3ω Method Research Articles

Thermal conduction across a boron nitride and SiO2 interface

The need for efficient heat removal and superior thermal conduction in nano/micro devices has triggered tremendous studies in low-dimensional materials with high thermal conductivity. Hexagonal boron nitride (h-BN) is believed to be one of the candidates for thermal management and heat dissipation due to its novel physical properties, i.e. as a thermal conductor and electrical insulator. Here we report the interfacial thermal resistance between few-layer h-BN and its SiO2 substrate using the differential 3ω method. The measured interfacial thermal resistance is around ~1.6 × 10−8 m2K W−1 for monolayer h-BN and ~3.4 × 10−8 m2K W−1 for 12.8 nm-thick h-BN in metal/h-BN/SiO2 interfaces. Our results suggest that the voids and gaps between the substrate and thick h-BN flakes limit the interfacial thermal conduction. This work provides a deeper understanding of utilizing h-BN flakes as a lateral heat spreader in electronic and optoelectronic nano/micro devices with further miniaturization and integration.

Thermal conductivity of Gd2Zr2O7 thin films at various temperatures by using the 3ω method

Recently, Gd2Zr2O7 has been investigated as a buffer layer of YBa2Cu3O7−x superconductor. Thermal properties of Gd2Zr2O7 below room temperature are not well known yet despite of its active studies. For the study of the thermal property at low temperature, the Gd2Zr2O7 films with various thicknesses are deposited on the Al2O3 substrate by using the RF magnetron sputtering. Thermal conductivities of Gd2Zr2O7 thin films are measured by using the 3 omega method from 80K to room temperature. We confirm the interfacial thermal resistance and its temperature dependence. The interfacial thermal resistance decreases with increasing temperature unlike the reported temperature dependence of the thermal conductivity. The importance of interfacial effect on the thermal conductivity is being emphasized at very low temperatures.

Thermal conductivity of bulk GaN grown by HVPE: Effect of Si doping

The thermal conductivity of bulk GaN grown by Hydride Phase Vapor Epitaxy with intentional Si doping was measured using the 3ω method. The effect of Si concentration ranging from 1.6 × 1016 to 7 × 1018 cm−3 on the thermal conductivity was studied over the temperature range of 295–470 K. The room temperature thermal conductivity was found to decrease with increasing Si doping from 245 to 210 W/m · K. Also, for each Si doped sample the thermal conductivity decreases with increasing temperature. The experimental data were analysed by a modified Callaway model and the contribution of different resistive phonon scattering process was examined. It was found that in n‐type GaN the phonon‐free‐electron scattering became an important resistive process that leads to a reduction of the thermal conductivity at high temperatures. At the highest free electron concentrations, electronic thermal conduction was found to play a role in addition to lattice thermal conduction and compete with the effects of phonon‐free‐electron scattering.

RETRACTED: Cross- and in-plane thermal conductivity of AlN thin films measured using differential 3-omega method

Thickness dependency and interfacial structure effects on thermal properties of AlN thin films were systematically investigated by characterizing cross-plane and in-plane thermal conductivities, crystal structures, chemical compositions, surface morphologies and interfacial structures using an extended differential 3ω method, X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy. AlN thin films with various thicknesses from 100 to 1000 nm were deposited on p-type doped silicon substrates using a radio frequency reactive magnetron sputtering process. Results revealed that both the cross- and in-plane thermal conductivities of the AlN thin films were significantly smaller than those of the AlN in a bulk form. The thermal conductivities of the AlN thin films were strongly dependent on the film thickness, in both the cross- and in-plane directions. Both the XRD and AFM results indicated that the grain size significantly affected the thermal conductivity of the films due to the scattering effects from the grain boundary.

Thermal characterization of natural and synthetic spider silks by both the 3ω and transient electrothermal methods

Thermal conductivity, thermal diffusivity, and volumetric heat capacity of three spider silks are measured in this paper as a benchmark for further studies. These silks include the major and minor ampullate silks of the Nephila clavipes spider, and a synthetic spider silk fiber made from recombinant dragline silk proteins purified from transgenic goats' milk. Two complementary measurement techniques are employed in the thermal characterization of these microscale single fibers for self-verification. One is the transient electrothermal technique (TET) and the other is the 3ω method. Experimental measurements indicate that thermal properties of the dragline silk are very close to those of the minor ampullate silk, whereas the ones for the synthetic silk are much lower due in part to its low crystallinity. The directly measured thermal conductivity, thermal diffusivity, and volumetric heat capacity of the major and minor ampullate silks are 1.2–1.26Wm−1K−1, 5.7–6×10−7m2s−1, and 2–2.17 MJm−3K−1, respectively. The thermal conductivity and thermal diffusivity of the as-spun synthetic silk are 0.24Wm−1K−1 and 1.6×10−7m2s−1 respectively. As part of this study, a detailed comparison of the TET and 3ω methods is provided showing the complementary nature of the techniques and illustrating the strengths and weaknesses of each.

Thermal characteristics and performance of Ag-water nanofluid: Application to natural circulation loops

The goal of this study is to investigate the thermal conductivity, viscosity and thermal performance in a single-phase natural circulation mini loop of Ag-water nanofluid which can be a potential working fluid for natural convective flat-plate solar collectors. The silver-water nanofluid with 5wt% concentration, which contains also polyvinylpyrrolidone (PVP) with 1.25wt%, was purchased. Then, the sample was diluted with de-ionized water to four different concentrations of 0.25, 0.5, 0.75 and 1wt%. Thermal conductivity and viscosity were measured by 3ω method and Brookfield rheometer, respectively. An effectiveness factor was used to define the thermal performance of Ag-water nanofluids for different inclination angles and heating powers. The results showed that nanofluid samples are thermally less conductive than the literature, at ambient temperature (23°C). The viscosity of nanofluid decreases significantly with increasing temperature and increases with increasing concentration. Our measurements appear to be more compatible with PVP solution results available in the literature. Effectiveness is enhanced up to 11% with 1wt% concentrated nanofluid compared to de-ionized water and the effectiveness of the mini loop indicates an enhancement with increase in inclination angle and particle concentration at whole applied power. According to obtained results, it is concluded that Ag-water nanofluid has a promising potential to be used in natural convective flat-plate solar collector.

Thermal Conductivity Measurement of Thermoelectric Thin Films by a Versatility-Enhanced 2ω Method

The 2ω method is a technique to measure the cross-plane thermal conductivity, κ, of a film sample based on sinusoidal Joule-heating of a metal film deposited on the sample surface and its thermoreflectance (TR) measurement of surface temperature cooling due to the heat dissipation. The 2ω method is being paid attention because it is more cost-effective and easier to use than the conventional time domain thermoreflectance (TDTR) method or the 3ω method. In some cases, however, it is difficult to apply the conventional 2ω method to the κ measurement of high thermal resistance films such as general thermoelectric films due to its non-linear TR signal response to (2ω)−0.5. Here, we present a 2ω method based on a versatile TR signal analysis which enables the κ measurement of high thermal resistance film more explicitly than the conventional analysis based on a linear TR signal response. This method determines explicitly the thermal conductivities of PbTe films and PbTe/GeS superlattices grown on BaF2(111) substrates by hot wall epitaxy: κ = 2.1 ± 0.13 Wm−1 K−1 and κ = 0.71 ± 0.05 Wm−1 K−1, respectively. Furthermore, a significant impact of PbTe film crystallinity on thermal conductivity is demonstrated by comparative measurements between polycrystalline PbTe film and epitaxial PbTe film grown on the BaF2(111) substrates. These results demonstrate that our method can be a powerful tool to measure the thermal conductivity of thermoelectric films.

Measurement Techniques for Thermal Conductivity and Interfacial Thermal Conductance of Bulk and Thin Film Materials

Thermal conductivity and interfacial thermal conductance play crucial roles in the design of engineering systems where temperature and thermal stress are of concerns. To date, a variety of measurement techniques are available for both bulk and thin film solid-state materials with a broad temperature range. For thermal characterization of bulk material, the steady-state method, transient hot-wire method, laser flash diffusivity method, and transient plane source (TPS) method are most used. For thin film measurement, the 3ω method and the transient thermoreflectance technique including both time-domain and frequency-domain analysis are widely employed. This work reviews several most commonly used measurement techniques. In general, it is a very challenging task to determine thermal conductivity and interfacial thermal conductance with less than 5% error. Selecting a specific measurement technique to characterize thermal properties needs to be based on: (1) knowledge on the sample whose thermophysical properties are to be determined, including the sample geometry and size, and the material preparation method; (2) understanding of fundamentals and procedures of the testing technique, for example, some techniques are limited to samples with specific geometries and some are limited to a specific range of thermophysical properties; and (3) understanding of the potential error sources which might affect the final results, for example, the convection and radiation heat losses.

Temperature-dependent specific heat of suspended platinum nanofilms at 80–380 K**Project supported by the National Natural Science Foundation of China (Grant Nos. 51327001 and 51636002), and partially supported by CREST, JST, and JSPS KAKENHI (Grant Nos. 16H04280, 26289047, 16K14174, and 16K06126).

Metallic nanofilms are important components of nanoscale electronic circuits and nanoscale sensors. The accurate characterization of the thermophysical properties of nanofilms is very important for nanoscience and nanotechnology. Currently, there is very little specific heat data for metallic nanofilms, and the existing measurements indicate distinct differences according to the nanofilm size. The present work reports the specific heats of 40-nm-thick suspended platinum nanofilms at 80–380 K and ∼5×10−4 Pa using the 3ω method. Over 80–380 K, the specific heats of the Pt nanofilms range from 166–304 J/(kg·K), which are 1.65–2.60 times the bulk values, indicating significant size effects. These results are useful for both scientific research in nanoscale thermophysics and evaluating the transient thermal response of nanoscale devices.

Thermal Conductivity of Alumina Films Prepared by Inclined Incidence

Background: Thin films produced by the oblique angle deposition (OAD) method are promising nanocolumns’ materials. Their specific properties depend on the self-shadowing effect and formation of columnar grains by OAD. It determines the coating compliance, and consequently its resistance to spallation, as well as its thermal conductivity. The aims of this paper are to introduce readers to discuss how thermal conductivity of thin films varies with inclined angle and temperature. Methods: Alumina thin films are fabricated by electron-beam evaporation with oblique angle deposition method. The thermal conductivity is measured by the 3ω method. The film thicknesses are measured by cross-sectional scanning electron microscopy. Results: The thermal conductivity (λf) of alumina thin films is dependent of film thickness at various inclined angles. While the λf of alumina thin films decreases with the increasing inclined angles at various film thicknesses. The λf of alumina thin films increases with the increasing temperature at various inclined angles. Conclusion: At the various inclined angles, the thermal conductivity of alumina thin films decreases with the increasing porosity. The cross sectional surface of the 1.1 μm thickness alumina thin film deposited at various inclined angles is the cause that the porosity increases with the increasing inclined angles. It increases with the increasing temperature. So the oblique angle deposition method is an effective way to control the thermal conductivity of thin films. Keywords: E-beam evaporation, oblique angle deposition method, thermal conductivity.

In-plane Thermal Conductivity Measurement of Conjugated Polymer Films by Membrane-based AC Calorimetry

We investigated the anisotropy in the thermal conductivities of π-conjugated polymer films of poly(3-hexylthiophene-2,5-diyl), poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene], poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), and poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos). It was found that the in-plane thermal conductivity of the films, measured by membrane-based ac calorimetry, was approximately two times higher than the through-plane one measured by the 3ω method. We also found that the anisotropy of the electronic contribution is not negligible for the PEDOT:Tos films.

Amorphous/epitaxial superlattice for thermoelectric application

An amorphous/epitaxial superlattice system is proposed for application to thermoelectric devices, and the superlattice based on a PbGeTeS system was prepared by the alternate deposition of PbS and GeTe using a hot wall epitaxy technique. The structure was analyzed by high-resolution transmission electron microscopy (HRTEM) and X-ray analysis, and it was found that the superlattice consists of an epitaxial PbTe-based layer and a GeS-based amorphous layer by the reconstruction of the constituents. A reduction in thermal conductivity due to the amorphous/epitaxial system was confirmed by a 2ω method. Electrical and thermoelectric properties were measured for the samples.

Thermal Boundary Conductance: A Materials Science Perspective

The thermal boundary conductance (TBC) of materials pairs in atomically intimate contact is reviewed as a practical guide for materials scientists. First, analytical and computational models of TBC are reviewed. Five measurement methods are then compared in terms of their sensitivity to TBC: the 3ω method, frequency- and time-domain thermoreflectance, the cut-bar method, and a composite effective thermal conductivity method. The heart of the review surveys 30 years of TBC measurements around room temperature, highlighting the materials science factors experimentally proven to influence TBC. These factors include the bulk dispersion relations, acoustic contrast, and interfacial chemistry and bonding. The measured TBCs are compared across a wide range of materials systems by using the maximum transmission limit, which with an attenuated transmission coefficient proves to be a good guideline for most clean, strongly bonded interfaces. Finally, opportunities for future research are discussed.

Thermal conductivity of biological cells at cellular level and correlation with disease state

This paper reports the thermal conductivity k of matched pair cell lines: two pairs of a normal and a cancer cell, one pair of a primary and metastatic cell. The 3ω method with a nanoscale thermal sensor was used to measure k at the single-cell level. To observe the difference in k between normal and cancer cells, the measurements were conducted for Hs 578Bst/Hs 578 T (human breast cells) and TE 353.Sk/TE 354.T (human skin cells). Then k of WM-115/WM-266-4, a primary and metastatic pair of human skin cell, was measured to find the effect of disease progression on k. The measured k data for normal and disease cell samples show statistically meaningful differences. In all cases, k decreased as the disease progressed. This work shows that thermal-analysis schemes, such as the 3ω method, have a potential to detect diseases at the cell level.

Scanning thermal microscopy based on a quartz tuning fork and a micro-thermocouple in active mode (2ω method).

A novel probe for scanning thermal microscope using a micro-thermocouple probe placed on a Quartz Tuning Fork (QTF) is presented. Instead of using an external deflection with a cantilever beam for contact detection, an original combination of piezoelectric resonator and thermal probe is employed. Due to a non-contact photothermal excitation principle, the high quality factor of the QTF allows the probe-to-surface contact detection. Topographic and thermal scanning images obtained on a specific sample points out the interest of our system as an alternative to cantilevered resistive probe systems which are the most spread.

Characterization and simulation of liquid phase exfoliated graphene-based films for heat spreading applications

This paper concerns the thermal properties of graphene-based films for heat spreading applications. Following liquid phase exfoliation (LPE) films were made by two different methods, vacuum filtration and drop coating. Temperature decreases of up to 6 °C and 4 °C were measured at a heat flux density of 1200 W/cm2 for the vacuum filtrated and drop coated films respectively. For the first time in this paper, three different methods were combined to evaluate and predict the thermal performance of such graphene-based films. Resistance thermometers were used to monitor the hotspot temperature decrease versus the Joule heat flow as a result of using graphene-based heat spreaders. The 3ω method was used to experimentally determine the in-plane and through-plane thermal conductivities of such films. A finite element model of the hotspot test structure was setup using the in-plane and through-plane thermal conductivities (110 and 0.25 W/mK, respectively) obtained from the 3ω measurements. Simulations were performed to predict the hotspot temperature decrease with excellent agreement obtained between all methods. The results indicate that the alignment and purity of the graphene-based films, as well as their thermal boundary resistance with respect to the chip, are key parameters when determining the thermal performance of graphene-based heat spreaders.

Effects of Graphene Nanopetal Outgrowths on Internal Thermal Interface Resistance in Composites.

Thermal resistance at the interface between fiber and matrix is often the determining factor influencing thermal transport in carbon fiber composites. Despite its significance, few experimental measurements of its magnitude have been performed to date. Here, a 3ω method is applied to measure the interfacial thermal resistance between individual carbon fibers and an epoxy matrix. The method incorporates bulk and interfacial regions to extract interfacial characteristics. Measured values indicate an average thermal interface resistance of 18 mm(2) K/W for an interface between bare fiber and epoxy, but the average value drops to 3 mm(2) K/W after a microwave plasma chemical vapor deposition of two-dimensional graphene nanopetals on the carbon fiber surface.

Long-term Room Temperature Instability in Thermal Conductivity of InGaZnO Thin Films

ABSTRACTThe cross-plane thermal conductivities of InGaZnO (IGZO) thin films in different morphologies were measured on three occasions within 19 months, using the 3ω method at room temperature 300 K. Amorphous (a-), semi-crystalline (semi-c-) and crystalline (c-) IGZO films were grown by pulsed laser deposition (PLD), followed by X-ray diffraction (XRD) for evaluation of film quality and crystallinity. Semi-c-IGZO shows the highest thermal conductivity, even higher than the most ordered crystal-like phase. After being stored in dry low-oxygen environment for months, a drastic decrease of semi-c-IGZO thermal conductivity was observed, while the thermal conductivity slightly reduced in c-IGZO and remained unchanged in a-IGZO. This change in thermal conductivity with storage time can be attributed to film structural relaxation and vacancy diffusion to grain boundaries.

Thermal conductivity study of micrometer-thick thermoelectric films by using three-omega methods

Thermal conductivity is a key parameter of thermoelectric (TE) films. However, experimental reports on thermal conductivity of TE films are very limited due to the challenge in practical measurement. In this work, we report the use of some three-omega (3ω) methods to study the thermal conductivity of micrometer-thick Bi2Te3 TE films prepared by pulsed electroplating. The measurement devices are fabricated using sputtered SiO2 as dielectric layer and Au lines as heaters. The differential method and the slope method are separately used to determine the cross-plane thermal conductivity of the films. The characterization methods are demonstrated to be feasible and reliable from the reasonable changes of the 3ω voltage with frequency and thickness and the consistent measurement results using these two methods. The cross-plane thermal conductivity of the electroplated film is found to decrease from 1.8 Wm−1K−1 to 1.0 Wm−1K−1 as the pulse potential increases from −100 mV to 50 mV, which is attributed to the refined microstructure of the films. In addition, the thermal conductivity anisotropy of the Bi2Te3 film is evaluated by using a two-wire 3ω method and the factors contributing to the measurement uncertainty are discussed.

Thermal Conductivity Measurement of Liquid-Quenched Higher Manganese Silicides

Higher manganese silicides (HMSs, MnSiγ, γ ∼ 1.75) show promise for use as low-cost and environmentally friendly thermoelectric materials. To reduce their thermal conductivity, we partially substituted the Mn site with heavy elements using liquid quenching. Fabricated samples possess a curly ribbon-shape with about a 10-μm thickness and 1-mm width, with high surface roughness. In this study, we determined the thermal conductivity of the curly-ribbon-shaped samples using two independent methods: the 3ω method with two heat flow models, and the steady-state method using a physical property measurement system (PPMS; Quantum Design). We succeeded in estimating the thermal conductivity at the temperature range of 100–200 K using the PPMS. The estimated thermal conductivity of non-doped HMSs shows a constant value without temperature dependence of 2.2 ± 0.8 W K−1m−1 at 100–200 K. The difference of thermal conductivities of W-doped and non-doped HMSs was not recognized within the measurement error.