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10 May 2004

Volume 84, Issue 19, pp. 3723-3937

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3933 (2004); http://dx.doi.org/10.1063/1.1745103 (3 pages)

A. Cassinese, G. M. De Luca, A. Prigiobbo, M. Salluzzo, and R. Vaglio
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Influence of vapors of volatile organic compounds on spectral shift of bending vibrations of freely suspended ferroelectric liquid-crystal films

Serguei V. Yablonskii, Kazuyuki Nakano, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 84, 3723 (2004); http://dx.doi.org/10.1063/1.1697630 (3 pages)

Online Publication Date: 29 April 2004

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The influence of the vapors of volatile inert fluorocarbon compounds on the mechanical properties of freely suspended ferroelectric liquid-crystal films has been studied. It was shown that spectral shift of bending vibrations of freely suspended films depends on the mass variations of the associated ambient gas as well as on the adsorption of the vapors of volatile fluorocarbon compounds onto the film surface. It was also shown that adsorption layers similar to surfactants decrease the film surface tension by 11%–35% (4–12.5 dyn/cm). © 2004 American Institute of Physics.
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68.15.+e Liquid thin films
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
68.03.Cd Surface tension and related phenomena
68.43.Mn Adsorption kinetics
62.10.+s Mechanical properties of liquids

Effect of surface NH3 anneal on the physical and electrical properties of HfO2 films on Ge substrate

Nan Wu, Qingchun Zhang, Chunxiang Zhu, Chia Chin Yeo, S. J. Whang, D. S. H. Chan, M. F. Li, Byung Jin Cho, Albert Chin, Dim-Lee Kwong, A. Y. Du, C. H. Tung, and N. Balasubramanian

Appl. Phys. Lett. 84, 3741 (2004); http://dx.doi.org/10.1063/1.1737057 (3 pages) | Cited 57 times

Online Publication Date: 29 April 2004

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Metal-oxide-semiconductor capacitors were fabricated on germanium substrates by using metalorganic-chemical-vapor-deposited HfO2 as the dielectric and TaN as the metal gate electrode. It is demonstrated that a surface annealing step in NH3 ambient before the HfO2 deposition could result in significant improvement in both gate leakage current and the equivalent oxide thickness (EOT). It was possible to achieve a capacitor with an EOT of 10.5 Å and a leakage current of 5.02×10−5 A/cm2 at 1 V gate bias. X-ray photoelectron spectroscopy analysis indicates the formation of GeON during surface NH3 anneal. The presence of Ge was also detected within the HfO2 films. This may be due to Ge diffusion at the high temperature (∼400 °C) used in the chemical-vapor deposition process. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
68.55.-a Thin film structure and morphology
66.30.Ny Chemical interdiffusion; diffusion barriers
84.32.Tt Capacitors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures

Ferro- and piezoelectric properties of polar-axis-oriented CaBi4Ti4O15 films

Kazumi Kato, Desheng Fu, Kazuyuki Suzuki, Kiyotaka Tanaka, Kaori Nishizawa, and Takeshi Miki

Appl. Phys. Lett. 84, 3771 (2004); http://dx.doi.org/10.1063/1.1738521 (3 pages) | Cited 26 times

Online Publication Date: 29 April 2004

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Polar-axis-oriented CaBi4Ti4O15 (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The 500-nm-thick film showed the columnar structure and consisted of well-developed grains. The a/b-axis orientation of the ferroelectric films is considered to be associated with the preferred orientation of Pt foil. The film showed good ferro- and piezoelectric properties. The Pr and Ec were 25 μC/cm2 and 306 kV/cm, respectively, at an applied voltage of 115 V. The d33 was characterized as 30 pm/V by piezoresponse force microscopy. The values were twice as large as those of the CBTi144 thin film with random orientation. The polar-axis-oriented CBTi144 films would open up possibilities for devices as Pb-free piezoelectric materials. © 2004 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.65.-j Piezoelectricity and electromechanical effects
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Modification of the refractive index of lithium niobate crystals by transmission of high-energy 4He2+ and D+ particles

B. Andreas, K. Peithmann, K. Buse, and K. Maier

Appl. Phys. Lett. 84, 3813 (2004); http://dx.doi.org/10.1063/1.1741031 (3 pages) | Cited 11 times

Online Publication Date: 29 April 2004

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We report reductions of the refractive index of congruently melting lithium niobate crystals of up to 6×10−3 by exposure of z-cut samples with high-energy 4He2+ and D+ particles which are transmitted through the crystals. © 2004 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.D- Solid-liquid transitions
61.80.Jh Ion radiation effects
61.82.Ms Insulators

Neutron reflectivity study of ultrathin SiO2 on Si

Valérie Bertagna, René Erre, Marie-Louise Saboungi, Sébastien Petitdidier, Didier Lévy, and Alain Menelle

Appl. Phys. Lett. 84, 3816 (2004); http://dx.doi.org/10.1063/1.1741034 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2004

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Neutron reflectivity was applied to the study of ultrathin silicon oxide films, of interest due to the requirement for reduced dimensions of the elemental components in microelectronic devices [I. Eisele and W. Hansch, Thin Solid Films 369, 60 (2000); C. Battaglin et al., Thin Solid Films 351, 176 (1999)]. Silicon oxides were prepared using three different ways: Chemical, electrochemical, and thermal oxidation. From neutron reflectivity, it was possible to derive the oxide thickness, the Si/SiO2 interface roughness, and the density of the layer. In complementary measurements, the chemistry of the chemical and thermal surface layers was obtained by infrared spectroscopy. The anodic oxides were found to be as dense as thermal oxides, but the chemical one was less dense. This result was checked by Fourier transform infrared spectroscopy. © 2004 American Institute of Physics.
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78.66.Nk Insulators
81.65.Mq Oxidation
68.35.Ct Interface structure and roughness
78.30.Hv Other nonmetallic inorganics
81.05.Cy Elemental semiconductors

Hydrogen-induced degradation in epitaxial and polycrystalline (Ba,Sr)TiO3 thin films

Jang-Sik Lee, Y. Li, Y. Lin, Sang Yeol Lee, and Q. X. Jia

Appl. Phys. Lett. 84, 3825 (2004); http://dx.doi.org/10.1063/1.1745105 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2004

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A comparative study of hydrogen-induced degradation in epitaxial and polycrystalline (Ba,Sr)TiO3 (BST) thin films has been carried out. Epitaxial BST was prepared on SrRuO3 (SRO)/SrTiO3 (STO), whereas polycrystalline BST was deposited on SRO/SiOx/Si. After the Pt top electrode deposition, we have measured the dielectric response and leakage current characteristics before and after annealing in forming gas (6% hydrogen/94% argon) at 450 °C for 1 h. Even though both samples have the same capacitor architecture, Pt/BST/SRO, the degree of degradation after annealing in forming gas was found to be quite different. Epitaxial BST films were highly immune to hydrogen degradation; however, polycrystalline BST films degraded severely in terms of both dielectric and electrical properties. We show that the grain boundary is one of the main sources of hydrogen-induced degradation. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
61.72.Mm Grain and twin boundaries
68.35.Fx Diffusion; interface formation
77.22.Ch Permittivity (dielectric function)
81.40.Gh Other heat and thermomechanical treatments
81.15.Fg Pulsed laser ablation deposition
81.15.Cd Deposition by sputtering

H-related defect complexes in HfO2: A model for positive fixed charge defects

Joongoo Kang, E.-C. Lee, K. J. Chang, and Young-Gu Jin

Appl. Phys. Lett. 84, 3894 (2004); http://dx.doi.org/10.1063/1.1738946 (3 pages) | Cited 29 times

Online Publication Date: 29 April 2004

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Based on first-principles theoretical calculations, we investigate the hydrogenation effect on the defect properties of oxygen vacancies (VO) in HfO2. A defect complex of VO and H behaves as a shallow donor for a wide range of Fermi levels, with a positive charge state, and this complex is energetically stable against its dissociation into VO and H. We suggest that the VO–H complex is responsible for the formation of positive fixed charges, which neutralize negative fixed charges during the postannealing process of SiOx/HfO2 stack. © 2004 American Institute of Physics.
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61.72.J- Point defects and defect clusters
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Dv Composition, segregation; defects and impurities

Ordered domains and boundary structure in Ba(Cd1/3Ta2/3)O3 perovskite dielectrics

J. Sun, Shaojun Liu, N. Newman, and David J. Smith

Appl. Phys. Lett. 84, 3918 (2004); http://dx.doi.org/10.1063/1.1741035 (3 pages) | Cited 6 times

Online Publication Date: 29 April 2004

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Ordered domains and boundaries have been observed in Ba(Cd1/3Ta2/3)O3 perovskite dielectrics by electron microscopy. Individual nanoscale domains were found to be well ordered with hexagonal symmetry. Electron diffraction revealed a twinned crystallographic relationship between domains. High-resolution electron microscopy showed further details of the boundary structure. Conservative twin boundaries along the (001) and (110) planes and nonconservative antiphase boundaries with a projected displacement vector of the type [001] were observed. The relationship between the energy and structure of the domain boundaries is briefly discussed. © 2004 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.Mm Grain and twin boundaries

Domain-engineered Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals: Enhanced piezoelectricity and optimal domain configurations

Dan Liu and JiangYu Li

Appl. Phys. Lett. 84, 3930 (2004); http://dx.doi.org/10.1063/1.1745114 (3 pages) | Cited 11 times

Online Publication Date: 29 April 2004

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In this letter, we report a mesoscopic theory of ferroelectrics to explain the dramatically enhanced piezoelectricity in relaxor ferroelectric single crystals poled along a nonpolar axis, where the coexistence of several variants leads to complicated domain configurations. The engineered domain configuration is constructed first using energy minimization approach, and the effective moduli of single crystals with engineered domain configuration are then determined using the lamination theory. Using this approach, we calculate the effective electromechanical moduli of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) crystals poled along [001] and [011] directions, which agree well with experimental observations. In addition, we demonstrate that PMN-PT crystals electromechanically poled by an electric field along [001] direction and an additional positive shear stress σ12 possess superior electromechanical coupling factors k31 and k33 simultaneously, while crystals with other domain configurations demonstrate much lower k31. The analysis reveals that greatly enhanced electromechanical coupling can be obtained in domain-engineered ferroelectric crystals, and offers insight on the design and optimization of ferroelectrics for enhanced functional properties. © 2004 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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