We present a study of the atomic and chemical structure of the surface of a fully strained, TiO2-terminated, ferroelectric BaTiO3 (BTO) (001) epitaxial film on a SrTiO3 substrate after controlled exposure to water. The epitaxial quality was checked by atomic force microscopy and X-ray diffraction. Quantitative low-energy electron diffraction compared with multiple scattering simulations was used to measure the structure of the first few atomic layers of BTO surface. The surface chemistry was investigated using high-resolution X-ray photoelectron spectroscopy. Finally, temperature-programmed desorption measured the desorption energies. We find that water undergoes mainly dissociative adsorption on the polarized BTO(001) surface. There are two competing sites for dissociative adsorption: oxygen vacancies and on-top Ti surface lattice atoms. The Ti on-top site is the dominant site for OH– chemisorption. One fifth of the surface Ti atoms bind to OH–. The concentration of surface oxygen vacancies acts mainly to favor initial physisorption. Before exposure to water, the outward pointing polarization in the BTO film is stabilized by atomic rumpling in the TiO2 termination layer. After exposure to water, the chemisorbed OH– species provide the screening, inverting the surface dipole layer and stabilizing the bulk polarization. Molecular adsorption is observed only for high water coverage.

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Multiferroic response of nanocrystalline lithium niobate J. Appl. Phys. 111, 07D907 (2012) Non-radiative complete surface acoustic wave bandgap for finite-depth holey phononic crystal in lithium niobate Offsets of hysteresis loops along the polarization axis have been observed on a step graded Pb͑Zr,Ti͒O 3 ͑PZT͒ thin film using a Sawyer-Tower ͑ST͒ circuit. However, the same effect may be artificially reproduced by adding adequate resistors and diodes in parallel with a nongraded PZT thin film. The hypothesis that the offsets were mainly due to the asymmetrical charging up of the standard capacitor used in the ST circuit, allows us to establish that the graded ferroelectric sample behaves as a kind of rectifying device. It is concluded that the presence of asymmetrical leakage currents in compositionally graded devices may allow the elucidation of the origin of the offsets often observed in these structures. Correlatively, it is demonstrated that such offsets do not represent an abnormal static polarization but a dc voltage. The E m 4 power law dependence of the offsets ͑where E m is the amplitude of the electric field͒ was found to be attributable to the nonlinear increase of the net leakage current.

A hybrid structure that supports the coupling of a cavity mode and a Tamm plasmon (TP) mode is demonstrated as a spectrally selective thermal emitter for the mid-infrared spectral range. Unlike conventional TP structures, the presented hybrid structure contains an optical cavity sandwiched between the distributed Bragg reflector (DBR) and the metallic mirror of a typical TP structure. In simulation, the TP-cavity hybrid structure exhibits a strong peak (absorptance = 0.993) in the absorption spectrum with a high quality factor (Q = 135), and this absorptance peak can exist over a wide range of resonance wavelengths by adjusting the cavity thickness. Moreover, the hybrid structure shows a small polarization dependence (for incident angles less than 30°, the resonance wavelength of TM and TE differ by less than 2 nm) and a shift of less than 20 nm in the absorptance peak wavelength for incident angles between 0° and 8°. The absorptance peak of the hybrid structure is stronger and sharper than that of a pure TP structure made from the same materials, which has a maximum absorptance of 0.898 and Q-factor of 28, and a Fabry–Perot cavity structure topped with a 5 nm Au layer, which has a maximum absorptance of 0.899 and Q-factor of 25. Upon heating, a strong and narrow bandwidth thermal emittance peak is observed with a maximum emittance value of 0.90 and a Q-factor of 88 at a wavelength of 4.731 μm. This easy-to-fabricate and high-performance infrared thermal emitter is ideal for applications where narrowband infrared light sources are required.

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The effective barrier height between an electrode and a ferroelectric (FE) depends on both macroscopic electrical properties and microscopic chemical and electronic structure. The behavior of a prototypical electrode/FE/electrode structure, Pt/BaTiO 3 /Nb-doped SrTiO 3 , under in-situ bias voltage is investigated using xray photoelectron spectroscopy. The full band alignment is measured and is supported by transport measurements. Barrier heights depend on interface chemistry and on the FE polarization. A differential response of the core levels to applied bias as a function of the polarization state is observed, consistent with Callen charge variations near the interface.