Nano@Tech Lecture Series

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Nano@Tech Lecture Series

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https://hdl.handle.net/1853/70938

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Event Series

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Institute for Electronics and Nanotechnology (IEN)

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Now showing 1 - 10 of 10

Thermally Responsive Materials for Clean Water and Energy

(Georgia Institute of Technology, 2022-11-08) Menon, Akanksha

The global demand for energy and water is projected to increase by 40% and 55%, respectively, by 2050. Meeting these targets in an efficient, affordable, and sustainable manner necessitates significant scientific and technological advances. The inherent challenge lies in the complexity of water-energy systems due to interactions that span multiple length- and timescales, and this is where leveraging advances in materials provides an opportunity to make them more efficient. This talk will focus on functional materials that are thermally responsive – ranging from ionic liquids to inorganic salt hydrates, and semiconducting polymers – to enable low energy chemical separations (clean water) and to decarbonize heat (clean energy). Ionic liquids combine high ionic strength and affinity for water owing to hydrophilic functional groups, while hydrophobic moieties impart a critical temperature above which these materials release water. The novelty of these materials is that the enthalpy of separation is approximately three orders of magnitude lower than conventional liquid-vapor thermal separations that vaporize water, and the critical temperature can be achieve using solar energy. Another set of materials that are thermally responsive are salt hydrates that can undergo reversible thermochemical reactions to store and release energy in the form of heat. To mitigate stability challenges associated with volumetric changes accompanying the thermochemical reaction, an inorganic-organic composite material is designed by encapsulating the salt into a hydrogel matrix. The novelty of the approach is that it creates a highly porous matrix around the particles to achieve a form-stable composite for a highly reversible thermal battery unlike conventional approaches of impregnating the salt into a porous matrix. The last class of materials that will be highlighted are semiconducting polymers for direct conversion of heat into electricity via the thermoelectric effect. The flexible nature of the polymer and the use of solution-processing techniques opens new avenues for wearable electronics that harvest body heat or provide personal cooling to lower energy demands. These examples demonstrate the potential of dynamic and responsive materials to modulate heat and mass transport for the next generation energy and water systems.
Ultrasound for Brain Imaging and Therapy

(Georgia Institute of Technology, 2022-10-25) Shi, Chengzhi

The development of acoustic metamaterials and the resulted manipulation of ultrasound wave propagation have led to many important technologies that can potentially be applied in medical diagnostics and therapy such as transcranial ultrasound, enhanced cavitation effect for histotripsy and thrombolysis, and noninvasive kidney stone management. In this talk, we will focus on two metamaterial applications in medical imaging and therapy: transcranial imaging enabled by non-Hermitian complementary acoustic metamaterial (NHCMM) and fast sonothrombolysis through vortex ultrasound induced shear stress. High-resolution transcranial imaging using noninvasive high-frequency ultrasound is challenging due to the impedance mismatch between skull and soft tissues and the intrinsic loss because of the porous skull. The development of active NHCMM can compensate the transmission loss resulting from both effects simultaneously that enhances transcranial transmission for high-resolution imaging. For the treatment of blood clots, sonothrombolysis has been demonstrated to be effective. However, the treatment usually last for more than 15 hours when treating a large clot, which is undesirable for the patient and surgeon and can sometimes become life threatening for severe cases of cerebral venous sinus thrombosis (CVST). The active metasurface generated vortex ultrasound induces contactless shear stress in the blood clot that drastically enhances fibrinolysis in blood clots that remarkably reduce the required treatment time with low risk of hemorrhage, especially in treating large, completely occluded, acute clots. Such capability makes the vortex ultrasound based endovascular sonothrombolysis a life-saving tool for severe cerebral venous sinus thrombosis, which has an increasing trend among young patients due to the COVID-19 pandemic.
Biomimetic Scaffolds for Tissue Repair and Regeneration

(Georgia Institute of Technology, 2022-09-27) Xia, Younan

We are seeking to augment rotator cuff repair and peripheral nerve regeneration by developing biomimetic scaffolds capable of recapitulating the compositional, structural, mechanical, and cellular features of the native tissues. Rotator cuff tears are prevalent in the elderly population. Unfortunately, successful repair remains a major clinical challenge, with high post-operative failure rates. At the root of these failures is the poor healing at the repaired tendon-to-bone insertion, and the lack of regeneration of the native attachment structure. We are developing biomimetic scaffolds to augment the surgical repair and healing of the tendon-to-bone attachment. The research is built around the premise that scaffolds can be designed with hierarchical, functionally-graded structures to match the native enthesis for the regeneration of a robust interface between the reattached tendon and bone. When combined with mesenchymal stem cells, the translational potential of the scaffolds in enhancing the formation of a mechanically functional tendon-to-bone insertion are tested in a clinically relevant rotator cuff injury-and-repair model. Peripheral nerve injury is a large-scale problem that annually affects more than one million people in the US. We are developing nerve guidance conduits based on electrospun fibers for the surgical repair of large defects in thick nerves. The conduit facilitates nerve regeneration across a gap by providing a protective environment, limiting the possible directions of axonal sprouting, concentrating neurotrophic factors, and offering physical guidance to neurite extension. Specifically, we are working with conduits featuring a multi-tubular design to recapitulate the fascicles typical of a peripheral nerve while providing good mechanical strength to resist kinking and distortion during surgery. We augment nerve regeneration by leveraging the physical cue arising from the uniaxial alignment of electrospun fibers and nanoscale grooves engraved in the surface of the fibers, in addition to the biological cues provided by Schwann cells and/or encapsulated neurotrophic factors. A combination of in vitro and in vivo models are used to optimize the design and parameters of the conduits for peripheral nerve repair and functional recovery.
Next-Generation Vertical GaN Power Devices Using Selective-Area Doping Techniques

(Georgia Institute of Technology, 2022-09-13) Pavlidis, Spyridon

In recent years, there has been a surge of research and commercial interest in gallium nitride (GaN)-based devices for power conversion applications. This is largely motivated by the wide bandgap of GaN, which offers a unipolar limit of performance that is larger than that of silicon and silicon carbide. While lateral transistors have already been commercially adopted, high power applications require vertical devices to control chip size. Recent improvements in native GaN substrate quality and epitaxy have unlocked the potential of vertical GaN power devices, but effective strategies for selective area doping, in particular p-type doping, remain a major challenge. In this talk, two vertical devices that rely on selective area doping will be discussed. Firstly, the use of magnesium (Mg) implantation and ultra-high pressure annealing (UHPA) will be explored for the development of GaN junction barrier Schottky (JBS) diodes. Effective crystal repair and carrier activation post implantation via UHPA, which is a capless technique, will be demonstrated. The impact of UHPA on the formation of rectifying contacts will then be investigated, followed by the key demonstration of a 900 V GaN JBS diode with state-of-the-art specific on resistance (RON,sp). The second device that will be studied is the GaN superjunction (SJ) diode. Here, lateral polar junctions (LPJs) are adopted. This approach exploits the natural doping asymmetry between the N-polar and Ga-polar crystal orientations to simultaneously grow N-polar GaN for the n-type pillars and Ga-polar GaN for the p-type pillars, which represents a uniquely different strategy compared to conventional semiconductor technologies. It will be shown that the N-polar GaN camel diode can be used to tune the barrier height and reduce leakage. In this way, the first charge-balanced GaN superjunction device will be demonstrated. All in all, these innovations represent key experimental building blocks for future high-power GaN power devices.
Micro-/Nano-scale Tools for Biomarker Discovery and Electronic Point-of-Care Diagnostics for Infectious Diseases

(Georgia Institute of Technology, 2022-04-26) Sarkar, Aniruddh

The current COVID-19 pandemic and other recent outbreaks such as Ebola, MERS, SARS, and H1N1 have underscored the need for early detection and continued surveillance of emerging and re-emerging infectious diseases. The heterogeneity of disease in COVID-19 – a large number of mild or asymptomatic cases coupled with the relatively rapid degradation in symptoms in some patients – poses a unique challenge for the healthcare system and emphasizes the need for developing predictive biomarkers of disease severity. We are harnessing microscale and nanoscale technology to solve these challenges by developing devices for high-throughput discovery and inexpensive electronic detection of diagnostic & prognostic biomarkers. Here, I will present our progress with these approaches in the context of COVID-19 and beyond.
Advances in Cellulose Nanomaterial Utilization in Renewable Materials

(Georgia Institute of Technology, 2022-04-05) Meredith, J. Carson

This talk will review several recent advances in utilizing cellulose nanocrystals (CNCs) in commodity materials applications. The talk will focus on developments relevant to the coatings industry, particularly waterborne coatings utilized in latex paints as well as those useful as barrier coatings for packaging materials. Waterborne acrylic latexes are found in a large variety of commercial coating and paint products, but most of these products continue to contain volatile organic solvents (VOCs). I will present recent work that demonstrates who CNCs can be used as additives to waterborne acrylic formulations to displace the use of VOCs. Notably, because CNCs enable the development of hardness in otherwise soft acrylics, the VOC is no longer needed to enable film formation during the early drying stage. We have investigated two modes of addition of CNC: addition direct to the aqueous phase after the latex is produced and addition to the monomer phase prior to polymerization. In the latter case, the latex is then produced after CNC is dispersed in monomer droplets, by miniemulsion polymerization. This presentation will also feature research on the utilization of CNC dispersions as coatings on conventional polymer films such as PET and cellulose acetate, in order to impart high oxygen barrier properties to these films.
Harnessing In Vivo Enzymatic Activity to Engineer Synthetic Breath Biomarkers of Disease

(Georgia Institute of Technology, 2022-03-29) Chan, Leslie

Breath testing is a non-invasive and rapid diagnostic tool that is underutilized in the clinic due to scarcity of known breath biomarkers. Thousands of volatile organic compounds (VOCs) are excreted from the body in breath after having been produced endogenously as volatile metabolites or introduced exogenously via diet or environmental exposure. However, efforts to identify disease-specific VOCs have been hindered by technological and statistical limitations with currently-used -omic approaches. As an alternative approach to biomarker discovery, my lab has developed a diagnostic platform that leverages aberrant enzymatic activity during disease to engineer synthetic breath biomarkers. This platform technology consists of nanoparticle sensors that are delivered in vivo and release bio-orthogonal VOC reporters upon activation by targeted enzymatic activity. VOC trafficking pathways from tissues to breath offers a mechanism by which we can engineer exhaled biomarkers for diseases of different organ systems. In my talk, I will discuss how we designed and validated our volatile-releasing nanosensors for use in respiratory disease and future applications in gastrointestinal disease.
Enhancing Converse Magnetoelectric Coupling through Strain Engineering in Artificial Multiferroic Heterostructures

(Georgia Institute of Technology, 2022-02-22) Garten, Lauren M.

Magnetoelectricity presents a unique opportunity to control the magnetic response of a material with an applied electric field or vice versa. Unfortunately only a few materials exhibit controllable magnetoelectric coupling (ME) within a single phase, and even then, the response is typically small and below room temperature. One route to enhance ME coupling is to create a composite between a ferroelectric and ferromagnetic material. This type of ME coupling can be mediated in multiple ways, but the current most successful method is through strain transfer across an interface. These artificial multiferroic heterostructures can exhibit ME coupling up to six orders of magnitude larger than within a single material. Still further improvement must be made before ultra-low power memory, logic, magnetic sensors, and wide spectrum antennas can be realized. In this talk I will describe how ME coupling can be enhanced by simultaneously exploiting multiple strain engineering approaches. This work is conducted on heterostructures composed of Fe0.5Co0.5/Ag multilayers on (011) Pb(In1/2N1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 piezoelectric crystal substrates. When grown and measured under strain these heterostructures exhibit an effective converse magnetoelectric coefficient on order of 10-5 s/m: the highest directly measured, non-resonant value to-date. Additionally, this response occurred at room temperature and at low electric fields (< 2 kV/cm). This large effect is enabled by the magnetization reorientation caused by changing the magnetic anisotropy with strain and using multilayered magnetic materials to minimize the internal stress from deposition. This work highlights how multicomponent strain engineering enables enhanced magnetoelectric coupling in heterostructures and provides an approach to realize new energy efficient magnetoelectric applications.
The New Wave of Quantum Magnetism

(Georgia Institute of Technology, 2022-02-08) Mourigal, Martin

Magnetism is a fascinating phenomenon with roots in the ancient world. Although its precise understanding calls for relativistic quantum mechanics and field theory, it is integral to everyday technologies. In magnetic insulators, electrons are closely bound to a crystal lattice and carry strongly interacting magnetic dipoles; as a result, phases of matter with no classical analogs are possible. Such quantum magnetic phases are of great fundamental interest as a testbed of our understanding of many-particle quantum mechanics. In the first part of this lecture, I will discuss some of the central ideas in quantum magnetism, from the Heisenberg model to the more recent concepts introduced by Kitaev and others. Then, I will explain our research program to search for these simple models in bulk materials and understand their properties using neutron spectroscopy. Finally, I will discuss the challenges of utilizing these quantum magnets in electronic devices and beyond.
Creative Epitaxy: Finding Ways to Violate Assumptions that Breach Material Barriers

(Georgia Institute of Technology, 2022-01-11) Doolittle, William Alan

Epitaxial processes are considered routine for applications spanning established industries from the silicon and GaN semiconductor industries to cutting edge research. As many as 10,000 epitaxial reactors crank out billions of dollars’ worth of light emitting diode chips for solid state white lighting alone. Those metrics increase 100-fold for silicon applications. Epitaxy is core to countless industries but is mostly performed in ways that have not changed for decades. But epitaxy can also be performed in non-standard ways to overcome “perceived” barriers to materials synthesis. Several examples will be given in this talk including: 1) Dynamic control of surface chemistry so as to enable higher solubility of desirable impurities; 2) Dynamic control of surface energy facilitating 3D control of alloy composition and material properties; 3) Electrothermal control of epitaxy to enable metastable phase materials; and 4) the “invention” of the widest semiconductor known. Each of these example problems has been solved by a common “thought process” wherein the fundamental assumption behind the limitation was defined and ways of violating the identified assumption was explored leading to new functionality in materials. The importance of the process – assumption identification and violation – will be discussed in hopes of conveying an important approach to solving hard problems. New emerging industries such as optoelectronics, neuromorphic computing and power electronics will be highlighted as beneficiaries of these unique approaches.