2D Atomic and Molecular Lattices: Rational Synthesis and New Properties
Who: Prof. Thomas J. Kempa, Dept. of Chemistry, Dept. of Materials Science and Engineering, Johns Hopkins University
When: Wed, 24-Jul-2019, 11am
Where: Physics Conference Room (S11-02-07)
Host: Assoc Prof Goki Eda
Our group develops rational chemical solutions to challenges in materials research. This talk will focus on our recent efforts in synthesizing 2D atomic and molecular lattices and in discovering new properties within them. Atomic Lattices: 2D transition metal dichalcogenides (TMD) have enjoyed widespread adoption in opto-electronic, catalytic, and device studies. However, methods offering explicit control over the dimensionality, morphology, and crystalline phase of TMDs are rare. We show that Si substrates bearing phosphide moieties can control the dimensionality and morphology of MoS2 crystals grown over them. On surfaces with a high density of Si–P dimers, MoS2 crystals form 1D-like ribbons, which are largely single-layer, exceptionally uniform, and of the semiconducting 2H phase. The widths of these 1D crystals can be tuned from the nano- to the micron-scale. Cluster expansion and density functional theory calculations support a mechanism for the substrate-directed growth responsible for transforming MoS2 from a 2D to 1D crystal morphology. Moreover, 1D MoS2 crystals exhibit a significantly blue shifted photoluminescence (PL), compared to 2D crystals, at room temperature. Notably, this PL is precisely and progressively tunable through synthetic control of the 1D crystal width. Molecular Lattices: Metal-organic frameworks (MOFs) are versatile materials that have been used as tunable scaffolds for energy storage, catalysis, and separations. We are focused on developing new approaches for the synthesis and characterization of hierarchically structured and stimuli responsive MOFs. We demonstrate the synthesis of 2D MOFs composed of molecular complexes containing strongly-coupled di-Mo cores. These materials exhibit anomalous gas adsorption characteristics, redox activity, and photo-tunable charge transport. Notably, we demonstrate the versatility of chemical vapor deposition and the unique opportunities this method presents for the preparation of layered 2D MOFs. We show that single crystal device studies allow for not only detailed investigation of charge transport mechanisms within these materials, but also in situ identification of the unique response of these MOFs to optical, electronic, and chemical stimuli. Collectively, our studies underscore the importance of rational synthesis in elaborating materials with unique and prescribed properties.
About the speaker:
Tom completed his Ph.D. studies in 2012 under Prof. Charles Lieber at Harvard University and a post-doctoral fellowship with Prof. Daniel Nocera, then at MIT. In July 2015, Tom joined the faculty of the Department of Chemistry at Johns Hopkins University as an Assistant Professor. Since 2017 he has held a joint appointment in the Department of Materials Science and Engineering. The Kempa group synthesizes and studies materials with novel structures, phases, and topologies with a current research focus on porous molecular solids, 2D materials, and multi-component nanostructures. These materials have unique properties rendering them useful for addressing outstanding challenges in fundamental science, energy sustainability, and optoelectronics. The Kempa group's expertise spans the areas of physical, inorganic, and materials chemistry. Tom has been the recipient of several grants and accolades including an NSF CAREER Award, a Toshiba Distinguished Young Investigator Award, and a Dreyfus Foundation Fellowship in Environmental Chemistry.
Surprising Physics of Nanopore Transport
Who: Prof Aleksei Aksementev, Department of Physics, The University of Illinois at Urbana-Champaign, USA
When: : Tue, 6-Aug-2019, 2pm
Where: Physics Conference Room (S11-02-07)
Host: : Dr Utkur Mirziyodovich Mirsaidov
Transport of molecules through nanoscale pores is a process fundamental to the biology of all living organisms and a key element of many technological processes. Driven by diffusion, electrophoresis, or direct mechanical pulling, the transport can be highly selective and is regulated through a variety of mechanisms, including steric exclusion, electrostatic trapping and dehydration. In this lecture, I will review our discovery of new mechanisms that can govern transport of biomolecules to and through nanoscale pores. I will describe how the physical insights uncovered through computer simulations can be applied to block nanoscale transport in the absence of physical gates, to deliver biomolecules for nanopore sensing and to kill cancer cells.
About the speaker:
Prof Aleksei Aksimentiev has a background in soft matter physics and now deploys computational methods to investigate physical phenomena at the interface of solid-state nanodevices and biological macromolecules. In the focus of his current research program are systems comprising silicon-based synthetic membranes and biomolecules— DNA, proteins, and lipids—assembled into novel silicon circuits that can act as sensors, tweezers, and scaffolds for assembly of biosynthetic complexes. His theoretical work on DNA translocation through nanopores is recognized as the first computational study of that kind. He is an expert in modeling membrane proteins and molecular motors. His pioneering work on modeling ionic transport through membrane channels is a seminal demonstration of the utility and predictive power of the molecular dynamics method, which now has many followers. Within the NIH Center for Macromolecular Modeling and Bioinformatics , he directs the development of the software solutions for computer modeling in biotechnology, which are used by many researchers worldwide.
Time / Location: 7pm - 10pm / NUS football Field
|Dates:||Friday 30 August 2019|
|Friday 13 September 2019|
|Friday 18 October 2019|
|Friday 1 November 2019|
Date / Location: Thursday 26 December 2019 / NUS football FieldFor more information and queries, please contact: Dr Abel Yang