Browsing by Author "Susarla, Sandhya"

Now showing 1 - 4 of 4
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    High-K dielectric sulfur-selenium alloys
    (AAAS, 2019) Susarla, Sandhya; Tsafack, Thierry; Owuor, Peter Samora; Puthirath, Anand B.; Hachtel, Jordan A.; Babu, Ganguli; Apte, Amey; Jawdat, BenMaan I.; Hilario, Martin S.; Lerma, Albert; Calderon, Hector A.; Hernandez, Francisco C. Robles; Tam, David W.; Li, Tong; Lupini, Andrew R.; Idrobo, Juan Carlos; Lou, Jun; Wei, Bingqing; Dai, Pengcheng; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.
    Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.
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    Molecular Simulation of MoS2 Exfoliation
    (Springer Nature, 2018) Zhou, Guoqing; Rajak, Pankaj; Susarla, Sandhya; Ajayan, Pulickel M.; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya
    A wide variety of two-dimensional layered materials are synthesized by liquid-phase exfoliation. Here we examine exfoliation of MoS2 into nanosheets in a mixture of water and isopropanol (IPA) containing cavitation bubbles. Using force fields optimized with experimental data on interfacial energies between MoS2 and the solvent, multimillion-atom molecular dynamics simulations are performed in conjunction with experiments to examine shock-induced collapse of cavitation bubbles and the resulting exfoliation of MoS2. The collapse of cavitation bubbles generates high-speed nanojets and shock waves in the solvent. Large shear stresses due to the nanojet impact on MoS2 surfaces initiate exfoliation, and shock waves reflected from MoS2 surfaces enhance exfoliation. Structural correlations in the solvent indicate that shock induces an ice VII like motif in the first solvation shell of water.
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    Multicomponent Chalcogenides
    (2019-08-27) Susarla, Sandhya; Ajayan, Pulickel M
    Transition metal dichalcogenides (TMDs), a class of two-dimensional (2D) materials, are proposed to be the next generation materials for optoelectronic, spintronic, and valleytronic devices due to their direct semiconducting bandgap, strong spin-orbit coupling and non-equivalent K points in momentum space. However, pristine TMDs fall short for these purposes due to their fixed band gap and low life times of intrinsic excitons. From a materials design perspective, alloying and heterostructure formation with TMDs are some of viable solutions. The first part of this thesis discusses TMDs design for optoelectronics and valleytronics. For optoelectronic applications, multicomponent alloying is used: different strategies like binary, non-isomorphous quaternary, and isomorphous quaternary alloying have been adopted. For valleytronics, the focus is on tuning the long-lifetime interlayer (IL) excitons present in vertical 2D heterostructures by straining and twisting. The second part of this thesis details the synthesis and emergent properties of a bulk binary chalcogen alloy (S-Se). Combining insulating S and Se results in the formation of a flexible alloy with very high dielectric constant and strength. It is believed that this S-Se alloy could perfectly bridge the gap between conventional brittle ceramics and flexible polymers.
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    The emergence of three-dimensional chiral domain walls in polar vortices
    (Springer Nature, 2023) Susarla, Sandhya; Hsu, Shanglin; Gómez-Ortiz, Fernando; García-Fernández, Pablo; Savitzky, Benjamin H.; Das, Sujit; Behera, Piush; Junquera, Javier; Ercius, Peter; Ramesh, Ramamoorthy; Ophus, Colin
    Chirality or handedness of a material can be used as an order parameter to uncover the emergent electronic properties for quantum information science. Conventionally, chirality is found in naturally occurring biomolecules and magnetic materials. Chirality can be engineered in a topological polar vortex ferroelectric/dielectric system via atomic-scale symmetry-breaking operations. We use four-dimensional scanning transmission electron microscopy (4D-STEM) to map out the topology-driven three-dimensional domain walls, where the handedness of two neighbor topological domains change or remain the same. The nature of the domain walls is governed by the interplay of the local perpendicular (lateral) and parallel (axial) polarization with respect to the tubular vortex structures. Unique symmetry-breaking operations and the finite nature of domain walls result in a triple point formation at the junction of chiral and achiral domain walls. The unconventional nature of the domain walls with triple point pairs may result in unique electrostatic and magnetic properties potentially useful for quantum sensing applications.