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In this work, carbon nanotubes (CNTs) were grown on the silicon nanowires substrate with different thickness of Ni catalyst layer at temperatures 900Â°C using thermal chemical vapor deposition (CVD) to study their effects on surface morphology and field emission characteristics. Scanning electron microscopy (SEM) image was used to observe the surface morphology and structural properties, and Raman spectroscopy was employed to investigate the structural changes caused by different catalyst thickness. Our experimental results clearly demonstrate that catalyst thickness can effectively vary the field emission current of CNTs. Obvious changes in the surface density and morphology of CNTs caused by the variation of catalyst thickness can be clearly seen, which attributed to the grain size effect and thus an increase in emission current. The emission characteristics of CNTs were found to be dependent on the diameter of carbon nanotubes. Compared with CNTs grown on the different thickness of catalyst, CNTs grown on silicon nano wires with Ni catalyst of 7.5 nm exhibit the largest field emission current.