Past Events

Jan
13
Fri
2017
New Year Gathering 2017
Jan 13 @ 3:00 PM – 3:00 PM

Date: 

Fri, 13/01/2017 – 3:00pm

Location: 

S16, Level 6 – Theory Common Room /Pantry area

Event Type: 

Other Events

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.

Jan
18
Wed
2017
Carrier Transport at the Interface of 2-Dimensional Materials
Jan 18 @ 11:00 AM – 12:00 PM

Speaker: 

Prof. Yoo Won Jong (SKKU Advance Institute of Nano Technology (SAINT), Sungkyunkwan University)

Date: 

Wed, 18/01/2017 – 11:00am to 12:00pm

Location: 

Physics Conference Room (S11-02-07)

Location Map: 

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Event Type: 

Seminars

Abstract

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.

Jan
23
Mon
2017
Genomics and Epigenetics with 2D material Nano-Electronics
Jan 23 @ 2:00 PM – 4:00 PM

Speaker: 

Dr. Jean-Pierre Leburton (University of Illinois, USA)

Date: 

Mon, 23/01/2017 – 2:00pm to 4:00pm

Location: 

CA2DM Theory Common Room (S16-06)

Location Map: 

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Event Type: 

Seminars

‘This talk is part of a monthly workshop with clinicians organized jointly with Prof. C. N. Lee , Chairman, University Surgical Cluster, National University Health System (NUHS), to explore how 2D materials can address urgent needs in biomedical research. Exciting development of new materials has opened up novel possibilities in bio-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. Similarly new materials are needed to achieve novel bio sensing capabilities . 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 (2pm – 3:30 pm) Prof Lee and the speaker will stay after the talk to answer and discuss with interested students, postdocs and PI potential areas of collaborations between the various groups at NUS.”Abstract

Dr. Jean-Pierre Leburton will review some basic properties of cell biology, and present a scenario that integrates biology with MOS nano-electronics for genomics and bio-medical applications. This scenario involves probing the electrical activity of biomolecules passing through a nanopore, in a semiconductor membrane. Among solid-state porous membranes the use of the single-atom thickness of graphene or novel 2D materials like MoS2 are ideally suited for DNA, RNA or proteins sensing as they can scan molecules passing through a nanopore at high resolution.  Additionally, unlike most biological membranes, these new materials are electrically active, which can be exploited to manipulate in addition to sense biomolecules. We will describe a membrane designed as a quantum point contact FET as a viable device for electronically and optically sensing bio-molecules for applications in genomics and cancer detection.

About the Speaker

Dr. Leburton joined the University of Illinois in 1981 from Germany, where he worked as a research scientist with the Siemens A.G. Research Laboratory in Munich. In 1992, he held the Hitachi LTD Chair on Quantum Materials at the University of Tokyo, and was a Visiting Professor in the Federal Polytechnic Institute in Lausanne, Switzerland in 2000. He is involved with research in nanostructures modeling and in quantum device simulation. His present research interest encompasses non-linear transport in quantum wires and carbon nanotubes, and molecular and bio-nanoelectronics

Professor Leburton is author and co-author of more than 300 technical papers in international journals and books, and served in numerous conferences committees. In 1993 he was awarded the title of “Chevalier dans l’Ordre des Palmes Academiques “ by the French Government. He is a Fellow of the Institute of Electrical and Electronic Engineers (IEEE), the American Physical Society (APS), the Optical Society of America (OSA), the American Association for the Advancement of Science (AAAS), the Electrochemical Society (ECS) and the Institute of Physics (IOP). He is also a member of the New York Academy of Science. In 2004 he was the recipient of the ISCS Quantum Device Award, and of the Gold medal for scientific achievement by the Alumnus association of the University of Liege, Belgium. He is a Distinguished Lecturer for the IEEE Nanotechnology Council. In 2011 he was elected to Royal Academy of Sciences of Belgium. 

Jan
26
Thu
2017
Putting Knowledge into Use
Jan 26 @ 2:00 PM – 4:00 PM

Speaker: 

Dr. Patrick Jones

Date: 

Thu, 26/01/2017 – 2:00pm to 4:00pm

Location: 

CA2DM Theory Common Room (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

Academic Knowledge Transfer (KT) occurs in many ways, from training graduate students to engaging in the translation of research into technologies that can be licensed to commercial companies. As one moves from the traditional dissemination of research through people, publications and presentations to that of prototypes and intellectual property, how one approaches the relations between “teacher” and “learner” changes. This includes changes in how one structures and positions research for adoption by commercial “learners.”

In this presentation, Dr. Jones will share on the changing patterns around research and its commercialization. While there is no one solution to engaging with partners, there are patterns and approaches available. There are also patterns and approaches to avoid.  Examples from a variety of universities will be referenced to demonstrate how some of the approaches can be adopted in the roles of researchers and their tech transfer office in moving knowledge into use. 

About the Speaker

Dr. Patrick Jones

Dr. Patrick Jones is the principal of Sahale Consulting, a practice specializing in strategic planning and execution with an emphasis on intellectual property licensing, innovation management and strategic business development. Pat has extensive national and international private sector and public higher ed work experience. In the private sector, Pat has directed product strategy and new business development for venture-backed companies, managed international sales and marketing for a manufacturer of solid-state laser and optical systems, and conducted research and product development for an aerospace contract research firm. In the public sector, Pat has managed research operations and external engagement as Associate Vice President for Research and Innovation at the University of Oregon, held regular and affiliate faculty appointments in Chemistry at The Ohio State University and the University of Washington, directed Technology Transfer at the University of Arizona, and worked as a technology transfer specialist and Assistant Dean of Engineering at the University of Washington. Pat holds an interdisciplinary Ph.D. in Chemical Physics from the University of Colorado Boulder and a Masters in Business Administration from the University of Washington’s Foster School of Business.

Feb
23
Thu
2017
2D Materials Forum (Feb 2017)
Feb 23 @ 11:30 AM – 11:30 AM

Speaker: 

Junyong Wang

Date: 

Thu, 23/02/2017 – 11:30am

Location: 

S16 Level 6 – Theory conference room

Event Type: 

Seminars

Title 

‘Investigation of crystal anisotropy of few-layer semimetallic T’-MoTe2 by angle-resolved polarized Raman spectroscopy’

Abstract

The distorted octahedral T’ phase MoTe2 has received tremendous interests recently due to its novel electronic structures and anisotropic charge transport properties. Taking advantage of its reduced in-plane symmetry, we find an easy and non-destructive method for determining the crystal orientation for thin layer T’-MoTe2 flakes by Raman spectroscopy. The Bg and Ag modes show blue-shift and red-shift with increasing thickness, respectively, due to the anisotropic surface effect. By exploring the anisotropic Raman response of thin layer T’-MoTe2 based on angle-resolved polarized Raman spectroscopy, we found four types of angular dependent behaviors, which are further analyzed from the group theory. The intensity of Ag mode at around 162 cm-1 reaches its maximum when the polarized excitation laser is parallel to the metal-metal bonds direction in the parallel configuration. This study paves the way for investigation about correlation between physical and structural properties of thin film T’-MoTe2.

Getting to know the new OII & ILO
Feb 23 @ 3:00 PM – 4:00 PM

Speaker: 

Prof. Barbaros Oezyilmaz (OII) & Mr Sean P. Flanigan (ILO)

Date: 

Thu, 23/02/2017 – 3:00pm to 4:00pm

Location: 

CA2DM Theory Common Room (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

Getting to know the new OII​ 

The Office of Industry and Innovation (OII) is embedded in the new Centre of Advanced 2D Materials and Graphene Research Centre (CA2DM-GRC). Our role is to facilitate the ongoing flow of conversation in the area of 2D materials among academics, and between them and industry. Many recent scientific discoveries related to 2D materials have the potential to have important uses in a wide range of industries. However, how to translate such discoveries into viable products for companies is a formidable challenge. Beyond the obvious questions such as identifying key advantages over existing solutions for a particular industry there are also a number of challenges which go beyond fundamental research. Unlike academic research, companies for example require beyond the demonstration of a proof of principle under laboratory conditions thorough benchmarking and extensive reliability tests. Other topics which need careful consideration when embarking on research collaborations are related to potential IP issues. The OII has been founded to assist member of CA2DM in this effort.

In collaboration with ILO its goal is to provide in key research area a path towards a fruitful industry engagement. It is meant to facilitate the ongoing flow of conversation in the area of 2D materials among academics, and between them and industry. In this seminar to the Deputy Director for translation at CA2DM, Barbaros Oezyilmaz, and the Director of ILO, Sean Patrick Flanigan, will share their respective strategy and how they will coordinate their efforts in helping PIs in their effort. The role is to facilitate the ongoing flow of conversation in the area of 2D materials among academics, and between them and industry. We aim to surface ideas that carry the seeds of possible future development down the innovation value chain.

Geting to know the new ILO. 

Starting in 2015 ILO has been changing the approach to the protection and commercialization of NUS intellectual property.  Some of you may have already had a chance to engage with our commercialization officers under this new approach while others may have only heard rumours of a different approach.   This discussions, from the Director of ILO responsible for commercialization will provide an interactive forum to discuss our plans, our methodology and how we can work together to develop and realize upon your commercialization expectations.

About the Speakers

Barbaros ÖZYILMAZ is a Professor in the Department of Physics and the Department for Materials Science and Engineering, NUS. He is also the Head of Graphene Research at CA2DM and was recently appointed Deputy Director (Translation). He obtained his Ph.D. from New York University and did his postdoctoral research at Columbia University, joining NUS in 2007. He received the NRF Fellowship Award in 2008 and was awarded the NUS Young Scientist Award in 2013.

Sean P. Flanigan, BA, JD, RTTP (Director, Industry Liaison Office (ILO), National University of Singapore) & Chair, Alliance of Technology Transfer Professionals

Sean Flanigan is a lawyer, technology transfer practitioner and Past-President of the Association of University Technology Managers (AUTM), the largest professional organization of technology transfer professionals in the World.  Mr. Flanigan studied law at the University of Ottawa and has been a member of the Ontario Bar since 1993. Since joining the National University of Singapore in 2015 Mr. Flanigan has lead the Innovation Management team responsible for intellectual property (IP) commercialization and industrially supported research.  Prior to joining NUS Mr. Flanigan lead the team responsible for industrial liaison, technology development and transfer, new company creation and student entrepreneurship at the University of Ottawa for thirteen years.  He has created student incubator programs, applied research programs for small and medium sized enterprises and personally attended to the negotiation of dozens of early stage technology licenses. Mr. Flanigan has served as a Board member of several early stage technology based companies. In 2008 Mr. Flanigan became Vice President of AUTM for Canada and in 2012 was elected by his peers as President-Elect of AUTM.  During his Presidency of AUTM in 2013-2014 Mr. Flanigan championed a wholesale strategic shift in the organization’s structure including development of an entirely new governance structure and strategic plan while overseeing one of the most financially successful years and annual meetings in AUTM history.  From 2010 through 2014 he served as the Chair of the Governance committee of the Alliance of Technology Transfer Professionals (ATTP), the Global certification body for Academic Technology Transfer Professionals and between 2015 and 2017 he was Global Chair of ATTP. Mr. Flanigan has lectured extensively on technology transfer around the World and has published studies of the profession and the practice. 

 

Mar
9
Thu
2017
Opportunities and current landscape of transparent conductors
Mar 9 @ 3:00 PM – 4:00 PM

Speaker: 

Mr Jax Lee (李佳兴) ( Acting COO, Cima NanoTech)

Date: 

Thu, 09/03/2017 – 3:00pm to 4:00pm

Location: 

Physics Conference Room (S11-02-07)

Location Map: 

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Event Type: 

Seminars

Abstract

To discuss the opportunities and current landscape of transparent conductors (ITO, CNT, Graphene, Silver nano-wires, conductive polymers and metal meshes). Jax would be sharing his experiences on the phases, challenges and ingredients of bringing novel materials to commercialization, from lab to production to market. He would be offering his views on potential opportunities for new materials and expertise in the business development path to achieve the first minimum viable product and prototype. 

About the Speaker

Jax Lee is the acting COO of Cima NanoTech, a nanomaterial company with more than 100 patents on unique nanoparticles manufacturing methods, dispersion technology and self-assembling technology for highly conductive transparent conductors. Jax plays a driving role in bringing Cima NanoTech unique SANTE® Technology from lab to pilot to mass production and industry applications.

Currently, Cima’s Technology is used in EMI shielding, transparent heating and large format projective capacitive touch modules. During 5 years with Cima, he established a joint venture partnership with Foxconn using SANTE® Technology to manufacture large format touch modules and kick-started many joint development programs with many notable materials suppliers. Previous at Cima, he was leading the efforts in setting up a greenfield manufacturing efforts of CdTe, thin-film photovoltaic in Singapore and China. He was involved heavily in designing, sourcing of localized process mass production equipment and selection of new compatible auxiliary materials for the assembly of solar modules.  An alumus, he graduated at NUS Chemical Engineering, in his free time he is a keen scuba diver and hiker. 

 

Mar
30
Thu
2017
Open workshop: ab initio theories for electronic excitations and spectroscopy
Mar 30 @ 10:00 AM – Apr 4 @ 11:30 AM

Speaker: 

Dr Valerio Olevano (Institut Néel, Grenoble, France) & Dr Paolo. E. Trevisanutto (NUS)

Date: 

Thu, 30/03/2017 – 10:00am to Tue, 04/04/2017 – 11:30am

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

Programme: 

  Session 1   30 Mar (10:00 – 11:30)
  Session 2   31 Mar (10:00 – 11:30)
  Session 3   03 Apr (14:00 – 15:30)
  Session 4   04 Apr (10:00 – 11:30)
 

Synopsis

The workshop consists of a cycle of 4 seminars on methods beyond density-functional theory (DFT) ab initio theories to calculate excitations and spectroscopy. DFT [1] is to be considered today as the standard model of condensed matter theory, and in the last 50 years revealed a very successful approach [2] to calculate ab initio ground-state properties (atomic structures, elastic constants, etc.).

In the first seminar, a critical review of DFT will be presented, showing the successes but insisting in particular to its limits, namely the possibility for DFT to access excitations, excited state properties and spectroscopy.

In the second seminar, we will introduce time-dependent density-functional theory (TDDFT) [3], an extension of DFT able to address excited-state properties and spectroscopy like optical absorption, energy-loss spectra (EELS), etc. TDDFT is an in principle exact theory to calculate neutral excitations. However, like in DFT, the exchange-correlation functional, a fundamental ingredient of the theory, is unknown. One must resort to approximations and, unlike DFT, the local-density approximation (LDA) has limited validity, in particular on optical absorption spectra. We will introduce the fundamentals of TDDFT and discuss the limits of standard approximations with the help of examples on prototypical systems (bulk silicon, graphite, graphene, etc.), also presenting recent developments [4].

In the third seminar, we will introduce the ab initio many-body perturbation theory (MBPT) relying on the Green function (instead than the density like in DFT) as fundamental degree of freedom. MBPT is an in principle exact framework to calculate both ground and excited states, both neutral (like TDDFT) but also charged excitations. We will focus in particular on the GW approximation of the self-energy, showing its performances in the calculation of band gaps, band plots, ARPES spectral functions, also in prototypical systems.

Also within the framework of MBPT, in the 4th seminar we will talk on the Bethe-Salpeter equation (BSE) approach to calculate optical spectra and neutral excitations, in particular excitons. The BSE is an equation that allows to directly calculate the two-particle Green function, whose poles are the neutral excitations of a system. With respect to TDDFT, BSE provides access also to, e.g., exciton wavefunctions. We will show examples of calculations of excitations and spectra on bulk solids (silicon, etc.) and isoltated systems (helium atom, etc.) and discuss the limits of the approximations usually done on the kernel of the BSE.

References

[1] P. Hohenberg, W. Kohn, Phys. Rev. 136, B864 (1964);  W. Kohn, L. J. Sham, ibid 140, A1133 (1965).

[2] S. Redner, Physics Today 58, 49 (June 2005).

[3] W. E. Runge and E. K. U. Gross, Phys. Rev. Lett. 52, 997 (1984); E. K. U. Gross and W. Kohn, Phys. Rev. Lett. 55, 2850 (1985).

[4] V. Olevano, M. Palummo, G. Onida and R. Del Sole, Phys. Rev. B 60, 14224 (1999); L. Reining, V. Olevano, A. Rubio, and G. Onida, Phys. Rev. Lett. 88, 066404 (2002); F. Sottile, M. Marsili, V. Olevano, and L. Reining, Phys. Rev. B 76, 161103(R) (2007); P. E. Trevisanutto, L. A. Constantin, A. Terentjevs, V. Olevano and F. Della Sala, Phys. Rev. B 87, 205143 (2013).

About the Speakers

Valerio Olevano is research director since 2012 at the CNRS (French national research council) where he also obtained a permanent position in 2000. He earned in 1993 his Laurea in physics at the University of Rome ‘La Sapienza’ (computational subnuclear physics, lattice QCD) and his PhD in 1999 at the University of Rome ‘Tor Vergata’ (computational ab initio condensed matter theory, DFT and beyond). He also got an European grant for acquiring expertise in XPS/UPS photoemission and research staff working in developments of the ab initio Bethe-Salpeter equation to calculate optical spectra in solids. His present research lines insist on developments and applications of ab initio many-body theory within the GW approximation and beyond, as well as methods based on the Bethe-Salpeter equation.

Valerio Olevano is a developer of the ABINIT first-principles code framework, and the main developer of DP (a linear response time-dependent DFT code, www.dp-code.org) and EXC (an exciton code for the dielectric and optical properties based on the solution of the Bethe-Salpeter equation, www.bethe-salpeter.org).

Paolo E. Trevisanutto is a senior research fellow in the Centre for Advanced 2D materials & Graphene research at NUS, which he joined in 2014.  His current research interests are concerned with the development and applications of ab initio Many Body Perturbation Theory (MBPT) and Time Dependent Density Functional Theory (TD-DFT) methods in two dimension materials.

He obtained his Ph.D. in Physics at University College London in 2008 under the supervision of Prof. A.L. Shluger. From 2007 to 2014, he was a postdoctoral researcher in several European Institutes connected to the European Theoretical Spectroscopy Facility network (ETSF) such as CNRS (France), Max Planck Institut (Germany) and, CNR (Italy).

 

 

Apr
7
Fri
2017
2D Materials Forum (Apr 2017)
Apr 7 @ 11:00 AM – 11:00 AM

Speaker: 

Dr. Aleksandr Rodin

Date: 

Fri, 07/04/2017 – 11:00am

Location: 

S16 Level 6 – Theory conference room

Event Type: 

Seminars

Title:
Spin-Orbit Interaction in Buckled 2D Systems

Abstract:

Spin-orbit coupling in 2D materials can be either extrinsic or intrinsic. An example of the former is Rashba effect, where an external electric fields results in a formation of Dirac cones. Intrinsic SOC, on the other hand, typically leads to a gap opening, as seen in Xene’s and some transition metal dichalcogenides. It turns out that for certain lattice geometries, atomic spin-orbit interaction can give rise Rashba-like dispersion without an external field. We study a lattice which manifests this behaviour using tight-binding formalism and DFT calculations.

Apr
19
Wed
2017
Nanofluidics with two-dimensional materials
Apr 19 @ 11:00 AM – 1:00 PM

Speaker: 

Prof Slaven Garaj (NUS)

Date: 

Wed, 19/04/2017 – 11:00am to 1:00pm

Location: 

Physics Conference Room (S11-02-07)

Location Map: 

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Event Type: 

Seminars

Abstract

The curious behavior of water and ions in constrictions with dimensions comparable to the size of ions is of particular interest for many applications, including filtration membranes, single-biomolecule analysis, supercapacitors, etc. The nanofluidic behavior of such structures depends on their dimensionality: ranging from the edge-enhanced ionic current in 0D graphene nanopores [1,2], anomalous ionic flow in 1D nanotubes, to frictionless water transport in 2D graphene [3] and graphene-oxide nanochannels [4, 5].  We set to investigate ionic flow in graphene-based nanostructures, including scalable GO membranes, and model systems consisting of individual graphene channels only about 1 nm in height. By measuring mobility of a wide selection of aqueous salts ions in channels of GO membranes [5], we demonstrated that the dominant mechanisms for the ion rejection are (a) size exclusion due to compression of the ionic hydration shell in narrow channels; and (b) electrostatic repulsion due to the membrane surface charge.  Armed with the insight into the physical mechanism governing the ionic flow, we are able to engineer new membranes with decreased the ionic cut-off size and increased charge selectivity. At the end, I will present some new results leading to promising applications in desalination and electrodialysis.

[1] Garaj, S. et al. Graphene as a subnanometre trans-electrode membrane. Nature 467, 190 (2010).

[2] Garaj, S. et al. Molecule-hugging graphene nanopores. Proc Natl Acad Sci USA 110, 12192 (2013).

[3] Radha, B. et al. Molecular transport through capillaries made with atomic-scale precision. Nature 538, 222 (2016).

[4] Nair, R. R. et al. Unimpeded Permeation of Water Through Helium-Leak–Tight Graphene-Based Membranes. Science 335, 442 (2012).

[5] Hong, S. et al. Scalable Graphene-Based Membranes for Ionic Sieving with Ultrahigh Charge Selectivity. Nano Lett. 17, 728 (2017).

About the Speaker

Slaven Garaj is Assistant Professor at the Departments of Physics and of Biomedical Engineering at the National University of Singapore, as well as a member of the NUS Centre for Advanced 2D Materials and NUSNNI-Nano Core. He is also a Singapore NRF Fellow (2012).

Slaven explores nanoscale phenomena emerging at the interface of solid-state devices and soft-matter systems. He is interested in behaviour of water molecules and ions in atomic-scale confinements; control and analysis of individual biomolecules using physical methods; and electrical and structural properties of 2D materials. The research is often guided by the desire to address a real technological challenges and includes: ultra-fast, inexpensive DNA sequencing using physical methods; nanopore devices for detection, fingerprinting and sequencing of individual proteins; electrical sensors based on 2D materials; 2D materials as next-generation membranes for filtration and water desalination.

Slaven received his PhD from Swiss Federal institute of Technology Lausanne (EPFL), Switzerland, in the field of solid-state physics. He continued his research career at Harvard University, working at the intersection of nano-electronics and biophysics, particularly by developing novel methods for electrical (4th generation) DNA sequencing based on nanopores. Throughout his career, his different research projects attracted general public attention and were featured in international media and professional magazines (such as BBC News, New Scientist, Technology Review, MRS Bulletin, etc). 

Apr
20
Thu
2017
What can aberration-corrected microscopy do for two-dimensional materials?
Apr 20 @ 11:00 AM – 1:00 PM

Speaker: 

Prof Stephen Pennycook

Date: 

Thu, 20/04/2017 – 11:00am to 1:00pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

The aberration-corrected scanning transmission electron microscope (STEM) provides much more than enhanced resolution. Using accelerating voltages below the damage threshold allows direct, real space atomic imaging and spectroscopy with minimal damage [1]. Point defect configurations and electronic structure can be directly determined [2,3], including localized plasmon resonances [4]. Furthermore, energy transfer from the beam can excite atomic migration or metastable configurations that can be quantified through density functional theory [5], and can even be used for nanofabrication [6,7]. Future possibilities include adding a monochromator for nanoscale band gap mapping, and imaging at different temperatures and under applied bias.

References

[1]   O. L. Krivanek, M. F. Chisholm, V. Nicolosi, T. J. Pennycook, G. J. Corbin, N. Dellby, M. F. Murfitt, C. S. Own, Z. S. Szilagyi, M. P. Oxley, S. T. Pantelides, and S. J. Pennycook, ‘Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy,’ Nature, 464, 571–574 (2010).

[2]   W. Zhou, M. Kapetanakis, M. Prange, S. T. Pantelides, S. J. Pennycook, and J.-C. Idrobo, ‘Direct Determination of the Chemical Bonding of Individual Impurities in Graphene,’ Phys Rev Lett 109 (2012) 206803.

[3]   Y. Gong, Z. Liu, A. R. Lupini, G. Shi, J. Lin, S. Najmaei, Z. Lin, A. L. Elías, A. Berkdemir, G. You, H. Terrones, M. Terrones, R. Vajtai, S. T. Pantelides, S. J. Pennycook, J. Lou, W. Zhou, and P. M. Ajayan, ‘Band Gap Engineering and Layer-by-Layer Mapping of Selenium-Doped Molybdenum Disulfide,’ Nano Lett, 14, 442–449 (2014).

[4]   W. Zhou, J. Lee, J. Nanda, S. T. Pantelides, S. J. Pennycook, and J.-C. Idrobo, ‘Atomically localized plasmon enhancement in monolayer graphene,’ Nature nanotechnology, 7, 161–165 (2012).

[5]   S. J. Pennycook, W. Zhou, S. T. Pantelides, Watching Atoms Work: Nanocluster Structure and Dynamics, ACS Nano. 9 (2015) 9437–9440.

[6]   J. Lin, O. Cretu, W. Zhou, K. Suenaga, D. Prasai, K. I. Bolotin, N. T. Cuong, M. Otani, S. Okada, A. R. Lupini, J.-C. Idrobo, D. Caudel, A. Burger, N. J. Ghimire, J. Yan, D. G. Mandrus, S. J. Pennycook, and S. T. Pantelides, Nat. Nano., 9, (2014) 436.

[7]   S. Jesse, Q. He, A. R. Lupini, D. N. Leonard, M. P. Oxley, O. Ovchinnikov, R. R. Unocic, A. Tselev, M. Fuentes-Cabrera, B. G. Sumpter, S. J. Pennycook, S. V. Kalinin, and A. Y. Borisevich, ‘Atomic-Level Sculpting of Crystalline Oxides: Toward Bulk Nanofabrication with Single Atomic Plane Precision,’ Small, 11, 5895–5900 (2015).

About the Speaker

Stephen J. Pennycook is a new member at our Centre. He is a Professor in the Materials Science and Engineering Dept., National University of Singapore, an Adjunct Professor in the University of Tennessee and Adjoint Professor in Vanderbilt University, USA. Previously, he was Corporate Fellow in the Materials Science and Technology Division of Oak Ridge National Laboratory and leader of the Scanning Transmission Electron Microscopy Group. He completed his PhD in physics at the Cavendish Laboratory, University of Cambridge in 1978. Since then he has been actively pursuing the development and materials applications of atomic resolution Z-contrast microscopy and electron energy loss spectroscopy. Pennycook is a Fellow of the American Physical Society, the American Association for the Advancement of Science, the Microscopy Society of America, the Institute of Physics and the Materials Research Society. He has received the Microbeam Analysis Society Heinrich Award, the Materials Research Society Medal, the Institute of Physics Thomas J. Young Medal and Award and the Materials Research Society Innovation in Characterization Award. He has 38 books and book chapters, over 400 publications in refereed journals and has given over 200 invited presentations. His latest book is “Scanning Transmission Electron Microscopy.”

 

May
18
Thu
2017
Space Solar: Closer than we think?
May 18 @ 9:00 AM – 4:30 PM

Date: 

Thu, 18/05/2017 – 9:00am to 4:30pm

Location: 

NUS Uhall Auditorium, Level 2 Lee Kong Chian Wing, 119077

Event Type: 

Other Events

This inaugural workshop is a one-day platform for researchers, academics, policy makers and industry to engage in discussion on the nascent field of space-based solar power.
Topics covered on the day will include satellite research activities, renewable energy sources for Singapore, commercial applications in space, and the challenges of creating technology that can change the face of solar power generation.
 

PROGRAMME

Time

Programme

Speaker

8.30 am 

Registration 

 

9.00 am

Opening and Welcome Address

Prof Armin Aberle 

CEO

Solar Energy Research Institute of Singapore

MORNING SESSION : SATELLITES and SOLAR

9:15am

 

Overview of space solar power

Dr. Lin Fen

Solar Energy Research Institute of Singapore

09:45am

Past, recent, and future R&D of solar power satellite and

wireless power transfer in Japan

Prof Naoki Shinohara

Kyoto University

10:15

Formation flying of low earth orbit satellites for space based solar power application

Prof Low Kay Soon

National University of Singapore (NUS)

10:45am

Tea Break

 

11:15am

Renewable energy sources for Singapore – beyond roof-top solar

Dr Narasimalu Srikanth

Energy Research Institute @ NTU 

11:45am

Space: the final frontier for 2D materials

Prof Antonio Castro Neto, Centre for Advance 2D Materials

12:15noon

TBC

Faculty of Science 

NUS

12:45pm

Lunch 

 

AFTERNOON SESSION : SPACE SOLAR

02:00pm

RF and antenna technologies for space based solar power application

A/Prof Guo Yong Xin

National University of Singapore

02:30pm

Overview of energy storage system for Space Solar Power (SSP)

A/Prof Sanjib Panda

National University of Singapore

03:00pm

High efficiency light weight solar cells for space applications

Dr. Noren Pan

CEO

Microlink Devices

03:30pm

Panel Discussion     

Moderator: Lum Chune Yang

Prof Armin Aberle, SERIS

Prof Naoki Shinohara, Kyoto University

Dr. Noren Pan, Microlink Devices

Prof Low Kay Soon, NUS

Prof Narasimalu Srikanth, ERI@N

04:15pm

Closing remarks

National Research Foundation

04:30pm

Ends

 

 

Please register your attendance online before 12 May.
For enquiries, please contact Chee Shin Yee at dprchee@nus.edu.sgRefreshments will be provided.

May
26
Fri
2017
Ultrathin Structured 2D surfaces: Hybridizing 2D Materials & Metasurfaces
May 26 @ 11:00 AM – 1:00 PM

Speaker: 

Prof Cheng-Wei Qiu

Date: 

Fri, 26/05/2017 – 11:00am to 1:00pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

I will report some of the most recent developments in my group as well as in the field of the interfacial engineering of manipulation of light-matter interactions, via the artificially constructed structures of ultrathin thickness compared to the wavelength. In particular, the low-dimension and high-frequency scaling may promise a lot more interesting applications, while the challenges in design principle and fabrication capability will become critical limits. Nano-patterned surfaces to modulate and structure novel light behavior will be studied and the following advanced functionalities will be discussed: 3D meta-hologram, high-pixelated nanopriting, dynamic OAM generation, and more interestingly, the 2D-material meta-lens of

Jun
12
Mon
2017
Connecting Layered Materials to Semiconductors: The Ubiquity of Schottky Barriers and Tunnel Junctions
Jun 12 @ 2:00 PM – 4:00 PM

Speaker: 

Prof Arthur F. Hebard

Date: 

Mon, 12/06/2017 – 2:00pm to 4:00pm

Location: 

CA2DM Theory Common (S16-06)

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Event Type: 

Seminars

Abstract

It is widely recognized that interfaces between metals and most semiconductors form Schottky barriers with rectifying properties that are essential components of present-day electronics. This talk will begin with a tutorial overview of Schottky barriers and describe the physical concepts that are necessary and sufficient to gain a working understanding of their operation. Research will then be described which uncovers surprising phenomenology that points to new physics and novel device concepts. These phenomena include magnetodielectric coupling in nonmagnetic Au/GaAs:Si Schottky barriers, the formation of Schottky barriers at the interface of one-atom-thick zero-gap semiconductors (graphene), and the Schottky barriers formed by contacting freshly exfoliated flakes of van der Waals crystals such as Bi2Se3 (a topological insulator), layered transition metal dichalcogenides (such as TaS2, TiSe2 and NbSe2) harboring charge density waves and freshly cleaved Bi-2212 (a high Tc cuprate superconductor) to doped Si and GaAs wafers. Interestingly, modifications to the thermionic emission equation provide an excellent description of current-voltage characteristics at low temperatures where tunneling is known to be important, thereby providing a segue to a full tunneling description. Temperature, frequency and magnetic field dependence of current-voltage and capacitance-voltage characteristics will be described. 

About the Speaker

Arthur Foster Hebard is a Distinguished Professor of Physics at University of Florida in Gainesville, Florida. He is particularly noted for leading the discovery of superconductivity in Buckminsterfullerene in 1991. Art Hebard attended The Hotchkiss School and graduated with a BA in Physics from Yale University in 1962. He obtained his PhD from Stanford University in 1971 under William M. Fairbank with thesis Search for fractional charge using low temperature techniques. After a spell as a Research Associate at Stanford, he became a member of the Technical Staff at AT&T Bell Telephone Laboratories. He moved to the University of Florida as a Professor in 1996, and in 2007 was given the title of Distinguished Professor.

He is the author of more than 250 refereed scientific publications and 90 invited presentations, and has been issued 10 patents. He was awarded the 2008 James C. McGroddy Prize for New Materials by the American Physical Society, and a co-recipient of the 2015 Oliver E. Buckley Condensed Matter Prize, also given by the American Physical Society, ‘For discovery and pioneering investigations of the superconductor-insulator transition, a paradigm for quantum phase transitions.’

His research interests include thin-film physics, graphene, fullerenes and fullerene derived compounds, superconductivity, dilute magnetic semiconductors, magnetism in thin films and at thin film interfaces, interface capacitance, magnetocapacitance of complex oxides and semiconductors. Notable recent work has been on the use of graphene for solar cells.

Jun
14
Wed
2017
Detecting Anomalous Dimensions in the Strange Metal Phase of the Cuprates
Jun 14 @ 11:00 AM – 12:30 PM

Speaker: 

Prof Philip W. Phillips

Date: 

Wed, 14/06/2017 – 11:00am to 12:30pm

Location: 

Physics Conference Room (S11-02-07)

Location Map: 

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Event Type: 

Seminars

Abstract

We all learned that conserved quantities such as the current in a metal cannot acquire an anomalous dimension in any theory that respects charge conservation. A recent theory of the strange metal of the cuprates has reached the conclusion that all of the properties of this phase can be understood if the current does in fact acquire an anomalous dimension.  I will show how this seemingly contradictory prediction can be understood and also show that a finger print of such an anomaly is the Aharanov-Bohm flux through a strange metal ring. In the presence of an anomalous dimension, the AB phase deviates strikingly from the standard result and offers a precise diagnostic as to what is strange about the strange metal. I will also construct a Virasoro algebra for such anomalous currents and show that they correspond to a new class of non-local yet conformal theories.About the speaker

Philip Phillips is a theoretical condensed matter physicist who has an international reputation for his work on transport in disordered and strongly correlated low-dimensional systems. He is the inventor of various models for Bose metals, Mottness, and the random dimer model, which exhibits extended states in one dimension, thereby representing an exception to the localization theorem of Anderson’s.
 
His research focuses sharply on explaining current experimental observations that challenge the standard paradigms of electron transport and magnetism in solid state physics. Departures from paradigms tell us that there is much to learn. Such departures are expected to occur in the presence of strong-electron interactions, disorder, and in the vicinity of zero-temperature quantum critical points. The common question posed by experiments that probe such physics is quite general. Simply, how do strong Coulomb interactions and disorder conspire to mediate zero-temperature states of matter? It is precisely the strongly interacting electron problem or any strongly coupled problem for that matter, such as quark confinement, that represents one of the yet-unconquered frontiers in physics. Understanding the physics of strong coupling is Phillips’ primary focus. In latter years, he has developed a number of approaches to the physics of cuprate high-Tc superconductors based on the gauge/gravity duality or the AdS/CFT conjecture, in which a strongly coupled quantum theory is mapped onto a weakly interacting theory of gravity, and he is one of the visible players in this field of mapping string theory and other models/tools from quantum gravity to condensed matter settings.
 
Professor Phillips received his bachelor’s degree from Walla Walla College in 1979, and his Ph.D. from the University of Washington in 1982. After a Miller Fellowship at Berkeley, he joined the faculty at Massachusetts Institute of Technology (1984-1993). He joined the University of Illinois in 1993.

Jun
22
Thu
2017
Cavitation: Acoustic Implosions in Water. A new Approach to Structuring of Materials
Jun 22 @ 11:00 AM – 12:30 PM

Speaker: 

Dr. Daria Andreeva- Bäumler

Date: 

Thu, 22/06/2017 – 11:00am to 12:30pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

Nonlinear modulation of microstructures concerns questions also relevant for understanding of the origin of life, material science, geo- and bio- science. Recent examples are the formation of chiral and hierarchically structured porous metal composites, epitaxial strain induced transitions in layered oxides, switchable infrared nanophotonic elements based on phase change materials, design of autonomous motors, etc.

However, the main question is, how to establish a dynamic control of useful characteristics, for example dynamic control of crystal / grain size and composition modulation in solids. A possible answer is to develop a new generation of dynamic impactors that can trigger oscillations of structures and functions.

In  my talk I focus on ultrasonically triggered cavitation, that can be defined as growth and violent collapse of microbubbles, as a unique but underappreciated approach to generating a strong shock impact and thus rapid increase of temperature and pressure at a localized area (

Jun
23
Fri
2017
2D Materials Forum (Jun 2017)
Jun 23 @ 11:30 AM – 1:30 PM

Speaker: 

Dr. Seunghyun Hong

Date: 

Fri, 23/06/2017 – 11:30am to 1:30pm

Location: 

S16 Level 6 – Theory conference room

Event Type: 

Seminars

Title :

Charge- and Size-Selective Ion Sieving through Graphene based Membranes

Abstract :

Ionic selectivity is a major attribute to consider when designing novel membranes for separation technologies. As one of promising candidates for next generation nanofiltration, graphene oxides (GO) membranes with tunable physiochemical properties offers an excellent framework to make highly efficient ion-selective channels without compromising ultrahigh water permeance. Here, I demonstrate ultrahigh charge and size selective ion transport in GO-based membranes with microscopic drift-diffusion method. I identified primary mechanisms governing ionic rejection in GO membranes from precise investigation for a range of ionic species: surface charge groups inside the GO nanochannels are responsible for electrostatically repulsing co-ions. Furthermore, I describe the chemical confinement of interlayer channel in GO membranes, enabling to achieve accurate size selective sieving while water flow is weakly affected. These ionic selectivity opens up new venue for electrodialysis and desalination to GO. 

Molecular Transport through Atomic-scale Capillaries
Jun 23 @ 2:00 PM – 3:00 PM

Speaker: 

Dr. Radha Boya (University of Manchester, United Kingdom)

Date: 

Fri, 23/06/2017 – 2:00pm to 3:00pm

Location: 

CA2DM Theory Common (S16-06)

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Event Type: 

Seminars

Abstract

Nanometre-scale pores and capillaries have long been studied because of their importance in many natural phenomena and their use in numerous applications. A more recent development is the ability to fabricate artificial capillaries with nanometre dimensions, which has enabled new research on molecular transport and led to the emergence of nanofluidics. But surface roughness in particular makes it challenging to produce capillaries with precisely controlled dimensions at this spatial scale. We have developed a method for fabrication of narrow and smooth capillaries through van der Waals assembly, with atomically flat sheets at the top and bottom separated by spacers made of two-dimensional crystals with a precisely controlled number of layers. We use graphene and its multilayers as archetypal two-dimensional materials to demonstrate this technology, which produces structures that can be viewed as if individual atomic planes had been removed from a bulk crystal to leave behind flat voids of a height chosen with atomic-scale precision.

Water transport through the channels, ranging in height from one to several dozen atomic planes, is characterized by unexpectedly fast flow (up to 1 metre per second) that we attribute to high capillary pressures (about 1,000 bar) and large slip lengths. For channels that accommodate only a few layers of water, the flow exhibits a marked enhancement that we associate with an increased structural order in nanoconfined water. Our work opens up an avenue to making capillaries and cavities with sizes tunable to ångström precision, and with permeation properties further controlled through a wide choice of atomically flat materials available for channel walls.

References

B. Radha et al., Molecular transport through capillaries made with atomic-scale precision. Nature 538, 222-225 (2016).

 

Jun
28
Wed
2017
Workshop on Electron-electron Interactions in Topological Materials
Jun 28 @ 8:00 AM – Jun 30 @ 6:00 PM

Date: 

Wed, 28/06/2017 – 8:00am to Fri, 30/06/2017 – 6:00pm

Location: 

Yale-NUS College

Location Map: 

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Event Type: 

Conferences

More information at http://graphene.nus.edu.sg/InteractingTopologicalElectrons2017

Jul
24
Mon
2017
Seeing Small: Enabling New Discoveries in Nanomaterials Through Advanced Transmission Electron Microscopy
Jul 24 @ 2:00 PM – 3:00 PM

Speaker: 

Prof. Paulo.J. Ferreira

Date: 

Mon, 24/07/2017 – 2:00pm to 3:00pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

Aberration-Corrected TEM/STEM, and In-Situ TEM have emerged as powerful tools for the characterization of nanomaterials. Aberration-Corrected TEM/STEM enable atomic and structural imaging resolution below 0.1 nanometers while performing chemical analysis at the atomic level, while in-situ TEM allows dynamic real-time imaging of nanomaterials behavior. In this talk, a brief overview of Aberration-Corrected TEM/STEM, and in-situ TEM will be presented and related to the quest for investigating nanomaterials. Subsequently, two examples showing the power of these techniques in providing scientific insight will be discussed.  First, using aberration-corrected HAADF/STEM imaging and STEM simulations, as well as EELS analyses, the atomic structure and composition of Li-ion battery materials will be discussed. Second, aberration-corrected STEM and in-situ TEM of Pt, Pt-alloy and Ag nanoparticles will be presented. 

About the Speaker

Professor Paulo.J. Ferreira

Robert & Jane Mitchell Endowed Faculty Fellowship in Engineering

Director of the Center for Electron Microscopy

Materials Science & Engineering Program

The University of Texas at Austin

Austin, TX, 78712, USA

Jul
25
Tue
2017
Spin-/Orbital-correlation in Fe-based high-temperature superconductors: Unusually stronger quantum fluctuation with larger spins in FeSe
Jul 25 @ 2:30 PM – 3:30 PM

Speaker: 

Prof. Wei Ku (Shanghai Jiao Tong University)

Date: 

Tue, 25/07/2017 – 2:30pm to 3:30pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

 

Abstract

Like the high-temperature superconductivity found in other systems, superconductivity in Fe-based systems is often found near an long-range ordered phase. This talk will introduce our understanding of the strong spin- and orbital-correlations. In particular, a counter-intuitive enhancement of quantum fluctuation with larger spins, together with a few novel physical phenomena, is discovered in studying the recently observed emergent magnetism in high-temperature superconductor FeSe under pressure. Starting with experimental crystalline structure from our high-pressure X-ray refinement, we analyze theoretically the stability of the magnetically ordered state with a realistic spin-fermion model. We find surprisingly that in comparison with the magnetically ordered Fe-pnictides, the larger spins in FeSe suffer even stronger long-range quantum fluctuation that diminishes their ordering at ambient pressure. This ”fail-to-order” quantum spin liquid state then develops into an ordered state above 1GPa due to weakened fluctuation accompanying the reduction of anion height and carrier density. The ordering further benefits from the ferro-orbital order and shows the observed enhancement around 1GPa. We further clarify the controversial nature of magnetism and its interplay with nematicity in FeSe in the same unified picture for all Fe-based superconductors. In addition, the versatile itinerant carriers produce interesting correlated metal behavior in a large region of phase space. Our study establishes a generic exceptional paradigm of stronger quantum fluctuation with larger spins that complements the standard knowledge of insulating magnetism.

 

 

Jul
27
Thu
2017
Ultrafast optically induced dynamics in solids: Non-linear optics on the few-fs timescale
Jul 27 @ 11:00 AM – 12:00 PM

Speaker: 

Dr. Michael Sejer Wismer (Max Plank Institute of Quantum Optics, Germany)

Date: 

Thu, 27/07/2017 – 11:00am to 12:00pm

Location: 

CA2DM Theory Common (S16-06)

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Event Type: 

Seminars

Abstract

The generation of pulses as short as a few cycles at optical frequencies allows for new regimes of nonlinear optics in solid media [1,2]. Few-cycle pulses have been shown to drive currents in insulating materials with large band gaps (~ 9 eV) at electric field strengths on the order of 1 V/Å, without causing structural changes to the medium. 
In this talk I will present results on numerical calculations of few-cycle pulses interacting with electrons in crystalline media. A 5 fs pulse tuned to the fundamental band gap in GaAs exhibits nonlinear dynamics beyond Rabi oscillations, which is due to the significant influence of intraband motion. We argue that the modulation in transition energies caused by intraband motion leads to the appearance of anharmonic resonances.
I will also present results for the optical Faraday effect, which is likewise investigated for ultrashort pulses. Circularly polarised pump pulses with field strength close to the damage threshold are numerically shown to rotate incoming UV probe pulse which would require up to 100 T for the conventional Faraday effect. In addition, pump-probe spectroscopy of the induced ellipticity is predicted to exhibit features that have not yet been measured experimentally. 

[1] “Observation of high-order harmonic generation in a bulk crystal”, Ghimire et al., Nature Phys., 2011.

[2] “Optical-field-induced current in dielectrics Agustin”, Schiffrin et al., Nature, 2013

[3] “Strong-Field Resonant Dynamics in Semiconductors”, Wismer et al., Phys. Rev. Lett. 2016.

[4] “Ultrafast optical Faraday effect in transparent solids”, Wismer et al. arXiv:1612.08433.

 

About the Speaker

Michael Sejer Wismer
Max Plank Institute of Quantum Optics, 
Hans-Kopfermann Straße 1, Garching bei München, Germany

Aug
2
Wed
2017
Experimental quantum optics using novel materials
Aug 2 @ 11:00 AM – 12:00 PM

Speaker: 

Tobias Vogl (Australian National University)

Date: 

Wed, 02/08/2017 – 11:00am to 12:00pm

Location: 

Physics Conference Room (S11-02-07)

Event Type: 

Seminars

Abstract

Although most research on 2D materials is targeting electronic applications, recent advances have opened a new platform for single photon generation based on these novel materials. Single photons are a key resource for quantum optics and optical quantum information processing. The integration of scalable room temperature quantum emitters into photonic circuits remains to be a technical challenge.
First, I will explain the basics of quantum information processing, including quantum computing and quantum cryptography and outline how 2D materials can be used here. Next, I will present our latest experiment, where we utilized a defect center in hexagonal boron nitride (hBN) attached by Van der Waals force onto a multimode fiber as a single photon source. We performed an optical characterization of the source in terms of spectrum, state lifetime, power saturation and photostability. A special feature of our source is that it allows for easy switching between fiber-coupled and free space single photon generation modes. In order to prove the quantum nature of the emission we measure the second-order correlation function. For both fiber-coupled and free space emission, the second-order correlation function dips below 0.5 indicating operation in the single photon regime. The results so far demonstrate the feasibility of 2D material single photon sources for scalable photonic quantum information processing. Furthermore, I will show our new experiment of a high-speed and high purity single photon source.About the speaker

Tobias Vogl studied physics and mathematics at the Ludwig-Maximilian-University of Munich (LMU) in Germany, where he received his B.Sc. and M.Sc. degree in 2014 and 2016, respectively. During his time in Harald Weinfurter’s group at the LMU he first focussed on quantum hacking, demonstrating loopholes in free space quantum cryptography applications, while later he developed a mobile free space quantum key distribution experiment for short distance secure communication. Prior to the work on quantum cryptography he worked in Volodymyr Pervak’s group on multilayer chirped coatings. Other research areas of interest include conventional cryptography and fundamentals of quantum mechanics.
In 2016 he joined Ping Koy Lam’s group at the The Australian National University in Canberra, Australia as a PhD student. He is focusing on implementing 2D materials into quantum optics experiments, ranging from single photon generation to quantum optomechanics. He fiber-integrated a single photon source based on hexagonal boron nitride operating at room temperature. Current work includes building a near-ideal high-speed and high purity single photon source and theoretical modelling of electronical properties of 2D materials.
Tobias Vogl is a member of the Elite Network of Bavaria and the German Physical Society from which he was honoured for excellent performance in the field of physics. During his career he received multiple scholarships and fellowships.

Aug
21
Mon
2017
Electric properties of single-walled carbon nanotube and nanoparticle complex for neuron-like signal generation
Aug 21 @ 2:00 PM – 3:30 PM

Speaker: 

Prof Hirofumi Tanaka

Date: 

Mon, 21/08/2017 – 2:00pm to 3:30pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

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Event Type: 

Seminars

Abstract

Complex of single-walled carbon nanotube (SWNT) and nanoparticles (NP) has potential of innovative electric nanodevices. In the present work, we measured individual electric property of SWNT/NP complex and found material of NP differed electric property of the complex widely. We also found polyoxometalate complex might be used as neuron firing device in brain computing.

1.Introduction

For the future development of molecular electronics, nanoscale molecular devices should be constructed using nanometer-sized electrical wiring. To obtain high-quality devices composed of a few molecules, the nanoscale wiring and the device should have a constant interface. For this purpose, single-walled nanotube (SWNT) has been synthesized with several nanoparticles like 5,15-Bispentyl-porphyrinato Zinc(II) (BPP-Zn), N,N’-bisalkyl-1,4,5,8-naphthalenediimide (Cx-NDI, where x is number of methylene units in the alkyl side-chain) and 1:12 phosphomolybdic acid (PMo12). Then, the electrical property of the complex was measured by using point-contact current imaging atomic force microscopy (PCI-AFM, Fig.1).[1,2] Each nanoparticle showed different electric properties on SWNT. Especially, POM generated pulse like neuron behavior, which might be used in brain-like computing in the future.

2. Experimental Method      

First of all, we prepared BPP-Zn which has two pentyl groups to increase a solubility of SWNT/porphyrin complex [2]. SWNT (0.5 mg) was added to a DMF solution of BPP-Zn (0.1 mM, 5 mL), and then sonicated for 30 min. The solution was centrifuged at 1000 G and the supernatant was collected. SWNT/BPP-Zn complex was collected by a filter (0.5 mm, MILIPORE) and excess BPP-Zn was removed by rinsing by with CHCl3 (100 mL). The SWNT/BPP-Zn was added to DMF (2 mL) and complex was sonicated for 30 min. The DMF solution of SWNT/BPP-Zn complex was casted to a mica substrate and the surface was observed by the tapping-mode AFM (Fig. 2(a)). On the half of the substrate, Au was deposited as electrode with 30 nm thick. After finding individual complex, some of them was dispersed on substrate and check electric properties of the random network.

3.Results and Discussion    

The complex having 2.5-4.5 nm heights was observed. Since a diameter of SWNT is about 1.1-1.5 nm, height of porphyrin-aggregate on SWNT is about 1-3 nm, corresponding 2-6 porphyrin monomers. We measured the conduction property of the complex using PCI-AFM successfully. The results reveal the conduction property of SWNT/porphyrin complex. I-V curve was symmetric where porphyrin aggregate was not absorbed on SWNT, while it was asymmetric where porphyrin was absorbed. This means porphyrin nanoparticles work as rectification devices on the SWNT wiring.

Figure 2(b) shows an AFM image of SWNT/C3-NDI complex. It shows nanoparticles about 3-5 nm diameter of NDI adsorbed on the sidewall of SWNT. By changing the number of methylene unit of NDI, the shape of I-V curve changed. The results show that the majority of SWNT was metallic using C3-NDI to make a complex, while semiconducting when C9-NDI. Besides, the rectification ratio increased and band gap decreased as the size of the molecular nanoparticles increased.   

The rectification properties of SWNT/PMo12 complex were strongly determined by the property of nanotubes. Rectification ratio decreased and band gap increased as particle size was larger if SWNT is semiconducting, while opposite in the case of metallic SWNT. PMo12 also has interesting electric properties. I-V curve obtained by PCI-AFM always show peaks. The peak called negative differential resistance (NDR). Because NDR is one of the components of noise generator, a network of SWNT/PMo12 was fabricated and bias was applied. Amplitude of current, noise strength, was increased as bias increased from 0V to 125V (Fig. 3). Further, current became unstable when 150 V was applied to the same device and then generated pulse current (Fig. 4). The pulses are obtained as special case of the instability. The phenomena are expected to be utilized as neuron devices used in brain computing.

Conclusion

All BPP-Zn, NDI and PMo12 molecules can behave as rectification device on SWNT. PCI-AFM is a useful technique to detect the electrical properties of such kinds of systems described above. It is important to control rectification properties of the complex to realize electronic nanodevices. PMo12/SWNT network generated pulse when 150V was applied. It is expected to be used as neuron firing devices in neuronal computing in the future.

References

[1] a) Y. Otsuka, Y. Naitoh, T. Matsumoto, T. Kawai, Jpn. J. Appl. Phys., Part 2 41 (2002) L742. b) A. Terawaki, Y. Otsuka, H. Y. Lee, T. Matsumoto et al., Appl. Phys. Lett. 86 (2005) 113 901. c) Y. Otsuka, Y. Naitoh, T. Matsumoto, T. Kawai, Appl. Phys. Lett. 82 (2003) 1944. d) T. Yajima, H. Tanaka, T. Matsumoto, Y. Otsuka et al., Nanotechnology, 18 (2007) 551.

[2] H. Tanaka, T. Yajima, T. Matsumoto, Y. Otsuka et al., Adv. Mater. 18 (2006) 1411.

About the Speaker

Prof. Dr. Hirofumi Tanaka

Department of Human Intelligent Systems,

Graduate School of Life Science and Systems Engineering,

Kyushu Institute of Technology (Kyutech),

2-4, Hibikino, Wakamatsu, Kitakyushu 808-0196, Japan.

Prof. Tanaka completed his doctorate in materials science studying the structural and magnetic properties of ferromagnetic nanoalloys at Osaka University in 1999. Next, he studied the conductivity of metallic nanowires with double-probe scanning tunneling microscopy as a special postdoctoral researcher at RIKEN under Prof. M. Aono. After that, he advanced the molecular-ruler method in which precise multilayers of self-assembled molecular monolayers are used as lithographic resists to yield nanostructures with precise nanometer-scale spacings as a postdoctoral researcher at the Pennsylvania State University under Prof. Paul Weiss (presently UCLA, chief editor of ACS Nano). He then joined the Research Center for Molecular-Scale Nanoscience at the Institute for Molecular Science in 2003 under Prof. T. Ogawa as an assistant professor, where he directed research in molecular electronics using carbon nanotube electrodes. He found that gold nanoparticles can switch to metallic conduction of SWNTs to semiconducting simply by nanoparticle adsorption. This work led to the development of molecular electronics to study electrical properties affected by interactions between molecular nanoparticles and SWNT or graphene nanoribbon. He has also focused on the development of atomic switches, exploring the ultimate miniaturization of electrical switches, and controlled by photo irradiation 2004-2008 in a key technology project of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and receive an excellent journal award from Japan Society of Applied Physics in 2012. After moving to Osaka University in 2008, he focused on graphene nanoribbons as electrical wires. In 2012, he earned best paper award of Japanese Society of Applied Physics. He moved to department of Human Intelligence Systems, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology as a full professor in April 2014 and is focusing on bio-mimic and/or neuromorphic electric nanodevices. His wide knowledge of materials from metals and inorganic materials to organic materials, and techniques on measurement and fabrication help leading efforts molecular electronics and in combining nanocarbon and nanoparticles to realize a new world of electronic nanosystems.

See group website : http://www.brain.kyutech.ac.jp/~tanaka/index-e.html.

Aug
23
Wed
2017
Exciton spectrum in 2D transition metal dichalcogenides
Aug 23 @ 11:00 AM – 12:00 PM

Speaker: 

Dr. Maxim Trushin (NUS Centre for Advanced 2D Materials, Singapore)

Date: 

Wed, 23/08/2017 – 11:00am to 12:00pm

Location: 

Physics Conference Room (S11-02-07)

Event Type: 

Seminars

Abstract

We develop an analytically solvable model able to qualitatively explain non-hydrogenic exciton spectra observed recently in two-dimensional (2D) semiconducting transition-metal dichalcogenides. Our exciton Hamiltonian explicitly includes additional angular momentum associated with the pseudospin degree of freedom unavoidable in 2D semiconducting materials with honeycomb structure. We claim that this is the key ingredient for understanding the non-hydrogenic exciton spectra that was missing so far.About the speaker

Maxim Trushin is a Senior Research Fellow at the Center for Advanced 2D Materials, National University of Singapore. He obtained his PhD from the University of Hamburg in 2005. From 2006 to 2012 he worked as academic employee at the University of Regensburg (Ratisbonne) and at the University of Konstanz (Constance) from 2012 to 2017. In the period between 2009 and 2010, he was a research fellow at the University of Texas at Austin under a German Research Foundation fellowship. Maxim’s expertise and research interests lie in the theoretical understanding of the electronic properties of semiconductor nanostructures, spintronics, and the optical and transport properties of two-dimensional materials and hybrid structures.

Sep
14
Thu
2017
Origins of Nonlocal Resistance in Multiterminal Graphene: Spin Hall and Valley Hall vs. Other Competing Effects
Sep 14 @ 11:00 AM – 12:00 PM

Speaker: 

Prof Branislav K. Nikolić (University of Delaware USA)

Date: 

Thu, 14/09/2017 – 11:00am to 12:00pm

Location: 

CA2DM Theory Common (S16-06)

Location Map: 

Click here for map

Event Type: 

Seminars

Abstract

The recent experimental observation of nonlocal voltage, several microns away from the nominal current path, near the Dirac point (DP) in multiterminal graphene devices with adatom-induced spin-orbit coupling or in multiterminal graphene on hexagonal boron nitride (G/hBN) heterostructures has been interpreted as the result of the direct and inverse spin Hall effect (SHE) or the direct and inverse valley Hall effect (VHE), respectively [1]. However, subsequent experiments reproducing the nonlocal signal in graphene with adatoms have also demonstrated insensitivity to the applied in-plane magnetic field, thereby suggesting its disconnect with SHE physics or any other spin-related mechanism. The theoretical interpretation of nonlocal signal in G/hBN heterostructures in terms of topological valley currents carried by the Fermi sea states just beneath the gap opened in graphene due to inversion symmetry breaking does not explain the long-standing puzzle of why the highly insulating state of G/hBN is rarely observed. Furthermore, using Landauer-Büttiker (LB) theory, as a rigorous quantum transport approach employed over the past three decades to obtain observable nonlocal voltage and the corresponding nonlocal resistance, we obtained [1] zero nonlocal signal in the same geometry used in experiments (where the channel connecting the two crossbars is much longer that its width) and for the same simplistic Hamiltonian which gives (not directly observable) quantized VH conductivity characterizing topological valley currents. In this talk, I will show how to resolve these puzzles by using first-principles Hamiltonians of graphene with adatoms or G/hBN heterostructures combined with numerically exact calculations of the nonlocal resistance based on the multiterminal LB formula [2,3]. In the case of multiterminal graphene with adatoms, we find several background mechanisms which generate nonlocal resistance even when spin-orbit coupling is switched off [2]. We also proposed a specific device geometry where nonlocal resistance due to the SHE can be isolated by removing such background contributions [2]. This will be compared with the direct and inverse intrinsic SHE as the sole origin of nonlocal resistance in graphene/transition-metal-dichalcogenide heterostructures where graphene acquires homogeneous proximity spin-orbit coupling. In the case of multiterminal G/hBN heterostructure, we demonstrate [3] the key role played by the Fermi surface edge states and the corresponding edge currents (which were missed in previous theoretical analyses based on simplistic Hamiltonian) that can explain both the nonlocal resistance and metallic-like resistivity observed in experiments while being in full accord with the very recent Josephson interferometry-based imaging of the spatial profile of edge supercurrents in G/hBN wires.

References

A. Cresti, B. K. Nikolić, J. H. García, and S. Roche, Riv. Nuovo Cimento 39, 587 (2016).
D. V. Tuan, J. M. Marmolejo-Tejada, X. Waintal, B. K. Nikolić, S. O. Valenzuela, and S. Roche, Phys. Rev. Lett., 117, 176602 (2016).
J. M. Marmolejo-Tejada, J. H. Garcìa, P.-H. Chang, X.-L. Sheng, A. Cresti, S. Roche, and B. K. Nikolić, arXiv:1706.09361

About the Speaker 

Branislav K. Nikolić is a Professor of Physics at the University of Delaware and a Senior Visiting Scientist at RIKEN Center for Emergent Matter Science in Japan. He received his Ph.D.  in theoretical condensed matter physics from Stony  Brook  University, and B.Sc. degree from the University of Belgrade, Serbia. He was visiting Professor at the University of Regensburg, National Taiwan University and Centre de Physique  Théorique  de  Grenoble-Alpes.  His  research  is  focused  on  nonequilibrium  many-body  quantum   systems,   first-principles   quantum   transport   and   high-performance   computing   applied   to   nanostructures   of   interest to spintronics, nanoelectronics,  thermoelectrics  and  nano-bio  interface.  His most notable contributions include studies of the spin Hall effect, spin pumping and spin  torque  in  the  presence  of  spin-orbit  coupling, decoherence of transported spins, spin-dependent  shot  noise, nonequilibrium electron-magnon and electron-phonon systems, topological insulator based devices for spintronic and thermoelectric applications and graphene based devices for ultrafast DNA sequencing.

Jan
9
Tue
2018
Advanced optical nanostructures for bio-photonics and neural engineering
Jan 9 @ 11:00 AM – 1:00 PM

Speaker: Dr Francesco De Angelis
Date: Tue, 09/01/2018 – 11:30am to 12:30pm
Location: S16 Level 6 – Theory conference room
Event Type: Seminars

Abstract

In the last years we introduced different 2D and 3D nanostructures and devices for managing the electromagnetic field at the nanoscales through the generation of surface plasmons polaritons. Firstly, we will briefly revise our past achievements concerning plasmonic nanostructures and their applications to bio-sensing. Secondly, we will show our recent achievements and future perspectives of plasmonic nanopores for next generation sequencing of DNA and protein (European Project FET-Open “Proseqo”, GA N°687089). In the final part we will present the exploitation of 3D nano-devices in combination with CMOS arrays for intracellular recording of action potentials in mammalian neurons and intracellular delivery of biomolecules, genic materials and nanoparticles. Also, the active interaction of the cell membrane with such 3D devices will be discussed. The developed platform may enable significant advances in the investigation of the neuronal code, development of artificial retinas and low-cost in-vitro platforms devoted to the pharmacological screening of drugs for the central nervous system.  As future perspective we will also discuss potential application of our system for the investigation of electrical activities of plant roots that in the near future may revolutionize plant biology. This project is supported by the European Community through the IDEAS grant program (“Neuroplasmonics”, GA N° 616213).

Biography

He is currently Senior Scientist at the Italian Institute of Technology and Supervisor of Nanostructure Facility (clean room). He leads the Plasmon technology Unit (about 25 members) and his main expertise relies on micro and nano-optical devices for biomedical applications. He currently holds an IDEAS-ERC Consolidator grant whose aim is to develop radically new interfaces between electrical/optical devices and neuronal networks. He published more than 100 papers on peer-review impacted journals; total impact factor > 700; H index = 37, citations>5000.  https://scholar.google.it/citations?user=-rjEmUYAAAAJ&hl=it

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