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Georges Hamaoui

Enseignant Chercheur

Assistant Professor

Activités de recherche

Intérêts et experiences de recherche:

• Phénomènes de transport de chaleur étudier à l'échelle nanométrique : expérimentalement, théoriquement et par simulation

• Gestion de chaleur multiéchelles : thermoélectricité, diode/transistor thermique, production d'énergie thermophotovoltaïque…

• Transfert de chaleur radiatif en champs proche et lointain (régimes diffusive et balistique)

• Contrôle de la conductivité thermique dans des nanostructures composites à base de polymère (nanocomposites)

• Caractérisation thermophysique de metamatériaux à base de Black Silicon

• Matériaux irradiés avec des ions lourds, matériaux organiques et matériaux à changement de phase

• Interfaces de contacts entre métal-semiconducteur, métal silicide-semiconducteur, graphene-semiconducteur et diamant-semiconducteur

• Matériaux 2D comme les matériaux chalcogénure (disulfure de molybdène MoS2, …)

• Dispositifs thermiques actifs à l'échelle nanométrique basés sur les technologies électroniques

• Métrologie de mesure des propriétés thermophysiques avec calcul d’erreurs : diffusivité, effusivité et conductivité thermique ; chaleur spécifique volumétrique ; température de surface ou point chaud ; et la résistance d’interface de Kapitza

• Caractérisation thermophysique optique (laser moduler) multiéchelles par :

- Radiométrique photothermique dans le domaine fréquentiel à hautes fréquences (PTR)

- PTR hybride : modulation dans les domaines fréquentiel et spatial

- Thermoreflectance hybride dans les domaines fréquentiel et spatial (FSDTR)

• Caractérisation thermique en contact de micro-/nano- structures soit par « scanning thermal microscopy » (SThM) basée sur le principe de l’« atomic force microscopy » (AFM) ou par méthode 3-omega

• Simulation et développement de modèles par COMSOL Multiphysics afin d’établir des schémas de systèmes innovants pour la gestion de la chaleur.



Research activity

An enthusiastic, adaptive and fast-learning person with scientific curiosity, I enjoy collaborating with scientists and teachers from different disciplines and cultures, to develop new skills and solve new challenges. By my work I aim to aid others and to encourage change in order to help the scientific community in its research toward a better future.


Research experiences and interests:

• Nanoscale heat transport phenomena studied experimentally, theoretically and by simulations

• Multiscale heat management applications: thermoelectricity, thermal diode/transistor, thermophotovoltaics energy production…

• Radiative heat transfer in the near and far fields (diffusive and ballistic regimes)

• Thermal conductivity tuning in polymer composite nanostructures (Nanocomposites)

• Thermophysical characterization of metamaterials based on Black Silicon

• Irradiated materials with heavy ions, organic materials and phase-change materials

• Interfaces at metal-semiconductor, metal silicide-semiconductor contacts and diamond-semiconductor

• 2D materials and graphene-semiconductor contacts

• Nanoscale active thermal devices based on electronic technologies

• Measurement metrology of thermophysical properties with error calculation: thermal diffusivity, effusivity and conductivity; volumetric heat capacity; surface or hot spot temperature; and Kapitza thermal interface resistance

• Multiscale optical (laser modulation) thermophysical characterization by:

o High frequency domain photothermal radiometry technique (PTR)

o Hybrid PTR in the frequency and spatial domains

o Hybrid Thermoreflectance in the frequency and spatial domains (FSDTR)

• Thermal characterization in contact with micro-/nano- structures by either scanning thermal microscopy (SThM) based on the principle of atomic force microscopy (AFM) or 3-omega method

• Simulation and development of models by COMSOL Multiphysics in order to establish plans of innovative systems for heat management application.


Mes dernières références

My latest references

Thermophysical properties of methacrylic polymer films with guest-host and side-chain azobenzene

Thermophysical properties of methacrylic polymer films with guest-host and side-chain azobenzene

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.


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.


Kapitza thermal resistance characterization of epitaxial graphene–SiC(0001) interface

Kapitza thermal resistance characterization of epitaxial graphene–SiC(0001) interface

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. 


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. 


Electronic contribution in heat transfer at metal-semiconductor and metal silicide-semiconductor interfaces

Electronic contribution in heat transfer at metal-semiconductor and metal silicide-semiconductor interfaces

In this article, we reported the measurements of the Kapitza resistance at metal-silicon and metal silicide-silicon interfaces. The thermal boundary resistance (TBR) for the annealed samples is found lower than that for the unannealed one, meaning that the heat transfer from metal to silicon is improved due to new bonds created by the interdiffusion of the two layers. For platinum and platinum monosilicide samples, a constant TBR is found for different doping concentrations, which may be attributed to the presence of a charge carrier’s distribution far from the interface and to the Schottky barrier (energy bands case 1 in Fig. 6). Via a comparison to a previous study on titanium and n-type silicon couples, the change of TBR values is ascribed to the presence of a “hot” electrons current at the interface (balanced by a “cold” electron current in the opposite semiconductor-metal direction). For that reason, we suspect the existence of a new heat transfer mode at the interface, which should be related to the coupling of electrons from the metal and electrons from the n-doped semiconductor. The barrier modifications can increase or decrease the electron-phonon and electron-electron couplings between the metal and the dielectric with n- and p-doping. This new hypothesis deserves to be systematically investigated since its implications are critical for theoretical models. Such mechanisms can improve the heat transmission at the interface of silicon-based devices and open novel ways to use them, like in Schottky thermal diodes or even in thermal ohmic contacts.

In this article, we reported the measurements of the Kapitza resistance at metal-silicon and metal silicide-silicon interfaces. The thermal boundary resistance (TBR) for the annealed samples is found lower than that for the unannealed one, meaning that the heat transfer from metal to silicon is improved due to new bonds created by the interdiffusion of the two layers. For platinum and platinum monosilicide samples, a constant TBR is found for different doping concentrations, which may be attributed to the presence of a charge carrier’s distribution far from the interface and to the Schottky barrier (energy bands case 1 in Fig. 6). Via a comparison to a previous study on titanium and n-type silicon couples, the change of TBR values is ascribed to the presence of a “hot” electrons current at the interface (balanced by a “cold” electron current in the opposite semiconductor-metal direction). For that reason, we suspect the existence of a new heat transfer mode at the interface, which should be related to the coupling of electrons from the metal and electrons from the n-doped semiconductor. The barrier modifications can increase or decrease the electron-phonon and electron-electron couplings between the metal and the dielectric with n- and p-doping. This new hypothesis deserves to be systematically investigated since its implications are critical for theoretical models. Such mechanisms can improve the heat transmission at the interface of silicon-based devices and open novel ways to use them, like in Schottky thermal diodes or even in thermal ohmic contacts.


Thermophysical characterisation of Vo2 thin films hysteresis and its application in thermal rectification

Thermophysical characterisation of Vo2 thin films hysteresis and its application in thermal rectification

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.



<p>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.</p><p><br></p><p><br></p>

Kapitza thermal resistance studied by high-frequency photothermal radiometry

Kapitza thermal resistance studied by high-frequency photothermal radiometry

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.


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.


Size effect of graphene nanoplatelets on the properties of high-density polyethylene nanocomposites: Morphological, thermal, electrical and mechanical characterization

Size effect of graphene nanoplatelets on the properties of high-density polyethylene nanocomposites: Morphological, thermal, electrical and mechanical characterization

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.


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.


Degradation of thermal transport properties in fine-grained isotropic graphite exposed to swift heavy ion beams

Degradation of thermal transport properties in fine-grained isotropic graphite exposed to swift heavy ion beams

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.


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.