Ultrafast Epitaxial Growth Kinetics in Functional Oxide Thin Films Grown by Pulsed Laser Annealing of Chemical Solutions

Abstract

The crystallization process and physical properties of different functional oxide thin films (Ce 0.9 Zr 0.1 O 2-y , LaNiO 3 , Ba 0.8 Sr 0.2 TiO 3 and La 0.7 Sr 0.3 MnO 3) on single crystal substrates (Y 2 O 3 :ZrO 2 , LaAlO 3 and SrTiO 3) are studied by pulsed laser annealing (PLA). A Nd:YAG laser source (λ=266 nm, 10 Hz and τ~3 ns) is employed to crystallize chemical solution deposited (CSD) amorphous/nanocrystalline films in atmospheric conditions. We provide new insight on the influence of photochemical and photothermal interactions on the epitaxial crystallization kinetics of oxide thin films during the transformation from amorphous/polycrystalline material (i.e. atomic diffusion, epitaxial growth rates and activation energies of nucleation and crystallization). The epitaxial growth is investigated by varying the laser fluence and the applied number of pulses. The morphology, structure and epitaxial evolution of films are evaluated by means of atomic force and transmission electron microscopies, and X-ray diffraction. Highly epitaxial oriented films of 20-40 nm in thickness are obtained by PLA. The crystallization kinetics of laser treatments is determined to be orders of magnitude faster than thermal treatments with similar activation energies (1.5-4.1 eV), mainly due to the large temperature gradients inducing modified atomic diffusion mechanisms derived mainly from photothermal interactions, as well as a minor contribution of photochemical effects. The fast heating rates achieved by PLA also contribute to the fast epitaxial growth due to reduced coarsening of polycrystalline material. The measurement of the physical properties (electrical resistivity and magnetism) of laser processed CSD films has revealed significantly good functionalities, close to those of thermally grown films, but with much shorter processing times.

Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances

“…This finding was attributed to the development of large temperature gradients and fast diffusion rates during laser processing. In addition, the rapid heating rates of laser irradiation are likely to prevent excessive coarsening of random orientations, contributing to a fast epitaxial growth . Microstructural analysis of the BST/LNO/LAO sample indicated that the BST film was completely epitaxial.…”

“…Conventionally, the thermal treatment of MO films and nanostructures is conducted in an oven or a furnace in the temperature range of 300–1000 °C, depending on the material system, thermodynamics, and the intended effect . This process is associated with such issues as high thermal budget (thermal power), long processing times, and high degree of energy loss because sample dimensions are considerably smaller than the heated volume, and almost all of the energy is used to raise and lower the temperature of the substrate and the furnace itself.…”

“…Absorption of laser radiation results in rapid photothermal and/or photochemical effects, which influences the crystallization and growth kinetics of thin films. Prior studies have demonstrated the evolution of polycrystalline, textured, and epitaxial microstructures of diverse MO films (e.g., tin‐doped indium oxide (ITO), Ga 2 O 3 , ZnO, TiO 2 , VO 2 , WO 3 , BaSrTiO 3 (BST), Pb(Zr,Ti)O 3 (PZT), La 1− x Sr x MnO 3 (LSMO)) deposited by methods such as chemical solution deposition (CSD), pulsed‐laser deposition (PLD), and sputtering . The large temperature gradients and high diffusion rates during laser processing lead to epitaxial growth rates that are orders of magnitude larger and effective heating times much shorter than that for conventional thermal treatment .…”

“…Prior studies have demonstrated the evolution of polycrystalline, textured, and epitaxial microstructures of diverse MO films (e.g., tin‐doped indium oxide (ITO), Ga 2 O 3 , ZnO, TiO 2 , VO 2 , WO 3 , BaSrTiO 3 (BST), Pb(Zr,Ti)O 3 (PZT), La 1− x Sr x MnO 3 (LSMO)) deposited by methods such as chemical solution deposition (CSD), pulsed‐laser deposition (PLD), and sputtering . The large temperature gradients and high diffusion rates during laser processing lead to epitaxial growth rates that are orders of magnitude larger and effective heating times much shorter than that for conventional thermal treatment . Furthermore, the laser irradiation technique has been utilized for processing of complex nanostructures, such as site‐specific growth of nanowires (NWs) (e.g., ZnO, TiO 2 ) and nanorods (NRs) (e.g., Fe 2 O 3 , Ag/ZnO), spatial patterning of nanocrystals (e.g., ZnO) and NWs (e.g., Al 2 O 3 ), fabrication of nanosheets (e.g., Fe 2 O 3 ) and clustered nanostructures (e.g., Ag–ZnS@ZnO, Ag/WO 3− x ), production of oxide nanoparticles (NPs) by laser ablation in liquid (e.g., CuO, MnO x , Y 3 Fe 5 O 12 , Ag/TiO 2 , Y 2 O 3 :Eu 3+ , Gd 2 O 3 :Eu 3+ , Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce), Fe@Fe 2 O 3 , or Fe 3 O 4 ), in situ formation of nanocomposites (e.g., Co 3 O 4 , MoO 2 , and Fe 3 O 4 particles embedded in graphene, ZnO particles embedded in poly(methyl methacrylate)), selective patterning of hybrid electrodes (e.g., Ni/NiO), direct scribing of fine structures (e.g., ITO), and direct writing of microdevices (e.g., TiO 2 , Cu/Cu 2 O).…”

Unveiling the Nucleation and Coarsening Mechanisms of Solution-Derived Self-Assembled Epitaxial Ce0.9Gd0.1O2–y Nanostructures

“…Chemical solution deposition (CSD) has appeared among the different processing techniques as an adaptable, low-cost and very powerful ex-situ approach for the bottom-up fabrication of functional oxide architectures with good stoichiometric control. For instance, it has been employed to successfully fabricate a broad range of oxides such as Pb(Zr,Ti)O3, (Ba,Sr)TiO3, LaNiO3, Ce1-xGdxO2-y (CGO), (La,Sr)MnO3, BiFeO3 and YBa2Cu3O7-x (YBCO) either as polycrystalline and epitaxial films, or in the form of interfacial nanostructures 10,35,38,[48][49][50][51][52][53][54][55] . Some attempts have been made to evaluate nucleation and coarsening in closed systems.…”