National University of Singapore, Singapore) Room-temperature colossal magnetoresistance in terraced single-layer graphene

Oral

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Lu Jiong (NUS, Singapore) Graphene: a versatile platform for the remote control of excitons in 2D semiconductors

Invited Parallel Session

- Nicolas Leconte (University of Seoul, South Korea) Relaxation Effects in Twisted Bilayer Graphene: a Multi-Scale Approach

Oral 40 Max Lemme (AMO GmbH, Germany) Application Potential and Fabrication Bottlenecks of Electronic Devices based on 2D Materials

Keynote

16 Sharon Xiaodai Lim (National University of Singapore, Singapore) Nanosurfer Flash-mobs: Electric-Field-Choreographed Silver Migration on Graphene Oxide

Poster

51 Zheng Liu (NTU, Singapore) TMDs: from synthesis to electronics

Invited Plenary -

Jan Mischke (University of Duisburg-Essen, Germany) Direct PE-CVD growth of graphene on GaN under N2 atmosphere in a 4” cold-wall CVD reactor

Oral

41 Vaidotas Miseikis (IIT Pisa, Italy) Crystals on demand: seeded growth of graphene for scalable high-performance optoelectronics

Invited Plenary

22 Saroj Nayak (Indian Institute of Technology Bhubaneswar, India) Giant Enhancement of Thermal Conductivity of Aluminium Graphene Composites

Oral

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Bryce Nelson (Merck, USA) Enabling Cutting-Edge Research in 2D Nanomaterials

Invited Industrial

Forum 28 Kostya Novoselov (National University of Singapore, Singapore) Materials in the Flatland

Plenary 12 Ricardo Oliveria (2DM, Singapore) Expanding the frontier of materials application through the use of high performance graphene

Invited Industrial

Forum 29 Barbaros Ozyilmaz (NUS, Singapore) Synthesis and Properties of 2D Amorphous Carbon

Keynote -

Elena Polyakova (GrapheneLab, USA) Graphene as a toughening agent for polymer matrices

Invited Industrial

Forum - Stephan Roche (ICREA / ICN2, Spain) Predictive Modelling for Industrial Research Guidance in Two-Dimensional Materials and Beyond

Keynote

17 Massimo Spina (National University of Singapore, Singapore) Ionic mobility engineering in graphitic nanochannels

Oral 43 Jie Su (National University of Singapore, Singapore) On-surface synthesis and characterization of open-shell graphene molecules

Poster

52 Guy Trambly de Laissardière (University of Cergy-Pontoise / CNRS, France) Magnetism of Magic-Angle Twisted Bilayer Graphene

Oral

44 Aravind Vijayaraghavan (The University of Manchester, UK) Graphene enhanced elastomer composites and their applications

Invited Parallel Session -

Marc Vila Tusell (ICN2 / CSIC & BIST, Spain) Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport

Oral

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Marc Vila Tusell (ICN2 / CSIC & BIST, Spain) Tunable Circular Dichroism and Valley Polarization in the Modified Haldane Model

Poster

53 John Wang (NUS, Singapore) 2D Materials: 2D Atomic, 2D Molecular, 2D Morphological and 2D Holey, Which One?

Invited Plenary

23 Zihao Wang (The University of Manchester, UK) Composite super-moiré lattices in double aligned graphene heterostructures

Oral 46

Rune Wendelbo (Abalonyx, Norway) Towards Industrial Applications of Graphene Oxide

Invited Industrial

Forum 30 Oliver Whear (Aixtron, UK) Aixtron 2D Materials Grown on Sapphire

Invited Plenary 24

Hyunsoo Yang (NUS, Singapore) Spin devices using 2D and topology materials

Invited Plenary -

Jianbo Yin (ICFO, Spain) Tunable valley Hall effect in gapped bilayer graphene with infrared light

Invited Parallel Session -

Tingkai Zhao (Northwestern Polytechnical University, China) Preparation and Performance of Carbon Dot Stabilized Copper Sulphide/Carbon Nanotubes Hybrid Composite as Supercapacitor Electrode Materials

Oral

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Yanwu Zhu (The Sixth Elements, China) Title to be defined

Invited Industrial

Forum -

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PLENARY

Graphene Singapore Summit 2019 November 11-12, 2019

K. S. Novoselov School of Physics and Astronomy, University of Manchester, M13 9PL, UK [email protected]

Materials in the Flatland One of the most important “property” of graphene is that it has opened a floodgate of experiments on many other 2D atomic crystals: BN, NbSe2, TaS2, MoS2, etc. The resulting pool of 2D crystals is huge, and they cover a massive range of properties: from the most insulating to the most conductive, from the strongest to the softest. If 2D materials provide a large range of different properties, sandwich structures made up of 2, 3, 4 … different layers of such materials can offer even greater scope. Since these 2D-based heterostructures can be tailored with atomic precision and individual layers of very different character can be combined together, - the properties of these structures can be tuned to study novel physical phenomena or to fit an enormous range of possible applications, with the functionality of heterostructure stacks is “embedded” in their design. Already now such materials bring to life a number of exciting applications. In my lecture I will review some of them.

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KEYNOTES


Francesco Bonaccorso Istituto Italiano di Tecnologia, Graphene Labs, Via Morego 30, Genova, Italy BeDimensional SpA, Via Albisola 121, Genova, Italy [email protected]

Liquid phase production of 2D crystals for energy applications

Two-dimensional (2D) materials are entering several application areas,[1-5] improving the performance of existing devices or enable new ones.[1-5] A key requirement for the implementation of 2D materials in the energy field is the development of industrial-scale, reliable, inexpensive production processes,[2] while providing a balance between ease of fabrication and final product quality. In this context, the production of 2D materials by solution processing[2,6] represents a simple and cost-effective pathway towards the development of 2D materials-based energy devices, presenting huge integration flexibility compared to other production methods. Here, I will first present our strategy to produce 2D materials on large scale by wet-jet milling[7] of their bulk counterpart and then an overview of their applications for energy devices.[3,8-15] The research leading to these results has received funding from the European Unionʹs Horizon 2020 research and innovation program under grant agreements No. 785219 - GrapheneCore2 References 1. A. C. Ferrari, F. Bonaccorso, et al., Nanoscale, 7, 4598-4810 (2015). 2. F. Bonaccorso, et al., Materials Today, 15, 564-589, (2012). 3. F. Bonaccorso, et. al., Nature Photonics 4, 611-622, (2010). 4. F. Bonaccorso, Z. Sun, Opt. Mater. Express 4, 63-78 (2014). 5. G. Iannaccone, et al., Nature Nanotech 13, , 183, (2018). 6. F. Bonaccorso, et. al., Adv. Mater. 28, 6136-6166 (2016). 7. A. E. Del Rio Castillo et. al., Mater. Horiz. 5, 890 (2018). 8. F. Bonaccorso, et. al.,. Science, 347, 1246501 (2015). 9. J. Hassoun, et al. Nano Lett. 14, 4901-4906 (2014). 10. F. Bonaccorso, et al. Adv. Funct. Mater. 25, 3870-3880 (2015). 11. F. Biccari, et al. Adv. Energy Mater. 7, 1701349 (2017). 12. A. Agresti, et al. ACS Energy Letters 4, 1862-1871 (2019). 13. A. Capasso, et al. Adv. Ener. Mater. 6, 1600920, (2016). 14. L. Najafi, et al. ACS Nano 12, 10736 (2018). 15. S. Bellani et al., Advanced Functional Materials 29, 1807659 (2019).

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Vladimir Fal’ko

David Ruiz-Tejerina National Graphene Institute, University of Manchester, Booth St E, M13 9PL, Manchester, UK [email protected]

Moiré superlattices in TMD heterostructures

Atomically-thin layers of two-dimensional materials can be assembled in vertical stacks held together by relatively weak van der Waals forces, allowing for coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation. A profound consequence of using these degrees of freedom is the emergence of a periodicity in the local atomic registry of the constituent crystal structures, known as a moiré superlattice. We find that there are two principall diferent regimes in the moire SL formation: (a) strong lattice reconstruction of almost aligned lattice matched crystals - due to in the interlayer affinity coupling resulting in the formation of domains with different stackings and strongly strained domain walls, which act as ‘quantum dots’ for electrons/holes; (b) hybridisation-induced SL effects in almost non-deformed heterostructures of lattice mismatched 2D crystals. Then, we study how moiré superlattice effects on the electronic properties of almost aligned lattice-misatched MoSe2/WS2 and MoTe2/MoSe2 heterobilayers get enhanced by resonant hybridization of conduction-band states in different layers, promoted by alignment of their band edges. In particular, we find [1,2] that in semiconducting heterostructures built of incommensurate MoSe2 and WS2 monolayers, A exciton undergoes an almost resonant interlayer hybridisation, resulting in the enhancement of the moiré superlattice effects, as an electron in the exciton explores efficiently the local arrangement of atoms in the two layer. MoSe2 and WS2 are specifically chosen for the near degeneracy of their conduction band edges to promote the hybridisation of intra- and interlayer excitons, which manifests itself in a pronounced exciton energy shift as a periodic function of the interlayer rotation angle. This occurs as hybridised excitons (hX) are formed by holes residing in MoSe2 bound to a twist-dependent superposition of electron states in the adjacent monolayers [2]. For heterostructures with almost aligned pairs of monolayer crystals, resonant mixing of the electron states leads to pronounced effects of the heterostructure’s geometrical moiré pattern on the hX dispersion and optical spectrum, including the appearance of new lines in their optical absorption spectra that correspond to the electron-photon umklapp processes. We also show that similar resonant hybridization is possible for B excitons in some TMD heterostructures, and that they should naturally appear in twisted homobilayers of various transition-metal dichalcogenides [2].. References

[1] Alexeev, Ruiz–Tijerina, Danovich, Hamer, Terry, Nayak, Ahn, Pak, Lee, Sohn, Novoselov, Gorbachev, Shin, Fal’ko, Tartakovskii, Nature 567, 81 (2019).

[2] Ruiz-Tijerina, Fal'ko, Phys Rev B 99, 125424 (2019).

Figures

Figure 1: Absorption by moire superlattice excitons in aligned MoSe2/WS2.

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Max Lemme AMO GmbH, Germany [email protected]

Application Potential and Fabrication Bottlenecks of Electronic Devices based on 2D Materials

Graphene has been researched intensely over the past 15 years, and it has quickly been followed by a number of related 2D materials. While physicists, chemists, material scientists and engineers continue to report new highlights on a daily basis, there are no end-customer microelectronics products on the market today. Although 2D materials are demonstrated as promising active elements in in electronics, optoelectronics or sensing, the process technology is not yet mature. In this talk, I will introduce several promising applications, for which 2D materials clearly could make a difference, such as photodetectors 1–3 and sensors 4–7. I will further discuss the major bottlenecks towards integration of graphene and 2D materials into semiconductor processing lines 8. References (1) Riazimehr et al., High Responsivity and Quantum Efficiency of Graphene/Silicon Photodiodes Achieved by Interdigitating Schottky and Gated Regions. ACS Photonics 2019, 6 (1), 107–115. (2) Yim et al., Wide Spectral Photoresponse of Layered Platinum Diselenide-Based Photodiodes. Nano Lett. 2018, 18 (3), 1794–1800. (3) Schall et al., 50 GBit/s Photodetectors Based on Wafer-Scale Graphene for Integrated Silicon Photonic Communication Systems. ACS Photonics 2014, 1 (9), 781–784. (4) Smith et al., Piezoresistive Properties of Suspended Graphene Membranes under Uniaxial and Biaxial Strain in Nanoelectromechanical Pressure Sensors. ACS Nano 2016, 10 (11), 9879–9886. (5) Wagner et al. Highly Sensitive Electromechanical Piezoresistive Pressure Sensors Based on Large-Area Layered PtSe2 Films. Nano Lett. 2018, 18 (6), 3738–3745. (6) Fan et al., Graphene Ribbons with Suspended Masses as Transducers in Ultra-Small Nanoelectromechanical Accelerometers. Nat. Electron. 2019, 2, 394–404. (7) Wittmann et al. Graphene Membranes for Hall Sensors and Microphones Integrated with CMOS-Compatible Processes. ACS Appl. Nano Mater. 2019, 2 (8), 5079–5085. (8) Neumaier, D.; Pindl, S.; Lemme, M. C. Integrating Graphene into Semiconductor Fabrication Lines. Nat. Mater. 2019, 18 (6), 525.

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Stephan Roche ICREA / ICN2, Spain [email protected]

Predictive Modelling for Industrial Research Guidance in Two-Dimensional Materials and Beyond

I will discuss several aspects of quantum simulation strategies which enable predictability and direct comparison with experimental data, in the context of industrial research. For polycrystalline 2D materials, amorphous graphene and reduced oxide graphene, charge, thermal and spin transport studies will be presented, illustrating the unprecedented level of quantitative capability of order N methods and their usefulness as guiding tools for materials and device optimization.

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INVITED PLENARY


Vincent BOUCHIAT Riadh Othmen, Cécile Delacour, Antoine Bourrier Grapheal & Neel Institut, 25 rue des Martyrs, Grenoble, France [email protected]

CVD Graphene monolayers for bioelectronics and wound care sensors

After a decade and thousands of publications, graphene produced by CVD on copper foils remains at the sweet spot for quality and cost-effective production of large size, high-mobility graphene transferred on insulators. Use of these monolayers has been so far scarce in industrial applications. I will present the application of this technology for biological (1) and medical applications from both the academic and industrial point of view. We have first explored the use of graphene-on -polymer for biosensing and tissue engineering. I will show results of in-vitro cellular growth (neurons and skin fibroblasts) on graphene-covered substrate which shows the stimulation of growth (2) and migration of cells promoted by the graphene substrate together with the possibility of probing their electrical activity down to the sub-cellular scale (3). We are also developing a novel technology platform that exploits the features of monolayer graphene, for wound care. The first-generation of our system is a graphene-based scaffold that looks like a very thin, transparent plaster. Based on that material, we are building an innovative bandage technology platform based on graphene-on -insulator film in order to better support chronic wounds. In particular, I will insist on the possibility to combine therapeutics (bio electrostimulation & healing) with diagnostics (biosensing) features in the same device. Following these properties, we have elaborated a graphene-based scaffold that looks like a very thin, transparent plaster integrated in commercial bandage that is indented to be applied in direct contact with an open wound. We believe these films will have some impact in healthcare, as they target some important and poorly addressed diseases such as pressure ulcers and diabetic foot ulcers. I will present the preclinical results on animal studies and the perspectives of their commercial (3) use for wound-care, in particular in the treatment and diagnostics of chronic wounds that affect the diabetics and elderly. Our bandage platform (4) is based on the integration of a monolayer graphene polycrystalline layer back-bonded onto a biocompatible polymer layerb. The resulting film can directly be applied onto the bed-wound and is inserted in a commercial bandage. Graphene surface combines healing (speed-up of wound closure) and antibacterial action, optical transparency and electrical conductivity. It is obtained by integrating a large uniform graphene monolayer into a bandage in order to provide a bio- stimulating and electrically-active platform directly applied in contact with the wound. It allows the development of a range of intelligent dressings that combine on the same product both therapeutic and diagnostic actions. -Therapeutic action: graphene functions as a growth matrix, promoting healing but at the same time acting as an electrode in close contact with the wound. This allows the application of electrical pulses whose actions promote faster healing and reduce pain. -Diagnostic action: Graphene it plays at the same time the role of a biosensor to monitor the wound evolution and early stage detection of infection by pH and biomarker sensing. References

[1] A. Bourrier et al. Adv. Health. Mat. vol. 8 , 1801331, (2019) [2] F. Veliev et al. Biomaterials. 86, 33-41, (2016) [3] F. Veliev et al. 2D Mat 5, 045020 (2018) [4] www.grapheal.com

Figures Figure 1: Principle of the graphene-coated bandage platform: a single monolayer of polycristalline, CVD Graphene is

assembled onto a biocompatible polymer and integrated in a bandage.

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mailto:[email protected]


Kuan Eng Johnson Goh1,2* Institute of Materials Research and Engineering, Agency for Science Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis, #08-03, Singapore 138634 Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551 [email protected]; [email protected]; [email protected]

Developing 2D Semiconductors for Spin-valley Qubits Quantum computing with few to tens of qubits can now be performed on several technology platforms, and the assertion of quantum supremacy appears imminent based on recent reports. Nevertheless, the task of scaling up to a universal quantum computer to handle real world problems (deemed intractable for classical computers) remains a distant reality. Amongst other priorities, increasing the number of qubits whilst maintaining a manageable error rate is paramount. The engineering challenge for building a full-fledge quantum computer is the reliable scale-up of the number of qubits. This a multidisciplinary problem requiring scientific and engineering breakthroughs in materials, processes, multi-qubit architectures, quantum measurement techniques in the least. In this talk, I will introduce our recent efforts to establish the capabilities for building spin-valley qubits based on layered 2D semiconductors. The unique spin-valley coupling in such materials is expected to suppress decoherence since a spin flip requires the concomitant change of valley. In addition, their compatibility with electrostatically gated planar qubit architectures are desirable for reducing system complexity and hence scalability. I shall present some of our recent results in materials engineering and initial device results toward this goal.

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Roman Gorbachev University of Manchester, UK [email protected]

Novel methods and materials for 2D heterostructures. In the last years, a novel field has emerged which deals with structures and devices assembled layer-by-layer from various atomically-thin crystals. These new multi-layer structures have proved to be extremely versatile, showing exceptional electronic and optical properties, new physics and new functionality. In this talk I will introduce new techniques developed recently in Manchester that allow heterostructure assembly in ultra-high vacuum and compare properties of archetypal atomically thin crystals fabricated in different environments. Focusing on particular materials, I will discuss our recent work on indium monoselenide and present a range of results on its structural, optical and electronic properties. Optical, in-plane electronic transport and vertical resonant tunnelling experiments will be discussed. I will also present our recent work on revealing its subband structure (for the multilayer crystals) and its evolution in transverse electric field. Lastly, I will talk about composite TMD/TMD and TMD/InSe heterostructures, with particular focus on their optical properties and lattice reconstruction (TEM) driven by minimisation of the lattice adhesion energy.

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Vaidotas Miseikis Camilla Coletti Istituto Italiano di Tecnologia, Piazza San Silvestro, 12, Pisa, Italy [email protected]

Crystals on demand: seeded growth of graphene for scalable high-performance optoelectronics

We present our work on the tailored growth of high-quality single-crystal graphene for optoelectronic applications. By deterministically seeding matrices of graphene crystals [1], we resolve the typical scalability issues of CVD graphene, such as the random nature of single-crystal graphene as well as the presence of grain boundaries in polycrystalline samples, which inevitably cause reduction of carrier mobility. Semi-dry transfer approach can allow deterministic placement of graphene on target wafers with minimised loss in quality, enabling the application of graphene in next generation integrated optoelectronics [2]. Optical lithography is used to pre-pattern the graphene growth substrates (copper foil) with chromium nucleation seeds. This allows us to grow arrays of large graphene crystals matching the geometry of our designed devices. Aligned semi-dry transfer is then used to place the crystals directly on the target photonic circuits at predetermined locations. We perform statistical spectroscopic and electrical measurements to confirm the high quality and homogeneity of seeded graphene matrices. Furthermore, we demonstrate several applications of our material. These include electro absorption modulators, where two graphene layers can modulate the optical signal in a waveguide at 50 GB/s [3] as well as scalable graphene photodetectors which utilise a polymeric dielectric to enable bias-free photodetection due to the PTE effect, with a record bandwidth of 67 GHz and a responsivity of 6 V/W. The research leading to these results has received funding from the European Unionʹs Horizon 2020 research and innovation program under grant agreements No. 785219 - GrapheneCore2. References

[1] Miseikis, V. et al. 2D Materials, 4 (2017) 021004 [2] Romagnoli, M. et al. Nature Reviews Materials, 3 (2018) 392–414 [3] Giambra, M. A. et al. Optics Express 27, (2019) 20145

Figures

Figure 1: a) Seeded matrix of large graphene crystals. b) Array of high-speed graphene electro-absorption modulators. c) Proposed wafer-scale integration of graphene via multiple stamping approach.

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John Wang Department of Materials Science and Engineering National University of Singapore [email protected]

2D Materials: 2D Atomic, 2D Molecular, 2D Morphological and 2D

Holey, Which One? There is a giant group of various 2D functional materials, including 2D Atomic, 2D Molecular and 2D Morphological. The common 2D atomic and molecular materials, such as graphene, graphene oxides and transition metal dichalcogenides (TMD), have been extensively exploited over the past decade. A group of the new 2D morphological and 2D holey materials are now rapidly emerging, and they can offer even better performance than those of the common 2D atomic and molecular materials. We have been exploring a group of 2D morphological and 2D holey materials more recently, which are the key active materials of the next generation energy, catalysis and environmental technologies. For high performing energy storage, electrocatalysis and conversion, both the number and population of active sites can be maximized by the approaches such as site-engineering, control in feature size, pore configurations and exposed surface area in these new 2D materials. One of the precursor-based approaches is to derive these new 2D materials from Metal Organic Frameworks (MOFs), where MOFs can be grown into various 2D, 1D and 0D morphologies. They offer great flexibility in control over varying length scales from atomic scales up to bulk structure, allowing for access to an almost endless variety of MOF-based and MOF-derived active materials. MOF-derived 2D active materials are shown to be exceptionally high performing for both electrodes and electrocatalysts. An on-going exciting development is the single atom catalysts assembled in 2D morphology and 2D holey forms. In this talk, we present the latest development of the new 2D morphological and 2D holey materials, conducted in our labs.

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Oliver Whear Oliver Whear Aixtron, UK [email protected]

Aixtron 2D Materials Grown on Sapphire AIXTRON has formed a new team to grow 2D materials directly on to semiconductor wafers using our mature closed coupled showerhead technology platform. In this talk we will introduce our latest technology for the highly scalable growth of 2D materials, our market insights, and latest results from the lab. Results shown will be for graphene, hexagonal boron nitride, tungsten disulphide and molybdenum disulphide on sapphire wafers ranging from 50mm – 150mm diameter.

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INVITED PARALLEL SESSION


Jean-Christophe P. Gabriel CEA/IRAMIS – Saclay, France, & NTU/ ERI@N, Singapore [email protected] & [email protected] .

2D nanosheet based lyotropic liquid crystals: from synthesis to structure and applications

In this presentation I will present the very rich zoology that has been brought to light in the field of 2D mineral/inorganic polyelectrolyte colloidal suspensions. Indeed, if one can produce such suspensions with sufficiently high concentration, some ordering can take place leading to lyotropic mesophases. We will give example of such bidimensional systems and results ranging from the demonstration of the nematic structure of smectic clays nanosheet suspensions (Gabriel et al J. Phys. Chem.) to the discovery of the first lamellar phase based on covalent nanosheets in H3Sb3P2O14 (Gabriel et al. Nature et PNAS 2018). Lamellar phases are very significant as they are the basis of life such as we know it, because they enable the essential requirement: liquid compartmentation,. This lamellar phase firther stricking property is its exeptionnal hyperswelling behavior, so large that it enable light diffraction enabling rare liquid opalescence. Such a variety of behaviors make of these 2D inorganic polyelectrolyte suspensions some very interesting models for the development of new theoritical approaches but enable also applications, some of which will be described (Desvaux, Ang. Chemie; Camerel, Nanoletters & Adv. Funct. Mater.).

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INVITED INDUSTRIAL FORUM


Bryce Nelson Merck (USA)

Enabling Cutting-Edge Research in 2D Nanomaterials Innovative and high-quality nanomaterials are critical to accelerate 2D research for energy and electronics applications. Through academic collaborations and internal R&D, we have developed high-quality graphene oxides, graphene derivatives, and 2D nanomaterials including germanane and black phosphorus. In collaboration with Northwestern University, 2D nanomaterials were formulated into well-characterized ready-to-use inks containing few-layered graphene, exfoliated hexagonal boron nitride or transition metal dichalcogenides. Our high-quality inks enable device fabrication through scalable additive manufacturing methods like aerosol, inkjet, gravure, screen printing and 3D printing. A variety of applications have since been demonstrated with these materials, including printed electronics, printed micro-supercapacitors, next generation lithium-ion batteries, and photodetectors. We will highlight a few examples illustrating the use of these 2D nanomaterials for high-temperature lithium ion battery separators, barrier materials in printed electronic devices, and bioactive 3D printable scaffolds.

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Ricardo Oliveria 2DM, Singapore [email protected]

Expanding the frontier of materials application through the use of high performance graphene

There are many companies worldwide claiming to produce “graphene materials”, but showing huge disparity in their properties. Because of that, many industrial applications were hindered by quality and price of graphene. High quality graphene is required for most industrial applications eg high-end composites (electrical/thermal properties), electronic and energy storage applications. On the other hand, high price of graphene hinders the development of mass market materials. In this space, 2D Materials Pte. Ltd. (2DM) manufactures high performance graphene as an industrial additive to enhance the properties of industrial materials such as paints & coatings, batteries, composites, polymers, cements, and lubricants. Our vision is to expand the frontier of materials application through the use of high performance graphene in many segments. Some examples of customer’s trials will be presented and the performance-price correlation will be discussed focusing on the value added to customers’ products.

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Rune Wendelbo Abalonyx AS, Forskningsveien 1, 0373-Oslo, Norway [email protected]

Towards Industrial Applications of Graphene Oxide Graphene oxide (GO), also known as graphitic oxide, has the advantage over other graphene type materials of being easy to modify to satisfy a wide range of requirements. GO is most often prepared by the so called Hummers method1 or modifications thereof. As producers of GO and GO-derivatives in Kg-quantities and customers on all five continents we have in recent years gained valuable insight in up-coming real industrial applications world-wide. Corrosion protection is the first application of GO now being industrialized by the Swedish company Provexa AB, and we see several other technologies on the horizon, to be reviewed. Loudspeaker membranes, certain uses in production of electronics, water treatment, sports equipment and batteries are other applications in the pipeline. From the industrial end-user perspective, cost, reliable availability and hazards are the most important concerns apart from relevant chemistry. Industrial production costs are strongly related to production volumes. Availability is related to proven production capacity, preferably by more than one producer with proven consistency regarding quality.

30

ORALS


L. Antonio Benítez 1,2 Williams Savero Torres 1, Juan F. Sierra 1, Matias Timmermans 1, Jose H. Garcia 1, Stephan Roche 1,3, Marius V. Costache 1, and Sergio O. Valenzuela 1,3. 1 Catalan institute of Nanoscience and Nanotechnology (ICN2), CIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain. 2 Universitat Autònoma de Barcelona (UAB), Bellaterra, 08193 Barcelona, Spain and 3 Institució Catalana de Recerca i Estudis Avançats (ICREA), 08810 Barcelona, Spain. [email protected]

Tunable room-temperature spin galvanic (SGE) and spin Hall effects (SHE) in proximitized graphene

When graphene is in proximity to a transition metal dichalcogenide (TMDC), it preserves its electronic properties while acquiring and enhanced spin orbit interaction (SOI) together with a complex spin texture with out-of-plane and winding in-plane components [1]. Among the relevant consequences of this unique type of SOI, we demonstrate anisotropic spin dynamics with spin lifetimes that varies orders of magnitude depending on the spin orientation [2]. Recently, further studies in graphene-TMDC heterostructures suggest enhanced spin-to-charge conversion (StC) efficiency with the coexistence of SHE [3] and SGE [4]. In this talk, I will describe an unambiguous demonstration of StC conversion in graphene by proximity of WS2 at room temperature (RT) [5]. In contrast to prior reports, our device allows us to evaluate the TMDC conductivity and to carry out the experiments when it is not conducting. Furthermore, our measurement protocol relying on spin precession readily separates the contributions of the SHE and SGE. Notably, we find that the magnitude and sign of SHE and SGE present remarkable tunability by electrostatic back-gating. Our findings provide a rich platform to explore novel strategies to generate and manipulate spin currents in 2D materials with high efficiency References

[1] M. Gmitra and J. Fabian. Phys Rev. B. 92, 155403 (2015) [2] L. Antonio Benítez, et al. Nature Phys. 14, 303 (2018) [3] Jose H. Garcia, et al. Nano Lett. 17, 5078 (2017); A. Avsar, et al. Nat. Commun. 5, 4875 (2014); C. K. Safeer, et

al. Nano Lett. 19, 1074 (2019). [4] Talieh S. Ghiasi, et al. Nano Lett.19, 5959 (2019) [5] L. Antonio Benítez, et al. Submitted. arXiv:1908.07868.

Figures

Figure 1: RT modulation of the output non-local resistance due to spin precession in the ISHE (a) and the SGE (b) configuration.

32

https://arxiv.org/abs/1908.07868


Milan Blaskovic Slaven Garaj National University of Singapore, Centre for Advanced 2D Materials, Nano/Bio Physics Lab, 6 Science Drive 2, Singapore, Singapore [email protected] / [email protected]

Temperature dependence of interaction between DNA and graphitic surfaces – modelling true nature of interactions

Graphitic surfaces have shown significant potential in single-molecule detection applications due to

excellent mechanical and electronical properties, as well as their functionalization possibilities [1]. In addition, it

has been shown that interaction of single layer of graphene with surrounding molecules is strongly affected with

the choice of underlying supporting substrate, which could as well affect interactions with DNA molecules [2].

We investigated temperature dependence of interactions of individual single-stranded DNA oligomers

with two graphitic surfaces, HOPG surface, and CVD grown monolayer graphene supported on SiO2/Si

substrate, inside a liquid environment, where we identified and quantified (1) all the relevant forces contributing

to the total interactions, and (2) differences in measured forces at different surfaces. By using atomic force

microscopy (AFM), we measured force vs. distance curves for the interaction between a DNA tethered on a

AFM tip and graphitic surfaces (Fig 1). We observed characteristic plateaus in the curves, which are associated

with peeling (near-equilibrium detachment) of the DNA molecule from the surface. Single-molecule forces were

measured at range of temperatures (5°C – 45°C) in pH 7 PB buffer solution with added 0.03M of NaCl.

Measurements were combined with measurements of macroscopic properties of water interacting with

underlying surfaces - interfacial free energies at different temperatures.

Linear increase of molecular forces with changes in interfacial energies at different temperatures

suggested that changes in total force are attributed to changes in hydrophobic interactions and uncovered

intimate connection between nanoscopic parameters (measured force) and macroscopic parameters (interfacial

free energy). The total interaction is the combination hydrophobic, van der Waals, and entropic-elastic forces.

From intercepts on y-axis, in the limit when hydrophobic interaction goes to zero, for the first time, we could

detect values of vdW forces of DNA nucleotides with graphitic surfaces (~ 15-20 pN monolayer graphene, ~35-

40 pN HOPG). We observe (2) striking differences in vdW forces between surfaces of single layer graphene

and bulk HOPG interacting with individual DNA molecules, indicating translucency of graphene to molecular

interactions.

The insight obtained from our experiments can be used to modulate DNA-graphene interaction and

possibly control to movement of individual biomolecule; to completely eliminate interactions for nanopore-based

DNA sequencing

References

[1] Garaj, S., Liu, S., Golovchenko, J. A. & Branton, D. Molecule-hugging graphene nanopores. Proc. Natl. Acad. Sci. 110, 12192–12196 (2013)

[2] Rafiee J. et al. Wetting transparency of graphene. Nature Materials. 11, 217-222 (2012)

[3] Tang et. al. J.Phys.Chem C, 122, 12, 6721-6729 (2018)

33


Figures

Figure 1. Characteristic force vs. distance curve for interaction of individual DNA molecule with the surface (left), and schematics of the experiment (right)

Figure 2: Temperature dependence of the total force dependence of interaction between graphene and HOPG with DNA oligomers (left), DNA-HOPG and DNA-graphene force as a function of interfacial free energy for different substrates (right)

34


Lapo Bogani Michael Slota, Tian Pei, Pascal Gehring, Nicola Dotti, Hatef Sadeghi, Colin J. Lambert, Klaus Müllen, Akimitsu Narita University of Oxford, Department of Materials, 16 Parks Road, OX1 3PH, Oxford, UK [email protected]

Quantum Manipulation of Molecular Graphene Magnetic states in graphene nanostructures have undergone intense theoretical scrutiny, because their coherent manipulation would be a milestone for spintronic and quantum computing devices. In nanoribbons, experimental investigations are however hampered by lack of the required atomic control of the edges, and that the proposed graphene terminations are chemically unstable. Several questions remain thus unsolved: how can molecular spins be assembled into hybrid structures? What is the influence of the graphene environment on the spin? Can molecules be used to control coherent currents in graphene devices? Here we try to provide an answer to these questions, exploring spin-graphene interactions by using molecular magnetic materials.

Here we show our results using bottom-up shaping of graphene, first by graphene nanoribbons made via molecular routes. We observe the predicted delocalized magnetic edge states, and comparison with a non-graphitized reference material allows clear identification of fingerprint behaviours.[1] We quantify the spin-orbit coupling parameters, define the interaction patterns, and unravel the spin decoherence channels. We then show how such molecular structures can be included into molecular devices, producing magnetoresistive effects that are opposite to non-molecular devices.[2] Even without any optimization, the spin coherence time is in the µs range at room temperature, and we perform room temperature quantum inversion operations between spins [3] References

[1] M. Slota et al., Nature, 2018, https://doi.org/10.1038/s41586-018-0154-7. [2] T. Pei et al., Nature, submitted [3] F. Lombardi, submitted.

Figures

Figure 1: Schematic representation of a molecular graphene nanoribbon with edge (yellow) and localized (red) spin states.

35


Alessandra Bonanni Wei Li Ang; Zhao Xuan Cheng Division of Chemistry & Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 [email protected]

Nano-graphene oxide as electroactive label for the detection of biomolecules

Electroactive carbon nanomaterials such as nano-graphene oxide have shown great promise as electrochemical labels for the detection of biomolecules. Specifically, the presence of electrochemically reducible oxygen containing groups (OCGs) distributed along the surfaces and at the edges of the graphene sheets enables the material to become extremely electroactive.[1] The intrinsic electrochemical signal generated by electrochemically reducible OCGs on graphene oxide nanocolloids (GONCs) was used here for applications in food science and DNA analysis. The unique interactions between graphene oxide nanocolloids and single-stranded DNA nitrogenous bases allowed the assessment of food contaminations by using a DNA aptamer as biorecognition element,[2] and the detection of a single nucleotide polymorphism during genosensing.[3] A novel approach using GONCs simultaneously as platform and label for aptasensing will be also shown, as well as the possibility of using the same material as label for electrochemical PCR. References

[1] Zhou, M.; Wang, Y. L.; Zhai, Y. M.; Zhai, J. F.; Ren, W.; Wang, F. A.; Dong, S. J., Chem - Eur J, 15 (2009) 6116-6120.

[2] Cheng, Z. X.; Ang, W. L.; Bonanni, A., ChemElectroChem, 6 (2019) 3615-3620. [3] Bonanni, A.; Chua, C. K.; Zhao, G.; Sofer, Z.; Pumera, M., ACS Nano 6 (2012) 8546-8551

Figures

Figure 1: Schematic of GONCs used as platform and label for aptasensing.

36


Alexander S. Botin1,2,3,* Andrey I. Poletaev 2, Tamara S. Popova 1

1 Sklifosovsky Institute of Emergency Medicine, Moscow, Russia 2 Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia 3 Institute of Biochemical Technology and Nanotechnology; RUDN University, Moscow, Russia Contact@E-mail: [email protected]

Polygraphene as Carbon Nanomatrix for Detoxication and Sterilization of Gaseous and Liquid Media for Air and Water Treatment.

Nanocomposite of PolyGraphene (PG) obtained as expanded graphite after hydro-termic treatment of modified graphite became to be able to interact as sorbent PG with wide range of organic pollutants. It was studied the sorption properties of carbon material as an example of PolyGraphene (PG) concerning of organic pollutants. PG - version of ultrafine carbon sorbent, which was developed on the basis of the modified oxygen-containing expanded graphite (OCEG). Materials like PG have a very high absorption capacity, especially with respect to hydrophobic compounds (1:30 - 1: 100). For this reason, such materials are effectively used for the purification of aqueous solutions and suspensions from a wide range of organic pollutants (from benzene to oils). Since the envelopes of bacteria and viruses, as well as many toxins, are hydrophobic, forms of graphite obtained by thermal decomposition can effectively sorb and retain toxins, antibiotics, virus particles, pathogenic microorganisms, and many xenobiotics (for example, diclofenac). These facts indicate possible biotechnological applications of PG. Electron microscopy of various samples of PG showed that this material is a stack of graphene sheets with a multiplicity of 1-10-100, depending on the preparation technology. Repeated chemical modification and thermo-activation allows to obtain a material with stacks of lesser frequency, up to single sheets of graphene. Various technological options for producing PG were investigated and the best option was de-termined in terms of the ratio of functional characteristics and the cost of the resulting sorbent. It was shown that PG can be used in several areas: as an active base and modifier as an immunosorbent - the main bioactive component of test systems for immunodiagnostics of viral infections; absorber for water purification from harmful impurities - including biological; absorber for air sterilization. For microbiological purification of gas mixtures, PG were used in fluidized bed filters to avoid the overshoot of microorganisms through a fine sorbent. The study of sterilization of liquid media showed that PG filters are able to delay and inactivate up to 106 cells per 1 mg of sorbent. The study of filters based on PG showed that water from a polluted open source (urban pond) after a single filtration through a filter with PG acquires the properties of drinking water in accordance with sanitary indicators. The presence of oxidized carbon residues gives PG the ability to bind heavy metal ions. Filters combining PG with activated carbon had the highest efficiency. In this embodiment, the filter is capable of removing not only metal ions, but also chlorine ions. The use of PG for cleaning gas mixtures has another attractive prospect: chemical modification of carbon residues (oxidation) allows doping the sorbent with catalytic additives, which, for example, can oxidize carbon monoxide to dioxide, and also perform other detoxification functions. PG-based sorbents can serve as the basis for the creation of complex systems with the introduction of additional components having specific sorption characteristics. This suggests that sorbents based on PG are promising material for various applications in the field of environmental ecology and endoecology - the normalization of parameters of the internal environment of the body. Keywords: graphene, PolyGraphene, stability, antimicrobial activity, detoxification.

37



Xiaorui Gao Ximeng Liu, Zongkui Kou, John Wang* Department of Materials Science and Engineering, National University of Singapore, 117574, Singapore [email protected], [email protected]

Significant Role of Al in 2D Layered Double Hydroxides for Enhancing Electrochemical Performance of Flexible Asymmetric Supercapacitor

We have purposely developed ternary NiCo2Alx layered double hydroxides (LDHs) with varying levels of Al stoichiometry, grown directly on mechanically flexible and electrically conducting carbon cloth (CC@NiCo2Al-LDH). Al plays a significant role in determining the structure, morphology and electrochemical behavior of NiCo2Alx-LDHs. At an increasing level of Al in NiCo2Alx-LDHs, there is a steady evolution from one-dimensional nanowire to two-dimensional nanosheets. The CC@NiCo2Al-LDH at an appropriate level of Al and with the nanowire-nanosheet mixed morphology exhibits both significantly enhanced electrochemical performance and excellent structural stability, with an about 2.3-fold capacitance of NiCo2-OH. When applied as the anode in a flexible asymmetric supercapacitor (ASC), the CC@NiCo2Al-LDH gives rise to a remarkable energy density of 44 Wh kg−1 at the power density of 462 W kg−1, together with remarkable cyclic stability with 91.2% capacitance retention over 15000 charge-discharge cycles. The present study demonstrates a new pathway to significantly improve the electrochemical performance and stability of transition metal LDHs, which are otherwise unable in structure and poorly performing in both rate and cycling capability. References

[1] Xiaorui Gao, Ximeng Liu, Dajun Wu, Bin Qian, Zongkui Kou*, Zhenghui Pan, Yajun Pang, Linqing Miao, and John Wang*, Adv. Funct. Mater. 2019, 1903879

[2] Ximeng Liu, Lei Zhang, Xiaorui Gao,* Cao Guan, Yating Hu, and John Wang*, ACS Appl. Mater. Interfaces 2019, 11, 23236-23243

Figures

Figure 1: (A) Schematic illustration of the synthesis procedure, (B) SEM and TEM images, and (C) electrochemical performances of the CC@NiCo2Alx-LDH and CC@NiCo2-OH

38



Junxiong Hu1,2,3 Jian Gou2,3, Ming Yang4, A. T. S. Wee2,3, A. Ariando1,2,* 1NUSNNI, National University of Singapore, Singapore 117411 2Department of Physics, National University of Singapore, Singapore 117542 3Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117551 4Institute of Materials Research & Engineering, A*STAR (Agency for Science, Technology and Research), Singapore 138634 *Corresponding author: [email protected]

Room-temperature colossal magnetoresistance in terraced single-layer graphene

Disorder-induced magnetoresistance (MR) effect is quadratic at low perpendicular magnetic fields and linear at high fields [1,2]. This effect is technologically appealing, especially in the two-dimensional (2D) material like graphene, since it offers potential applications in the 2D magnetic sensor with nanoscale resolution. However, it is a great challenge to realize a graphene magnetic sensor based on this effect because of the difficulty in controlling the spatial distribution of disorder and enhancing the MR sensitivity in the single-layer regime. Here, we report a room-temperature colossal MR of up to 5,000% at 9 T in a terraced single-layer graphene [3]. By laminating a single layer of graphene on a terraced substrate, like SrTiO3, which induces a sample-wide strain at the steps and terraces in graphene, we demonstrate a universal one order of magnitude enhancement in the room-temperature MR compared to conventional single-layer graphene devices. Strikingly, a colossal MR of >1,000% is also achieved in the terraced graphene even at a high carrier density of ~ 1012 cm-2. Our results open a new route for tailoring physical property of 2D materials by engineering the strain through terraced substrate. References

[1] R. Xu,A.Husmann,T. Rosenbaum, M.-L. Saboungi, J.Enderby, and P. Littlewood, Nature (London) 390 (1997) 57. [2] A. Husmann, J. Betts,G.Boebinger, A. Migliori,T.Rosenbaum, and M.-L. Saboungi, Nature (London) 417 (2002)

421. [3] Junxiong Hu et al. Room-temperature colossal magnetoresistance in terraced single-layer graphene. (Submitted,

2019).

Figures

Figure 1: Design and room-temperature local MR of terraced single-layer graphene.

39


Nicolas Leconte Srivani Javvaji, Jiaqi An and Jeil Jung University of Seoul, South Korea [email protected]

Relaxation Effects in Twisted Bilayer Graphene: a Multi-Scale Approach

We introduce a multi-scale approach to obtain accurate atomic and electronic structures for atomically relaxed twisted bilayer graphene. High-level exact exchange and random phase approximation (EXX+RPA) correlation data provides the foundation to parametrize systematically improved force fields for molecular dynamics simulations that allow relaxing twisted layered graphene systems containing millions of atoms making possible a fine sweeping of twist angles. These relaxed atomic positions are used as input for tight-binding electronic band-structure calculations where the distance and angle-dependent interlayer hopping terms are extracted from density functional theory calculations and subsequent representation with Wannier orbitals. We benchmark our results against published force fields and widely used tight-binding models and discuss their impact in the spectrum around the flat band energies. We find that our relaxation scheme yields a magic angle of twisted bilayer graphene consistent with experiments between 1.0◦ ∼ 1.1◦ using commonly accepted Fermi velocities

of graphene υF ≃ 1.0 ∼ 1.1 × 106 m/s that is enhanced by about 14%∼20% compared with often used local density approximation estimates. Finally, we present high-resolution spectral function calculations for comparison with experimental ARPES. Additional force field parameters are provided for hBN-layered materials. References

[1] N. Leconte, S. Javvaji, JQ An and J. Jung, arXiv:1910.12805 (2019)

40


Jan Mischke Erik Weisenseel, Wolfgang Mertin, Gerd Bacher University of Duisburg-Essen & CENIDE, Bismarckstr. 81, 47057 Duisburg, Germany [email protected]

Direct PE-CVD growth of graphene on GaN under N2 atmosphere in a 4” cold-wall CVD reactor

Gallium nitride (GaN) has gathered a lot of attention over the last years as the material of choice for modern ultra-violet Light Emitting Diodes (UV-LEDs) [1]. One performance limiting bottleneck towards more efficient UV-LEDs is the poor p-type conductivity of AlxGa1-xN which is used as a top layer material for current spreading and current injection into the active region of the LED. A promising approach to tackle this challenge is to use graphene on top of the AlxGa1-xN-layer as a transparent electrode due to its high conductivity and low absorption losses over a broad spectral range [2]. A common method to establish graphene contacts is the transfer of graphene layers from metallic substrates such as copper foil, which are grown via a chemical vapor deposition (CVD) process. However, these transfer processes are hardly upscalable and potentially damaging to the graphene layers. Recently, we showed the potential of a plasma-enhanced CVD (PE-CVD) process to grow graphene on copper foils at low temperatures in a 4” Black Magic CVD system from AIXTRON [3]. This plasma-enhanced process was then adapted onto non-metallic substrates. Here, we report the successful growth of graphene directly on GaN based LEDs via PE-CVD under N2 atmosphere and reduced temperatures (800 °C) in a. N2, instead of the commonly used H2, as a process gas is shown to minimize the surface degradation of the GaN-LED during the PE-CVD process while enabling the growth of graphene [Figure 1]. By reducing the CH4 flux from 15 to 5 sccm the quality of the grown layers is increased as evidenced by an improvement of the sheet resistance from ~ 77 kΩ/□ to ~ 3 kΩ/□. Transmission measurements show a loss of 6 ± 1% in transparency which indicates the growth of 2-3 graphene layers. Analyzing fully processed devices yield a significant improvement (by a factor of 4) of the lateral current spreading, demonstrating the potential of PE-CVD graphene grown under N2 atmosphere as transparent top contact in GaN-LEDs [Figure 2]. References [1] M. Kneissl, T.-Y. Seong, J. Han, H. Amano, Nature Photonics 13 (2019) 233-244 [2] R.R. Nair, P. Blake, A.N. Grigorenko, K.S. Novoselov, T.J. Booth, T. Stauber, N.M.R. Peres, A.K. Geim, Science, 5881

(2008) 1308 [3] B. Bekdüz, Y. Beckmann, J. Mischke, J. Twellmann, W. Mertin, G. Bacher, Nanotechnology 29 (2018) 45, 455603

Figures

Figure 1: SEM images of the GaN surface under H2 (left) and N2 (right) atmosphere after the PE-CVD process with corresponding Raman spectra of the graphene layers (lower panel).

Figure 2: Microscopic image of a GaN-LED without (left) and with (right) graphene current spreading layers at 20 mA current injection.

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Saroj Kumar Nayak1,* Sunil Kumar Pradhan1,*, Arijit Mitra, Mihir Sahoo, Balaram Polai1, Arijit Mitra1, Bijoy Sathpathy1, Arun Sahu3, Subrat Kar3, Parlapalli V. Satyam2, Pulickel M Ajayan4 1School of Basic Science, Indian Institute of Technology, Bhubaneswar, India, 752050 2Institute of Physics, Bhubaneswar-751005, India, 751005 3National Aluminium Co. Ltd, Bhubaneswar, India, 751013 4Department of Materials Science and Nano Engineering, Rice University, Houston, USA 77005 [email protected]

Giant enhancement of thermal conductivity of aluminium-graphene composite through electron phonon engineering

We will present our recent study of electron phonon engineering in aluminium based devices. For example, a novel approach was applied for the development of Aluminium (Al) based composite materials for the fabrication of devices to be used as solar thermal collectors for domestic and industrial use. We report here the enhancement of thermal conductivity of 410 W/mK for the Al-graphene composite sintered devices (incorporation of 5% by weight of graphene into the Al system), which is higher than the bulk Al at room temperature. Also, we have observed that, the Co-efficient of thermal expansion (CTE) of Al-Graphene composite devices have less values compared to pristine sintered Al at different temperatures which indicates the Al-Graphene composites have higher strength compared to Al. The fabricated devices and synthesize composite materials have been evaluated in terms of different micro-structural characterization tools like field emission scanning electron microscopy(FE-SEM), energy dispersive X-ray analysis (EDAX), electron probe micro analyser (EPMA) etc for qualitative and quantitative analysis, which shows well distribution of the constituents of Al-Graphene composite materials over the scan areas. The sintered samples have also been evaluated through density measurement and they are found to be ≈ 97.5 % density after sintering. The morpho-structural investigation of the device by X-ray micro CT(computed tomography) reveals the quality of product and the absence of the pores. It shows high dense sample with no voids and cracks, implying uniformity. Interestingly, the electrical conductivity of the composite remained similar or better than that of pristine aluminium- while giant enhancement observed in the thermal conductivity of the composite. The thermal fusing of Al based composite materials can be well deployed as solar thermal collectors for solar water heating. Theoretical and computational studies provide the atomic level understanding of interplay between electron and phonon dynamics in aluminium from atom to bulk.

42


Massimo Spina Nathan Ronceray, Mordjann Hind Souilamas, Kittipitch Yooprasertchuti, Slaven Garaj Centre for Advanced 2D Materials, National University of Singapore, Singapore [email protected]

Ionic mobility engineering in sub-nanometer graphitic channels Nanochannels based on carbon materials have been intensively studied in the last decade because of their promising application in nanofiltration [1, 2] and the novel physical phenomena arising between graphitic surfaces at the nanoscale [3–6]. More recently, atomically-smooth graphitic channels with sub-nm heights have been fabricated and used to investigate the physics of ions and water molecules in slits comparable to the smallest ion sizes. It has been shown that water flows very fast inside those channels [3], while ionic mobilities are influenced by the distortion of their hydration shells within the narrow channels [4]. In this work, we investigated ionic flow in atomically-smooth graphitic channels with height ranging from 7Å to 35nm. We show that the mobilities of ions in such confinements do not scale with hydration shell in a simple fashion, and we further explored the role of the surface charge, physical confinement and chemical interactions. Engineering ionic mobilities within the graphitic channels, we could induce strong current driven by the salinity gradient. Such osmotic power generators – driven by mobility engineering, rather than surface charge – are more resilient on the variation of chemical environment and show orders of magnitude increase in osmotic power density compared to commercial membranes. References [1] S. Hong et al., Nano Lett. 17, 728–732 (2017). [2] J. Abraham et al., Nat. Nanotechnol. 12, 546–550 (2017). [3] B. Radha et al., Nature. 538, 222–225 (2016). [4] A. Esfandiar et al., Science. 358, 511–513 (2017). [5] E. Secchi, A. Niguès, L. Jubin, A. Siria, L. Bocquet, Phys. Rev. Lett. 116, 154501 (2016). [6] Q. Xie et al., Nat. Nanotechnol. 13, 238–245 (2018) Figures

Figure 1: AFM image of few-nm high graphene spacers and their height profile.

43

Graphene Singapore Summit 2019

November 11-12, 2019

Guy Trambly de Laissardière1 Javad Vahedi1, Andreas Honecker1, Robert Peters2

1 Laboratoire de Physique Théorique et Modélisation, CNRS UMR 8089, Université de Cergy-Pontoise, Cergy-Pontoise, France

2 Department of Physics, Kyoto University, Kyoto, Japan

[email protected]

Magnetism of Magic-Angle Twisted Bilayer Graphene

The recent discovery of correlated insulators and superconductivity in twisted bilayer graphene at so-called “magic angles” [1,2] has stimulated an avalanche of experimental and theoretical activities. The Moiré pattern of the bilayers at these magic angles leads to localization of the low energy electrons in the AA-stacking regions, reflected by very flat regions in the band structure that replace the Dirac cone of an isolated graphene layer [3,4]. This reduction of the kinetic energy enhances the relative importance of interactions and thus renders the bilayer systems much more susceptible to correlation effects than a single layer. Here we investigate the question of magnetic instabilities at half filling in these systems using a combination of real-space Hartree-Fock and dynamical mean-field theories [5], starting from a tight-binding description of the non-interacting bilayer systems [3,6] to which we add a local Hubbard interaction U in order to model the Coulomb repulsion between electrons of opposite spin. We find that indeed localized antiferromagnetic states emerge for values of the Coulomb interaction U that is an order of magnitude smaller than what would be required to render an isolated layer antiferromagnetic. Ferromagnetic states have recently been observed in experiments on doped twisted bilayers [7], and according to our results, the same should be possible for antiferromagnetism at half filling. References

[1] Y. Cao, V. Fatemi, A. Demir, S. Fang, S. L. Tomarken, J. Y. Luo, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, E. Kaxiras, R. C. Ashoori, and P. Jarillo-Herrero, Nature, 556 (2018) 80

[2] Y. Cao, V. Fatemi, S. Fang, K. Watanabe, T. Taniguchi, E. Kaxiras, and P. Jarillo-Herrero, Nature, 556 (2018) 43 (2018)

[3] G. Trambly de Laissardière, D. Mayou, and L. Magaud, Nano Letters, 10 (2010) 804

[4] R. Bistritzer and A. H. MacDonald, Proc. Natl. Acad. Sci. USA 108, (2011) 12233

[5] M. Raczkowski, R. Peters, T. T. Phùng, N. Takemori, F. F. Assaad, A. Honecker, and J. Vahedi, preprint arXiv:1908.04307 (2019)

[6] G. Trambly de Laissardière, D. Mayou, and L. Magaud, Phys. Rev. B, 86 (2012) 125413

[7] A. L. Sharpe, E. J. Fox, A. W. Barnard, J. Finney, K. Watanabe, T. Taniguchi, M. A. Kastner, D. Goldhaber-Gordon, Science 365, (2019) 605

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Marc Vila1,2

Jose H Garcia1, Aron W. Cummings1, Stephen R. Power1,3,4, Christoph Groth5, Xavier Waintal5, Stephan Roche1,6

1 - Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain. 2 - Department of Physics, Universitat Autònoma de Barcelona, Campus UAB, Bellaterra, 08193 Barcelona, Spain. 3 - Universitat Autònoma de Barcelona, Campus UAB, Bellaterra, 08193 Barcelona, Spain. 4 - School of Physics, Trinity College Dublin, Dublin 2, Ireland. 5 - Univ. Grenoble Alpes, CEA, IRIG-PHELIQS, 38000 Grenoble, France. 6 – ICREA - Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain. [email protected]

Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport

Improved fabrication techniques have enabled the possibility of ballistic transport and unprecedented spin manipulation in ultraclean graphene devices. Spin transport in graphene is typically probed in a nonlocal spin valve (Figure 1, left) and is analyzed using spin diffusion theory, but this theory is not necessarily applicable when charge transport becomes ballistic or when the spin diffusion length is exceptionally long. Here, we study these regimes by performing quantum simulations of graphene nonlocal spin valves [1]. We find that conventional spin diffusion theory fails to capture the crossover to the ballistic regime (Figure 1, right) as well as the limit of long spin diffusion length. We show that the latter can be described by an extension of the current theoretical framework. Finally, by covering the whole range of spin dynamics, our study opens a new perspective to predict and scrutinize spin transport in graphene and other two-dimensional material-based ultraclean devices. References

[1] M. Vila et. al., submitted (2019). Figures

Figure 1: Left: Sketch of the lateral nonlocal spin valve. Red (black) regions denote the contacts (sample). Right: Nonlocal resistance (Rnl) versus magnetic field for diffusive spin transport (dashed lines), quasiballistic spin transport (solid lines) and ballistic spin transport (inset).

45


Zihao Wang1

C. R. Woods1,2, Yi Bo Wang1, A. Knothe2, Jun Yin1, Yaping Yang2, Lin Li2, M. Hollwill2, A. Mishchenko1,2, A. K. Geim1,2, Vladimir. I. Fal’ko1,2, K. S. Novoselov1,2,3 1School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK 2National Graphene Institute, University of Manchester, Oxford Road, Manchester, M13 9PL, UK 3Department of Materials Science and Engineering, 9 Engineering Drive 1, Singapore [email protected]

Composite super-moiré lattices in double aligned graphene heterostructures

Van der Waals heterostructures, as vertical stacks assembled by different 2D crystals, have been widely used to produce combinations with predetermined functionalities. Apart from the selection and the sequence of 2D crystals, controlling the twist angle between stacking layers opened the use of another degree of freedom, especially for two crystals with similar lattice mismatch, which forms moire pattern. Unlike the singly aligned heterostructures with one moire pattern, we reported a doubly aligned structure in which fully encapsulated graphene simultaneously aligned to the top and bottom hBNs.[1] In this case, two periodic potentials due to the moire pattern are applied on graphene simultaneously (which can be proved by two secondary Dirac points in transport measurement and two sets of hexagonal patterns in Fourier transformation of AFM image as shown below and their differential will create another set of supermoires, among which the one with largest period can be independent of the difference in the lattice constants between two crystals and break through the restrictions of this lattice mismatch to achieve the period much larger than 14nm. This would open up the prospect for the design of graphene band reconstruction at arbitrary low Fermi energies. References

[1] Yankowitz et al., Emergence of superlattice Dirac points in graphene on hexagonal boron nitride. Nat. Phys. 8,

382-386 (2012).

Figures

Figure 1: Left: Rxx as a function of carrier concentration n with two moire periods 15.3nm (blue),14.0nm (green). The

moiré and super-moiré peaks marked by arrows and labelled with their periods in the unit of nanometres. Largest supermoire with the period 36.3nm, marked by red. Right: Fourier transform of the AFM image showing two sets of distinct hexagonal patterns (red and green dashed hexagons).

46


Tingkai Zhao Xin Zhao, Xiarong Peng Northwestern Polytechnical University, No.127 Youyi West Road, Xi’an, China [email protected]

Preparation and Performance of Carbon Dot Stabilized Copper Sulphide/Carbon Nanotubes Hybrid Composite as Supercapacitor

Electrode Materials Abstract Carbon dot stabilized copper sulphide/carbon nanotube (CD@CuS/CNT) hybrid composite was synthesized by a simple one-pot hydrothermal reaction at 180℃ using copper sulphate and sodium thiosulphate as Cu and S sources. The microstructures and morphologies of hybrid composites were characterized by X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscope (SEM) and transmission electron microscope (TEM)(see Figure 1). Moreover, a high-performance asymmetric supercapacitor device was assembled to improve the electrochemical performance of CuS as well as carbon based supercapacitors1. The CD@CuS/CNT hybrid composite exhibited a maximum specific capacitance of 736.1F·g-1 at the current density of 1A·g-1. Furthermore, the CD@CuS/CNT hybrid composite showed good cycling stability with more than 92% capacitance retention after 5000 cycles. These excellent results suggested that CD@CuS/CNT hybrid composite has promising application potential for supercapacitors2. References

[1] L. Dong, et al, J. Mater. Chem. A, 4(2016), 4659. [2] T. Zhao, et al, Comp. Part B, 150(2018), 60.

Figures

Figure 1: (a,b) TEM, and (c,d) HRTEM images of CD@CuS-CNTs

47

POSTERS


ANG WEI LI DR ALESSANDRA BONANNI NTU SINGAPORE [email protected]

Use of Graphene Oxide Nanocolloids as electrochemical labels for PCR detection of Genetically Modified Food

The use of Graphene Oxide materials as electrochemical labels in the Polymerase Chain Reaction (PCR) for

DNA detection was investigated owing to the various advantages it presents over the more commonly

employed fluorescent labels, including a simplified protocol, cost reduction as well as an enhanced specificity

and efficiency of the PCR process. In this study, the effectiveness of Graphene Oxide Nanocolloids (GONC) as

electrochemical labels for PCR was investigated by observing its electrochemical behaviour after conjugating

GONCs with single-stranded DNA (ss-DNA) and double-stranded DNA (dsDNA). GONC labelled DNA primers

were also employed in the PCR amplification of the 35S promoter sequence commonly found in Genetically

Modified (GM) foods to determine their suitability towards the detection of GM food. Upon successive

conjugation of GONC to ssDNA or dsDNA, a measurable electrochemical signal of the GONC material was

observed with the obtained results portraying a lower signal for the GONC conjugates with dsDNA than

ssDNA. Moreover, GONC conjugates containing both the sense and antisense primers of the 35S promoter

sequence gave similar electrochemical performances in terms of their sensitivity and linear response

towards changes in GONC concentration. A higher sensitivity and lower linear response were observed for

GONC conjugates with ssDNA than dsDNA. In addition, GONC labelled primers employed in the PCR

amplification process of the 35S promoter sequence in GMO maize powder showed no interference during

the PCR amplification process on the PCR product and was chosen as a suitable label for the primers utilised

for subsequent DNA detection. The obtained findings are essential towards the understanding of the

suitability of GONC as electrochemical labels in DNA detection and their subsequent application in DNA

based GM food detection.

49


Magdalena Grzeszczyk1 M. R. Molas1,2, M. Bartos2,3, K. Nogajewski1,2, A. Bogucki1, C. Faugeras2, P. Kossacki1, A. Babiński1, M. Potemski1 1Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland 2Laboratoire National des Champs Magnetiques Intenses, CNRS-UGA-UPS-INSA-EMFL, Grenoble, France 3Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic [email protected]

The effect of environment on optical properties of monolayer MoSe2 Recent studies demonstrate stacking-induced modifications on the electronic and optical properties of transition metal dichalcogenides (TMDs). [1,2] Using various metals and their fundamental physical properties we are able to change amount of carriers in a chosen material, creating a non-invasive doping method of TMDs. We present effects of Pt, Au, Mo and Zr substrates on MoSe2 (values of work functions vary within energy band gap of 1L MoSe2 - given in eV units in Fig. 1(a)). Results of Raman scattering measurements confirm monolayer thickness of exfoliated layers (Fig. 1(b)). The Raman spectra are not significantly affected by either the metal on which the flakes were deposited or strain and disorder that could have been introduced into the flakes during the fabrication process. Presented in Fig. 1(c) are results of photoluminescence (PL) and reflectance contrast (RC). Well separated features corresponding to the emission from the n = 1 ground state neutral exciton (X0 ~1.66 eV) and the charged exciton (trion, X- ~1.63 eV) are observed in all samples. Our results show that the intensity of the PL peaks changes as a function of the substrate. The relative intensity of the X- emission grows with the lowering metal work function. These studies demonstrate that selection of suitable substrates can be used to inject appropriate types of charge carriers into the respective bands of 2D TMDs. Efforts to better understand that type of interfaces and doping processes may be of great value for future applications in electronic devices. References

[1] A. Raja et al. Nature Communications, 8, (2017) 15251. [2] C. Steinke et al. Physical Review B, 96, (2017) 045431.

Figures Figure 1: (a) Scheme of energy levels diagram. (b) Room-temperature Raman scattering spectra and (c) photoluminescence (PL) and reflectance contrast (RC) spectra of studied structures measured at T = 5 K.

50


Sharon Lim Xiaodai Yong Han Jerome Leow, Yun Xuan Patria Lim, Jianfeng Wu, Chorng-Haur Sow National University of Singapore, Department of Physics, 2 Science Drive 3, Singapore 117542 [email protected]/[email protected]

Nanosurfer Flash-mobs: Electric-Field-Choreographed Silver Migration on Graphene Oxide

We present for the first time the ability to direct and control the migrating path of silver nanoparticle across graphene oxide (GO). With the help of a focused laser beam, we demonstrated choreographed nanoparticle assembly on the GO via directed electric-field. Silver migration and the resultant dendrite formation on GO was characterized through electrical testing coupled with Fluorescence Microscopy. The proposed mechanism for silver migration in the GO involves the interlayer water between GO sheets serving as the electrolyte for the electrochemical process. This interlayer water facilitates the disappearance of dendrites through oxidation and dissolution into the water. Furthermore, we demonstrate that the shape of Ag dendrite formation can be controlled a combination of applied electric field and patterned regions of reduced GO film created by focused laser beam. This paves the way to an alternative low-cost silver nanoparticle assembly method requiring only a low-powered laser and low voltage. References

[1] YHJ Leow, PYX Lim, SX Lim, J Wu, CH Sow, Nanoscale Adv., 1 (2019), 2180-2187

Figures

Figure 1: Silver dendrites assisted micro-display on GO film, whose visibility is tunable by external applied potential is created.

51


Presenting Author: Jie SU Co-authors: Mykola Telychko1,2†, Pavel Jelínek3,4*, Jishan Wu1*, Jiong Lu1,2*

1Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore. 2Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore. 3Institute of Physics, The Czech Academy of Sciences, Prague 16200, Czech Republic. 4Regional Centre of Advanced Technologies and Materials, Palacký University, Olomouc 78371, Czech Republic. Email: [email protected]

On-surface synthesis and characterization of open-shell graphene molecules

Abstract Clipping triangular motifs along the zigzag orientation of graphene creates an entire family of ZTGMs (also known as non-Kekulé polynuclear benzonoid compounds), which are predicted to possess multiple unpaired π-electrons and high-spin ground states with large net spin scaling linearly with the number of carbon atoms of zigzag edges (N, N>2). However, the scalable synthesis of large ZTGMs and the direct observation of their edge states have been long-standing challenges due to the molecules’ high chemical instability. Here we report the bottom-up synthesis of π-extended [5]triangulene with atomic precision via surface assisted cyclodehydrogenation of a rationally-designed molecular precursor on metallic surfaces. Atomic force microscopy (AFM) measurements unambiguously resolve its ZTGM-like skeleton consisting of 15 fused benzene rings, while scanning tunneling spectroscopy measurements reveal edge-localized electronic states. Bolstered by density functional theory (DFT) calculations, our results show that [5]triangulenes synthesized on Au(111) retain the open-shell π-conjugated character with magnetic ground states.

References

[1] J. Su et al., Sci. Adv., 5 (2019) eaav7717 Figures

Figure 1: (a) nc-AFM image of a [5]triangulene on Cu(111) surface. (b) The corresponding STM and the molecular structure of [5]triangulene molecule. Scale bar: 4 Å.

52


Marc Vila1,2

Nguyen Tuan Hung3, Stephan Roche1, 4, Riichiro Saito3

1 - Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain. 2 - Department of Physics, Universitat Autònoma de Barcelona, Campus UAB, Bellaterra, 08193 Barcelona, Spain. 3 – Department of Physics, Tohoku University, Sendai 980-8578, Japan. 4 – ICREA - Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain. [email protected]

Tunable Circular Dichroism and Valley Polarization in the Modified Haldane Model

Circularly polarized light is at the core of many different and intriguing properties such as circular dichroism [absorption is different between left- and right-handed circularly polarized light ( and )] and valley

polarization ( and are absorbed at a specific valley K/K’ in a hexagonal two-dimensional material). In this

presentation, I will discuss the optical properties of a recently proposed modification of the Haldane model [1]. We study the polarization dependence of optical absorption for the modified Haldane model, which exhibits protected antichiral edge modes in presence of sample boundaries and is argued to be realizable in Weyl semimetals or in magnetic transition metal dichalcogenides [2]. A rich optical phase diagram (Figure 1, left) is unveiled, in which the correlations between perfect circular dichroism, pseudospin and valley polarization can be tuned independently upon varying the Fermi energy. Importantly, perfect circular dichroism and valley polarization are achieved simultaneously (Figure 1, right), a feature not yet observed in known optical materials. This unprecedented combination of optical properties suggests some interesting novel photonic device functionality (e.g. light polarizer) which could be combined with valleytronics applications (e.g. generation of valley currents). References

[1] E. Colomés and M. Franz, Phys. Rev. Lett. 120 (2018) 086603. [2] M. Vila, N. T. Hung, S. Roche, R. Saito, Phys. Rev. B. 99 (2019) 161404(R)

Figures

K K'

K K'

Figure 1: (Left) Optical phase diagram of the modified Haldane model [2]. Circular dichroism, valley polarization and

pseudospin polarization is represented by the values , and , respectively. (Right) Tunability of circular

dichroism and valley polarization with varying Fermi energy.

53

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