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Institute for Electronics and Nanotechnology (IEN)

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Publication Search Results

Now showing 1 - 10 of 291
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    XPS data for an article "Selective Permeation "Up" a Chemical Potential Gradient to Enable an Unusual Solvent Purification Modality"
    (Georgia Institute of Technology, 2023-05-25) Lively, Ryan P. ; White, Haley D. ; Yoon, Young Hee ; Ren, Yi ; Roos, Conrad J. ; Wang, Yuxiang ; Koros, William J.
    The XPS data show the estimation of 4 types of C-bonds in carbon membranes pyrolyzed in various conditions. As the pyrolysis temperature increases, the relative amount of carbon-carbon bonds increases, while carbon-oxygen, and carbon-nitrogen bonds seem to decrease. Additionally, samples that were exposed to methanol have lower amounts of carbon-carbon bonds and increased amounts of carbon-oxygen bonds relative to samples that were not soaked in methanol. This collection of data was used to hypothesize a representative structure that reflects the average composition and bonding of carbons.
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    An engineer’s perspective on antiferromagnetic spintronics
    (Georgia Institute of Technology, 2023-03-07) Rakheja, Shaloo
    Antiferromagnets (AFM) materials have ordered spin moments that alternate between individual atomic sites, which gives them a vanishing macroscopic magnetic signature and picosecond intrinsic timescale. In his 1970 Nobel Lecture, Louis Néel claimed that antiferromagnets are “extremely interesting from theoretical standpoint, but do not seem to have any applications.” Traditionally, AFM materials have played a secondary role to ferromagnets, which are used as active elements in commercial spintronic devices like magnetic sensors and non-volatile magnetic memory. However, it was recently suggested that spin transfer torque could in principle be used to manipulate the magnetic order in AFMs, leading to either stable AFM order precessions for their use as high-frequency oscillators, or switching of the AFM order for their use as magnetic memories. My presentation will focus on recent theoretical and experimental developments in the field of spintronic devices using antiferromagnets as their active elements. I will specifically talk about two unique AFM materials, Cr2O3, a single-phase magnetoelectric material that can be manipulated solely with electric fields and the Weyl semi-metal Mn3Sn in which spin torque can induce chiral spin rotations. Cr2O3-based ferromagnet-free random access memory has been experimentally demonstrated, while in the case of Mn3Sn, spin torque driven dynamics were found to induce chiral oscillations, from the megahertz to the terahertz frequency range. These materials can overcome the central challenge of manipulating and reading the AFM’s order parameter via microelectronics compatible circuitry, thus allowing us to develop antiferromagnetic spintronics along a similar route as ferromagnetic spintronics. I will conclude my talk by summarizing the limits, challenges, and opportunities of AFM spintronics for future technologies such as high-density, secure nonvolatile memory, compact narrowband terahertz sources, and spike generators.
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    Atomically-Precise Materials Prepared Using Ion Soft Landing
    (Georgia Institute of Technology, 2023-02-21) Johnson, Grant E.
    Scientific challenges that underlie efficient energy storage, chemical conversions and separations, and quantum computing may be addressed using unconventional mass spectrometry techniques that provide unprecedented molecular-level insight. Novel materials not obtainable through conventional synthesis methods may be prepared using a versatile deposition approach known as ion soft landing. A wide range of polyatomic ions, clusters, and nanoparticles with precise composition and charge may be delivered to supports with predetermined coverage and kinetic energy, thereby circumventing the heterogeneity, contamination, and aggregation that often confound characterization and modeling of materials. In this presentation, I will illustrate several recent applications of ion soft landing in energy related research. Precisely controlling the size, shape, and elemental composition of alloy nanoparticles is central to developing catalysts that efficiently promote reactions. Magnetron sputtering combined with gas aggregation prepares bare ionic nanoparticles with unique composition and morphology that are size-selected and deposited onto electrodes. For energy storage, sub-nanometer metal oxides known as polyoxometalates are leading candidates for use in advanced molecular batteries and supercapacitors. Insights are obtained into how the redox properties of polyoxometalates evolve with metal substitution by leveraging the atom-by-atom selectivity of ion soft landing. The impact of substrate and intermolecular interactions on the vibrational properties of polyoxometalate-based molecular qubit arrays is investigated, as is the influence of the size and stoichiometry of ionic liquid clusters on the desolvation, reduction, and separation of metals ions at electrodes. Combined with state-of-the-art characterization techniques and high-level theoretical modeling, ion soft landing is providing transformative insights into the properties of materials in the size regime where each atom counts.
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    LEEFT with Nano for Water Disinfection
    (Georgia Institute of Technology, 2023-02-07) Xie, Xing
    Water is a basic human need. Nevertheless, more than 10% of the world’s population lacks access to safe drinking water. An effective water disinfection method is still not readily accessible to these people. In developed urban areas, water is typically disinfected in a centralized facility through chlorine-based methods that inevitably generates harmful disinfection byproducts. In addition, current water disinfection systems are vulnerable to natural disasters. Next-generation water disinfection should minimize the use of chemicals, the consumption of energy, and the impact on the environment, while having high resilience for different application scenarios. The recently developed water disinfection approach based on locally enhanced electric field treatment (LEEFT) has a great potential to transform current water disinfection strategies and systems. The LEEFT is a physical treatment process that aims to utilize a strong electric field to disrupt cell membranes and thus inactivate pathogens. The electrodes installed in a LEEFT device are typically modified with one-dimensional nanostructures, such that the electric field is greatly enhanced locally near the tips of the nanostructures. LEEFT can potentially be applicable at all scales, from portable devices to point-of-use household units and from distributed community-scale treatment clusters to centralized treatment plants. This talk will cover the recent progress on the development of the LEEFT technology.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.