Structure Controlled Preparation And Performance Research Of Vertically Aligned Carbon Nanotube Array Thermal Interface Materials

A vertically aligned carbon nanotube(VACNT)array is composed of numerous carbon nanotubes(CNTs)which all stand perpendicularly and closely on growth substrates.This unique structure can exert the excellent thermal transport performance of individual CNT in macro-scale.Therefore,VACNT arrays have been proposed as promising candidate of next-generation thermal interface materials(TIMs).However,current VACNT arrays still are far away from commercial application,because their thermal transport performance is still much lower than theoretical values and the strong bonding between VACNT arrays and growth substrates limits next-step packaging in devices.The dissertation focuses on the structural controlled preparation of VACNT arrays to decrease the interface resistances of VACNT arrays,improve thermal transport performance and simplify packaging process.(1)Spinnable and well-aligned VACNT arrays were firstly prepared on copper foil and unique thermal contraction property was discovered in the arrays.The copper foil facilitated fast sub-surface diffusion of Fe catalysts during annealing process and good alignment can offer strong inter-tube van der Waals’ interaction force in the arrays.Therefore,after removing Fe catalysts,the CNTs in the arrays can move on substrate surface and aggregate into densified VACNT arrays during annealing process.Finally,densified and freestanding VACNT arrays were obtained intact and on a large scale through a simple annealing process.Subsequently,it was found that the density and thermal conductivity of VACNT arrays can be increased by 36%and 35%respectively through thermal contraction process.(2)VACNT arrays with smooth surface were prepared.Through in-situ deposition of thin carbon layer on catalyst surface before the growth of VACNT arrays,the disordered growth of the free tips of VACNT arrays was restrained.The carbon layer on the surface of VACNT arrays can decrease the roughness of the top of the arrays and seamlessly connect all the free tips of the CNTs in the array.This unique structure guarantees the participation of all the carbon nanotubes in the array in the heat transport process,so the heat transfer routes were increased considerably.Consequently,the VACN T array on copper foil shows a record low thermal resistance of 1.3 mm2 K W-1 including the lateral contact resistance,which is 4 times lower than the best result prev iously reported.(3)A fast,clean and scalable press transfer method was developed for VACNT arrays.Through density adjustment and weak-gas etching,the adhesion force between VACNT arrays and growth substrates was weakened.Therefore,VACNT arrays can be pressed onto various substrates with different shapes at absence of transfer media.Patterned VACNT arrays also can be transferred using this method.For the first time,thin VACNT arrays with a thickness of 20 μm were transferred onto target substrates,showing a very low thermal resistance of～26 K mm2 W-1.