Polystyrene (PS) thin films spin coated on either silicon or quartz substrates were prepared to investigate the thin film's thickness effects on both the heat transport and glass phase transition temperature of the PS. This characterisation has been achieved through a scanning thermal microscope setup (SThM) using doped silicon thermoresistive nanoprobe. Thermal conductance and thermomechanical analyses were performed. Our first results show that thermomechanical analysis measurement on ultrathin films on a substrate depends on the substrate thermal properties and confirm that the PS phase transition temperature is dependent on the interactions between PS ultrathin films and their respective substrates.

Thermal characterization of morphologically diverse copper phthalocyanine thin layers by Scanning Thermal Microscopy

High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (GnPs) and multiwall carbon nanotubes (MWCNTs) were fabricated using melt mixing followed by compression molding. The influences of size and weight ratio of both carbon-based nanofillers on the electrical, thermal, and mechanical properties of hybrid nanocomposites were evaluated. This study proves that the size and weight ratio of carbon-based nanofillers play a critical role in determining these properties. The optimum size and weight ratio of GnPs and MWCNTs are determined at the maximum achieved enhancement for each property. The HDPE-based nanocomposites containing GnPs with larger surface area and MWCNTs with higher aspect ratio display the highest electrical conductivity at GnPs/MWCNTs weight ratio of 2/3. The combination of GnPs with larger surface area and MWCNTs with lower aspect ratio provides the maximum Young's modulus enhancement of hybrid nanocomposites at 1/4 weight ratio of GnPs and MWCNTs. The nanocomposite containing GnPs with the largest lateral size and MWCNTs with a higher aspect ratio at a 3/2 weight ratio exhibits the highest thermal conductivity. Also, at around the percolation threshold of GnPs, the incorporation of MWCNTs with larger aspect ratio into the HDPE-based nanocomposites containing GnPs with the largest lateral size shows a distinct synergic effect on the thermal conductivity and Young's modulus, while an additive effect on the electrical conductivity and thermal stability.

Spatially localized measurement of isotropic and anisotropic thermophysical properties by photothermal radiometry

The microstructural changes induced by ion implantation may lead to advantageous modifications of chromium disilicide’s (CrSi2) electrical and thermal prop- erties. As a potential thermoelectricmaterial, CrSi2 has attracted attention due to its semiconductor properties and high thermal stability. This contribution investigates the influence of different ion species and implantation conditions on the microstructure, electrical resistivity q and thermal conductivity j behaviors in amorphous CrSi2 thin films. * 260-nm-thick CrSi2 films were produced by mag- netron sputtering and deposited onto a SiO2/Si substrate. Samples were implanted at room temperature either with Ne or Al ions to form a concentration–depth pla- teau reaching a concentration of & 1.0 at.% (Ne), or & 0.008 at.% (Al). Ne and Al implantations were also performed with the targets heated at 250 °C. The microstructural modifications were characterized via TEM and STEM-EDX. The electrical resistivity q was measured by the van der Pauwmethod, and the thermal conductivity j measurements were obtained with SThM. The results obtained show that room temperature Al and Ne implantations cause the reduction of q as comparedto thepristinefilm. Incontrast, theqvalues are significantlyhigher forNe and Al implantations in heated substrates. The microstructure evolution, electrical and thermal behaviors are discussed considering the effects of radiation damage and the formation of dense nanocrystallite arrays during the implantation process.

We present in this study a novel way to determine the three-dimensional (3D) temperature field o f a R adio Fre- quency Silicon On Insulator (RF SOI) electronic chip, using several resistance temperature detectors (RTDs) embedded at different locations of the chip. The RTDs are designed and placed at different locations to experimentally obtain the temperature at key locations of the chip enabling the calibration of a multiphysical numerical model that provides the 3D temperature field in the whole chip under operating conditions. The obtained results provide useful insights on the role of different parameters (e.g. used materials properties, heat source power, substrate, boundary conditions, etc.) to engineers interested in the modelling and optimization of heat transport and thermal management of electronic chips for RF applications.

Thermophysical parameters of azobenzene-containing polymer thin films with different substituents in the side-chain, and guest-host sys- tems were investigated. In this work, the PTR and the SThM were proposed as suitable methods for thermophysical characterization of organic samples. The combination of these thermal techniques with AFM imaging provides complementary information about the heat transport properties of azobenzene polymer thin films. These observations lead to the conclusion, that the polymer system, into which the azobenzenes are incorporated, can affect the heat transport in azo dye thin films. This is accomplished through the following ef- fects: the first one is related to thermophysical properties of the polymer matrix itself, into which azobenzenes are embedded, and the second one is caused by the spatial organization of the active residues, which have higher stability and restriction of the rotation in side-chain position than in the guest-host system. The obtained thermophysical properties, which are responsible for the heat transport and its storage, can be very useful in designing azobenzene polymer thin films based devices through accurate knowledge of their thermal behavior in the system.

In summary, this work presented the thermal characterization of the interfaces resistances for two types of graphene monolayers epitaxially grown on a SiC(0001) substrate. Each sample denotes a type of graphene/SiC interface with either a buffer layer or without a buffer layer. The TBRs measured values indicate that the presence of an insulating BL reduces the interfacial heat conduction, while the presence of more mobile charge carriers in the QFSMG slightly enhance, via electronic contributions, the heat transfer between the free-standing graphene monolayer and the substrate. In other words, despite a higher phonon-phonon interaction though the BL/SiC interface, the electronic contribution between the QFSMG and SiC takes over the interfacial heat transfer as in the case of metal/metal contact compared to the semiconductor/semiconductor ones, where the phononic contribution decreases but the interface conductance increases with the electronic one58. Furthermore, the accordance of the present thermal results with previous electrical ones proves the capability of epitaxial monolayer graphene with hydrogen intercalation (without a BL) to enhance the thermal performance of graphene-based thermal devices. Therefore, these materials can also be used as cornerstone for epitaxial graphene-based nanoelectronics for better heat management applications like in thermal diodes with rectifying properties or thermal transistors. 

Hysteresis loops exhibited by the thermophysical properties of VO2 thin films deposited on either a sapphire or silicon substrate have been experimentally measured using a high frequency photothermal radiometry technique. This is achieved by directly measuring the thermal diffusivity and thermal effusivity of the VO2 films during their heating and cooling across their phase transitions, along with the film-substrate interface thermal boundary resistance. These thermal properties are then used to determine the thermal conductivity and volumetric heat capacity of the VO2 films. A 2.5 enhancement of the Vo2 thermal conductivity is observed during the heating process, while its volumetric heat capacity does not show major changes. This sizeable thermal conductivity variation is used to model the operation of a conductive thermal diode, which exhibits a rectification factor about 30% for small temperature differences (70 °C) on its terminals. The obtained results grasp thus new insights on the control of heat currents.

High-density polyethylene (HDPE)-based nanocomposites incorporating three different types of graphene nanoplatelets (GnPs) were fabricated to investigate the size effects of GnPs in terms of both lateral size and thickness on the morphological, thermal, electrical, and mechanical properties. The results show that the inclusion of GnPs enhance the thermal, electrical, and mechanical properties of HDPE-based nanocomposites regardless of GnP size. Nevertheless, the most significant enhancement of the thermal and electrical conductivities and the lowest electrical percolation threshold were achieved with GnPs of a larger lateral size. This could have been attributed to the fact that the GnPs of larger lateral size exhibited a better dispersion in HDPE and formed conduc- tive pathways easily observable in scanning electron microscope (SEM) images. Our results show that the lateral size of GnPs was a more regulating factor for the above-mentioned nanocomposite properties compared to their thickness. For a given lateral size, thinner GnPs showed significantly higher electrical conductivity and a lower percolation threshold than thicker ones. On the other hand, in terms of thermal conductivity, a remarkable amount of enhancement was observed only above a certain filler concentra- tion. The results demonstrate that GnPs with smaller lateral size and larger thickness lead to lower enhancement of the samples’ mechanical properties due to poorer dispersion compared to the others. In addition, the size of the GnPs had no considerable effect on the melting and crystallization properties of the HDPE/GnP nanocomposites.

The irradiation of polycrystalline isotropic graphite with swift heavy ions (4.8 and 5.9 MeV/u Au and 4.8 MeV/u U) in the elec- tronic energy-loss regime leads to significant structural damage and modifications of thermophysical properties. Analysis of the irradiated sample cross-sections by Raman spectroscopy and SEM provide clear evidence of defect production and at high fluences of a transition towards a glassy carbon-like material. To quantify the radiation-induced effects on thermal effusivity and thermal conductivity, the technique of frequency domain photothermal radiometry in combination with a three-layer model was success- fully applied. The analysis of the relative effusivity degradation shows a single ion impact mechanism of the accumulated ra- diation damage with a track diameter of 5–6 nm. Such a tremendous degradation can lead to inefficient heat dissipation and finally to thermomechanical failure of graphite beam dumps and production targets in ion accelerators. The risk due to largely reduced thermal conductivity values in high-dose environments have to be considered when designing and esti- mating the long-term operation conditions of beam-intercepting devices for the new generations of high power accelerators such as the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, the High Luminosity Large Hadron Collider (HL–LHC) and the Future Circular Collider (FCC), both at CERN in Geneva.

Kapitza thermal resistance is determined using high-frequency photothermal radiometry (PTR) extended for modulation up to 10 MHz. Interfaces between 50 nm thick titanium coatings and silicon or stainless steel substrates are studied. In the used configuration, the PTR signal is not sensitive to the thermal conductivity of the film nor to its optical absorption coefficient, thus the Kapitza resistance is di- rectly determined from single thermal parameter fits. Results of thermal resistances show the significant influence of the nature of the substrate, as well as of the presence of free electrons at the interface.

Passionné, possédant une curiosité scientifique et une capacité d’apprentissage et d’adaptation rapide, j'aime collaborer avec des scientifiques ou enseignants de différentes disciplines, pour développer de nouvelles compétences et résoudre de nouveaux défis. Par mon travail je vise à encourager le changement afin d'aider la communauté scientifique dans sa recherche vers un avenir meilleur.