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The operating regime of MIM diodes is governed by its cutoff frequency. High frequency operation requires ultralow diode capacitance, C D , and low diode resistance, R D . Capacitance can be lowered by fabricating structures with minimal diode area or using a thick dielectric. However, increasing the dielectric thickness will exponentially increase diode resistance by hindering electron tunneling probability through a wider energy barrier. [13] In addition to the barrier width, the height of the tunneling barrier also affects device resistance. Whereas the width is controlled by the insulator thickness, the barrier height is primarily governed by the metal work functions as well as the insulator electron affinity. [14] Diode rectification performance is also dictated by current-voltage asymmetry, nonlinearity, and responsivity. Generally, these figures of merit are controlled by the metal work functions (specifically the work function difference) along with the insulator thickness and dielectric properties. [15][16][17][18][19] A large difference in metal work functions creates a highly asymmetric tunneling barrier that influences the forward and reverse currents, yielding high current asymmetry and nonlinearity. [20] Alternatively, asymmetric diode response can be realized by utilizing multiple insulating layers that have dissimilar electron affinities and dielectric constants. Double-barrier metal-insulator-insulator-metal (MIIM) diodes have shown enhanced asymmetry, nonlinearity, and responsivity versus their single-barrier MIM counterparts. [15,[21][22][23] There are two primary mechanisms that govern tunneling phenomenon in MIIM structures: resonant tunneling and step tunneling. Resonant tunneling occurs when a triangular quantum well is created between the two barriers (Figure 1a). When bias is applied such that the Fermi level of one of the metals coincides with a bound energy state within the quantum well, then electron tunneling is abruptly enhanced, leading to sharp turn on voltage and high asymmetry. The quantum well formed between insulators must be sufficiently deep and wide enough to form bound quantum states. [23,24] The turn on voltage at which bound states form, and thus resonant tunneling begins, can be adjusted by changing the thickness of the first insulator, although the thicker insulator will reduce tunneling current. This work reports important fundamental advancements in multiwall carbon nanotube (MWCNT) rectenna devices by creating and optimizing new diode structures to allow optical rectification with air-stable devices.The incorporation of double-insulator layer tunnel diodes, fabricated for the first time on MWCNT arrays, enables the use of air-stable top metals (Al and Ag) with excellent asymmetry for rectification applications. Asymmetry is increased by as much as 10 times, demonstrating the effectiveness of incorporating multiple dielectric layers to control electron tunneling in MWCNT diode structures. MWCNT tip opening also reduces device resistance up to 75% due to an increase in...

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The solid oxide fuel cell single cells with porous cathodes prepared at various sintering temperatures, having remarkable differences in micro/meso porosity, were studied using impedance, cyclic voltammetry and chronoamperometry measurement methods. Atomic force microscopy, scanning electron microscopy, focused ion beam-scanning electron microscopy, Brunauer-Emmett-Teller and X-ray diffraction methods were used to describe the cathode material physical and porosity characteristics. It was demonstrated that the porosity and surface area of a cathode strongly depend on the cathode sintering temperature. Influence of single cell working temperature, electrode polarization and oxidant and or fuel partial pressure onto the single cell electrochemical behavior, has been analyzed. Power density vs. current density plots show that the electrical power of single cells depend noticeably on the cathode porosity, O 2 partial pressure in the cathode as well as on H 2 partial pressure in the anode compartment. Impedance data were analyzed in detail, using equivalent circuit fitting as well as difference derivative impedance vs. log frequency plots method. It was concluded that the characteristic time constants for the cathode and anode processes are very similar and the exact separation of the anode and cathode processes characteristics is complicated.Increasing interest in the operation of the solid oxide fuel cells (SOFC) at temperatures considerably lower than 1273 K has raised the need for a better understanding of the factors limiting the performance of the complex solid oxide based catalyst electrodes. [1][2][3][4][5][6][7][8][9][10][11][12] Strontium activated lanthanum cobaltite La 1−x Sr x CoO 3−δ (LSC) is a perovskite-type oxide with high electronic and oxide ion conductivity at moderate temperatures (773-973 K) and is therefore considered as catalyst for medium-temperature devices such as fuel cells, ceramic membrane electrolysers and synthetic fuel reactors. The mixed electronic-ionic conductivity of LSC is believed to account for the low overpotentials of the processes at SOFC cathode as mixed conductivity expands the catalytically active area of the electrode beyond the triple phase boundary. 7 The rate of oxygen reduction process on and inside of the cathode is limiting for SOFC single cell. [2][3][4][5][6]8,9 It was established that the polarization resistance of the cathode process depends on the processing route of the cathode and electrolyte powder. [10][11][12] In addition, the structure, thickness and porosity of active layers depend on the coating technology (screen printing, slurry spraying) and also on the procedure and characteristics applied during sintering (temperature and duration of sintering, co-firing, infiltration of active particles) of cathodes and anodes. [3][4][5][6]9 Besides, it was demonstrated that the interaction between electrolyte and perovskite type cathode is sensitive to the processing procedures used for preparation of anode and electrolyte and it is crucial for electrocatalytic p...