Cesium-Lanthanide CVD precursors
Since cesium compounds alone are difficult to vaporise due to their polymeric or ionic nature, the search for volatile double-metal precursors has been performed, such as mixed Cs-Y β-diketonates. (Cs[Y(tfac)3] , Cs[Y(hfac)4, Cs[Y(ptac)4], and others).
They were generally synthesized by mixing solution of Cs(diket) with YX3 (X = Cl, NO3, OAc) in the low-polar solvent, such as CCl4 :
4 ML + LnX3 -> 3MX + M[LnL4]
Cesium-yttrium tetrakis (1,1,1-trifluoro -5,5-dimethylhexane-2,4-dionate) Cs[Y(ptac)4]
Fig. CsY(ptac) Vapor pressure vs temperature
Cesium-yttrium tetrakis (1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionate) Cs[Y(ptac)4] (M=) was synthesized by ion exchange reaction between Cs(ptac) and YCl3 in carbon tetrachloride: Cs(ptac) + YCl3 (CCl4, 60°C, 4h)-> Cs[Y(ptac)4] + 3CsCl (yield 30%)
Cs[Y(ptac)4] was characterised by microanalysis, atomic absorbtion, IR spectroscopy, NMR, TGA. It was determined that it is more stable and volatile than Cs(ptac) : Cs[Y(ptac)4] sublimes 160-180°C without decompositon (sublimation yield 58%).
CyY(ptac)4: Vapor pressure and TGA
Fig. CsY(ptac)4 - vapor pressure vs temperature (Table)
The thermal properties and temperature dependency of saturated vapour pressure of Cs[Y(ptac)4] was measured by TGA (flow method). Thermal and thermodynamic characteristics of melting of Cs[Y(ptac)4] were determined by TGA: melting point 215.40 ± 1.90 ºС, ∆mpН = 22.84 ± 0.54 kJ/mol, ∆mpS = 46.77 ± 1.98 J/mol·K.
The variation of saturated vapor pressure of Cs[Y(ptac)4] with temperature was investigated, the obtained data are presented in a Table and formulas below.[i]
Р0/Т0 = 2,505/296,55 = 0.008447(p/p0) = - ∆sublH/RT+∆sublS/R
∆sublH=106,5 ± 2,3 kJ/mol, ∆sublS=174,8 ± 2,3 J/mol·K, R2=0,9809
Vapor pressure equation was derived from the obtained vapor pressure values at different temperatures (Table): ln(p, Torr/ 760 Torr) = 21,03002- 12,81954*10-3/T (K).
[i] A.A. Vorobjev, Course Thesis, http://www.bibliofond.ru/view.aspx?id=555884
Cs[Y(ptac)4] for Cs- containing films of MgO
Cesium-yttrium tetrakis(1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionate) Cs[Y(ptac)4] , combined with Mg(thd)2(TMEDA) as Mg source,
was applied for the growth of Cs- and Mg,Cs-containing yttrium oxide-fluoride films by low-pressure (LP) CVD. The correlations between temperature conditions of deposition processes and layer properties were investigated, the deposited layers were characterised
by SEM and AFM. Layer composition studied by EDS; the analysis results demonstrated the presence of Mg, Cs, Y, C, O and F in the films composition. The content of caesium in the deposited layers was ~2,5 at %.[i]
[i] E.S. Vikulova, K.V. Zherikova, L.N. Zelenina, T.P. Chusova, S.V. Sysoev, V. Shevtsov, A.P. Zubareva, N.B. Morozova, I.K. Igumenov, Key Eng. Mater. (Vol.Materials Integration), 2012, vol.508, p.215-219, « Comprehensive Approach for the Construction of New Material for Electronic Multipliers », DOI 10.4028/www.scientific.net/KEM.508.215
Cesium-yttrium tetrakis (2,2,6,6-tetramethyl-3,5-heptanedionate) Cs[Y(thd)4]
Cesium-yttrium tetrakis (2,2,6,6-tetramethyl-3,5-heptanedionate) Cs[Y(thd)4] (M =) is yellow crystalline compound subliming at 230°C without decomposition. It was synthesized by the methathesis reaction between cesium 2,2,6,6-tetramethyl-3,5-heptanedionate and yttrium chloride in carbon tetrachloride: Cs(thd) + YCl3 (CCl4, 60°C, 36h)-> Cs[Y(thd)4] + 3CsCl
In another study the attempt of synthesis of Cs[Y(thd)4] resulted in the product subliming at 230°C and containing large amount of Cs ( x2.5
compared to Cs[Y(thd)4] formula, which is even higher than Cs(thd). Nevertheless, the compound is volatile and is therefore it is very promising for MOCVD applications. The composition and structure of the obtained product needs to be determined by single
crystal XRD.[i]
[i] A.A. Vorobjev, Course Thesis, http://www.bibliofond.ru/view.aspx?id=555884
Cesium-yttrium tetrakis (hexafluoracetylacetonate) Cs[Y(hfac)4]
The crystal structure of cesium-yttrium tetrakis (hexafluoracetylacetonate) (cesium tetrakis(hexafluoroacetylacetonato)yttrate(III)) was determined by single
crystal XRD. It was determined that it represents a novel stereoisomer having dodecahedral eight-coordination.[i]
[i] M. J. Bennett , F. A. Cotton , P. Legzdins , S. J. Lippard, Inorg. Chem., 1968, 7 (9), pp 1770–1776, DOI: 10.1021/ic50067a016, « Crystal structure of cesium tetrakis(hexafluoroacetylacetonato)yttrate(III). Novel stereoisomer having dodecahedral eight-coordination”
Cesium-lantanum tetrakis (hexafluoracetylacetonate) Cs[La(hfac)4]
Cesium-lantanum tetrakis (hexafluoracetylacetonate) Cs[La(hfac)4] was reported to be synthesized by the cation exchange column procedures. The rare earth (La) was fixed on Dowex 50 in either hydrogen or the cesium form; in the former case the excess acid form resin was converted to the Cs form before the rare earth was eluted with 0·4 M Cs(hfac) in 50% ethanol. The losses were insignificant even when loading the rare earth onto the resin from ∼ 1 M solutions in HCl, presenting an advantage when starting with the rare earth oxide (since it precludes the formation of the oxychloride) [i]
Cesium-lantanum tetrakis (hexafluoracetylacetonate) Cs[La(hfac)4] may be potentially applied as Cs-La single source MOCVD precursor.
[i] C, E. Higgins, J. Inorg. Nucl. Chem., 1973, Vol 35, Iss. 6p. 1941–1944
Cesium-europium tetrakis (hexafluoracetylacetonate) Cs[Eu(hfac)4]
Cesium-europium tetrakis (hexafluoracetylacetonate) Cs[Eu(hfac)4] was synthesized by the cation exchange column procedure, same as lanthanum analogue Cs[La(hfac)4].[i]
The crystal structure of Cs[Eu(hfac)4] has been determined by single crystal XRD. It was found that it is isomorphic with yttrium analogue Cs[Y(hfac)4].
Cesium-europium tetrakis (hexafluoracetylacetonate) Cs[Eu(hfac)4] may be potentially applied as Cs-Eu single source MOCVD precursor.[ii]
[i] C, E. Higgins, J. Inorg. Nucl. Chem., 1973, Vol 35, Iss. 6p. 1941–1944
[ii] J. H. Burns, M. D. Danford, Inorg. Chem., 1969, 8 (8), pp 1780–1784, DOI: 10.1021/ic50078a048,
http://pubs.acs.org/doi/abs/10.1021/ic50078a048 , « Crystal structure of cesium tetrakis (hexafluoroacetylacetonato)europate and -americate. Isomorphism with the Yttrate »
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