Symposium MS01: Extreme Mechanics

Irina Chuvashova, Carnegie Science

Thermal Conductivity of Earth Minerals at Extreme Conditions

Written by Tianyu Liu

The thermal conductivity of the lower mantle of Earth has been experimentally estimated. The lower mantle is a solid mineral layer that could let heat pass. Various methods have been proposed to quantify the thermal conductivity, or heat-conducting rate, of Earth’s lower mantle; however, experimental evidence remains scarce. Irina Chuvashova from Carnegie Science has added an experimental data of 12.6 W/(m K).  

Chuvashova and co-workers adopted a diamond anvil cell to determine the thermal conductivities of two main iron-bearing minerals in the lower mantle, Ferropericlase and Bridgmanite, under high pressure. The researchers placed the mineral films between two diamond crystals. Due to the hardness, the two diamond crystals could exert ultrahigh forces from 25 GPa to 60 GPa onto the films without cracking. Ultrahigh pressure is necessary to mimic the high-pressure environment inside the Earth. Through black-body theory and laser heating, Chuvashova and co-workers calculated that the thermal conductivities of Ferropericlase and Bridgmanite were 43 W/(m K) and 5 W/(m K), respectively, at 40 GPa. Considering the amount of the two minerals in the lower mantle, the researchers estimated that the lower mantle possessed a thermal conductivity of 12.6 W/(m K), close to the theoretical values.


Symposium FF01: Beyond Graphene 2D Materials – Synthesis, Properties and Device Applications

Manish Chhowalla, University of Cambridge

Ultra Clean van der Waals Contacts Using Indium Alloys on Two-Dimensional Semiconductors

Written by Tomojit Chowdhury

Contact configuration is one of the most crucial parameters that dictates the over-all performance of transistor devices. The Chhowalla Group at the University of Cambridge proposed an alternative contact design that exhibited improved device performance. They chose indium as their contact metal due to its exceptionally low melting temperature (156˚C) compared to other commonly known contact metals, such as gold (Au) and titanium (Ti). “Clearly indium electrodes can be patterned on atomically thin transition metal dichalcogenide (TMD) sheets under very gentle evaporation conditions,” said Chhowalla, alluding to the “soft” physical nature of the metal. In addition, he showed how platinum (Pt) and indium (In) could be alloyed under mild conditions, and thus could be simultaneously deposited atop layered TMDs ensuring “ultra-clean” contacts with atomically sharp metal-semiconductor (Schottky) interface. Such “work function engineering of metal contacts on 2D semiconductors” allowed fabrication of field-effect transistor devices with exceptional carrier mobility.


Symposium SB07: Bioelectrical Interfaces

Róisín Owens, University of Cambridge

Interfacing Human Cell Membrane Models with Bioelectronics for Ion Channel Monitoring

Written by Alana F. Ogata

“You might be familiar with Moores law, but not as much with Erooms law,” says Roisin Owens as she explains how, despite improvements in drug design technology, drug discovery is increasingly slow and expensive. How do you make drug discovery screening methods more efficient and predictive to improve success rates at the clinical trial phase? Owens addresses this issue by studying human membrane models to probe a major mechanism in electrical cell signaling- ion flux through the cell membrane. Supported lipid bilayers (SLB) are excellent biomimetic models for studying interactions between drugs and cell membranes. A supported lipid monolayer formed on top of an organic electrochemical transistor (OECT) creates devices that are sensitive to the nature of the lipid monolayer by measuring electrical currents. Permeability of the lipid monolayer directly influences the current output and can capture time-resolved disruption of the lipid monolayer upon addition of antibiotic molecules. In addition, supported lipid bilayers functionalized with ATP-gated P2X2 channels were successfully studied with the same OECT technology revealing how channels open in response to ATP. Recent work aims to develop a multimodal sensing technology by combining electrical and optical measurements using SLB-OECT devices to further study ion flux in cell membrane models.

 


Symposium MS01: Extreme Mechanics

Ali Khourshaei Shargh, University of Rochester

Atomistic Simulations of Shock Compression of Single Crystal and Core-shell Cu@Ni Nanoporous Metals

Written by Jahlani Odujole

Have you ever wondered about the characteristics of nanoporous metals and why they are useful? Ali Shargh, standing in for his research partner Niaz, offered an overview of how core-shelling can be used to enhance strength and ductility properties in materials. It has been recently discovered that nanoporous metals are light and have high surface volume. These metals have been shown to be better shock absorbers than single crystal materials. The simulation methods of Monte Carlo with the embedded atom method forcefield resulted in Shock Hugoinot plots that display shock pressure versus shock temperature. There was no recovery observed for high temperatures. As shock increased, the face-centered cubic lattice structure decreased. Shargh provided information on this purely theoretical method and how it could potentially be applied to real systems.


Symposium SB07: Bioelectrical Interfaces

Patricia Jastrzebska-Perfect, Columbia University

Mixed-Conducting Particulate Composites for Soft Electronics

Written by Alana F. Ogata

Patricia Jastrzebska-Perfect’s research is driven by a need for materials composed of both hard and soft components that can interface with biological substrates. A major challenge in developing neural interface devices is the large mechanical mismatch between hard and soft materials. Mixed conducting particulate composite materials can achieve the strength and stability required for bonding and provide biocompatibility necessary for device integration into brain tissue. Jastrzebska-Perfect incorporates PEDOT:PSS particles into an electronically insulating scaffolding matrix to create devices capable of recording neurophysiological data in rodents. Additionally, mixed-conducting particle composite devices show high spatiotemporal bipotential sensing capabilities in humans for intra-operative neural recordings. Devices placed on the wrists of patients can measure electrophysiological signals as the patient sequentially moves each finger.


Symposium MS02: Mechanically Coupled and Defect-Enabled Functionality in Atomically Thin Materials

Seung Sae Hong, Stanford University

Extreme Tensile Strain States in La0.7Ca0.3MnO3 Nanomembranes

Written by Jahlani Odujole

The main goal of Seung Sae Hong’s group was to apply tensile strength in a two-dimensional (2D) membrane and found that atomically-controlled 2D interfaces were highly useful. The researchers were able to get thin films under atomic scale control while maintaining a high degree of freedom. The main focus in this presentation was on complex oxides because these materials present a different kind of magnetism. Nanomembranes can be made from thin-film growth. Pulse laser deposition was applied for epitaxial growth. SrTiO3 was the substrate with Sr3Al2O6 used as a sacrificial layer. The researchers found an unprecedented degree of mechanical freedom. Bulk crystals/ceramics break easily in most cases, which was problem that the researchers were seeking to mitigate. Nanomembranes can achieve very large strain rates. This property can also be used to re-design membranes which allows for continuous control within a material. The 2D materials can be re-stretched and redesigned. This versatile experimental platform can be applied to cryogenic transport and optics storage. Thick membranes were shown to be easily broken, while thin membranes kept stretching without cracking. Normalized x-ray diffraction intensity, with clear phase boundaries, was shown to be a great indicator of deformation behavior. Axial tensile strain can change magnetic phase properties. Density functional theory (DFT) calculations were shown to match well with results.


Symposium FF03: Building Advanced Materials via Particle-Based Crystallization and Self-Assembly of Molecules with Aggregation-Induced Emission

Litao Sun, Southeast University

Exploring the Surface Effects of Sub-10-nm Materials from the Atomic Scale

Written by Alana F. Ogata

Differences in materials behavior observed for transitions from the macroscale to nanoscale is a well-known phenomenon in the materials world. These discrepancies are enhanced when studying nanomaterials that are sub-10 nm in size where crystalline nanoparticles can exhibit liquid-like properties. Crystalline materials that behave as liquids sounds like a juxtaposition, but is one that Litao Sun brings to life with in situ TEM imaging of sub-10 nm metal particles. Surface atoms occupy ~62% of the atomic positions available in a sub-10 nm nanoparticle compared to larger nanoparticles where this percentage can drop to 0.036%. Surface atoms are flexible and can be reconstructed into different geometries giving rise to the liquid-like behavior of sub-10 nm nanoparticles. Sun showed a video of a nanoparticle with clear lattice fringes, indicating crystallinity, being pressed to a flat disc and completely recovering shape upon removal of the probe. The sub-10 nm particle can be squished multiple times and bounce back to its original state while maintaining crystalline structure. Sub-10 nm nanoparticles covered with a single layer of graphene will deform under the same external force and retain this deformation due to the rigid nature of graphene.


Symposium FF01: Beyond Graphene 2D Materials – Synthesis, Properties and Device Applications

James Hone, Columbia University

Approaching the Intrinsic Limit in Transition Metal Dichalcogenide van der Waals Heterostructures

Written by Tomojit Chowdhury

Disorders, both external and internal, in two-dimensional (2D) transition metal dichalcogenides (TMDs) are critical to the study of the intrinsic behavior of 2D TMDs. Devices made from TMD crystals containing significant disorders with defect density on the order of 1013/cm2, show low quantum yield and carrier mobility. James Hone of Columbia University introduced a new growth technique, flux synthesis, that was shown to produce 2D TMD crystals with 2-3 orders of magnitude lower defect density. Materials obtained by this method exhibited increased photoluminescence. Most importantly, the Hone group was able to observe bright trionic (trion: a localized quasi-particle consisting of three charged particles, which have a lifetime on the order of 10s of picoseconds) emission, with average trion-lifetime of 250 ps, demonstrating the first known measurement of intrinsic trion lifetime. The last part of his talk was focused on Moiré superlattices created by stacking and twisting 2D tungsten diselenide (WSe2) layered structures, implicating superconductive states, which was observed in twisted bilayer graphene structures by the Jarillo-Herrero Group at MIT.


Symposium EN07: Materials Science for Efficient Water Splitting

Gideon Segev, Tel Aviv University

“All Electric” Ion Pumps

Written by Tianyu Liu

“Whiskey is for drinking; water is for fighting!” Gideon Segev from Tel Aviv University showed this Mark Twain’s quote in his presentation to highlight the challenge of fresh water scarcity. As a researcher from Israel, where fresh water is limited, Segev has a deep motivation to make drinkable water easily accessible. He said that reverse osmosis, a widely used technique for seawater desalting, was economically unaffordable for under-developed regions.

To circumvent the problems of reverse osmosis, Segev and co-workers developed portable, “all-electric” ion pumps that could desalinate water in a regular glass cup. The core component of the ion pump was an electronic ratchet, which utilized a spatially varying electric field to pump ions out from saltwater. This mechanism allowed ion transport without any electrochemical reaction, which significantly boosted the stability of the pump. Segev and co-workers were still exploring optimal operating parameters to maximize the performance of the ion pump.


Symposium FF01: Beyond Graphene 2D Materials – Synthesis, Properties and Device Applications

Iuliana Radu, IMEC, Belgium

Towards Large Scale Manufacturability of (Mostly) Electronic Devices with 2D Materials

Written by Tomojit Chowdhury

This section of the symposium was focused on the large-scale, industrial applications of two-dimensional (2D) materials-based electronic devices. Iuliana Radu from IMEC identified a number of challenges in the scalability of 2D materials-based transistor devices, and compared the performance of existing 2D field-effect transistors (FETs) to that of the Si-based devices. In an attempt to answer the question, “Can 2D materials replace Si?”, Radu highlighted the course of action in order to overcome the inferior performances of 2D materials-based electronic devices compared to the Si-analogues. In this context, Radu demonstrated a state-of-the-art approach—“2D transfer with a laser release layer” to efficiently transfer wafer-scale 2D materials atop target device substrates without the use of a polymer. Additionally, she pointed out that dielectric gating and channel defectivity of these devices needed careful manipulation to produce high on/off, high mobility FET devices for industrial usage.