The lower performance of pseudocapacitive supercapacitors in high‐frequency applications such as alternating current (AC) line filtering has been ascribed to presumed slow kinetics of redox processes compared to ion diffusion in electric double layer capacitors. A nickel‐deposited ruthenium/ruthenium‐oxide symmetric supercapacitor exhibiting remarkable electrochemical properties, particularly very high frequency response (>1 kHz) is developed. The electrodes are prepared via a simple process consisting of electrochemical reduction of ruthenium chloride on commercially available nickel foil as the current collector. A symmetric supercapacitor comprising nickel/ruthenium/ruthenium‐oxide electrodes and a polystyrene‐based thin spacer exhibits particularly fast scan rates, high power density of 1500 mW cm−2 (88 kW cm−3) with a maximum energy density of 0.58 µWh cm−2 (34 mWh cm−3), and excellent capacitance retention. Notably, supercapacitors prepared by the same synthetic method albeit using conventional gold substrate instead of nickel exhibit significantly lower frequency response. The exceptional electrochemical properties of the nickel/ruthenium/ruthenium‐oxide supercapacitor and simple electrode synthesis point to promising applicability in AC line filtering and power conditioning. In a broader context, this work demonstrates that, contrary to the widely held presumption, the kinetics of redox reactions at the active layers of pseudocapacitors may not be the primary barriers to high‐frequency applications.

A new orthorhombic binary phase in the tin mono-selenide system, γ-SnSe, was deposited from solution onto an intermediate layer of PbS on GaAs substrates. Its structure is based on orthorhombic...

Optimising the photoelectrochemical performance of hematite photoanodes for solar water splitting requires better understanding of the relationships between dopant distribution, structural defects and photoelectrochemical properties. Here, we use complementary characterisation techniques including electron microscopy, conductive atomic force microscopy (CAFM), Rutherford backscattering spectroscopy (RBS), atom probe tomography (APT) and intensity modulated photocurrent spectroscopy (IMPS) to study this correlation in Ti-doped (1 cat.%) hematite films deposited by pulsed laser deposition (PLD) on F:SnO2 (FTO) coated glass substrates. The deposition was carried out at 300 °C, followed by annealing at 500 °C for 2 h. Upon annealing, Ti was observed by APT to segregate to the hematite/FTO interface and into some hematite grains. Since no other pronounced changes in microstructure and chemical composition were observed by electron microscopy and RBS after annealing, the non-uniform Ti redistribution seems to be the reason for a reduced interfacial recombination in the annealed films, as observed by IMPS. This results in a lower onset potential, higher photocurrent and larger fill factor with respect to the as-deposited state. This work provides atomic-scale insights into the microscopic inhomogeneity in Tidoped hematite thin films and the role of defect segregation in their electrical and photoelectrochemical properties.

We have studied columnar PbSe thin films obtained using chemical bath deposition. The columnar microstructure resulted from an oriented attachment growth mechanism, in which nuclei precipitating from solution attached along preferred crystallographic facets to form highly oriented, size-quantized columnar grains. This is shown to be an intermediate growth mechanism between the ion-by-ion and cluster growth mechanisms. A structural zone model depicting the active growth mechanisms is presented for the first time for semiconductor thin films deposited from solution. The columnar films showed well-defined twinning relations between neighboring columns, which exhibited 2D quantum confinement, as established by photoluminescence spectroscopy. In addition, anisotropic nanoscale electrical properties were investigated using current sensing AFM, which indicated vertical conductivity, while maintaining quantum confinement.

We have studied the degradation of the photoluminescence (PL) of a phase-separated film of a polyfluorene blend, F8BT/PFO, on the submicron length scale using near-field scanning optical microscopy, visualizing the PL of blend compositions that do not exist macroscopically in equilibrium. In the initial scans, the topography and the PL were anticorrelated, as the emission was dominated by the PFO-rich phase. This behavior changed at longer illumination times, where the emission was dominated by the F8BT-rich phase; i.e., the topography and PL were correlated. Using macroscopic investigation of the mechanisms that govern the PL, we could explain the time dependence of the PL spatial distribution: while the degradation of F8BT was driven by photobleaching, both faster absorption degradation and photobleaching processes dominate the degradation of PFO. In addition, we found that energy transfer does not protect the PFO from degradation and does not improve its resistance to oxidation.

widespread use in solar cells and microelectronic devices. [1][2][3][4][5] In solar cells, the incorporation of the thin insulating layer enables reduction of leakage currents leading to overall improved efficiency. Certain electronic components, such as MIS diodes, depend on the insulator properties, which, if tuned properly, will perform current multiplication, thus acting as electronic switches. [6,7] A common application of MIS and SIS junctions is in electromagnetic radiation detection, [1] where excited charge carriers, driven by the depletion layer's electric field, tunnel through a thin insulating layer. To date, MIS and SIS junctions were incorporated as electromagnetic radiation detectors for the ultraviolet (UV), visible, and infrared (IR) spectral regions, where the wavelength sensitivity is determined by the choice of metal (work function) and the semiconductor (bandgap) materials. As examples, UV MIS detectors were presented using Si/SiO 2 core-shell particles, [8] and visible blind IR detectors were constructed using multilayers of SiO 2 /TiO 2 in a MIS structure. [9] In order to push the detection limits into the short wavelength infrared (SWIR) spectral band (1.3-1.5 um), Yu et al. combined Ge based detectors with insulators using low temperature diffusion processing. [10] Other devices where amorphous insulating layers play an important role are thin film transistors. Amorphous oxides have many advantages including high optical transparency, high electron mobility, and homogeneous microstructure with no grain boundaries. [11] The device structure and material properties, e.g., metal work function, insulator thickness/composition, and semiconductor type/doping level, all play crucial roles in determining device electrical properties and efficiency.The most common insulating materials in such devices are oxides of the semiconductor layer. To form the oxide layer, the semiconductor surface is typically exposed and chemically reacted with either wet or dry oxygen at elevated temperatures prior to film deposition. Control over the thickness is achieved through reaction parameters, such as duration and temperature. [12] Tuning oxide thickness is crucial for device performance; too thin an oxide results in negligible barrier, while too thick results in complete insulation. Many theoretical studies attempted to pinpoint the exact role of the insulating layer, however, it appears that several mechanisms take place simultaneously, and different thickness regimes should be individually considered. [6,13] As an example, in an Al-SiO 2 -SiThe electronic properties of the heterojunction formed by chemical bath deposition of a thorium-and oxygen-doped PbS nanostructured layer on GaAs substrate as a function of postgrowth thermal treatments are studied. A correlation is found between the heterojunction conductance and the duration of thermal treatment in air. In contrast to previous reports on the effect of air annealing on PbS films, where the conductance increased due to oxygen incorporation within the PbS, i...

Chemical epitaxy of copper sulfide thin films on GaAs resulted in a previously unreported base-centered orthorhombic phase of Cu2−xS.

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