Flexible graphite film(FGF),as a traditional interface heat dissipation material,has high anisotropy.It is a challenge to enhance both in-plane and through-plane thermal conductivity of FGF.For this reason,the effects...Flexible graphite film(FGF),as a traditional interface heat dissipation material,has high anisotropy.It is a challenge to enhance both in-plane and through-plane thermal conductivity of FGF.For this reason,the effects of oxygen content,layer spacing,density and particle size on the in-plane and through-plane thermal conductivity of FGF were studied by both molecular simulation and experimental investigation.The simulation results indicate that the ways to improve the thermal conductivity of FGF include reducing oxygen content and layer spacing,increasing the density and matching the size of graphite sheets.The FGF prepared from room temperature exfoliated graphite(RTFGF)has a wide range of adjustable density(1.3–2.0 g/cm^(3))and thickness(50–400μm).The thermal conductivity of the RTFGF is significantly improved after heat treatment owing to reduced oxygen content and layer spacing,which is consistent with the simulation results.Moreover,RTFGF with both high in-plane(518 W·m^(-1)·K^(-1))and through-plane(7.2 W·m^(-1)·K^(-1))thermal conductivity can be obtained by particle size matching of graphite.展开更多
Highly thermally conductive graphitic film(GF)materials have become a competitive solution for the thermal management of high-power electronic devices.However,their catastrophic structural failure under extreme altern...Highly thermally conductive graphitic film(GF)materials have become a competitive solution for the thermal management of high-power electronic devices.However,their catastrophic structural failure under extreme alternating thermal/cold shock poses a significant challenge to reliability and safety.Here,we present the first investigation into the structural failure mechanism of GF during cyclic liquid nitrogen shocks(LNS),which reveals a bubbling process characterized by“permeation-diffusion-deformation”phenomenon.To overcome this long-standing structural weakness,a novel metal-nanoarmor strategy is proposed to construct a Cu-modified graphitic film(GF@Cu)with seamless heterointerface.This well-designed interface ensures superior structural stability for GF@Cu after hundreds of LNS cycles from 77 to 300 K.Moreover,GF@Cu maintains high thermal conductivity up to 1088 W m^(−1)K^(−1)with degradation of less than 5%even after 150 LNS cycles,superior to that of pure GF(50%degradation).Our work not only offers an opportunity to improve the robustness of graphitic films by the rational structural design but also facilitates the applications of thermally conductive carbon-based materials for future extreme thermal management in complex aerospace electronics.展开更多
Effective thermal management of electronic integrated devices with high powder density has become a serious issue,which requires materials with high thermal conductivity(TC).In order to solve the problem of weak bondi...Effective thermal management of electronic integrated devices with high powder density has become a serious issue,which requires materials with high thermal conductivity(TC).In order to solve the problem of weak bonding between graphite and Cu,a novel Cu/graphite film/Cu sandwich composite(Cu/GF/Cu composite)with ultrahigh TC was fabricated by electro-deposition.The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electrodeposition.TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated.The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content,and the strong texture orientation of deposited Cu resulted in high TC.Under the optimizing preparing condition,the highest in-plane TC reached 824.3 W·m^-1·K^-1,while the ultimate tensile strength of this composite was about four times higher than that of the graphite film.展开更多
Graphene and thin graphite films deposited on SiO2/Si are irradiated by swift heavy ions(209Bi, 9.5 Me V/u) with the fluences in a range of 1011ions/cm2–1012ions/cm2 at room temperature. Both pristine and irradiated ...Graphene and thin graphite films deposited on SiO2/Si are irradiated by swift heavy ions(209Bi, 9.5 Me V/u) with the fluences in a range of 1011ions/cm2–1012ions/cm2 at room temperature. Both pristine and irradiated samples are investigated by Raman spectroscopy. For pristine graphite films, the 'blue shift' of 2D bond and the 'red shift' of G bond with the decrease of thickness are found in the Raman spectra. For both irradiated graphene and thin graphite films, the disorder-induced D peak and D' peak are detected at the fluence above a threshold Φth. The thinner the film, the lower the Φthis. In this work, the graphite films thicker than 60 nm reveal defect free via the absence of a D bond signal under the swift heavy ion irradiation till the fluence of 2.6 × 1012ions/cm2. For graphite films thinner than 6 nm, the area ratios between D peak and G peak increase sharply with reducing film thickness. It concludes that it is much easier to induce defects in thinner films than in thicker ones by swift heavy ions. The intensities of the D peak and D' peak increase with increasing ion fluence, which predicts the continuous impacting of swift heavy ions can lead to the increasing of defects in samples. Different defect types are detected in graphite films of different thickness values. The main defect types are discussed via the various intensity ratios between the D peak and D' peak(HD/HD).展开更多
By pre-treating substrate with different methods and patterning the catalyst, selective and patterned growth of diamond and graphitic nano-structured carbon films have been realized through DC Plasma-Enhanced Hot Fila...By pre-treating substrate with different methods and patterning the catalyst, selective and patterned growth of diamond and graphitic nano-structured carbon films have been realized through DC Plasma-Enhanced Hot Filament Chemical Vapor Deposition (PE-HFCVD). Through two-step processing in an HFCVD reactor, novel nano-structured composite diamond films containing a nanocrystalline diamond layer on the top of a nanocone diamond layer have been synthesized. Well-aligned carbon nanotubes, diamond and graphitic carbon nanocones with controllable alignment orientations have been synthesized by using PE-HFCVD. The orientation of the nanostructures can be controlled by adjusting the working pressure. In a Microwave Plasma Enhanced Chemical Vapor Deposition (MW-PECVD) reactor, high-quality diamond films have been synthesized at low temperatures (310℃-550℃) without adding oxygen or halogen gas in a newly developed processing technique. In this process, carbon source originates from graphite etching, instead of hydrocarbon. The lowest growth temperature for the growth of nanocrystalline diamond films with a reasonable growth rate without addition of oxygen or halogen is 260℃.展开更多
Achieving efficient thermal management urges to exploit high-thermal-conductivity materials to satisfy the boosted demand of heat dissipation.It is critical to adopt standardized characterization protocols to evaluate...Achieving efficient thermal management urges to exploit high-thermal-conductivity materials to satisfy the boosted demand of heat dissipation.It is critical to adopt standardized characterization protocols to evaluate the intrinsic thermal conductivity of thermal management materials.However,for the most representative laser flash method,the lack of standard measurement methodology and systematic description on the thermal diffusivity and influencing factors has led to significant deviations and confusion of the thermal conduction performance in the emerging thermal management application.Here,the measurement error factors of thermal diffusivity by the common laser flash analyzer(LFA)are discussed.Taking high-thermal-conductivity graphitic film(GF)as a typical case,the key factors are analyzed to guide the measurement protocol of related carbon-based thermal management materials.The basic principle of the LFA measurement,actual pre-processing conditions,instrument parameters setting,and data analysis are elaborated for accurate measurements.Furthermore,the graphene thick films and common isotropic materials are also extended to meet various thermal measurement requirements.Based on the existing practical problems,we propose a feasible test flow to achieve a unified and standardized thermal conductivity measurement,which is beneficial to the rapid development of carbon-based thermal management materials.展开更多
Exfoliated graphite(EG)is promising oil sorbent as well as an intermediate product for the preparation of flexible graphite films(FGFs).It has been a critical challenge to energy conservation and pollution abatement f...Exfoliated graphite(EG)is promising oil sorbent as well as an intermediate product for the preparation of flexible graphite films(FGFs).It has been a critical challenge to energy conservation and pollution abatement for the traditional EG production technique.Here,we propose a simple and effective preparation method to acquire EG in which flake graphite is intercalated and exfoliated at room temperature,not involving any pollutant emission.The influence factors in the preparation process were explored,such as the amount of H_(2)SO_(4)and H_(2)O_(2),the temperature for the preparation of room temperature exfoliated graphite(RTEG).In contrast to the EG by high temperature exfoliation(HTEG),RTEG exhibits a homogeneous structure and a significantly increased volume and surface area.Moreover,EG blocks with high oil sorption capacity and excellent reuse performance can be obtained by RTEG method.Especially,FGFs fabricated by RTEG has high flexibility,thermal conductivity and electrical conductivity.It suggests that this environment-friendly technology is suitable for large-scale industrial implementation of graphite-based oil sorbents and flexible materials.展开更多
基金We would like to acknowledge the support provided by National Key R&D Program of China(2021YFC2902904).
文摘Flexible graphite film(FGF),as a traditional interface heat dissipation material,has high anisotropy.It is a challenge to enhance both in-plane and through-plane thermal conductivity of FGF.For this reason,the effects of oxygen content,layer spacing,density and particle size on the in-plane and through-plane thermal conductivity of FGF were studied by both molecular simulation and experimental investigation.The simulation results indicate that the ways to improve the thermal conductivity of FGF include reducing oxygen content and layer spacing,increasing the density and matching the size of graphite sheets.The FGF prepared from room temperature exfoliated graphite(RTFGF)has a wide range of adjustable density(1.3–2.0 g/cm^(3))and thickness(50–400μm).The thermal conductivity of the RTFGF is significantly improved after heat treatment owing to reduced oxygen content and layer spacing,which is consistent with the simulation results.Moreover,RTFGF with both high in-plane(518 W·m^(-1)·K^(-1))and through-plane(7.2 W·m^(-1)·K^(-1))thermal conductivity can be obtained by particle size matching of graphite.
基金the National Natural Science Foundation of China(Nos.52272046,52090030,52090031,52122301,51973191)the Natural Science Foundation of Zhejiang Province(LR23E020003)+4 种基金Shanxi-Zheda Institute of New Materials and Chemical Engineering(2021SZ-FR004,2022SZ-TD011,2022SZ-TD012,2022SZ-TD014)Hundred Talents Program of Zhejiang University(188020*194231701/113,112300+1944223R3/003,112300+1944223R3/004)the Fundamental Research Funds for the Central Universities(Nos.226-2023-00023,226-2023-00082,2021FZZX001-17,K20200060)National Key R&D Program of China(NO.2022YFA1205300,NO.2022YFA1205301,NO.2020YFF0204400,NO.2022YFF0609801)“Pioneer”and“Leading Goose”R&D Program of Zhejiang 2023C01190.
文摘Highly thermally conductive graphitic film(GF)materials have become a competitive solution for the thermal management of high-power electronic devices.However,their catastrophic structural failure under extreme alternating thermal/cold shock poses a significant challenge to reliability and safety.Here,we present the first investigation into the structural failure mechanism of GF during cyclic liquid nitrogen shocks(LNS),which reveals a bubbling process characterized by“permeation-diffusion-deformation”phenomenon.To overcome this long-standing structural weakness,a novel metal-nanoarmor strategy is proposed to construct a Cu-modified graphitic film(GF@Cu)with seamless heterointerface.This well-designed interface ensures superior structural stability for GF@Cu after hundreds of LNS cycles from 77 to 300 K.Moreover,GF@Cu maintains high thermal conductivity up to 1088 W m^(−1)K^(−1)with degradation of less than 5%even after 150 LNS cycles,superior to that of pure GF(50%degradation).Our work not only offers an opportunity to improve the robustness of graphitic films by the rational structural design but also facilitates the applications of thermally conductive carbon-based materials for future extreme thermal management in complex aerospace electronics.
基金supported by the National Natural Science Foundation of China(Grant Nos.51605293 and 51702213)the Shanghai Science and Technology Commission(18060502300).
文摘Effective thermal management of electronic integrated devices with high powder density has become a serious issue,which requires materials with high thermal conductivity(TC).In order to solve the problem of weak bonding between graphite and Cu,a novel Cu/graphite film/Cu sandwich composite(Cu/GF/Cu composite)with ultrahigh TC was fabricated by electro-deposition.The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electrodeposition.TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated.The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content,and the strong texture orientation of deposited Cu resulted in high TC.Under the optimizing preparing condition,the highest in-plane TC reached 824.3 W·m^-1·K^-1,while the ultimate tensile strength of this composite was about four times higher than that of the graphite film.
基金supported by the National Natural Science Foundation of China(Grant Nos.11179003,10975164,10805062,11005134,and 11275237)
文摘Graphene and thin graphite films deposited on SiO2/Si are irradiated by swift heavy ions(209Bi, 9.5 Me V/u) with the fluences in a range of 1011ions/cm2–1012ions/cm2 at room temperature. Both pristine and irradiated samples are investigated by Raman spectroscopy. For pristine graphite films, the 'blue shift' of 2D bond and the 'red shift' of G bond with the decrease of thickness are found in the Raman spectra. For both irradiated graphene and thin graphite films, the disorder-induced D peak and D' peak are detected at the fluence above a threshold Φth. The thinner the film, the lower the Φthis. In this work, the graphite films thicker than 60 nm reveal defect free via the absence of a D bond signal under the swift heavy ion irradiation till the fluence of 2.6 × 1012ions/cm2. For graphite films thinner than 6 nm, the area ratios between D peak and G peak increase sharply with reducing film thickness. It concludes that it is much easier to induce defects in thinner films than in thicker ones by swift heavy ions. The intensities of the D peak and D' peak increase with increasing ion fluence, which predicts the continuous impacting of swift heavy ions can lead to the increasing of defects in samples. Different defect types are detected in graphite films of different thickness values. The main defect types are discussed via the various intensity ratios between the D peak and D' peak(HD/HD).
文摘By pre-treating substrate with different methods and patterning the catalyst, selective and patterned growth of diamond and graphitic nano-structured carbon films have been realized through DC Plasma-Enhanced Hot Filament Chemical Vapor Deposition (PE-HFCVD). Through two-step processing in an HFCVD reactor, novel nano-structured composite diamond films containing a nanocrystalline diamond layer on the top of a nanocone diamond layer have been synthesized. Well-aligned carbon nanotubes, diamond and graphitic carbon nanocones with controllable alignment orientations have been synthesized by using PE-HFCVD. The orientation of the nanostructures can be controlled by adjusting the working pressure. In a Microwave Plasma Enhanced Chemical Vapor Deposition (MW-PECVD) reactor, high-quality diamond films have been synthesized at low temperatures (310℃-550℃) without adding oxygen or halogen gas in a newly developed processing technique. In this process, carbon source originates from graphite etching, instead of hydrocarbon. The lowest growth temperature for the growth of nanocrystalline diamond films with a reasonable growth rate without addition of oxygen or halogen is 260℃.
基金supported by the National Natural Science Foundation of China(Nos.52272046,52090030,52090031,52122301,51973191)the Natural Science Foundation of Zhejiang Province(LR23E020003)+4 种基金Shanxi-Zheda Institute of New Materials and Chemical Engineering(2021SZ-FR004,2022SZ-TD011,2022SZ-TD012,2022SZ-TD014)Hundred Talents Program of Zhejiang University(188020*194231701/113,112300+1944223R3/003,112300+1944223R3/004)the Fundamental Research Funds for the Central Universities(Nos.226-2023-00023,226-2023-00082,2021FZZX001-17,K20200060)National Key R&D Program of China(NO.2022YFA1205300,NO.2022YFA1205301,NO.2020YFF0204400,NO.2022YFF0609801)"Pioneer"and"Leading Goose"R&D Program of Zhejiang 2023C01190。
文摘Achieving efficient thermal management urges to exploit high-thermal-conductivity materials to satisfy the boosted demand of heat dissipation.It is critical to adopt standardized characterization protocols to evaluate the intrinsic thermal conductivity of thermal management materials.However,for the most representative laser flash method,the lack of standard measurement methodology and systematic description on the thermal diffusivity and influencing factors has led to significant deviations and confusion of the thermal conduction performance in the emerging thermal management application.Here,the measurement error factors of thermal diffusivity by the common laser flash analyzer(LFA)are discussed.Taking high-thermal-conductivity graphitic film(GF)as a typical case,the key factors are analyzed to guide the measurement protocol of related carbon-based thermal management materials.The basic principle of the LFA measurement,actual pre-processing conditions,instrument parameters setting,and data analysis are elaborated for accurate measurements.Furthermore,the graphene thick films and common isotropic materials are also extended to meet various thermal measurement requirements.Based on the existing practical problems,we propose a feasible test flow to achieve a unified and standardized thermal conductivity measurement,which is beneficial to the rapid development of carbon-based thermal management materials.
文摘Exfoliated graphite(EG)is promising oil sorbent as well as an intermediate product for the preparation of flexible graphite films(FGFs).It has been a critical challenge to energy conservation and pollution abatement for the traditional EG production technique.Here,we propose a simple and effective preparation method to acquire EG in which flake graphite is intercalated and exfoliated at room temperature,not involving any pollutant emission.The influence factors in the preparation process were explored,such as the amount of H_(2)SO_(4)and H_(2)O_(2),the temperature for the preparation of room temperature exfoliated graphite(RTEG).In contrast to the EG by high temperature exfoliation(HTEG),RTEG exhibits a homogeneous structure and a significantly increased volume and surface area.Moreover,EG blocks with high oil sorption capacity and excellent reuse performance can be obtained by RTEG method.Especially,FGFs fabricated by RTEG has high flexibility,thermal conductivity and electrical conductivity.It suggests that this environment-friendly technology is suitable for large-scale industrial implementation of graphite-based oil sorbents and flexible materials.
