The ultrathin limit of improper ferroelectricity

AbstractThe secondary nature of polarization in improper ferroelectrics promotes functional properties beyond those of conventional ferroelectrics. In technologically relevant ultrathin films, however, the improper ferroelectric behavior remains largely unexplored. Here, we probe the emergence of the coupled improper polarization and primary distortive order parameter in thin films of hexagonal YMnO3. Combining state-of-the-art in situ characterization techniques separately addressing the improper ferroelectric state and its distortive driving force, we reveal a pronounced thickness dependence of the improper polarization, which we show to originate from the strong modification of the primary order at epitaxial interfaces. Nanoscale confinement effects on the primary order parameter reduce the temperature of the phase transition, which we exploit to visualize its order-disorder character with atomic resolution. Our results advance the understanding of the evolution of improper ferroelectricity within the confinement of ultrathin films, which is essential for their successful implementation in nanoscale applications.

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In Situ Characterization of Ultrathin Films by Scanning Electrochemical Impedance Microscopy

Analytical Chemistry ◽

10.1021/acs.analchem.6b00011 ◽

2016 ◽

Vol 88 (6) ◽

pp. 3354-3362 ◽

Cited By ~ 11

Author(s):

Arturo Estrada-Vargas ◽

Aliaksandr Bandarenka ◽

Volodymyr Kuznetsov ◽

Wolfgang Schuhmann

Keyword(s):

Ultrathin Films ◽

Electrochemical Impedance ◽

In Situ Characterization

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In situ TEM Studies of agglomeration of sub-nanometer Ru layers in Ru/C multilayers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121685 ◽

1992 ◽

Vol 50 (1) ◽

pp. 256-257

Author(s):

Tai D. Nguyen ◽

Ronald Gronsky ◽

Jeffrey B. Kortright

Keyword(s):

Layered Structure ◽

Driving Force ◽

High Energy ◽

Superior Performance ◽

In Situ Tem ◽

Rayleigh Instability ◽

Practical Applications ◽

Transmission Electron ◽

Diffraction Patterns

Nanometer period Ru/C multilayers are one of the prime candidates for normal incident reflecting mirrors at wavelengths < 10 nm. Superior performance, which requires uniform layers and smooth interfaces, and high stability of the layered structure under thermal loadings are some of the demands in practical applications. Previous studies however show that the Ru layers in the 2 nm period Ru/C multilayer agglomerate upon moderate annealing, and the layered structure is no longer retained. This agglomeration and crystallization of the Ru layers upon annealing to form almost spherical crystallites is a result of the reduction of surface or interfacial energy from die amorphous high energy non-equilibrium state of the as-prepared sample dirough diffusive arrangements of the atoms. Proposed models for mechanism of thin film agglomeration include one analogous to Rayleigh instability, and grain boundary grooving in polycrystalline films. These models however are not necessarily appropriate to explain for the agglomeration in the sub-nanometer amorphous Ru layers in Ru/C multilayers. The Ru-C phase diagram shows a wide miscible gap, which indicates the preference of phase separation between these two materials and provides an additional driving force for agglomeration. In this paper, we study the evolution of the microstructures and layered structure via in-situ Transmission Electron Microscopy (TEM), and attempt to determine the order of occurence of agglomeration and crystallization in the Ru layers by observing the diffraction patterns.

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Epitaxial growth manner and structure of superconducting oxide films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173145 ◽

1990 ◽

Vol 48 (4) ◽

pp. 2-3

Author(s):

Yoshichika Bando ◽

Takahito Terashima ◽

Kenji Iijima ◽

Kazunuki Yamamoto ◽

Kazuto Hirata ◽

...

Keyword(s):

Ultrathin Films ◽

Film Surface ◽

High Energy ◽

Epitaxial Films ◽

Layer By Layer ◽

Initial Growth ◽

In Situ Growth ◽

High Quality ◽

Activated Reactive Evaporation

The high quality thin films of high-Tc superconducting oxide are necessary for elucidating the superconducting mechanism and for device application. The recent trend in the preparation of high-Tc films has been toward “in-situ” growth of the superconducting phase at relatively low temperatures. The purpose of “in-situ” growth is to attain surface smoothness suitable for fabricating film devices but also to obtain high quality film. We present the investigation on the initial growth manner of YBCO by in-situ reflective high energy electron diffraction (RHEED) technique and on the structural and superconducting properties of the resulting ultrathin films below 100Å. The epitaxial films have been grown on (100) plane of MgO and SrTiO, heated below 650°C by activated reactive evaporation. The in-situ RHEED observation and the intensity measurement was carried out during deposition of YBCO on the substrate at 650°C. The deposition rate was 0.8Å/s. Fig. 1 shows the RHEED patterns at every stage of deposition of YBCO on MgO(100). All the patterns exhibit the sharp streaks, indicating that the film surface is atomically smooth and the growth manner is layer-by-layer.

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Characterization of the glycoconjugates of boar testis and epididymis

Reproduction ◽

10.1530/reprod/120.2.325 ◽

2000 ◽

pp. 325-335 ◽

Cited By ~ 29

Author(s):

A Calvo ◽

LM Pastor ◽

S Bonet ◽

E Pinart ◽

M Ventura

Keyword(s):

Ricinus Communis ◽

Lectin Histochemistry ◽

Apical Part ◽

Seminiferous Tubules ◽

In Situ Characterization ◽

Intense Staining ◽

Terminal Galactose ◽

Boar Spermatozoa

Lectin histochemistry was used to perform in situ characterization of the glycoconjugates present in boar testis and epididymis. Thirteen horseradish peroxidase- or digoxigenin-labelled lectins were used in samples obtained from healthy fertile boars. The acrosomes of the spermatids were stained intensely by lectins with affinity for galactose and N-acetyl-galactosamine residues, these being soybean, peanut and Ricinus communis agglutinins. Sertoli cells were stained selectively by Maackia ammurensis agglutinin. The lamina propria of seminiferous tubules showed the most intense staining with fucose-binding lectins. The Golgi area and the apical part of the principal cells of the epididymis were stained intensely with many lectins and their distribution was similar in the three zones of the epididymis. On the basis of lectin affinity, both testis and epididymis appear to have N- and O-linked glycoconjugates. Spermatozoa from different epididymal regions showed different expression of terminal galactose and N-acetyl-galactosamine. Sialic acid (specifically alpha2,3 neuraminic-5 acid) was probably incorporated into spermatozoa along the extratesticular ducts. These findings indicate that the development and maturation of boar spermatozoa are accompanied by changes in glycoconjugates. As some lectins stain cellular or extracellular compartments specifically, these lectins could be useful markers in histopathological evaluation of diseases of boar testis and epididymis.

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