The Research Of Synthesis And Adhesion Performance Of Carbon Nanotube Arrays Based Gecko-inspired Dry Adhesive

Carbon nanotube arrays（VACNTs）,with their excellent mechanics,electricity,thermal performance and robustness in extreme circumstances,become a potential material for gecko-inspired dry adhesives and further application on wall-climbing robots.In view of the present problems existing in the VACNTs controllable preparation,we design growth substrates with different thicknesses of support and catalyst layers and regulate the hydrogen pretreatment time,hydrogen concentration,deposition time and reaction pressure in the process of chemical vapor deposition to explore their influence on the morphology structure,degree of defects,purity,quality,and adhesion performance of prepared VACNTs.Bsed on the understanding of growth mechanism,this work would help to realize the controllable preparation of VACNTs.In this paper,the main achievements and conclusions are as follows:1.The thicknesses of the support layer and catalyst layer have a significant effect on the VACNTs growth.The thickness of the Fe layer directly determines the distribution of the catalyst particles,which as growth templates further influence the morphology of the VACNTs.Porous Al₂O₃ make molten Fe into their pore and form uniform particle size distribution,but thick layer of Al₂O₃ increase the diffusion loss.And denser SiO₂ layer effectively block the Fe particles diffusion.2.By adjusting the hydrogen concentration during pretreatment stage and deposition stage,the growth rate of VACNTs can be controlled to achieve rapid growth.AFM observations show that a suitable pretreatment concentration of hydrogen reduces Fe membrane to metal state and forms uniform distribution of Fe particles.In the experiments,the substrates of SiO₂/Al₂O₃/Fe = 300 nm/15 nm/1 nm are used,and the VACNTs prepared under the hydrogen concentration of 25% reach the height of 949μm,the growth rate is 23.72 μm/min.Raman spectra indicate that the VACNTs present higher graphitization degree and have the relatively best purity and quality.3.The effect mechanism of hydrogen concentration on the adhesion performance of VACNTs is proposed.When the hydrogen ratio is low（0%⁵%）,the growth heights of VACNTs are too low to form large area of line contact with the target surfaces.And when the hydrogen ratio is too high（25%³5%）,the excess hydrogen transform the catalyst phase from FeC₃ to BCC Fe,which makes greater defect degree of prepared VACNTs.On the substrate of SiO₂/Al₂O₃/Fe = 300 nm/20 nm/2 nm,the VACNTs growth under the hydrogen concentration of 15% show good adhesion performance,and the shear adhesion force reaches 32 N/cm2,3.2 times that of a gecko foot.