Articles by Courtney Keiser in JoVE
High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings Timothy M. Benseman1,2,3, Yang Hao1,2, Vitalii K. Vlasko-Vlasov1, Ulrich Welp1, Alexei E. Koshelev1, Wai-Kwong Kwok1, Ralu Divan4, Courtney Keiser5, Chiharu Watanabe6, Kazuo Kadowaki6 1Materials Science Division, Argonne National Laboratory, 2Department of Physics, University of Illinois at Chicago, 3Department of Physics, CUNY Queens College, 4Center for Nanoscale Materials, Argonne National Laboratory, 5Department of Physics, University of Northern Iowa, 6Institute for Materials Science, University of Tsukuba Europium thenoyltrifluoroacetonate (EuTFC) has an optical luminescence line at 612 nm, whose activation efficiency decreases strongly with temperature. If a sample coated with a thin film of this material is micro-imaged, the 612 nm luminescent response intensity may be converted into a direct map of sample surface temperature.
Other articles by Courtney Keiser on PubMed
Observation of Low Energy Raman Modes in Twisted Bilayer Graphene Nano Letters. Aug, 2013 | Pubmed ID: 23859121 Two new Raman modes below 100 cm(-1) are observed in twisted bilayer graphene grown by chemical vapor deposition. The two modes are observed in a small range of twisting angle at which the intensity of the G Raman peak is strongly enhanced, indicating that these low energy modes and the G Raman mode share the same resonance enhancement mechanism, as a function of twisting angle. The ~94 cm(-1) mode (measured with a 532 nm laser excitation) is assigned to the fundamental layer breathing vibration (ZO' mode) mediated by the twisted bilayer graphene lattice, which lacks long-range translational symmetry. The dependence of this mode's frequency and line width on the rotational angle can be explained by the double resonance Raman process that is different from the previously identified Raman processes activated by twisted bilayer graphene superlattice. The dependence also reveals the strong impact of electronic-band overlaps of the two graphene layers. Another new mode at ~52 cm(-1), not observed previously in the bilayer graphene system, is tentatively attributed to a torsion mode in which the bottom and top graphene layers rotate out-of-phase in the plane.
Temperature-activated Layer-breathing Vibrations in Few-layer Graphene Nano Letters. Aug, 2014 | Pubmed ID: 25019216 We investigated the low-frequency Raman spectra of freestanding few-layer graphene (FLG) at varying temperatures (400-900 K) controlled by laser heating. At high temperature, we observed the fundamental Raman mode for the lowest-frequency branch of rigid-plane layer-breathing mode (LBM) vibration. The mode frequency redshifts dramatically from 81 cm(-1) for bilayer to 23 cm(-1) for 8-layer. The thickness dependence is well described by a simple model of coupled oscillators. Notably, the LBM Raman response is unobservable at room temperature, and it is turned on at higher temperature (>600 K) with a steep increase of Raman intensity. The observation suggests that the LBM vibration is strongly suppressed by molecules adsorbed on the graphene surface but is activated as desorption occurs at high temperature.