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Piezoelectric non-linearity in PbSc<sub>0.5</sub>Ta<sub>0.5</sub>O<sub>3</sub> thin films
Chopra, A.,Kim, Y.,Alexe, M.,Hesse, D. Pergamon Press 2014 The Journal of physics and chemistry of solids Vol.75 No.11
Epitaxial (001)-oriented PbSc<SUB>0.5</SUB>Ta<SUB>0.5</SUB>O<SUB>3</SUB> (PST) thin films were deposited by pulsed laser deposition. Local piezoelectric investigations performed by piezoelectric force microscopy show a dual slope for the piezoelectric coefficient. A piezoelectric coefficient of 3pm/V was observed at voltages up to 0.8V. However, at voltages above 0.8V, there is a steep increase in piezoelectric coefficient mounting to 23.2pm/V. This nonlinear piezoelectric response was observed to be irreversible in nature. In order to better understand this nonlinear behavior, voltage dependent dielectric constant measurements were performed. These confirmed that the piezoelectric non-linearity is indeed a manifestation of a dielectric non-linearity. In contrast to classical ferroelectric systems, the observed dielectric non-linearity in this relaxor material cannot be explained by the Rayleigh model. Thus the dielectric non-linearity in the PST films is tentatively explained as a manifestation of a percolation of the polar nano regions.
Nanostructured Ferroelectrics: Fabrication and Structure–Property Relations
Han, Hee,Kim, Yunseok,Alexe, Marin,Hesse, Dietrich,Lee, Woo WILEY‐VCH Verlag 2011 Advanced Materials Vol. No.
<P><B>Abstract</B></P><P>With the continued demand for ultrahigh density ferroelectric data storage applications, it is becoming increasingly important to scale the dimension of ferroelectrics down to the nanometer‐scale region and to thoroughly understand the effects of miniaturization on the materials properties. Upon reduction of the physical dimension of the material, the change in physical properties associated with size reduction becomes extremely difficult to characterize and to understand because of a complicated interplay between structures, surface properties, strain effects from substrates, domain nucleation, and wall motions. In this Review, the recent progress in fabrication and structure‐property relations of nanostructured ferroelectric oxides is summarized. Various fabrication approaches are reviewed, with special emphasis on a newly developed stencil‐based method for fabricating ferroelectric nanocapacitors, and advantages and limitations of the processes are discussed. Stress‐induced evolutions of domain structures upon reduction of the dimension of the material and their implications on the electrical properties are discussed in detail. Distinct domain nucleation, growth, and propagation behaviors in nanometer‐scale ferroelectric capacitors are discussed and compared to those of micrometer‐scale counterparts. The structural effect of ferroelectric nanocapacitors on the domain switching behavior and cross‐talk between neighboring capacitors under external electric field is reviewed.</P>
Persistent Photoconductivity in Strained Epitaxial BiFeO<sub>3</sub> Thin Films
Bhatnagar, Akash,Kim, Young Heon,Hesse, Dietrich,Alexe, Marin American Chemical Society 2014 NANO LETTERS Vol.14 No.9
<P>A drastic change in the conductivity of strained BiFeO<SUB>3</SUB> (BFO) films is observed after illuminating them with above-band gap light. This has been termed as persistent photoconductivity. The enhanced conductivity decays exponentially with time. A trapping character of the sub-band levels and their subsequent gradual emptying is proposed as a possible mechanism.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-9/nl502183j/production/images/medium/nl-2014-02183j_0005.gif'></P>
Heon Kim, Young,Bhatnagar, Akash,Pippel, Eckhard,Alexe, Marin,Hesse, Dietrich American Institute of Physics 2014 Journal of Applied Physics Vol.115 No.4
Microstructure and electronic structure of highly strained bismuth ferrite (BiFeO3) thin films grown on lanthanum aluminate substrates are studied using high-resolution transmission and scanning transmission electron microscopies and electron energy loss spectroscopy (EELS). Monoclinic and tetragonal phases were observed in films grown at different temperatures, and a mix of both phases was detected in a film grown at intermediate temperature. In this film, a smooth transition of the microstructure was found between the monoclinic and the tetragonal phases. A considerable increase in the c-axis parameters was observed in both phases compared with the rhombohedral bulk phase. The off-center displacement of iron (Fe) ions was increased in the monoclinic phase as compared with the tetragonal phase. EEL spectra show different electronic structures in the monoclinic and the tetragonal phases. These experimental observations are well consistent with the results of theoretical first-principle calculations performed. (C) 2014 AIP Publishing LLC.
Gao, Xingsen,Liu, Lifeng,Birajdar, Balaji,Ziese, Michael,Lee, Woo,Alexe, Marin,Hesse, Dietrich WILEY-VCH Verlag 2009 Advanced Functional Materials Vol.19 No.21
<P>A novel nanopatterning method using pulsed laser deposition through an ultrathin anodic aluminium oxide (AAO) membrane mask is proposed to synthesize well-ordered nanodot arrays of magnetic CoFe<SUB>2</SUB>O<SUB>4</SUB> that feature a wide range of applications like sensors, drug delivery, and data storage. This technique allows the adjustment of the array dimension from ∼35 to ∼300 nm in diameter and ∼65 to ∼500 nm in inter-dot distance. The dot density can be as high as 0.21 Terabit in.<SUP>−2</SUP>. The microstructure of the nanodots is characterized by SEM, TEM, and XRD and their magnetic properties are confirmed by well-defined magnetic force microscopy contrasts and by hysteresis loops recorded by a superconducting quantum interference device. Moreover, the high stability of the AAO mask enables the epitaxial growth of nanodots at a temperature as high as 550 °C. The epitaxial dots demonstrate unique complex magnetic domains such as bubble and stripe domains, which are switchable by external magnetic fields. This patterning method creates opportunities for studying novel physics in oxide nanomagnets and may find applications in spintronic devices.</P> <B>Graphic Abstract</B> <P>Well-ordered arrays of magnetic CoFe<SUB>2</SUB>O<SUB>4</SUB> nanodots are synthesized by a nanopatterning method using pulsed laser deposition through an ultrathin anodic aluminium oxide membrane. This technique allows a wide-range adjustment of array periodicity and dot dimension, as well as epitaxial growth of the nanodots. The epitaxial dots demonstrate complex magnetic domains such as bubble and stripe domains. <img src='wiley_img/1616301X-2009-19-21-ADFM200900422-content.gif' alt='wiley_img/1616301X-2009-19-21-ADFM200900422-content'> </P>