1. Aoyagi, H., Horinaka, H., Kamiya, Y., Kato, T., Kosugoh, T., Nakamura, S., Nakanishi, T., Okumi, S., Saka, T., Tawada, M. and Tsubata, M, 1992, Phys.Lett.A167: 415.
2. Bell, R.L., 1973, “Negative Electron Affinity Devices”, Clarendon, Oxford.
3. Bernier, G., Beerens, J., De Boeck, J., Deneffe, K., van Hoof, C. and Borghs, G., 1989, Solid StateComm. 69: 727.
4. Campbell, D.M., Tessler, L.R., Lassailly, Y., De Laharpe, P., Hermann, C, Lampei, G., Puech, P., Pisani, P., Landa, G., Carles, R., Daran, E., Munoz-Yague, A. and Fontaine, C., 1994, Ecole Thematique CNRS-PIRMAT, Marseille, September 12 - 14 1994.
5. Chelikowsky, J.R. and Cohen, M.L., 1976, Phys.Rev.B14: 556.