The Effect of Catalyst Sublimation Temperature on the Purity of Multi-Walled Carbon Nanotube Vertically Aligned Arrays

Current thermal interface materials including solders, greases, and phase change materials do not have the mechanical compliance required to fill cavities, and thermal conductance necessary to dissipate heat generated in modern microelectronic devices. The inability to dissipate heat properly from the microprocessor device creates a thermal bottleneck which limits device efficiency and leads to early life degradation. Individual multiwalled carbon nanotubes have a high thermal conductivity on the order of 3000 W/(mK) which far surpasses the thermal conductivity range of 0.19 – 8 W/(mK) for present day thermal interface materials. The promising mechanical and thermal properties of carbon nanotubes (CNT) led to the development of CNT arrays, with expectations of creating an interface material with both high thermal conductivity and compliance. This led to a wealth of research and investment dollars in the scientific community to characterize the growth parameters necessary to produce high quality carbon nanotube arrays for thermal applications. Although significant progress has been made, synthesis of high purity carbon nanotube arrays at the industrial level is not cost effective and those produced do not possess the exceptional heat transfer capabilities predicted computationally.
The most widely available and cost effective means of producing carbon nanotubes arrays is by chemical vapor deposition (CVD). This experimental study varied the ferrocene catalyst sublimation temperature over a range of 100ºC - 180ºC, in CVD growth, to determine the impact on structural formation of vertically aligned carbon nanotube arrays. The diameter distribution, areal density, array height, and CNT density are calculated using measurements from scanning electron microscope and transmission electron microscope images to assess array quality. Raman spectroscopy was used as a tool to quantify the amount of disordered carbon within the array. It is found that decreasing the sublimation temperature improved the carbon nanotube arrays for thermal interface material applications using the current growth procedure.