Chemical capacitance measurements are used to study the defect chemistry of La0.6Sr0.4FeO3–δ thin films and their polarization (η) and pO2 dependence. Important point defects are oxygen vacancies (), electrons (e′) and holes (h˙).

The electrochemical properties of La0.6Ba0.4CoO3-δ (LBC) and La0.6Sr0.4CoO3-δ (LSC) dense thin film model electrodes, deposited by pulsed laser deposition at 600°C on yttria-stabilized zirconia (100) electrolytes, were investigated by electrochemical impedance spectroscopy (EIS) at 450–600°C and 10−4 to 1 bar pO2. This comparative study reveals the influence of the A-site dopant size on the catalytic activity for the oxygen exchange, chemical capacitance and electronic conductivity. For both thin films the overall oxygen reduction is still limited by the oxygen surface exchange, although an extraordinarily high activity for the oxygen reduction reaction (ORR) was measured (LBC ∼0.18 Ωcm²/LSC ∼0.6 Ωcm² at 604°C and 0.21 bar pO2). Moreover, LBC exhibits a rather low activation energy for the ORR (1.19 ± 0.11 eV) together with a high electronic conductivity (839 S·cm−1 at ∼442°C). Based on these excellent electrochemical properties, LBC may also be a highly promising material for porous cathodes in intermediate temperature (400–600°C) solid oxide fuel cells.

We report the observation of second-harmonic generation (SHG) in stoichiometric silicon nitride waveguides grown via low-pressure chemical vapor deposition (LPCVD). Quasi-rectangular waveguides with a large cross section were used, with a height of 1 µm and various different widths, from 0.6 to 1.2 µm, and with various lengths from 22 to 74 mm. Using a mode-locked laser delivering 6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the incoming power was coupled through the waveguide, making maximum average powers of up to 15 mW available in the waveguide depending on the waveguide cross section. Second-harmonic output was observed with a delay of minutes to several hours after the initial turn-on of pump radiation, showing a fast growth rate between 10 −4 to 10 −2 s −1 , with the shortest delay and highest growth rate at the highest input power. After this first, initial build-up (observed delay and growth), the second-harmonic became generated instantly with each new turn-on of the pump laser power. Phase matching was found to be present independent of the used waveguide width, although the latter changes the fundamental and second-harmonic phase velocities. We address the presence of a second-order nonlinearity and phase matching, involving an initial, power-dependent build-up, to the coherent photogal-vanic effect. The effect, via the third-order nonlinearity and multiphoton absorption leads to a spatially patterned charge separation, which generates a spatially periodic, semi-permanent, DC-field-induced second-order susceptibility with a period that is appropriate for quasi-phase matching. The maximum measured second-harmonic conversion efficiency amounts to 0.4% in a waveguide with 0.9 × 1 µm 2 cross section and 36 mm length, corresponding to 53 µW at 532 nm with 13 mW of IR input coupled into the waveguide. The according χ (2)-susceptibility amounts to 3.7 pm/V, as retrieved from the measured conversion efficiency.

Optoelectronic signal processing offers great potential for generation and detection of ultra-broadband waveforms in the THz range, so-called T-waves. However, fabrication of the underlying high-speed photodiodes and photoconductors still relies on complex processes using dedicated III-V semiconductor substrates. This severely limits the application potential of current T-wave transmitters and receivers, in particular when it comes to highly integrated systems that combine photonic signal processing with optoelectronic conversion to THz frequencies. In this paper, we demonstrate that these limitations can be overcome by plasmonic internal photoemission detectors (PIPED). PIPED can be realized on the silicon photonic platform and hence allow to leverage the enormous opportunities of the associated device portfolio. In our experiments, we demonstrate both T-wave signal generation and coherent detection at frequencies of up to 1 THz. To proof the viability of our concept, we monolithically integrate a PIPED transmitter and a PIPED receiver on a common silicon photonic chip and use them for measuring the complex transfer impedance of an integrated T-wave device.Terahertz signals (T-waves) offer promising perspectives for a wide variety of applications, comprising high-speed communications 1-3 , microwave photonics 4 , spectroscopy 5,6 , life sciences 7,8 , as well as industrial metrology 9,10 . Optoelectronic signal processing techniques are particularly attractive both for T-wave generation 1,11,12 and detection [13][14][15] , especially when broadband operation is required. On a conceptual level, optoelectronic T-wave generation relies on mixing of two optical signals oscillating at frequencies and b f in a high-speed photodetector, for which the photocurrent depends on the incident optical power 11 . The photocurrent oscillates with a difference frequency THz   Rx,1 U t modulates the device sensitivity. The PIPED photocurrent is then given by the product of the time-variant sensitivity with the time-variant optical power   Rx P t .

In this study, five different mixed conducting cathode materials were grown as dense thin films by pulsed laser deposition (PLD) and characterized via in-situ impedance spectroscopy directly after growth inside...