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6 Mar 2006

Volume 88, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 88, 103107 (2006); http://dx.doi.org/10.1063/1.2182096 (3 pages)

A. B. Djurišić, Y. H. Leung, K. H. Tam, L. Ding, W. K. Ge, H. Y. Chen, and S. Gwo
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Dielectric tunability of SrTiO3 thin films in the terahertz range

P. Kužel, F. Kadlec, H. Němec, R. Ott, E. Hollmann, and N. Klein

Appl. Phys. Lett. 88, 102901 (2006); http://dx.doi.org/10.1063/1.2183370 (3 pages) | Cited 18 times

Online Publication Date: 6 March 2006

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We have developed an interdigited electrode structure for applying a static electric field to a ferroelectric thin film, which enables nearly full transmission of a perpendicularly polarized terahertz wave. This approach has been used to determine the electric field dependence of the complex permittivity of a SrTiO3 thin film on a sapphire substrate up to about 2 THz employing time-domain terahertz spectroscopy. We have demonstrated up to 10% variation of the film permittivity at 300 GHz at room temperature induced by an applied electric field of 100 kV/cm. No dielectric dispersion is observed between 1 MHz and about 500 GHz. The field-induced changes are attributed to soft mode hardening.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
84.40.-x Radiowave and microwave (including millimeter wave) technology

Magnetocapacitance without magnetoelectric coupling

G. Catalan

Appl. Phys. Lett. 88, 102902 (2006); http://dx.doi.org/10.1063/1.2177543 (3 pages) | Cited 210 times

Online Publication Date: 7 March 2006

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The existence of a magnetodielectric (magnetocapacitance) effect is often used as a test for multiferroic behavior in new material systems. However, strong magnetodielectric effects can also be achieved through a combination of magnetoresistance and the Maxwell-Wagner effect, unrelated to true magnetoelectric coupling. The fact that this resistive magnetocapacitance does not require multiferroic materials may be advantageous for practical applications. Conversely, however, it also implies that magnetocapacitance per se is not sufficient to establish that a material is multiferroic.
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75.80.+q Magnetomechanical effects, magnetostriction
75.47.Gk Colossal magnetoresistance
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Final thermally stimulated discharge current in nonpolar materials

Eugen R. Neagu and Aglaia Vassilikou-Dova

Appl. Phys. Lett. 88, 102903 (2006); http://dx.doi.org/10.1063/1.2182014 (3 pages)

Online Publication Date: 8 March 2006

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The final thermally stimulated discharge current technique is used to study the molecular movements in nonpolar dielectrics. The main peak is an apparent peak being very sensitive to the experimental conditions. The experimental conditions can be chosen so that the thermal activation energy W, a characteristic parameter which has to be independent of the experimental conditions, can be determined. Five relaxations have been identified for Teflon FEP (a copolymer of tetrafluoroethylene with hexafluoropropylene) in the temperature range from 30 to 320 K. W is in the range from 0.06 to 0.53 eV.
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77.84.Jd Polymers; organic compounds
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation

Highly sensitive gas sensor based on integrated titania nanosponge arrays

A. S. Zuruzi, A. Kolmakov, N. C. MacDonald, and M. Moskovits

Appl. Phys. Lett. 88, 102904 (2006); http://dx.doi.org/10.1063/1.2185247 (3 pages) | Cited 32 times

Online Publication Date: 9 March 2006

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Highly sensitive gas sensors were fabricated using nanostructured titania pad arrays. Nanostructured titania (NST) formed is sponge-like consisting of interconnected nanoscale wires and walls, which are made up of anatase nanocrystals. Electrical characterization indicates that contacts were ohmic and NST was highly sensitive to O2. Variations of hundreds of oxygen molecules over a 20 μm NST square pad sensing element were detected at 250 °C. The NST-based sensor operates at lower temperatures, has fast response time, and superior sensitivity relative to oxygen sensors based on porous undoped titania reported in the literature.
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82.80.-d Chemical analysis and related physical methods of analysis
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Microwave dielectric dispersion process in perovskite ferroelectric systems

J. de Los S. Guerra, M. H. Lente, and J. A. Eiras

Appl. Phys. Lett. 88, 102905 (2006); http://dx.doi.org/10.1063/1.2172072 (3 pages) | Cited 12 times

Online Publication Date: 10 March 2006

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The microwave dielectric dispersion process was investigated in relaxor and normal ferroelectric compositions of Pb1−xLaxTiO3 ceramics. The results revealed the following remarkable features: (i) the mechanism responsible for the microwave dielectric dispersion process in perovskite ferroelectric systems may be associated to the vibration of the boundaries of polar regions, independently of their size and dynamical properties; (ii) the characteristic frequency, fR, is governed by the ratio between the force constant and the effective mass of such boundaries; (iii) the temperature dependence of fR above the temperature of the maximum of the dielectric permittivity directly reflects the ferroelectric-type phase transition.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point

Thermodynamic and electrostatic analysis of threading dislocations in epitaxial ferroelectric films

I. B. Misirlioglu, S. P. Alpay, M. Aindow, and V. Nagarajan

Appl. Phys. Lett. 88, 102906 (2006); http://dx.doi.org/10.1063/1.2178194 (3 pages) | Cited 18 times

Online Publication Date: 10 March 2006

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The role of threading dislocations on the electrical properties of epitaxial ferroelectric films is analyzed using a thermodynamic formalism and basic electrostatics. The modeling is carried out for a 300 nm thick (001) PbZr0.2Ti0.8O3 on (001) SrTiO3 which displays a large population of threading dislocations as determined by transmission electron microscopy. Results show that although the phase transformation characteristics of ferroelectric films containing threading dislocations are altered such that the transformation is “smeared” over a temperature interval due to local strain variations, these defects do not have as profound an effect on the electrical properties as the misfit dislocations.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
73.61.Ng Insulators
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
65.40.G- Other thermodynamical quantities
77.80.B- Phase transitions and Curie point

Characterization of domain walls in BaTiO3 using simultaneous atomic force and piezo response force microscopy

Christian Franck, Guruswami Ravichandran, and Kaushik Bhattacharya

Appl. Phys. Lett. 88, 102907 (2006); http://dx.doi.org/10.1063/1.2185640 (3 pages) | Cited 14 times

Online Publication Date: 10 March 2006

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In this letter a method to simultaneously measure the physical and the polarization thickness of a 90° domain wall in a ferroelectric perovskite is presented. This method combines accurate atomic force microscopy and piezoresponse force microscopy scans of the same area with little drift and an analysis of the entire scanned area. It is found that the physical thickness is significantly narrower (about seven and a half times) than the polarization thickness in a 90° domain wall in BaTiO3. Evidence of the trapping of defects at such domain walls is also found.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Polarization fatigue and frequency-dependent recovery in Pb(Zr,Ti)O3 epitaxial thin films with SrRuO3 electrodes

L. Pintilie, I. Vrejoiu, D. Hesse, and M. Alexe

Appl. Phys. Lett. 88, 102908 (2006); http://dx.doi.org/10.1063/1.2186074 (3 pages) | Cited 16 times

Online Publication Date: 10 March 2006

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Fatigue is investigated in epitaxial Pb(Zr,Ti)O3 films grown on SrRuO3/SrTiO3 substrates with Pt or SrRuO3 (SRO) top electrodes. It was experimentally determined that fatigue occurs irrespective of whether the top electrode is Pt or SRO. The fatigue behavior is strongly dependent on the frequency. A polarization recovery was observed for both types of top electrodes, but the recovery is almost complete for a SRO top electrode and only about 40% from the initial polarization value for Pt top electrodes. The results are tentatively explained by the frequency response of the deep traps and by migration of oxygen vacancies.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
77.22.Ej Polarization and depolarization
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