Wen-Hui Ma

EVIDENCE OF FERROELECTRICITY WEAKENING IN THE POLYCRYSTALLINE PBTIO3 THIN FILMS

Studies on the polycrystalline PbTiO3 thin films deposited on (001) redoped n‐Si substrates by metalorganic chemical vapor deposition (MOCVD) under reduced pressure indicated the evidence of ferroelectricity weakening [Appl. Phys. Lett. 65, 1906 (1994)] when the grain size of PbTiO3 was down to the scale of ∼1100 A. X‐ray diffraction patterns demonstrated that the perovskite unit cells have a contraction along the c‐axis direction. All transverse optical phonon modes in the films were observed shift downward in the Raman spectrum measured at 300 K. And the spontaneous polarization of PbTiO3 is determined to be 52 μC/cm2 by using Si substrates as the bottom electrodes. The three related experimental observations are conjected to be attributable to the finite size effect and the surface conditions in the ferroelectric thin film.

Raman spectroscopy and x-ray diffraction study of PbTiO3 thin films prepared by sol–gel technique

PbTiO3 (PT) thin films were prepared by the sol–gel technique on Si(111) single crystal, fused quartz, and NaCl substrates using two precursor solutions: methanol and 2-methoxyethanol. Raman spectroscopy and x-ray diffraction were used to determine the effects of the precursor solution, substrate, annealing temperature, and film thickness on the film structure and crystallization behavior. The results indicate that the precursor solution plays an important role in the fabrication of pure perovskite PbTiO3 films. The films deposited from methanol solution are able to form the perovskite structure at lower crystallization temperature (∼430 °C). In contrast, the films deposited from 2-methoxyethanol solution easily form the pyrochlore phase. This is ascribed to the different mechanism of hydrolysis and condensation polymerization of the two precursor solutions. The Raman scattering results on various substrates have significant and interesting differences, especially for the films deposited from 2-methoxyeth...

Raman-spectroscopy study of PbTiO3 thin films grown on Si substrates by metalorganic chemical vapor deposition

Raman spectra have been investigated in PbTiO3 thin films grown on Si by metalorganic chemical vapor deposition. A large grazing-angle scattering technique was taken to measure the temperature dependence of Raman spectra below room temperature. All Raman modes in the thin films are assigned and compared with those in the bulk single crystal, a newA1(TO) soft mode at 104 cm−1 was recorded which satisfies the Curie-Weiss relationω2 =A(Tc −T). Intensities of theA1(1TO) andE(1TO) modes were anomalously strengthened with increasing temperature. Raman modes for the thin films exhibit remarkable frequency downshift and upshift which is related to the effect of internal stress.

(001)-oriented PbTiO3 ferroelectric thin films grown on Si by metal-organic chemical vapour deposition

PbTiO3 ferroelectric thin films have been prepared on Si(001) by metal-organic chemical vapour deposition. The as-grown films were characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. It is shown that the films were highly (001) oriented and had essentially the same lattice constants as the bulk single crystal. However, the as-grown films were subject to internal stress as shown by a downshift in the Raman modes when compared with a bulk single crystal.

Microstructure and epitaxial characteristics of PbTiO3 ferroelectric thin film on NaCI by mocvd

Abstract Ferroelectric PbTiO3 thin films have been epitaxially grown on (100) NaCl cleavage surface by MOCVD using tetraethyllead and titanium isopropoxide as precursors. The microstructures and epitaxial characteristics of as-grown thin films were investigated by means of transmission electron microscopy. TEM studies have shown that the epitaxial thin film was highly (001) oriented and even near single-crystal epitaxy if without a small volume of 45° rotated grains, the average grain size is around 1000 A. Lowangle grain boundary formed universally when islands coalesced during the early stage of epitaxial growth. A possible growth mechanism has been given to explain this epitaxial phenomenon by consideration of two-dimensional coincidence superlattice. 90° ferroelectric domains were also observed both in the large matrix grains and small 45° rotated grains.

Direct observation of ferroelectric domains in MOCVD-grown PbTiO3 thin films by means of transmission electron microscopy

Abstract Transmission electron microscopic observations of domain structures have been made on the PbTiO3 ferroelectric thin films prepared on (100) NaCl by metalorganic chemical vapor deposition (MOCVD). Both single-domain and alternating 90[ddot] a-a and a-c domain configurations were observed in the as-deposited thin films. 180 domain boundaries were also detected in the films which can compensate the polarization charges in grain boundaries. Domain formation in closely-packed polycrystalline thin films was different from that in free crystallites without boundary clamping. Domain width was found to decrease with decreasing grain size and domain splitting cannot be observed in ultrafine grains less than about 40 nm. An interesting phenomenon of polar microregions was also observed and attributed to the effect of surface electric field arising from electron irradiation during the observations.

Transmission electron microscopy study of ferroelectric PbTiO3 thin films by metalorganic chemical vapor deposition

Abstract PbTiO3 thin films have been grown on (100) NaCl by metalorganic chemical vapor deposition. The films were characterized by means of transmission electron microscopy. It is shown that the films were highly c-axis oriented with low-angle grain boundaries. Domain structures and epitaxial mechanisms were also studied

Epitaxial growth of ferroelectric PbTiO3 thin films by metalorganic chemical vapor deposition

Abstract High-quality PbTiO3 thin films have been grown on LaAlO3 and SrTiO3 substrates by metalorganic chemical vapor deposition. The as-deposited films were examined using scanning electron microscopy and x-ray diffraction techniques. The films were mirror-like smooth and fine-grained, the PbTiO3 films on LaAlO3 were epitaxially grown with (001) and (100) double textures and the films on SrTiO3 were near single crystal epitaxy

Metalorganic chemical vapor deposition of ferroelectric PbTiO3 thin films on amorphous substrate

Abstract PbTiO3, thin films have been grown on amorphous glass substrate by metalorganic chemical vapor deposition. The as-deposited films were investigated using x-ray diffraction and scanning electron microscopy techniques. PbTiO3, thin films fabricated were polycrystalline with highly c-axis-oriented textures. The films were dense-packed and showed uniformly distributed fine grain size. Growth mechanism and domain structure of the ferroelectric thin films on amorphous substrate were also studied.

Ferroelectric PbTiO3/Au/PbTiO3 multilayers on LaAlO3 substrate by metalorganic chemical vapor deposition

Abstract We have successfully fabricated PbTiO 3 /Au/PbTiO 3 multilayers on (012) LaAlO 3 substrate using metalorganic chemical vapor deposition technique. The multilayers show smooth surface, fine grain size, good stoichiometry and sharp interfaces. The PbTiO 3 grown on LaAlO 3 were highly a-axis-oriented due to good lattice match of c-axis of PbTiO 3 with a or b axes of the LaAlO 3 substrate, while the top PbTiO 3 was a highly c-axis-oriented polycrystalline film which is formed through seeded lateral growth on Au electrode and bottom PbTiO 3 at the small holes in Au film.