Growth of Uniform CNT Layer on Copper Foil-the Effect of Synthesis Methods/Conditions

摘要

Carbon nanotubes (CNTs) with unique thermal and electrical properties, and inherently large surface area are an attractive candidate for integration into thermal structures and for a flexible thermal interface material in power electronics packages. However, reproducible and controllable synthesis of CNTs on reactive substrates such as metals, ceramics and carbon materials has been a challenge compared to growth on conventional, inert substrates such as SiO_2. In this study two different growing methods, pre-coated catalyst thermal chemical vapor deposition (THCVD) and floating catalyst thermal chemical vapor deposition (FCCVD), were used to investigate direct growth of high quality CNT layers on copper foil substrates. SEM images and initial testing results indicated that the synthesis method, growth conditions and especially substrate surface treatment significantly impact CNTs growth, and structure/morphology, as well as interfacial strength and thermal performance. Using either THCVD or FCCVD with Fe as the catalyst, only sparse, poorly-aligned CNT forests were grown on Cu foil substrates. In contrast, uniform, dense, aligned CNT layers were successfully formed with both THCVD and FCCVD under optimized processing conditions when a thin buffer layer of Al_2O_3 was deposited on the Cu foil by atomic layer deposition (ALD) prior to CNT growth. Futhermore, the length, alignment and areal density of CNTs could be controlled by varying the thickness of the Al_2O_3 layer.