Several iron carbonyls are existing, the most known are pentacarbonyliron Fe(CO)5, diiron nonacarbonyl Fe2(CO)9, and triiron dodecacarbonyl Fe3(CO)12, some of them hav been applied as CVD precursors for the growth if metallic iron films.
Pentacarbonyl iron Fe(CO)5 ( M = 195.90) is yellow poisonous liquid (d = 1.453 g/ml), melting at -25°C (another data mp. -20.5°C), boiling at 103°C/ 760Torr [4]. Fe(CO)5 has monomeric molecule, trigonal bipyramidal geometry (Berry-Pseudo Rotation), it has 18-VE (valence electrons).
Vapor pressure (Torr): 0.01/30°C, 0.03/40°C, 0.08/50°C, 0.17/60°C, 0.35/70°C, 0.71/80°C, vapor pressure equation logP(Torr) = 8.514 – 2105/T(K).
Synthesis: reaction of metallic iron with carbon monoxide CO at 1-100 atm pressure and 150-300°C temperature: Fe (met.) + 5 CO, 1-100 atm, 150-300°C → Fe(CO)5
Deposition:
Fe(CO)5 was applied for the deposition of metallic iron Fe films either in ultra-high vacuum system or conventional CVD reactor. Metal iron films have high purity, strongly adherent and not tarnishing with time were obtained.
The mechanism of molecule decomposition/films growth is well-studied:
1)The reaction on the 1st monolayer involves dissociation of CO to give an oxygen over-layer.
2) Further dissociation of CO is not observed anymore; the decomposition
proceeds as follows: (CO)5Fe → Fe(s) + 5 CO(g)
The initially formed oxygen overlayer is displaced by further FeCO)5 molecules (adsorbing and dissociating) as deposition continues; impurities were only found inside the films.
The deposited iron Fe films were characterized by Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES). [[i]]
[i] The Chemistry of Metal CVD, International Research Training Group, “Materials and Concepts for Advanced Interconnects”, Prof. Dr. Heinrich Lang
Iron pentacarbonyl Fe(CO)5 (combined with Ni(CO)4 as nickel source) was applied as precursor for the deposition of thin films of elemental Fe and a
wide composition range of Fe-Ni (permalloy) alloys by atmospheric pressure MOCVD at a growth temperature of 200°C. The maximum magnetoresistance was achieved at
a ~90 % Ni10 % composition, whereas the maximum sensitivity occurred at ~ 80 % Ni20 % Fe, similar to literature data. The application of an 80 mT magnetic field during deposition, as well as annealing of samples
at temperatures over the 200°C growth temperature improved the magnetic properties.[[i]]
[i] Dr. P.A. Lane, Dr. P.J. Wright, P.E. Oliver, Ch.L. Reeves, A.D. Pitt, J.M. Keen, M.C. L. Ward, M. E. G. Tilsley, N.A. Smith, Chem.Vap.Dep. 1997, Vol.3, Iss.2, p. 97-101
https://doi.org/10.1002/cvde.19970030208, « Growth of Iron, Nickel, and Permalloy Thin Films by MOCVD for Use in Magnetoresistive Sensors »
Iron pentacarbonyl (Fe(CO)5), combined with di-tert.-butyldisulphide S(tBu)2 (TBDS) as sulfur source, was used as iron precursor for the growth of thin layers of iron pyrite (FeS2) on glass and glassy carbon substrates by low pressure MOCVD. For varying iron pentacarbonyl partial pressures (0.25, 0.5 and 1 Pa) the effect of variation S(tBu)2 partial pressure from 1 to 100 Pa was studied (with other parameters kept constant). A critical S(tBu)2-partial pressure ~30 Pa where a drastic change in the layer properties occurs was determined (for a deposition temperature of 475 °C). Pyrrhotite type phases (Fe1-xS) are forming below this S(tBu)2 partial pressure, although there is an excess of S precursor in the gas phase. If the layers contain The electrical properties of pyrrhotite-containing,FeSx-films significantly change. The pyrrhotite phase formation did depend on the growth rate, and therefore was not controlled kinetically. Thus, the S pressure above the growing pyrite film is an important parameter controlling the solid phase. In order to prepare pyrite thin films of good electronic quality, even very small concentrations of secondary S-Fe phases must be avoided.[i]
[i] B. Thomas, T. Cibik, C. Höpfner, K. Diesner, G. Ehlers, S. Fiechter, K. Ellmer, J. Mater. Sci.: Materials in Electronics, 1998, Vol.9, Issue 1, pp 61–64, « Formation of secondary iron-sulphur phases during the growth of polycrystalline iron pyrite (FeS2) thin films by MOCVD », link.springer.com/article/10.1023/A:1008943203807
Nonacarbonyldiiron (diiron nonacarbonyl) Fe2(CO)9 (M=): golden solid, mp. 100 °C (decomp.), decomposes in THF producing Fe(CO)5 and Fe(CO)4.
Fe2(CO)9 molecule is a dimer bonded by bridging carbonyl groups ( μ-CO´s), it has no Fe-Fe bond.
Synthesis: exposure of pentacarbonyl iron to UV radiation:
2 Fe(CO)5 + hν → Fe2(CO)9 + CO