Speaker: Lu Junpeng (Research Fellow)
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Speaker: Silvija Grade?ak
Affiliation: Department of Materials Science and Engineering, MIT
Abstract Details: The recent advances in imaging techniques have generated much excitement and opened up new fields of research in materials science, biology and other disciplines. The atomic- scale study of interfaces, imaging of individual dopant atoms in crystals, discovery of carbon nanotubes, or imaging of biomolecules are just some of the great successes of electron microscopy during the past years, arguably the most exciting period since beginning of the field. The integration of these methods is rapidly proceeding with the need of understanding variety of new (nanostructured) materials under development. This tutorial will provide practical guidelines – based on fundamental understanding of the electron-matter interaction – for the use of scanning and transmission electron microscopy (SEM and TEM, respectively). The emphasis will be on new developments and real-case scenarios. It will help students to understand results, avoid artifacts, and open-up new fields of their own research.
*This is a three-part tutorial taking place on 12, 16, and 19 Jun.
About the Speaker: Prof. Grade?ak's research focuses on nano-photonics and electronics and is based on the synthesis, characterization and integration of low-dimensional systems. By taking the advantage of unique material properties on a nanoscale, she explores novel optoelectronic applications such as nanoscale light-emitting sources, single photon sources, or nanowire lasers.
Understanding the properties of such nanosystems requires multidisciplinary approach and new instrumental tools. Prof. Grade?ak uses rational synthesis of free-standing nanoscale objects like nanocrystals, nanotubes, and nanowires and combine spectroscopic techniques, transport measurements and advanced electron microscopy techniques to directly correlate structural and physical properties on the nanometer scale. Experimental techniques and methodologies that are being developed as a part of her research endeavor are generally applicable to any material system where interplay between nanostructure, properties, and performance becomes significant.
Website of Prof. Grade?ak's research group: http://web.mit.edu/gradecakgroup/index.html
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Speaker: Ming Yang
Affiliation: CA2DM & IMRE, Singapore
Abstract Details: The interface of dissimilar oxide materials hosts rich varieties of exotic phenomena not found in its constituent materials and has attracted a tremendous amount of research interests, both for fundamental physics and practical applications. An ideal example is the interface of two different non-magnetic insulators, polar LaAlO3 on nonpolar SrTiO3. Remarkably, conducting interface was observed with a step function insulator-metal transition at four LaAlO3 unit cells on SrTiO3, as well as unexpected interfacial magnetism. The mechanisms responsible for these remain controversial. Here, using density functional theory calculations and x-ray photoemission spectroscopy, we establish that the interplay of electronic reconstructions, surface oxygen vacancies, and lattice distortions fully compensates the polarization potential divergence in LaAlO3/SrTiO3, explaining naturally the experimental observations. While lattice distortions play a dominant role in insulating state, a spontaneous appearance of 1/4 oxygen vacancies per AlO2 sub-layer at the LaAlO3 surface accompanied by 0.5e- charge- transfer into the interface is responsible for interface conductivity and the discontinuous transition in LaAlO3/SrTiO3. In addition, we also found that surface oxygen vacancies contribute to the formation of weak interfacial magnetism in LaAlO3/SrTiO3 prepared at low oxygen partial pressure. In contrast, the strong magnetism in LaAlO3/SrTiO3 prepared at high oxygen partial pressure is due to interfacial cationic intermixing at the presence of surface oxygen vacancies.
About the Speaker: Ming Yang obtained his Ph. D degree in Physics at the National University of Singapore, and then worked at NUS as postdoctoral research fellow before joining the Institute of Materials Research and Engineering, Singapore. His research interests are in condensed matter physics and materials physics at nanoscale, focusing mainly on understanding and predicting electronic, optical, and magnetic properties at the surface and interface of semiconductors, oxides, and two-dimensional materials by using first-principles calculations and spectroscopic techniques."
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Speaker: Silvija Grade?ak
Affiliation: Department of Materials Science and Engineering, MIT
Abstract Details: bstract
The recent advances in imaging techniques have generated much excitement and opened up new fields of research in materials science, biology and other disciplines. The atomic- scale study of interfaces, imaging of individual dopant atoms in crystals, discovery of carbon nanotubes, or imaging of biomolecules are just some of the great successes of electron microscopy during the past years, arguably the most exciting period since beginning of the field. The integration of these methods is rapidly proceeding with the need of understanding variety of new (nanostructured) materials under development. This tutorial will provide practical guidelines – based on fundamental understanding of the electron-matter interaction – for the use of scanning and transmission electron microscopy (SEM and TEM, respectively). The emphasis will be on new developments and real-case scenarios. It will help students to understand results, avoid artifacts, and open-up new fields of their own research.
*This is a three-part tutorial taking place on 12, 16, and 19 Jun.
About the Speaker: Prof. Grade?ak's research focuses on nano-photonics and electronics and is based on the synthesis, characterization and integration of low-dimensional systems. By taking the advantage of unique material properties on a nanoscale, she explores novel optoelectronic applications such as nanoscale light-emitting sources, single photon sources, or nanowire lasers.
Understanding the properties of such nanosystems requires multidisciplinary approach and new instrumental tools. Prof. Grade?ak uses rational synthesis of free-standing nanoscale objects like nanocrystals, nanotubes, and nanowires and combine spectroscopic techniques, transport measurements and advanced electron microscopy techniques to directly correlate structural and physical properties on the nanometer scale. Experimental techniques and methodologies that are being developed as a part of her research endeavor are generally applicable to any material system where interplay between nanostructure, properties, and performance becomes significant.
Website of Prof. Grade?ak's research group.
Click HERE for directions
—
To view all the upcoming seminars, you can visit: https://graphene.nus.edu.sg/news-events/events/
You may also Like & Subscribe our following channels below to receive instant notifications for new announcements.
Speaker: Silvija Grade?ak
Affiliation: Department of Materials Science and Engineering, MIT
Abstract Details: The recent advances in imaging techniques have generated much excitement and opened up new fields of research in materials science, biology and other disciplines. The atomic- scale study of interfaces, imaging of individual dopant atoms in crystals, discovery of carbon nanotubes, or imaging of biomolecules are just some of the great successes of electron microscopy during the past years, arguably the most exciting period since beginning of the field. The integration of these methods is rapidly proceeding with the need of understanding variety of new (nanostructured) materials under development. This tutorial will provide practical guidelines – based on fundamental understanding of the electron-matter interaction – for the use of scanning and transmission electron microscopy (SEM and TEM, respectively). The emphasis will be on new developments and real-case scenarios. It will help students to understand results, avoid artifacts, and open-up new fields of their own research.
*This is a three-part tutorial taking place on 12, 16, and 19 Jun.
About the Speaker: Prof. Grade?ak's research focuses on nano-photonics and electronics and is based on the synthesis, characterization and integration of low-dimensional systems. By taking the advantage of unique material properties on a nanoscale, she explores novel optoelectronic applications such as nanoscale light-emitting sources, single photon sources, or nanowire lasers.
Understanding the properties of such nanosystems requires multidisciplinary approach and new instrumental tools. Prof. Grade?ak uses rational synthesis of free-standing nanoscale objects like nanocrystals, nanotubes, and nanowires and combine spectroscopic techniques, transport measurements and advanced electron microscopy techniques to directly correlate structural and physical properties on the nanometer scale. Experimental techniques and methodologies that are being developed as a part of her research endeavor are generally applicable to any material system where interplay between nanostructure, properties, and performance becomes significant.
Website of Prof. Grade?ak's research group: http://web.mit.edu/gradecakgroup/index.html
Click HERE for directions
—
To view all the upcoming seminars, you can visit: https://graphene.nus.edu.sg/news-events/events/
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Speaker: Hridis Pal
Affiliation: Georgia Tech, USA
Abstract Details: Graphene has been at the forefront of research for almost a decade, thanks to its unusual electronic properties. It is well known that the properties of this single layer material get modified substantially with the addition of a second layer. The most commonly studied form of graphene bilayers is one where the two layers are mutually rotated by sixty degrees--the so called Bernal stacking. However, recently there has been a surge of interest in bilayer graphene structures where the layers are rotated by an arbitrary angle instead of sixty degrees. The current understanding of these systems may be summarized as follows: at large angles the layers are essentially decoupled, and the system manifests single layer properties. With decreasing angle, however, the Fermi velocity gets renormalized, and at small enough angles, bands flatten and electrons get localized. In this talk, we will show that this current understanding is incomplete: non-trivial physics such as band flattening and localization can happen at large angles as well, as long as the system is sufficiently close to some commensuration. To this end, we formulate a long-wavelength theory near commensuration valid at arbitrary angles of rotation, generalizing existing long-wavelength theories valid only at small angles. We then use our theory to show that in the stong coupling limit and at large angles, the system becomes locally gapped and mimics the properties of a Kagome-like lattice. We discuss the implications of our model.
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Speaker: David Prendergast
Affiliation: The Molecular Foundry, Lawrence Berkeley Natl. Lab., USA
Abstract Details: The control of energy flow in devices is often dictated by materials interfaces and a detailed understanding of such interfaces under working conditions is required for their further optimization. Soft X-ray spectroscopy is an intrinsic surface sensitive probe capable of revealing molecular scale details at interfaces. Coupled with first-principles modeling of the structure and dynamics at the junction between two materials, one can begin to interpret measured spectra and to make direct connections between structure and function. Here we present details of recent studies relevant to various model electrode interfaces in the context of electrochemistry [1] and photoelectrochemistry [2], indicating the importance of first-principles theoretical simulation in the interpretation of X-ray spectroscopy and the associated insight into the processes behind interfacial energy transfer and storage.
[1] The structure of interfacial water on gold electrodes studied by x-ray absorption spectroscopy J.-J. Velasco-Velez, et al., Science 346, 831 (2014).
[2] Atomic Scale Perspective of Ultrafast Charge Transfer at a Dye-Semiconductor Interface. K. R. Siefermann, et al., J. Phys. Chem. Lett. 5, 2753 (2014).
About the Speaker: Dr. David Prendergast is the Facility Director for Theory at The Molecular Foundry, a US Department of Energy Nanoscale Science Research Center and User Facility at Lawrence Berkeley National Laboratory. He received his PhD in Physics from University College Cork, Ireland in 2002, under Prof. Stephen Fahy, and worked as a postdoctoral fellow in the groups of Giulia Galli (then at Lawrence Livermore National Laboratory) and Steven Louie (at the University of California, Berkeley) before joining the scientific staff at The Molecular Foundry in 2007. His research focuses on the development and application of first-principles theory and high-performance computing resources to the modeling of nanoscale phenomena in materials systems. He has specific expertise in the direct simulation of X-ray spectroscopy using these methods and provides prediction and interpretation of measured X-ray spectra in complex and dynamic systems of relevance to energy harvesting and storage.
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Speaker: Marko Kralj
Affiliation: Institute of Physics Zagreb, Croatia
Abstract Details: The properties of graphene can be exploited in various applications e.g. by controlling the density of states at the Fermi energy or the strain and related pseudomagnetic fields. Besides electric field, a chemical adsorption either 'on top' or 'underneath' graphene, where typically charge transfer processes take place, is a suitable tool for the charge carrier and many-body interaction modifications. In epitaxial graphene systems deposition of atoms and molecules often leads to intercalation where species are pushed between graphene and its support. Besides the charge donation, the intercalation can affect the binding interaction and more subtle properties of graphene, e.g. spin-polarization. In fact, properties of many layered materials, including copper- and iron-based superconductors, dichalcogenides, topological insulators, graphite and epitaxial graphene, can be manipulated by intercalation. Another direction of graphene electronic structure tailoring is related to a precise stress control which can be realized by graphene growth on flat or specifically on stepped surfaces and we focus to such systems in order to exploit uniaxial strain engineering.
We studied the intercalation and entrapment of alkali atoms under epitaxal graphene on Ir(111) in real and reciprocal space by means of LEEM, STM, ARPES, LEED and vdW-DFT. The microscopic mechanism and dynamics of intercalation process is explained, where we find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Graphene wrinkles, their structure, ordering and formation dynamics are characterized in great detail on relevant nano- and micrometer scales. Finally, the way to obtain uniaxially strained graphene by growing it on a stepped single crystal substrate and subsequently transferring it to a dielectric support by preserving uniaxial pattern will be presented.
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Speaker: Leonardo Degiorgi
Affiliation: ETH-Zürich, Switzerland
Abstract Details: The ferropnictides harbor a structural tetragonal-to-orthorhombic transition at Ts that may either coincide or precede a transition into a long-range antiferromagnetic order at TN, usually ascribed to a spin-density-wave (SDW) state. We measure the in-plane optical reflectivity of BaFe2As2 over a broad spectral range, covering the energy interval from the far infrared (FIR) to the ultraviolet (UV), at several combinations of uniaxial pressure, used to detwin the specimen, and temperature. Our goal is to probe the anisotropic response in the real part ?1(?) of the optical conductivity, extracted from the reflectivity data via Kramers-Kronig transformations. We thus elucidate how the anisotropic optical metallic response evolves as a function of stress, considered as an external symmetry breaking field, and across the ferro-elastic structural transition at Ts = TN = 135 K. The infrared response reveals that the dc transport anisotropy in the orthorhombic antiferromagnetic state is determined by the interplay between the Drude spectral weight and scattering rate, but that the dominant effect is clearly associated with the metallic spectral weight. In the paramagnetic tetragonal phase, though, the dc resistivity anisotropy of strained samples is almost exclusively due to stress-induced changes in the Drude weight rather than anisotropy in the scattering rate. This result definitively establishes that the primary effect driving the resistivity anisotropy in the paramagnetic orthorhombic phase (i.e., the electronic nematic state) is the anisotropy of the Fermi surface.
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Speaker: Dr. Zhao Weijie
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To view all the upcoming seminars, you can visit: https://graphene.nus.edu.sg/news-events/events/
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