VCU Department of Physics Colloquia: Spring 2018

Nano PhD Student Literature Review

Investigation of Safe, Rechargeable All Solid State Li-ion Batteries

Sweta Prabha

Department of Physics, Virginia Commonwealth University

Friday, April 27 at 4:00 pm in 701 W. Grace St., Room 2310

The lithium-ion battery was discovered in 1981 by Prof. Goodenough and it has found widespread use due to its rechargeability, high energy density and high power density. One of the greatest drawback of Li-ion batteries is its safety as there has been incidents of its failure due to the presence of flammable liquid electrolyte. Various attempts has been made to replace the flammable electrolyte by a solid state electrolyte, one of which was presented by Dr. M.H. Braga in the form of a glass electrolyte. Braga’s group along with Dr. Goodenough published an article1 in 2017 that claimed to develop a new strategy for an all solid state rechargeable Li-ion battery that yielded high energy density and an increase in number of charging-discharging cycles. The article attracted a lot of attention from researchers in the battery world as the published energy density was larger than is theoretically possible, and the explanation for this high energy density was not fully supported by all the available evidence. The battery used a Li anode, a Sulfur cathode and a glass electrolyte. The voltage was said to be generated by stripping and plating of lithium metal on the cathode. Sulfur was said to act as a redox center and not take part in the reaction, although it determined the voltage of the battery. The explanation violates the basic laws of thermodynamics2 for a closed system as it argues that work was done by the battery, while there is no net change in the Gibbs free energy of the reactants. Insufficient evidence about the microscopic characterization of the cathode has been provided, making it difficult to assess alternative mechanisms of the battery. Additional research is needed to better understand the origin of the high energy density, and high recyclability of the battery. A critical literature review has been done on this work to better understand the properties and results of the high energy storage device. 

References:

1. Braga. et al. Energy. Environ. Sci. 2017, 10, 331.

2. Steingart. et al. Energy. Environ. Sci. 2018, 11, 221.

Multi-modal Optical Imaging Technology, Application, and Translation

Dr. Yu Chen

Fischell Department of Bioengineering, University of Maryland, College Park

Friday, April 13 at 4:00 pm in 701 W. Grace St., Room 2310

Optical Coherence Tomography (OCT) is an established medical imaging technology which is analogous to ultrasound imaging but has significantly higher resolution (~10 mm) to enable 3D imaging of tissue microstructures in situ and in real-time with a penetration depth of ~1-2 mm. OCT can be extended to functional imaging modalities such as Doppler OCT (DOCT) for blood flow detection and polarization-sensitive OCT (PS-OCT) for detection of tissue birefringence. We have developed a forwarding-imaging needle-type OCT probe for avoiding the hemorrhage and guiding neurosurgical interventions. The needle probe has a thin diameter of 0.7 mm. The feasibility of vessel detection and neurosurgical guidance were demonstrated on sheep brain in vivo and human brain ex vivo. In addition, we further reduced the probe size to 0.3 mm using an optical Doppler sensing (ODS) fiber probe that can integrate with microelectrode recording (MER) to detect the blood vessels lying ahead to improve the safety of this procedure. We further combine high-resolution OCT with large-field-of-view magnetic resonance imaging (MRI) to provide multi-scale imaging.

In addition, we have developed a novel mesoscopic 3D optical molecular imaging technique – Fluorescence Laminar Optical Tomography (FLOT), which can achieve ~100 µm resolution and 2-3 mm penetration depth. Biomedical applications of FLOT include tissue engineering, neuroscience, and oncology. For functional mapping of brain activities, we applied FLOT to record 3D neural activities evoked in the whisker system of mice by deflection of a single whisker in vivo.  We utilized FLOT to investigate the cell viability, migration, and bone mineralization within bone tissue engineering scaffolds in situ, which allows depth-resolved molecular characterization of engineered tissues in 3D. Moreover, we investigated the feasibility of the OCT/FLOT multi-modal imaging system to monitor the drug distribution and therapeutic effects during and after photo-immunotherapy (PIT) in situ and in vivo, which can be used to optimize PIT regimen and elucidate PIT mechanism.

 

Nano PhD Student Literature Review

Electrical and Morphological Properties of Magnetocaloric Nano ZnNi Ferrite

Mr. Tyler Selden

Department of Physics, Virginia Commonwealth University

Friday, April 6 at 4:00 pm in 701 W. Grace St., Room 2310

The magnetocaloric effect (MCE) is a fundamental property of magnetic materials. The MCE describes the thermal behavior of a magnetic material when exposed to a changing magnetic field. The first application of MCE was suggested by Debye in 1926 and independently Giauque in 1927, adiabatic demagnetization, used to reach temperatures lower than liquid helium1. The MCE can be calculated directly using one of the Maxwell equations 2. Currently there is a great push to make MCE devices energy efficient for near room temperature refrigeration. In order to create rear room temperature refrigeration by MCE devices tailoring of the magnetic and thermal properties of materials is needed. Hemeda et al, were able to fabricate Zn1-xNixFe2O4 (with x=0, 0.2, 0.4, 0.6, 0.8 and 1) compositions by a combustion technique. The samples were characterized with XRD, TEM, and SEM. The XRD peaks corresponded to a single phase spinal cubic structure, which was also confirmed by the lattice spacing observed in the TEM images. Magnetic entropy change was calculated by measuring the magnetization of the sample against a varying temperature in a constant magnetic field. The maximum value of change was observed near the Curie temperature. All of these observations make these materials candidates for magnetocaloric applications3

 

References:

1. Handbook of Magnetism and Advanced Magnetic Materials, 5 Volume Set. (Wiley-Interscience, 2007).

2. Stanley, H. E. Introduction to Phase Transitions and Critical Phenomena. (Oxford University Press, 1971).

3. Hemeda, O. M. et al. Electrical and morphological properties of magnetocaloric nano ZnNi ferrite. J. Magn. Magn. Mater. 394, 96–104 (2015).

 

 

 

Superatomic Solids and Frameworks from Metal Chalcogenide Building Blocks

Dr. Christopher Bejger

Department of Chemistry, University of North Carolina at Charlotte

Friday, Mar. 30 at 4:00 pm in 701 W. Grace St., Room 2310

Synthetic metal-chalcogenide molecular clusters are aggregates of metal and chalcogen units stabilized by organic ligands. Such clusters are akin to nanoscale transition metals, or superatoms, due to their size, redox activity, and collective electronic properties. These features make superatoms useful precursors for the synthesis of new functional materials with tunable properties. This lecture will discuss two strategies for the preparation of solid-state materials comprising molecular cluster superatom building blocks. The hierarchical assembly of trinuclear nickel clusters and fullerenes using shape complementarity, as well as halogen and chalcogen bonding, will be highlighted. Additionally, the design of crystalline, redox active, framework solids from Co6Se8 and Co4S4 superatoms will be presented.

 

Ion Trap Reactors to the Rescue:  A Tool to Solve Problems in Organic and Organometallic Chemistry

Dr. Scott Gronert

Department of Chemistry, Virginia Commonwealth University

Friday, Mar. 23 at 4:00 pm in 701 W. Grace St., Room 2310

Ion trap mass spectrometers are versatile instruments that can be modified to act as reactors and be used to study bimolecular reactions in the gas phase.  Many catalytic organometallic systems are well suited to gas-phase studies because they are not particularly sensitive to solvent effects and therefore data from the gas phase is relevant to condensed-phase chemistry.   Moreover it is possible in the gas phase to isolate and probe the chemistry of highly reactive intermediates that have proven difficult to characterize in solution.  In this seminar, the focus will be on (1) the elucidation of an alternative mechanism for cyclopropanations with copper(I) carbenes, (2) the discovery of a novel Ir(III) complex capable of C-H activation processes, and (3) the development of a general method for producing and studying the C-X cleavage reactions of Fe(I), Co(I) and Ni(I) species. In each case, the experimental data are complemented with computational modeling to gain deep insights into the mechanisms and intermediates.  The work highlights the ability of ion trap reactors to provide targeted information that is relevant to the design and optimization of metal-centered catalysts.

 

Voltage Control of Nanoscale Magnetism: Application to Low Power Computing

Dr. Jayasimha Atulasimha

Department of Mechanical and Nuclear Engineering & Electrical and Computer Engineering, Virginia Commonwealth University

Friday, Mar. 16 at 4:00 pm in 701 W. Grace St., Room 2310

We have recently demonstrated strain and acoustic wave induced switching of magnetization in magnetostrictive Cobalt and Nickel nanomagnets [1-4] and magnetostrictive soft layer of a magnetic tunnel junction [5]. However, one common issue observed in all experiments involving magnetostrictive elements with lateral dimensions ~100-300 nm is the lack of reliability with which the magnetization is switched. This is possibly due to a combination of many factors: low magneto mechanical coupling in Cobalt and Nickel, thermal noise at room temperature and defects that pin the magnetization. This problem can potentially get worse when one scales to lateral dimensions less than 50 nm to compete with STT-RAM.

This talk will discuss the above experimental work with complementary modeling that accounts for defects and thermal noise and recent work on polarized neutron reflectometry to understand depth dependent magnetization rotation due to differential strain transfer [6] to access the potential extent to which such energy efficient strain switched nanomagnetic devices could scale to < 50nm lateral dimensions while being robust to switching error.

Furthermore, recent simulations show that direct voltage control of magnetic anisotropy (VCMA) in conjunction with magnetic magnetic skyrmion states [7-9] may offer a robust mechanism for switching nanomagnets. For example, inclusion of DMI can lead to an intermediate skyrmion state during the reversal of a perpendicular-MTJ from the ferromagnetic “up” to “down” state. Recent simulations (unpublished) that show that forcing such reversal through a specific (skyrmion) state could be more robust to both thermal noise and defects than precessional VCMA switching schemes will also be discussed.

 Acknowledgements:

The strain control of magnetism research was performed in J. Atulasimha’s group at VCU (N. D'Souza, M. Salehi Fashami, M. M. Al-Rashid) in collaboration with S. Bandyopadhyay group at VCU (A. Biswas, H. Ahmad) G. P. Carman group at UCLA (W. Y. Sun, P. Nordeen, A.C. Chavez), J. P. Wang group at U. of Minnesota (Z. Zhao, M. Jamali, D. Zhang) and B. Kirby and D. B. Gopman at NIST.

Simulations on VCMA switching of skyrmions/skyrmion mediated switching was performed in Atulasimha’s group (D. Bhattacharya, M. M. Al-Rashid).

Grants that supported work at VCU include:  NSF grants NEB2020: ECCS-1124714, CAREER: CCF-1253370, SHF: CCF-1216614, ECCS 1609303; SRC under NRI task 2203.001; VCU Quest Commercialization Grant and Virginia Microelectronics Seed Grant.

 REFERENCES:

[1] N. D'Souza, M. Salehi Fashami, S. Bandyopadhyay and J. Atulasimha, Nano Letters, 16, 1069, 2016.

[2] V. Sampath, N. D’Souza, D. Bhattacharya, G. M. Atkinson, S. Bandyopadhyay, and J. Atulasimha,  

      Nano Letters, 16, 5681, 2016.

[3] M. Salehi-Fashami, M. Al-Rashid, W.Y. Sun, P. Nordeen, S. Bandyopadhyay, A.C. Chavez, G.P. Carman, J. 

     Atulasimha, Nanotechnology (letter), 27, 43LT01, 2016.

[4] A. Biswas, H. Ahmad, J. Atulasimha, S. Bandyopadhyay, Nano Letters, 17 (6), 3478, 2017.

[5] Z. Zhao, M. Jamali, N. D'Souza, D. Zhang, S. Bandyopadhyay, J. Atulasimha, J. P. Wang, Appl. Phys. Lett., 109,  

     102403, 2016.

[6] M. M. Al-Rashid, B. Kirby, J. Atulasimha, unpublished.

[7] D. Bhattacharya, M. M. Al-Rashid, J. Atulasimha, Scientific Reports, 6, 31272, 2016.

[8] D. Bhattacharya, M. M. Al-Rashid, J. Atulasimha, Nanotechnology, 28, 425201 2017

[9] D. Bhattacharya, J. Atulasimha, arXiv: 1707.07777v1

Tailoring Carbon Nanostructures for Energy Storage Applications

Dr. Bingqing Wei

Department of Mechanical Engineering, University of Delaware

Friday, Mar. 2 at 4:00 pm in 701 W. Grace St., Room 2310

Sustainable and renewable energy sources from hydropower, solar, and wind power are expected to release the heavy burdens on the current energy infrastructure and the environmental concerns. As these renewable energy sources such as solar and wind power are intermittent, reliable electrochemical energy storage systems, mainly including rechargeable batteries and electrochemical capacitors, are purposely explored to promote efficient utilization of these energy sources and are a growing challenge. The development of high energy storage devices has been one of the most important research areas in recent years and relies mostly on the successful engineering of electrode materials. Carbon nanostructures such as carbon nanotubes (CNTs) and graphene have been full of surprises since their emergence and are intensively investigated for use as electrode materials in energy storage devices. Utilizing CNTs, graphene, and their composites for various energy storage applications such as Li-ion and L-S batteries, and supercapacitors are under scrutiny because of their improved electrochemical activity, cost-effectiveness, benign environmental nature, and promising electrochemical performance. In this presentation, I will discuss our research strategies and efforts to employ carbon nanostructures for different energy storage applications including flexible and even stretchable electricity storage devices.

Nanoporous materials for electrochemical analysis in complex biological solutions

Dr. Maryanne Collinson

Department of Chemistry, Virginia Commonwealth University

Friday, Feb. 23 at 4:00 pm in 701 W. Grace St., Room 2310

Electrochemical measurements are difficult to make in complex biologic solutions because as soon as the electrode is placed in solution, irreversible biofouling takes place.  Recently we developed a means to make electrochemical measurements in such solutions by using nanoporous gold and/or platinum electrodes.  These electrodes are composed of nanometer sized pores that serve as a sieve, screening out large biomolecules but allowing small redox molecules to interact with the pristine surface (Collinson et al Analytical Chemistry 2013).  Such electrodes are ideal tools to make electrochemical measurements in complex solutions including blood and plasma.  The focus of this talk will be on the fabrication and characterization of different types of nanoporous electrodes and their ability to successfully make redox measurements in solutions containing known biofouling agents.

 

Tomography of the Atomic Nucleus

Dr. Simonetta Liuti

Department of Physics, University of Virginia

Friday, Feb. 16 at 4:00 pm in 701 W. Grace St., Room 2310

The history of our exploration of subatomic matter has witnessed a major breakthrough with every new probe being introduced. In the 1950’s Hofstadter and collaborators using elastic electron scattering measured for the first time the electromagnetic form factors of nucleons and nuclei and provided the first information on the nuclear spatial charge and magnetization distributions. In the late 1960’s and early 70’s, Friedman, Kendall and Taylor using Deep Inelastic Scattering of electrons off the nucleon, discovered its underlying quark structure displayed in their longitudinal momentum distributions.

 I will discuss probes at the next frontier that will allow us to access dynamically correlated distributions in both momentum and coordinate space -- the Wigner distributions -- at the femtoscale. Deeply Virtual Compton Scattering, namely a high energy lepton scattering off a nucleon target producing a high energy real photon and a small angle recoil proton, is one of such probes. I will explain how a detailed mapping of the quarks and gluons in the nucleon and nucleus in phase space, or a phase-space tomography, besides providing for the first time images of quarks and gluons spatial distributions, is essential for understanding the so far elusive nucleon mass and spin decompositions in terms of its quark and gluon components. 

String Compactifications for Particle Physics

Dr. James Gray, 

Department of Physics, Virginia Tech

Friday, Feb. 9 at 4:00 pm in 701 W. Grace St., Room 2310

I will review the current status of solutions to string theory which attempt to make contact with phenomenological particle physics. I will start with a description of the goals of, and approaches utilized in, this subfield of string theory. I will then go on to highlight both what is currently well understood and what the biggest outstanding problems are in the field. 

DNA ‘nanomapping’ using CRISPR/Cas9 as a programmable nanoparticle

Dr. Jason Reed, 

Department of Physics, Virginia Commonwealth University

Friday, Feb. 2 at 4:00 pm in 701 W. Grace St., Room 2310

I will discuss two technical advances in DNA nanotechnology and single molecule genomics: (1) a novel labeling technique (CRISPR-Cas9 nanoparticles) that enables high speed-AFM (HS-AFM) to map specific sequences in DNA directly, and (2) using DVD optics to image DNA molecules with high-speed AFM.  This new ‘nanoparticle’ method employs a relatively simple one-step labeling chemistry, and is sensitive enough to detect small structural variants (<30bp) in single DNA molecules.  The HS-AFM/CRISPR technique can be complementary to both sequencing and other physical mapping approaches; it is well suited to detecting structural genomic variations, as well as to aiding de novo sequence assembly using NGS sequencing data.  It also has many potential translational applications, including detecting causal mutations in cancer. 

 

Structural and Optical Properties of the MoTe2-WTe2 Alloy System

Dr. Patrick Vora, George Mason University

Friday, Jan. 26 at 4:00 pm in 701 W. Grace St., Room 2310

The structural polymorphism intrinsic to select transition metal dichalcogenides provides exciting opportunities for engineering novel devices. Of special interest are memory technologies that rely upon controlled changes in crystal phase, collectively known as phase change memories (PCMs). MoTe2 is ideal for PCMs as the ground state energy difference between the hexagonal (2H, semiconducting) and monoclinic (1T’, metallic) phases is minimal. This energy difference can be made arbitrarily small by substituting W for Mo on the metal sublattice, thus improving PCM performance. Therefore, understanding the properties of Mo1-xWxTe2 alloys across the entire compositional range is vital for the technological application of these versatile materials.

We combine Raman spectroscopy with aberration-corrected scanning transmission electron microscopy and x-ray diffraction to explore the MoTe2-WTe2 alloy system. The results of these studies enable the construction of the complete alloy phase diagram, while polarization-resolved Raman measurements provide phonon mode and symmetry assignments for all compositions. Temperature-dependent Raman measurements indicate a transition from 1T’- MoTeto a distorted orthorhombic phase (Td) below 250 K and facilitate identification of the anharmonic contributions to the optical phonon modes in bulk MoTeand Mo1-xWxTe2 alloys. We also identify a Raman-forbidden MoTemode that is activated by compositional disorder and find that the main WTe2 Raman peak is asymmetric for x<1. This asymmetry is well-fit by the phonon confinement model and allows the determination of the phonon correlation length. Our work is foundational for future studies of Mo1-xWxTe2 alloys and provides new insights into the impact of disorder in transition metal dichalcogenides.

 

Fall 2017 Physics Department Colloquium