Calcium β-diketonates are one of the most popular precursors for MOCVD of calcium-contaning thin films, because of their volatility, suitable thermal stability and non-sensitivity to air.
Calcium bis(acetylacetonate) has trimeric structure [Ca3(acac)6], based on mass-spectrometric studies. Thus, the detection of Ca3(acac)6 and possibly Ca2(acac)4 in the unionized vapor of the calcium complex (as well as in the negative-ion mass spectra) indicated the polymeric (most probably trimeric) structure of the Calcium bis(acetylacetonate). [[i]]
[i] CG Macdonald and JS Shannon, Australian Journal of Chemistry 1966, 19(9) 1545 – 1566, Full text doi:10.1071/CH9661545, “Mass spectrometry and structures of metal acetylacetonate vapours”
Liquid calcium bis(hexafluoracetylacetonate) tetraglyme adduct [Ca (hfac)2(tetraglyme)] (in combination with Ba(hfac)2(methylethylpentaglyme) and Cu(thd)2) has been applied as calcium MOCVD precursor for the growth of BaCaCuO(F) films, which were subsequently converted to high-temperature-superconducting phase Tl2Ba2Can-1CunO4+2n (n = 2.3) (TBCCO) by ex-situ anneal in the presence of Tl2O at temperatures 820-900°C. The film growth psocess was mass transport-limited, ligand exchange processes have been observed. [[i]]
[i] B.J. Hinds, D.B. Studebaker, J. Chen, R.J. McNeely, B. Han, J.L. Schindler, T.P. Hogan, C.R. Kannewurf and T.J. Marks , Proc. Tenth European Conf. Chemical Vapour Deposition, J. Phys. IV France 05 (1995) C5-391-C5-406, DOI: 10.1051/jphyscol:1995546
http://hal.archives-ouvertes.fr/docs/00/25/39/08/PDF/ajp-jp4199505C546.pdf
”MOCVD Routes to Tl2Ba2Can-1CunO4+2n Superconductor and Dielectric Insulator Thin Films”
Trimeric calcium bis(2,2,6,6-tetramethyl-3,5-heptanedonate) [Ca3(thd)6] is one of the most popular precursors for the growth of Ca-containing layers by MOCVD or ALD.
Calcium bis(2,2,6,6-tetramethyl-3,5-heptanedonate) is white amorphous solid, having melting point ca. 223-225°C. [[i]]
The crystal structure of calcium bis(2,2,6,6-tetramethyl-3,5-heptanedonate) was studied by X-ray crystallography; this is the first structurally characterized homoleptic β-diketonate of calcium). It was determined that it has trimeric structure [Ca3(tmhd)6]; with novel triangular core having all calcium ions six-co-ordinate, held together by tmhd ligands in a wide range of co-ordinating modes.[[ii]]
The vapor phase structure of calcium bis(2,2,6,6-tetramethyl-3,5-heptanedonate) has been studied by mass spectrometric, electronographic and gas chromatographic studies. [[iii] ]
According to the mass-spectrometric studies, saturated vapors of alkaline earth β-diketonates (including Ca(thd)2) contain a mixture of polymeric forms (ML2)n. The electronographic study Ca(thd)2 revealed that of the best agreement with measurement data is achieved for geometric structure with coordination polyhedron [МО4] having symmetry configuration D2d, and planes of chelate fragments of ligands mutually perpendicular. [[iv]]
[i] J. E. Schwarberg, R. E. Sievers, R. W. Moshier
Anal. Chem., 1970, 42 (14), pp 1828–1830, DOI: 10.1021/ac50160a068
[ii] V-Cumaran Arunasalam, Simon R. Drake, Michael B. Hursthouse, K. M. Abdul Malik, Stewart A. S. Miller and D. Michael P. Mingos, J. Chem. Soc., Dalton Trans., 1996, 2435-2442. ”Synthesis, structure and characterisation of magnesium and calcium β-diketonate complexes [Ca3(tmhd)6] and [Ca2(tmhd)4(EtOH)2](Htmhd = 2,2,6,6-tetramethylheptane-3,5-dione)”
[iii]a)Морозова Н.Б., Жаркова Г.И., Стабников П.А. и др. Синтез и физико-химические исследования β-дикетонатов щелочноземельных металлов. – Новосибирск, 1989. – С. 28.
b) TurnipseedS.B., BarklayR.M., SieversR.E. // J. Inorg. Chem. – 1991. – 30. – P. 1164 – 1170.
c) Алиханян А.С., Малкерова И.П., Кузьмина Н.П. и др. // Журн. неорган. химии. – 1994. – 39, № 9. – С. 1534 – 1538.
[iv] Гиричева Н.И., Исакова Н.А., Гиричев Г.В. и др. // Журн. структур. химии. – 1999. – 40, № 3. – С. 468 – 476.
Ca(thd)2 for Ca-stabilized ZrO2 by MOCVD
Calcium bis-(2,2,6,6-tetramethyl-3,5-heptanedionate) triglyme adduct [Ca(tmhd)2·triglyme] has been applied as calcium source for MOCVD growth of calcium-stabilized ZrO2 (CSZ) films (with Cp2ZrMe2 as Zr precursor). Colorless crack-free CSZ films well adherent to the substrates have been obtained at 500 °C on fused quartz substrates. The microstructure and chemical composition of the films was studied by XRD, XPS and EDXS, the complete stabilization of zirconia in its cubic-fluorite phase by 17-38% Ca content has been demonstrated. [[i][PS1] ]
Ca(thd)2 for CaF2 films growth by ALD
Ca(thd)2 has been applied as calcium precursor for the ALD growth of CaF2 films, by using TiF4 as fluorine source. The good stoichiometry low-impurity level CaF2 films were obtained at 350 °C-400 °C, the crystallinity, morphology, composition, thicknesses, refractive indices (n=1.43 for CaF2), and transmittance of the films were studied [[ii][PS2] ]
[i] Giovanni Carta, Naida El Habra, Gilberto Rossetto, Pierino Zanella, Maurizio Casarin, Davide Barreca, Cinzia Maragno and Eugenio Tondello, Surface and Coatings Technology, Volume 201, Issues 22-23, 25 September 2007, Pages 9289-9293, Euro CVD 16, 16th European Conference on Chemical Vapor Deposition “MgO and CaO stabilized ZrO2 thin films obtained by Metal Organic Chemical Vapor Deposition”
[ii]Tero Pilvi, Mikko Ritala, Markku Leskelä, Martin Bischoff, Ute Kaiser, and Norbert Kaiser, Applied Optics, Vol. 47, Issue 13, pp. C271-C274 (2008) doi:10.1364/AO.47.00C271, “Atomic layer deposition process with TiF4 as a precursor for depositing metal fluoride thin films”
Liquid calcium bis(2,2,6,6-tetramethyl-3,5-heptanedonate) (N,N’,N’-tripentyldiethylenetriamine) adduct [Ca(thd)2][TPDETA) have been prepared; it has been proposed as potential precursor for MOCVD of Ca-containing thin films[]
[Ca(DFHD)2H2O], the stable and volatile β-diketonate complex of calcium with new β-diketone ligand 1,1,1,2,2,3,3,7,7,7-decafluoroheptane-2,4-dione (HDFHD) has been applied as calcium for MOCVD growth on silicon substrates of (111) oriented CaF2 thin films. Changes in the film growth rate with time have been observed, attributed to slow precursor decomposition ([Ca(DFHD)2H2O]. [[i]]
[i] Simon C. Thompson, David J. Cole-hamilton, Douglas D. Gilliland, Michael L. Hitchman, John C. Barnes, Advanced Materials for Optics and Electronics, Volume 1, Issue 2, pages 81–97, April 1992