3826 J. Phys. Chem. zyxwvut 1984, 88, zyxwvu 3826-3833 move down. Thus the separation effect of zyxwvuts eq 33 will be repeatedly established along the countercurrent column leading to an en- richment of 6Li on its top with an enrichment factor which in- creases exponentially with column length. A plant for the 6Li production for a 2.5-GW (thermal) fusion reactor (600 g of 6Li/day) easily could be combined with that for the production of the necessary deuterium (200 g of D/day) which is also based on an exchange process in liquid ammonia.4s Both installations hardly exceed the dimensions of the bell tower of a small village church and would yield nuclear fuel on a cost level of a few percent of the value of the produced electrical energy. The deuterium enrichment process which also has its origin in fundamental research on metal-ammonia solutions46 already is (45) S. Walter and U. Schindewolf, Chem. Ing. Tech., 37, 1185 (1965). in operation for the large-scale production of heavy water?' The 6Li-enrichment process is being developed in our laboratory. Thus the purely academic work on the metal-ammonia solutions has lead to a spinoff which one day might yield the unlimited nuclear fuel of the future. Acknowledgment. The experimental work of our laboratory mentioned in this review has been supported by the Deutsche Forschungsgemeinschaft and the Fonds der chemischen Industrie. We gratefully acknowledge this support. Registry No. Sodium, 7440-23-5; ammonia, 7664-41-7. (46) W. K. Wilmarth and J. C. Dayton, J. Am. Chem. SOC., 75, 4553 (47) E. Nitschke and S. Walter, Chem. Eng. World, 1, 54 (1970). (1953). Behavior of n-Type and p-Type Silicon in Anhydrous Liquid Ammonia. Solvated Electron Generation: A Supraband-Edge Reaction M. Herlem,* D. Guyomard, C. Mathieu, Laboratoire de Chimie Analytique des milieux rPactionnels, ESPCI, 75231 Paris CZdex OS, France J. Belloni, Laboratoire de Physicochimie des Rayonnements, Universitt? de Paris-Sud, 91 400 Orsay, France and J. L. Sculfort Laboratoire d%lectrochimie Interfaciale du CNRS, 921 90 Meudon, France (Received: August 24, 1983; In Final Form: March 1, 1984) The behavior of n-type and p-type silicon electrodes (single crystal (100)) is studied in anhydrous basic liquid ammonia with variable solvated electron concentration. In dilute medium, Fermi level pinning on the surface states occurs and the photoelectrochemical cell p-Si/NH3 + KBr (0.1 mol dm-3) + NH2- (2 X lo-' mol dm-3) + e;/counterelectrode delivers a large V, (more than 0.5 V). In concentrated medium ([e;] > 2 X mol dm-3) the strong interaction of e; species toward the SC surface creates a thin conductive layer on the surface which gives a new interface state distribution. Then no photoeffects occur at n-Si or p-Si electrodes. Introduction silicon in aqueous or nonaqueous Numerous papers concern the behavior of n-type or p-type The nonaqueous (1) D. Laser and A. J. Bard, J. Phys. Chem., 80, 459 (1976). (2) G. Nagasubramanian, B. L. Wheeler, F. R. F. Fan, and A. J. Bard, (3) G. Nagasubramanian, B. L. Wheeler, F. R. F. Fan, and A. J. Bard, (4) K. D. Legg, A. B. Ellis, J. M. Bolts, and M. S. Wrighton, Proc. Narl. (5) A. J. Bard, A. B. Bocarsly, F. R. F. Fan, E. G. Walton, and M. S. (6) J. N. Chazalviel, Surf. Sci., 88, 204 (1980). (7) J. N. Chazalviel, J. Electrochem. zyxwvutsrqp SOC., 127, 1822 (1980). (8) J. N. Chazalviel, J. Electrochem. Soc., 129, 963 (1982). (9) J. N. Chazalviel and T. B. Truong, J. Electroanal. Chem., 114, 299 (10) J. N. Chazaviel and T. B. Truong, J. Am. Chem. SOC., 103, 7447 (1 1) J. A. Turner, J. Manassen, and A. J. Nozik, Appl. Phys. Lett., 37, (12) B. L. Loo, K. W. Frese, and S. R. Morrison, Appl. Surf. Sci., 8,290 J. Am. Chem.Soc., 129, 1742 (1982). J. Am. Chem. SOC., 130, 1680 (1983). Acad. Sci., U.S.A., 74, 4116 (1977). Wrighton, J. Am. Chem. SOC., 102, 3671 (1980). (1980). (1981). 488 (1980). (1981). solvents were used to avoid water or oxygen traces which allow the growth of SiO, or SiOz thin layer on the silicon. This layer seems to play an important part in the redox charge transfer process at the interface, in this way, different results obtained with n-type and p-type silicon were explained by either partial or complete Fermi level pinning,'-1° an inversion mechanism," or interface states arising from the oxide Using oxide-free silicon electrodes in anhydrous medium, we were able to show the influence of pH on the flat-band potential of the semicond~ctor.'~ This pH influence was recently observed (13) M. J. Madou, B. L. Loo, K. W. Frese, and S. R. Morrison, Surf. Sci., (14) D. G. Canfield and S. R. Morrison, Appl. Surj. Sci., 10,493 (1982). (15) D. Guyomard, M. Herlem, C. Mathieu, C. Miossec, and J. L. (16) G. Van Amerongen, M. Herlem, R. Heindl, D. Guyomard, and J. L. (17) P. Brondeel, M. Madou, W. P. Gomes, P. Hanselaer, and F. Cardon, (18) H. J. Byker, V. E. Wood, and A. E. Austin, J. Electrochem. Soc., 129, 108, 135 (1981). Sculfort, J. Electroanal. Chem., 138, 435 (1982). Sculfort, J. Electrochem. SOC., 129, 1998 (1982). Solar En. Mater., I, 23, 33 (1982). 1982 (19821. (l9) A. Heller, H. J. Lewerentz, and B. Miller, J. Am. Chem. SOC., 103, 200 (1981). 0022-3654/84/2088-3826$01.50/0 0 1984 American Chemical Society