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Speaker: Prof. Yoo Won Jong
Affiliation: SKKU Advance Institute of Nano Technology (SAINT), Sungkyunkwan University
Abstract Details: Two dimensional (2D) materials are recently being investigated very intensively, with some of them holding great promise as semiconducting materials for future low power nano-electronics, as they present a range of achievable bandgaps and ultra-thin body with efficient electrostatic control. These properties, combined with mechanical flexibility, enable 2D materials to be very promising candidates that can meet major requirements for electronic and photonic devices operated in emerging future mobile and IoT environment. However, formation of proper electrical contacts to nanoscale 2D materials (e.g. transition metal dichalcogenides: TMDs) is becoming a major challenge in realizing the desirable performance of the 2D material-based devices. According to recent studies, the observed two-terminal mobility in single-layer TMD devices is unexpectedly low [1], due to high contact resistance (Rc) induced between metal contact and TMDs. It is known that many 2D crystals are subjected to strong Fermi level pinning when they are in contact with metals, where the pinning is responsible for the observed high Schottky barrier height and high Rc. In this presentation, we address our findings on Schottky barrier heights at the interfaces [2] formed between molybdenum dichalcogenides and various metals such as Ti, Cr, Au, Pd. For MoS2 and MoTe2, via I – V characteristics for various temperatures. Meanwhile, we explore the different metal-MoS2 contacts and investigate the charge carrier injection mechanisms and their transition across the interfacial barrier [3]. Low temperature measurements on MoS2 field effect transistor are carried out and Rc as the function of temperature is studied. As the result, the obvious transition from thermionic emission at high temperature to quantum mechanically tunneling of charge carriers at low temperature along the junction is observed. Furthermore, at a low temperature, the nature of the tunneling behavior is found dependent on I-V characteristics. Interestingly, direct tunneling at a low bias and Fowler-Nordheim tunneling at a high bias is realized for a Pd-MoS2 contact due to the effective barrier shape modulation by biasing. However, at the same bias conditions only direct tunneling is observed for a Cr-MoS2 contact. Acknowledgments This work was supported by the Global Research Laboratory (GRL) Program (2016K1A1A2912707)  and Global Frontier R&D Program (2013M3A6B1078873) at the Center for Hybrid Interface Materials (HIM), both funded by the Ministry of Science, ICT&Future Planning via the National Research Foundation of Korea (NRF). References: [1] A. Allain, J. Kang, K. Banerjee and A. Kis, “Electrical contacts to two-dimensional semiconductors”, Nat. Mater., 14, 1195 (2015) [2] H.-M. Li, D.-Y. Lee, M. S. Choi, D. Qu, X. Liu, C.-H. Ra, and W. J. Yoo, “Metal semiconductor barrier modulation for high photoresponse in transition metal dichalcogenide field effect transistors” Sci. Rep., 4, 4041 (2014) [3] F. Ahmed, M. S. Choi, X. Liu, and W. J. Yoo, “Carrier transport at the metal–MoS2 interface” Nanoscale, 7, 9222 (2015)
About the Speaker: Prof Won Jong Yoo Deputy Director, SKKU Advanced Institute of Nano-Technology Professor, Department of Nano Science and Technology, Sungkyunkwan University 2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do 440-746 Korea (email) yoowj@skku.edu (Tel) 82-31-290-7468 Won Jong Yoo received his BS and MS degrees from Seoul National University in Korea.  In 1993, he received his Ph.D. degree from Rensselaer Polytechnic Institute in USA in the area of the plasma etching properties of semiconductor materials. Before joining Sungkyunkwan University (SKKU) in 2006, he has been an associate professor with National University of Singapore (NUS) where he conducted his research on silicon devices and plasma processes. His main industrial experience was research and development in the areas of semiconductor material/device processes at Samsung Semiconductor Research Center, Korea. He has been leading the collaboration research between Samsung and SKKU for developing future graphene and 2D devices as the director of Samsung-SKKU Graphene Center. He is currently working as the deputy director of SAINT which is one of the leading nano science focused R&D institutions. The areas of his current research interests are the electronic and photonic application of 2D materials including graphene and transition metal dichalcogenides (TMD), the investigation of interfaces formed by using 2D materials, and the investigation of electrical transport occurring in 2D nano-structures.  He has authored or co-authored about 200 journal and conference papers.  He has organized a premier conference, Recent Progress in Graphene/2D Research (RPGR) in 2016.
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Speaker: CA2DM
Abstract Details:

CA2DM is having it’s New Year’s Gathering on 13 January 2017.
All are encouraged to attend.Kindly register to facilitate the ordering of snacks and drinks.

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Speaker: Dr. Ji Wei
Affiliation: Department of Physics, Renmin University of China, Beijing 100872, China
Abstract Details:

In this talk, Prof Ji Wei will briefly summarize the recent progresses on the modelling of interlayer interactions of various two-dimensional materials, e.g. weakened van der Waals interaction in twisted graphene1 and ReS22, covalent-like quasi-bonding in PtS23/PtSe24 and BP5,6, and subtle balance between inter- and intra-layer interactions in organic molecules7. In addition, air stability of BP was theoretically and experimentally investigated, which reveals the atomic details for the air degradation of BP8.

References:

1Jiang-Bin Wu et al., ACS Nano 9 (7), pp 74407449 (2015).
2Xiaofeng Qiao et al., Nanoscale 8, 8324-8332 (2016)
3Yuda Zhao et al., Advanced Materials 28 (12), 23992407 (2016)
4Yuda Zhao et al., Advanced Materials, DOI: 10.1002/adma.201604230
5Jingsi Qiao et al., Nature Commun. 5, 5475 (2014)
6Zhxin Hu et al., Nanoscale 8, 2740 (2016)
7Yuhan Zhang et al., Phys. Rev. Lett. 116, 016602 (2016)
8Yuan Huang et al., Chem. Mater., 28 (22), pp 83308339(2016)

About the Speaker:

Dr. JI, Wei is a computational physicist, working in the field of surface and interface modeling of low-dimensional materials. His research interests include surface and interface modeling of emerging electronic materials and devices. Recently, he is interested in theoretical modeling of electronic, optical, and vibrational properties of two-dimensional materials. He has been also developing theoretical methods for describing beam effects in scanning transmission microscope and understanding ultrahigh resolution in noncontact atomic force microscope. He received his Ph.D in condensed matter physics from the Institute of Physics, Chinese Academy of Science in 2008. Prior to joining Renmin University of China, he spent four years in McGill University as a visiting scholar and then a postdoctoral fellow. He was originally appointed as an Associated Professor by Renmin University in 2010 and was early promoted to Full Professor in 2014. He was supported by the national Young Top-Notch Talent Program in 2014 and the National Science Fund for Excellent Young Scholars in 2016, and awarded Chang-Jiang Young Scholars in 2015. He also serves as trustees in the youth committee and computational materials science division of the Chinese Materials Research Society."

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Speaker: Ho-Kin Tang and Jia Ning Leaw
Affiliation: CA2DM, NUS
Abstract Details:

The electronic properties of graphene have been extensively studied in the past decade. However, there is still ongoing debate on the role of the electron-electron interactions in graphene. Experimentally, a significant enhancement of the Fermi velocity has been observed.[1] In this work, we adapt the quantum Monte Carlo method to graphene with long range Coulomb interaction. We compute the Fermi velocity of this system's low-energy excitations and find that its enhancement depends on the distance to the phase transition: away from the Mott insulator phase transition the Fermi velocity is logarithmically enhanced as we approach the Dirac point due to long-range part of the Coulomb potential; close to the phase transition, the Fermi velocity enhancement is suppressed by short- range part of the potential. Interestingly, we find that realistic graphene samples are typically located in an intermediate region where long- and short-range interactions compete.

Besides studying the renormalization of the Fermi velocity, we also look at the Mott insulator phase transition. This phase transition opens a gap in graphene band structure, which may be relevant for its application on low power electronic devices. In the second part of this talk, we will discuss two different Mott insulating phases – the charge- density -wave (CDW) phase and the spin-density- wave (SDW) phase. We will show that the Gross-Neveu phase transition, which is usually considered in the literature, is the CDW phase transition. We will also consider the Gross-Neveu model with spin, and show how the SDW phase transition is different from the CDW phase transition.

[1] Elias, D. C., et al. 'Dirac cones reshaped by interaction effects in suspended graphene.' Nature Physics 7.9 (2011): 701-704."

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Speaker: Dr. Vinicius Rosa, Assistant Professor
Affiliation: Faculty of Dentistry, NUS
Abstract Details: The global market for bone graft substitutes will worth US$ 3.2 billion in 2022. The market for hip and knee orthopaedic surgical joint replacement products is expected to reach US $33 billion in the same year. Hence, the development of materials and strategies that can promote faster healing of prosthetic devices and improved regeneration of bony defects is of high interest. Graphene and its derivatives (graphene oxide and reduced graphene oxide) have remarkable mechanical properties, can be chemically modified and allow the attachment of molecules and proteins. Due to these characteristics, these carbon-based materials have received increasing attention for several biomedical applications. As graphenes can improve mechanical properties of several biomaterials, induce, and increase cell differentiation towards osteoblasts, they have emerged as alternatives to promote bone regeneration. In this seminar, Dr. Rosa will discuss the key achievements made with graphenes for bone tissue engineering and the possible graphene-mediated mechanisms leading to the enhanced regeneration.
About the Speaker: Dr. Vinicius ROSA Assistant Professor, Oral Sciences, Faculty of Dentistry, NUS. Faculty, Centre for Advanced 2D Materials and Graphene Research Centre, NUS. Dr. Rosa obtained D.D.S. (Doctor of Dental Surgery) in 2005 and has received the "Academy of Dental Materials Student Award", an award presented by the Academy of Dental Materials to the most outstanding student researcher in the field of Dental Materials. In 2007, the M.Sc. dissertation on the deterioration of strength of bioceramics received the George C. Paffenbarger Research Award that recognizes the best paper in the field of Dental Materials annually. In 2010, Dr. Rosa defended the Ph.D. thesis “Dental Pulp Tissue Engineering in Full-length Human Root Canals” and started studying the interactions of material with cells and host living tissue. The article arising from it thesis is in the top 1% globally for Dentistry and has received the Edward H. Hatton Award. In 2012, Dr. Rosa joined Faculty of Dentistry/NUS to develop with novel cell models and materials for tissue regeneration. In 2014, Dr. Rosa was appointed as a Faculty by the Centre for Advanced 2D Materials and Graphene Research Centre /NUS where focus on the use of graphene to improve bone tissue tissue engineering and regeneration.
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Speaker: Dr. Luke Fleet
Affiliation: Senior Editor, Nature Physics, Nature Research
Abstract Details: Nature-branded journals continue to strive to publish the most significant advances in science, whose importance can be appreciated not only by specialists, but can be communicated to broad audiences. This talk will give insight into nature’s journals, policies and procedures.
About the Speaker: Luke is a Senior Editor at Nature Physics, responsible for selecting and handling a broad range of manuscripts in applied physics. Following a PhD from the University of York, on semiconductor spintronics in collaboration with the RIEC at Tohoku University, he undertook postdoctoral research at Imperial College London and the London Centre for Nanotechnology in molecular spintronics and organic electronics. He joined Nature Research in 2013 as an assistant editor at Nature Communications, before moving to Nature Physics early in 2014.
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Speaker: Prof Igor Herbut
Affiliation: Simon Fraser University, Canada
Abstract Details: I will review recent progress in our understanding of strongly interacting electronic systems that have their Fermi surfaces reduced to points. The first example will involve the familiar Dirac electrons in two dimensions described by the Hubbard, or a Hubbard-like, model. Recent confluence of field-theoretic and numerical methods leads a rather detailed and quantitative picture of metal-insulator quantum phase transition in this system, at which sharp quasiparticles disappear and Mott gap and Neel order parameter simultaneously emerge at a critical interaction strength. A connection to the observed quantum Hall effect at the neutrality point in graphene under magnetic field will be noted. The second example will go beyond Dirac 'relativistic' dispersion, and concern the effect of Coulomb interactions in systems such as gray tin or mercury telluride, where due to strong spin-orbit coupling and the ensuing band inversion electronic bands touch quadratically at the Fermi level.  We will examine the stability of the putative non-Fermi liquid ground state proposed by Abrikosov and Beneslavskii in the 70's, and discuss a general mechanism for an instability of such scale-invariant interacting phases.
About the Speaker: Igor Herbut is Full Professor at the Department of Physics, Simon Fraser University (Canada). He is well know for his contributions to quantum condensed matter theory and mathematical physics, in particular, in the applications of field and gauge theories to quantum phase transitions, strong correlations, disordered systems, superconductivity, Dirac fermions, graphene physics, supersymmetry, index theorems, and topology. He is single author of one book and ~35 research papers, and co-author of another ~65. These include 21 papers in Physical Review Letters and 2 in Physical Review X. Igor is ranked within the top 0.75% of the most influential authors of APS publications in 2006 according to SARA (www.physauthorsrank.org)
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Speaker: Dr. Phan Toan Thang
Abstract Details: Prof Phan’s talk is part of a monthly workshop with clinicians organized jointly with Prof. C. N. Lee , Director of the Heart Institute (NHG), to explore how 2D materials can address urgent needs in biomedical research. Exciting development of new materials has opened up novel possibilities in medical applications. The clinical needs are varied. Major areas need better materials: e.g. Non clotting surfaces which are bio-compatible, able to withstand shear stress forces of blood flows, able to tolerate binding if needed; materials which can be implanted into 2mm diameter coronary arteries without causing scarring reaction, with no tissue ingrowth; materials that can prevent bacteria from fouling or colonising implanted devices or catheters. Stents used in the airways, intestines bile ducts, brain cavities that remains open for longer periods. Through regular interactions between clinicians and material engineers, it would be possible to come to closer understanding of the needs and the options available. This series of talks aim to set up structures in collaboration, development, testing, refinement, animal and clinical trials, product development, and reaching the patients by commercialization. Q&A (4.45pm – 6.00pm) Prof Lee and Prof. Phan will stay after the talk to answer discuss with interested students, postdocs and PI potential areas of collaborations between the various groups at NUS. Bringing stem cell therapy research from lab to bedside and market faces many challenges ranging from ethical and religious controversial, healthcare regulation, high standard bio-manufacturing to patient affordability or insurance reimbursement. Taking all these points into consideration, it appears that stem cells derived from human umbilical cord membrane tissue or CLSC are the ideal source of stem cells that can make translational stem cell therapy happen in reality. Every month, tens of thousand of umbilical cord tissue units are collected and cryopreserved in US, EU and Asia together with cord blood for future use as the source of autologous stem cell transplant . With regards of allogenic stem cell therapy, freely donated umbilical cord tissue samples are easily and inexpensively collected and qualified in the Colorado Cord Blood Bank. With billions of stem cells isolated from a single cord membrane tissue at low passages in FDA-licensed GMP Stem Cell Facility in Colorado, the cost of CLSC products can be potentially lower and make more affordable to healthcare receivers. Translational stem cell therapy is an expensive game and highly capital intensive. To keep it sustainable and make it profitable is another big challenge. Over 30 mins of presentation and discussion, the author will share with the audience his story to make CellResearch Corp become a most successful stem cell biotech company in Singapore with today valuation of $700mil. This seminar aims to enhance the interactions among 2D scientists and medical doctors for more future collaborations and success stories.
About the Speaker: A/Prof Department of Surgery, Yong Loo Lin School of Medicine, NUS. Founder Director and Group Chief Scientific Officer, CellResearch Corp Group of Companies. A graduate of the Military Medical University, Hanoi, Vietnam in 1991, Prof. Phan Toan Thang has had a strong interest in wound healing since the earliest days of his medical and scientific career. His interest led him to hands-on experience during his four-year surgical residency in Hanoi at the at the Army Hospital 103. Prof. Phan's commitment and excellence in laboratory research was proven when he spent two years at the prestigious Wound Healing Institute and Department of Dermatology in Oxford, England. He arrived in Singapore in 1997 to join the Department of Plastic Surgery at the Singapore General Hospital. In 1998, he met Dr Ivor Lim, and together they established the Wound Healing and Stem Cell Research Group focusing on skin and keloid scar biology. The Wound Healing and Stem Cell Research Group was the first group in the world to explore the role of epithelial-mesenchymal interactions in keloid pathogenesis, and is recognised today as one of the world leading groups in keloid and scar biology research. Prior to taking up his faculty position at the Department of Surgery, Yong Loo Lin School of Medicine and Faculty of Dentistry at the National University of Singapore, Prof. Phan completed two years of post-doctoral research at the Stanford University Institute for Stem Cell Research and Regenerative Medicine Prof. Phan is author of more than 80 publications in international peer-reviewed journals, two book chapters, has more than 40 granted patents and serves as a reviewer for prestigious international scientific journals as well as local and international research funding bodies. His recent innovative research work is the discovery of a novel source of stem cells from the umbilical cord lining membrane with translational potential for regenerative medicine, tissue engineering and cell-based therapy.
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Speaker: Dr. Wei Han
Affiliation: International Center for Quantum Materials (ICQM), Peking University
Abstract Details: Spintronics aims to use the spin degrees of freedom for future information technologies. Spin orbit Torque, that uses spin currents generated by spin-orbit interactions in non-magnetic heavy metals, has attracted enormous attention due to potential application to development of more powerful spintronic devices. A key challenge for spintronics, especially spin orbit torque, is the efficient generation of spin currents from charge currents. In this talk, I will present our recent results towards more efficient spin and charge conversion. I will first briefly discuss the role of interface transparency for the spin orbit torque at the interface between platinum and a ferromagnetic material [1]. The efficiency of the effective spin orbit torque could be modulated by engineering the interface. Then, I will mainly discuss the potential to use emergent 2D quantum materials for spin and charge conversion since they provide new mechanisms of spin currents generation [2]. The facet-dependent spin Hall effect and spin orbit torque in single crystalline antiferromagnetic IrMn3 will be discussed [3]. This result suggests a novel mechanism of the spin current generation arising from the triangular spin configurations in the single crystalline IrMn3. At the end, I will present the spin to charge conversion in the spin-momentum locked surface states of the topological Kondo insulator (SmB6), of which pure surface states exist at low temperatures [4]. References: [1] Weifeng Zhang*, Wei Han*, Xin Jiang, See-Hun Yang, and Stuart Parkin, Nature Physics 11, 496–502 (2015). [2] Wei Han, APL Materials 4, 032401 (2016). [3] Weifeng Zhang*, Wei Han*, See-hun Yang, Yan Sun, Yang Zhang, Binghai Yan, and Stuart S. P. Parkin, Science Advances, 2: e1600759 (2016). [4] Qi Song, Jian Mi, Dan Zhao, Tang Su, Wei Yuan, Wenyu Xing, Yangyang Chen, Tianyu Wang, Tao Wu, Xian Hui Chen, X. C. Xie, Chi Zhang, Jing Shi, and Wei Han, Nature Communications (In press) (2016).
About the Speaker: Dr. Wei Han has been a tenure-track assistant professor in the International Center for Quantum Materials (ICQM) at Peking University since 2014. After he received his Ph.D. in physics at University of California, Riverside in 2012, Dr. Han spent two and half years at IBM Almaden Research Center as a postdoctoral associate. Dr. Han is the recipient of the 2012 APS GMAG student dissertation award and the 2016 IUPAP Young Scientist Prize in Magnetism (C9). His main research focus has recently been on graphene spintronics, spin orbit torque in magnetic heterostructures, and two-dimensional quantum interfaces/materials. Contact Dr. Wei Han, ICQM, Peking University; Email: weihan@pku.edu.cn Group Page: http://www.phy.pku.edu.cn/~LabSpin/links.html"
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Speaker: Prof. Olle Eriksson
Affiliation: Uppsala University, Sweden
Abstract Details:

n this presentation I will outline the basic ideas behind dynamical mean field theory and show examples of how it can be used to describe correlated electronic structures of a wide class of materials.

Examples of materials that will be discussed are lanthanides, transition metal oxides as well as diluted magnetic semiconductors. Both ground state properties, such as magnetic moments and equilibrium volumes, as well as excited state information will be presented. The latter will be focused on valence band spectra as well as x-ray absorption spectra.

About the Speaker: Olle Eriksson received his PhD from Uppsala University 1989. After spending three years as a postdoc at Los Alamos National Lab, he returned to an Assistant Professor at Uppsala University, 1991. After a short visit as a visiting scientist in Los Alamos, 1996-1997, he became an Associate Professor 1997 and chair professor 1999. He is currently leading a research division of 90 scientists at Uppsala University. Prof. Eriksson has supervised 42 PhD students to examination and been the advisor of 26 postdocs. He has published some 600 scientific articles of which several are found in The Physical Review Letters, PNAS, Nature and Science. He has received several awards and distinctions for his work in theory of materials. Research ID is: orcid.org/0000-0001-5111-1374 https://scholar.google.com/citations?user=Ijb0QJIAAAAJ&hl=en
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