Hosted by: Dr. Charles Black

Novel functional materials are usually characterized by emerging ordering in atomic and electronic structures beyond the conventional unit-cell level. Examples include artificial superlattices, self-assembled nanostructures, ferroic domain structures, and charge-density waves. Such complex ordering gives rise to large supercells containing too many atoms, making it a formidable task for diffraction-based structure determination. On the other hand, the maturation of aberration-corrected TEM/STEM presents an alternative real-space approach to probe the complex ordering, through directly imaging the atomic structure with picometer precision, as well as the spatially-resolved spectroscopy to map the electronic structure. Here I will give several examples showing the power of advanced STEM on resolving the complex ordering: i) By developing an imaging condition optimized for oxygen contrast, we can image sensitively the octahedral structure in perovskite oxides with picometer precision. It further enabled us to reveal an extraordinary 2D ordered octahedral tilting in the solid electrolyte Li0.5-3xNd0.5+xTiO3, and to demonstrate its dependence on the competition between Li% and lattice strain.[1] ii) Through atomic displacement mapping using high-resolution imaging, and electric polarization mapping based on 4D-STEM, we made the first experimental discovery of 2D antiferroelectricity in In2Se3, and resolved the true nature of its superstructure that had been under debate for over four decades.[2] iii) In the last example, we applied atomic-scale electron energy-loss spectroscopy to unravel the distinct configurations and valence states of Ce dopants in Mn3O4 nanocatalysts, which suggested an effective oxygen-storage/release route that is responsible for the enhanced redox catalytic activity from Ce doping.[3] [1] Nature Materials 14, 1142-1149 (2015). [2] Physical Review Letter 125, 047601 (2020). [3] Chemistry of Material 31, 5769-5777 (2019).

Hosted by: Chang-Yong Nam

Macromolecular self-assembly has evolved to become an important and valuable tool for bottom-up patterning and fabrication at the nanometer scale. From block copolymer lithography to nanocrystal superlattices to biomolecular assemblies, bottom-up patterning is reaching an unprecedent level of control over complex patterns at the nanoscale with an increasing degree of precision. There is no question that the lithographic landscape has been transformed in the past few years with the introduction of extreme ultraviolet (EUV) lithography and the maturity of multiple patterning techniques. At dimensions below 10 nm, emphasis is shifting away from resolution to precision, highlighting the importance of the uniformity achieved by block copolymers and the exquisite precision afforded by biomolecular assemblies. Moreover, an opportunity may be opening for new, higher complexity, information-rich architectures where hybrid nanoparticle-(bio)molecule assemblies may shine. With features defined at the molecular level and the potential to modular and hierarchical structures, self-assembly offers a path to highly uniform, 2D and 3D architectures. In this talk I will review the current state of bottom-up patterning with soft matter and I will discuss research plans at The Molecular Foundry related to molecular-scale assembly hoping we can foster collaborations across the various NSRCs. Bio-sketch: Dr. Ricardo Ruiz is a Staff Scientist at Lawrence Berkeley National Laboratory where he uses Soft Matter Physics to solve nanofabrication challenges at the single-digit nm scale. From 2006 to 2019 he held various appointments at Hitachi GST/ HGST/ Western Digital where he contributed to magnetic bit patterned media and non-volatile memories, and he managed a research Group dedicated to block copolymer and nanoparticle lithography. He received his PhD in Physics from Vanderbilt University in 2003. He is a Fellow of the American Physical Society. To join, select from the following options: 1) Web Browser a) https://primetime.bluejeans.com/a2m/live-event/ygxfdcgf 2) Laptop paired with room system (Best Experience) a) Dial: bjn.vc or 199.48.152.152 in the room system. b) Go to https://primetime.bluejeans.com/a2m/live-event/ygxfdcgf/room-system/ c) Enter the pairing code displayed on your room system screen into your browser. 3) Room System a) Dial: bjn.vc or 199.48.152.152 in the room system. b) Enter Meeting ID: 149812585 and Passcode: 5815 4) Joining via a mobile device? a) Open this link : https://primetime.bluejeans.com/a2m/live-event/ygxfdcgf b) Download the app if you don't have it already. c) Enter event ID : ygxfdcgf 5) Phone Dial one of the following numbers, enter the participant PIN followed by # to confirm: +1 (415) 466-7000 (US) PIN 9862228 # +1 (760) 699-0393 (US) PIN 2298814590 # 6) Joining from outside the US? https://www.bluejeans.com/numbers/primetime-attendees/event?id=ygxfdcgf

Hosted by: Mircea Cotlet

The efficient transport and interconversion of energy between photons and matter underpins life on earth, and inspires modern technology. Contrary to natural systems, however, in modern energy conversion systems ranging from solar panels to computers, semiconductors to photocatalysts, energy moves slowly, randomly and often inefficiently towards target conversion sites. My work aims to investigate how energy can be directed in molecules and materials in ways that are efficient and targeted, moving beyond stochastic fluctuation driven energy migration. My comprehensive research in the multidimensional ultrafast electronic spectroscopic of functional materials, natural photosynthetic proteins, and photocatalysts has set important precedents in this direction. In a recent study, we discovered how quantum nuclear vibrations participate during a photoinduced electron transfer reaction like a sequence of ratchets, progressively enhancing electron transfer efficiency and rate (submitted). By studying nuclear coherences, we were able to measure unprecedented dynamics along three distinct reaction coordinates for an intermolecular ET reaction. This electronic-nuclear interplay often manifests in the form of an anomalous dispersion of nuclear coherences coupled to the reaction (JACS, 2019). Our breakthrough work on reactivity of transition metal photocatalysts unraveled how quantum vibrational coupling can lead to selective and targeted bond activation (Chem, 2019). We were able to show that quantum vibrational coupling can acts as a conduit to shuttle energy from light absorbing moiety of the transition metal complex to the active reaction site. We also showed that a directional electron density and energy migration from light absorbing ligands to the functional site opens a controlled photoactivation pathway (JACS 2018). The insights from these and other works strongly indicate that exploiting order/synchronization provided by electronic-nuclear interdependencies can help extracting more energy from solar light conversion, speeding up quantum information transport, enhancing carrier transport, and increasing photocatalytic efficiency.

Hosted by: Mircea Cotlet

The first demonstration of transient demagnetization after femtosecond optical excitation was a seminal achievement in condensed matter physics that led to the birth of the field of ultrafast magnetism. Today, we continue to work towards unravelling the nature of the mechanisms that underlie these processes and develop methods for exploiting them to harness new magnetic phenomena. With the recent emergence of quantum material systems hosting novel intrinsic magnetic order, we now have an exciting new playground to study the transient interactions between photons and spin excitations and phases. In this talk, I will discuss our efforts in using such systems to both control the properties of electromagnetic radiation and coherently drive collective magnetic phenomena with light, focusing on three examples. First, I will highlight our efforts aimed at manipulating terahertz pulses by leveraging magneto-plasmonic resonances in micro-structured graphene. I will then examine how light can be used to directly manipulate magnetic order. Here, ultrafast optical quenching of magneto-crystalline anisotropy in the multiferroic skyrmion-host GaV4S8 can drive coherent collective breathing and rotational skyrmion lattice excitations. Finally, I will discuss our recent work involving the ferromagnetic van der Waals crystal CrI3. Our experiments shed light on the nature of angular momentum transfer in this material and reveal a strong coupling between the spin and lattice degrees of freedom. This manifests as coherent spin-coupled phonons whose vibrational amplitude is highly sensitive to the helicity of the driving optical pulse. Together, these three examples codify the immense promise that ultrafast optics holds in understanding and utilizing the novel magnetic properties of quantum materials. Moreover, they point a path towards generating dynamic states with light that may be the key to unlocking the next generation of high-speed memory and nanoscale magneto-optical technology.

Hosted by: Mircea Cotlet

Low dimensional nanomaterials, like zero-dimensional quantum dots (QDs) and two-dimensional van der Waals materials (2D-vdW), have aroused strong research interest owing to their fascinating electrical, optical, and magnetic properties. Optoelectronic properties of these low dimensional nanomaterials are important for exploring their applications in a wide range such as photovoltaics, photodetectors, light emitting diodes and quantum information. In this talk, I will first discuss optoelectronic characterizations of hybrids composed by QDs and 2D-vdW using home-built scanning photocurrent microscope, demonstrating the potential applications in photovoltaics and photodetectors. Then I will show the enhancement in optoelectronic properties of 2D materials through self-assemble. In the last part, I will discuss the future facility developments and research directions in this fascinating and promising research area.