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21 Mar 2011

Volume 98, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 123101 (2011); http://dx.doi.org/10.1063/1.3567492 (3 pages)

Linus C. Chuang, Michael Moewe, Kar Wei Ng, Thai-Truong D. Tran, Shanna Crankshaw, Roger Chen, Wai Son Ko, and Connie Chang-Hasnain
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Stabilization of positive charge on polytetrafluoroethylene electret films treated with titanium-tetrachloride vapor

Dmitry Rychkov and Reimund Gerhard

Appl. Phys. Lett. 98, 122901 (2011); http://dx.doi.org/10.1063/1.3565166 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2011

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The surface of polytetrafluoroethylene films was treated with titanium-tetrachloride vapor. The treatment was carried out in a flow reactor by means of molecular-layer deposition, a method from the arsenal of chemical nanotechnology. X-ray photoelectron spectroscopy reveals that such a treatment results in considerable changes in the chemical composition at and near the surface of the fluoropolymer film. Both, defluorination and oxidation of the surface were observed. At the same time, samples treated with titanium tetrachloride show a significant enhancement in the thermal stability of the positive homocharge. The thermally stimulated surface-potential-decay curves were observed to shift to higher temperatures by more than 100 °C
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.am Polymers and organics
68.35.bm Polymers, organics
79.60.Fr Polymers; organic compounds

Time dependence of piezoelectric d33 coefficient of cellular ferroelectret polypropylene film

Yongping Wan, Longtao Xie, Xiaoqing Zhang, and Zheng Zhong

Appl. Phys. Lett. 98, 122902 (2011); http://dx.doi.org/10.1063/1.3569950 (3 pages) | Cited 3 times

Online Publication Date: 21 March 2011

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Due to the inherent viscosity of polymer, piezoelectric response in the thickness direction (d33) of cellular ferroelectret films usually depends on the time of measurement. In this letter, the micromechanical theory of viscoelastic composite was extended to predict the time dependence of the overall piezoelectric d33 coefficient of voided charged polymer foam. Experiments were carried out to find the time spectra of piezoelectric d33 coefficient of voided charged polypropylene film. Theoretical simulation agrees well with experiment data.
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77.65.-j Piezoelectricity and electromechanical effects
77.55.H- Piezoelectric and electrostrictive films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.-d Dielectric properties of solids and liquids

First principles prediction of a morphotropic phase boundary in the Bi(Zn1/2Ti1/2)O3−(Bi1/2Sr1/2)(Zn1/2Nb1/2)O3 alloy

Valentino R. Cooper, Asegun S. Henry, Shigeyuki Takagi, and David J. Singh

Appl. Phys. Lett. 98, 122903 (2011); http://dx.doi.org/10.1063/1.3570626 (3 pages) | Cited 1 time

Online Publication Date: 22 March 2011

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The magnitude and direction of polarization within alloys of the tetragonally distorted Bi(Zn1/2Ti1/2)O3 (BZT) and the rhombohedrally oriented (Bi1/2Sr1/2)(Zn1/2Nb1/2)O3 are explored using density functional theory. For compositions with ≥ 50% of BZT, we find that the polarization is mainly in the [001] direction. Conversely, for low concentrations of BZT the polarization is rhombohedrally oriented. Based on these results we propose a phase diagram with a monoclinic phase that appears when the BZT concentration is roughly 50%. At this concentration, the material may have a useful piezoelectric response.
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77.22.Ej Polarization and depolarization
81.30.Dz Phase diagrams of other materials
61.66.Fn Inorganic compounds
77.65.-j Piezoelectricity and electromechanical effects

Optical properties of La-incorporated HfO2 upon crystallization

Tuo Wang, Junwei Wei, Michael C. Downer, and John G. Ekerdt

Appl. Phys. Lett. 98, 122904 (2011); http://dx.doi.org/10.1063/1.3567522 (3 pages) | Cited 2 times

Online Publication Date: 22 March 2011

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The imaginary part of the dielectric constant (ε2) and the band gap energy (Eg) of as-deposited and crystallized HfO2 and La-incorporated HfO2 (La–HfO2) are extracted from spectroscopic ellipsometry. As-deposited amorphous HfO2 and La–HfO2 have similar absorption tails, which implies the existence of disorder in the amorphous film structure. Upon crystallization, the absorption tails are reduced and Eg increases for both HfO2 and La–HfO2. But disorder still exists and interband states form in pure HfO2, whereas disorder in crystalline La–HfO2 is largely reduced, which might be the result of La atoms incorporating into the HfO2 host, forming a new HfLaxOy network after crystallization.
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78.66.Nk Insulators
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
71.20.Ps Other inorganic compounds

Materials and electrical characterization of physical vapor deposited LaxLu1−xO3 thin films on 300 mm silicon

L. F. Edge, T. Vo, V. K. Paruchuri, R. Iijima, J. Bruley, J. Jordan-Sweet, B. P. Linder, A. J. Kellock, T. Tsunoda, and S. R. Shinde

Appl. Phys. Lett. 98, 122905 (2011); http://dx.doi.org/10.1063/1.3562321 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2011

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LaxLu1−xO3 thin films were deposited on 300 mm silicon wafers by physical vapor deposition and fabricated into field-effect transistors using a gate-first process flow. The films were characterized using transmission electron microscopy, Rutherford backscattering spectrometry, and synchrotron x-ray diffraction. The results show the films remain amorphous even at temperatures of 1000 °C. The dielectric properties of LaxLu1−xO3 (0.125 ≤ x ≤ 0.875) thin films were evaluated as a function of film composition. The amorphous LaxLu1−xO3 thin films have a dielectric constant (K) of 23 across the composition range. The inversion thickness (Tinv) of the LaxLu1−xO3 thin films was scaled to <1.0 nm.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.43.Er Other amorphous solids
77.22.Ch Permittivity (dielectric function)
81.15.Cd Deposition by sputtering
73.61.Ng Insulators

Enhanced electrocaloric effect in ferroelectric poly(vinylidene-fluoride/trifluoroethylene) 55/45 mol % copolymer at ferroelectric-paraelectric transition

S. G. Lu, B. Rožič, Q. M. Zhang, Z. Kutnjak, and Bret Neese

Appl. Phys. Lett. 98, 122906 (2011); http://dx.doi.org/10.1063/1.3569953 (3 pages) | Cited 15 times

Online Publication Date: 23 March 2011

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The electrocaloric effect (ECE) of the ferroelectric poly(vinylidene-fluoride/trifluoroethylene) 55/45 mol % copolymer was directly measured over a broad temperature range using a specially designed calorimetry method. The data reveal a large ECE occurring at the ferroelectric-paraelectric (FE–PE) phase transition where an adiabatic temperature change ∼ 12 °C was induced under a field of 120 MV/m, which is much higher than that previously observed at above the FE–PE transition. The directly measured ECE also confirms the earlier results deduced from the indirect method. The experimental data also show that there are secondary effects contributing to the observed ECE in the polymer.
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77.80.B- Phase transitions and Curie point
77.70.+a Pyroelectric and electrocaloric effects

Impact of ultrathin Al2O3 barrier layer on electrical properties of LaLuO3 metal-oxide-semiconductor devices

Yiqun Liu, Shaoping Shen, Leonard J. Brillson, and Roy G. Gordon

Appl. Phys. Lett. 98, 122907 (2011); http://dx.doi.org/10.1063/1.3563713 (3 pages) | Cited 1 time

Online Publication Date: 24 March 2011

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Temperature-dependent current-voltage measurements showed Poole–Frenkel conduction behavior through high-κ LaLuO3 films made by atomic layer deposition on Si. The energy levels that trap electrons were around 0.66 eV below the conduction band and were identified as oxygen vacancy levels. Oxygen treatments were done to decrease oxygen vacancies but an interfacial layer formed and the interface state density (Dit) increased. Therefore, ultrathin Al2O3 was used to protect the interface during oxygen treatments. Electrical properties were improved and no interfacial layer developed. Dit was below 9×1011 eV−1 cm−2 and leakage was 5×10−4 A/cm2 at 1 V for 1 nm equivalent oxide thickness.
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84.32.Tt Capacitors

Large magnetodielectric response in Pr0.6Ca0.4MnO3/polyvinylidene fluoride nanocomposites

K. Devi Chandrasekhar, A. K. Das, and A. Venimadhav

Appl. Phys. Lett. 98, 122908 (2011); http://dx.doi.org/10.1063/1.3571443 (3 pages) | Cited 4 times

Online Publication Date: 24 March 2011

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We have studied the magnetic field effect on low frequency dielectric properties of Pr0.6Ca0.4MnO3/polyvinylidene fluoride nanocomposite with 22.5% volume fraction of Pr0.6Ca0.4MnO3 nanoparticles. A strong magnetodielectric response was observed below 120 K where Pr0.6Ca0.4MnO3 nanoparticles show the magnetic phase transition indicating a direct correlation between magnetism and dielectric properties. A large change in the dielectric permittivity ∼ 30% has been observed in a magnetic field of 4.6 T with loss as low as 0.17 at 70 K. The observed magnetodielectric response has been attributed to the decrement of polaron activation barrier of Pr0.6Ca0.4MnO3 nanoparticles with the increase in magnetic field.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
77.22.Ch Permittivity (dielectric function)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
71.38.-k Polarons and electron-phonon interactions

Modeling the charge decay mechanism in nitrogen-rich silicon nitride films

Yongling Ren, Klaus J. Weber, and Natalita M. Nursam

Appl. Phys. Lett. 98, 122909 (2011); http://dx.doi.org/10.1063/1.3571291 (3 pages)

Online Publication Date: 25 March 2011

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The stability of negative charge in nitrogen-rich silicon nitride films deposited by plasma-enhanced chemical vapor deposition is investigated by analyzing the influence of storage temperature, postdeposition thermal annealing, and the presence of a tunnel oxide. The results are compared to a charge decay model. Comparison of experimental and modeled results indicates that (i) the tunnel oxide is almost entirely responsible for charge retention in samples with an oxide-nitride-oxide (ONO) structure, with the trap properties playing an insignificant role; (ii) thermionic emission over the tunnel oxide barrier is the limiting charge decay mechanism; and (iii) thermal annealing of the films at 800 °C leads to an increase in the oxide-nitride barrier height by ∼ 0.22 eV, which results in a significant increase in the charge stability. Annealed ONO samples are predicted to maintain a negative charge density of >5×1012 cm−2 for well in excess of 100 years at a storage temperature of 100 °C.
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79.40.+z Thermionic emission
81.40.Gh Other heat and thermomechanical treatments
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electrostatic control of the domain switching dynamics in congruent LiNbO3 via periodic proton-exchange

Michele Manzo, Fredrik Laurell, Valdas Pasiskevicius, and Katia Gallo

Appl. Phys. Lett. 98, 122910 (2011); http://dx.doi.org/10.1063/1.3571559 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2011

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We propose a model for the poling-inhibiting action of proton-exchange, associated to nonuniform fields induced in the crystal by the vanishing of ferroelectricity in the β-phase of HxLi1−xNbO3. Predictions are corroborated by experimental results on the poling of 0.5 mm thick congruent LiNbO3 substrates with periods around 8 μm, yielding regular bulk domain structures with aspect ratios as high as 250.
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77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
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