A5005199471- Thermal properties of materials
- Thermography and Photoacoustic Techniques
- Nuclear Physics and Applications
- Thermal Radiation and Cooling Technologies
- Radiation Detection and Scintillator Technologies
- Advanced Thermoelectric Materials and Devices
- Graphene research and applications
- Heat Transfer and Optimization
- Particle Detector Development and Performance
- Force Microscopy Techniques and Applications
- 3D IC and TSV technologies
- Silicon Carbide Semiconductor Technologies
- Adhesion, Friction, and Surface Interactions
- Electronic Packaging and Soldering Technologies
- Atomic and Subatomic Physics Research
- Diamond and Carbon-based Materials Research
- Surface and Thin Film Phenomena
- Carbon Nanotubes in Composites
- GaN-based semiconductor devices and materials
- Random lasers and scattering media
- Electronic and Structural Properties of Oxides
- Heat Transfer Mechanisms
- Semiconductor materials and devices
- Ultrasonics and Acoustic Wave Propagation
- Nanofluid Flow and Heat Transfer
Cambridge Scientific (United States)
2024
Massachusetts Institute of Technology
2005-2022
Boston University
2011-2018
National Nuclear Security Administration
2018
Kansas State University
2011-2016
University of Michigan
2013-2014
Masdar Institute of Science and Technology
2009
Indian Institute of Technology Madras
2008
Gustavus Adolphus College
1995-1998
Fraunhofer Institute for Surface Engineering and Thin Films
1997
The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. results illustrate how allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which transport effects are important described. An analytical solution for anisotropic flow layered structures given, a method measuring both cross-plane in-plane conductivities of thermally thin films As verification, technique used extract...
The control of heat conduction through the manipulation phonons as coherent waves in solids is fundamental interest and could also be exploited applications, but has not been experimentally confirmed. We report experimental observation use finite-thickness superlattices with varying numbers periods. measured thermal conductivity increased linearly increasing total superlattice thickness over a temperature range from 30 to 150 kelvin, which consistent phonon process. First-principles Green's...
Size effects in heat conduction, which occur when phonon mean free paths (MFPs) are comparable to characteristic lengths, being extensively explored many nanoscale systems for energy applications. Knowledge of MFPs is essential understanding size effects, yet largely unknown most materials. Here, we introduce the first experimental technique can measure MFP distributions over a wide range length scales and Using this technique, distribution silicon time obtain good agreement with...
A frequency-domain thermoreflectance method for measuring the thermal properties of homogenous materials and submicron thin films is described. The can simultaneously determine conductivity heat capacity a sample, provided diffusivity greater, similar3x10(-6) m(2)/s, also measure in-plane cross-plane conductivities, as well boundary conductance between material layers. Two implementations are discussed, one based on an ultrafast pulsed laser system continuous-wave lasers. theory analysis its...
Conventional theory predicts that ultrahigh lattice thermal conductivity can only occur in crystals composed of strongly bonded light elements, and it is limited by anharmonic three-phonon processes. We report experimental evidence departs from these long-held criteria. measured a local room-temperature exceeding 1000 watts per meter-kelvin an average bulk value reaching 900 boron arsenide (BAs) crystals, where arsenic are heavy respectively. The high values consistent with proposal for...
Materials with high thermal conductivity (κ) are of technological importance and fundamental interest. We grew cubic boron nitride (cBN) crystals controlled abundance isotopes measured κ greater than 1600 watts per meter-kelvin at room temperature in samples enriched 10B or 11B. In comparison, we found that the isotope enhancement is considerably lower for phosphide arsenide as identical isotopic mass disorder becomes increasingly invisible to phonons. The ultrahigh conjunction its wide...
Semiconductors with high thermal conductivity and electron-hole mobility are of great importance for electronic photonic devices as well fundamental studies. Among the ultrahigh–thermal materials, cubic boron arsenide (c-BAs) is predicted to exhibit simultaneously electron hole mobilities >1000 centimeters squared per volt second. Using optical transient grating technique, we experimentally measured 1200 watts meter kelvin ambipolar 1600 second at same locations on c-BAs samples room...
The thermal boundary conductances between c-axis oriented highly ordered pyrolytic graphite and several metals have been measured in the temperature range 87–300 K are found to be similar those of metal–diamond interfaces. values obtained indicative interface conductance sidewalls multiwall carbon nanotubes (CNTs) and, therefore, relevance for accurate characterization properties CNTs, graphene, design performance composite materials electronic devices based on these structures. A modified...
We present a pump-probe optical technique for measuring the thermal conductivity of liquids. The uses reflective geometry which does not depend on properties liquid and requires as little single droplet to produce result. An analytical solution is given bidirectional heat flow in layered media, including effects radial from coaxial Gaussian laser spots, interface resistances, accumulation multiple pulses. In addition, several experimental improvements over previous configurations are...
The increasing interest in the extraordinary thermal properties of nanostructures has led to development various measurement techniques. Transient thermoreflectance method emerged as a reliable technique for conductivity thin films. In this method, determination usually relies much on accuracy heat capacity input. For new nanoscale materials with unknown or less-understood properties, it is either questionable assume bulk difficult obtain form those conventional measurement. paper, we...
We derive a generally applicable formula to calculate the precision of multi-parameter measurements that apply least squares algorithms. This formula, which accounts for experimental noise and uncertainty in controlled model parameters, is then used analyze thermal property with pump-probe thermoreflectance techniques. compare time domain frequency (FDTR) when measuring bulk materials thin films, considering simultaneous various combinations properties, including conductivity, heat capacity,...
A thermal property microscopy technique based on frequency domain thermoreflectance (FDTR) is presented. In FDTR, a periodically modulated laser locally heats sample while second probe beam monitors the surface reflectivity, which related to properties of with an analytical model. Here, we extend FDTR into imaging capable producing micrometer-scale maps several thermophysical simultaneously. Thermal phase images are recorded at multiple frequencies chosen for maximum sensitivity interest...
Frequency-domain thermoreflectance is extended to the characterization of thin metals films on low thermal diffusivity substrates. We show how a single noncontact measurement can yield both thickness and conductivity metal film with high accuracy. Results are presented from measurements gold aluminum 20–100 nm thick fused silica substrate. The verified independently atomic force microscope cross sections, through electrical via Wiedemann–Franz law. values in good agreement results for all at...
Suspended graphene has the highest measured thermal conductivity of any material at room temperature. However, when is supported by a substrate or encased between two materials, basal-plane heat transfer suppressed phonon interactions interfaces. We have used frequency domain thermoreflectance to create conductance maps contacts, obtaining simultaneous measurements and cross-plane boundary for 1–7 graphitic layers titanium silicon dioxide. find that similar on Our results implications in...
As the size of gallium nitride (GaN) transistors is reduced in order to reach higher operating frequencies, heat dissipation becomes critical bottleneck device performance and longevity. Despite importance characterizing physics governing thermal transport thin GaN films, literature far from conclusive. In this letter, we report measurements conductivity a film with thickness ranging 15–1000 nm grown on 4H-SiC without transition layer. Additionally, measure when it 1 μm-thick temperature...
Silicon carbide is used as a substrate for high-power GaN devices because of its closely matched lattice spacing with and high thermal conductivity. In these devices, resistance at the GaN–SiC interface bottleneck to heat flow, making this property an important factor in device design. letter, we report first measurements boundary conductance epitaxial grown directly on SiC without transition layer. We find that increases from approximately 230 MW/m2K 300 K 330 600 K. Our measured values are...
The thermal conductivity is a key property in determining the friction-induced temperature rise on surface of sliding components. In this study, Frequency Domain Thermoreflectance (FDTR) method used to measure range tribological materials (AISI 52100 bearing steel, silicon nitride, sapphire, tungsten carbide and zirconia). FDTR technique validated by comparing measurements pure germanium with well-known values, showing discrepancies less than 3%. For most studied, values measured are...
Thermal transport between CTAB passivated gold nanorods and solvent is studied by an optical pump−probe technique. Increasing the free concentration from 1 mM to 10 causes a ∼3× increase in layer's effective thermal interface conductance corresponding shift longitudinal surface plasmon resonance. The transition occurs near critical micelle concentration, revealing importance of role ligand on transport.
Pump-probe thermoreflectance is an optical technique used to measure heat transfer in bulk materials and micro- nanoscale samples. The measurement typically uses two light sources, referred as the pump probe. generates a time-dependent flux at sample surface, while probe monitors temperature response through proportional change surface reflectivity. Combined with model, measured infer transport properties such cross-plane thermal conductivity, in-plane capacity, boundary conductance between...
Measuring anisotropic thermal conductivity has always been a challenging task in metrology. Although recent developments of pump-probe thermoreflectance techniques such as variable spot sizes, offset beams, and elliptical beams have enabled the measurement conductivity, metal film transducer for absorption modulated pump laser beam detection signal. However, existence would cause in-plane heat spreading, suppressing sensitivity to conductivity. In addition, also adds complexity data...
Dilute nanoparticle suspensions of alumina in decane and isoparaffinic polyalphaolefin (PAO) exhibit thermal conductivity shear viscosity that are enhanced compared to continuum models assume well-dispersed particles. An optical technique has been used measure the longitudinal these at frequencies from 200to600MHz evaluate an effective hydrodynamic particle size. The measurements indicate for decane-based nanofluids nanoparticles do not form clusters. In case PAO nanofluids, corresponding...
Optical pump-probe techniques based on thermoreflectance, such as time domain thermoreflectance and frequency (FDTR), have been widely used to characterize the thermal conductivity of thin films conductance across interfaces. These typically use a transducer layer absorb pump light improve signal. The transducer, however, complicates interpretation measured signal because approximation that all energy from beam is deposited at surface not always accurate. In this paper, we consider effect...
The thermal conductivities of nanoparticle suspensions Al2O3 in C10H22 (decane) and isoparaffinic polyalphaolefin (PAO) have been measured using two dissimilar techniques: a transient hotwire measurement based on the heat loss resistivity heated wire solution, decay grating generated by interference picosecond light pulses. Agreement between techniques is good, indicating that either reliable way for measuring conductivity colloidal suspensions. Suspensions with volume concentrations from...