JabRef references

Author	Title	Year	Journal/Proceedings	Reftype	DOI/URL
Burg, B.R., Tong, J.K., Hsu, W.-C. and Chen, G.	Decoupled cantilever arms for highly versatile and sensitive temperature and heat flux measurements [Abstract] [BibTeX]	2012	Rev. Sci. Instrum. Vol. 83, pp. 104902	article	URL
Abstract: Microfabricated cantilever beams have been used in microelectromechanical systems for a variety of sensor and actuator applications. Bimorph cantilevers accurately measure temperature change and heat flux with resolutions several orders of magnitude higher than those of conventional sensors such as thermocouples, semiconductor diodes, as well as resistance and infrared thermometers. The use of traditional cantilevers, however, entails a series of important measurement limitations, because their interactions with the sample and surroundings often create parasitic deflection forces and the typical metal layer degrades the thermal sensitivity of the cantilever. The paper introduces a design to address these issues by decoupling the sample and detector section of the cantilever, along with a thermomechanical model, the fabrication, system integration, and characterization. The custom-designed bi-arm cantilever is over one order of magnitude more sensitive than current commercial cantilevers due to the significantly reduced thermal conductance of the cantilever sample arm. The rigid and immobile sample section offers measurement versatility ranging from photothermal absorption, near-field thermal radiation down to contact, conduction, and material thermal characterization measurements in nearly identical configurations.
BibTeX: @article{Burg2012, author = {Brian R. Burg and Jonathan K. Tong and Wei-Chun Hsu and Gang Chen}, title = {Decoupled cantilever arms for highly versatile and sensitive temperature and heat flux measurements}, journal = {Rev. Sci. Instrum.}, year = {2012}, volume = {83}, pages = {104902}, url = {http://dx.doi.org/10.1063/1.4758093} }
Cahill, D.G., Braun, P.V., Chen, G., Clarke, D.R., Fan, S., Goodson, K.E., Keblinski, P., Mahan, G.D., Majumdar, A., Maris, H.J., Phillpot, S.R., Pop, E. and Shi, L.	Nanosacle thermal transport II: 2003--2012 [Abstract] [BibTeX]	2014	Appl. Phys. Rev.	article
Abstract: A diverse spectrum of technology drivers such as improved thermal barriers, higher efficiency thermoelectric energy conversion, phase-change memory, heat-assisted magnetic recording, thermal management of nanoscale electronics, and nanoparticles for thermal medical therapies are motivating studies of the applied physics of thermal transport at the nanoscale. This review emphasizes developments in experiment, theory, and computation in the past ten years and summarizes the present status of the field. Interfaces become increasingly important on small length scales. Research during the past decade has extended studies of interfaces between simple metals and inorganic crystals to interfaces with molecular materials and liquids with systematic control of interface chemistry and physics. At separations on the order of $sim 1$ nm, the science of radiative transport through nanoscale gaps overlaps with thermal conduction by the coupling of electronic and vibrational excitations across weakly-bonded or rough interfaces between materials. Major advances in the physics of phonons include first principles calculation of the phonon lifetimes of simple crystals and application of the predicted scattering rates in parameter-free calculations of the thermal conductivity. Progress in the control of thermal transport at the nanoscale is critical to continued advances in the density of information that can be stored in phase change memory devices and new generations of magnetic storage that will use highly localized heat sources to reduce the coercivity of magnetic media. Ultralow thermal conductivity---thermal conductivity below the conventionally predicted minimum thermal conductivity---has been observed in nanolaminates and disordered crystals with strong anisotropy. Advances in metrology by time-domain thermoreflectance (TDTR) have made measurements of the thermal conductivity of a thin layer with micron-scale spatial resolution relatively routine. Scanning thermal microscopy and thermal analysis using proximal probes has achieved spatial resolution of 10 nm, temperature precision of 50 mK , sensitivity to heat flows of 10 pW, and the capability for thermal analysis of sub-femtogram samples.
BibTeX: @article{Cahill2014, author = {David G. Cahill and Paul V. Braun and Gang Chen and David R. Clarke and Shanhui Fan and Kenneth E. Goodson and Pawel Keblinski and Gerald D. Mahan and Arun Majumdar and Humphrey J. Maris and Simon R. Phillpot and Eric Pop and Li Shi}, title = {Nanosacle thermal transport II: 2003--2012}, journal = {Appl. Phys. Rev.}, year = {2014} }
Chen, P., Katcho, N.A., Feser, J.P., Li, W., Glaser, M., Schmidt, O.G., Cahill, D.G., Mingo, N. and Rastelli, A.	Role of Surface-Segregation-Driven Intermixing on the Thermal Transport through Planar Si/Ge Superlattices [Abstract] [BibTeX]	2013	Phys. Rev. Lett. Vol. 111, pp. 115901	article	URL
Abstract: It has been highly debated whether the thermal conductivity kappa of a disordered SiGe alloy can be lowered by redistributing its constituent species so as to form an ordered superlattice. By ab initio calculations backed by systematic experiments, we show that Ge segregation occurring during epitaxial growth can lead to kappa values not only lower than the alloy’s, but also lower than the perfect superlattice values. Thus we theoretically demonstrate that kappa does not monotonically decrease as the Si- and Ge-rich regions become more sharply defined. Instead, an intermediate concentration profile is able to lower kappa below both the alloy limit (total intermixing) and also the abrupt interface limit (zero intermixing). This unexpected result is attributed to the peculiar behavior of the phonon mean free path in realistic Si/Ge superlattices, which shows a crossover from abrupt-interface- to alloylike values at intermediate phonon frequencies of 3 THz. Our calculated kappa's quantitatively agree with the measurements when the realistic, partially intermixed profiles produced by segregation are considered.
BibTeX: @article{Chen2013b, author = {Peixuan Chen and N. A. Katcho and J. P. Feser and Wu Li and M. Glaser and O. G. Schmidt and David G. Cahill and N. Mingo and A. Rastelli}, title = {Role of Surface-Segregation-Driven Intermixing on the Thermal Transport through Planar Si/Ge Superlattices}, journal = {Phys. Rev. Lett.}, year = {2013}, volume = {111}, pages = {115901}, url = {http://prl.aps.org/abstract/PRL/v111/i11/e115901} }
Chen, Z., Wei, Z., Chen, Y. and Dames, C.	Anisotropic Debye model for the thermal boundary conductance [Abstract] [BibTeX]	2013	Phys. Rev. B Vol. 87, pp. 125426	article	URL
Abstract: Most standard models for the thermal boundary conductance (TBC) assume isotropic properties and thus are inappropriate for layered and chainlike materials such as graphite, Bi2Te3, and high-density polyethylene (HDPE). To model such anisotropic materials, here a framework is introduced whereby the first Brillouin zone and the isoenergy surfaces of the Debye dispersion relation are both generalized from spherical to ellipsoidal. This model is checked by comparison with the experimental specific heat capacity of graphite and HDPE, as well as the phonon irradiation of graphite calculated from lattice dynamics. The anisotropic TBC model performs at least six times better than the standard isotropic diffuse mismatch model at explaining the measured TBC between graphite and various metals reported by Schmidt et al. [ J. Appl. Phys. 107 104907 (2010)]. The model further reveals an unexpected guideline to engineer the TBC: due to phonon focusing effects, in many cases the TBC across an interface can be increased by reducing a phonon velocity component parallel to the plane of the interface.
BibTeX: @article{Chen2013, author = {Z. Chen and Z. Wei and Y. Chen and C. Dames}, title = {Anisotropic Debye model for the thermal boundary conductance}, journal = {Phys. Rev. B}, year = {2013}, volume = {87}, pages = {125426}, url = {http://prb.aps.org/abstract/PRB/v87/i12/e125426} }
Corbin, E.A. and King, W.P.	Electrical noise characteristics of a doped silicon microcantilever heater-thermometer [Abstract] [BibTeX]	2011	Appl. Phys. Lett. Vol. 99, pp. 263107	article	URL
Abstract: We measure the electrical noise characteristics of doped silicon microcantilevers during cantilever self-heating over the temperature range 296-781 K.
BibTeX: @article{Corbin2011, author = {Elise A. Corbin and William P. King}, title = {Electrical noise characteristics of a doped silicon microcantilever heater-thermometer}, journal = {Appl. Phys. Lett.}, year = {2011}, volume = {99}, pages = {263107}, url = {http://apl.aip.org/resource/1/applab/v99/i26/p263107_s1} }
Corbin, E., Park, K. and King, W.	Room-temperature temperature sensitivity and resolution of doped-silicon microcantilevers [Abstract] [BibTeX]	2009	Appl. Phys. Lett. Vol. 94, pp. 243503	article	URL
Abstract: An atomic force microscope microcantilever having an integrated solid-state resistor can be used as a heater or a resistive thermometer. The temperature sensitivity and resolution of these cantilevers were investigated under steady and periodic operation near 300 K. Overall, the temperature coefficient of resistance of the cantilever is 0.0029 K^-1 at 300 K. When the cantilever is placed under periodic heating conditions the temperature resolution is measured as low as 5 mK. This characterization of heated cantilevers enables precise measurement of small temperature changes, and could improve nanoscale thermal measurements.
BibTeX: @article{Corbin2009, author = {Corbin, E.A. and Keunhan Park and King, W.P.}, title = {Room-temperature temperature sensitivity and resolution of doped-silicon microcantilevers}, journal = {Appl. Phys. Lett.}, year = {2009}, volume = {94}, pages = {243503}, url = {http://dx.doi.org/10.1063/1.3154567} }
Dai, W., Yap, D. and Chen, G.	Wideband enhancement of infrared absorption in a direct band-gap semiconductor by using nonabsorptive pyramids [Abstract] [BibTeX]	2012	Optics Express Vol. 20 (Energy Express S4), pp. A519-A529	article	URL
Abstract: Efficient trapping of the light in a photon absorber or a photodetector can improve its performance and reduce its cost. In this paper we investigate two designs for light-trapping in application to infrared absorption. Our numerical simulations demonstrate that nonabsorptive pyramids either located on top of an absorbing film or having embedded absorbing rods can efficiently enhance the absorption in the absorbing material. A spectrally averaged absorptance of 83% is achieved compared to an average absorptance of 28% for the optimized multilayer structure that has the same amount of absorbing material. This enhancement is explained by the coupled-mode theory. Similar designs can also be applied to solar cells.
BibTeX: @article{Dai2012, author = {Weitao Dai and Daniel Yap and Gang Chen}, title = {Wideband enhancement of infrared absorption in a direct band-gap semiconductor by using nonabsorptive pyramids}, journal = {Optics Express}, year = {2012}, volume = {20 (Energy Express S4)}, pages = {A519--A529}, url = {http://dx.doi.org/10.1364/OE.20.00A519} }
Evans, W., Hu, L. and Keblinski, P.	Thermal conductivity of graphene ribbons from equilibrium molecular dynamics: Effect of ribbon width, edge roughness, and hydrogen termination [Abstract] [BibTeX]	2010	Appl. Phys. Lett. Vol. 96, pp. 203112	article	URL
Abstract: We use equilibrium molecular dynamic simulations to compute thermal conductivity of graphene nanoribbons with smooth and rough edges. We also study effects of hydrogen termination. We find that conductivity is the highest for smooth edges and is essentially the same for zigzag and armchair edges. In the case of rough edges, the thermal conductivity is a strong function of the ribbon width indicating the important effect of phonon scattering from the edge. Hydrogen termination also reduces conductivity by a significant amount.
BibTeX: @article{Evans2010, author = {Evans, W.J. and Lin Hu and Keblinski, P.}, title = {Thermal conductivity of graphene ribbons from equilibrium molecular dynamics: Effect of ribbon width, edge roughness, and hydrogen termination}, journal = {Appl. Phys. Lett.}, year = {2010}, volume = {96}, pages = {203112}, url = {http://dx.doi.org/10.1063/1.3435465} }
Evans, W.J. and Keblinski, P.	Thermal conductivity of carbon nanotube cross-bar structures [Abstract] [BibTeX]	2010	Nanotechnology Vol. 21, pp. 475704	article	URL
Abstract: We use non-equilibrium molecular dynamics (NEMD) to compute the thermal conductivity (kappa) of orthogonally ordered cross-bar structures of single-walled carbon nanotubes. Such structures exhibit extremely low thermal conductivity in the range of 0.02–0.07 W m-1 K-1. These values are five orders of magnitude smaller than the axial thermal conductivity of individual carbon nanotubes, and are comparable to the thermal conductivity of still air.
BibTeX: @article{Evans2010b, author = {William J. Evans and Pawel Keblinski}, title = {Thermal conductivity of carbon nanotube cross-bar structures}, journal = {Nanotechnology}, year = {2010}, volume = {21}, pages = {475704}, url = {http://dx.doi.org/10.1088/0957-4484/21/47/475704} }
Evans, W.J., Shen, M. and Keblinski, P.	Inter-tube thermal conductance in carbon nanotubes arrays and bundles: Effects of contact area and pressure [Abstract] [BibTeX]	2012	Appl. Phys. Lett. Vol. 100, pp. 261908	article	URL
Abstract: We use molecular dynamics simulations to compute junction thermal conductance of carbon nanotubes as a function of crossing angle and pressure, and conductivity of arrays and bundles consisting of multiple junctions as a function of pressure. Two types of arrays are investigated: crossbar structures consisting of alternating orthogonal layers of nanotubes and close-packed bundles of parallel oriented tubes. Conductance of 90 degree junction increases with pressure 4 fold before saturation; cross-plane thermal conductivity of crossbar structures increases by a factor of 2. For parallel junctions pressure doubles the conductance while thermal conductivity of nanotubes bundles is more or less pressure independent.
BibTeX: @article{Evans2012, author = {William J. Evans and Meng Shen and Pawel Keblinski}, title = {Inter-tube thermal conductance in carbon nanotubes arrays and bundles: Effects of contact area and pressure}, journal = {Appl. Phys. Lett.}, year = {2012}, volume = {100}, pages = {261908}, url = {http://dx.doi.org/10.1063/1.4732100} }
Felts, J.R., Kjoller, K., Lo, M., Prater, C.B. and King, W.P.	Nanometer-Scale Infrared Spectroscopy of Heterogeneous Polymer Nanostructures Fabricated by Tip-Based Nanofabrication [Abstract] [BibTeX]	2012	ACS Nano Vol. 6, pp. 8015–8021	article	URL
Abstract: There is a significant need for chemical identification and chemical imaging of nanofabricated structures and devices, especially for multiple materials integrated at the nanometer scale. Here we present nanofabrication, chemical identification, and nanometer-scale chemical imaging of polymer nanostructures with better than 100 nm spatial resolution. Polymer nanostructures of polyethylene, polystyrene, and poly(3-dodecylthiophene-2,5-diyl) were fabricated by tip-based nanofabrication. Nanometer-scale infrared measurements using atomic force microscopy infrared spectroscopy (AFM-IR) obtained quantitative chemical spectra of these nanostructures. We show chemical imaging of intersecting patterns of nanometer-scale polymer lines of different chemical compositions. The results indicate that for closely packed heterogeneous nanostructures, the spatial resolution of AFM-IR is not limited by nanometer-scale thermal diffusion, but is instead limited by the cantilever sensitivity and the signal-to-noise ratio of the AFM-IR system.
BibTeX: @article{Felts2012, author = {Jonathan R. Felts and Kevin Kjoller and Michael Lo and Craig B. Prater and William P. King}, title = {Nanometer-Scale Infrared Spectroscopy of Heterogeneous Polymer Nanostructures Fabricated by Tip-Based Nanofabrication}, journal = {ACS Nano}, year = {2012}, volume = {6}, pages = {8015–8021}, url = {http://pubs.acs.org/doi/abs/10.1021/nn302620f} }
Fletcher, P.C., Bhatia, B.S., Wu, Y., Shannon, M.A. and King, W.P.	Electrothermal atomic-force microscope cantilever with integrated heater and n-p-n back-to-back diodes [Abstract] [BibTeX]	2011	J. MEMS Vol. 20, pp. 644-653	article	URL
Abstract: This paper reports the integration of both electrical and thermal elements into the free end of an atomic-force microscope cantilever, where the electrode and heater–thermometer are electrically isolated by an NPN semiconductor back-to-back diode. The electrothermal cantilever can be self heated using an integrated solid-state heater to more than 600C. The tip voltage can be measured or controlled independent of the tip temperature, either in the direct or the alternating current mode. To our knowledge, this setup is the first microcantilever to have a solid-state junction and heater integrated near a scanning probe tip.
BibTeX: @article{Fletcher2011, author = {Patrick C. Fletcher and Bikramjit S. Bhatia and Yan Wu and Mark A. Shannon and William P. King}, title = {Electrothermal atomic-force microscope cantilever with integrated heater and n-p-n back-to-back diodes}, journal = {J. MEMS}, year = {2011}, volume = {20}, pages = {644-653}, url = {http://dx.doi.org/10.1109/JMEMS.2011.2127455} }
Fletcher, P.C., Lee, B. and King, W.P.	Thermoelectric voltage at a nanometer-scale heated tip point contact [Abstract] [BibTeX]	2012	Nanotechnology Vol. 23, pp. 035401	article	URL
Abstract: We report thermoelectric voltage measurements between the platinum-coated tip of a heated atomic force microscope (AFM) cantilever and a gold-coated substrate. The cantilevers have an integrated heater-thermometer element made from doped single crystal silicon, and a platinum tip. The voltage can be measured at the tip, independent from the cantilever heating. We used the thermocouple junction between the platinum tip and the gold substrate to measure thermoelectric voltage during heating. Experiments used either sample-side or tip-side heating, over the temperature range 25-275C.The tip–substrate contact is 4 nm in diameter and its average measured Seebeck coefficient is 3.4 microV K-1. The thermoelectric voltage is used to determine tip-substrate interface temperature when the substrate is either glass or quartz. When the non-dimensional cantilever heater temperature is 1, the tip-substrate interface temperature is 0.593 on glass and 0.125 on quartz. Thermal contact resistance between the tip and the substrate heavily influences the tip–substrate interface temperature. Measurements agree well with modeling when the tip-substrate interface contact resistance is 10^8 K W-1.
BibTeX: @article{Fletcher2012, author = {Patrick C Fletcher and Byeonghee Lee and William P King}, title = {Thermoelectric voltage at a nanometer-scale heated tip point contact}, journal = {Nanotechnology}, year = {2012}, volume = {23}, pages = {035401}, url = {http://iopscience.iop.org/0957-4484/23/3/035401} }
Ghossoub, M.G., Lee, J.-H., Baris, O.T., Cahill, D.G. and Sinha, S.	Percolation of thermal conductivity in amorphous fluorocarbons [Abstract] [BibTeX]	2010	Phys. Rev. B Vol. 82, pp. 195441	article	URL
Abstract: We report experimental evidence of the percolation of thermal conductivity in nanometer scale thin films of amorphous fluorocarbon, using time-domain thermoreflectance measurements. According to the theory of Phillips and Thorpe, rigidity percolation in covalent glasses results in a power-law dependence of the elastic modulus on the average coordination number. Our measurements show that thermal conductivity behaves similarly. We derive the relation between thermal conductivity and coordination number from the rigidity percolation model using the theory of minimum thermal conductivity. Experiments verify the individual validity of each of these models in the film samples. This paper elucidates the physics of heat conduction in covalently bonded amorphous solids near the percolation threshold.
BibTeX: @article{Ghossoub2010, author = {Ghossoub, Marc G. and Lee, Jung-Hyun and Baris, Oksen T. and Cahill, David G. and Sinha, Sanjiv}, title = {Percolation of thermal conductivity in amorphous fluorocarbons}, journal = {Phys. Rev. B}, year = {2010}, volume = {82}, pages = {195441}, url = {http://dx.doi.org/10.1103/PhysRevB.82.195441} }
Grosse, K.L., Bae, M.-H., Lian, F., Pop, E. and King, W.P.	Nanoscale Joule heating, Peltier cooling and current crowding at graphene–metal contacts [Abstract] [BibTeX]	2011	Nature Nanotechnology Vol. 6, pp. 287-290	article	URL
Abstract: The performance and scaling of graphene-based electronics1 is limited by the quality of contacts between the graphene and metal electrodes2–4. However, the nature of graphene–metal contacts remains incompletely understood. Here, we use atomic force microscopy to measure the temperature distributions at the contacts of working graphene transistors with a spatial resolution of 10 nm (refs 5–8), allowing us to identify the presence of Joule heating9–11, current crowding12–16 and thermoelectric heating and cooling17. Comparison with simulation enables extraction of the contact resistivity (150– 200 Vmm2) and transfer length (0.2–0.5 mm) in our devices; these generally limit performance and must be minimized. Our data indicate that thermoelectric effects account for up to one-third of the contact temperature changes, and that current crowding accounts for most of the remainder. Modelling predicts that the role of current crowding will diminish and the role of thermoelectric effects will increase as contacts improve.
BibTeX: @article{Grosse2011, author = {Kyle L. Grosse and Myung-Ho Bae and Feifei Lian and Eric Pop and William P. King}, title = {Nanoscale Joule heating, Peltier cooling and current crowding at graphene–metal contacts}, journal = {Nature Nanotechnology}, year = {2011}, volume = {6}, pages = {287--290}, url = {http://www.nature.com/doifinder/10.1038/nnano.2011.39} }
Guha, B., Otey, C., Poitras, C., Fan, S. and Lipson, M.	Near-field radiative cooling of nanostructures [Abstract] [BibTeX]	2012	Nano Letters Vol. 12, pp. 4546-4550	article	URL
Abstract: We measure near-field radiative cooling of a thermally isolated nanostructure up to a few degrees and show that in principle this process can efficiently cool down localized hotspots by tens of degrees at submicrometer gaps. This process of cooling is achieved without any physical contact, in contrast to heat transfer through conduction, thus enabling novel cooling capabilities. We show that the measured trend of radiative cooling agrees well theoretical predictions and is limited mainly by the geometry of the probe used here as well as the minimum separation that could be achieved in our setup. These results also pave the way for realizing other new effects based on resonant heat transfer, like thermal rectification and negative thermal conductance.
BibTeX: @article{Guha2012, author = {B. Guha and C. Otey and C. Poitras and S. Fan and M. Lipson}, title = {Near-field radiative cooling of nanostructures}, journal = {Nano Letters}, year = {2012}, volume = {12}, pages = {4546--4550}, url = {http://pubs.acs.org/doi/abs/10.1021/nl301708e} }
Hafeli, A.K., Rephaeli, E., Fan, S., Cahill, D.G. and Tiwald, T.E.	Temperature dependence of surface phonon polaritons from a quartz grating [Abstract] [BibTeX]	2011	J. Appl. Phys. Vol. 110, pp. 043517	article	URL
Abstract: We report the temperature dependence of the surface phonon polariton (SPhP) spectra of alpha SiO2 (quartz), propagated to the far-field by a grating, in the temperature range between 300 K and 800 K. Room temperature data for a 670 nm deep grating are compared to a simulated spectrum using a finite-difference frequency-domain approach. The inputs to the simulation are the dielectric functions measured by infrared ellipsometry and modeled as a set of damped oscillators. The simulated spectra are in good agreement with experiment. The width of the SPhP reflectivity dip depends on the depth of the grating. For a grating depth of 280 nm, the width of the reflectivity dip in the temperature range 300
BibTeX: @article{Hafeli2011, author = {Andrew K. Hafeli and Eden Rephaeli and Shanhui Fan and David G. Cahill and Thomas E. Tiwald}, title = {Temperature dependence of surface phonon polaritons from a quartz grating}, journal = {J. Appl. Phys.}, year = {2011}, volume = {110}, pages = {043517}, url = {http://link.aip.org/link/doi/10.1063/1.3624603} }
Hippalgaonkar, K., Huang, B., Chen, R., Sawyer, K., Ercius, P. and Majumdar, A.	Fabrication of microdevices with integrated nanowires for investigating low-dimensional phonon transport [Abstract] [BibTeX]	2010	Nano Lett. Vol. 10, pp. 4341-4348	article	URL
Abstract: Phonons in low-dimensional structures with feature sizes on the order of the phonon wavelength may be coherently scattered by the boundary. This may give rise to a new regime of heat conduction, which can impact thermal energy transport and conversion. Traditional methods used to investigate phonon transport in one-dimensional structures suffer from uncertainty due to contact resistance, defects, and limited control over sample dimensions. We have developed a new batch-fabrication technique for suspended microdevices with integrated silicon nanowires from silicon-on-insulator (SOI) wafers. The nanowires are defect-free and have extremely high aspect ratios (length/critical dimension >2000). The nanowire dimensions (length and critical dimension) can be precisely controlled during fabrication. With these novel devices, phonon transport in silicon nanowires is systematically investigated. The room temperature thermal conductivity of nanowires with critical width around 80 nm is about 20 W/(m K) and much lower than that in smooth VLS wires. This suggests that the surface morphology of the structures has a significant effect on the thermal conductivity, but this phenomenon is not currently understood. This fabrication technique can also be used for thermal transport investigation in a wide-range of low-dimensional structures.
BibTeX: @article{Hippalgaonkar2010, author = {Hippalgaonkar, Kedar and Huang, Baoling and Chen, Renkun and Sawyer, Karma and Ercius, Peter and Majumdar, Arun}, title = {Fabrication of microdevices with integrated nanowires for investigating low-dimensional phonon transport}, journal = {Nano Lett.}, year = {2010}, volume = {10}, pages = {4341--4348}, url = {http://pubs.acs.org/doi/abs/10.1021/nl101671r} }
Hohensee, G.T., Hsieh, W.-P. and Cahill, M.D.L.D.G.	Interpreting picosecond acoustics in the case of low interface stiffness [Abstract] [BibTeX]	2012	Rev. Sci. Instrum. Vol. 83, pp. 114902	article	URL
Abstract: Analysis of data acquired in time-domain thermoreflectance (TDTR) experiments requires accurate measurements of the thickness of the metal film optical transducer that absorbs energy from the pump optical pulse and provides a temperature dependent reflectivity that is interrogated by the probe optical pulse. This thickness measurement is typically accomplished using picosecond acoustics. The presence of contaminants and native oxides at the interface between the sample and transducer often produce a picosecond acoustics signal that is difficult to interpret. We describe heuristics for addressing this common difficulty in interpreting picosecond acoustic data. The use of these heuristics can reduce the propagation of uncertainties and improve the accuracy of TDTR measurements of thermal transport properties.
BibTeX: @article{Hohensee2012, author = {Gregory T. Hohensee and Wen-Pin Hsieh and Mark D. Losegoand David G. Cahill}, title = {Interpreting picosecond acoustics in the case of low interface stiffness}, journal = {Rev. Sci. Instrum.}, year = {2012}, volume = {83}, pages = {114902}, url = {http://link.aip.org/link/doi/10.1063/1.4766957} }
Hsieh, W.-P., Chen, B., Li, J., Keblinski, P. and Cahill, D.	Pressure tuning of the thermal conductivity of the layered muscovite crystal [Abstract] [BibTeX]	2009	Phys. Rev. B Vol. 80, pp. 180302	article	URL
Abstract: The physics of heat conduction in layered, anisotropic crystals is probed by measurements of the cross-plane elastic constant C₃₃ and thermal conductivity Λ of muscovite mica as a function of hydrostatic pressure. Picosecond interferometry and time-domain thermoreflectance provide high-precision measurements of C₃₃ and Lambda;, respectively, of micron-sized samples within a diamond-anvil cell; Λ changes from the anomalously low value of 0.46 W m^-1 K^-1 at ambient pressure to a value more typical of oxides crystals with large unit cells, 6.6 W m^-1 K^-1, at P = 24 GPa. Most of the pressure dependence of Λ can be accounted for by the pressure dependence of the cross-plane sound velocities.
BibTeX: @article{Hsieh2009, author = {Wen-Pin Hsieh and Bin Chen and Jie Li and Keblinski, P. and Cahill, D.G.}, title = {Pressure tuning of the thermal conductivity of the layered muscovite crystal}, journal = {Phys. Rev. B}, year = {2009}, volume = {80}, pages = {180302}, url = {http://link.aps.org/doi/10.1103/PhysRevB.80.180302} }
Hsieh, W.-P., Losego, M.D., Braun, P.V., Shenogin, S., Keblinski, P. and Cahill, D.G.	Testing the minimum thermal conductivity model for amorphous polymers using high pressure [Abstract] [BibTeX]	2011	Phys. Rev. B Vol. 83, pp. 174205	article	URL
Abstract: Pressure dependence of thermal conductivity provides a critical test of the validity of the model of the minimum thermal conductivity for describing heat transport by molecular vibrations of an amorphous polymer. We measure the pressure dependence of the thermal conductivity lambda(P) of poly(methyl methacrylate) using a combination of time-domain thermoreflectance and SiC anvil-cell techniques. We also determine lambda(P) from a computational model of amorphous polystyrene. In both cases, lambda(P) is accurately predicted by the minimum thermal conductivity model via the pressure dependence of the elastic constants and density.
BibTeX: @article{Hsieh2011, author = {Hsieh, Wen-Pin and Losego, Mark D. and Braun, Paul V. and Shenogin, Sergei and Keblinski, Pawel and Cahill, David G.}, title = {Testing the minimum thermal conductivity model for amorphous polymers using high pressure}, journal = {Phys. Rev. B}, year = {2011}, volume = {83}, pages = {174205}, url = {http://dx.doi.org/10.1103/PhysRevB.83.174205} }
Hsieh, W.-P., Lyons, A.S., Pop, E., Keblinski, P. and Cahill, D.G.	Pressure tuning of the thermal conductance of weak interfaces [Abstract] [BibTeX]	2011	Phys. Rev. B Vol. 84, pp. 184107	article	URL
Abstract: We use high pressure to reveal the dependence of interfacial heat transport on the stiffness of interfacial bonds. The combination of time-domain thermoreflectance and SiC anvil techniques is used to measure the pressure-dependent thermal conductance G(P) of clean and modified Al/SiC interfaces at pressures as high as P = 12 GPa. We create low-stiffness, van der Waals–bonded interfaces by transferring a monolayer of graphene onto the SiC surface before depositing the Al film. For such weak interfaces, G(P) initially increases approximately linearly with P. At high pressures, P > 8 GPa, the thermal conductance of these weak interfaces approaches the high values characteristic of strongly bonded, clean interfaces.
BibTeX: @article{Hsieh2011b, author = {Wen-Pin Hsieh and Austin S. Lyons and Eric Pop and Pawel Keblinski and David G. Cahill}, title = {Pressure tuning of the thermal conductance of weak interfaces}, journal = {Phys. Rev. B}, year = {2011}, volume = {84}, pages = {184107}, url = {http://prb.aps.org/abstract/PRB/v84/i18/e184107} }
Hsu, W.-C., Tong, J.K., Liao, B., Burg, B.R. and Chen, G.	Direct and quantitative broadband absorptance spectroscopy on small objects using Fourier transform infrared spectrometer and bilayer cantilever probes [Abstract] [BibTeX]	2013	Appl. Phys. Lett. Vol. 102, pp. 051901	article	URL
Abstract: A measurement platform is introduced that combines a bilayer cantilever probe with a Fourier transform infrared spectrometer to measure absolute spectral absorptance between wavelengths of 3 micron and 18 micron directly and quantitatively. The enhanced sensitivity provided by the cantilever probe enables the quantitative characterization of micro- and nanometer-sized samples. Validation of the technique is carried out by measuring the absorptance spectrum of a doped silicon thin film with a backside aluminum layer and found to agree well with the theoretical predictions. The presented technique is especially attractive for samples such as individual nanowires or nanoparticles, isolated molecules, powders, and photonic structures
BibTeX: @article{Hsu2013, author = {Wei-Chun Hsu and Jonathan K. Tong and Bolin Liao and Brian R. Burg and Gang Chen}, title = {Direct and quantitative broadband absorptance spectroscopy on small objects using Fourier transform infrared spectrometer and bilayer cantilever probes}, journal = {Appl. Phys. Lett.}, year = {2013}, volume = {102}, pages = {051901}, url = {http://link.aip.org/link/doi/10.1063/1.4790184} }
Hu, L., Desai, T. and Keblinski, P.	Determination of interfacial thermal resistance at the nanoscale [Abstract] [BibTeX]	2011	Phys. Rev. B Vol. 83, pp. 195423	article	URL
Abstract: Using molecular dynamics simulations and model graphene layers in an organic matrix we demonstrate that interfacial thermal resistance determined via thermal relaxation method is up to an order of magnitude larger than that determined from direct simulation method of heat transfer across the matrix-graphene-matrix interface. We provide an explanation of this difference based on the spectral analysis of the frequency-dependent vibrational temperature. The importance of our finding lies in the fact that the relaxation method mimics experimental laser-based pump-probe measurements of the interfacial thermal resistance, while the direct simulation method provides information relevant to predicting and understanding thermal conductivity of nanocomposites.
BibTeX: @article{Hu2011, author = {Lin Hu and Tapan Desai and Pawel Keblinski}, title = {Determination of interfacial thermal resistance at the nanoscale}, journal = {Phys. Rev. B}, year = {2011}, volume = {83}, pages = {195423}, url = {http://link.aps.org/doi/10.1103/PhysRevB.83.195423} }
Hu, L., Desai, T. and Keblinski, P.	Thermal transport in graphene-based nanocomposite [Abstract] [BibTeX]	2011	J. Appl. Phys. Vol. 110, pp. 033517	article	URL
Abstract: Using molecular dynamics simulations, we study model graphene nanoplatelets and carbon nanotubes in an organic matrix. We demonstrate that, despite relatively high interfacial thermal resistance between the filler and the matrix, the thermal conductivity enhancement of the nanocomposite can be very significant. Our results suggest that agglomeration and low aspect ratio of the conductive nanofiller additive are primarily responsible for the limited conductivity enhancement reported to date. Mapping of the simulation results on the homogenization model, accounting for interfacial resistance, allows us to predict the full potential of the nanocarbon filler addition for thermal conductivity enhancement.
BibTeX: @article{Hu2011c, author = {L. Hu and T. Desai and P. Keblinski}, title = {Thermal transport in graphene-based nanocomposite}, journal = {J. Appl. Phys.}, year = {2011}, volume = {110}, pages = {033517}, url = {http://link.aip.org/link/doi/10.1063/1.3610386} }
Hu, L., Evans, W.J. and Keblinski, P.	One-dimensional phonon effects in direct molecular dynamics method for thermal conductivity determination [Abstract] [BibTeX]	2011	J. Appl. Phys. Vol. 110, pp. 113511	article	URL
Abstract: We demonstrate that the use of the direct, heat source/sink method for thermal conductivity determination via molecular dynamics simulation leads to diverging thermal conductivity with increasing simulation cell length when the cross section of the cell is kept constant. A phonon transport theory based analysis shows that this divergence arises due to discrete phonon phase space sampling leading to behavior characteristics of one-dimensional systems, which are known for size divergent thermal conductivity. We also show that the divergence is particularly strong for thermal conductivity along the elastically soft direction in anisotropic crystals.
BibTeX: @article{Hu2011b, author = {L. Hu and W. J. Evans and P. Keblinski}, title = {One-dimensional phonon effects in direct molecular dynamics method for thermal conductivity determination}, journal = {J. Appl. Phys.}, year = {2011}, volume = {110}, pages = {113511}, url = {http://link.aip.org/link/doi/10.1063/1.3660234} }
Hu, L., Zhang, L., Hu, M., Wang, J.-S., Li, B. and Keblinski, P.	Phonon interference at self-assembled monolayer interfaces: Molecular dynamics simulations [Abstract] [BibTeX]	2010	Phys. Rev. B Vol. 81, pp. 235427	article	URL
Abstract: Using molecular dynamics simulations, we expose phonon interference effects in thermal transports across a self-assembled monolayer (SAM) of alkanethiol molecules covalently bonded to (111) gold substrate and physically bonded to silicon. In particular, we show that the thermal conductance of SAM-Au interface depends on the bonding strength at the SAM-Si interface and that the phonon transmission coefficients show strong and oscillatory dependence on frequency, with oscillatory features diminishing with increasing SAM thickness. To explore the generality of this behavior we analyze a simple model of point junction on a one-dimensional chain using the scattering boundary method.
BibTeX: @article{Hu2010, author = {Lin Hu and Lifa Zhang and Ming Hu and Jian-Sheng Wang and Baowen Li and Keblinski, P.}, title = {Phonon interference at self-assembled monolayer interfaces: Molecular dynamics simulations}, journal = {Phys. Rev. B}, year = {2010}, volume = {81}, pages = {235427}, url = {http://dx.doi.org/10.1103/PhysRevB.81.235427} }
Hu, M., Keblinski, P. and Schelling, P.	Kapitza conductance of silicon-amorphous polyethylene interfaces by molecular dynamics simulations [Abstract] [BibTeX]	2009	Phys. Rev. B Vol. 79, pp. 104305	article	URL
Abstract: We use nonequilibrium molecular dynamics simulation to elucidate the interfacial thermal conductance between single-crystal silicon and amorphous polyethylene. In particular, we investigate the role of solid stiffness and the bonding strength across the interface on the interfacial thermal conductance. Simulations of interfacial scattering of individual phonon wave packets indicate that neither diffuse mismatch model nor acoustic mismatch model describes the interfacial scattering process quantitatively. In general, transmission coefficients for longitudinal phonons are significantly higher than those for transverse phonons. We also observe that anharmonic processes can be important for interfacial conductance.
BibTeX: @article{Hu2009, author = {Ming Hu and Keblinski, P. and Schelling, P.K.}, title = {Kapitza conductance of silicon-amorphous polyethylene interfaces by molecular dynamics simulations}, journal = {Phys. Rev. B}, year = {2009}, volume = {79}, pages = {104305}, url = {http://dx.doi.org/10.1103/PhysRevB.79.104305} }
Intaraprasonk, V. and Fan, S.	Wave-vector space picture for radiationless focusing and beaming [Abstract] [BibTeX]	2009	Optics Letters Vol. 34, pp. 2967-2969	article	URL
Abstract: Radiationless interference of an electromagnetic wave occurs in the near field when the feature sizes of the waves are at the deep subwavelength scale. We present the propagation in such a regime using a wave-vector space picture. Using this picture, we reproduce the condition to achieve near-field focusing. We also design the initial field distribution needed for near-field beaming, where an intensity distribution maintains its shape as it propagates. We conclude the discussion by proposing a possible implementation of the near-field beaming scheme. (C) 2009 Optical Society of America
BibTeX: @article{Intaraprasonk2009, author = {Intaraprasonk, Varat and Fan, Shanhui}, title = {Wave-vector space picture for radiationless focusing and beaming}, journal = {Optics Letters}, year = {2009}, volume = {34}, pages = {2967-2969}, url = {http://www.opticsinfobase.org/abstract.cfm?URI=ol-34-19-2967} }
Kwon, B., Jiang, J., Schulmerich, M., Xub, Z., Bhargava, R., Liu, G. and King, W.	Bimaterial microcantilevers with black silicon nanocone arrays [Abstract] [BibTeX]	2013	Sensors and Actuators A Vol. 199, pp. 143-148	article	URL
Abstract: The performance of infrared (IR) sensing bimaterial cantilevers depends upon the thermal, mechanical and optical properties of the cantilever materials. This paper presents bimaterial cantilevers that have a layer of black silicon nanocone arrays, which has larger optical absorbance and mechanical compliance than single crystal silicon. The black silicon consists of nanometer-scale silicon cones of height 104–336 nm, fabricated using a three-step O2–CHF3–Ar + Cl2 plasma process. The average cantilever absorbance was 0.16 over the 3–10 micronm wavelength region, measured using a Fourier transform infrared (FTIR) microspectrometer. The measured cantilever responsivity to incident IR light compares well to a model of cantilever behavior that relate the spectral absorbance, heat transfer, and thermal expansion. The model also provides further insights into the influence of the nanocone height on the absorbance and responsivity of the cantilever. Compared to a cantilever with smooth single crystal silicon, the cantilever with black silicon has about 2× increased responsivity. The nanocone array fabrication technique for silicon bimaterial cantilevers presented here could be applied to other IR sensors.
BibTeX: @article{Kwon2013b, author = {B. Kwon and J. Jiang and M.V. Schulmerich and Z. Xub and R. Bhargava and G.L. Liu and W.P. King}, title = {Bimaterial microcantilevers with black silicon nanocone arrays}, journal = {Sensors and Actuators A}, year = {2013}, volume = {199}, pages = {143--148}, url = {http://www.sciencedirect.com/science/article/pii/S0924424713002483} }
Kwon, B., M.V. Schulmerich, Elgass, L., Kong, R., Holton, S., Bhargava, R. and King, W.	Infrared Microspectroscopy Combined with Conventional Atomic Force Microscopy [Abstract] [BibTeX]	2012	Ultramicroscopy Vol. 116, pp. 56-61	article	URL
Abstract: This paper reports nanotopography and mid infrared (IR) microspectroscopic imaging coupled within the same atomic force microscope (AFM). The reported advances are enabled by using a bimaterial microcantilever, conventionally used for standard AFM imaging, as a detector of monochromatic IR light. IR light intensity is recorded as thermomechanical bending of the cantilever measured upon illumination with intensity-modulated, narrowband radiation. The cantilever bending is then correlated with the sample's IR absorption. Spatial resolution was characterized by imaging a USAF 1951 optical resolution target made of SU-8 photoresist. The spatial resolution of the AFM topography measurement was a few nanometers as expected, while the spatial resolution of the IR measurement was 24.4 micron using relatively coarse spectral resolution (25–125 cm-1). In addition to well-controlled samples demonstrating the spatial and spectral properties of the setup, we used the method to map engineered skin and three-dimensional cell culture samples. This research combines modest IR imaging capabilities with the exceptional topographical imaging of conventional AFM to provide advantages of both in a facile manner
BibTeX: @article{Kwon2012a, author = {B. Kwon and M.V. Schulmerich, and L.J. Elgass and R. Kong and S.E. Holton and R. Bhargava and W.P. King}, title = {Infrared Microspectroscopy Combined with Conventional Atomic Force Microscopy}, journal = {Ultramicroscopy}, year = {2012}, volume = {116}, pages = {56--61}, url = {http://www.sciencedirect.com/science/article/pii/S0304399112000435} }
Kwon, B., Rosenberger, M., Bhargava, R., Cahill, D.G. and King, W.P.	Dynamic thermomechanical response of bimaterial microcantilevers to periodic heating by infrared radiation [Abstract] [BibTeX]	2012	Rev. Sci. Instrum. Vol. 83, pp. 015003	article	URL
Abstract: This paper investigates the dynamic thermomechanical response of bimaterial microcantilevers to periodic heating by an infrared laser operating at a wavelenegth of 10.35 micron. A model relates incident radiation, heat transfer, temperature distribution in the cantilever, and thermal expansion mismatch to find the cantilever displacement. Experiments were conducted on two custom-fabricated bimaterial cantilevers and two commercially available bimaterial microcantilevers. The cantilever response was measured as a function of the modulation frequency of the laser over the range of 0.01-30 kHz. The model and the method of cantilever displacement calibration can be applied for bimaterial cantilever with thick coating layer. The sensitivity and signal-to-noise of bimaterial cantilevers were evaluated in terms of either total incident power or incident flux. The custom-fabricated bimaterial cantilevers showed 9X or 190X sensitivity improvement compared to commercial cantilevers. The detection limit on incident flux is as small as 0.10 pW micron-2 Hz-1/2.
BibTeX: @article{Kwon2012, author = {Beomjin Kwon and Matthew Rosenberger and Rohit Bhargava and David G. Cahill and and William P. King}, title = {Dynamic thermomechanical response of bimaterial microcantilevers to periodic heating by infrared radiation}, journal = {Rev. Sci. Instrum.}, year = {2012}, volume = {83}, pages = {015003}, url = {http://dx.doi.org/10.1063/1.3680107} }
Kwon, B., Schulmerich, M., Bhargava, R. and King, W.	Infrared Emission from Heated Microcantilevers [Abstract] [BibTeX]	2013	Nanoscale and Microscale Thermophysical Engineering Vol. 17, pp. 141-153	article	URL
Abstract: An understanding of the thermal behavior of heated microcantilevers is essential to their use. In this article, we investigated the infrared (IR) emission of two silicon cantilevers with integrated solid-state heaters over the 2500–3000 cm-1 spectral range. Two cantilevers were examined: the first had a .The heater surface area of 17x20 micron and the second had a heater surface area of 170x100 micron. We calculated the spectral power emitted by the cantilever based on the Planck function, dielectric function of the doped silicon at elevated temperatures, and cantilever spectral emissivity.Measurements of the cantilever spectral power compared well with predictionsfirst cantilever had a radiative power of 4.2 micro-W at a heating power of 15.7 mW and maximum temperature of 1,150 K, and the second cantilever had a radiative power of 70.1 micro-W at a heating power of 54.9 mW and maximum temperature of 850 K. The cantilever emissive power depended on the spatial variation in the cantilever temperature and cantilever emissivity. It is also shown how the heated cantilever can be used as an IR source to acquire absorption spectra of polymer films in an IR spectrometer.
BibTeX: @article{Kwon2013, author = {B. Kwon and M.V. Schulmerich and R. Bhargava and W.P. King}, title = {Infrared Emission from Heated Microcantilevers}, journal = {Nanoscale and Microscale Thermophysical Engineering}, year = {2013}, volume = {17}, pages = {141--153}, url = {http://dx.doi.org/10.1080/15567265.2012.760693} }
Kwon, B., Wang, C., Park, K., Bhargava, R. and King, W.P.	Thermomechanical sensitivity of microcantilevers in the mid-infrared spectral region [Abstract] [BibTeX]	2011	Nano. Micro. Thermophys. Eng. Vol. 15, pp. 16-28	article	URL
Abstract: This article reports the thermomechanical sensitivity of bimaterial cantilevers over a mid-infrared (IR) spectral range (5–10 micron) that is critical both for chemical analyses via vibrational spectroscopy and for direct thermal detection in the 300–700 K range. A physics-based model of cantilever bending was developed by including heat transfer to and within the cantilever, temperature-dependent cantilever bending, and cantilever and optical system IR characteristics. Detailed measurements of the optical system IR characteristics were used as inputs to the model, including Fourier transform infrared (FT-IR) spectral characterization of cantilever absorbance as well as characterization of the light source and monochromator. Mechanical bending sensitivity and noise were modeled and measured for six commercially available microcantilevers, which consist of either an aluminum film on a silicon cantilever or a gold film on a silicon nitride cantilever. The spectral sensitivity of each cantilever was measured by recording cantilever deflection when illuminated with IR light from a monochromator. Predictions of cantilever bending sensitivity and noise compare very well with measurements over the entire spectral range with no fitting parameters or normalization. The results are used to rank the cantilevers for their potential use in IR measurements.
BibTeX: @article{Kwon2011, author = {B. Kwon and C. Wang and K. Park and R. Bhargava and W. P. King}, title = {Thermomechanical sensitivity of microcantilevers in the mid-infrared spectral region}, journal = {Nano. Micro. Thermophys. Eng.}, year = {2011}, volume = {15}, pages = {16--28}, url = {http://dx.doi.org/10.1080/15567265.2010.502925} }
Lau, W.T., Shen, J.-T. and Fan, S.	Exponential suppression of thermal conductance using coherent transport and heterostructures [Abstract] [BibTeX]	2010	Phys. Rev. B Vol. 82, pp. 113105	article	URL
Abstract: We consider coherent thermal conductance through multilayer photonic crystal heterostructures, consisting of a series of cascaded nonidentical photonic crystals. We show that thermal conductance can be suppressed exponentially with the number of cascaded crystals due to the mismatch between photonic bands of all crystals in the heterostructure.
BibTeX: @article{Lau2010, author = {Lau, Wah Tung and Shen, Jung-Tsung and Fan, Shanhui}, title = {Exponential suppression of thermal conductance using coherent transport and heterostructures}, journal = {Phys. Rev. B}, year = {2010}, volume = {82}, pages = {113105}, url = {http://dx.doi.org/10.1103/PhysRevB.82.113105} }
Lau, W.T., Shen, J.-T. and Fan, S.	Universal features of coherent photonic thermal conductance in multilayer photonic band gap structures [Abstract] [BibTeX]	2009	Phys. Rev. B Vol. 80, pp. 155135	article	URL
Abstract: We show that at the high-temperature limit, the coherent photonic thermal conductance of a multilayer photonic crystal can be significantly below the corresponding thermal conductance of vacuum. Moreover, the thermal conductance at this limit is independent of the thicknesses of the layers but dependent on the refractive indices of the layers only. Such universal features are directly related to the ergodic nature of the distribution of photonic bands in the frequency space.
BibTeX: @article{Lau2009, author = {Lau, Wah Tung and Shen, Jung-Tsung and Fan, Shanhui}, title = {Universal features of coherent photonic thermal conductance in multilayer photonic band gap structures}, journal = {Phys. Rev. B}, year = {2009}, volume = {80}, pages = {155135}, url = {http://dx.doi.org/10.1103/PhysRevB.80.155135} }
Levander, A.X., Tong, T., Yu, K.M., Suh, J., Fu, D., Zhang, R., Lu, H., Schaff, W.J., Dubon, O., Walukiewicz, W., Cahill, D.G. and Wu, J.	Effects of point defects on thermal and thermoelectric properties of InN [Abstract] [BibTeX]	2011	Appl. Phys. Lett. Vol. 98, pp. 012108	article	URL
Abstract: In contrast to most semiconductors, electrical conductivity of InN is known to increase upon high-energy particle irradiation. The effects of irradiation on its thermal and thermoelectric properties have yet to be investigated. Here we report the thermal conductivity of high-quality InN to be 120 W/m-K and examine the effects of point defects generated by irradiation on the thermal conductivity and Seebeck coefficient. We show that irradiation can be used to modulate the thermal and thermoelectric properties of InN by controlling point defect concentrations. The thermoelectric figure of merit of InN was found to be insensitive to irradiation.
BibTeX: @article{Levander2011, author = {A. X. Levander and T. Tong and K. M. Yu and J. Suh and D. Fu and R. Zhang and H. Lu and W. J. Schaff and O. Dubon and W. Walukiewicz and D. G. Cahill and J. Wu}, title = {Effects of point defects on thermal and thermoelectric properties of InN}, journal = {Appl. Phys. Lett.}, publisher = {AIP}, year = {2011}, volume = {98}, pages = {012108}, url = {http://dx.doi.org/doi/10.1063/1.3536507} }
Losego, M., Blitz, I., Vaia, R., Cahill, D. and Braun, P.	Ultralow Thermal Conductivity in Organoclay Nanolaminates [Abstract] [BibTeX]	2013	Nano Letters Vol. 13, pp. 2215-2219	article	URL
Abstract: Because interfaces impede phonon transport of thermal energy, nanostructuring can transform fully dense solids into ultralow thermal conductivity materials. Here we report a simple self-assembly approach to synthesizing organoclay nanolaminates with cross-planar thermal conductivities below 0.10 W m-1 K-1 5-fold decrease compared to unmodified clay. These organoclays are produced via alkylammonium cation exchange with colloidally dispersed montmorillonite clay sheets followed by solvent casting.Time-domain thermore- flectance (TDTR) is used to evaluate the thermal conductivity of the organoclay nanolaminates.Variations in both organic layer thickness and cation chemistry are investigated. At these interface densities (1.0-1.5 interfaces/nm), we demonstrate that thermal conductivity is relatively independent of nanolaminate spacing. A simple series resistance model describes the behavior and gives an interfacial thermal conductance value of 150 MW m-K-1 for the organic/clay interface, consistent with similar organic-inorganic interfaces. The wide range of compositional substitutions and structural variations possible in these materials, make organoclays a versatile new platform for investigating the underlying physics of nanolaminate structures.
BibTeX: @article{Losego2013, author = {M. Losego and I. Blitz and R. Vaia and D.G. Cahill and P.V. Braun}, title = {Ultralow Thermal Conductivity in Organoclay Nanolaminates}, journal = {Nano Letters}, year = {2013}, volume = {13}, pages = {2215--2219}, url = {http://dx.doi.org/10.1021/nl4007326} }
Losego, M.D., Grady, M.E., Sottos, N.R., Cahill, D.G. and Braun, P.V.	Effects of chemical bonding on heat transport across interfaces [Abstract] [BibTeX]	2012	Nature Materials Vol. 11, pp. 502-506	article	URL
Abstract: Interfaces often dictate heat flow in micro- and nanostructured systems. However, despite the growing importance of thermal management in micro- and nanoscale devices a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump–probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold–SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.
BibTeX: @article{Losego2012, author = {Losego, Mark D. and Grady, Martha E. and Sottos, Nancy R. and Cahill, David G. and Braun, Paul V.}, title = {Effects of chemical bonding on heat transport across interfaces}, journal = {Nature Materials}, year = {2012}, volume = {11}, pages = {502--506}, url = {http://dx.doi.org/10.1038/nmat3303} }
Losego, M.D., Moh, L., Arpin, K.A., Cahill, D.G. and Braun, P.V.	Interfacial thermal conductance in spun-cast polymer films and polymer brushes [Abstract] [BibTeX]	2010	Appl. Phys. Lett. Vol. 97, pp. 011908	article	URL
Abstract: Interfaces between inorganic materials and anharmonic polymers have potentially intriguing thermal transport behavior. The low thermal conductivity of amorphous polymers limits significant interfacial effects to polymer film thicknesses of only a few nanometers. We use time-domain thermoreflectance to directly measure interfacial effects in the thermal conductance of spun-cast poly(methyl methacrylate) (PMMA) thin films and PMMA brushes “grafted-from” the substrate. PMMA brushes are expected to have polymer chains partially aligned perpendicular to the substrate, yet only a modest increase (13 in thermal conductivity is observed over spun-cast layers.
BibTeX: @article{Losego2010, author = {Mark D. Losego and Lionel Moh and Kevin A. Arpin and David G. Cahill and Paul V. Braun}, title = {Interfacial thermal conductance in spun-cast polymer films and polymer brushes}, journal = {Appl. Phys. Lett.}, year = {2010}, volume = {97}, pages = {011908}, url = {http://link.aip.org/link/?APL/97/011908/1} }
Moh, L.C.H., Losego, M.D. and Braun, P.V.	Solvent quality effects on scaling behavior of poly(methyl methacrylate) brushes in the moderate- and high-density regimes [Abstract] [BibTeX]	2011	Langmuir Vol. 27, pp. 3698-3702	article	URL
Abstract: Herein, we give a detailed experimental analysis for scaling law behavior in the “moderately dense” and “high-density” brush regimes for poly(methyl methacrylate) brushes swollen in a range of solvent conditions. This expansive experimental analysis aims to validate decades of mean field theory predictions on power law scaling behavior of grafted polymer chains. Brushes with grafting densities (sigma) ranging from 0.1 to 0.8 nm-2 are prepared by atom-transfer radical polymerization. The swollen thickness (h) is characterized using liquid cell ellipsometry, and the solvent quality is varied using mixtures of acetone and methanol. In a good solvent, the exponential scaling behavior (h sigma n) has the typical n = 1/3 dependency for grafting densities of sigma < 0.4 nm-2. For grafting densities of >0.4 nm-2, n increases, indicating the transition from the moderately dense to the high-density brush regime. However, in a poor solvent, the scaling behavior is independent of sigma and scales as h sigma 0.80, approaching the theoretical expectations of h sigma 1. An abrupt transition between these scaling law behaviors occurs at the theta-solvent condition of 45% (v/v) methanol in acetone. While our experimental results parallel trends predicted by mean field theory, differences are observed and appear to be attributed to self-solvation of the polymer, polydispersity in the molecular weight, and chain termination.
BibTeX: @article{Moh2011, author = {Lionel C. H. Moh and Mark D. Losego and Paul V. Braun}, title = {Solvent quality effects on scaling behavior of poly(methyl methacrylate) brushes in the moderate- and high-density regimes}, journal = {Langmuir}, year = {2011}, volume = {27}, pages = {3698--3702}, url = {http://pubs.acs.org/doi/abs/10.1021/la2002139} }
Narayanaswamy, A., Shen, S., Hu, L., Chen, X. and Chen, G.	Breakdown of the Planck blackbody radiation law at nanoscale gaps [Abstract] [BibTeX]	2009	Appl. Phys. A: Materials Science and Processing Vol. 96, pp. 357-362	article	URL
Abstract: The Planck theory of blackbody radiation imposes a limit on the maximum radiative transfer between two objects at given temperatures. When the two objects are close enough, near-field effects due to tunneling of evanescent waves lead to enhancement of radiative transfer above the Planck limit. When the objects can support electromagnetic surface polaritons, the enhancement can be a few orders-of-magnitude larger than the blackbody limit. In this paper, we summarize our recent measurements of radiative transfer between two parallel silica surfaces and between a silica microsphere and a flat silica surface that show unambiguous evidence of enhancement of radiative transfer due to near-field effects above the Planck limit. © 2009 Springer-Verlag.
BibTeX: @article{Narayanaswamy2009, author = {Narayanaswamy, Arvind and Shen, Sheng and Hu, Lu and Chen, Xiaoyuan and Chen, Gang}, title = {Breakdown of the Planck blackbody radiation law at nanoscale gaps}, journal = {Appl. Phys. A: Materials Science and Processing}, year = {2009}, volume = {96}, pages = {357--362}, url = {http://dx.doi.org/10.1007/s00339-009-5203-5} }
Oh, D.-W., Changhyun, K., Ramanathan, S. and Cahill, D.G.	Thermal conductivity and dynamic heat capacity across the metal-insulator transition in thin film VO$_2$ [Abstract] [BibTeX]	2010	Appl. Phys. Lett. Vol. 96, pp. 151906	article	URL
Abstract: The thermal properties of VO₂ thin films, 90-440 nm thick, are measured by time-domain thermoreflectance (TDTR) across the metal-insulator transition (MIT). The thermal conductivity increases by as much as 60% in the metallic phase; this increase in conductivity is in good agreement with the expected electronic contribution to the thermal conductivity. For relatively thick layers, TDTR data are sensitive to the dynamic heat capacity and show a pronounced peak near the MIT temperature created by a contribution to the enthalpy from periodic transformations at the 10 MHz frequency of the thermal waves used in the experiment. The dynamic heat capacity increases as the amplitude ΔT of the thermal waves becomes comparable to the width of the MIT and reaches ≈30% of the bulk latent heat for ΔT≈1.6 K.
BibTeX: @article{Oh2010, author = {Dong-Wook Oh and Ko Changhyun and S. Ramanathan and D. G. Cahill}, title = {Thermal conductivity and dynamic heat capacity across the metal-insulator transition in thin film VO$_2$}, journal = {Appl. Phys. Lett.}, year = {2010}, volume = {96}, pages = {151906}, url = {http://dx.doi.org/10.1063/1.3394016} }
Otey, C. and Fan, S.	Numerically exact calculation of electromagnetic heat transfer between a dielectric sphere and plate [Abstract] [BibTeX]	2011	Phys. Rev. B Vol. 84, pp. 245431	article	URL
Abstract: We present a numerically exact calculation of electromagnetic heat transfer between a dielectric sphere and plate. We compare the calculation to a recent experiment. Our calculations unify various approximations previously used to treat this problem, and provide a basis for new physical insights into the design of nanoscale thermal transfer experiments.
BibTeX: @article{Otey2011, author = {Clayton Otey and Shanhui Fan}, title = {Numerically exact calculation of electromagnetic heat transfer between a dielectric sphere and plate}, journal = {Phys. Rev. B}, year = {2011}, volume = {84}, pages = {245431}, url = {http://dx.doi.org/10.1103/PhysRevB.84.245431} }
Otey, C., Lau, W.T. and Fan, S.	Thermal rectification through vacuum [Abstract] [BibTeX]	2010	Phys. Rev. Lett. Vol. 104, pp. 154301	article	URL
Abstract: We propose a mechanism for photon mediated thermal rectification through vacuum relying only on the temperature dependence of electromagnetic resonances. We also propose an example implementation consisting of two polytypes of silicon carbide, which exploits the interaction of temperature dependent surface phonon polaritons to achieve significant rectification.
BibTeX: @article{Otey2010, author = {Otey, C.R. and Wah Tung Lau and Shanhui Fan}, title = {Thermal rectification through vacuum}, journal = {Phys. Rev. Lett.}, year = {2010}, volume = {104}, pages = {154301}, url = {http://dx.doi.org/10.1103/PhysRevLett.104.154301} }
Otey, C., Zhu, L., Sandhu, S. and Fan, S.	Fluctuational electrodynamics calculation of near-field thermal transfer in non-planar geometries: a brief overview [Abstract] [BibTeX]	2013	Journal of Quantitative Spectroscopy and Radiative Transfer	article	URL
Abstract: Near-field electromagnetic heat transfer is of interest for a variety of applications, including energy conversion, and precision heating, cooling and imaging of nano-structures. This past decade has seen considerable progress in the study of near-field electromagnetic heat transfer, but it is only very recently that numerically exact methods have been developed for treating near-field heat transfer in the fluctuational electrodynamics formalism for non-trivial geometries. In this paper we provide a tutorial review of these exact methods, with an emphasis on the computational aspects of three important methods, which we compare in the context of a canonical example, the coupled dielectric sphere problem
BibTeX: @article{Otey2013, author = {C. Otey and L. Zhu and S. Sandhu and S. Fan}, title = {Fluctuational electrodynamics calculation of near-field thermal transfer in non-planar geometries: a brief overview}, journal = {Journal of Quantitative Spectroscopy and Radiative Transfer}, year = {2013}, url = {http://www.sciencedirect.com/science/article/pii/S0022407313001659} }
Prasher, R., Hu, X., Chalopin, Y., Mingo, N., Lofgreen, K., Volz, S., Cleri, F. and Keblinski, P.	Turning carbon nanotubes from exceptional heat conductors into insulators [Abstract] [BibTeX]	2009	Phys. Rev. Lett. Vol. 102, pp. 105901	article	URL
Abstract: Thermal conductivity (κ) of isolated carbon nanotubes (CNTs) is higher than the κ of diamond; however, in this Letter we show that the κ of a packed bed of three-dimensional random networks of single and multiwall CNTs is smaller than that of thermally insulating amorphous polymers. The thermoelectric power (Σ) of the random network of CNTs was also measured. The Σ of a single wall nanotube network is very similar to that of isolated nanotubes and, in contrast with κ, Σ shows a strong dependence on the tube diameter.
BibTeX: @article{Prasher2009, author = {Prasher, R.S. and Hu, X.J. and Chalopin, Y. and Mingo, N. and Lofgreen, K. and Volz, S. and Cleri, F. and Keblinski, P.}, title = {Turning carbon nanotubes from exceptional heat conductors into insulators}, journal = {Phys. Rev. Lett.}, year = {2009}, volume = {102}, pages = {105901}, url = {http://dx.doi.org/10.1103/PhysRevLett.102.105901} }
Rephaeli, E. and Fan, S.	Absorber and emitter for solar thermophotovoltaic systems to achieve efficiency exceeding the Shockley-Queisser limit [Abstract] [BibTeX]	2009	Optics Express Vol. 17, pp. 15145-15159	article	URL
Abstract: We present theoretical considerations as well as detailed numerical design of absorber and emitter for Solar Thermophotovoltaics (STPV) applications. The absorber, consisting of an array of tungsten pyramids, was designed to provide near-unity absorptivity over all solar wavelengths for a wide angular range, enabling it to absorb light effectively from solar sources regardless of concentration. The emitter, a tungsten slab with Si/SiO2 multilayer stack, provides a sharp emissivity peak at the solar cell band-gap while suppressing emission at lower frequencies. We show that, under a suitable light concentration condition, and with a reasonable area ratio between the emitter and absorber, a STPV system employing such absorber-emitter pair and a single-junction solar cell can attain efficiency that exceeds the Shockley-Queisser limit. (C) 2009 Optical Society of America
BibTeX: @article{Rephaeli2009, author = {Eden Rephaeli and Shanhui Fan}, title = {Absorber and emitter for solar thermophotovoltaic systems to achieve efficiency exceeding the Shockley-Queisser limit}, journal = {Optics Express}, year = {2009}, volume = {17}, pages = {15145--15159}, url = {http://www.opticsinfobase.org/oe/abstract.cfm?URI=OPEX-17-17-15145} }
Rosenberger, M.R., Kwon, B., Cahill, D.G. and King, W.P.	The impact of silicon nitride thickness on the infrared sensitivity of silicon nitride-aluminum microcantilevers [Abstract] [BibTeX]	2012	Sens. Act. Vol. A185, pp. 17-23	article	URL
Abstract: This paper investigates how silicon nitride thickness impacts the performance of silicon nitride–aluminum bimaterial cantilever infrared sensors. A model predicts cantilever behavior by considering heat transfer within and from the cantilever, cantilever optical properties, cantilever bending mechanics, and thermomechanical noise. Silicon nitride–aluminum bimaterial cantilevers of different thicknesses were designed and fabricated. Cantilever sensitivity and noise were measured when exposed to infrared laser radiation. For cantilever thickness up to 1200 nm, thicker silicon nitride results in improved signal to noise ratio due to increased absorptivity and decreased noise.
BibTeX: @article{Rosenberger2012, author = {Matthew R. Rosenberger and Beomjin Kwon and David G. Cahill and William P. King}, title = {The impact of silicon nitride thickness on the infrared sensitivity of silicon nitride-aluminum microcantilevers}, journal = {Sens. Act.}, year = {2012}, volume = {A185}, pages = {17--23}, url = {http://dx.doi.org/10.1016/j.sna.2012.07.006} }
Sasikumar, K. and Keblinski, P.	Effect of chain conformation in the phonon transport across a Si-polyethylene single-molecule covalent junction [Abstract] [BibTeX]	2011	J. Appl. Phys. Vol. 109, pp. 114307	article	URL
Abstract: We use nonequilibrium molecular dynamics simulations to study heat transfer across molecular junctions formed by alkane chains covalently bonded to crystalline silicon leads. We focus our studies on the role of chain conformation on phonon transport across junctions and along the chain. We find that in the case of straight chains, all trans conformations, the silicon-polyethylene junction conductance is 180 pW/K, and heat flows ballistically, i.e. with no resistance, along the chain. The introduction of gauche conformations (kinks) leads to a nonzero thermal resistance of the chain and also reduces the junction conductance to 100 pW/K. The chain thermal resistance is proportional to the number of gauche conformations indicating that they act as strong and independent phonon scattering centers. We attribute the 80% enhancement in junction conductance during extension from coiled to straight chain conformation to ballistic (coherent) phonon transport along a straight chain.
BibTeX: @article{Sasikumar2011, author = {Kiran Sasikumar and Pawel Keblinski}, title = {Effect of chain conformation in the phonon transport across a Si-polyethylene single-molecule covalent junction}, journal = {J. Appl. Phys.}, year = {2011}, volume = {109}, pages = {114307}, url = {http://jap.aip.org/resource/1/japiau/v109/i11/p114307_s1} }
Shen, M., Evans, W.J., Cahill, D. and Keblinski, P.	Bonding and pressure tunable interfacial thermal conductivity [Abstract] [BibTeX]	2011	Phys. Rev. B Vol. 84, pp. 195432	article	URL
Abstract: Stiffness of interfacial bonding between two materials plays a major role in controlling the thermal conductance of the interface. We use nonequilibrium molecular dynamics simulations to study interfacial thermal conductance at an epitaxial interface between two fcc crystals with interatomic interactions described by Lennard Jones (LJ) potentials. The interface stiffness was varied by two different methods: (i) application of pressure and (ii) direct change of the interfacial bonding strength by varying the depth of potential well parameter of the LJ potential. Our results show that when the interfacial bonding strength is low, interfacial stiffness increases linearly with pressure due to the anharmonicity of atomic interactions. Consequently, the interfacial conductance increases, first proportionally to interfacial stiffness, and then it saturates at a high value. Quantitatively similar behavior is observed when the stiffness of the interfacial bonding is increased by directly varying the depth of the potential well parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent and in fact slightly decreases with increasing pressure. This decrease can be explained by the change of overlap between the vibrational density of states (DOS) in the two crystalline materials
BibTeX: @article{Shen2011, author = {M. Shen and W. J. Evans and D. Cahill and P. Keblinski}, title = {Bonding and pressure tunable interfacial thermal conductivity}, journal = {Phys. Rev. B}, year = {2011}, volume = {84}, pages = {195432}, url = {http://prb.aps.org/pdf/PRB/v84/i19/e195432} }
Shen, M., Schelling, P.K. and Keblinski, P.	Heat transfer mechanism across few-layer graphene by molecular dynamics [Abstract] [BibTeX]	2013	Phys. Rev. B Vol. 88, pp. 045444	article	URL
Abstract: We use nonequilibrium molecular dynamics to study heat transfer across structures consisting of a few layers of graphene sandwiched between silicon crystals. We find that when heat transfers from a silicon lead on one side across the graphene layers to a silicon lead on the other side, the interfacial conductance is essentially independent of the number of layers, in agreement with recent experimental findings. By contrast, wave-packet simulations show that the transmission coefficient of individual vibrational modes depends strongly on frequency and the number of graphene layers, indicating significant interference effects. This apparent contradiction is resolved by a theoretical calculation, which shows that the integrated contribution of the phonons to the interfacial thermal conductance is essentially independent of the number of layers. When one atomic layer of graphene is heated directly, the effective interfacial conductance associated with heat dissipation to the silicon substrate is much smaller. We attribute this to the resistance associated with heat transfer between high and low frequency modes within heated graphene.
BibTeX: @article{Shen2013, author = {Meng Shen and Patrick K. Schelling and Pawel Keblinski}, title = {Heat transfer mechanism across few-layer graphene by molecular dynamics}, journal = {Phys. Rev. B}, year = {2013}, volume = {88}, pages = {045444}, url = {http://prb.aps.org/pdf/PRB/v88/i4/e045444} }
Shen, S., Mavrokefalos, A., Sambegoro, P. and Chen, G.	Nanoscale thermal radiation between two gold surfaces [Abstract] [BibTeX]	2012	Appl. Phys. Lett. Vol. 100, pp. 233114	article	URL
Abstract: In this letter, we measured the nanoscale thermal radiation between a microsphere and a substrate which were both coated with thick gold films. Although gold is highly reflective for thermal radiation, the radiative heat transfer between two gold surfaces was demonstrated to be significantly enhanced at nanoscale gaps beyond the blackbody radiation limit due to the tunneling of non-resonant evanescent waves. The measured heat transfer coefficient between two gold surfaces agreed well with theretical prediction.
BibTeX: @article{Shen2012, author = {Sheng Shen and Anastassios Mavrokefalos and Poetro Sambegoro and Gang Chen}, title = {Nanoscale thermal radiation between two gold surfaces}, journal = {Appl. Phys. Lett.}, year = {2012}, volume = {100}, pages = {233114}, url = {http://dx.doi.org/10.1063/1.4723713} }
Shen, S., Narayanaswamy, A. and Chen, G.	Surface phonon polaritons mediated energy transfer between nanoscale gaps [Abstract] [BibTeX]	2009	Nano Letters Vol. 9, pp. 2909-2913	article	URL
Abstract: Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar dielectrics and exhibit a large local-field enhancement near the interfaces at infrared frequencies. Theoretical calculations show that such surface waves can lead to breakdown of the Planck's blackbody radiation law in the near field. Here, we experimentally demonstrate that surface phonon polaritons dramatically enhance energy transfer between two surfaces at small gaps by measuring radiation heat transfer between a microsphere and a flat surface down to 30 nm separation. The corresponding heat transfer coefficients at nanoscale gaps are 3 orders of magnitude larger than that of the blackbody radiation limit. The high energy flux can be exploited to develop new radiative cooling and thermophotovoltaic technologies. © 2009 American Chemical Society.
BibTeX: @article{Shen2009, author = {Shen, Sheng and Narayanaswamy, Arvind and Chen, Gang}, title = {Surface phonon polaritons mediated energy transfer between nanoscale gaps}, journal = {Nano Letters}, year = {2009}, volume = {9}, pages = {2909--2913}, url = {http://dx.doi.org/10.1021/nl901208v} }
Shenogina, N., Godawat, R., Keblinski, P. and Garde, S.	How wetting and adhesion affect thermal conductance of a range of hydrophobic to hydrophilic aqueous interfaces [Abstract] [BibTeX]	2009	Phys. Rev. Lett. Vol. 102, pp. 156101	article	URL
Abstract: We quantify the strength of interfacial thermal coupling at water-solid interfaces over a broad range of surface chemistries from hydrophobic to hydrophilic using molecular simulations. We show that the Kapitza conductance is proportional to the work of adhesion—a wetting property of that interface—enabling the use of thermal transport measurements as probes of the molecular environment and bonding at an interface. Excellent agreement with experiments on similar systems [Z. B. Ge et al., Phys. Rev. Lett. 96, 186101 (2006)] highlights the convergence of simulation and experiments on these complex nanoscopic systems.
BibTeX: @article{Shenogina2009, author = {Shenogina, Natalia and Godawat, Rahul and Keblinski, Pawel and Garde, Shekhar}, title = {How wetting and adhesion affect thermal conductance of a range of hydrophobic to hydrophilic aqueous interfaces}, journal = {Phys. Rev. Lett.}, year = {2009}, volume = {102}, pages = {156101}, url = {http://dx.doi.org/10.1103/PhysRevLett.102.156101} }
Yu, Z., Sergeant, N., Skauli, T., Zhang, G., Wang, H. and Fan, S.	Enhancing far-field thermal emission with thermal extraction [Abstract] [BibTeX]	2013	Nature Communications, Vol. 4, pp. 1730	article	URL
Abstract: The control of thermal radiation is of great current importance for applications such as energy conversions and radiative cooling. Here we show theoretically that the thermal emission of a finite-size blackbody emitter can be enhanced in a thermal extraction scheme, where one places the emitter in optical contact with an extraction device consisting of a transparent object, as long as both the emitter and the extraction device have an internal density of state higher than vacuum, and the extraction device has an area larger than the emitter and moreover has a geometry that enables light extraction. As an experimental demonstration of the thermal extraction scheme, we observe a four-fold enhancement of the far-field thermal emission of a carbon-black emitter having an emissivity of 0.85.
BibTeX: @article{Yu2013, author = {Z. Yu and N. Sergeant and T. Skauli and G. Zhang and H. Wang and S. Fan}, title = {Enhancing far-field thermal emission with thermal extraction}, journal = {Nature Communications,}, year = {2013}, volume = {4}, pages = {1730}, url = {http://dx.doi.org/10.1038/ncomms2765} }
Zhang, L., Keblinski, P., Wang, J.-S. and Li, B.	Interfacial thermal transport in atomic junctions [Abstract] [BibTeX]	2011	Phys. Rev. B Vol. 83, pp. 064303	article	URL
Abstract: We study ballistic interfacial thermal transport across atomic junctions. Exact expressions for phonon transmission coefficients are derived for thermal transport in one-junction and two-junction chains, and verified by numerical calculation based on a nonequilibrium Green’s function method. For a single-junction case, we find that the phonon transmission coefficient typically decreases monotonically with increasing freqency. However, in the range between the point of equal frequency spectrum and that of equal acoustic impedance, it first increases then decreases, which explains why the Kapitza resistance calculated from the acoustic mismatch model is far larger than the experimental values at low temperatures. The junction thermal conductance reaches a maximum when the interfacial coupling equals the harmonic average of the spring constants of the two semi-infinite chains. For three-dimensional junctions, in the weak coupling limit, we find that the conductance is proportional to the square of the interfacial coupling, while for a intermediate coupling strength the conductance is approximately proportional to the interfacial coupling strength. For two-junction chains, the transmission coefficient oscillates with the frequency due to interference effects. The oscillations between the two envelope lines can be understood analytically, thus providing guidelines for designing phonon frequency filters.
BibTeX: @article{Zhang2011, author = {Lifa Zhang and Pawel Keblinski and Jian-Sheng Wang and Baowen Li}, title = {Interfacial thermal transport in atomic junctions}, journal = {Phys. Rev. B}, year = {2011}, volume = {83}, pages = {064303}, url = {http://prb.aps.org/pdf/PRB/v83/i6/e064303} }
Zhu, L., Otey, C.R. and Fan, S.	Negative differential thermal conductance through vacuum [Abstract] [BibTeX]	2012	Appl. Phys. Lett. Vol. 100, pp. 044104	article	URL
Abstract: We propose a scheme for achieving negative differential thermal conductance in near-field electromagnetic thermal transfer. As an example, we show that the scheme can be implemented with two slabs of silicon carbide brought in close proximity to each other. We also describe how a bistable thermal switch can be constructed in this manner.
BibTeX: @article{Zhu2012, author = {Linxiao Zhu and Clayton R. Otey and Shanhui Fan}, title = {Negative differential thermal conductance through vacuum}, journal = {Appl. Phys. Lett.}, year = {2012}, volume = {100}, pages = {044104}, url = {http://dx.doi.org/10.1063/1.3679694} }
Zhu, L., Sandhu, S., Otey, C., Fan, S., Sinclair, M.B. and Luk, T.S.	Temporal coupled mode theory for thermal emission from a single thermal emitter [Abstract] [BibTeX]	2013	Appl. Phys. Lett. Vol. 102, pp. 103104	article	URL
Abstract: We propose a temporal coupled mode theory for thermal emission from a single emitter supporting either a single mode or an orthogonal set of modes. This temporal coupled mode theory provides analytic insights into the general behaviors of resonant thermal emitters. We validate the coupled mode theory formalism by a direct numerical simulation of the emission properties of single emitters.
BibTeX: @article{Zhu2013, author = {L. Zhu and S. Sandhu and C. Otey and S. Fan and M. B. Sinclair and T. S. Luk}, title = {Temporal coupled mode theory for thermal emission from a single thermal emitter}, journal = {Appl. Phys. Lett.}, year = {2013}, volume = {102}, pages = {103104}, url = {http://link.aip.org/link/doi/10.1063/1.4794981} }
Zurbuchen, M.A., Cahill, D.G., Schubert, J., Jia, Y. and Schlom, D.G.	Determination of the thermal conductivity tensor of the $n=7$ Aurivillius phase Sr4Bi4Ti7O24 [Abstract] [BibTeX]	2012	Appl. Phys. Lett. Vol. 101, pp. 021904	article	URL
Abstract: A challenge in the preparation of advanced materials that exist only as thin films is to establish their properties, particularly when the materials are of low symmetry or the tensor properties of interest are of high rank. Using Sr4Bi4Ti7O24 as an example, we show how the preparation of oriented epitaxial films of multiple orientations enables the thermal conductivity tensor of this tetragonal material with a c-axis length of 64.7 A to be measured.The thermal conductivity tensor coefficients k33=1.10 W m-1 K-1 and k11=k22=1.80 W m-1 K-1were determined by growing epitaxial Sr4Bi4Ti7O24 films on (100), (110), and (111) SrTiO3 substrates.
BibTeX: @article{Zurbuchen2012, author = {M. A. Zurbuchen and D. G. Cahill and J. Schubert and Y. Jia and D. G. Schlom}, title = {Determination of the thermal conductivity tensor of the $n=7$ Aurivillius phase Sr4Bi4Ti7O24}, journal = {Appl. Phys. Lett.}, year = {2012}, volume = {101}, pages = {021904}, url = {http://link.aip.org/link/doi/10.1063/1.4733616} }