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5 Sep 2005

Volume 87, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 87, 101107 (2005); http://dx.doi.org/10.1063/1.2039987 (3 pages)

A. David, C. Meier, R. Sharma, F. S. Diana, S. P. DenBaars, E. Hu, S. Nakamura, C. Weisbuch, and H. Benisty
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Precise determination of band offsets and chemical states in SiN/Si studied by photoemission spectroscopy and x-ray absorption spectroscopy

S. Toyoda, J. Okabayashi, H. Kumigashira, M. Oshima, G. L. Liu, Z. Liu, K. Ikeda, and K. Usuda

Appl. Phys. Lett. 87, 102901 (2005); http://dx.doi.org/10.1063/1.2035894 (3 pages) | Cited 13 times

Online Publication Date: 29 August 2005

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We have investigated chemical states and band offsets in SiN/Si by photoemission spectroscopy and x-ray absorption spectroscopy. N 1s photoemission spectra in SiN for three kinds of layer-thickness films are fitted by a single component, suggesting that a nitrogen atom is surrounded by three silicon and nine nitrogen atoms for the first and the second nearest neighbor, respectively. Valence-band offsets between SiN and the Si substrates are determined to be 1.6 eV using valence-band spectra by subtracting the contribution from Si substrates. Band gap of SiN is estimated to be 5.6–5.7 eV from valence-band, N 1s core level, and N K-edge-absorption spectra. Furthermore, time-dependent measurements of N 1s photoemission spectra reveal that the x-ray irradiation time is a significant factor to determine the precise valence-band offsets excluding the differential charging effects.
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73.20.At Surface states, band structure, electron density of states
61.80.Cb X-ray effects
78.70.Dm X-ray absorption spectra
79.60.Jv Interfaces; heterostructures; nanostructures

Compositional symmetry breaking in ferroelectric bilayers

S. Zhong, S. P. Alpay, and J. V. Mantese

Appl. Phys. Lett. 87, 102902 (2005); http://dx.doi.org/10.1063/1.2039990 (3 pages) | Cited 26 times

Online Publication Date: 30 August 2005

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Compositional variations across ferroelectric bilayers result in broken spatial inversion symmetry that can lead to asymmetric thermodynamic potentials. For the case of insulating materials, ferroelectric multilayers will self-pole due to the electrostatic coupling between the layers. Polarization-graded ferroelectrics with smooth composition, temperature, or stress gradients are viewed as bilayer structures in the limit of the ever-increasing number of bilayer couples, thus permitting us to conclude that the unconventional hysteresis associated with “up” and “down” polarization graded structures are real phenomena, and not artifacts associated with free charge or asymmetric leakage current.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Metalorganic chemical vapor deposition of lead-free ferroelectric BiFeO3 films for memory applications

S. Y. Yang, F. Zavaliche, L. Mohaddes-Ardabili, V. Vaithyanathan, D. G. Schlom, Y. J. Lee, Y. H. Chu, M. P. Cruz, Q. Zhan, T. Zhao, and R. Ramesh

Appl. Phys. Lett. 87, 102903 (2005); http://dx.doi.org/10.1063/1.2041830 (3 pages) | Cited 86 times

Online Publication Date: 30 August 2005

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We have grown BiFeO3 thin films on SrRuO3/SrTiO3 and SrRuO3/SrTiO3/Si using liquid delivery metalorganic chemical vapor deposition. Epitaxial BiFeO3 films were successfully prepared through the systematic control of the chemical reaction and deposition process. We found that the film composition and phase equilibrium are sensitive to the Bi:Fe ratio in the precursor. Fe-rich mixtures show the existence of α-Fe2O3, while Bi-rich mixtures show the presence of β-Bi2O3 as a second phase at the surface. In the optimized films, we were able to obtain an epitaxial single perovskite phase thin film. Electrical measurements using both quasistatic hysteresis and pulsed polarization measurements confirm the existence of ferroelectricity with a switched polarization of 110–120 μC/cm2, ΔP( = P*−P̂). Out-of plane piezoelectric (d33) measurements using an atomic force microscope yield a value of 50–60 pm/V.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
82.30.-b Specific chemical reactions; reaction mechanisms
68.37.Ps Atomic force microscopy (AFM)

Correlation between dielectric anisotropy and positive or zero transverse piezoelectric coefficients in perovskite ferroelectric single crystals

Matthew Davis, Dragan Damjanovic, and Nava Setter

Appl. Phys. Lett. 87, 102904 (2005); http://dx.doi.org/10.1063/1.2041827 (3 pages) | Cited 7 times

Online Publication Date: 31 August 2005

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The transverse piezoelectric coefficient (d31⋆) has been calculated for tetragonal barium titanate (BT) and lead titanate (PT) cut along nonpolar axes, over a range of temperatures, using the phenomenological Landau-Ginzburg-Devonshire theory. It is shown that negative values of d31⋆ are favored when the transverse dielectric susceptibility η11 and shear coefficient d15 are large, such that polarization rotation is more significant than the collinear piezoelectric effect. This occurs in tetragonal BT close to its ferroelectric-ferroelectric phase transition to an orthorhombic phase. In PT, however, where no phase transition occurs, d15 is small and polarization “extension” due to d33 dominates: small or positive values of d31⋆ become prominent. This extends a previous result found for polycrystalline modified PT ceramics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
61.72.Nn Stacking faults and other planar or extended defects
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects

Influence of superlattice and antiphase domain boundaries on dielectric loss in Ba[Mg1/3(Nbx/4Ta(4−x)/4)2/3]O3 ceramics

Chen-Fu Lin, Horng-Hwa Lu, Tien-I Chang, and Jow-Lay Huang

Appl. Phys. Lett. 87, 102905 (2005); http://dx.doi.org/10.1063/1.2041831 (3 pages) | Cited 1 time

Online Publication Date: 31 August 2005

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The Ba[Mg1/3(Nbx/4Ta(4−x)/4)2/3]O3 ceramics (x = 0, 1, 2, 3, and 4) synthesized by a solid reaction method were sintered at 1650 °C for 9 h. The quality factor (Q, ∼ 1/tan δ,tan δ: dielectric loss) and superlattice structure were investigated by the cavity method and high-resolution electron microscopy. The excellent Q value of 17 600 obtained at appropriate Nb content (x = 1). The disorder structure (superlattice modulation ∼ 0.41 nm), 1:2 ordering structure (superlattice modulation ∼ 0.71 nm) and antiphase domain boundary (APB) were revealed in Ba[Mg1/3(Nbx/4Ta(4−x)/4)2/3]O3 ceramics. The formation of extra ordering structure (superlattice modulation ∼ 1.24 nm) on the APBs contributed to the improved Q value with the stabilization of ordering-induced domain boundaries.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.22.Gm Dielectric loss and relaxation
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.65.Cd Superlattices
68.37.Lp Transmission electron microscopy (TEM)

Polarization enhancement in two- and three-component ferroelectric superlattices

S. M. Nakhmanson, K. M. Rabe, and David Vanderbilt

Appl. Phys. Lett. 87, 102906 (2005); http://dx.doi.org/10.1063/1.2042630 (3 pages) | Cited 44 times

Online Publication Date: 2 September 2005

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Composition-dependent structural and polar properties of epitaxial short-period CaTiO3/‐SrTiO3/BaTiO3 superlattices grown on a SrTiO3 substrate are investigated with first-principles density-functional theory computational techniques. Polarization enhancement with respect to bulk tetragonal BaTiO3 is found for two- and three-component superlattices with a BaTiO3 concentration of more than 30%. Individual BaTiO3 layer thickness is identified as an important factor governing the polarization improvement. In addition, the degree of inversion-symmetry breaking in three-component superlattices can be controlled by varying the thicknesses of the component layers. The flexibility allowed within this large family of structures makes them highly suitable for various applications in modern nanoelectromechanical devices.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
68.65.Cd Superlattices
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