To understand the relation between different nanostructures and thermal properties, a simple yet effective model is in demand for characterizing the underlying phonons and electrons scattering mechanisms. Herein, we m...To understand the relation between different nanostructures and thermal properties, a simple yet effective model is in demand for characterizing the underlying phonons and electrons scattering mechanisms. Herein, we make a systematic review on the newly developed thermal reffusivity theory. Like electrical resistivity which has been historically used as a theory for analyzing structural domain size and defect levels of metals, the thermal reffusivity can also uncover phonon behavior, structure defects and domain size of materials. We highlight that this new theory can be used for not only metals, but also nonmetals, even for amorphous materials. From the thermal reffusivity against temperature curves, the Debye temperature of the material and the ideal thermal diffusivity of single perfect crystal can be evaluated. From the residual thermal reffusivity at the 0 K limit, the structural thermal domain （STD） size of crystalline and amorphous materials can be obtained. The difference of white hair and normal black hair from heat conduction perspective is reported for the first time. Loss of melanin results in a worse thermal protection and a larger STD size in the white hair. By reviewing the different variation of thermal reffusivity against decreasing temperature profiles, we conclude that they reflected the structural connection in the materials. Ultimately, the future application of thermal reffusivity theory in studying 2D materials and amorphous materials is discussed.展开更多
Interfacial thermal resistance plays a crucial role in efficient heat dissipation in modern electronic devices.It is critical to understand the interfacial thermal transport from both experiments and underlying physic...Interfacial thermal resistance plays a crucial role in efficient heat dissipation in modern electronic devices.It is critical to understand the interfacial thermal transport from both experiments and underlying physics.This review is focused on the transient opto-thermal Raman-based techniques for measuring the interfacial thermal resistance between 2D materials and substrate.This transient idea eliminates the use of laser absorption and absolute temperature rise data,therefore provides some of the highest level measurement accuracy and physics understanding.Physical concepts and perspectives are given for the time-domain differential Raman(TD-Raman),frequency-resolved Raman(FRRaman),energy transport state-resolved Raman(ET-Raman),frequency domain ET-Raman(FET-Raman),as well as laser flash Raman and dual-wavelength laser flash Raman techniques.The thermal nonequilibrium between optical and acoustic phonons,as well as hot carrier diffusion must be considered for extremely small domain characterization of interfacial thermal resistance.To have a better understanding of phonon transport across material interfaces,we introduce a new concept termed effective interface energy transmission velocity.It is very striking that many reported interfaces have an almost constant energy transmission velocity over a wide temperature range.This physics consideration is inspired by the thermal reffusivity theory,which is effective for analyzing structure-phonon scattering.We expect the effective interface energy transmission velocity to give an intrinsic picture of the transmission of energy carriers,unaltered by the influence of their capacity to carry heat.展开更多
The thermal conductivity of carbon-based nanomaterials(e.g.carbon nanotubes,graphene,graphene aerogels,and carbon fibers)is a physical property of great scientific and engineering importance.Thermal conductivity tailo...The thermal conductivity of carbon-based nanomaterials(e.g.carbon nanotubes,graphene,graphene aerogels,and carbon fibers)is a physical property of great scientific and engineering importance.Thermal conductivity tailoring via structure engineering is widely conducted to meet the requirement of different applications.Traditionally,the thermal conductivity-temperature relation is used to analyze the structural effect but this relation is extremely affected by effect of temperature-dependence of specific heat.In this paper,detailed review and discussions are provided on the thermal reffusivity theory to analyze the structural effects on thermal conductivity.For the first time,the thermal reffusivity-temperature trend in fact uncovers very strong structural degrading with reduced temperature for various carbon-based nanomaterials.The residual thermal reffusivity at the 0 K limit can be used to directly calculate the structure thermal domain(STD)size,a size like that determined by x-ray diffraction,but reflects phonon scattering.For amorphous carbon materials or nanomaterials that could not induce sufficient x-ray scattering,the STD size probably provides the only available physical domain size for structure analysis.Different from many isotropic and anisotropic materials,carbon-based materials(e.g.graphite,graphene,and graphene paper)have Van der Waals bonds in the c-axis direction and covalent bonds in the a-axis direction.This results in two different kinds of phonons whose specific heat,phonon velocity,and mean free path are completely different.A physical model is proposed to introduce the anisotropic specific heat and temperature concept,and to interpret the extremely long phonon mean free path despite the very low thermal conductivity in the c-axis direction.This model also can be applied to other similar anisotropic materials that feature Van der Waals and covalent bonds in different directions.展开更多
文摘To understand the relation between different nanostructures and thermal properties, a simple yet effective model is in demand for characterizing the underlying phonons and electrons scattering mechanisms. Herein, we make a systematic review on the newly developed thermal reffusivity theory. Like electrical resistivity which has been historically used as a theory for analyzing structural domain size and defect levels of metals, the thermal reffusivity can also uncover phonon behavior, structure defects and domain size of materials. We highlight that this new theory can be used for not only metals, but also nonmetals, even for amorphous materials. From the thermal reffusivity against temperature curves, the Debye temperature of the material and the ideal thermal diffusivity of single perfect crystal can be evaluated. From the residual thermal reffusivity at the 0 K limit, the structural thermal domain （STD） size of crystalline and amorphous materials can be obtained. The difference of white hair and normal black hair from heat conduction perspective is reported for the first time. Loss of melanin results in a worse thermal protection and a larger STD size in the white hair. By reviewing the different variation of thermal reffusivity against decreasing temperature profiles, we conclude that they reflected the structural connection in the materials. Ultimately, the future application of thermal reffusivity theory in studying 2D materials and amorphous materials is discussed.
基金supported by the National Natural Science Foundation of China(No.12204320 for J.L.and 52276080 for Y.X.)US National Science Foundation(CBET1930866 and CMMI2032464 for X.W)J.L.is grateful for the support from Shenzhen Science and Technology Program(JCYJ20220530153401003).
文摘Interfacial thermal resistance plays a crucial role in efficient heat dissipation in modern electronic devices.It is critical to understand the interfacial thermal transport from both experiments and underlying physics.This review is focused on the transient opto-thermal Raman-based techniques for measuring the interfacial thermal resistance between 2D materials and substrate.This transient idea eliminates the use of laser absorption and absolute temperature rise data,therefore provides some of the highest level measurement accuracy and physics understanding.Physical concepts and perspectives are given for the time-domain differential Raman(TD-Raman),frequency-resolved Raman(FRRaman),energy transport state-resolved Raman(ET-Raman),frequency domain ET-Raman(FET-Raman),as well as laser flash Raman and dual-wavelength laser flash Raman techniques.The thermal nonequilibrium between optical and acoustic phonons,as well as hot carrier diffusion must be considered for extremely small domain characterization of interfacial thermal resistance.To have a better understanding of phonon transport across material interfaces,we introduce a new concept termed effective interface energy transmission velocity.It is very striking that many reported interfaces have an almost constant energy transmission velocity over a wide temperature range.This physics consideration is inspired by the thermal reffusivity theory,which is effective for analyzing structure-phonon scattering.We expect the effective interface energy transmission velocity to give an intrinsic picture of the transmission of energy carriers,unaltered by the influence of their capacity to carry heat.
基金the National Natural Science Foundation of China(52276080 for Y.X)US National Science Foundation(CBET1930866 and CMMI2032464 for X.W).
文摘The thermal conductivity of carbon-based nanomaterials(e.g.carbon nanotubes,graphene,graphene aerogels,and carbon fibers)is a physical property of great scientific and engineering importance.Thermal conductivity tailoring via structure engineering is widely conducted to meet the requirement of different applications.Traditionally,the thermal conductivity-temperature relation is used to analyze the structural effect but this relation is extremely affected by effect of temperature-dependence of specific heat.In this paper,detailed review and discussions are provided on the thermal reffusivity theory to analyze the structural effects on thermal conductivity.For the first time,the thermal reffusivity-temperature trend in fact uncovers very strong structural degrading with reduced temperature for various carbon-based nanomaterials.The residual thermal reffusivity at the 0 K limit can be used to directly calculate the structure thermal domain(STD)size,a size like that determined by x-ray diffraction,but reflects phonon scattering.For amorphous carbon materials or nanomaterials that could not induce sufficient x-ray scattering,the STD size probably provides the only available physical domain size for structure analysis.Different from many isotropic and anisotropic materials,carbon-based materials(e.g.graphite,graphene,and graphene paper)have Van der Waals bonds in the c-axis direction and covalent bonds in the a-axis direction.This results in two different kinds of phonons whose specific heat,phonon velocity,and mean free path are completely different.A physical model is proposed to introduce the anisotropic specific heat and temperature concept,and to interpret the extremely long phonon mean free path despite the very low thermal conductivity in the c-axis direction.This model also can be applied to other similar anisotropic materials that feature Van der Waals and covalent bonds in different directions.
