Research Physicist
Dr. Joshua Martin is an expert in thermal and electrical transport measurements and instrumentation, focusing on semiconductors and energy materials. His research aims to improve measurement methods, instrumentation, and reference materials for microelectronics and energy conversion applications.
Dr. Martin is well-known for his work in thermoelectric materials used in waste heat recovery and solid-state refrigeration. He has designed and constructed a number of scientific instruments that characterize fundamental properties of bulk and thin film materials with improved measurement speed, accuracy, and reliability. These instruments allowed his team to devise new metrologies, protocols, and models to correct previously unknown or long-ignored sources of errors, resulting in a series of protocol papers describing best measurement practices.
His contributions include developing two Standard Reference Materials for instrument validation, standardizing measurement protocols, and both leading and participating in several international interlaboratory studies on thermal and electrical transport properties. Dr. Martin has received several awards for his work, including the 2021 Department of Commerce Silver Medal Award and the 2014 Department of Commerce Bronze Medal Award.
Dr. Martin’s expertise will provide valuable insights into advancing measurement science for semiconductors and energy conversion technologies at the ITCC.
He will present Development of Thermal Conductivity Reference Materials and host the Thermoreflectance Instrumentation and Methods Workshop.
Professor at Harvard School of Engineering
David R. Clarke is the inaugural holder of the Extended Tarr Family Professor of Materials in the Harvard School of Engineering and Applied Sciences. He holds a PhD in Physics from the University of Cambridge, a B.Sc. in Applied Sciences from Sussex University and was awarded a ScD from the University of Cambridge.
A member of the National Academy of Engineering since 1999, he is also a Fellow of both the American Physical Society and the American Ceramic Society, and received an Alexander von Humboldt Foundation Senior Scientist Award in 1993.
He shared the 2008 Japanese NIMS Award for Recent Breakthroughs in Materials Science for Energy and Environment, is a Distinguished Life Member of the American Ceramic Society and was recently listed as author of one of the 11 best papers in the 110 years of publications on ceramics and glasses.
His long-term interests in materials range from the fundamentals to the applied, from ceramics to metals to semiconductors and polymers. He has published over 450 papers in areas of materials ranging from thermal barrier coatings, to dielectric elastomers to fundamentals of oxidation to microelectronics reliability and the electrical and optical properties of ZnO and GaN.
At Harvard, he enjoys interacting with students at all levels, from teaching Freshman seminars on “Glass” and “Materials, Energy and Society”, graduate courses in composites and deformation of materials and the new undergraduate course in SEAS on “Fundamentals of Heat Transfer”, a required course for students studying Mechanical Engineering.
He will present “Thermal Radiation Effects in Materials.”
*The above biography was originally published on https://clarke.seas.harvard.edu/people/david-r-clarke
Materials Research Laboratory
David Cahill is the Grainger Distinguished Chair in Engineering, Professor of Materials Science and Engineering, and co-Director of the IBM-Illinois Discovery Accelerator Institute at the University of Illinois at Urbana-Champaign. He joined the faculty of the Department of Materials Science and Engineering at the U. Illinois after earning his Ph.D. in condensed matter physics from Cornell University and working as a postdoctoral research associate at the IBM Watson Research Center.
He served as department head from 2010 to 2018. His research program advances physical insights on thermal transport at the nanoscale; extremes of low and high thermal conductivity; the thermal conductivity of soft matter; the thermal science of magnetic materials; and the transport of heat and mass in battery materials.
Cahill received the 2018 Innovation in Materials Characterization Award of the Materials Research Society, the 2015 Touloukian Award of the American Society of Mechanical Engineers, and the Klemens Award from the International Conference on Phonon Scattering in Condensed Matter; and is a fellow of the MRS, the American Physical Society, the AAAS, and an elected member of the American Academy of Arts and Sciences.
He will present “Beam Deflection Methods and Their Application to Polymers and Fast Mapping of Thermal Conductivity and Interface Conductance.”
More Accurate Analytical Solution for the Modified Transient Plain Source Method
Abstract:
The Modified Transient Plain Source (MTPS) method is a popular one for thermal effusivity and even for other thermal properties tests. The theory used currently for the method assumes that heat capacity of the heater and thermal contact resistances on its surfaces are negligibly small. Obviously, this assumption causes some unknown errors – especially at the early moments of time. To minimize the errors caused by using this imperfect theory the manufacturers of the MTPS devices must run multiple calibrations using several reference materials of known thermal effusivity. Theoretically this kind of method could work as an absolute one with no calibrations at all if a more accurate theory was used – e.g. the Guarded Hot Plate method uses only the measured electric power per square area of the heater, plates’ temperature difference and the sample’s thickness to calculate the absolute value of thermal conductivity. I.e. using accurate theory of the MTPS method we could get absolute values of thermal effusivity.
Now a new, significantly more accurate, analytical solution for the MTPS method is obtained where effects of the heater’s either heat capacity or thermal contact resistance are properly accounted. The heater’s temperatures calculated using the new formulas were numerically compared to its temperatures calculated using the old working formula and were verified using the Finite Differences Method calculations. These new, relatively simple formulas are used to analyze the effect of the heater’s heat capacity or the thermal contact resistance on the various materials tests’ results, what practically was never done before. The heater’s areal heat capacity is calculated using its thickness and volumetric specific heat, or it possibly can be measured directly using its temperature rise rate at the very first moment of time. Thermal contact resistance on the heater’s surfaces is estimated as thickness of the Kapton film divided by the Kapton’s thermal conductivity. These values, as well as the substrate’s thermal effusivity, are used in the new formulas to improve significantly the accuracy and convenience of the MTPS method.
Technical Expert Thermal Insulation Material
Effect of moisture on wood fiber based thermal insulation material and hygrothermal simulation of a guarded hot plate
Abstract:
The impact of moisture on the thermal performance of insulation materials is a significant phenomenon particularly in the case of hygroscopic materials, where it can alter thermal conductivity by several percent compared to dry conditions. This paper investigates the influence of moisture on the thermal properties of wood fibre insulation using the guarded hot plate method, in accordance with ISO 8302 and ASTM Test Method C 177 standards.
The study involved an examination of a range of wood fibre materials with nominal densities spanning from 60 to 190 kg/m³ under diverse moisture conditions. The experiments were conducted at a mean temperature of 283.15 K with a range of temperature gradients, conditioning states, and test durations. The research assesses the migration of water within the specimen towards the cold plate of the guarded hot plate and correlated these findings with the thermal conductivity resuts.
The study demonstrates the considerable influence of moisture content on the apparent thermal conductivity of wood fibre insulation. To enhance measurement accuracy and repeatability of the measurements, a method was proposed which involved the placement of a polyethylene film between the layers of the sliced materials in order to prevent moisture migration during testing process. This approach yields more reliable thermal conductivity values.
Furthermore, the paper explores the coupled heat and moisture transfers in bio-based materials, detailing the physical phenomena, models developed over decades, and simulation tools at the material scale. Additionally, it covers standardised experimental methods for determining model input parameters and acknowledges the associated uncertainties.
The comparison between experimental results and simulations demonstrated that classical models are satisfactory in predicting moisture profiles within hygroscopic materials.
Senior Application Scientist
Hot Disk Thermal Conductivity Measurements of Insulation and SRM 1450b
Abstract:
With the rising demand for energy-efficient solutions in aerospace, building construction, and semiconductor industries, there is a critical need for novel thermally insulating materials. Traditional thermal characterization methods, while considered accurate, are time-consuming and require large samples, posing challenges for modern material development, where only small samples might be available at the R&D stage. Alternatively, the Hot Disk Transient Plane Source (TPS) technique offers rapid evaluation capabilities even with small specimens.
While the applicability of Hot Disk to thermal insulation has been studied before, previous reports primary focused on comparing thermal conductivity values obtained using Hot Disk measurements with those obtained using other technique(s) from the same lab or among the collaborators. However, to the best of the authors’ knowledge, no literature is available evaluating Hot Disk performance towards actual Standard Reference Material (SRM) with low thermal conductivity. This investigation has a unique opportunity to examine NIST-certified SRM 1450b, among other low thermal conductivity materials.
The presented work shows the application of Hot Disk to measure the thermal properties of various thermally insulating materials, including isotropic and anisotropic samples, with the thermal conductivity ranging from a few hundred mW/m-K (polyethylene, nylon, polyoxymethylene) to a couple dozen mW/m-K (extruded polystyrene, SRM 1450b). Furthermore, using the Anisotropic Module of the Hot Disk technique, the level of anisotropy of SRM 1450b is evaluated and reported for the first time.
Transport properties and microstructural evolution of Bi-Cu-Te ternary alloys
Abstract:
This study delves into the profound influence of defects and their evolution within the microstructure on the thermoelectric transport properties, with a primary focus on the Bi-Cu-Te ternary system. By systematically investigating the intricate relationships between composition, microstructure, and thermoelectric properties, this research offers a comprehensive framework for optimizing these alloys in potential thermoelectric applications. The candidate alloy compositions were selected using a self-consistent thermodynamically optimized database of Bi-Cu-Te and synthesized using flame melting.
The microstructure evolution was characterized using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and Electron Probe Microanalyzer (EPMA). The presence of γCu3Te2 intermetallic significantly enhanced hardness, with optimized compositions showing a doubling of hardness compared to conventional BiSbTe alloys. The observed morphologies of each alloy and their thermoelectric properties correlate with the Cu concentration variations. An optimized composition exhibited excellent electrical conductivity of 100 kS/m, Seebeck coefficient of -145 μV/K, and power factor of 1.85 mW/mK2. These results provide insights into tailoring the composition and microstructure of Bi-Cu-Te alloys to improve their efficiency for thermoelectric waste heat recovery.
Postdoctoral Researcher
Thermoreflectance methods
Abstract:
Ion implantation has been extensively employed to customize the band structure and electrical characteristics of materials for applications in semiconductor technologies. While research on the electronic properties of ion-implanted materials continues to be a field of active research, there is relatively less emphasis on its impact on heat transfer within the material. Ion irradiation introduces defects into the lattice of a material, acting as scattering centers for phonons, which consequently impacts thermal conductivity. However, various factors of the implantation process such as ion mass, energy and temperature create different kinds of defects inside the material when exposed to irradiation. The complex interaction of phonons with these defects dictates the resultant thermal transport of the implanted material.
In this work, we demonstrate the impact of swift heavy ions (SHI) on thermal transport in different crystalline insulators since SHIs mimic fission products in nuclear reactors. Time-domain (TDTR) and spatial-domain (SDTR) thermoreflectance methods were utilized to spatially resolve and isolate the conductivities at nanometer and micrometer sub-surface damaged regions . Our studies revealed that crystal structure, the strength of ionic bonding, and crystal complexity have a strong correlation with the thermal transport behavior of irradiated solids. Moreover, SHI-induced latent tracks can result in the switching of the anisotropic behavior of thermal conductivity in sapphire. We also present heat conduction properties of the double polymorph γ/β-Ga2O3 structures, fabricated by a self-organized γ-polymorph transformation induced in β-Ga2O3 by ion irradiation. Importantly, the formation of such double γ/β-Ga2O3 polymorph structures features an unprecedented sharpness of the γ/β interface leading to abrupt changes in thermal properties across homo-interfaces. Measured results were validated by multiscale modeling approaches ranging from molecular dynamics to semi-analytical phonon-mediated heat transport in irradiated solids.
Associate Professor
Time Domain Thermoreflectance: Tips, Tricks, and a few Extensions (workshop)
Abstract:
Time Domain Thermoreflectance (TDTR) is one of the most sought-after techniques for conducting nanoscale thermal measurements. Including electron-phonon coupling, picosecond acoustics, thermal conductivity, and thermal boundary conductance measurements all at once with built in normalization and noise correction is an outstanding prospect. Over the years many researchers have streamlined TDTR systems to attempt to simplify an otherwise complex system. On the flip side, many researchers have extended TDTR to enhance various capabilities and sensitivity (honestly, most of us have done both). In this talk, we’ll discuss a few major options and opportunities with TDTR that can be a great help to TDTR users to help tailor their optical setup, analysis process, and even their design of experiments with samples and controls. In particular, we’ll spend some time discussing Asynchronous Optical Sampling Systems (ASOPS) with TDTR, a technique that effectively removes path-length matching and optical delay stages from TDTR designs (but introduces a new set of tips, tricks, and considerations).
Beyond Bulk: Delving into the Vibrational World of Nanodiamonds and Nanocomposite Materials
Abstract:
The significance of understanding thermal transport on the nanoscale continues to increase with the miniaturization of various technology architectures. This principle applies to the design of bulk materials with nanoscale features – in terms of size or periodicity – such as crystal defects, precipitates, or dopants such as nanocrystals. The mechanical vibrations in nanocrystals in the range of GHz-THz are not only important for their role in thermal transport but also for sensing, particularly through their coupling to electromagnetic radiation (optomechanical coupling), which can be utilised for nano-thermometry and more.
In this presentation, I will present our recent work which elucidates the unique lattice dynamics of isolated nanodiamond particles, and the same particles embedded in a thermoelectric matrix. We use a combination of neutron spectroscopy and atomistic simulations to study the evolution of these unique modes which include earthquake-like Rayleigh surface waves (Rayleigh phonons), whole particle breathing modes (Lamb resonances), surface rattling modes, and soft and broad acoustic and optical phonon modes. These modes give rise to a distinctive vibrational density of states compared to bulk diamond. Undoubtedly, these modes play crucial roles in thermal transport, sensing, and catalysis in many nanocrystal systems beyond diamond.
As well as detailing these modes in nanodiamond, we study the impact on the thermal transport of thermoelectric material SnTe by the addition of nanodiamond particles, measured by light flash analysis. We demonstrate a large enhancement factor on the thermoelectric figure of merit originating from the suppression of phonon propagation due to the presence of nanodiamond particles and particle-induced defects. Our work underscores the significance of comprehending size-dependent lattice dynamics for harnessing the full potential of nanodiamonds in diverse technological applications.
Steady State Methods and Transient Methods
Abstract:
This study evaluates the measurement uncertainty of thermal conductivity in insulation materials using a guarded hot plate apparatus at high temperatures up to 700 °C. The combined uncertainties in power measurement, specimen dimensions, and temperature difference resulted in a relative expanded uncertainty (with a coverage factor of 2) of 4.6–6.8% for thermal conductivity measurements between 200 °C and 700 °C. To ensure low-uncertainty measurements of the temperature difference across the air gap, thermocouples measuring temperatures across various parts of the heater plates were calibrated to establish a strong correlation of calibration uncertainties between paired thermometers measuring the gap imbalance.
To mitigate lateral heat flow, we systematically adjusted the auxiliary heater set temperatures to minimize heat loss through the specimen’s lateral edges. Additionally, we measured the temperature difference (δT₀) between the hot plate and the guard plate with the specimen in place, maintaining the guard and cold plates at the measurement temperature without powering the hot plate. Subsequently, δT₀ was applied as an offset during measurements to compensate for lateral heat loss. Validation of this compensation method was confirmed by extrapolating measured thermal conductivities under conditions of a large temperature difference (1/ΔT → 0) between the hot and cold plates, comparing proper compensation, no compensation, and over-compensation. Keywords: guarded hot plate, thermal conductivity, high temperature, uncertainty
Research Engineer
Thermal conductivity measurements of thermal energy storage materials
Abstract:
Thermal Energy Storage (TES) is an important technology for energy conservation and utilizing fluctuating renewable energy sources and waste heat. Heat transport in TES applications is extremely important as it influences the thermal performance in charging and discharging of the heat storage system.
This work focuses on the use of already available and standardized measurement devices like Laser Flash (LFA), Heat Flow Meter (HFM) and Transient Hot Bridge (THB) to determine the thermal conductivity of phase change (PCM) and thermochemical materials (TCM). Thermal diffusivity a(T) measurements of an organic PCM based on the LFA method indicated a good reproducibility for the solid phase but challenges due to liquid capillary ascension and low viscosity in the liquid phase of the sample. In contrast, thermal conductivity experiments via the THB method have shown their assets in the liquid phase but on the other hand unsatisfactory results in the solid phase due to varying contact conditions between foil sensor and sample. A numerical investigation of a LFA liquid sample holder system filled with pure water has shown the transient and spatial temperature field distribution inside the sample holder system and the influence on the measured half time depending on the detector focus.
Furthermore, measurement protocols to analyze the effective thermal diffusivity aeff (T) and effective thermal conductivity λeff(T) of powdery TCM candidates were developed. The results represent the strong dependency on the actual bulk density of the measured sample. Finally, a detailed investigation on of packed beds consisting of a Yttria-stabilized zirconia powder with different particle diameters based on the LFA, THB and HFM method were performed and compared. The LFA results indicate a significant relation between the aeff (T) and the used gas conditions. Under ambient conditions, the HFM and THB method indicate comparable λeff (T) data while LFA showed significant higher values. Considerations about a non-uniform distribution of the powder inside the LFA sample holder system led to the assumption, that the evaluated bulk densities are not correct and also plane-parallelism is not given, which is a requirement for accurate LFA measurements.
Professor at Harvard School of Engineering
David R. Clarke is the inaugural holder of the Extended Tarr Family Professor of Materials in the Harvard School of Engineering and Applied Sciences. He holds a PhD in Physics from the University of Cambridge, a B.Sc. in Applied Sciences from Sussex University and was awarded a ScD from the University of Cambridge.
A member of the National Academy of Engineering since 1999, he is also a Fellow of both the American Physical Society and the American Ceramic Society, and received an Alexander von Humboldt Foundation Senior Scientist Award in 1993.
He shared the 2008 Japanese NIMS Award for Recent Breakthroughs in Materials Science for Energy and Environment, is a Distinguished Life Member of the American Ceramic Society and was recently listed as author of one of the 11 best papers in the 110 years of publications on ceramics and glasses.
His long-term interests in materials range from the fundamentals to the applied, from ceramics to metals to semiconductors and polymers. He has published over 450 papers in areas of materials ranging from thermal barrier coatings, to dielectric elastomers to fundamentals of oxidation to microelectronics reliability and the electrical and optical properties of ZnO and GaN.
At Harvard, he enjoys interacting with students at all levels, from teaching Freshman seminars on “Glass” and “Materials, Energy and Society”, graduate courses in composites and deformation of materials and the new undergraduate course in SEAS on “Fundamentals of Heat Transfer”, a required course for students studying Mechanical Engineering.
He will present “Thermal Radiation Effects in Materials.”
*The above biography was originally published on https://clarke.seas.harvard.edu/people/david-r-clarke
Materials Research Laboratory
David Cahill is the Grainger Distinguished Chair in Engineering, Professor of Materials Science and Engineering, and co-Director of the IBM-Illinois Discovery Accelerator Institute at the University of Illinois at Urbana-Champaign. He joined the faculty of the Department of Materials Science and Engineering at the U. Illinois after earning his Ph.D. in condensed matter physics from Cornell University and working as a postdoctoral research associate at the IBM Watson Research Center.
He served as department head from 2010 to 2018. His research program advances physical insights on thermal transport at the nanoscale; extremes of low and high thermal conductivity; the thermal conductivity of soft matter; the thermal science of magnetic materials; and the transport of heat and mass in battery materials.
Cahill received the 2018 Innovation in Materials Characterization Award of the Materials Research Society, the 2015 Touloukian Award of the American Society of Mechanical Engineers, and the Klemens Award from the International Conference on Phonon Scattering in Condensed Matter; and is a fellow of the MRS, the American Physical Society, the AAAS, and an elected member of the American Academy of Arts and Sciences.
He will present “Beam Deflection Methods and Their Application to Polymers and Fast Mapping of Thermal Conductivity and Interface Conductance.”
Thermophysics Research Manager
David is the Thermophysics Research Manager at Thermtest Inc. Over his five years with Thermtest, he has worked with every transient and steady-state measurement technique offered. He spends his time making improvements to the measurement platform, from better data analysis tools and upgraded calculation algorithms to the integration of whole new methods using transient sensors.
He will present “Measurement of Layered Samples Using the Transient Plane Source” and host a workshop on “Thermoreflectance Methods”.
Vice President
PCM with reflective airspace
Abstract:
The energy savings from use of a phase change material (PCM) depends on several factors including the positioning of the PCM between the exterior and interior air spaces. In the case of vertical heat flow across a reflective air space, the most favorable distribution of thermal resistances changes periodically to provide the discharge of energy in the desired direction. The PCM charging and discharging processes depend on the thermal resistance of adjacent air spaces. For vertical heat flow, the thermal resistance of an adjacent enclosed reflective air space changes with many factors including, heat flow direction through the air space, temperature difference across the air space, mean temperature of the air space, and the effective emittance. This forms a natural switch and the heat flow direction changes can improve and/or optimize the heat flow characteristics in the building element. This paper will include a numerical evaluation of the annual performance of a PCM application with an adjacent enclosed reflective air space.
Thermal diffusivity and conductivity of a flexible thermal protection system (FTPS)
Abstract:
A flexible thermal protection system (FTPS) is needed to enable the use of deployable and inflatable hypersonic decelerators on aerocapture, entry, descent, and landing missions. An ESA technology development study was completed to define an FTPS that may be integrated with a Mars-entry inflatable hypersonic decelerator. The FTPS consists of three functional layers: (i) a protective outer layer, resistant to high heat flux; (ii) an insulation layer to delay the entry heat pulse; and (iii) a gas barrier layer to prevent hot gases/decomposition products from damaging the underlying structure. The individual materials must comply with a series of requirements, e.g., thermophysical and – mechanical properties, flexibility, handling, and manufacturability. Insulation materials with hightemperature performance, flexibility and low thermal conductivity were selected and characterized.
This work reports measurements of thermal diffusivity and conductivity of selected individual layer materials as well as heat transfer through layered stacks. The basic measurements were performed with classical laboratory means e.g., laser-flash, DSC, or thermogravimetry. The fabric and felt structure, as well as the low thermal conductivity of these materials posed some measurement challenges.
Additionally, thermal conductance tests on 120 mm x 120 mm stacks, instrumented with thermocouples between the individual layers, were performed by applying a graphite crucible containing solidifying copper at one surface. The obtained thermophysical data was incorporated in a numerical model to describe the temperature development in the FTPS during atmospheric entry, which in turn was tested by plasma arc-jet testing.
Research Scientist
Dr. Hsin Wang is a distinguished scientist with expertise in the thermal transport properties of materials, energy conversion materials, and energy storage materials. He has also conducted extensive research on thermal and electronic transport study of irradiated materials.
Dr. Wang has been a subject matter expert (SMB) at NASA/DOE radioisotope power system (RPS) program NextGen program and member of the review board of eMMRTG. He has served as the Annex VIII leader on thermoelectric and thermal management materials at the International Energy Agency (IEA) advanced materials for transportation (AMT) since 2010. He was the chairman of ITCC board of directors from 2007-2011, ITCC Fellow and a current BOD member. He hosted ITCC23/ITES15 in Knoxville, TN in 2003 and International Thermoelectric Conference (ICT) in Nashville in 2014. He was the board member of the International Thermoelectric Society (ITS) from 2012-2019.
He will present “Thermal Conductivity of Materials in the Radioisotope Thermoelectric Generators (RTGs)”
Research Scientist
Method for determination of thermal conductivity of open and closed cell materials at cryogenic temperatures
Abstract:
Measurement of the thermal conductivity of open and closed cell materials in a non-vacuum environment at cryogenic temperatures requires the application of a suitable cryogen. In the temperature range below the boiling point of liquid nitrogen, usage of the noble gas helium having the lowest boiling point among all elements, represents a challenge. Because helium has a small molar mass of approximately 4 g/mol in comparison to approximately 28 g/mol for nitrogen gas, gaseous helium effuses almost 3 times faster through microscopic pores according to Graham’s law. Furthermore, gaseous helium has a significantly higher thermal conductivity at atmospheric pressure than nitrogen by an average factor of 7. This appears to result in a higher apparent thermal conductivity of the open and closed cell material.
The ASTM Standard Test Method for steady-state heat flux measurements and thermal transmission properties by means of the guarded-hot-plate apparatus was used to measure the thermal conductivity of thermally insulating cellular glass at cryogenic temperatures. Measurements were performed in helium as well as nitrogen atmospheres in the upper temperature range allowing an offset value, caused by the increased heat flow through helium, to be determined. The offset value was used to correct the thermal conductivity values obtained at lower temperatures in helium atmosphere.
Engineer
Investigations for experimental parameters of thermal conductivity measurements of expanded polystyrene boards using a heat flow meter and transient plane source apparatuses
Abstract:
The need for requiring building envelopes with high performance is continuously increasing with demands of energy efficiency and energy conservation in residential building applications. The thermal performance of a building envelope depends on thermal properties of its constituent materials including specific heat capacity and thermal conductivity. Among commercial instruments, both heat flow meter (HFM) and transient plane source (TPS) instruments can provide these thermal data using a relatively bulky specimen compared to differential scanning calorimeter (DSC).
Since two instruments measure thermal properties in different thermal states, assessing parameters that influence on the measured data is important in comparing the results. Furthermore, compared to HFM, TPS can be deployed in field environments as well as lab environments due to its sensor size. Considering a more complicated building envelope with thermal storage capability (e.g., phase change material) and multi-layers, understanding the role of the individual layers will be improved by correlating the relation between two instruments.
In this study, we ran 24 full factorial experiments to measure thermal conductivities of expanded polystyrene (EPS) boards with different densities, surface roughnesses, and temperatures using HFM and TPS instruments. The thermal conductivity data of EPS boards are statistically analyzed to obtain a ranked list of the importance of the factors and estimates of the effect sizes of each factors on the thermal conductivity measurements. The summary of the results is presented in the conference.
Co-founder & CEO
John Gaskins is co-founder and CEO of Laser Thermal. After nearly two decades of research at the University of Virginia in nanoscale property measurements, John now leads Laser Thermal in its pursuit to bring accessible and high-throughput thermal metrology tools to industry. In addition to leading Laser Thermal, he serves on the board of trustees for GENEDGE, Virginia’s member of the NIST MEP network, which serves manufacturers across the Commonwealth. He lives in Charlottesville with his wife and two children.
*This biography was originally published on https://laserthermal.com/leadership-team/
Research Physicist
Dr. Joshua Martin is an expert in thermal and electrical transport measurements and instrumentation, focusing on semiconductors and energy materials. His research aims to improve measurement methods, instrumentation, and reference materials for microelectronics and energy conversion applications.
Dr. Martin is well-known for his work in thermoelectric materials used in waste heat recovery and solid-state refrigeration. He has designed and constructed a number of scientific instruments that characterize fundamental properties of bulk and thin film materials with improved measurement speed, accuracy, and reliability. These instruments allowed his team to devise new metrologies, protocols, and models to correct previously unknown or long-ignored sources of errors, resulting in a series of protocol papers describing best measurement practices.
His contributions include developing two Standard Reference Materials for instrument validation, standardizing measurement protocols, and both leading and participating in several international interlaboratory studies on thermal and electrical transport properties. Dr. Martin has received several awards for his work, including the 2021 Department of Commerce Silver Medal Award and the 2014 Department of Commerce Bronze Medal Award.
Dr. Martin’s expertise will provide valuable insights into advancing measurement science for semiconductors and energy conversion technologies at the ITCC.
He will present Development of Thermal Conductivity Reference Materials and host the Thermoreflectance Instrumentation and Methods Workshop.
Research Scientist
Dr. Lucas Lindsay received a BS degree in physics from the College of Charleston in 2004. He did his PhD work on theoretical thermal transport in carbon nanostructures at Boston College and received his PhD in 2010. Following this he taught physics for two years at Christopher Newport University, then spent three years as a National Research Council Postdoctoral Fellow at the U.S. Naval Research Laboratory in Washington, D.C. He has been a research scientist in the Materials Science and Technology Division at Oak Ridge National Laboratory since 2014. He received the Department of Energy Early Career Award in 2019. His general research area is the theoretical description of vibrational and transport properties of condensed matter.
He will present Unveiling the Theory of Thermal Conductivity: Insights into Phonons and Heat Transfer Mechanisms.
Study of heat conduction in human skin irradiated with a dedicated laser for heating gold nanoparticles for cancer photothermoablation
Abstract:
The primary purpose of this study is to evaluate the process of heat conduction in skin subjected to photothermoablation in a customized chamber measured with a thermal imaging camera. Investigation of the effect of gold nanoparticles on the skin surface and their laser irradiation on the conditions of heat flow into the skin will be preliminarily determined by determining temperature-time curves. Both an experimental rig and Computational Fluid Dynamics (CFD) numerical calculations are used to verify the results. CFD uses mass, momentum and energy balances; however, in the present issue, the determination of the temperature field in the solid remains crucial in the first estimation of the results.
Tissue samples (medical waste after procedures) after gold application are transferred to the laser laboratory for irradiation with an electromagnetic energy source of about 1 W. During the study, spherical gold nanoparticles will be used, which, using different laser wavelengths – from visible light to short-wave infrared region (SWIR), will serve as a source for converting electromagnetic energy into heat.
Analyses of heat transfer over time are conducted using thermal imaging cameras with recording of the temperature change on the heated surface. Selected results of the measurement campaign will also be analysed using CFD-type tools to indicate the possibility of determining the depth and size of the heated area. The experimental and numerical results will be confronted with the literature on an ongoing basis. The present research results will be used in the future to determine the power, wavelength, heating time in terms of optimizing the process of photothermoablation of tumors.
Ballistic Thermal Transport in TiN/TiC Multilayers due to Interfacial Elastic Modulus Enhancement
Abstract:
The scale of microelectronics is gradually reducing towards dimensions comparable with the electron mean free path. Since there is a need to dissipate ever increasing amounts of waste heat in microelectronic applications the increased device and interface density is highly undesirable. Thus, the approach of engineering materials with high densities of interfaces to achieve desirable thermal conductivity solids requires a fundamental understanding.
In this work, we report on the thermal conductivity of a series of crystalline multilayers composed of alternating layers of titanium nitride and titanium carbide with varying interface densities. We deposit titanium nitride and titanium carbide superlattice films on MgO(001) by reactive magnetron sputtering in an ultra-high vacuum chamber. The alternating nitride carbide layers are formed using reactive mixtures of Ar/N and Ar/CH4, respectively. The 1 um thick samples are deposited at 1100 °C with alternating layer thicknesses between 1.5 and 15 nm. We directly measure the thermal conductivity of these films via the time-domain thermoreflectance technique. We find that the thermal conductivity increases with an increasing interface density indicating that the heat carriers are scattering less in the interfaces of the multilayers.
This finding contradicts the traditional theory and conventional understanding. The role of interfacial nonidealities and disorder on thermal transport across interfaces is traditionally assumed to add resistance to heat transfer. The increase in thermal conductivity could be related to their increase in their elastic modulus which was measured by picosecond acoustic and nanoindentation techniques. The increase in interface density leads to a monotonically increasing elastic moduli imply a high quality of interface formation which usually results in a higher thermal conductivity. Our results demonstrate a path toward engineering thermal conductivity, thus providing a novel approach to dissipate the ever-increasing amounts of waste heat in microelectronic devices and alleviate the concern for the continuation of Moore’s law.
Characterization of Thermal and Mechanical Properties of Plasma-Based Aluminum Fluoride Layers
Abstract:
Aluminum is highly valued in UV optics for its ability to reflect wavelengths as short as 90 nm effectively. However, its effectiveness as a reflector is compromised by a rapidly forming native oxide layer. To mitigate this issue, fluorine-containing layers, which inhibit oxidation and maintain high transmission rates, have been applied. Additionally, aluminum fluoride layers serve as effective barrier coatings in advanced Li-ion battery designs, preventing common failures such as significant temperature increases and thermal runaway. Despite these applications, the thermal and mechanical properties of aluminum fluoride thin films have not been thoroughly reported. To explore these properties, we employed plasma-generated aluminum fluoride passivation layers of varying thicknesses. Our measurements reveal that both the elastic modulus and thermal conductivity of the fluorinated layers increase with thickness. This variation suggests a thickness-dependent chemical composition, as evidenced by EDS/EDX spectra showing that thinner layers contain a higher proportion of aluminum and less fluorine compared to thicker layers, thus explaining the observed variations in modulus.
Realizing the low thermal conductivity of SnS by utilizing the phonon liquid-like behavior of Cu2Se
Abstract:
SnS is a highly promising multilayer chalcogenide material that shows great potential for thermoelectric applications. We use a simple hydrothermal route to synthesize SnS/Cu2Se (1%, 3%, 5%, and 7%) composites. SnS has a high Seebeck coefficient but lacks good electrical properties, so the introduction of Cu2Se to the SnS matrix can be a potential solution for the overall improvement of the composite. The addition of Cu2Se has resulted in the suppression of intrinsic thermal conductivity of SnS from 0.891 W/mK to 0.447 W/mK for SnS/Cu2Se 5% at 753 K. The specific heat capacity, as well as diffusivity, show a monotonic trend with respect to temperature. Increasing the Cu2Se% in the matrix has led to a decrease in the crystallite size.
While the dislocation density and microstrain showed an increasing trend. We have analyzed different physical and microstructural factors influencing thermal conductivity using numerical techniques. Physical factors like the distribution of Cu2Se, temperature, and pressure used for pelletizing, volume fraction, and inherent material properties are analyzed using an effective thermal conductivity approach, and the interfacial thermal conductivity is analyzed by the Hasselman-Johnson model. We also analyze microstructural factors, like dislocations, stacking faults, and point defects. The phonon relaxation time of each mode of vibration is also calculated by utilizing Raman spectroscopy. All these factors play crucial roles in the reduction of almost 50% in the thermal conductivity of the SnS/Cu2Se samples.
Faculty of Mechanical Engineering and Ship Technology
Theoretical investigations of the photothermal effect and energy conversion for metallic nanostructures deposited on insulated materials
Abstract:
Photothermal effect in metallic nanostructures has been extensively studied for a dozen years due their high biocompatibility and the effective energy conversion rate. Moreover, the immediate temperature increase, which occurs as a result of the illumination, could be applied in the biophysical systems where germs or tumors are to be completely inactivated or overheated. However, there is a low number lack of theoretical methods that could predict the temperature increase and the energy conversion rate, and yet assist in water purification station or clinical trials. This work aims to compare experiments with three different theoretical models, which have been developed and adjusted by authors.
The first theory includes the Rayleigh-Drude approximation within size and shape effects described by optical cross-sections, whereas the second model assumes the efficiency of the energy conversion measured by a laser-power meter. On the other hand, the third approach considers the combined analytical solutions for unsteady heat transfer and the nanofluidic equations determining the effective thermal diffusivity. All models are tested and examined using the platforms where cetyltrimethylammonium bromide (CTAB)-stabilized gold nanorods have been uniformly deposited on a thin 0.4-inch round sheet made of optical borosilicate glass. The platforms are subsequently subjected to 0.5-W visible- and infrared-range laser illumination. The obtained results indicate that the maximum temperature from experiments reaches 𝑇𝑚𝑎𝑥=121.0C o (249.8F o) in approximately ten seconds and remains constant for the rest of the illumination time. As long as each model provides a satisfactory trend over time, the first and the second theories exhibit the best agreement with experimental values (𝑇1=118.9C o (246.0F o) and 𝑇2=120.1C o (248.2F o)), and outperform the third model as respectively overestimated at the 25% level.
Graduate Student Researcher
Thermal Transport in Materials with Dynamic Conformational Disorder
Abstract:
Alkyl chains that undergo phase transitions between ordered and dynamically disordered states have been the centerpoint of numerous thermal energy applications, notably solid-state cooling through barocaloric effects. Understanding how heat flows along these chains can offer valuable insights for device engineering and efficiency. In this talk, I will discuss thermal transport in layered crystals whose alkyl chains undergo sharp order–disorder transitions, including hybrid perovskites and organic salts. As these materials offer tunable interchain chemistries, we measure the thermal conductivities of systematically varied structures through frequency-domain thermoreflectance (FDTR) to assess the role of non-covalent interactions and chain confinement. Quasielastic and inelastic neutron scattering measurements further enable us to understand how conformational disorder influences the type of thermal carriers and the amount of heat they carry. Our results demonstrate a molecular-level picture of thermal transport in these materials and suggest the critical structural features that dictate heat conduction.
Postdoctoral Research Associate
Thermal and Optical Properties of Rare Earth Oxides for Thermal Barrier Coatings
Abstract:
Rare earth oxides (REOs) show promising thermal properties required of next-generation thermal barrier coatings (TBCs) for ultrahigh temperature applications (1500 K+). TBCs mitigate conductive heating between hot components by reducing thermal conductivity through increased phonon-phonon scattering. New research aims to explore the fundamental mechanisms for this reduction and explore other properties of interest such as melting temperature and emissivity.
In this work, we perform a series of thermal and optical studies via pump-probe thermoreflectance, laser radiometry, and spectroscopic ellipsometry to elucidate the temperature-dependent thermal properties of REOs. With novel laser-based metrology, thermal conductivities, melting temperatures and emissivities of ceramics over 2000 K can be measured nondestructively. Understanding these trends is of utmost importance in choosing REOs that can endure cycling to operating temperatures.
Additionally, through ellipsometry, the lifetimes of optical phonons can be understood. Anharmonic scattering dominates thermal transport at high temperatures so measuring lifetimes with changing temperatures is important to understand fundamental energy transport in REOs. By investigating pertinent physical scattering mechanisms at relevant temperatures, we deconvolute key design considerations for next-generation TBCs.
Graduate Research Assistant
Exploring Thermal Transport in Liquid Metal and Eutectic Gallium-Indium Alloys: Implications for Flexible Electronics
Abstract:
Liquid metal and eutectic gallium-indium (EGaIn) alloys represent a promising avenue in the realm of next-generation electronic devices and wearable electronics, owing to their notable advantages such as flexibility, stretchability, and compatibility with unconventional substrates. Leveraging the combined thermal and electrical properties of these materials opens up avenues for novel applications, including flexible sensors, stretchable circuits, and wearable energy harvesters. Given that the efficiency and reliability of electronic devices crucially depend on effective heat dissipation into heat sinks, a thorough understanding of the thermal conductivity of liquid metal, particularly as influenced by processing parameters, becomes imperative for achieving optimized performance.
Traditionally, the Wiedemann-Franz (WF) Law, incorporating a constant Lorenz number (L0 = 2.45 × 10−8 WΩ K−2), has been utilized for determining the thermal conductivity of metallic systems. However, recent scrutiny has cast doubt on the applicability of the Sommerfeld value of the Lorenz number, particularly in thin metallic interconnects and length scales pertinent to contemporary technology. Therefore, a systematic investigation into the thermal conductivity of eutectic gallium-indium Ga0.858In0.142 (14.2 wt. % In), henceforth referred to as EGaIn, employing methods not reliant on electrical resistivity, assumes significance both technologically and scientifically. Moreover, the impact of processing history on the formation and growth of the surface oxide layer of liquid metal and its subsequent effects on thermal boundary resistance remain unexplored territories.
In this study, we present direct measurements of the thermal conductivity of EGaIn utilizing the laser-based pump-probe technique, specifically time-domain thermoreflectance (TDTR). Complementary to these measurements, we infer the electrical resistivity of EGaIn from existing literature, thereby verifying the validity of employing the constant Lorenz number in the WF Law to predict the thermal conductivity of EGaIn. Furthermore, by systematically characterizing the thermal boundary conductance of liquid metal in response to cycling and processing variations, we provide invaluable insights into the intricate interplay between processing conditions, surface oxidation, and thermal transport properties.
Our findings not only contribute to a deeper understanding of the thermal transport characteristics of liquid metal and EGaIn alloys but also inform the refinement of theoretical frameworks such as the WF Law for predicting the behavior of these materials. Moreover, elucidating the influence of processing history on thermal boundary resistance sheds light on potential strategies for optimizing heat dissipation in electronic devices utilizing liquid metal components. Overall, this work underscores the importance of interdisciplinary approaches in advancing the field of thermal management in flexible electronics and engineering for emerging electronic applications.
Research Intern
Investigation of porous metal foam enhanced PCM-based BTMS for CubeSat applications
Abstract:
CubeSats are nanosatellites of standard sizes and form factor. Due to their many advantages, such as low development and launch costs, there has been a surge in the number of CubeSats being launched yearly. However, the CubeSat form factor comes with its own disadvantages, one of which is the high heat dissipation in a small volume, leading to the need for a good thermal control system. Due to the limited power availability in CubeSats, passive thermal control methods are generally preferred. One such passive thermal control method is Phase Change Materials (PCM).
This paper studies the application of a PCM-based Battery Thermal Management System (BTMS) for satellites of the CubeSat form factor. Since weight is a constraint in all space missions, especially in CubeSats, efforts are made towards minimising the weight of the BTMS while maintaining the thermal performance. To this extent, the PCM is embedded in porous metallic foam and its performance is examined. The metallic porous medium not only reduces the weight of the BTMS but also enhances the thermal conductivity and uniformity of heat distribution within the PCM. Numerical simulations are performed to analyse the battery temperatures in orbit with and without the proposed BTMS.
Senior Research Chemist
Thermophysical properties of fluids – care, collecting, and connecting
Abstract:
Fluids in modern technology are being taxed to perform in applications with delicate balances of viscosity, stability, heat transfer, and system protection. Based on the “three-C’s” of care, collecting, & connecting, this talk will explore the arena of understanding lubricant, non-aqueous fluids, combining thermal, rheological and thermophysical analysis techniques. The fluids discussed in this talk encompass a wide range of applications, including coolants, heat transfer agents, and various petroleum-based packages. Working with fluids that naturally exhibit a relatively narrow range of stability and thermophysical properties requires care. Which techniques should be used? What are the characteristics and limitations of each fluid? Such a narrow range of values requires a large volume of samples for a deeper understanding, therefore collecting this extensive data requires efficiency and a high level of checks and balances. How do we know we have the right answer? How much variation do we really see? “Connecting” is how we use this knowledge to enable communications with customers and project leaders. What matters most? What alterations can be made? Educating them of the holistic view and the possibilities drives future successes.
Material Relocation Test Study of Pellet to Cladding Interaction in Fast Reactor Design
Abstract:
During Pellet to Cladding Interaction phenomenon, the confirmed material relocation due to thermal melting and thermal diffusion is studied based on ASTM E793, ASTM E2585 and ASTM E1461. These kinetic parameters of the PCI can be established into the fuel center-line melting criterion for assuring that the axial or radial relocation of molten fuel would not be allowed to contact with the cladding in Fast Reactor design.