Surface smoothness effect for the direct growth of carbon nanotubes on bulk FeCrAl metal substrates.

We investigate effects of surface smoothness and surface chemistry on the nature of multi-walled CNTs (MWCNTs) grown directly on FeCrAl substrates. A single sample was grown that contained a gradation in surface morphologies ranging from 2.9 nm to 30.2 nm RMS. The MWCNTs were grown using ethylene and H2 gases. Characterization was done using atomic force microscopy (AFM), scanning electron microscopy (SEM), and Auger elemental surface analysis. In smooth regions, MWCNTs demonstrated high-density vertical aligned growths; however, patches of approximately 10-20 microm where poor MWCNT growth occurred. In contrast, rough regions of the surface exhibited a continuous blanket layer of MWCNTs, albeit growth was spaghetti-like throughout this layer. The variation in nature of MWCNT growths was directly dependent on the surface roughness, which can affect surface growth chemistry of MWCNTs. Auger elemental analysis determined carbon was observed everywhere on the surface, but carbon was strongest over the smooth regions of high density growth; while relatively less carbon was detected over the patches with poor MWCNT growth, as well as over the blanket layer of the rough region. Oxygen was also measured, which was detected both within the patches of poor MWCNT growth in the smooth regions and over the blanket layer of the rough region. However, measurements of Cr and Al were exhibiting mixed trends: Cr was detected more strongly than Al over the rough region; whereas the opposite was observed in the patches of poor MWCNT growth in the smooth region. The surface smoothness affects the surface chemistry involving the nature of MWCNT growth and may also affect the surface chemistry involving the metal substrate itself; therefore, comparisons on the nature of MWCNT growths must also take careful consideration of the surface smoothness.