Condensed Matter and Biophysics seminars

Condensed Matter seminars are held Fridays at 2:30 p.m. in Physics Research Building, room 245.

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Series archives

  • Winter 2020

    February 25

    Shiva Pokhrel and Brendon Waters, Department of Physics & Astronomy, Wayne State University

    Experimental and theoretical insights of percolation transition in nanoparticle composites

    Abstract: Percolation, one of the standard models for disordered system, is a random probabilistic process which shows a phase transition. In this work, we investigate a flexible model system based on half-metallic spherocylindrical CrO2 nanoparticles, which can be gradually converted by annealing from metallic (CrO2) to insulating (Cr2O3) state. The composite samples with varying volume fraction were prepared by mixing Cr2O3 with CrO2. The percolation threshold and the power law scaling exponent near the threshold were identified experimentally by studying the changes in the electrical resistance of the pellets with different volume fractions. To more thoroughly investigate the microscopic origins of the observed trends in the bulk properties of the nanocomposite, a series of hard-particle simulations were conducted using the combination of Monte Carlo and mechanical contraction methods that can produce dense random packing of non-overlapped spherocylindrical particles. Using a scaling method to extrapolate to the infinite system-size limit, we determined several properties of critical behavior of the system and found them to be in good agreement with experimental results.


    February 11

    Arthur Bowman, Department of Physics & Astronomy, Wayne State University

    High Mobility n-type PdSe2 Field Effect Transistors Enabled by Contact Engineering

    Abstract: Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDs) have emerged as a promising candidate for post-silicon electronics. One such material of interest is palladium diselenide (PdSe2) because of its high electron mobility and excellent chemical stability. However, in spite of its relatively small bandgap, the performance of few-layer PdSe2 field-effect transistors (FETs) has been largely limited by the presence of a substantial Schottky barrier, which is likely due to Fermi-level pinning. In this work, we report the fabrication of high mobility n-type PdSe2 FETs, using a new method to significantly reduce the barrier height at the semiconductor/metal interface. As a result, we observed an order of magnitude reduction of contact resistance in comparison with conventional metal contacts. The effective mobility also improved from 133 cm^2 V^-1 s^-1 to ~ 256 cm^2 V^-1 s^-1 at room temperature, and from 260 cm^2 V^-1 s^-1 to ~ 670 cm^2 V^-1 s^-1 at 77 K. We believe the significantly improved device performance enabled by this novel contact engineering technique will enable further studies of the intrinsic properties of PdSe2 and other exciting new 2D material.


    January 28

    Professor Tao Huang, Department of Mathematics, Wayne State University

    Analysis of Ericksen-Leslie system modeling hydrodynamic flow of nematic liquid crystals

    Abstract: The Ericksen-Leslie model is a classic theory on modeling and analysis of the hydrodynamic flow of liquid crystals. In mathematical analysis, it is interesting to study the existence, uniqueness and partial regularity of global weak solutions, and the existence of singularities (defects) at finite time. In this talk, we will review our recent works related to these topics, especially for several simplified models.


    January 21

    Professor Robert Hovden, Department of Materials Science & Engineering, University of Michigan

    Probing atomic structure across higher dimensions in 2D materials using sub-Angstrom electron beams

    Abstract: Modern materials are designed atomic layer by atomic layer with architectural complexity extending into the third dimension. For charge ordered materials, dramatic electronic changes are associated with periodic lattice distortions that require higher dimensions to describe the crystal. Here I discuss how scanning / transmission electron microscopy can probe atomic structure across sub-Angstrom to micron length scales in both two, three, and higher dimensions for the hierarchical engineering and design of 2D materials.

    In 2D-materials—such as graphene, MoS2, and TaS2—reduced dimensionality leads to unique properties that could transform future of electronic devices. Local atomic structure of 2D materials dictates local topology which greatly influences electronic properties and implementation in actual devices. Using a modern electron microscope we can count the atoms across grain boundaries, identify stacking structure, and locate individual defects and dopants. Concurrently, diffraction techniques provide an understanding of structure across billions of atoms at larger length scales. In combination, we obtain a complete description of the structure of 2D materials and correlate them with macroscopic properties.

    For quantum materials with charge ordering, the crystal is described in higher dimensions by the addition a periodic lattice distortions (PLD). We show the persistence and restructuring of PLDs down to the ultrathin limit and across a metal-insulator phase transition using cryogenic scanning transmission electron microscopy. Using picometer precision, we unearth inhomogeneity in the charge order at room temperature, and emergent phase coherence at 93 K. Such local phase variations govern the long-range correlations of the charge-ordered state and locally change the periodicity of the modulations, resulting in wave vector shifts in reciprocal space. These atomically resolved observations underscore the importance of lattice coupling and phase inhomogeneity, and provide a microscopic explanation for putative "incommensurate" order.

  • Fall 2019

    October 1

    Kraig Andrews, Department of Physics, Wayne State University

    Improved Contacts and Device Performance in MoS2 Transistors using MoSe2 as an Interlayer

    Abstract: We report a new contact engineering method to minimize the Schottky barrier height (SBH) of MoS2 field-effect transistors (FETs) by using MoSe2 as an interlayer. We demonstrate that the addition of an ultrathin MoSe2 interlayer between the MoS2 channel and Ti electrodes reduces the SBH at the contacts by a factor of 4 from ~ 100 meV to ~ 25 meV, contact resistivity by about 60 times from ~6×10−5Ω 𝑐𝑚2 to ~1×10−6Ω 𝑐𝑚2, and current transfer length by a factor of 6 from ~ 425 nm to ~ 70 nm. The drastic reduction of SBH can be attributed to the synergy of Fermi level pinning close to the conduction band edge of the MoSe2 interlayer and the conduction band offset between the MoSe2 interlayer and MoS2 channel. As a result, the two-terminal effective mobility also improves from ~ 30-40 cm2V-1s-1 to 50-60 cm2V-1s-1 at room temperature.

  • Winter 2019

    April 16

    Dr. Arunima K. Singh, Assistant Professor, Arizona State University

    Computational Study of Nanoscale Surfaces and Interfaces

    Abstract: Surfaces and interfaces are at the heart of modern-day technology, playing a central role in a variety of fields including sensing, energy conversion, and nano-electronics. Recent advancements in ab-initio methods, materials informatics, and computing power present us with an exciting opportunity to predictively discover and design materials surfaces and interfaces. In this talk, through the example of two-dimensional materials, I will show how ab-initio simulations, combined with multi-scale modeling techniques and genetic algorithms can be used to computationally discover, synthesize, and functionalize nanostructured surfaces. I will show how such studies can be performed in a high throughput fashion to create databases of surfaces and their properties; drastically reducing the time needed to invent new materials for surface sensitive applications. In this light, I will show how we have identified scores of robust and synthesizable materials’ surfaces for photocatalysis.


    April 9

    Dr. Venkat Ganesan, Professor of Chemical Engineering, University of Texas at Austin

    In Pursuit of Mechanically Strong, Conducting Polymer Electrolytes

    Abstract: The design of polymer electrolytes often revolve around the goal of achieving simultaneously enhanced conductivities and mechanical strengths in the same material. Indeed, electrolytes possessing high conductivities but low mechanical strengths, exhibit undesirable features such as dendrite formation of the metallic lithium anode which leads to short circuit of the electrodes. Unfortunately however, factors that enhance the mechanical strength of a material often leads to a deterioration of the conductivity and vice versa. Hence, there is an outstanding interest in strategies which can simultaneous enhance both the conductivity and mechanical strength of the electrolyte material. In this talk, I will discuss some results emerging out of our research in using computational techniques to study three strategies which have been examined in this regard: (i) Addition of ceramic nanoparticles to the polymer electrolytes; (ii) Creating block copolymer versions of the polymeric electrolyte; (iii) Use of ionic liquids (either directly or in polymerized form) in the polymer electrolyte. In each case, a short overview of the new insights which emerged from computer simulations will be discussed.


    March 26

    Suzan Arslanturk, Computer Science, Wayne State University

    Machine Learning Applications in Medicine and Biology

    Abstract: Clinical datasets present unique opportunities for existing and emerging descriptive and predictive analytics methods and models. In this talk, I will first describe a novel data integration methodology to identify subtypes of cancer using multiple data types (mRNA, methylation, microRNA, copy number variation, somatic variants) that come from different platforms (microarray, sequencing, etc.). Next, I will focus on a machine learning methodology to better understand the human skeletal muscle cell atlas. In particular, developing long short-term memory (LSTM) units of a recurrent neural network (RNN) to be able to predict the time-dependent changes in the morphology of the skeletal muscle cells using Differential Expansion Microscopy (DiExM) and Expansion Microscopy (EM) images. Next, I will discuss motivations for the ongoing work in discovering resting state EEG networks in neonates.

  • Fall 2018

    September 11, 2018

    Namita Shokeen (WSU)

    Differential Dynamic Microscopy in soft matter research


    Kraig Andrews (WSU)

    Achieving Low-Resistance Ohmic Contacts to MoS2 and PdSe2 using Ultrathin Transition Metal Dichalcogenides as a Contact Interlayer


    September 18, 2018

    Xinxin Woodward (WSU)

    Study of lipid sorting and dynamics at curvature sites


    Yuwen Mei (WSU)

    Study of Mechanobiology of Pancreatic Cancer Cells (PANC-1) by Traction Force Microscopy


    September 25, 2018

    Maxim Tsoi (University of Texas at Austin)

    Voltage Controlled Antiferromagnetics for Spintronic Applications


    October 9, 2018

    Fengyuan Yang (Ohio State University)

    FMR-Drive Pure Spin Transport in Metals and Magnetic Insulators


    October 23, 2018

    Tyler L. Cocker (Michigan State University)

    Ultrafast Terahertz Microscopy: From Near Fields to Single Atoms


    November 27, 2018

    Joan Greve

    Precision Preclinical Imaging: Basic Science, Therapeutic Development, and Translation

    Abstract: Biomedical engineers are used to working at the interface of multiple disciplines and acting as interpreters in order to enable rapid and impactful collaborative science across a broad spectrum of disciplines. Due to the characteristics embodied by imaging: fundamentals based in the physical sciences and engineering, the capability to be applied to a plethora of (patho) physiologies, and clinical application, imaging naturally attracts biomedical engineers.

    Following a brief overview of several imaging modalities, the focus of this talk will be on preclinical magnetic resonance imaging (MRI), in particular, and how it can be used to further research in basic science, therapeutic development, and translation to the clinic. Examples discussed will primarily include the cardiovascular system. Complementary expertise that is requisite for the most successful imaging endeavors will also be highlighted (e.g. in silico methods, small animal models of the human condition, and rigorous pre- and post- statistical analysis). Emphasis will be placed on how highly-optimized preclinical imaging and thoughtful experimental design can result in unique and important conclusions that might only be gleaned by using such technology.

  • Winter 2018
  • Fall 2017 and prior

    View archive of fall 2017 and prior.