论文部分内容阅读
Nanomaterials have been highlighted as promising candidates for improving traditional tissue engineering materials due to the excellent thermal,mechanical,electrical,and optical properties.Why the nanomaterials are so different from corresponding bulk? Size effect plays a key role,and hence nanomaterials are called size matters.In this keynote,size effects on thermophysical properties of nanomaterials,including metallic nanofilm,carbon nanotube,and thermoelectric nanowire,will be discussed in detail.First,size effects on metallic nanofilms.A significant size effect has been revealed for heat and charge transport in metallic nanofilms at low temperatures.Below 50 K,the normally used elastic theories fail to predict the electrical and thermal conductivities,and the Wiedemann-Franz law breaks as well.The experimental results demonstrate that a new kind of electron scattering,i.e.electron Raman scattering,exists at low temperatures.Second,size effects on carbon nanotube(CNT).Raman spectroscopy technique has been developed to study the size effects on CNT.The local temperature rise of CNT is proportional to the G-band frequency shift,providing a perfect tool for non-contact measurement of temperature.Applying this technique,the heat transfer coefficients of several single-wall carbon nanotubes have been measured.A two-layer kinetic model has been established to predict the heat transfer coefficient,covering all the free molecular,transition and continuum regimes.Meanwhile,a length-dependent thermal conductivity has been observed for multi-wall carbon nanotubes,suggesting that the heat conduction occurs in both ballistic and diffusion ways.Third,size effect on thermoelectric nanowire.A novel T-type AC heating-DC detecting method has been developed to measure the Seebeck coefficient of individual nanowires.Based on this technique,the Seebeck coefficient,thermal conductivity,and electrical conductivity of the same Bi2S3 nanowire have been comprehensively determined.A metal-insulator transition has been observed for Bi2S3 nanowire at about 225 K,and a magnetic polaron theory based on size effects has been successfully applied to describe this new phenomenon.