This month’s featured research was presented by Humaira Taz at the Materials Research Society (MRS) Fall 2016 Meeting held in Boston, MA in November 2016. Her oral presentation in symposium EM2:Rare-Earths in Advanced Photonics and Spintronics was one of the top three graduate student presentations, for which they were awarded graduate student prizes sponsored by Thorlabs and Elsevier. The talk was titled “Novel Room Temperature Ferromagnetic Semiconductor: amorphous Fe-Dy-Tb-Oxide”. This research is also published in Scientific Reports (doi: 10.1038/srep27869).
Our collaborator at University of Tennessee-Chattanooga, Dr. Tatiana Allen, and I also presented a poster at the same meeting. The poster focused on the changes in the conductivity, cation states, and magnetic properties of the Fe-Tb-Dy-Oxide as a result of annealing cycles. This poster was a finalist for the best poster award.
Humaira’s poster can be viewed here.
Humaira Taz, , Tamil Sakthivel, Nana K. Yamoah, Connor Carr, Dhananjay Kumar, Sudipta Seal & Ramki Kalyanaraman. “Ferromagnetism, optical transparency, and semiconducting behavior in Fe-Dy-Tb based amorphous oxide films”. Scientific Reports. 2017
“We report a class of amorphous thin film material comprising of transition (Fe) and Lanthanide metals (Dy and Tb) that show unique combination of functional properties. Films were deposited with different atomic weight ratio (R) of Fe to Lanthanide (Dy + Tb) using electron beam co-evaporation at room temperature. The films were found to be amorphous, with grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy studies indicating that the films were largely oxidized with a majority of the metal being in higher oxidation states. Films with R = 0.6 were semiconducting with visible light transmission due to a direct optical band-gap (2.49 eV), had low resistivity and sheet resistance (7.15 × 10−4 Ω-cm and ~200 Ω/sq respectively), and showed room temperature ferromagnetism. A metal to semiconductor transition with composition (for R < 11.9) also correlated well with the absence of any metallic Fe0 oxidation state in the R = 0.6 case as well as a significantly higher fraction of oxidized Dy. The combination of amorphous microstructure and room temperature electronic and magnetic properties could lead to the use of the material in multiple applications, including as a transparent conductor, active material in thin film transistors for display devices, and in spin-dependent electronics.”
This month’s featured research was presented by Marie Kirkegaard at the National Technical Nuclear Forensics Center (NTNFC) Annual Academic-Laboratory Collaboration Meeting at Los Alamos National Laboratory (LANL) in August of 2016.
The ability to identify and characterize nuclear material in the wild is critical for nuclear security. While spectroscopic signatures have been cataloged for many of these materials, there has been less work done to understand how these signatures may be affected by environmental conditions.Marie’s current work examines uranyl fluoride, an important intermediate in the nuclear fuel cycle, using computational and spectroscopic methods to determine how the chemical and physical properties of the material change with environmentally-relevant perturbations in temperature and relative humidity.
“Uranyl fluoride (UO2F2UO2F2) is a hygroscopic powder with two main structural phases: an anhydrous crystal and a partially hydrated crystal of the same R3¯mR3¯m symmetry. The formally closed-shell electron structure of anhydrous UO2F2UO2F2 is amenable to density functional theory calculations. We use density functional perturbation theory (DFPT) to calculate the vibrational frequencies of the anhydrous crystal structure and employ complementary inelastic neutron scattering and temperature-dependent Raman scattering to validate those frequencies. As a model closed-shell actinide, we investigated the effect of LDA, GGA, and non-local vdW functionals as well as the spherically averaged Hubbard +U correction on vibrational frequencies, electronic structure, and geometry of anhydrous UO2F2UO2F2. A particular choice of Ueff=5.5Ueff=5.5 eV yields the correct U–Oyl bond distance and vibrational frequencies for the characteristic Eg and A1g modes that are within the resolution of experiment. Inelastic neutron scattering and Raman scattering suggest a degree of water coupling to the lattice vibrations in the more experimentally accessible partially hydrated UO2F2UO2F2 system, with the symmetric stretching vibration shifted approximately 47 cm−1 lower in energy compared to the anhydrous structure. Evidence of water interaction with the uranyl ion is present from a two-peak decomposition of the uranyl stretching vibration in the Raman spectra and anion–hydrogen stretching vibrations in the inelastic neutron scattering spectra. A first-order dehydration phase transition temperature is definitively identified to be 125 °C using temperature-dependent Raman scattering.”
This month’s featured research was presented by Patrick Caveney at the 2016 Synthetic Biology: Engineering, Evolution & Design (SEED) conference.
Patrick M. Caveney, S. Elizabeth Norred, Charles W. Chin, Jonathan B. Boreyko, Brandon S. Razooky, Scott T. Retterer, C. Patrick Collier, Michael L. Simpson. “Resource sharing controls gene expression bursting.” ACS Synthetic Biology (2016).
“Genes express proteins in bursts of activity with periods of no activity between bursts. Burst dynamics are characterized by a burst size (duration of a burst) and burst frequency (number of bursts per time). During a burst the gene draws on a limited pool of reusable resource. Little is known about the relationship between burst dynamics and resource sharing. Here we made cell-sized reaction chambers (both PDMS plastic and POPC lipid vesicles) and observed bursting dynamics as the size of the resource pools was varied. When the size of the resource pool was increased, the number of protein made increased. This increase in protein was achieved by increasing the burst size not burst frequency. This may be due to the fact that the 100 different molecules needed to make protein became localized. Localized components suggest large transcriptional burst sizes are correlated with large translational burst sizes. This correlation is confirmed with in vivo E.coli data. Our results demonstrate the link between bursting dynamics and resource sharing.”
This month’s featured poster was presented by Riddhi Shah at the 5th International Symposium on Diffraction Structural Biology, where she was awarded 1st prize.
The poster is available to view in the Bredesen Center offices on the 4th floor of Greve Hall. .