K. Nashimoto et al., MICROSTRUCTURE DEVELOPMENT OF SOL-GEL DERIVED EPITAXIAL LINBO3 THIN-FILMS, Journal of materials research, 10(10), 1995, pp. 2564-2572
Film growth and microstructural evolution were investigated for sol-ge
l derived LiNbO3 thin films deposited on lattice-matched single-crysta
l substrates. Epitaxial LiNbO3 films of about 100 nm nominal thickness
were prepared by spin coating a solution of the lithium niobium ethox
ide on sapphire (0001) substrates and anneaIing at 400 degrees C or 70
0 degrees C in a humidified oxygen atmosphere. These films exhibited a
n epitaxial relationship with the substrate of the type LiNbO3 (0001)
parallel to alpha-Al2O3 (0001) and LiNbO3 [100] parallel to alpha-Al2O
3 [100] as determined by x-ray pole figure analysis. Transmission elec
tron microscopy indicated the epitaxial films annealed at 400 degrees
C consisted of slightly misoriented similar to 5 nm subgrains and of n
umerous similar to 10 nm enclosed pores. The microstructure and orient
ation development of these films was consistent with a heteroepitaxial
nucleation and growth mechanism, in which epitaxial nuclei form at th
e substrate surface and grow upward into an amorphous and porous inter
mediate film. Epitaxial films annealed at 700 degrees C contained larg
er 150-200 nm subgrains and pinhoIes. Misorientations between adjacent
subgrains appeared to be significantly smaller in films annealed at 7
00 degrees C than those in films annealed at 400 degrees C. Hydrolysis
of the alkoxide precursor solution prior to spin coating promoted the
development of polycrystalline films on single-crystal sapphire subst
rates. Infrared spectra and thermal analysis indicated that, independe
nt of the degree of the solution hydrolysis, nucleation of LiNbO3 was
immediately preceded by decomposition of an amorphous carbonate interm
ediate phase.