Thermal Conduction Properties Of Low-dimension Inorganic Materials And Regulation Strategies

In 1822,Fourier’s Law was proposed to describe the behavior of classical thermal conduction.However,the limitations of this law have become distinct with unremittingly intensive research on low-dimensional systems.The understanding and cognizance of thermal conduction has been improved by non-diffusive phonon transport,or anomalous phonon transport,such as ballistic transport,super-diffusion transport,phonon hydrodynamics,coherent phonon transport,etc.In addition,with the background of rapid advances in material processing technology and booming nanomaterials,exploring the heat transport behavior in micro/nano-scale system will contribute to develop new thermal management devices,thermal control devices,and thermal energy conversion technologies to solve severe challenges in heat dissipation of integrated electronic devices,global energy shortages and other concerns.In this dissertation,we carried out some experiments to study properties of thermal conduction on low-dimension inorganic materials and regulation strategies.The main contents were as follows:1.The experiment methods for measuring thermal conduction in micro/nano scale.We introduced the thermal bridge method and E-beam method,which were developed to measure thermal conduction behavior of low-dimension materials.On the basis of the measurement principle,emphases were laid on analyzing the thermal contact resistance,internal thermal resistance of platforms of thermal bridge device,thermal radiation in high temperature and electron-beam selection.These issues had direct influence on measurement accuracy of above experiment methods.Thus,at the same time,we discussed corresponding solutions.2.The thickness-dependence of thermal conductivity on tellurium nanoribbons.High-quality tellurium nanoribbons were synthesized by modified solution chemical method,and then samples with different thicknesses were transferred to suspended thermal bridge device for measuring their thermal conductivity.The results show that relationship between thermal conductivity of tellurium nanoribbons and its thickness was approximately linear.According to our data,it was inferred that compared with that of bulk tellurium,the room-temperature thermal conductivity of tellurium with thickness of 60 nm is only one-half.By analysis,we considered that this size effect of thermal conductivity is caused by the contribution of phonon surface scattering.Bulk tellurium is a new thermoelectric material in the middle temperature region.Combined with this experiment,it was revealed that low-dimensional tellurium could be more excellent in terms of thermoelectric property,and applied for exploiting microthermoelectric systems in the future.3.The thermal conductivity and thermal boundary resistance of silicon carbide nanowires.The silicon carbide possesses high thermal conductivity,but current researches are scarce on thermal conduction behavior of its low-dimensional structure.Therefore,in the part,silicon carbide nanowires with different diameters were measured using the thermal bridge method and E-beam method.As a result,the diameter-dependent thermal conductivity was not observed.To make clear this phenomenon,we claimed that the scattering of phonons by the grain has dominated heat conduction process,rather than boundary scattering.Moreover,the thermal boundary resistance between silicon carbide nanowires has been researched,in order to understand why composite materials including silicon carbide nanowires show low thermal conductivity and provide a reference for further experiment.4.To regulate thermal conductivity of silicon carbide nanowires with strain.Many theoretical papers focused on the strain effect of thermal conduction on lowdimensional materials,but only graphene has been investigated in experiment.Thus,a set of procedures was designed for bending silicon carbide nanowires and generating strain.The thermal conductivity of three prepared samples was measured with thermalbridge method.The results showed that strain had a significant inhibitory effect on thermal conductivity at low temperature,and it’s almost negligible at room temperature.Furthermore,the stronger strain has more obvious influence.A 55% change was caused by strain of 1.93% at 20 K.For interpretation of these trends,we proposed that nonuniform stress can be analogous to defects.This was the first experiment to utilize strain for regulating thermal conduction on one-dimensional system,which paved a way to control heat transport on low-dimensional materials.Finally,the experiments and related results of this thesis were summarized and the shortcomings were pointed out.We,meanwhile,made a prospect on the future research and put forward some suggestions.