Archival Journals Publications

I. Kholmanov, Kim, J., Ou, E., Ruoff, R. S., and Shi, L., “Continuous Carbon Nanotube–Ultrathin Graphite Hybrid Foams for Increased Thermal Conductivity and Suppressed Subcooling in Composite Phase Change Materials,” ACS Nano, vol. 9, pp. 11699-11707, 2015. Publisher's Version
X. Chen, Zhou, J., Goodenough, J. B., and Shi, L., “Enhanced thermoelectric power factor of Re-substituted higher manganese silicides with small islands of MnSi secondary phase,” J. Mater. Chem. C, vol. 3, pp. 10500-10508, 2015. Publisher's VersionAbstract
Higher manganese silicides (HMS) are promising thermoelectric materials owing to the abundance of the constituent elements in the earth crust, environmental friendliness and good chemical stability at high temperatures. However, the metallic MnSi layers with a lateral size as large as [similar]50 [small mu ]m are formed in the melt-grown HMS samples. These large MnSi layers are characterized with relatively high electrical and thermal conductivities and low Seebeck coefficient, which can degrade the thermoelectric performance of the melt-grown samples. Here, we report the synthesis and thermoelectric properties of Re-substituted HMS with relatively small-size MnSi platelets via melt-quenching, followed by ball-milling, and consolidated by spark plasma sintering. As compared to the samples prepared by either solid-state reaction or mechanical alloying, the reduced lateral size of MnSi in the quenched sample leads to an increased carrier concentration without a reduction in the carrier mobility according to our electrical transport measurements. As a result, the thermoelectric power factor is increased to 1.9 +/- 0.2 [times] 10-3 W m-1 K-2 at 860 K, which is about 20% higher than that of the sample prepared by solid-state reaction. In addition, the lattice thermal conductivity of the quenched sample remains nearly the same as the samples prepared by two other synthesis methods. Therefore, a figure-of-merit ZT of 0.64 +/- 0.08 at 823 K is obtained for the quenched sample, compared to 0.57 +/- 0.07 and 0.26 +/- 0.03 obtained from the two other samples prepared by different methods.
R. Agarwal, Jurney, P., Raythatha, M., Singh, V., Sreenivasan, S. V., Shi, L., and Roy, K., “Effect of Shape, Size, and Aspect Ratio on Nanoparticle Penetration and Distribution inside Solid Tissues Using 3D Spheroid Models,” Advanced Healthcare Materials, vol. 4, pp. 2269–2280, 2015. Publisher's Version
P. Jurney, Agarwal, R., Roy, K., Sreenivasan, S. V., and Shi, L., “Size-Dependent Nanoparticle Uptake by Endothelial Cells in a Capillary Flow System,” Journal of Nanotechnology in Engineering and Medicine, vol. 6, no. 1, pp. 011007, 2015. Publisher's Version
C. - C. Chen, Li, Z., Shi, L., and Cronin, S. B., “Thermoelectric transport across graphene/hexagonal boron nitride/graphene heterostructures,” Nano Research, vol. 8, pp. 666-672, 2015. Publisher's Version
A. Paul, Shi, L., and Bielawski, C. W., “A eutectic mixture of galactitol and mannitol as a phase change material for latent heat storage,” Energy Conversion and Management, vol. 103, pp. 139 - 146, 2015. Publisher's Version
L. Shi, Dames, C., Lukes, J. R., Reddy, P., Duda, J., Cahill, D. G., Lee, J., Marconnet, A., Goodson, K. E., Bahk, J. - H., Shakouri, A., Prasher, R. S., Felts, J., King, W. P., Han, B., and Bischof, J. C., “Evaluating Broader Impacts of Nanoscale Thermal Transport Research,” Nanoscale and Microscale Thermophysical Engineering, vol. 19, pp. 127-165, 2015. Publisher's Version
I. Jo, Pettes, M. T., Lindsay, L., Ou, E., Weathers, A., Moore, A. L., Yao, Z., and Shi, L., “Reexamination of basal plane thermal conductivity of suspended graphene samples measured by electro-thermal micro-bridge methods,” AIP Advances, vol. 5, pp. 053206, 2015. Publisher's Version
L. Zhang, Xiao, P., Shi, L., Henkelman, G., Goodenough, J. B., and Zhou, J., “Suppressing the bipolar contribution to the thermoelectric properties of Mg2Si0.4Sn0.6 by Ge substitution,” Journal of Applied Physics, vol. 117, pp. 155103, 2015. Publisher's Version
X. Chen, Shi, L., Zhou, J., and Goodenough, J. B., “Effects of ball milling on microstructures and thermoelectric properties of higher manganese silicides,” Journal of Alloys and Compounds, vol. 641, pp. 30 - 36, 2015. Publisher's VersionAbstract
Abstract Bulk nanostructured higher manganese silicide (HMS) samples with different grain size are prepared by melting, subsequent ball milling (BM), and followed by spark plasma sintering (SPS). The effects of \BM\ time on the microstructures and thermoelectric properties of these samples are investigated. It is found that \BM\ effectively reduces the grain size to about 90 nm in the sample after SPS, which leads to a decrease in both the thermal conductivity and electrical conductivity. By prolonging the \BM\ time, MnSi and tungsten/carbon-rich impurity phases are formed due to the impact-induced decomposition of \HMS\ and contamination from the tungsten carbide jar and balls during the BM, respectively. These impurities result in a reduced Seebeck coefficient and increased thermal conductivity above room temperature. The measured size-dependent lattice thermal conductivities agree qualitatively with the reported calculation results based on a combined phonon and diffuson model. The size effects are found to be increasingly significant as temperature decreases. Because of the formation of the impurity phases and a relatively large grain size, the ŻT\} values are not improved in the ball-milled \HMS\ samples. These findings suggest the need of alternative approaches for the synthesis of pure \HMS\ with further reduced grain size and controlled impurity doping in order to enhance the thermoelectric figure-of-merit of \HMS\ via nanostructuring.
X. Chen, Weathers, A., Carrete, J., Mukhopadhyay, S., Delaire, O., Stewart, D. A., Mingo, N., Girard, S. N., Ma, J., Abernathy, D. L., Yan, J., Sheshka, R., Sellan, D. P., Meng, F., Jin, S., Zhou, J., and Shi, L., “Twisting phonons in complex crystals with quasi-one-dimensional substructures,” Nat Commun, vol. 6, pp. 6723, 2015. Publisher's VersionAbstract
A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain the low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.
J. Kim, Ou, E., Sellan, D. P., and Shi, L., “A four-probe thermal transport measurement method for nanostructures,” Review of Scientific Instruments, vol. 86, pp. 044901, 2015. Publisher's Version
A. Weathers, Khan, Z. U., Brooke, R., Evans, D., Pettes, M. T., Andreasen, J. W., Crispin, X., and Shi, L., “Significant Electronic Thermal Transport in the Conducting Polymer Poly(3,4-ethylenedioxythiophene),” Advanced Materials, vol. 27, pp. 2101–2106, 2015. Publisher's Version
L. A. Jauregui, Pettes, M. T., Rokhinson, L. P., Shi, L., and Chen, Y. P., “

Gate Tunable Relativistic Mass and Berry's phase in Topological Insulator Nanoribbon Field Effect Devices

,” Sci. Rep., vol. 5, pp. 8452, 2015. Publisher's Version
K. S. Olsson, Klimovich, N., An, K., Sullivan, S., Weathers, A., Shi, L., and Li, X., “

Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

,” Applied Physics Letters, vol. 106, pp. 051906, 2015. Publisher's Version
E. Fleming, Wen, S., Shi, L., and da Silva, A. K., “Experimental and theoretical analysis of an aluminum foam enhanced phase change thermal storage unit,” International Journal of Heat and Mass Transfer, vol. 82, pp. 273 - 281, 2015. Publisher's Version
V. Singh, Agarwal, R., Jurney, P., Marshall, K., Roy, K., Shi, L., and Sreenivasan, S. V., “

Scalable Fabrication of Low Elastic Modulus Polymeric Nanocarriers With Controlled Shapes for Diagnostics and Drug Delivery

,” Journal of Micro and Nano-Manufacturing, vol. 3, pp. 011002, 2015. Website
S. N. Girard, Chen, X., Meng, F., Pokhrel, A., Zhou, J., Shi, L., and Jin, S., “Thermoelectric Properties of Undoped High Purity Higher Manganese Silicides Grown by Chemical Vapor Transport,” Chemistry of Materials, vol. 26, pp. 5097-5104, 2014. Publisher's Version
J. Buongiorno, Cahill, D. G., Hidrovo, C. H., Moghaddam, S., Schmidt, A. J., and Shi, L., “Micro- and Nanoscale Measurement Methods for Phase Change Heat Transfer on Planar and Structured Surfaces,” Nanoscale and Microscale Thermophysical Engineering, vol. 18, pp. 270-287, 2014. Publisher's VersionPDF icon phasechangemeasurements.pdf
H. Fateh, Baker, C. A., Hall, M. J., and Shi, L., “High fidelity finite difference model for exploring multi-parameter thermoelectric generator design space,” Applied Energy, vol. 129, pp. 373 - 383, 2014. Publisher's VersionAbstract
Abstract Thermoelectric generators (TEGs) are being studied and developed for applications in which waste heat, for example, from the exhaust of motor vehicles is converted into usable electricity. \{TEGs\} consisting of \{TE\} elements integrated with an exhaust heat exchanger require optimization to produce the maximum possible power output. Important optimization parameters include \{TE\} element leg length, fill fraction, leg area ratio between n- and p-type legs, and load resistance. A finite difference model was developed to study the interdependencies among these optimization parameters for thermoelectric elements integrated with an exhaust gas heat exchanger. The present study was carried out for \{TE\} devices made from n-type Mg2Si and p-type MnSi1.8 based silicides, which are promising \{TE\} materials for use at high temperatures associated with some exhaust heat recovery systems. The model uses specified convection boundary conditions instead of specified temperature boundary conditions to duplicate realistic operating conditions for a waste heat recovery system installed in the exhaust of a vehicle. The 1st generation, and an improved 2nd generation \{TEG\} module using Mg2Si and p-type MnSi1.8 based silicides were fabricated and tested to compare \{TE\} power generation with the numerical model. Important results include parameter values for maximum power output per unit area and the interdependencies among those parameters. Heat transfer through the void areas was neglected in the numerical model. When thermal contact resistance between the \{TE\} element and the heat exchangers is considered negligible, the numerical model predicts that any volume of \{TE\} material can produce the same power per unit area, given the parameters are accurately optimized. Incorporating the thermal contact resistance, the numerical model predicts that the peak power output is greater for longer \{TE\} elements with larger leg areas. The optimization results present strategies to improve the performance of \{TEG\} modules used for waste heat recovery systems.