Improved field emission property of vertically array carbon nanotube assembled with CdS QDs

Abstract

Summary form only given. CdS is a promising material for flat panel displays, light-emitting diodes, lasers, logic gates, and transistors. CdS has attracted special interest because it exhibits high photosensitivity and its band gap energy (2.41 eV) and electron affinity (4.5 eV) appear in the visible spectrum [1]. In this work, CdS deposition on surface of the vertical aligned carbon nanotube (VACNT) on silicon wafer is fabricated by chemical bath deposition (CBD) method. The field emission (FE) properties of CdS-VACNT are investigated. Silicon wafers were ultrasonically cleaned in de-ionized water, acetone, and iso-propanol alcohol, and were dried at 100 °C in an atmospheric pressure oven. VACNT arrays were grown by Plasma Enhanced Chemical Vapour Deposition (PE-CVD) at 500 οC using a magnetron sputtered, 7 nm-thick Ni catalyst with photolithographically defined 6 μm spacing. The VACNT fabrication process is described in detail elsewhere. VACNT substrate was dipped into an ethanol solution containing 0.5 M Cd(Nθ3)2 for 5 min, rinsed with ethanol and then dipped for another 5 min into 0.5 M Na2S menthol solution and rinsed again with menthol. The two step dipping procedure is termed as one CBD cycle and it repeated 5 times for VACNT covered with CdS QDs. Fig. 1(a) and (b) show the SEM image of CdS covered on VACNTs. It can be seen that the VACNTs grown in a hexagonal array with a length of 5 μm. The CdS covered on the surface of the VACNTs. Fig. 2(a) and (b) TEM image of single nanotube before and after covering with CdS. It can be seen that the CdS QDs adsorbed uniformly on the surface of single carbon nanotube. The FE measurements of VACNT and CdS-VACNTs were taken. The typical plot of the FE current density J versus the applied electric field E and the corresponding Fowler-Nordheim (F-N) plots of the VACNT and CdS-VACNTs are represent in Fig. 3(a) and (b), respectively. Here we define the turn-on field as the applied electric fields required to the produce a current of 10 μA/cm . The turn-on field for VACNTs and CdS-VACNTs are 3.5 and 2.4 V/μm, respectively. Field emission properties are usually described in terms of parameters defined by the Fowler Nordheim (F-N) theory. The field emission enhancement factor β for VACNTs and CdS-VACNTs are calculated by fitting the slope value of F-N curves to be 1218 and 3998.