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This Letter reports the high gas response for hydrogen gas (H2) in Pd/TiO2/Si/Al based metal‐oxide semiconductor (MOS) sensor. Titanium oxide (TiO2) thin film deposited on the p‐type silicon (Si) substrate is used as the gate oxide of the MOS sensor. The surface morphology of thermally evaporated TiO2 thin film is investigated for the film structure using atomic force microscopy and scanning electron microscopy. The proposed MOS sensor characterised by capacitance–voltage (C–V) and conductance–voltage (G–V) measurements under exposure of different concentration of H2 gas at room temperature in the ambient‐air atmosphere. The maximum gas response of 65% calculated from the change in capacitance and 84% calculated from the change in conductance are obtained for the exposure of 4% of H2 gas. The obtained maximum gas responses are highly promising for low concentration detection of hydrogen gas (4%) using the fabricated MOS sensor operated at room temperature under zero bias voltage condition. [ABSTRACT FROM AUTHOR]

In this paper, TiN film has been deposited and optimized at room temperature for high power radio-frequency microelectromechanical system (RF-MEMS) applications. Being hard, titanium nitride is used in the contact area. The contact material should have low resistance and high hardness. TiN thin films were deposited by DC magnetron reactive sputtering using a four inch high purity titanium target in a nitrogen (N2) environment. X-ray diffraction (XRD) analysis is used to confirm crystal structure and purity of TiN film. The effect of various N2 pressure on resistivity and hardness of TiN thin film is investigated. The resistivity of the film decreases and hardness increases with N2 pressure. [ABSTRACT FROM AUTHOR]

Strain effects have a significant role in mediating classic ferroelectric behavior such as polarization switching and domain wall dynamics. These effects are of critical relevance if the ferroelectric order parameter is coupled to strain and is therefore, also ferroelastic. Here, switching spectroscopy piezoresponse force microscopy (SS-PFM) is combined with control of applied tip pressure to exert direct control over the ferroelastic and ferroelectric switching events, a modality otherwise unattainable in traditional PFM. As a proof of concept, stress-mediated SS-PFM is applied toward the study of polarization switching events in a lead zirconate titanate thin film, with a composition near the morphotropic phase boundary with co-existing rhombohedral and tetragonal phases. Under increasing applied pressure, shape modification of local hysteresis loops is observed, consistent with a reduction in the ferroelastic domain variants under increased pressure. These experimental results are further validated by phase field simulations. The technique can be expanded to explore more complex electromechanical responses under applied local pressure, such as probing ferroelectric and ferroelastic piezoelectric nonlinearity as a function of applied pressure, and electro-chemo-mechanical response through electrochemical strain microscopy. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

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.