@article{rost_borman_hossain_lim_quiambao-tomko_tomko_brenner_maria_hopkins_2020, title={Electron and phonon thermal conductivity in high entropy carbides with variable carbon content}, volume={196}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2020.06.005}, abstractNote={Due to their diverse bonding character and corresponding property repertoire, carbides are an important class of materials regularly used in modern technologies, including aerospace applications and extreme environments, catalysis, fuel cells, power electronics, and solar cells. The recent push for novel materials has increased interest in high entropy carbides (HECs) for such applications. The extreme level of tunability alone makes HECs a significant materials platform for a variety of fundamental studies and functional applications. We investigate the thermal conductivity of high entropy carbide thin films as carbon stoichiometry is varied. The thermal conductivity of the HEC decreases with an increase in carbon stoichiometry, while the respective phonon contribution scales with elastic modulus as the excess carbon content increases. Based on the carbon content, the HECs transition from an electrically conducting metal-like material with primarily metallic bonding to a primarily covalently-bonded crystal with thermal conductivities largely dominated by the phononic sub-system. When the carbon stoichiometry is increased above this critical transition threshold dictating bonding character, the electronic contribution to thermal conductivity is minimized, and a combination of changes in microstructure, defect concentration and secondary phase formation, and stiffness influence the phononic contribution to thermal conductivity. Our results demonstrate the ability to tune the thermal functionality of high entropy materials through stoichiometries that dictate the type of bonding environment.}, journal={ACTA MATERIALIA}, author={Rost, Christina M. and Borman, Trent and Hossain, Mohammad Delower and Lim, Mina and Quiambao-Tomko, Kathleen F. and Tomko, John A. and Brenner, Donald W. and Maria, Jon-Paul and Hopkins, Patrick E.}, year={2020}, month={Sep}, pages={231–239} }
 @article{radue_runnerstrom_kelley_rost_donovan_grimley_lebeau_maria_hopkins_2019, title={Charge confinement and thermal transport processes in modulation-doped epitaxial crystals lacking lattice interfaces}, volume={3}, ISSN={["2475-9953"]}, DOI={10.1103/PhysRevMaterials.3.032201}, abstractNote={Elizabeth Radue,1 Evan L. Runnerstrom,2,3 Kyle P. Kelley,2,3 Christina M. Rost,1 Brian F. Donovan,4 Everett D. Grimley,2 James M. LeBeau,2 Jon-Paul Maria,2,3 and Patrick E. Hopkins1,5,6,* 1Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904, USA 2Department of Materials Science, North Carolina State University, Raleigh, North Carolina 27695, USA 3Department of Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania 16801, USA 4Department of Physics, United States Naval Academy, Annapolis, Maryland 21402, USA 5Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, USA 6Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA}, number={3}, journal={PHYSICAL REVIEW MATERIALS}, author={Radue, Elizabeth and Runnerstrom, Evan L. and Kelley, Kyle P. and Rost, Christina M. and Donovan, Brian F. and Grimley, Everett D. and LeBeau, James M. and Maria, Jon-Paul and Hopkins, Patrick E.}, year={2019}, month={Mar} }
 @article{rost_rak_brenner_maria_2017, title={Local structure of the MgxNixCoxCuxZnxO(x=0.2) entropy-stabilized oxide: An EXAFS study}, volume={100}, ISSN={["1551-2916"]}, DOI={10.1111/jace.14756}, abstractNote={Entropy-stabilized oxides (ESOs) provide an alternative route to novel materials discovery and synthesis. It is, however, a challenge to demonstrate that the constituent elements in an entropy-stabilized crystal are homogeneously and randomly dispersed among a particular sublattice, resulting in a true solid solution with no evidence of local order or clustering. In this work, we present the application and analysis of extended X-ray absorption fine structure (EXAFS) on the prototype ESO composition MgxNixCoxCuxZnxO (x=0.2). In so doing, we can quantify the local atomic structure on an element-by-element basis. We conclude that local bond lengths between metal and oxygen vary around each absorbing cation, with notable distortion around the Cu–O polyhedra. By the second near neighbor (i.e., the cation-cation pair), interatomic distances are uniform to the extent that the collected data can resolve. Crystal models that best fit the experimental scattering data include cations that are distributed randomly on an FCC sublattice with minimal positional disorder, with an interleaved FCC anion sublattice with oxygen ions displaced from the ideal locations to accommodate the distortions in the cation polyhedra. Density functional theory calculations of the ESO system yield a significant broadening in the positional distribution for the oxygen sublattice compared to that for the cation sublattice for all peaks, showing consistency with the conclusion from the experimental data that the distortion from an ideal rock salt structure occurs primarily through disorder in the oxygen sublattice.}, number={6}, journal={JOURNAL OF THE AMERICAN CERAMIC SOCIETY}, author={Rost, Christina M. and Rak, Zsolt and Brenner, Donald W. and Maria, Jon-Paul}, year={2017}, month={Jun}, pages={2732–2738} }
 @article{faraji_yildiz_rost_stano_farahbakhsh_zhu_bradford_2017, title={Radial growth of multi-walled carbon nanotubes in aligned sheets through cyclic carbon deposition and graphitization}, volume={111}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2016.10.012}, abstractNote={Carbon coated aligned multi-walled carbon nanotube (AMWCNT/C) sheets were used for studying the controlled radial growth of MWCNTs. Pyrolytic carbon (PyC) was deposited on the surface of nanotubes using multiple cycles of chemical vapor infiltration. Morphological and structural characterization showed that when graphitization was done in one step, after the deposition of multiple cycles of PyC, the presence of a large amount of disordered carbon on the surface of nanotubes led to a poorly graphitized coating structure that did not resembled nanotube walls anymore. Graphitization of the AMWCNT/C sheets after each deposition cycle prevented the development of disordered carbon during the subsequent PyC deposition cycles. Using the cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. TEM observation and X-ray data confirmed radial growth of nanotubes, while spectra collected from Raman spectroscopy revealed that radially grown CNTs had the same quality as graphitized pristine nanotubes. The focus of this study was to compare the effect of cyclic graphitization with a one-step graphitization method to gain insight on the necessary parameters needed to radially grow high quality CNTs.}, journal={CARBON}, author={Faraji, Shaghayegh and Yildiz, Ozkan and Rost, Christina and Stano, Kelly and Farahbakhsh, Nasim and Zhu, Yuntian and Bradford, Philip D.}, year={2017}, month={Jan}, pages={411–418} }
 @article{rak_rost_lim_sarker_toher_curtarolo_maria_brenner_2016, title={Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations}, volume={120}, number={9}, journal={Journal of Applied Physics}, author={Rak, Z. and Rost, C. M. and Lim, M. and Sarker, P. and Toher, C. and Curtarolo, S. and Maria, J. P. and Brenner, D. W.}, year={2016} }
 @article{beechem_mcdonald_fuller_talin_rost_maria_gaskins_hopkins_allerman_2016, title={Size dictated thermal conductivity of GaN}, volume={120}, DOI={10.1063/1.4962010}, abstractNote={The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3–4 μm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (1015–1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends—and their overall reduction relative to bulk—are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to the increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.}, number={9}, journal={Journal of Applied Physics}, author={Beechem, T. E. and McDonald, A. E. and Fuller, E. J. and Talin, A. A. and Rost, C. M. and Maria, J. P. and Gaskins, J. T. and Hopkins, P. E. and Allerman, A. A.}, year={2016} }
 @article{rost_sachet_borman_moballegh_dickey_hou_jones_curtarolo_maria_2015, title={Entropy-stabilized oxides}, volume={6}, journal={Nature Communications}, author={Rost, C. M. and Sachet, E. and Borman, T. and Moballegh, A. and Dickey, E. C. and Hou, D. and Jones, J. L. and Curtarolo, S. and Maria, J. P.}, year={2015} }
 @article{faraji_stano_rost_maria_zhu_bradford_2014, title={Structural annealing of carbon coated aligned multi-walled carbon nanotube sheets}, volume={79}, ISSN={0008-6223}, url={http://dx.doi.org/10.1016/J.CARBON.2014.07.049}, DOI={10.1016/j.carbon.2014.07.049}, abstractNote={Sheets of aligned multi-walled carbon nanotubes (AMWCNTs) were used to study the structural annealing of pyrolytic carbon (PyC) coatings with various thicknesses on MWCNTs. PyC was deposited using chemical vapor infiltration and the thickness was controlled via the infiltration time. Structural annealing of the PyC coated AMWCNT (AMWCNT/C) sheets at 2150 °C provided different results for different thickness coatings. Transmission electron microscopy images showed that the carbon deposited from acetylene formed laminar PyC coatings, resembling rough tube walls, on the CNT surfaces. Following the high temperature heat treatment, coatings from short PyC deposition times changed their structure, resulting in radial growth of the MWCNTs. Raman and X-ray diffraction measurements also revealed that the radially grown MWCNTs had graphitic quality very close to pristine nanotubes after annealing. Electrical conductivity of AMWCNT/C sheets after high temperature heat treatment was twice that of pristine AMWCNT sheets. The focus of this study was to determine the PyC coating thickness at which a rough PyC coating would no longer change its structure into new CNT walls. The samples treated longer than 30 min had much more disordered PyC deposited on the surface and the additional material did not form additional tube walls after thermal annealing.}, journal={Carbon}, publisher={Elsevier BV}, author={Faraji, Shaghayegh and Stano, Kelly and Rost, Christina and Maria, Jon-Paul and Zhu, Yuntian and Bradford, Philip D.}, year={2014}, month={Nov}, pages={113–122} }