Field emission properties of Fe70Pt30 catalysed multiwalled carbon nanotubes

Multi-walled carbon nanotubes were grown on nanocrystalline Fe70Pt30 film using low-pressure chemical vapour deposition (LPCVD) method. The growth time was varied between 5 min to 30 min. SEM micrograph of this film revealed that the size of nanoparticles varied from 5 nm to 10 nm. The diameter of the carbon nanotubes varied from 20 nm to 50 nm as verified by TEM. HRTEM image confirmed that the carbon nanotubes are bamboo-shaped multiwalled carbon nanotubes (MWNTs). Field emission characteristics of MWNTs at various growth times (5 min, 15 min and 30 min) with working distances (50 mu m, 100 mu m and 150 mu m) were also studied. The carbon nanotubes grown for 30 min with working distance 150 mm exhibited the lowest turn-on field of 2.45 V/mu m. The turn-on field increases from 2.45 V/mu m to 6.21 V/mu m as the growth time decreases from 30 min to 5 min whereas for lower working distances (100 mm and 50 mu m), the turn-on field increases from 4.74 V/mu m to 6.74 V/mu m and from 8.79 V/mu m to 14.49 V/mu m respectively. The turn-on field (E-to) and field enhancement factor (beta) were studied as a function working distance (d) and growth time respectively to see the effect of these parameters on field emission properties. The field enhancement factor (beta) was also studied as a function of radius of apex curvature (r). It was found the field enhancement factor (beta) decreases with the increase in radius of apex curvature (r) and growth time whereas the value of field enhancement factor (beta) increases as working distance (d) increases. On the basis of the dependence of beta on radius of apex curvature (r) a relationship of beta alpha r(-1/2) is fitted.