Photoelectrochemical evidence of nitrogen incorporation during anodizing sputtering – deposited Al–Ta alloys

Abstract

Anodic films were grown to 20 V on sputtering-deposited Al-Ta alloys in ammonium biborate and borate buffer solutions. According to glow discharge optical emission spectroscopy, anodizing in ammonium containing solution leads to the formation of N containing anodic layers. Impedance measurements did not evidence significant differences between the dielectric properties of the anodic films as a function of the anodizing electrolyte. Photoelectrochemical investigation allowed evidencing that N incorporation induces a red-shift in the light absorption threshold of the films due to the formation of allowed localized states inside their mobility gap. The estimated Fowler threshold for the internal photoemission processes of electrons resulted to be independent of the anodizing electrolyte confirming that N incorporation does not appreciably affect the density of states distribution close to the conduction band mobility edge. The transport of photogenerated carriers has been rationalized according to the Pai-Enck model of geminate recombination.

Photoelectrochemical and EPR features of polymeric C3N4 and O-modified C3N4 employed for selective photocatalytic oxidation of alcohols to aldehydes

“…Generation and transport of photoexcited charge carriers in the photocatalytic process can be indirectly monitored by photoelectrochemical measurements. In fact, the photocurrent yield "Qph" can be calculated according to [32] and for photon energy close to the absorption edge, the dependence of the light absorption coefficient on h is described by the following relationship [33]:…”

Substrate Purity Effect on the Defect Formation and Properties of Amorphous Anodic Barrier Al2O3

“…In contrast, charge carriers generated from localized states within the energy gap characteristic of amorphous oxides present poor mobility and are easily recombined. 38,39 Although the bandgap (BG) energy of amorphous Al 2 O 3 is reported at about 6.5 eV, 40 the current PEC analysis indicates evident photoresponses at sub-gap energies in the anodically grown barrier oxide layers. For wide bandgap semiconductors, such as Al 2 O 3 , 41 the observed photocurrents at energy levels below the expected bandgap energy typically originate from internal photoemission of e/h pairs from the metal Fermi level into in-gap states in the oxide layer, following the classical Fowler behavior.…”

“…The higher amount of e-h pairs effectively separated within the oxides grown on the Al99.99 can be explained by changes in the amount of charge carriers generated and/or on the degree of confinement and probability of recombination. 38,39 Both possibilities, which could indeed coexist, can explain the higher amounts of e-h pairs effectively separated on the Al99.99 samples. The different defect concentrations detected on the oxides grown on substrates of both purities also provoked changes on the configuration and/or density of midgap states constituted for each oxide.…”

“…The lack of long-order characteristic of amorphous oxides generates located energy states within the forbidden energy region (midgap states) because of the only partial overlapping of the electronic wavefunctions. 38,39 For both substrate purities, the anodic oxides show lower photocurrent intensities for thicker oxide layers. This could be related to (i) increased effective energy barriers for injection of photoinduced charge carriers from the Al substrate into the oxide layers and/or to (ii) decreased structural defect densities with increasing layer thicknesses.…”

Electrochemical Oxidation of Hf–Nb Alloys as a Valuable Route to Prepare Mixed Oxides of Tailored Dielectric Properties

“…For all the investigated specimens, recorded photocurrent is anodic (see phase angle in Figure S7 in the Supporting Information) and its intensity decreases by scanning U E toward cathodic direction. The detected change in photocurrent sign is typical of insulating materials for which both anodic and cathodic photocurrents can be generated depending on the direction of electric field across the layer, i.e., depending on applied potential with respect to the oxide flat band potential . For this reason, photocurrent sign inversion potential, U inv , is usually considered as a proxy of oxides U fb .…”