Growth of Tungsten Nanotip and Its Field Emission Characteristics

Summary form only given. A considerable attention has been paid to development of a nanotip for the electron source and the cantilever of scanning microscopes. A point electron source is strongly desired to improve performance of high-resolution electron beam instruments. A single carbon nanotube (CNT) is expected as one of the most promising materials to achieve a small apex radius of the device. There has been a report on field emission characteristics of the single CNT. This paper describes a novel finding that a single crystalline tungsten nanotip with an apex radius as small as 4.2 nm is grown on the top of the conventional polycrystalline tungsten tip prepared by electrochemical etching. An electron emission current of 1 nA is obtained at an electric field as low as xxx V/mum and an electron emission current as high as 0.1 mA is achieved from a single tungsten nanotip emitter. Tungsten nanotip emitter was fabricated as follows. A conventional tungsten tip with an apex radius of 100 nm was formed by electrochemical etching and was coated with BN film. The BN film was grown by plasma-assisted chemical vapor deposition. Borontrichloride and nitrogen were used as source gases. The growth temperature was fixed at 650degC. The tungsten tip with BN film was set in the high vacuum chamber. DC bias was supplied between the anode electrode and the tungsten tip sample. As a result, it was found that a tungsten nanotip was grown on the conventional tungsten tip though the formation mechanism was not understood yet. It was observed by transmission electron microscope that a single crystalline tungsten nanotip with (110) crystallographic orientation was grown. Field emission characteristics were measured in the chamber evacuated to 1times10^-9 torr. The turn-on electric field at an emission current of 1 nA was estimated to be 8.8times10^-2 V/mum for the conventional tungsten emitter On the other hand the turn-on electric field was estimated to be as low - as 2.6times10^-2 V/mum for the tungsten nanotip field emitter. An electron emission current as high as 0.1 mA was achieved. These field emission characteristics of the single tungsten nanotip are comparable with those of the single CNT