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Winkler defends doctoral thesis

Posted in News on March 14th, 2014 by admin – Comments Off

Winkler Defense

Christopher Winkler has successfully defended his doctoral thesis on the “Characterization of the Dynamic Behavior of Bismuth Ferrite Thin Films Under DC Bias Using In Situ Transmission Electron Microscopy.” Chris has accepted a senior research scientist position at Virginia Tech.

For more information, see the ICTAS Nanoscale Characterization and Fabrication Laboratory website.

Barr, Vetterick, Taheri, and colleagues publish in Acta Materialia

Posted in News on January 27th, 2014 by admin – Comments Off

Christopher Barr, Greg Vetterick, Dr. Taheri, and colleagues’ latest paper, titled “Anisotropic radiation-induced segregation in 316L austenitic stainless steel with grain boundary character” has been published online in the Acta Materialia.

From the abstract: “Radiation-induced segregation (RIS) and subsequent depletion of chromium along grain boundaries has been shown to be an important factor in irradiation-assisted stress corrosion cracking in austenitic face-centered cubic (fcc)-based alloys used for nuclear energy systems. A full understanding of RIS requires examination of the effect of the grain boundary character on the segregation process. Understanding how specific grain boundary structures respond under irradiation would assist in developing or designing alloys that are more efficient at removing point defects, or reducing the overall rate of deleterious Cr segregation. This study shows that solute segregation is dependent not only on grain boundary misorientation, but also on the grain boundary plane, as highlighted by markedly different segregation behavior for the Σ3 incoherent and coherent grain boundaries. . .”

The accepted proof of the paper can be accessed here.

More information is available on the Springer website.

Scotto D’Antuono, Taheri, and colleagues publish in Scripta Materialia

Posted in News on January 13th, 2014 by admin – Comments Off

Daniel Scotto D’Antuono, Dr. Taheri, and colleagues’ latest paper, titled “Grain Boundary Misorientation Dependence of β Phase Precipitation in an Al-Mg Alloy” has been published online in the Scripta Materialia.

From the abstract: “Precipitation of β phase (Al3Mg2) in an Al-Mg alloy is investigated by in situ heating and precession diffraction-based orientation imaging in a transmission electron microscope. Initial β formation occurs more readily at low angle grain boundaries rather than at high angle boundaries, however larger precipitates are found at high angle boundaries. We propose a mechanism for β formation based on boundary energy and grain boundary free volume. These results advance the understanding of Β phase formation, aiding future corrosion prevention.”

The accepted proof of the paper can be accessed here.

More information is available on the Elsevier website.

Spurgeon, Sloppy, Taheri and colleagues publish in ACS Nano

Posted in News on December 8th, 2013 by admin – Comments Off

Steven Spurgeon, Dr. Jennifer Sloppy, Dr. Taheri, and colleagues’ latest paper, titled “Thickness-Dependent Crossover from Charge- to Strain-Mediated Magnetoelectric Coupling in Ferromagnetic / Piezoelectric Oxide Heterostructures” has been published online in the ACS Nano.

From the abstract: “Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La0.7Sr0.3MnO3 / PbZr0.2Ti0.8O3 system using spatially-resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-eg orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications.”

The uncorrected proof of the paper can be accessed on the ACS website: ACS Nano.

Barr and Spurgeon win MRS awards

Posted in News on December 7th, 2013 by admin – Comments Off

Christopher Barr and Steven Spurgeon recently won awards for their research at the 2013 Fall MRS Meeting in Boston.

Barr’s poster, titled “Anisotropic Behavior of Radiation Induced Segregation with Grain Boundary Character and Grain Size in Model Fcc Ni-Cr Alloys,” was selected for a silver poster award in Symposium ZZ — Nanostructured Materials in Extreme Environments. The award consists of a certificate and a $100 honorarium.

Spurgeon was invited to present a talk, titled “Thickness-Dependent Crossover from Charge- to Strain-Mediated Magnetoelectric Coupling in Ferromagnetic/Piezoelectric Oxide Heterostructures,” and was awarded a gold graduate student research award. This prestigious award is given to only eight of 240 applicants and consists of a plaque and $400 honorarium.

For more information about the award, visit MRS Fall 2013 Meeting Awards.

Ghassemi, Lang, Taheri, and colleagues publish in Journal of Applied Physics

Posted in News on August 13th, 2013 by admin – Comments Off

Dr. Ghassemi, Andrew Lang, Dr. Taheri, and colleagues’ latest paper, titled “Evolution of strain in aluminum gallium nitride/gallium nitride high electron mobility transistors under on-state bias” has been published online in the Journal of Applied Physics.

From the abstract: “On-state degradation of AlGaN/GaN high electron mobility transistors (HEMTs) was quantified as a function of defect generation and strain evolution using high-resolution transmission electron microscopy. Observation of devices under on-state stress conditions elucidated defect formation mechanisms, which is known to be caused by hot electrons. Geometric phase analysis indicated a 25% decrease of the in-plane tensile strain in the AlGaN barrier after extended bias. Changes in sheet polarization charge density were estimated based on observations of the defect formation and resulting strain relaxation. We propose three regimes of degradation during HEMT device operation, and suggest the presence of a critical point at which defects become stable or permanent.”

The paper can be viewed directly here.

The paper can also be accessed on the AIP website: AIP Publishing.

Spurgeon receives M&M 2013 travel award and second place poster prize

Posted in News on August 13th, 2013 by admin – Comments Off

Steven Spurgeon MM Poster

Steven Spurgeon was recently awarded a $1,000 travel grant to attend the 2013 Microscopy and Microanalysis Conference in Indianapolis, Indiana.

There he presented a poster, titled “Evidence for a thickness-dependent crossover from charge- to strain-mediated magnetoelectric coupling in La0.7Sr0.3MnO3 / PbZr0.2Ti0.8O3 thin film oxide heterostructures.” Steven was awarded second place in the physical science division for his submission.

For more details, see the Microscopy Society of America.

Photo courtesy of the Microscopy Society of America.

Spurgeon publishes highlight on strain control of BiFeO3 magnetic ordering in MRS Bulletin

Posted in News on July 16th, 2013 by admin – Comments Off

Steven Spurgeon has published a research highlight in the Materials Research Society Bulletin‘s August 2013 issue discussing strain control of magnetic ordering in BiFeO3.

From the article: “Researchers in pursuit of higher density memories have set their sights on a new generation of spintronic materials, in which both electron charge and spin are used to convey information. The magnetoelectric multiferroic BiFeO3 (BFO), which exhibits direct coupling between ferroelectric and antiferromagnetic order, is particularly interesting for such an application. However, the complex interplay of strain and magnetic response in this system is only poorly understood. Now, Daniel Sando and colleagues at the Unité Mixte de Physique CNRS / Thales shed light on the fundamental mechanisms governing antiferromagnetism and demonstrate tunable control of this ordering for spintronics devices.. . . .”

The article can be viewed directly here or on the Materials Research Society Bulletin website.

Ghassemi, Taheri, and colleagues publish in Journal of Applied Physics

Posted in News on July 10th, 2013 by admin – Comments Off

Drs. Ghassemi, Taheri, and colleagues’ latest paper, titled “Stoichiometry of LaAlO3 films grown on SrTiO3 by pulsed laser deposition” has been published online in the Journal of Applied Physics.

From the abstract: “We have studied the stoichiometry of epitaxial LaAlO3 thin films on SrTiO3 substrate grown by pulsed laser deposition as a function of laser energy density and oxygen pressure during the film growth. Both x-ray diffraction (θ-2θ scan and reciprocal space mapping) and transmission electron microscopy (geometric phase analysis) revealed a change of lattice constant in the film with the distance from the substrate. . . .”

The paper can be viewed directly here.

The paper can also be accessed on the Springer website: AIP Publishing.

DCG hosts summer research interns

Posted in News on May 15th, 2013 by admin – Comments Off

The DCG will be hosting several research interns this summer. These students will design and complete a hands-on laboratory research project, under the guidance of graduate students in the group.

The interns include:

  • Kate Dillione from Brown University
  • Daniel Foley from the University of Maryland–College Park
  • Joseph Ludy from Rutgers University
  • Adam Falcone from Drexel University