Search

We have developed an excimer laser annealing method to achieve low electrical resistivity (ρ) and a high work function in amorphous In2O3:Zn (IZO) films on polyethylene terephthalate (PET) substrates. The effect of excimer laser irradiation of the films on crack formation, electrical properties (ρ, carrier concentration, and Hall mobility), and work function were investigated. KrF excimer laser irradiation produced cracks in the surface of the IZO films on PET as a result of thermal expansion of the PET substrate. By inserting an amorphous SiO2 layer as a heat barrier between the IZO layer and PET substrate, crack formation was prevented. Moreover, it was found that the work function of IZO film could be controlled by the laser fluence and repetition rate. Irradiation of a 150-nm-thick amorphous IZO film on a SiO2-coated PET substrate achieved a low ρ of 3.55 × 10−4 Ω cm and a high work function of 5.4 eV due to the reduction of oxygen and carbon while maintaining a flat surface.

Thin films of Bi 2 VO 5.5 (BVO) were prepared on polycrystalline yttria-stabilized zirconia (YSZ) and single-crystal SrTiO 3 [STO] (100) and (110) substrates by a coating-pyrolysis process. X-ray diffraction (XRD) θ–2θ scans showed that the crystallinity of the films increased with increasing heat-treatment temperature. The crystallinity of the BVO (001) films was so high that the XRD peak intensity of the 002 reflection was comparable with that of the STO 100 reflection. XRD pole-figure analysis and reciprocal-space mapping revealed that the films on YSZ are uniaxially c -axis oriented, while epitaxial BVO films with the (001) orientation have grown on STO (100). On the other hand, the occurrence of epitaxial (114) orientation in the BVO films was discovered by the present study and is similar to the case of (116)-oriented SrBi 2 Ta 2 O 9 films on STO (110).

Epitaxial thin films of Bi 2 VO 5.5 (BVO) were prepared on La-doped SrTiO 3 (LSTO) by a coating-pyrolysis process. The BVO films were (001)- and (114)-oriented on LSTO(100) and (110), respectively. Atomic force microscopic observations showed that very dense surfaces were obtained in the BVO films annealed at 600 °C and p O 2 =10 −4 atm. The step heights of the BVO(001) film were in the range of 2–12 nm, each approximately corresponding to a multiple of the c -axis parameter of BVO. The low- p O 2 -processed and O 2 -postannealed BVO films resulted in reproducible P – E hysteresis loops for both orientations, although somewhat leaky characteristics were observed at higher applied voltages. Anisotropic behavior based on the orientation difference was clearly observed.

We have studied the effects of UV-lamp irradiation in a fluorine-free metal-organic deposition (FF-MOD) process for epitaxial YBa2Cu3O7 (YBCO) films. We found that the irradiation dramatically improves the elemental homogeneity in a precursor film, and increases the thickness of epitaxial growth by twofold with respect to the same process without irradiation. We obtained a 1.05-μm-thick epitaxial YBCO film, which is thickest for FF-MOD processes. A possible reason for the improved element uniformity is simultaneous decompositions of three metal-organic ingredients by photons, which strongly reduce grain growths in a precursor film that have been known as an unavoidable feature in the conventional all-pyrolytic MOD.

Using a coating-pyrolysis process, an α-Fe 2 O 3 film, which consists of densely packed epitaxial α-Fe 2 O 3 particles with a rectangular shape, was obtained when an iron 2-ethylhexanoate solution was spin-coated onto an α-Al 2 O 3 (012) substrate rinsed with methanol, and subsequently annealed in air. When the α-Al 2 O 3 substrate was rinsed with other conventional solvents, such as toluene, etc., round-shaped particles were formed on the substrate. Since densely packed rectangular crystals of α-Fe 2 O 3 were formed only on the substrate rinsed with methanol, methanol molecules adsorbed on the α-Al 2 O 3 substrate are considered to promote α-Fe 2 O 3 to form a densely packed layer of rectangular crystals. The ordered adsorption of iron 2-ethylhexanoate molecules through methanol molecules is discussed.

NiO/Pd epitaxial superlattices were successfully grown by a reactive evaporation method and their structures were studied by various X-ray diffraction (XRD) methods. We prepared (111) oriented films and (100) oriented films on α-Al2O3(00·1) and MgO(100) substrates, respectively. The XRD patterns of 2θ/θ scans were analyzed by an extended step model calculation. In-plane alignment was investigated by pole figure method and reciprocal space mapping. The specimens can be epitaxially grown up to a certain thickness of the NiO layer tNiO [tNiO≤20 A for (111) oriented film and tNiO≤10 A for (100) oriented film] with the lattice shrinking of the NiO of approximately 10%. On the other hand, those beyond the critical thickness have texture structure with the lattice spacing of bulk NiO.

Epitaxial films of vanadium(III) oxide V2O3 were prepared on the C-, A-, and R-planes of α-Al2O3 substrates by a coating-pyrolysis process. The final heat treatment was carried out at 1000°C in a precisely controlled gas flow of a CO–CO2 mixture (pCO/pCO2=10−1) at ambient pressure. This condition corresponds to an oxygen partial pressure of ~10−12 atm. The X-ray diffraction θ–2θ scanning and pole-figure analysis showed that the 0.5-μm-thick V2O3 films chiefly comprise the grains grown epitaxially to the substrate surfaces and a small amount of uniaxially oriented crystallites with the c-axis perpendicular to the substrate surfaces. In the films grown on the C- and A-planes of α-Al2O3, epitaxial grains grown 60°-rotated in the basal plane relative to the substrates (or 180° domains) were also present. The occurrence of the uniaxially c-axis-oriented and 180° domains may be attributed to the crystallization from the film surface accompanying the reduction of the precursors, which contain higher-valence vanadium ions, by the CO–CO2 mixed gas, whereas the epitaxial grains grow from the film/substrate interface.

Epitaxially grown hematite (α-Fe 2 O 3 ) films were obtained on the R -, A - and C -planes of sapphire (α-Al 2 O 3 ) substrates by a coating-pyrolysis process in air and in an argon atmosphere. The X-ray diffraction θ –2 θ scanning and pole-figure analysis showed that the films have grown epitaxially to the substrate surfaces after heat treatment at 500°C and higher. The crystallinity of the films was evaluated in terms of a full width at half maximum (FWHM) of the α-Fe 2 O 3 104 peak in the φ scans. The crystallinity of the films increased after annealing in air up to 1000°C, while the highest epitaxy was obtained at 600°C in argon. The degraded crystallinity of the films prepared in argon at higher temperatures is attributed to the reaction between the film and the substrate due to a decrease in local oxygen partial pressure caused by an organic residue in the prefired films.

Non-c-axis oriented epitaxial films of bismuth layer-structured ferroelectrics, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), were prepared on SrTiO3(110) by coating-pyrolysis process. These films were found to be (106)-oriented (pseudo-tetragonal indices). Interestingly, this orientation is ‘stealthy’ or unseen in the conventional XRD θ–2θ scans due to extinction rule so that its presence was revealed by XRD pole-figure measurement and reciprocal-space mapping. The crystallographic relationship of the films and substrates was SBT, SBN (106)∥SrTiO3 (110) and SBT, SBN [010]∥SrTiO3 [001]. This epitaxial relationship was also discussed from the standpoint of ion arrangement.

Pb(Zr,Ti)O3 thin films (Pb:Zr:Ti=1:0.52:0.48) were prepared on various single-crystal substrates via dipping-pyrolysis process by use of metal naphthenates as starting materials. The alignments of these films were examined by X-ray diffraction (XRD) θ–2θ scans and β scans (pole figures). The films grown on Nb-doped SrTiO3, MgO or LaAlO3 showed an epitaxial relationship with substrates after heat treatment at 750°C, while those grown on sapphire and Si wafers exhibited polycrystalline or amorphous characteristics. Epitaxial films on SrTiO3 and LaAlO3 were found to consist of a c-axis oriented tetragonal phase, to minimize the lattice misfit with the substrates. These epitaxial films exhibited very smooth surfaces by SEM and AFM observations. In addition, the fluctuation of in-plane alignment was significantly dependent on the lattice-misfit values.

Epitaxially grown La 0.7 Sr 0.3 MnO 3 (LSMO) films were prepared on SrTiO 3 (001), LaAlO 3 (001) and MgO(001) single-crystal substrates by dipping-pyrolysis process. The fluctuation of alignments (mosaicity) of the films was evaluated based on X-ray diffraction 2 θ / θ scans, β scans (pole figures) and asymmetric 2 θ / ω scans (reciprocal-space maps). Lattice types and epitaxy were examined in the films after heat treatment at 1473–1873 K; the lattice type of the films on SrTiO 3 was pseudocubic, whereas those on LaAlO 3 and MgO were pseudocubic or rhombohedral, depending on the heat-treatment temperature. A mosaic spread (Δ ω ) of the LSMO film varied with the lattice-mismatch value between film and substrate. The LSMO films on SrTiO 3 (lattice misfit ≈1%) showed high epitaxy with a low Δ ω (≈0.50°), whereas the films on MgO (misfit ≈8%) exhibited a larger Δ ω (≈2.8°). Also, surface morphology of the film was found to markedly depend on the kind of substrate materials and annealing temperature.

BaTiO3 thin films were prepared by using metal organic acid salts on MgO(100) substrates, which have large lattice-misfit with BaTiO3. Amorphous films prefired at 470°C were crystallized to BaTiO3 phase by heat treatment at higher temperature. Crystallinity and in-plane alignment of the prepared films were found to depend on the heat-treatment conditions. BaTiO3 films with high crystallinity but poor (100)-orientation were obtained in air at higher than 1200°C. Whereas, (100)-oriented epitaxial BaTiO3 film was fabricated by annealing at 900°C under low oxygen partial pressure (p(O2)). Low carbon dioxide partial pressure (p(CO2)) is also found to be essential for preparation of epitaxial BaTiO3 films on MgO substrates by using metal organic acid salts.