Facile fabrication of conducting hollow carbon nanofibers/Si composites for copper phthalocyanine-based field effect transistors and high performance lithium-ion batteries

In this paper, we describe the preparation and dual-use of carbon nanofibers/Si (CNFs/Si) composites as the source/drain contacts for copper phthalocyanine (CuPc) based thin film transistors (TFTs) and as anode materials for high performance lithium-ion batteries. The CNFs/Si composites are prepared by a facile chemical vapor deposition (CVD) technique with iron nitrate as the catalyst source and acetylene as the carbon source. In the CNFs/Si structure, Si particles are tightly wrapped by CNFs with an average diameter of 15-30 nm and length of 1-2 mu m. It can be seen that the catalysts are grown on the top tip of the CNFs. Based on the superior properties of the CNFs coating, the CNFs/Si composites are applied in different fields. Compared with CuPc based OTFTs with Au contacts, the performances of organic thin film transistors (OTFTs) with CNFs/Si contacts are significantly improved. For OTFTs with CNFs/Si contacts, they show the on-state current increasing from 9 x 10(-9) to 3 x 10(-7) A at the gate voltage of -40 V, field effect mobility increasing from 1.9 x 10(-4) to 4.2 x 10(-3) cm(2) V-1 s(-1), and threshold voltage shifting from 15 to 30 V for the saturation regime. These are attributed to the more effective charge-carrier injection of CNFs/Si contacts than of Au contacts. Besides, the CNFs/Si composites are also promising lithium storage host materials. They show excellent rate capability as anode materials for lithium batteries. The initial discharge and charge capacities of CNFs/Si composites at 0.05 C are 1491.6 and 1168.7 mAh g(-1), respectively. For comparison, the initial discharge and charge capacities of the CNFs/Si composites at 0.60 C are 1197.8 and 941.4 mAh g(-1), respectively. After twenty cycles, the discharge and charge capacities at 0.60 C are 834.4 and 733.9 mAh g(-1), respectively.