| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Nanomaterials | Tuesday Sessions |
| Session NM-TuP |
| Session: | Nanomaterials Poster Session |
| Presenter: | Soichiro Matsunaga, Hitachi Ltd, Japan |
| Authors: | S. Matsunaga, Hitachi Ltd, Japan Y. Suwa, Hitachi Ltd, Japan K. Kasuya, Hitachi Ltd, Japan S. Katagiri, Hitachi Ltd, Japan |
| Correspondent: | Click to Email |
We investigated a tungsten (310) surface, which has been widely used as electron emitting surface of cold field emitters (CFE). The intensity of electron beams emitted from a CFE rapidly decreases even under an ultra-high vacuum (UHV) environment of 10-8 Pa [1]. There has been a recent report that a stable operation region with high current angular density appeared by operating a CFE under an extreme-high vacuum (XHV), from 10-9 to 10-10 Pa[2]. That study revealed that the decreasing of the emitted beam is caused by residual hydrogen gas in CFE gun chambers, and they used a non-evaporative getter (NEG) to evacuate the hydrogen gas from the gun chamber. In the stable operation region of a NEG-evacuated CFE, we have observed unexpected increasing and step-wise shifting of the beam current.
In order to understand the mechanisms behind the unexpected beam fluctuations, we performed electron emission experiments and computational simulation of the emission surface. Results showed that the step-wise fluctuation is related to the adsorption of a single carbon monoxide (CO) molecule onto the W(310) surface. We performed a first principle calculation of the CO-adsorbed W(310) surface in order to understand the mechanism behind the step-wise fluctuation. To study the site of electron emission on the single-CO-molecule-adsorbed surface, we developed a calculation method to evaluate the heterogeneous potential barrier height of the surface under strong electric fields. On the basis of these experimental and calculation results, we propose that the adsorption and diffusion of a single CO molecule on W(310) surface cause the step-wise fluctuations of the current.
[1] S. Yamamoto, et al., “Field emission current instability induced by migrating atoms on W(310) surface”, Surf. Sci., 71., 191 (1978)
[2] K. Kasuya, et al., “Stabilization of tungsten 310 cold field emitter”, J. Vac. Sci. Technol. B, 28, L55 (2010)