Bis(cyclopentadienyl)cobalt (II) (Cobaltocene) Co(η5-C5H5)2[[i],[ii]] is black paramagnetic solid (1.76 BM) with melting point 173 °C, reacting rapidly with O2, but less sensitive to H2O. It is synthesized by methathesis reaction between anhydrous cobalt chloride and sodium cyclopentadienide: CoCl2 + 2 Na(C5H5) → Co(η5-C5H5)2 + 2 NaCl
[i] H.-B.-R. Lee, J.Y. Son, H.Kim, Appl. Phys. Lett., 2007, 90, 213509-1–213509-3
[ii] H.-B.-R. Lee and H. Kim, Electrochem. Solid-State Lett., 2006, 9, G323–G325.
Co(η5-C5H5)2 has been applied as precursor for the growth of metallic Co films in a cold-wall reactor at 400–700 °C with H2 carrier gas (pre-requisite for pure films) and precursor partial pressure 40 mTorr. Deposition rate was 0.6 nm/min, SiO2 on Si surface was necessary (otherwise no deposition occurred). Decomposition mechanism of Co(η5-C5H5)2 is similar as for other metallocenes.
Pure cobalt films have been produced in the presence of plasma [1050]
Cobalt bis(cyclopentadienyl) Co(C5H5)2, (and for comparison Co2(CO)8, Co(C5H5)(CO)2 and CoCF3(CO)4 ) has been applied as precursor for the growth of CoSi2 layers by MOCVD (using SiH4 and Si2H6 as silicon co-precursors), as well as metallic Co films. Strongly textured (111)-β Co layers were grown from Co(C5H5)2 (as well as Co(C5H5)(CO)2 and CoCF3(CO)4 ) at temperatures over 300°C in H2 at atmospheric pressure; on Si substrates growth from Co(C5H5)2 was inhibited. Co(C5H5)2 pre-reacted with (SiH4 (or Si2H6), what resuled in the carbon contamination in the layers; the Co/Si ratio and the C content in the layers was nearly independent of the growth conditions. The carbon incorporation using Co(C5H5)2 precursor could be avoided by a pulsed growth method in which the Co precursor and the Si precursor were introduced alternately into the reactor. [[i]]
[i] G.J.M. Dormans, G.J.B.M. Meekes, E.G.J. Staring, Journal of Crystal Growth, Volume 114, Issue 3, November 1991, p.364-372, “ OMCVD of cobalt and cobalt silicide”