Preparation and tribological properties of novel carbon nanotube self-assembled composite films

Carbon nanotube (CNT) composite thin films were prepared on a single-crystal silicon substrate by a self-assembling process from a specially formulated solution. Rare earth solution (RES) surface modification and appropriate acid-treatment methods were used to functionalise carbon nanotubes (CNTs). Silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared first. The terminal thiol groups (-SH) in the film was oxidised to sulphonic acid groups (-SO3H) in situ to enhance the film with good chemisorption ability. Treated Caron nanotubes were deposited on the oxidised MPTS-SAM by means of chemisorption with the SO3H group. The surface energy, chemical composition, phase transformation and surface morphology of the films were analysed using contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy. As a result, a conclusion could be made that some lanthanum elements react with -SO3H groups on the surface of the substrate by a chemical bond, which will improve the bonding strength between the films and the CNTs. Since the CNT thin films were well adhered to the silicon substrate, it might find promising application in the surface-modification of single-crystal Si and SiC in microelectromechanical systems (MEMS).