Weekly colloquia via webex.

2021

Dec
1
2021
Kirsten McMichael, Rensselaer Polytechnic Institute

Oct
20
2021
“Investigating Microbes with Deep Learning Techniques”

The Earth may be described as a microbial planet with microbes found in complex communities that perform a wide range of important functions, from microbial communities in the human gut, to communities in soil that affect the growth of plants. This recognition has spurred considerable interest in high-throughput imaging and modeling techniques. In this presentation, I will talk about our efforts in aiding both. These efforts include: developing a computational framework to reduce the cost of wet-lab experiments, using a Rotationally Invariant Variational Autoencoder to digest high-throughput imaging data, and exploring whether a Recurrent Neural Network could be used to design autonomous experiments in microbiology.

 

WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=mdeed47ee1182e964b9e579999033bc2b 4:00 pm

Oct
13
2021
"Smart Oxides for Neuromorphic Computing"

      The current computing architecture based on semiconductor transistors has reached the limit of physical size. The transistor made nowadays is already at the nanoscale, making it impossible to keep Moore’s law in the near future. Neuromorphic computing, a new computing architecture mimicking the function of a mammal’s neuron system, has been extensively studied and considered to be the most promising new computing scheme, but its development is severely hindered by lack of a crucial component, a commercializable, nanoscale memristor. In short, the memristor is a material that can adjust its resistivity based on the history of current running through it. Memristors can have a novel ‘memory’ effect in the current-voltage curve, which can be used to simulate how neurons work in biological systems. A central challenge in this emerging field is a predictive-microscopic theory to understand and simulate such a novel memory effect. We propose that the memristive effect observed in transition metal oxides is closely tied to the quantum transport of electrons through dynamical disordered environment, and the engineering of Anderson localized states in amorphous phases could make transition metal oxides ‘smart’ enough for neuromorphic computing. I will present our work in the niobium-based oxides and demonstrate different mechanisms for making new memristors. Possibilities for exploring new memristors using exotic quantum mechanical effects will be discussed.

 

      This work is supported by the Air Force Office of Scientific Research under award No. FA955018-1-0024,  ‘Cross-disciplinary Electronic-ionic Research Enabling Biologically Realistic Autonomous Learning (CEREBRAL) MURI’.

 


Sep
29
2021
“Probing and tuning plasmon excitations in low dimension materials”

The control and tuning of the optical properties of materials and the localization of electromagnetic energy are long standing quests for scientists. For metallic surfaces and nanomaterials, they are driven by collective electronic excitations such as surface plasmons. The surface plasmons are at the origin of the color of centuries old stained glass and used in present applications such as biosensing thanks to their dependence on the size and the shape of the nanoparticules and on the external medium. They can also be probed with sub-nanometer resolution by Electron Energy Loss Spectroscopy (EELS).

 

In this colloquium, we analyze recent efforts to tune the surface plasmon excitations of nanoparticules and 2D materials in link with applications such as electrochromism (smart windows) or Surface Enhanced Raman Spectroscopy (SERS).

 

In particular, we first investigate the EELS response of very elongated metallic nanorods as a case study. The control of the optical properties of semi-conducting nanocrystals will then be presented in context of electrochromism and of the heat and light management of buildings by smart windows. This raises fundamental questions about the origin of optical properties of system with discrete energy levels such as quantum dots and molecules.

 

Finally, we present an effective way to engineer the electronic and optical properties of graphene in the visible range via corrugation. As a 2D material, graphene sustains very localized excitations and we show here that corrugation is at the origin of plasmon-like optical excitation at visible frequencies. SERS signal of femtomolar solutions of ZnPc and CuPc molecules are measured.

 

 

Professor Luc Henrard, University of Namur
Webex link: https://rensselaer.webex.com/rensselaer/j.php?MTID=m925a786be72a124e6ff3219770553345 4:00 pm

Sep
22
2021

Sep
15
2021

Sep
8
2021
“Defect Related Applications in Nanomaterials”

 

The incorporation of defects in nanomaterials, particularly semiconducting transition metal dichalcogenides (TMDs), layered hexagonal boron nitride (hBN), and BaZrS3 perovskites, have promise for various applications.  In this colloquium, density functional theory (DFT) calculations are performed to optimize and engineer defects in these nanomaterials for single photon emitter (SPE), detector, solar cell, and Li ion battery applications.  In the case of SPEs, we discuss our methodology to identify the defects which could be responsible for the antibunched photons observed in monolayer WSe2 and layered hBN.  For detectors, we propose a strain mechanism to remove any undesired oxygen adatoms from the TMD surface to make the TMDs potentially better NH3 sensors and identify metal dopants with the potential to detect stress-related biomolecules.  For solar cells, Ti-alloyed BaZrS3 thin films are developed with the hope to create stable and efficient photovoltaic devices.  In addition to Ti, other dopants investigated including Hf, Y, and Ta show some promise as well.  For Li ion battery applications, the reaction mechanism for Li and F ions at the surface of defective hBN are investigated to determine how the ions interact and determine the best defects to create a reversible LiF compound formation reaction.

Zachary Ward, Rensselaer, Physics, Applied Physics and Astronomy
https://rensselaer.webex.com/rensselaer/j.php?MTID=m8a20783ad036294d3c6297975931a8b5 4:00 pm

Apr
21
2021
"Keeping electrons from getting distracted in nanoscale wires.”

Resistance in nanoscale wires is increasingly the main bottleneck to the performance of semiconductor computing devices. With reducing dimensions, scattering of electrons at surfaces, interfaces and grain boundaries increases rapidly and causes a sharp increase of resistivity of conventional metals at the nano scale compared to bulk. We use first-principles calculations of ballistic electron transport and electron-phonon scattering to explore several complementary strategies to design materials for future nanoscale interconnects. Specifically, we investigate the possibility of protection against scattering in topological metals and identify challenges in realizing practical interconnects using such materials. We identify anisotropy and directionality of electronic states in metals as the most promising way to achieve conductors that scale well to the nano scale, mitigating surface scattering by getting the electrons to encounter the surface less frequently. With high-throughput calculations of thousands of known intermetallics and metallic compounds, we identify promising candidates for narrow interconnects in future computing devices.

 

Bio: Ravishankar Sundararaman is an assistant professor at Rensselaer Polytechnic Institute since 2016, with appointments in the Department of Materials Science and Engineering and the Department of Physics, Applied Physics and Astronomy. He received a PhD in Physics from Cornell University in 2013, and was a postdoctoral fellow in the Joint Center for Artificial Photosynthesis at Caltech. His research team pushes the limits of first-principles materials design using combined quantum-classical simulations for electrochemical, plasmonic and nano-electronic applications, and leads the development of the JDFTx open-source software for such calculations. He is the recipient of the AIME Robert Lansing Hardy Award and the Rensselaer School of Engineering Research Excellence Award in 2020.

via Webex: https://rensselaer.webex.com/rensselaer/j.php?MTID=m7f2a1da1e18b71f47f7668b0afa0cf86 4:45 pm

Apr
14
2021
“Scalable Fabrication of Plasmonic Metamaterials "

The combination of glancing angle deposition and nanosphere lithography is a powerful nanofabrication technique to design regular arrays of plasmonic nanostructures or metamaterials. This method, referred to as nanosphere shadowing lithography, is a simple and scalable physical vapor deposition based on nanosphere monolayers due to shadowing effect. The nanostructure morphology or topology can be controlled by tuning the vapor flux directions with respect to the monolayers polarly and azimuthally as well as by alternating the deposited materials. We have designed and fabricated a series of planar and quazi-three dimensional plasmonic nanostructures with tunable plasmonic response, strong Fano resonance, or large circular dichroism response. If a two-source co-evaporation system is used, alloy or mixed composition nanostructures or even hybrid nanostructures can be created and properties of two or more materials could co-exist and adjusted. Such a simple but scalable fabrication method has a great potential for large scale metamaterial and meta-device development.

 

Dr. Yiping Zhao received his B.S. degree in Electronics from Peking University in 1991, and MS degree in condensed matter physics from Institute of Semiconductors, Chinese Academy of Sciences in 1994.  He obtained his Ph.D. degree in Physics at Rensselaer Polytechnic Institute in 1999.  He is currently a Distinguished Research Professor at the Department of Physics and Astronomy in University of Georgia, Fellow of  SPIE (the International Society of Optics and Photonics), Fellow of AVS (American Vacuum Society),  and Fellow of IAAM (International Association of Advanced Materials). Dr. Zhao is the author or co-author of more than 297 peer reviewed journal papers, 34 conference proceeding papers, 2 books, 8 book chapters, and 12 US patents. His major research interests are nanostructures and thin films fabrication and characterization, plasmonic nanostructures, chemical and biological sensors, nano-photocatalysts, antimicrobial materials, nanomotors, and nanotechnology for stroke treatment.

Virtual seminar. 4:45 pm

Mar
24
2021
“Harnessing biosystems for quantum information science”

A prevailing attitude in quantum information science holds that architectures for quantum sensing and information processing require exceptional isolation from sources of decoherence. In this viewpoint, such environmental effects, including electromagnetic and thermal noise, must be mitigated by austere regimes of shielding and cooling. Yet there may be another possibility. Could robust room-temperature alternatives be envisioned using biosystems that are optimized for certain quantum processes in warm, wet, and wiggly environments? Time permitting, we will explore in this seminar a number of collective and cooperative mechanisms that can enhance coherent phenomena at multiple scales, including superradiance, optomechanical pumping far from equilibrium, many-body (van der Waals) dispersion, and spin filtering through chiral molecules. These exciton, phonon, plasmon, polariton, magnon, and other quantized effects may be exploited to develop novel platforms for quantum biosensing, opening avenues for the tantalizing realization of a test-tube quantum biocomputer and advanced biomedical diagnostics and therapeutics.

 

About the Quantum Biology Laboratory:

With a transformative vision that extends from the subatomic to the clinical scale, the QBL studies how collective behaviors in living matter can be manifested, controlled, and exploited for the development of advanced tools, diagnostics, and therapies to address neurodegenerative, oncological, immunological, and oxidative metabolic disorders. Investigators in the QBL use tools from theoretical physics, condensed matter, quantum optics, molecular biology, biochemistry, genomics, spectroscopy, and high-performance computing to solve an array of problems relevant to human disease processes and clinical medicine. To learn more, visit www.quantumbiolab.com.

Virtual seminar: https://rensselaer.webex.com/rensselaer/j.php?MTID=m168af79fdb0e9eddcc6e4b38c032f5b6 4:45 pm

Mar
17
2021
"Designer 2D materials for new sensing paradigms"

Emerging 2D quantum materials have gained increasing attention due to their unique electronic and optical properties, and have shown promise in sensing applications. The realization of sensing devices using these materials still faces several challenges. For example, it is critical to gain clear understandings of (1) the fundamental light-matter interactions and their relations to the atomic structures, which govern many key material properties and device performances; and (2) the coupling with other nanostructures and molecules, which is a required structure for sensing devices and systems. This talk introduces new discoveries and pioneering works on these critical challenges, and novel applications of these materials in biochemical sensing. The first part of this talk presents multi-dimensional engineering techniques to augment material performance, including 2D Janus conversion, 1D nanoscrolling, and 0D atomic defect creation. The characterization techniques employed, including low-frequency Raman spectroscopy, polarization- and time-resolved spectroscopy, and ultrafast electron diffraction, can be widely used in other material systems. The second part of this talk focuses on the interaction of 2D materials with organic molecules and related sensing applications. In particular, a novel enhancement effect of molecular Raman signals on 2D surface was discovered, which offers a new paradigm of biochemical sensing with high specificity, high multiplexity, and low noise. The selection rule for the 2D material substrates has been revealed, which is critical for device design. Two sensing applications for Alzheimer’s disease and respiratory viruses will also be discussed. Overall, the works presented in this talk are significant in fundamental quantum science, and offer important guidelines for practical applications in sensing and quantum technologies. The methodologies used here also provide a framework for the future study of many emerging materials and sensing scenarios.
Bio:
Shengxi Huang is an assistant professor in the Department of Electrical Engineering, Department of Biomedical Engineering, and Materials Research Institute at The Pennsylvania State University. Shengxi earned her PhD degree in Electrical Engineering and Computer Science at MIT in 2017, under the supervision of Prof. Mildred Dresselhaus. Following that, she did postdoctoral research at Stanford University with Profs. Tony Heinz and Jonathan Fan. She obtained her bachelor’s degree with the highest honors at Tsinghua University, China. Shengxi is the recipient of multiple awards, including NSF CAREER Award, Johnson & Johnson STEM2D Scholar’s Award (6 awardees worldwide in 6 disciplines), Kavli Fellowship for Nanoscience, Jin Au Kong Award for Best PhD Thesis at MIT, and Ginzton Fellowship at Stanford. Shengxi’s research interests involve light-matter interactions of quantum materials and nanostructures, as well as the development of new quantum optical platforms and biochemical sensing technologies.

Virtual Seminar: https://rensselaer.webex.com/rensselaer/j.php?MTID=m9f7e1c24f5d87ab887d0d3d155ffd6b0 4:45 pm

Mar
10
2021
"Revealing Light-Matter Interactions at the Nanoscale using Single-Molecule Super-Resolution Microscopy."

Metal nanoparticles (NPs) sustain a collective oscillation of their free electrons, called a localized surface plasmon resonance (LSPR), when excited by an electromagnetic wave. When this incident wave is resonant with the LSPR frequency, the field intensity is strongly increased in the near field of the NP. Plasmonics thus provides a unique tool for the manipulation and confinement of light well beyond the diffraction limit. This has opened up a wide range of applications based on extreme light concentration, including nanophotonic lasers and amplifiers, biochemical sensing, and optical metamaterials. However, many difficulties remain in experimentally measuring the shape, size, and enhanced field properties of the localized electromagnetic modes in the vicinity of the NPs due to the limitations of optical microscopy. Here, I will discuss how we can unravel the coupling of light to a nano-antenna through single-molecule fluorescence imaging. This technique is a powerful tool to optically study structures beyond the diffraction limit by localizing isolated fluorophores and fitting the emission profile to the microscope point-spread function. By using the random motion of single dye molecules in solution to stochastically scan the surface, and by assessing emission intensity, wavelength, lifetime, and density of emitters as a function of position, we gain new insight into the properties of these systems and pave the way for the development of devices operating at the single photon level.

Virtual seminar: https://rensselaer.webex.com/rensselaer/j.php?MTID=m88270650a404ec65f6a7e9531de7d22d 4:45 pm

Mar
3
2021
“Electromechanical systems enabled by interfacial slip in 2D material heterostructures”

Understanding the mechanical deformability of nanomaterials is critical to realizing a host of next generation technologies like stretchable electronics, three dimensional multifunctional surfaces, and nanoscale machines. Due to their unparalleled mechanical strength and stability, two-dimensional (2D) materials like graphene and MoS2 represent the ultimate limit in size of both mechanical atomic membranes and molecular electronics. Moreover, many of the most interesting properties of 2D materials and new functionality arise from the van der Waals interfaces between layers and in engineering multilayer heterostructures. Open questions include how the interface affects the mechanical properties of 2D heterostructures and how to integrate the outstanding mechanical properties and electronic functionality of 2D materials together. In this presentation, we will examine the impact of the van der Waals interface on the mechanics of bending and crumpling of 2D atomic membranes, slip in nanoelectromechanical drumhead resonators, and optoelectronic devices from crumpled 2D heterostructures. Taken together, these experiments show that interfacial slip strongly affects the mechanics of 2D materials and heterostructures and leads to membranes which are orders of magnitude more deformable than conventional 3D materials.

Virtual seminar: https://rensselaer.webex.com/rensselaer/j.php?MTID=mbe31d5a8e4dbcc457b76f6189e906c93 4:45 pm

Feb
24
2021
“One-Step Annealing of Graphene Ink for Developing Flexible Dopamine Sensors with Record-Low Limit of Detection ”

Existing analytical tools for detection of dopamine - an important neurotransmitter - are not suitable for point-of-care (POC) testing.(1) For developing low-cost and efficient POC diagnostics, electrochemical biosensors are at the forefront, due to simple operation, portability, real-time readout, affordability, and high sensitivity.(2-3) To develop sensitive biosensors, two-dimensional (2D) materials are highly attractive by being atomically thin with high specific surface area. Selective detection of target analytes can also be achieved by engineering the 2D layer through various physical and chemical processes. For electrochemical detection of dopamine, while several reports have used graphene as the sensing layer, the lowest limit of detection of sensors only based on graphene as their active layer is around 1 nM. We recently showed that a record-low limit of detection of 5 pM – in both buffer and serum – can be achieved through a facile, onestep annealing process (4). Using various characterization techniques, we studied the effect of different annealing conditions on surface functionalities, defects, and anisotropic electrochemical activity and the corresponding impact on the sensor response. An all-ink sensor was also developed on polyimide which is a flexible substrate. This low-temperature annealing process provides a simple approach to develop flexible biosensors which can be integrated with printed electronics to create an integrated sensor-readout system for POC testing and affordable health monitoring.

 

 

Virtual Seminar: https://rensselaer.webex.com/rensselaer/j.php?MTID=m9958b203e0c7e5c9d23585b0a3cbf2a4 4:45 pm

Feb
17
2021
“Control of conductivity type and semiconductor-to-metal phase transition in MoTe2 bulk crystals and FET devices”

2D materials are few-atom-thin layers with promising application in future electronics, including quantum computing, flexible and transparent electronics, chemical and bio- sensors. Molybdenum ditelluride, MoTe2, is the prime example of such materials class. It exists in two thermodynamically stable crystal forms: semiconducting 2H phase and semimetallic 1T’. Reversibility of the 2H«1T’ phase transition can be controlled by temperature or by external stimuli, such as strain [1] or ionic liquid gating [2], which makes this material attractive for advanced 2D electronics.

 

This talk will describe a growth of 2H and 1T’ MoTe2 single crystals, where crystal structure and electrical properties are controlled by the growth conditions. In addition, a conductivity type in 2H structure can be tuned by scaling down the channel thickness in FET devices fabricated from exfoliated thin layers. The reversible 2H«1T’ phase transition in bulk single crystals will be compared with electric-field-induced phase change in memristive thin-film devices [3].

 

[1] W. Hou et al., Strain-Based Room-Temperature Non-Volatile MoTe2 Ferroelectric Phase Change Transistor. Nature Nanotechnology 14 (2019) 668

[2] D. Zakhidov et al., Reversible Electrochemical Phase Change in Monolayer to Bulk-like MoTe2 by Ionic Liquid Gating. ACS Nano 14 (2020) 2894

[3] F. Zhang et al. Electric-Field Induced Structural Transition in Vertical MoTe2 and Mo1-xWxTe2 based Resistive Memories. Nature Materials 18 (2019) 55

 

 

Speaker’s bio: Albert Davydov is a leader of Nanostructured Functional Materials Group at NIST. He has extensive experience in fabrication, processing and microstructural characterization of a wide range of electronic materials including 2D and quantum materials. His expertise also includes thermodynamic modelling and experimental study of phase diagrams for metal and semiconductor material systems. He serves as a Head of the Semiconductor Task Group for the International Centre for Diffraction Data (ICDD), member of Advisory Board with the Applied Physics Review journal, member of the Science Advisory Board with the nanoelectronics COmputing REsearch (nCORE) program at SRC, and co-Chair of SPIE Optics & Photonics Conference on Low-dimensional Materials and Devices.

 

Virtual Seminar: https://rensselaer.webex.com/rensselaer/j.php?MTID=m2ae616683f247c65db644ec1675c708f 4:45 pm

Feb
10
2021
Picture a Scientist!

Women in Physics (WiP) to host a discussion of the documentary PICTURE A SCIENTIST following a screening held February 5-7th. The film follows the experiences and careers of three women in science as they encounter gender discrimination, harassment, and racism. The documentary has been extremely well-received since its opening last year, and we are excited to be able to share it with the RPI community. 

 

To register for the screening, please see Announcements on the Physics department homepage.

 

Film synopsis:

PICTURE A SCIENTIST chronicles the groundswell of researchers who are writing a new chapter for women scientists. Biologist Nancy Hopkins, chemist Raychelle Burks, and geologist Jane Willenbring lead viewers on a journey deep into their own experiences in the sciences, ranging from brutal harassment to years of subtle slights. Along the way, from cramped laboratories to spectacular field stations, we encounter scientific luminaries - including social scientists, neuroscientists, and psychologists - who provide new perspectives on how to make science itself more diverse, equitable, and open to all.

 

 

 

Virtual Discussion 4:45 pm

Feb
3
2021
"New Quantum Magnets - Design and Discovery"

Identification, understanding, and manipulation of novel electronic and magnetic states is essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic and electric field are subject to intense investigation. Hall effect measurement is sensitive to both electronic topological sates and chiral spin textures, giving rise to large anomalous, and topological Hall effects, respectively.  In this talk I will present our recent results on two materials, one which shows an anomalous Hall effect (AHE), and the other which manifests a topological Hall effect (THE), both with unconventional origin. In the first part I will talk about the AHE we discovered in a collinear antiferromagnet CoNb3S6, that is not allowed in the conventional theory. In the second part, I will present a THE in the kagome-net magnet YMn6Sn6, for which we have recently formulated a new fluctuation based mechanism.

Relevant references:

[1] N. J. Ghimire et al., Science Advances 6, eabe2680 (2020)

[2] N. J. Ghimire and I. I. Mazin, Nature Materials 19, 130 (2020)

[3] N. J. Ghimire et al., Nature Communications 9, 3280 (2018)

[4] T. Giulia et al., Physical Review Research 2, 023051 (2020)

Biography:

Nirmal J. Ghimire received his PhD from The University of Tennessee at Knoxville in 2013 working as a graduate research assistant at the nearby Oak Ridge National Laboratory. He was a postdoctoral research associate in Los Alamos National Laboratory from 2013 – 2015, and a Director's Postdoctoral Fellow at Argonne National Laboratory from 2015-2018. He joined GMU in 2018, where he is currently an Assistant Professor. He co-leads the materials group of the Quantum Science and Engineering Center at GMU. His research focuses in discovering and understanding emergent phenomena in quantum materials via designing and synthesizing materials and measuring their magnetic and transport properties. 

WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=m77069a79aab2fbc2da8aa0f8384bfa45 4:45 pm

2020

Dec
2
2020
"Dark matter, LZ, and a Snowball"

Dark matter is still one of the greatest mysteries of the Universe. The nature of the particles and fields that constitute dark matter remains elusive. While high mass dark matter was initially favored by theory, the lack of discoveries of supersymmetry at the LHC sends a clear message: we must look everywhere for dark matter. In the >10GeV/c^2 mass range, the LUX-ZEPLIN (LZ) experiment will be the most sensitive direct detection dark matter experiment to detect the rare interactions between dark and ordinary matter, with a projected spin-independent cross-section sensitivity of 1.6 x 10^{-48} cm^2 for a 40 GeV WIMP mass, for a 1000 live day run. LZ uses dual-phase liquid xenon TPC technology to detect dark matter, and is nearing the end of construction, 4850 ft underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota. Meanwhile, new efforts are made to look in the sub-GeV mass ranges, using new techniques. One of those is the snowball chamber, a “reverse bubble chamber” that uses supercooled water to look for dark matter. In this talk, I will give an overview of dark matter, a status update of the LZ experiment, and will introduce the Snowball chamber concept.

Webex: https://rensselaer.webex.com/rensselaer/j.php?MTID=m72a38e52a06ee9512837d83cd142edba 4:45 pm

Nov
18
2020

Nov
11
2020
"Spintronics of Magnetic Topological Insulators"

Spintronics exploits the spin degree of freedom and replaces electron waves with spin waves in signal processing devices for eliminating the energy losses. The new proposed solution for high-performance spintronic materials is based on magnetic topological insulator MnBi2Te4 and axionic metamaterials from MnBi2Te4 family. Axion insulator is a theoretically predicted state of matter capable to mutually convert electric and magnetic signals, and whose properties are reminiscent of cosmological axion dark matter (which explains its name). MnBi2Te4 is the most promising material for realization of solid-state axion insulator. Besides new fundamental physics, axion insulators offer a wide spectrum of applications related to non-linear optics, spintronics, and noise-tolerant quantum computers. This presentation will describe the first experimental realization of room-temperature axionic single-spin switch in topological metamaterial MnBi2Te3/MnBi2Te4. The metamaterial was in situ created in the scanning tunneling microscopy (STM) experiment by removing top Te atomic layer using STM tip. Room temperature STM study of MnBi2Te3/MnBi2Te4 revealed atomic scale variations of exchange gap and formation of nanoscale spin bubbles pinned at subsurface defects. We found that individual spin states in MnBi2Te3 can be reversibly switched using local electric field of STM tip with magnetoelectric response comparable to the theoretically predicted response of axion insulator. The observed topological surface magnetism develops significantly above bulk Néel temperature.

 

 

Dr. Igor Altfeder, Ohio State University
https://rensselaer.webex.com/rensselaer/j.php?MTID=mf357066be69497f61afa562f6a9ec48f 4:45 pm

Nov
4
2020
”Carbon Nanotechnology: An efficient platform for virus enrichment and detection”

The global COVID-19 pandemic is exerting devastating impacts on individual livelihoods, local communities, and the global economy. Accurate, real-time, and widespread testing is needed in order to track the disease, prevent further infections, and gain basic fundamental understanding of the disease, such as the number of infections, infection rate, etc. This talk will discuss the design and fabrication of disposable cartridges using a label-free virus enrichment platform consisting of microarrays of CNTs in conjunction with metal nanoparticles. These trapped viruses are detected and identified using Raman spectroscopy in conjunction with Machine Learning models. More importantly, after viral capture, these viruses remain viable permitting subsequent in-depth characterizations by various conventional methods. This technology successfully enriched rhinovirus, influenza virus, coronavirus and parainfluenza viruses, and maintained the stoichiometric viral proportions when the samples contained more than one type of virus, thus emulating coinfection. Viral capture and detection took only a few minutes with a 70-fold enrichment enhancement; detection could be achieved with as little as 102 EID50/mL, with a virus specificity > 90%. This enrichment method coupled to Raman virus identification constitutes an innovative system that could be used to quickly track and monitor viral outbreaks in real-time.

WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=m3b8eaef57b7ef6779c28f65158b84c41 4:45 pm

Oct
28
2020
“All-solid-state battery”

All-solid-state batteries are being considered as one of the most promising technologies for safer, high-energy, and long-term energy storage. However, key materials issues remain unsolved and serious barriers must be overcome for their full-scale commercialization. In this presentation I will discuss some of our approaches to understand the key challenges in solid electrolyte materials. Based on a modified electrochemical measurement and first-principles computations, we show that the electrochemical stability window of solid electrolytes was significantly overestimated from the conventional measurement. Electrochemical decompositions of solid electrolytes occur and can lead to interfacial resistances in solid state batteries. Suppressing the (electro)chemical reactions between electrode and electrolyte by engineering their interphase enables a high performance all-ceramic lithium battery. I will further show the general belief that solid electrolytes can prevent lithium dendrite formation is incorrect. Using time-revolved neutron depth profiling, we visualize the deposition of lithium dendrites directly inside the solid electrolytes, thus highlighting the important role of electronic conductivity in dendrite formation. I will conclude my presentation by outlining my future research.

WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=mb7e43fdde395c6131476495268b5925b 4:45 pm

Oct
21
2020
"Looking for new physics of novel 2D materials"

The isolation of graphene using the mechanical exfoliation technique opened the possibility of obtaining other 2D crystals for the investigation of their physical properties [1,2]. Indeed, short after the first reports on the physical properties of graphene, other 2D materials were isolated and investigated [2]. Thanks to simulations, we have an estimate of potential 2D crystals that can be obtained by exfoliation which amount to ca. 1800 [3], and high throughput computation has been an important tool to investigate them [4]. In this talk, I will present some of the interesting physical properties that we have found in new 2D materials, and I will discuss why simple models, such as tight binding, are still very important for understanding new physics.

Andres Botello-Mendez, IFUNAM-Mexico
WebEx:https://rensselaer.webex.com/rensselaer/j.php?MTID=m9a25a410c59fcdd8eba6780282a20740 4:45 pm

Oct
14
2020
WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=m45a61a5e6ba6c827cfe7ba8b928894c6 4:45 pm

Oct
7
2020
WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=m498c139acd90d695bcc8380e2d138451 4:45 pm

Sep
30
2020
WebEx link. https://rensselaer.webex.com/rensselaer/j.php?MTID=m986f2aeb3ea30714602d4e466ab78523
Dr. Stephanie Tomasulo, US Naval Research Laboratory
WebEx: https://rensselaer.webex.com/rensselaer/j.php?MTID=m986f2aeb3ea30714602d4e466ab78523 4:45 pm

Sep
9
2020
Professor Humberto Terrones, Rensselaer

Feb
26
2020
DEFECT ENGINEERING IN 2D MATERIALS

The rise of two-dimensional (2D) materials has opened up possibilities for exploring new physical phenomena that motivate the synthesis of more complex low dimensional systems. In this colloquium, we will discuss doping routes that allow the tunability of electronic properties in 2D semiconducting transition metal dichacogenides (TMDs). Zero dimensional (0D) defects such as vacancies and substitutional dopants within tungsten disulfide (WS2) monolayers, will be discussed. In particular, TMD substitutional doping with CH units can be achieved using a novel radio-frequency plasma assisted (RF-PA) approach. Electron microscopy studies confirmed the presence of CH units within the WS2 lattice of plasma treated islands, and DFT calculations confirm the stability of these CH species in sulfur mono-vacancies. Furthermore, field effect transistors fabricated using these CH-doped WS2 exhibit an ambipolar behavior, instead of the n-type transport showed by pristine WS2. The photoluminescence (PL) emission (at 77K) of defective TMD monolayers will also be presented. In particular, sulfur mono-vacancies are concentrated along the edges of triangular WS2 monocrystals. We observed the appearance of bound excitons located 300 meV below the neutral (A) exciton. DFT calculations reveal that sulfur monovacancies introduce midgap states exactly 300 meV below the edge of the conduction band. High–resolution scanning transmission electron microscopy (HR-STEM) images indicate that edges of the WS2 monolayers that exhibit bound excitons contain a very large concentration of sulfur mono-vacancies. Finally, the challenges and new directions in defect engineering of 2D materials will be introduced.

Dr. Ana Laura Elias, SUNY Binghamton
Low Center for Industrial Innovation (CII) 3051 4:00 pm

Feb
19
2020
Studying Neutrinos with SNO+

SNO+ is a multi-purpose experiment whose main purpose is to study the nature of the neutrino mass through observation of neutrino-less double beta decay. Detection of this rare process would indicate that neutrinos are elementary Majorana particles, different from the rest of the standard model family of particles. SNO+ can also measure neutrino oscillation parameters, detect geo and reactor anti-neutrinos and low energy solar neutrinos while its main goal is to search for neutrino-less double beta decay in the isotope Tellurium-130. The first of the three SNO+ phases started in May 2017, with the detector filled with ultra-pure water. SNO+ began the transition to the scintillator phase in late 2018. Later this year, the double-beta decay phase will start when the ultra-pure liquid scintillator will be loaded with 3.9 tonnes of natural tellurium, for a half-life sensitivity larger than 2x10^26 years. Previous results, current status, and the potential and prospect of SNO+ for precise solar neutrino measurements and neutrino-less double beta decay search will be presented.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Feb
12
2020
"Challenges of making and characterizing large area 2D materials"

Since 2004 two-dimensional (2D) materials including graphene, transition metal dichalcogenides (TMDCs) and their heterostructures have continued to draw intense research world-side due to their fascinating new fundamental science and diverse potential applications.  However, making and characterization large area 2D materials remain a big challenge. In this talk, I will discuss some recent developments in this area of research including a metal organic chemical vapor deposition technique to produce large area 2D materials. I will also show how we can probe the perfection of the large area 2D materials using a combination of local probe techniques such as atomic force microscopy and transmission electron microscopy, and a unique, newly developed global characterization technique at Rensselaer called azimuthal refection high-energy electron diffraction (ARHEED).

Biography: Professor Gwo-Ching Wang is Travelstead Institute Chair of physics. Her research mainly focuses on the growth and characterization of advanced materials. She is Fellow of American Physical Society, American Vacuum Society, American Association for the Advancement of Sciences, and the Materials Research Society. She served as the Chairman of the Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute from 2000 to 2010.

Gwo-Ching Wang, Physics, Applied Physics and Astronomy, Rensselaer
Low Center for Industrial Innovation (CII) 3051 4:00 pm 4:00 pm

Jan
29
2020
Moiré Excitons in 2D Semiconducting Superlattices

The moiré superlattice formed between two-dimensional (2D) materials provides a powerful tool to engineer novel quantum phenomena. The most striking phenomena emerge in the “strong-coupling” regime, where the periodic moiré potential dominates over the relevant kinetic energy and qualitatively changes the quasiparticle behaviors in both real and momentum space. Electrons in the “strong-coupling” regime have shown intriguing phenomena. However, a similar opportunity to engineer bosonic phases has not been experimentally explored. In this talk, I will show the emergence of intra- and inter-layer moiré excitons, i.e. bosons composed of tightly-bound electron-hole pairs, in WSe2/WS2 superlattices in the “strong-coupling” regime. The strong moiré potential trapped excitons into a periodic boson lattice in the real space, exhibiting exotic behaviors. I will also discuss strongly correlated electron phases emerging in this platform.

Dr. Chenhao Jin, Cornell University
Low Center for Industrial Innovation (CII) 3051 4:00 pm

2019

Nov
20
2019
Metasurface enabled Spatio-temporal Shaping of Optical Fields

Over the last decade, flat optical elements composed of an array of deep-subwavelength dielectric or metallic nanostructures of nanoscale thicknesses – referred to as metasurfaces – have revolutionized the field of optics and nanophotonics. Because of their ability to impart an arbitrary phase, polarization or amplitude modulation to an optical wavefront as well as perform multiple optical transformations simultaneously on the incoming light, they promise to replace the traditional bulk optics in applications requiring compactness, integration and/or multiplexing.

In this talk, we discuss the ability of metasurfaces to arbitrarily shape both the temporal and spatial evolution of optical fields, ranging from the deep-ultraviolet to the terahertz frequency range. This requires independent control over the amplitude, phase and/or polarization, achieved here by designing individual metasurface elements to act as nanoscale half-wave plates. We will discuss the various nanofabrication strategies and material constraints governing for their design for operation at these various frequency ranges and outline the advantages of the metasurface approach to light shaping over the more traditional use of spatial light modulators to do the same.

Finally, we demonstrate the versatility of spatial shaping metasurfaces to be directly integrated on integrated photonic chips for their applications as an interface to quantum or biological systems. Through spatial multiplexing of metasurfaces integrated with grating out-couplers directly on a nanophotonic chip, we show the ability to create arbitrary optical fields in the far-field for applications in cold atom traps, biosensing or LIDAR.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Nov
6
2019
Two-dimensional materials, metamaterials, and machine learning

 This talk will address two-dimensional materials properties and the use of machine learning to predict and understand dynamical phenomena. The discovery of graphene and related two-dimensional materials enables the possibility of engineering metamaterials with desired electronic and optical properties. Plasmonic nanocrystals are optical metamaterials that consist of engineered structures at the sub-wavelength scale. They exhibit optical properties, such as negative-refractive-index and epsilon-near-zero (ENZ) behavior, that are not found under normal circumstances in nature. We will describe a systematic approach for constructing graphene-based tunable metamaterials that exhibit anisotropic ENZ behavior. Subsequently, we will focus on graphene and Dirac solids that constitute two-dimensional materials where the electronic flow is ultra-relativistic. When graphene is deposited on a substrate with roughness, a local random potential develops through an inhomogeneous charge impurity distribution. This disordered potential induces a chaotic pattern in the electronic flow in the form of current branches. We will describe the physics that governs this ultra-relativistic electronic branched flow and demonstrate analytically and numerically the laws of the onset of branching. Finally we will address Machine learning (ML) methods that are currently employed for understanding physical systems as well as for designing materials. We use ML techniques in graphene and produce results that show how ML can predict the electronic branching by learning from past temporary states of the flow. In addition to the data-driven forecasting, we show how unsupervised neural networks can solve differential equations. We focus on energy-conserving equations and propose an architecture that is time invariant and guarantees the energy conservation through an embedded Hamiltonian symplectic structure.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Oct
30
2019
The Herta Leng Memorial Lecture

In this talk I will describe how a radio astronomy search for more of the puzzling objects known as quasars led to the accidental discovery of some even more puzzling radio sources, or pulsars. I will briefly outline the properties of pulsars and recount some earlier instances where pulsars were nearly discovered.

 

Bio: Jocelyn Bell Burnell inadvertently discovered pulsars as a graduate student in radio astronomy in Cambridge, opening up a new branch of astrophysics - work recognised by the award of a Nobel Prize to her supervisor.

 

She has subsequently worked in many roles in many branches of astronomy, working part-time while raising a family. She is now a Visiting Academic in Oxford, and the Chancellor of the University of Dundee, Scotland.  She has been President of the UK’s Royal Astronomical Society, in 2008 became the first female President of the Institute of Physics for the UK and Ireland, and in 2014 the first female President of the Royal Society of Edinburgh. She was one of the small group of women scientists that set up the Athena SWAN scheme.

 

She has received many honours, including a $3M Breakthrough Prize in 2018.

 

The public appreciation and understanding of science have always been important to her, and she is much in demand as a speaker and broadcaster.  In her spare time she gardens, listens to choral music and is active in the Quakers. She has co-edited an anthology of poetry with an astronomical theme – ‘Dark Matter; Poems of Space’.

'The discovery of pulsars - a graduate student's tale' (Contact: Dr. Esther Wertz, 518-276-2674)
Sage 3303 4:00 pm

Oct
23
2019
Corning’s innovative past, present and future

Founded in 1851, Corning Incorporated has a longstanding track record of creating life-changing innovations. Starting with railroad signal lights and the mass production of Edison's light bulb, and including the high performance window glass for every US space mission, and currently the strong glass on almost every touchscreen in the world, Corning's material innovations have had a far-reaching impact.

 

In this talk, I'll give a brief history of Corning's biggest innovations and the attendant science, discuss how our persistent support of R&D undergirds our success, and close with our plans to continue innovation for another 168 years.

Dr. Donnell Walton, Corning Incorporated
Center for Biotechnology and Interdisciplinary Studies (CBIS), Bruggeman 4:00 pm

Oct
16
2019
Random matrix theory and perfect transmission in opaque materials

We think of materials such as eggshells, white paint and snow as being opaque because the random arrangement of scatterers within these media frustrates the passage of light. It turns out that they are only opaque in a statistical sense.  Remarkably, it is possible to ‘sculpt’ light to make these media transparent. We describe how random matrix theory sheds light on this subject and discuss recent experimental successes.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Oct
9
2019
Materials discovery using machine learning

Recently, machine learning tools have been used to aid in the search for novel materials with desirable properties. Materials informatics – the combination of machine learning with materials science – is a promising area of research which opens up new avenues for materials discovery and the unearthing of physical insights. In this talk, we will use materials informatics to search for new two-dimensional (2D)magnetic materials. The recent discovery of intrinsic ferromagnetism in monolayer CrI3 and bilayer Cr2Ge2Te6 created great interest in 2D materials with intrinsic magnetic
order. How many of these materials exist? What are their properties? We use materials informatics to study the magnetic and thermodynamic properties of 2D materials. Crystal structures based on monolayer Cr2Ge2Te6, of the form A2B2X6, are studied using density functional theory (DFT) calculations and machine learning tools. Magnetic properties, such as the magnetic moment are determined. The formation energies are also calculated and used to estimate the chemical stability. We show that machine learning, combined with DFT, provides a computationally efficient means to predict properties of two-dimensional (2D) magnets. In addition, data analytics provides insights into the microscopic origins of magnetic ordering in 2D. This non-traditional approach to materials research paves the way for the rapid discovery of chemically stable 2D magnetic materials.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Oct
2
2019
X-ray Nanovision: topological defects and ferroic order revealed

Topological defects in ferroic order are extensively studied as templates for unique physical phenomena and in the design of low-dimensional, reconfigurable functional elements such as high-density memory “bits.” Since such defects may offer localized non-bulk properties and low dissipative spatial controllability within a chemically homogenous nanoscale medium, the ability to noninvasively detect and probe the 3D morphology and dynamic of ferroelectric vortex-core in operando, with sub-nanometre precision remains a daunting experimental task. Here, we develop and demonstrate the applicability of X-ray Bragg coherent diffractive imaging (BCDI) to address these challenges in individual ferroelectric and multiferroic nanocrystals. Applicability of BCDI to a wider class of systems are discussed.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Sep
25
2019
Light-matter interactions of quantum materials and their novel sensing applications

Emerging quantum materials, such as novel two-dimensional (2D) materials and topologically nontrivial materials, have gained increasing attention due to their unique electronic and photonic properties. The realization of the optoelectronic applications of these materials still faces several challenges. For example, it is critical to gain clear understandings of (1) the fundamental light-matter interactions, which govern many of the key material properties, and (2) the coupling with other nanostructures, which is a required structure for devices and systems. This talk introduces new discoveries and pioneer work using optical spectroscopic techniques on these critical challenges, and novel applications of 2D materials in sensing. The first part of this talk presents the essential material properties investigated using spectroscopy, including interlayer coupling of Moirè patterns of 2D materials, and anisotropic light-matter interactions of 2D materials and Weyl semimetals. The second part of this talk focuses on the interaction of 2D materials with other nanostructures and the related applications. The interactions of 2D materials and selected organic molecules revealed novel enhancement effect of Raman signals for molecules on 2D surface, which offers a new paradigm in biochemical sensing. The works presented in this talk are significant in fundamental nanoscience, and offer important guidelines for practical applications in optoelectronics, sensing, and quantum technologies. The methodologies used here also provide a framework for the future study of many new quantum materials.

Low Center for Industrial Innovation (CII) 3051 4:00 pm

Sep
18
2019
Multi-TeV Particle Astrophysics with the HAWC Observatory

High-energy gamma-ray observations are an essential probe of cosmic-ray acceleration mechanisms. The detection of the highest energy gamma rays and the shortest timescales of variability are the key to improve our understanding of the acceleration processes and the environment of the cosmic accelerators.

The High Altitude Water Cherenkov (HAWC) experiment is a large field of view, multi-TeV, gamma-ray observatory continuously operating at 14,000 ft since March, 2015. The HAWC observatory has an order of magnitude better sensitivity, angular resolution, and background rejection than the previous generation of water-Cherenkov arrays. The improved performance allows us to discover TeV sources, to detect transient events, to study the Galactic diffuse emission at TeV energies, and to measure or constrain the TeV spectra of GeV gamma-ray sources. In addition, HAWC is the only ground-based instrument capable of detecting prompt emission from gamma-ray bursts above 100 GeV.

In this colloquium I will present the most recent results using the first three years of data from the HAWC observatory. I will also briefly mention the exciting perspectives of building a next-generation gamma-ray experiment at very high altitude in the Southern Hemisphere.

Low Center for Industrial Innovation (CII) 3051 4:00 pm