Structural Refinement of X-Ray Diffraction Profile for Artificial Superlattices

Ishibashi, Y.; Ohashi, Naoki; Tsurumi, Takaaki

doi:10.1143/jjap.39.186

Cited by 34 publications

(21 citation statements)

References 26 publications

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“…5 shows XRD profiles of superlattices. The simulation of XRD profile was done using the supercell model developed by ourselves [8]. The observed profiles agreed well with simulation, indicating fabrication of the superlattices with designed structures.…”

Section: Ellipsometrysupporting

confidence: 65%

Anomalous dielectric and optical properties in perovskite-type artificial superlattices

Tsurumi

Harigai

Tanaka

et al. 2004

Science and Technology of Advanced Materials

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Perovskite-type BaTiO 3 /SrTiO 3 (BTO/STO) artificial superlattices were fabricated by molecular beam epitaxy process and their dielectric properties and refractive indices were measured. A large leakage current was observed in the films on Nb-doped STO substrate. Dielectric permittivity was therefore measured using planer interdigital electrodes. Fine planer electrodes were necessary to reduce the penetration of electric flux into the substrate. Interdigital electrodes were formed by electron-beam lithography. Dielectric permittivity of superlattices along the film surface was determined using electromagnetic field analysis. It was found that the dielectric permittivity of the BTO/STO superlattice with the period of 10 unit cells showed a maximum value above 30,000, which was almost independent from frequency up to 110 MHz. The refractive index of superlattices measured with a spectroscopic ellipsometer also showed the highest value when the period was 10 unit cells. This indicated that the structure of superlattices affected not only the ionic polarization but also the electric polarization. The origin of anomalous properties observed in superlattices may be interpreted by the strains induced into the film. q

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Section: Ellipsometrysupporting

confidence: 65%

Anomalous dielectric and optical properties in perovskite-type artificial superlattices

Tsurumi

Harigai

Tanaka

et al. 2004

Science and Technology of Advanced Materials

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“…This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO3 to SrTiO3 of less than one a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed.The construction of artificial ferroelectric oxide superlattices with fine periodicity presents exciting possibilities for the development of new materials with extraordinary properties and furthermore is an ideal probe for understanding the fundamental physics of ferroelectric materials.The most studied system at present is BaTiO 3 /SrTiO 3 [1,2,3,4,5,6,7,8] In BaTiO 3 /SrTiO 3 , first principles studies [5] suggest that both the SrTiO 3 and BaTiO 3 layers are polarized such that the polarization is approximately uniform throughout the superlattice. The driving force behind this is the large electrostatic energy penalty for a buildup of charge at the interface caused by discontinuous polarization in the normal direction.…”

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confidence: 99%

“…The most studied system at present is BaTiO 3 /SrTiO 3 [1,2,3,4,5,6,7,8] In BaTiO 3 /SrTiO 3 , first principles studies [5] suggest that both the SrTiO 3 and BaTiO 3 layers are polarized such that the polarization is approximately uniform throughout the superlattice. The driving force behind this is the large electrostatic energy penalty for a buildup of charge at the interface caused by discontinuous polarization in the normal direction.…”

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confidence: 99%

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Unusual Behavior of the Ferroelectric Polarization inPbTiO3/SrTiO3Superlattices

et al. 2005

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Artificial PbTiO3/SrTiO3 superlattices were constructed using off-axis RF magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ferroelectric polarization as the ratio of PbTiO3 to SrTiO3 was changed. For PbTiO3 layer thicknesses larger than the 3-unit cells SrTiO3 thickness used in the structure, the polarization is found to be reduced as the PbTiO3 thickness is decreased. This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO3 to SrTiO3 of less than one a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed.The construction of artificial ferroelectric oxide superlattices with fine periodicity presents exciting possibilities for the development of new materials with extraordinary properties and furthermore is an ideal probe for understanding the fundamental physics of ferroelectric materials.The most studied system at present is BaTiO 3 /SrTiO 3 [1,2,3,4,5,6,7,8] In BaTiO 3 /SrTiO 3 , first principles studies [5] suggest that both the SrTiO 3 and BaTiO 3 layers are polarized such that the polarization is approximately uniform throughout the superlattice. The driving force behind this is the large electrostatic energy penalty for a buildup of charge at the interface caused by discontinuous polarization in the normal direction. The electrostatic model proposed by Neaton and Rabe [5] to explain their first principles results for BaTiO 3 /SrTiO 3 superlattices is very similar to the electrostatic model applied to calculate the effect of the depolarization field in ultra-thin ferroelectric films with realistic electrodes [18,19,20]. Experimentally it was recently shown that the reduced polarization observed in monodomain thin PbTiO 3 can be explained by the presence of a depolarization field resulting from imperfect screening of the polarization [21]. Recent work also suggests that, under certain conditions, the electrostatic energy due to depolarization fields will drive the system to form domains as observed by Fong et al. [23] and Nagarajan et al. [24]. In this letter we use PbTiO 3 /SrTiO 3 superlattices to probe the effect of a reduced ferroelectric thickness in a dielectric environment. Our data show that the behaviour observed in PbTiO 3 thin films is reproduced for PbTiO 3 layers thicker than three unit cells. However, for thinner ferroelectric layers a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed.The superlattices of PbTiO 3 /SrTiO 3 were prepared on conducting 0.5% Nb doped (001) SrTiO 3 substrates using off-axis RF magnetron sputtering with conditions similar to those used for growing high quality epitaxial c-axis PbTiO 3 thin films [21]. For all the samples discussed in this paper, the SrTiO 3 thickness was fixed at three unit cells (about 12Å). At room temperature the in-plane lattice parameters of tetragonal ferroelec...

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“…• were compared directly to simple one-dimensional kinematic calculations of the scattered intensity profile [22][23][24] . Fits reveal that the as grown sample possessed approximately 18.5(6) and 25.5(7) atomic planes of Pt and Ni respectively in each metallic layer, with approximate lattice parameters of 0.397nm and 0.3535nm for the Pt and Ni respectively, significantly larger than accepted bulk values for the constituent metals (0.3924nm and 0.3524nm respectively).…”

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confidence: 99%