No abstract

An experimental system of a four-pad 3ω-method with noise cancellation circuit was designed to measure simultaneously thermal conductivity, thermal diffusivity and heat capacity of an individually suspended wire. The closed solution of temperature oscillation, in which the heat transport in the wire is modelled as one-dimensional diffusion in vacuum, was developed in the frequency domain for fitting the experimental results. Both the closed solution and the series solution were used to determine the thermal properties. The measurements on an individual polyacrylonitrile-based carbon fibre 7 µm in diameter were performed using both the closed solution and the series solution, which yielded the thermal conductivity of 84.4 W m−1 K−1, the heat capacity of 1.23 MJ m−3 K−1 and the thermal diffusivity of 7.16 × 10−5 m2 s−1 at room temperature. The relative uncertainties of the measurements were analysed.

The nanocrystalline diamond films with different morphologies and roughness were synthesized by a bias-assisted hot filament chemical vapor deposition method. It was found that the nanocrystalline diamond film exhibited low-k dielectric properties with the increase of CH4 concentration during diamond deposition. The low-k nanocrystalline diamond film with grain size of around 40nm and dielectric constant of 2.4 was obtained at the CH4 concentration of 16% and the bias of −140V. The low dielectric constant can be mainly attributed to the decrease of diamond grain sizes and the formation of more nanopores in as-grown nanocrystalline diamond film, both of which were discussed in details based on the grain size determined band gap expansion effect and the two-phase dielectric mixing model, respectively.