Thermal Conductivity Of Films Research Articles

Enhanced Thermal Conductivity of All-Organic Aramid Nanofiber Films via Interfacial Coupling Reaction

Enhanced Thermal Conductivity of All-Organic Aramid Nanofiber Films via Interfacial Coupling Reaction

Ordered Alignment of Liquid Crystalline Graphene Fluoride for Significantly Enhancing Thermal Conductivities of Liquid Crystalline Polyimide Composite Films

The low thermal conductivity coefficient (λ) of polyimide (PI) films are limiting their application in high-power electronic equipment, and the disordered alignment of fillers discourage efficient improvement of λ for PI-based composite films. Herein, polyethylene glycol trimethylnonyl ether is used to perform liquid crystalline modification on graphene fluoride (LC-GeF) to achieve ordered alignment. Intrinsically thermally conductive liquid crystalline PI (LC-PI) matrix is utilized to fabricate thermally conductive LC-GeF/LC-PI composite films. In-plane λ (λ∥) and through-plane λ (λ⊥) of 15 wt % LC-GeF/LC-PI composite films reach 4.21 and 0.63 W/(m·K), 446.8% and 320.0% higher than λ∥ (0.77 W/(m·K)) and λ⊥ (0.15 W/(m·K)) of normal PI films, 99.5% and 96.9% higher than λ∥ (2.11 W/(m·K)) and λ⊥ (0.32 W/(m·K)) of LC-PI films, also higher than 15 wt % GeF/LC-PI composite films. Additionally, LC-GeF/LC-PI composite films possess more excellent insulating, mechanical, and thermal properties than GeF/LC-PI composite films.

Fabrication of light‐weight ultrahigh molecular weight polyethylene films with hybrid porous structure and the thermal insulation properties

AbstractAccording to the infrared stealth mechanism, controlling the surface temperature of objects can effectively hide the infrared radiation and resist the infrared detection. In this paper, a high infrared transparent polymer ultrahigh molecular weight polyethylene (UHMWPE) is selected as the matrix of a thermal insulation material. UHMWPE porous films with high porosity and hybrid pore structure are obtained through the thermal induced phase separation combining with particle leaching method. The film structures with micropores and macropores are adjusted through the variation of the mass ratio of UHMWPE/liquid paraffin, the dosage and the particle size of NaCl. The thermal conductivity of the UHMWPE film is as low as 0.034 W/(m K), while the density is only 54.4 mg/cm3. The classical Maxwell‐Eucken model is used to discuss the relationship between the pore structure and the thermal conductivity of the films. It is determined that the hybrid porous structure can reduce heat conduction and gas–solid coupling effect simultaneously, thus the thermal conductivity is significantly reduced. Moreover, the porous films exhibited remarkable flexibility and hydrophobicity. Based on these properties, the porous films are highly promising in the field of thermal insulation protection and infrared stealth.

Thermal conductivity and mechanical durability of graphene composite films containing polymer-filled connected multilayer graphene patterns

Due to its high thermal conductivity, graphene has received much attention as a thermal interface material (TIM) for dissipating heat, which would otherwise be accumulated in heat sources, to heatsinks. However, the weak interlayer force induces tearing of graphene under repeated deformation; hence, the application of graphene as a TIM in the manufacturing of flexible electronics has been limited. To overcome this hurdle, the graphene composite (GC) films, in which thermoplastic polymers were infiltrated into connected multilayer graphene (MLG) patterns, were fabricated in this study. While the connected MLG patterns attained high in-plane thermal conductivity (κx), the polymers prevented tearing of the graphene. To investigate the effect of the graphene content on the κx of the GC films, the area of MLG patterns was carefully adjusted by coating a graphene solution through metal masks with various opening sizes. The κx of the GC-4 film was calculated as 53 W/m·K, which was slightly changed after 10,000 folding test cycles with a 1.5-mm bending radius.

Calculated Lattice Thermal Conductivity of Magnetite Thin Films based on Modified Callaway Model

Thermal conductivity is an important parameter for semiconductor materials used in the nanoscale applications. In this study, the lattice thermal conductivity (LTC) of magnetite thin films was simulated by Modified Callaway Model. To fit the experimental data, some quantities, such as mean bond length, the lattice constant, and volume per atom were calculated. Also, the model is based on some other quantities, such as gruneisen parameter, electron concentration, and surface roughness that were found through fitting theoretical with experimental LTC. As a result, this model could work comparably well in all sizes, and the relationship between the fitting parameters and the thickness of the magnetite films was estimated.

Dimension Effects on Thermal Conductivity of Graphene Films Revealed by Experimentally Calibrated Multiscale Modeling

Dimension Effects on Thermal Conductivity of Graphene Films Revealed by Experimentally Calibrated Multiscale Modeling

Anomalous Thermal Conductivity in Amorphous Niobium Pentoxide Thin Films: A Correlation Study between Structure and Thermal Properties

Anomalous Thermal Conductivity in Amorphous Niobium Pentoxide Thin Films: A Correlation Study between Structure and Thermal Properties

О порогах плавления системы «пленка - подложка» при облучении низкоэнергетическим сильноточным электронным пучком

The effect of film material thermal conductivity on the melting threshold of the film-substrate system depending on the film thickness during a low-energy high-current electron beam (LEHCEB) irradiation was analyzed based on the numerical solution of the one-dimensional unsteady heat equation with a volumetric thermal source. Experimentally obtained oscillograms of the beam current at the collector and the accelerating voltage were used to simulate the heating source. Numerical variations of the film thermal conductivity were carried out within a wide range, overlapping the entire range for real materials. The dependence of the melting threshold of a homogeneous material on thermal conductivity was determined. The general regularities of the behavior of film and substrate melting thresholds depending on the film thickness were also established.

Simultaneous Evaluation of Heat Capacity and In-plane Thermal Conductivity of Nanocrystalline Diamond Thin Films

ABSTRACT As wide bandgap electronic devices have continued to advance in both size reduction and power handling capabilities, heat dissipation has become a significant concern. To mitigate this, chemical vapor deposited (CVD) diamond has been demonstrated as an effective solution for thermal management of these devices by directly growing onto the transistor substrate. A key aspect of power and radio frequency (RF) electronic devices involves transient switching behavior, which highlights the importance of understanding the temperature dependence of a material’s heat capacity and thermal conductivity when modeling and predicting a devices electro-thermal response. Due to the complicated microstructure near the interface between CVD diamond and electronic material, it is difficult to measure both properties simultaneously. In this work, we use time-domain thermoreflectance (TDTR) to simultaneously measure the in-plane thermal conductivity and heat capacity of a 1-µm-thick CVD diamond film via multi-frequency analysis. We obtain temperature dependent thermal properties by using the pump beam to heat the sample according to increasing power. This mitigates the need for a more complicated setup using a thermal stage but has limited upper temperature boundaries based on the sample geometry and thermal properties. The results show that the in-plane thermal conductivity varied slightly with an average of 103 W/m-K over a temperature range of 302–327 K, while the specific heat capacity has a strong temperature dependence over the same range and compares well with heat capacity data of natural diamond in literature.

Atomistic calculations of thermal conductivity in films made from graphene sheets for electron emitter applications

Simulations for the thermal conductivity of carbon fibers (CFs) are carried out based on a molecular dynamics (MD) approach. Our calculations are geared toward providing a general trend for thermal conductivity and its dependence on sample length and to probe the suitability of this material for high power applications from the thermal management standpoint. Since abundant data are not available for carbon fibers, calculations are first carried out in silicon to validate the predictions. The MD results yield a bulk thermal conductivity of 148 W m−1 K−1 for silicon in good agreement with published reports. However, for CF, a much lower bulk value of ∼14 W m−1 K−1 is predicted. This suggests that thermal management would likely be an issue for this material and that CF emitters of lengths below 2 µm should be avoided. The predicted increases in thermal conductivity with temperature may help alleviate the issue to a minor degree. Carbon nanotubes would likely be a better alternative in this context of field emitter arrays.

Controlled Lattice Thermal Conductivity of Transparent Conductive Oxide Thin Film via Localized Vibration of Doping Atoms.

Amorphization using impurity doping is a promising approach to improve the thermoelectric properties of tin-doped indium oxide (ITO) thin films. However, an abnormal phenomenon has been observed where an excessive concentration of doped atoms increases the lattice thermal conductivity (κl). To elucidate this paradox, we propose two hypotheses: (1) metal hydroxide formation due to the low bond enthalpy energy of O and metal atoms and (2) localized vibration due to excessive impurity doping. To verify these hypotheses, we doped ZnO and CeO2, which have low and high bond enthalpies with oxygen, respectively, into the ITO thin film. Regardless of the bond enthalpy energy, the κl values of the two thin films increased due to excessive doping. Fourier transform infrared spectroscopy was conducted to determine the metal hydroxide formation. There was no significant difference in wave absorbance originating from the OH stretching vibration. Therefore, the increase in κl due to the excessive doping was due to the formation of localized regions in the thin film. These results could be valuable for various applications using other transparent conductive oxides and guide the control of the properties of thin films.

Thermal Conductivity of β-Phase Ga2O3 and (AlxGa1-x)2O3 Heteroepitaxial Thin Films.

Heteroepitaxy of β-phase gallium oxide (β-Ga2O3) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of (2̅01)-oriented β-Ga2O3 heteroepitaxial thin films were investigated. Unintentionally doped β-Ga2O3 thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward ⟨112̅0⟩ via metal-organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the β-Ga2O3 thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the β-Ga2O3 films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick β-Ga2O3 thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye-Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of β-Ga2O3 films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the β-Ga2O3 films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the β-Ga2O3/sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown (2̅01)-oriented β-(AlxGa1-x)2O3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(AlxGa1-x)2O3 films exhibit lower thermal conductivities (2.8-4.7 W/m·K) than the β-Ga2O3 thin films. The dominance of the alloy disorder scattering in β-(AlxGa1-x)2O3 is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown β-phase Ga2O3 and (AlxGa1-x)2O3 thin films and lays the groundwork for the thermal modeling and design of β-Ga2O3 electronic and optoelectronic devices.

Effect of pH variation and annealing on covalently assembled nanodiamond films

This work examines the effect of using low-ionic strength zwitterionic buffer and post-deposition thermal annealing on the microstructure and thermal conductivity of continuous nanocrystalline diamond films that are deposited via the directed covalent assembly of detonation nanodiamonds. Variation of the zwitterionic buffer pH was found to tune the surface coverage, film thickness, thermal conductivity, and film morphology as quantified by apparent porosity and pore size distribution. The sequential annealing of these films up to 400 °C, showed the anticipated severance of amide bonds holding the nanodiamonds together, followed by the detrimental aggregation of the nanodiamonds to segregated islands, losing film continuity and increasing apparent porosity. The change in thermal conductivity with annealing was subjective to buffer pH, suggesting that the morphology changes associated with annealing may have a complex relationship with thermal conductivity. The thermal conductivity data were further analyzed using a phonon hopping model to quantify the degree of phonon movement across boundaries. Overall, the results demonstrate a way to achieving porous, low-cost nanocrystalline diamond thin films with tunable film morphology and thermal conductivity.

Temperature and Strain Effects in Micro-Raman Thermometry for Measuring In-Plane Thermal Conductivity of Thin Films

ABSTRACT Micro-Raman thermometry is an effective method for measuring thermal conductivity of thin films. It features noncontact and nondestructive probing and convenience of sample preparation. However, there is a concern of its accuracy when using the Raman peak shift as the temperature transducer since it responds to both temperature and strain upon optical heating. In this work, a series of detailed experiments are carried out to evaluate contributions to Raman signals from temperature only vs. from thermomechanical strain. It is shown that using proper calibration, contributions to Raman signals from temperature only and from thermomechanical strain can be decoupled and thermal conductivity can be evaluated correctly. These procedures are then applied to bismuth telluride thin films to illustrate measurement of thin film thermal conductivity.

A two-sensor 3ω-2ω method for thermal boundary resistance measurement

Thermal boundary resistance (TBR), which measures an interface's resistance to the thermal flow, is of critical importance among various areas, such as electronics cooling and thermoelectric materials. As for measuring TBR, electrical techniques are generally less sensitive compared to optical ones, but they are easily operable and compatible with the measurement of other electric properties; thus, it is highly desirable to develop electrical methods with higher accuracy and larger measurement range. Here, a two-sensor 3ω-2ω method with a novel experimental procedure design is proposed, which can well address those deficiencies in the conventional 3ω method. Two parallel metal sensors are fabricated, with one of them being wide and the other being narrow. The temperature changes of these two sensors are measured by detecting the 3ω and 2ω signals, respectively. The measurement includes three steps: (1) obtain thin film's thermal conductivity from the wide sensor's 3ω thermal response; (2) obtain substrate thermal conductivity from the narrow sensor's 2ω thermal response; and (3) derive an effective TBR from the narrow sensor's 3ω thermal response. Moreover, it is found the TBRs of metal/dielectric and dielectric/substrate interfaces are distinguishable due to the considerable difference between their contact areas, which enables us to separate these two TBRs by varying the contact area (heater's width). Then, our method is employed to probe the TBRs between the Al2O3 nanofilm and Si as well as SiC substrates at room temperature and good agreement with the previous measurements is achieved, verifying its feasibility. Our present scheme will be helpful for the experimental study of interfacial thermal transport.

Anisotropic thermal conductivity measurement of organic thin film with bidirectional 3ω method.

Organic thin film materials with molecular ordering are gaining attention as they exhibit semiconductor characteristics. When using them for electronics, the thermal management becomes important, where heat dissipation is directional owing to the anisotropic thermal conductivity arising from the molecular ordering. However, it is difficult to evaluate the anisotropy by simultaneously measuring in-plane and cross-plane thermal conductivities of the film on a substrate because the film is typically as thin as tens to hundreds of nanometers and its in-plane thermal conductivity is low. Here, we develop a novel bidirectional 3ω system that measures the anisotropic thermal conductivity of thin films by patterning two metal wires with different widths and preparing the films on top and extracting the in-plane and cross-plane thermal conductivities using the difference in their sensitivities to the metal-wire width. Using the developed system, the thermal conductivity of spin-coated poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with thickness of 70nm was successfully measured. The measured in-plane thermal conductivity of PEDOT:PSS film was as high as 2.9Wm-1K-1 presumably due to the high structural ordering, giving an anisotropy of 10. The calculations of measurement sensitivity to the film thickness and thermal conductivities suggest that the device can be applied to much thinner films by utilizing metal wires with a smaller width.

Thickness Dependence and Anisotropy of Capped Diamond Thermal Conductivity on Cooling of Pulse-Operated GaN HEMTs

A capped thin-film diamond heat spreader is modeled for the reinforcement of hotspot cooling in the application of pulse-operated GaN-based high-electron mobility transistors (HEMTs). To precisely evaluate the cooling performance, thickness dependence and anisotropy of diamond film thermal conductivity are considered. A 3-D transient thermal model based on the finite element method is developed to simulate the pulse behavior. The sharp temperature oscillation occurring in the periodic pulse mode from the microsecond to millisecond time scales introduces substantial difficulty and challenge for accurate modeling. To this end, a scale-down model mimic of a recently reported GaN-based amplifier with kilowatts peak power level is built to significantly reduce the computational time and increase the accuracy while maintaining crucial thermal characteristics. The thermal characteristics under periodic pulse mode are revealed and the dynamic steady-state peak junction temperature is reliably obtained. The impacts of thermal boundary resistance (TBR), substrate material, duty cycle, and pulse period on the performance of the diamond heat spreader have been scrutinized. For the GaN-on-SiC HEMTs working at 2.5% duty cycle, 200-μs pulse period, and 19.58 W/mm peak power density, a 2-μm-thick diamond heat spreader can reduce the dynamic steady-state peak junction temperature by 14.7%.

Simultaneous Exfoliation and Functionalization of Large-Size Boron Nitride Nanosheets for Reinforcing Thermal Conductivity of Polymer Film

Simultaneous Exfoliation and Functionalization of Large-Size Boron Nitride Nanosheets for Reinforcing Thermal Conductivity of Polymer Film

Determination on the Thermal Conductivity and Thermal Contact Resistance of Thin Composite Phase Change Films as a Thermal Interfacial Material

Determination on the Thermal Conductivity and Thermal Contact Resistance of Thin Composite Phase Change Films as a Thermal Interfacial Material

Електродугове напилення композиційних металополімерних покриттів

A method for forming composite electric arc coatings by using a modernized EM-14M spraying gun with a powder feed unit of free powder to a high-temperature heterophase jet during spraying is proposed. Samples of a metal-polymer composite coating of the composition steel Sv-08-G2S-O — polymer P-EP-219 were obtained. Experimentally established the necessary zone for the supply of polymer powder was to prevent its destruction in the high-temperature zone of the arc discharge and the optimal modes of deposition metal-polymer coatings: current 90…100 A, arc voltage 25 V, compressed air pressure 0,4…0,6 MPa, polymer powder consumption 25 g/min, spraying distance 100...120 mm. If these modes are observed, the conditions for the formation of a high-quality metal-polymer coating with a thickness of 0.5-0.8 mm with a maximum content of the polymer component of 40 %(vol.) are provided. A scanning electron microscope REMMA-102-02 was used to investigate the microstructure of the sprayed coatings. It has been established that the porosity of composite coatings is reduced from 13 % to 7 % in comparison with convention steel coatings. The phases were identified by determining their microhardness on cross sections with a load on the indenter of 50 g. It was found that the microhardness of the metal matrix is 1716 MPa; polymer component — 128 MPa. It is shown that the deposited coatings are characterized by the presence on their surface of a continuous polymer film with a thickness of 10 to 100 μm, which is formed as a result of the fact that the polymer solidifies later than the crystallization of metal particles. It has been experimentally confirmed that the thermal conductivity of metal-polymer coatings deposited from the SV-08G2S-O – P-EP-219 composition decreases by 46 % in comparison with the thermal conductivity of convention coatings from SV-08G2S-O wire. The proposed coatings are recommended to be used as anticorrosion and heat-insulating coatings on various structures due to the thin surface polymer film and low thermal conductivity.