Structural and morphological dependence of carbon nanotube arrays on catalyst aggregation

► The thickness of the catalyst film has a direct effect on the areal density of the catalytic particles and then the alignment of the CNT array. ► Both the size and areal density of the catalyst also change with the CNT growth in accordance with Ostwald ripening process, with the bottom of the CNT array varying from well-aligned to disordered and adhesion between catalyst particles and the substrate getting enhanced. ► Introducing alumina as buffer layer and annealing the catalyst film at low pressure are two effective approaches to downsize the catalyst particles and then the diameter, wall number of the CNTs.