Chem. Mater. 1991, 3, 14-17
14
Table 11. Fe/Co Ratio of T h i n Films Prepared by P C V D U s i n g Fe(CO)5/Co(CO)8N0 and Fe(CO)5/Co2(CO)8 Precursors at Different VaDorization TemDeratures'
T , "C Fe(CO), ("C) CO(CO)~NO( O C ) 20 -1 20 20 2 20 5 0
COACO)~ ("C)
4 20 20 45 45 45
6 t I&=
- -- -m Cn
Fe/Co ratio 1.40 1.25
1 .oo 0.78 0.66 0.21 0.13
These results represent the average values of at least two different films, and the margin of error was & l o % .
-
Therefore, PCVD experiments using a 345-nm long-pass filter to selectively excite this M r*NO absorption band of CO(CO)~NO should yield Co-rich films relative to control experiments using no filter. On the contrary, if a 325-nm bandpass filter is used such that the percent transmittance at 374 nm is reduced to -0.1, Fe-rich films should be obtained. The results in Table I demonstrate that the relative proportions of Fe and Co in alloy thin films, as determined by XRF, can be manipulated in a predictable fashion using this selective excitation approach. The only published report on wavelength control of film composition was by Armstrong et al.,1° in which two different Fe/Ni ratios were obtained by using metallocene precursors and two different lasers as irradiation source. Under their experimental conditions, "significant carbon content" was found in the resulting films,l0 compared with the 1 and e l , res p e c t i ~ e l y . ~The ~ ~ dependence of the structure on the equilibrium water partial pressure and cation-exchange illustrates the structural importance of intercalant iondipole interaction^.^-^ Structural investigations to date have not revealed the presence of discrete solvation complexes but have indicated the general intercalant site coordination for selected Recent stability (1) Subba Rao, G. V.; Shafer, M. W. Intercalated Layered Materials; D. Reidel: Dordrecht, Holland, 1979; pp 99-199. (2) Rouxel, J. Intercalated Layered Materials; D. Reidel: Dordrecht, Holland, 1979; pp 201-250. (3) Schdlhorn, R. Intercalation Chemistry; Academic Press: New York, 1982; pp 315-374. (4) Schollhorn, R. Inclusion Compounds; Academic Press: London, 1984; pp 249-349. (5) Lerf, A.; Schollhorn, R. Inorg. Chem. 1977, 16, 2950-2956. (6) Schollhorn, R.; Weiss, A. Z. Naturforsch. 1973, 28b, 711-715. (7) Wiegers, G. A.; van der Meer, R.; van Heiningen, H.; Kloosterboer, H. J.; Alberink, A. J. A. Mater. Res. Bull. 1974, 9, 1261-1266. (8) Whittingham, M. S.Mater. Res. Bull. 1974, 9, 1681-1690.
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Figure 2. TGA of ~NH4+~o.os[Ca2+o.on~NH~~~.~1~N showing the three steps corresponding to the deintercalation of NH," (I),NH38(11),and NH4+.(111). Steps I and I1 are generally more clearly resolved for the higher charge density metal cations. studies and complete structural refinement of the monousing neutron layer compound (7Li+)o,22(ND,)o,63Ti~20~z2powder diffraction (NPD) data illustrate for the first time the presence of discrete, monovalent Li+(ND,), complexes between the T i s 2 layers.12 Highly stoichiometric Tis, (Til,,,,,S2) was used as the host material.13 Both the intercalates and the host were prepared, handled, and investigated under rigorous inert-atmosphere conditions.14J5 Both the metal (M) and NH, undergo redox reactions during the intercalation process, with NH, forming NH4+,which intercalates more slowly than M.15 These compounds exhibit charge compensation, with NH4+ intercalation continuing until the total charge transferred to the Tisz conduction band is about 0.23 mol of e-/mol of TiS2.I5Hence, they are best where n x described as M,n+(NH4+)y,(NH3)yTiS2(nX+Y')-,
+
(9) Graf, H.; Lerf, A.; Schollhorn, R. J. Less-Common Met. 1977,55, 213-220. (10) Bas-Alberink, A. J. A.; Haange, R. J.; Wiegers, G. A. J. LessCommon Met. 1979, 63, 69-80. (11) Patel, S. N.; Balchin, A. A. J . Mater. Sci. 1985, 20, 917-921. (12) Young, Jr., V. G.; McKelvy, M. J.; Glaunsinger, W. S.; Van Dreele, R. B. Chem. Mater. 1990,2, 75-81. (13) McKelvy, M. J.; Glaunsinger, W. S.J. Solid State Chem. 1987, 66., 181-188. (14) Bernard, L.; McKelvy, M.; Glaunsinger, W.; Colombet, P. Solid State Ionics 1985, 15, 301-310. (15) McKelvy, M.; Bernard, L.; Glaunsinger, W.; Colombet, P. J. Solid State Chem. 1986, 65, 79-88. ~~~
~
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0 1991 American Chemical Society
