1,720,961 research outputs found
Superlattice formation of (Ba,Sr)TiO3 prepared by metal-organic chemical vapor deposition
No full textDielectric superlattices of (Ba0.5Sr0.5)TiO3 (BST) grown by a metal-organic chemical vapor deposition (MOCVD) have been studied by transmission electron microscopy (TEM). A selected area of electron diffraction patterns clearly show satellite spots that indicate the formation of superlattice of BST film. A superlattice distance is 6.75 Angstrom, that is, 2.4 times of (110) BST plans distance. A high-resolution TEM study revealed that the superlattices were induced by the periodic composition modulation of Ba and Sr atoms. A possible atomic arrangement model of the superlattice was proposed by a simulation with a national center for electron microscopy simulation system (NCEMSS). (C) 2001 Elsevier Science B.V. All rights reserved
Effects of post-annealing on the interface microstructure of (Ba,Sr)TiO3 thin films
No full textThe effects of post-annealing on the interface microstructure of Ba0.6Sr0.4TiO3 (BST) thin films prepared by metalorganic chemical vapor deposition have been studied by a transmission electron microscopy (TEM). As-deposited BST film was partially crystallized on (1 1 1) textured Pt/SiO2/Si substrate. After a post-annealing process at 750 degreesC, the BST films were preferably crystallized with (1 1 I) plane. However, the lattice of crystallized BST was distorted at the BST/Pt interface, though Ba0.6Sr0.4TiO3 has a cubic structure. From a high-resolution TEM study we found that the adjacent BST crystallitas with different orientations lead to the lattice distortion. A selected area electron diffraction pattern clearly shows the split-spots from the distorted lattices which has 4-5 degrees distortion angles. (C) 2001 Elsevier Science B.V. All rights reserved
Crystallization behavior of ferroelectric YMnO3 thin films on Si(100) substrates
No full textYMnO3 thin films have been sputtered on Si(1 0 0) substrates under different ambient conditions. Microstructures of the YMnO3 thin films have been investigated with transmission electron microscopy (TEM) after a rapid thermal annealing process at 850degreesC in N-2 ambient. The YMnO3 film deposited in Ar ambient had random orientations. However. two layers were apparently formed in the YMnO3 film deposited in Ar + O-2 ambient. One was a c-axis oriented YMnO3 layer in the top region and the other was a random oriented YMnO3 layer in the bottom region, which was clearly elucidated by a dark-field TEM image. As the c-axis oriented YMnO3 layer was formed on the poly-YMnO3 layer. stress by thermal expansion difference was relieved and no crack was formed, The memory window was improved due to the partial c-axis oriented YMnO3 layer. (C) 2002 Elsevier Science B.V. All rights reserved
Microstructure control of YMnO3 thin films on Si (100) substrates
No full textThe microstructure of the sputtered-YMnO3, thin films on Si (100) substrates was controlled by only using thermal treatment processes and YMnO3 thin films having a well-defined bi-layered microstructure were fabricated. These YMnO3 thin films have two distinct layers, i.e. approximately 40 nm-thick top layer of {00l}-oriented YMnO3, and approximately 60 nm-thick bottom layer of polycrystalline YMnO3 in the 100 rim-thick film. The abrupt change of the crystalline orientation from the {00l}-preferred orientation to the random orientation is mainly due to a high stress induced by die {00l}-oriented YMnO3 layer, which was confirmed by a full width at half-maximum in Si (004) rocking curves. The controlled c-axis/polycrystalline YMnO3 thin films showed a better memory window and low leakage current density than purely c-axis-oriented YMnO3 thin film and the purely polycrystalline YMnO3 thin film. (C) 2002 Elsevier Science B.V. All rights reserved
Two-layer crystallization of amorphous YMnO3 thin films on Si(100) substrates
No full textDuring a rapid thermal annealing process at 850degreesC in a N-2 ambient, an as-deposited amorphous YMnO3 thin film on Si (100) substrates was crystallized with two distinct layers. High-resolution transmission electron microscopy showed a top layer of c-axis-oriented Y-MnO3 and a bottom layer of polycrystalline YMnO3 in the 100-nm-thick YMnO3 thin film. The abrupt change of the crystalline orientation from the c-axis-preferred orientation to the random orientation is caused primarily by high stress induced by the c-axis-oriented YMnO3 layer. High-resolution X-ray diffraction showed that the c-axis-oriented YMnO3/polycrystalline YMnO3 structure effectively relieved the stress
Characterization for crystallization of SrBi2Nb2O9 thin films on Si substrates
No full textFerroelectric layered-perovskite SrBi2Nb2O9 (SBN) thin films have been deposited on Si (100) substrates by metalorganic decomposition method. The crystallization process of the SBN thin films post-annealed under various temperature conditions was investigated using transmission electron microscopy (TEM). The SBN thin films annealed up to 600 degreesC had a fluorite-like phase and had nano-sized round grains. High resolution TEM study revealed that the fluorite-like phase was cubic Bi2O3. However, the SBN thin film annealed at 700 degreesC had a layered-perovskite SBN phase with very large grains about 0.2 - 0.3 mum. It was found that these large grains originated from the agglomeration of the small round grains having similar orientations rather than from the growth of small grains
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Improvement of electrical properties of ferroelectric gate oxide structure by using Al2O3 thin films as buffer insulator
No full textSrBi2Nb2O9 (SBN) and Al2O3 thin films were prepared by r.f.-sputtering as a ferroelectric material and as a buffer insulator for metal /ferroelectric/insulator/semiconductor (MFIS) structure, respectively. The electrical properties of those films on Si substrate were studied. Coercive field that decisively affects the memory window was greatly increased by inserting an Al2O3 insulator between SBN and Si, and thus the memory window also increased with the increasing electric field to the SBN. The Al2O3 intermediate layer between the perovskite SBN film and Si substrate prevent SBN from the serious inter-diffusion into Si substrate. Memory windows of MFIS structure were in the range of 0.7-3.4 V when the gate voltage varied from 3 to 9 V. Memory windows of MFIS structure were found to be dependent on the thickness and stoichiometry of the buffer layer. We obtained the maximum memory window in the MFIS structure with an optimized insulator thickness of 11.4 nm. (C) 2003 Elsevier B.V. All rights reserved
Enhancement of electrical properties of Pt/SrBi2Nb2O9/Pt structures by remote oxygen plasma annealing
No full textThe effect of remote oxygen plasma rapid thermal annealing (RTA) on the characteristics of Pt/SrBi2Nb2O9(SBN)/Pt capacitors is investigated. Remote oxygen plasma RTA can provide reactive oxygen, leading to improving the oxygen deficiencies. It is advantageous to reduce the thermal budget, resulting in smoother surface morphology. In addition, electrical properties of SBN films are enhanced, even at relatively lower temperature than the conventional furnace annealing in oxygen ambient. The film annealed by remote oxygen plasma RTA exhibits larger remnant polarization (2P(r)) of 22.6 muC/cm(2) at +/- 5 V and lower leak-age current density of 1.21 X 10(-8) A/cm(2) at the applied voltage of 5 V, compared with furnace-annealed films. Therefore, remote oxygen plasma RTA is considered to be a promising method to reduce the thermal budget as well as to enhance electrical properties of the SBN films
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