Search

Fatigue failure in ferroelectrics has been intensively investigated in the past few decades. Most of the mechanisms discussed for ferroelectric fatigue have been built on the “hypothesis of variation in charged defects”, but these are rarely evidenced by experimental observation. Here, using a combination of complex impedance spectra techniques, piezoresponse force microscopy and first-principles theory, we examine the microscopic evolution and redistribution of charged defects during the electrical cycling in BiFeO 3 thin films. The dynamic formation and melting behaviors of oxygen vacancy ( V O ) order are identified during the fatigue process. It reveals that the isolated V O tends to self-order along grain boundaries to form a planar-aligned structure, which blocks the domain reversals. Upon further electrical cycling, migration of V O within vacancy clusters is accommodated with a lower energy barrier (∼0.2 eV) and facilitates the formation of a nearby-electrode layer incorporated with highly concentrated V O . The interplay between the macroscopic fatigue and microscopic evolution of charged defects clearly demonstrates the role of ordered V O clusters in the fatigue failure of BiFeO 3 thin films. [ABSTRACT FROM AUTHOR]

Abstract: Optical, magnetocapacitance and dielectric properties of different composite films of BiFeO3–poly(vinylidene-fluoride) (with concentration of BiFeO3; 70, 60, 50 and 40wt%) are reported here for first time. The grain size was observed to be ∼50nm by using atomic force microscopy. A peak in refractive index appears at ∼455nm, which is found to be shifting towards lower wavelengths, while simultaneously the value of the optical energy band gap is found to increase with an increase in the concentration of PVDF in the composite. It was observed that PVDF, which works as matrix, increases the magnetocapacitance. The magnetocapacitance (MC) of BFO60 (BiFeO3; 60wt%) was found higher than Nb doped BiFeO3, which may be useful for device applications. [Copyright &y& Elsevier]

The control of polarization rotation (PR) is a key issue of applying undoped zinc oxide (ZnO) as information storage devices. A systematic study of ZnO thin films by conducting piezoresponse force microscopy (PFM) technique on samples with different electrodes, film thicknesses, and deposition oxygen partial pressures, P O 2 allows disclosing the possible factors those affecting the PR behavior. The results clearly indicate that higher work function conductive material, such as Pt, is a promising candidature as the top electrode and bottom electrode to ensure the PR occur and maintain in ZnO films. From the effects of film thickness study, PR behavior can be observed in film downscaled to 15 nm. However, in order to avoid current leakage and maintain the rotated polarization state, thicker film with about 240 nm is preferred. In addition, in the film deposited with a low P O 2 (>5 × 10−6 Torr), more atomic point defects such as oxygen vacancy may lead the sample into a large leakage current and deteriorate the PR behavior. Hence, by this systematic study, it is proved that the PR behavior of undoped ZnO thin films can be optimized with proper deposition parameters. Image 1 • Possible factors affecting the PR behavior are studied comprehensively. • Pt is a promising electrode candidature for PR behavior comparing with Au and ITO. • Unambiguous PR behavior is found in film with a thickness reduced to 15 nm. • P O 2 below 5 × 10−6 Torr might hinder the PR behavior. [ABSTRACT FROM AUTHOR]

Reports on the optical characterization of positive electrode (e.g. MEH-PPV/Alq3) composite made by studying its absorption and photoluminescence spectra. Growing of the MEH-PPV films over glass substrate using spin cast technique; Conclusion that optical properties of MEH-PPV films is greatly improved by using a bilayer heterostructure with Alq3.

Bias-induced oxygen ion dynamics underpins a broad spectrum of electroresistive and memristive phenomena in oxide materials. Although widely studied by device-level and local voltage-current spectroscopies, the relationship between electroresistive phenomena, local electrochemical behaviors, and microstructures remains elusive. Here, the interplay between history-dependent electronic transport and electrochemical phenomena in a NiO single crystalline thin film with a number of well-defined defect types is explored on the nanometer scale using an atomic force microscopy-based technique. A variety of electrochemically-active regions were observed and spatially resolved relationship between the electronic and electrochemical phenomena was revealed. The regions with pronounced electroresistive activity were further correlated with defects identified by scanning transmission electron microscopy. Using fully coupled mechanical-electrochemical modeling, we illustrate that the spatial distribution of strain plays an important role in electrochemical and electroresistive phenomena. These studies illustrate an approach for simultaneous mapping of the electronic and ionic transport on a single defective structure level such as dislocations or interfaces, and pave the way for creating libraries of defect-specific electrochemical responses. [ABSTRACT FROM AUTHOR]

Nonlinear optics is an essential component of modern laser systems and optoelectronic devices. It has also emerged as an important tool in probing the electronic, vibrational, magnetic, and crystallographic structure of materials ranging from oxides and metals, to polymers and biological samples. This review focuses on the specific technique of optical second harmonic generation ( SHG), and its application in probing ferroelectric complex oxide crystals and thin films. As the dominant SHG interaction mechanism exists only in materials that lack inversion symmetry, SHG is a sensitive probe of broken inversion symmetry, and thus also of bulk polar phenomena in materials. By performing in-situ SHG polarimetry experiments in different experimental conditions such as sample orientation, applied electric field, and temperature, one can probe ferroelectric hysteresis loops and phase transitions. Careful modeling of the polarimetry data allows for the determination of the point group symmetry of the crystal. In epitaxial thin films with a two-dimensional arrangement of well-defined domain orientations, one can extract information about intrinsic material properties such as nonlinear coefficients, as well as microstructural information such as the local statistics of the different domain variants being probed. This review presents several detailed examples of ferroelectric systems where such measurements and modeling are performed. The use of SHG microscopic imaging is discussed, and its ability to reveal domain structures and phases not normally visible with linear optics is illustrated. [ABSTRACT FROM AUTHOR]