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Atomic Layer Deposition of LaPO4 and Ca:LaPO4**


  • The authors would like to acknowledge Spyridon Diplas for support with XPS measurements and data analysis, Anette Eleonora Gunnæs for support with TEM measurements and analysis and the Department of Geosciences at the University of Oslo for use of the XRF instrument.


Thin films of lanthanum phosphate (LaPO4) are produced by atomic layer deposition (ALD) for the first time, using a precursor combination of (CH3)3PO4, La(thd)3 (Hthd = 2,2,6,6-tetramethylhepta-3,5-dione), H2O, and O3. The deposition process is studied via an in-situ quartz crystal microbalance (QCM) and found to be a two-step process in which both water and ozone contribute to the growth. The best results are obtained when both water and ozone are pulsed simultaneously. The growth is self-limiting by nature, and a stoichiometric LaPO4 phase can be obtained for a 1:1 pulsed ratio of the two precursors. The resulting LaPO4 films are amorphous as deposited, and crystallize to the monoclinic structure after annealing in air for 10 h at 1350 °C. The LaPO4 thin films can also be doped by calcium during growth by replacing some of the La(thd)3 pulses by Ca(thd)2. Films where 4.4% of the lanthanum in LaPO4 is replaced by calcium are obtained.