Search results for "Node"

In vitro incorporation of amino acids into proteins stimulated by RNA from unfertilized sea urchin eggs.

1964

Photoelectrochemical study on anodic aluminum oxide films. Internal photoemission processes at the metal-oxide interface

1991

A photoelectrochemical investigation has been carried out on aluminum oxide films grown anodically at constant rate up to different thicknesses. Depending on the potential both anodic and cathodic photocurrents were observed at photon energies well below the optical bandgap expected for these layers. This finding is explained with the presence of internal photoinjection processes both for electrons and holes from the base metal into the oxide film. The analysis of the photocurrent spectra has given the threshold energies for both processes. The effect of the image force at the metal/oxide interface has been taken into account in order to derive the mobility gap of the films and the energeti…

The influence of nitrogen incorporation on the optical properties of anodic Ta2O5

2012

Abstract Anodic oxides were grown on sputter-deposited Ta in different aqueous solutions. A photoelectrochemical investigation was performed in order to estimate the band gap of the films as a function of the anodizing bath composition and formation voltage, i.e. thickness. Photoelectrochemical results provided evidence of sub-band gap photocurrent for films formed in a bath containing ammonium ions at pH 9. Elemental depth profiles obtained by glow discharge optical emission spectroscopy revealed the presence of nitrogen species in the outer part of the anodic films, which is bonded to Ta according to XPS analysis. A mechanism of nitrogen incorporation is proposed in order to account for t…

A photoelectrochemical study on anodic tantalum oxide films

1993

Both anodic and cathodic photocurrents have been detected on tantalum oxide films depending on polarization. The optical band gap, E g opt , has been derived for anodic films grown in different conditions as well as for native oxides. Cathodic photocurrents at hv<E g opt have been attributed to electron injection at the metal/oxide interface. A change in the sign of the photocurrent with the wavelength of the incident light has been observed near to the flat band potential. The latter has been estimated from the fitting of the photocurrent vs potential curves

Influence of the crystallization process on the photoelectrochemical behaviour of anodic TiO2 films

1997

On the basis of kinetic and photoelectrochemical studies we show that the formation of amorphous or strongly disordered TiO2 films on electropolished titanium rods can occur upon anodization in 0.5 M H2SO4 solution in a range of thickness which depends on the anodization rate. This finding is confirmed both by the changes in the shape of the photocurrent vs. potential curves with the energy of the incident photons, and by the impedance behaviour of the junction. Our data indicate that TiO2 films having different degree of disorder are formed depending on the anodization rate and oxide thickness. Crystalline films are formed at very low growth rates since very low thicknesses. Amorphous or s…

Influences of Structure and Composition on the Photoelectrochemical Behaviour of Anodic Films on Zr and Zr-20at.%Ti

2008

Abstract A photoelectrochemical investigation on anodic films of different thickness grown on sputter-deposited Zr and Zr–20 at.%Ti was carried out. The estimated optical band gap and flat band potential of thick ( U F  ≥ 50 V) anodic films were related to their crystalline structure and compared with those obtained for thinner ( U F  ≤ 8 V/SCE) anodic oxides having undetermined crystalline structure. The E g values obtained by photocurrent spectroscopy were also compared with the experimental band gap estimated by other optical ex situ techniques and with the available theoretical estimates of the zirconia electronic structures in an attempt to reconcile the wide range of band gap data rep…

Photoelectrochemical characterization of amorphous anodic films on Ti-6at.%Si

2013

Abstract The solid state properties of anodic films grown galvanostatically on sputtering-deposited Ti–6at.%Si alloys were studied as a function of the formation voltage (5–40 V). From the photocurrent spectra a band gap of ∼3.4 eV was estimated for all the investigated thicknesses, which is almost coincident with the value measured for amorphous TiO 2 . The photocharacteristics allowed to estimate the flat band potential of the films, which resulted to be more anodic for thicker layers and allowed to evidence a change from n-type semiconducting material to insulator by increasing the formation voltage. A dielectric constant of ∼31 was estimated by differential capacitance measurements. The…

Photoelectrochemical investigation of passive layers formed on Fe in different electrolytic solutions

2004

Abstract The passive films formed on Fe in different electrolytic solutions, spanning almost the overall pH range, and with different growth procedures were investigated systematically by photocurrent spectroscopy. The potentiodynamic growth curves are compared both in aerated and de-aerated electrolytes and a potentiostatic growth procedure is also employed. For high positive formation potentials, similar anodic spectra are recorded in all solutions giving an optical gap very close to that expected for crystalline Fe2O3. The origin of photocurrent spikes is also investigated and the effect of the formation potential upon the measured absorption threshold is discussed taking into account th…

Amorphous semiconductor-electrolyte junctions. Photoelectrochemical behaviour of thin Nb2O5anodic films

1987

An approach to the study of the photocharacteristics of amorphous semiconductor/electrolyte junctions is proposed which takes into account the main differences in the electronic structure and the transport properties of the amorphous semiconductors (a-SC) with respect to the crystalline counterparts. The influence of the wavelength of the incident light on the photocurrent vs electrode potential curves is explained on the basis of the geminate recombination theory in a-SC. The implications of the model are shortly discussed.

Dynamic doping in planar ionic transition metal complex-based light-emitting electrochemical cells

2013

Using a planar electrode geometry, the operational mechanism of iridium(III) ionic transition metal complex (iTMC)-based light-emitting electrochemical cells (LECs) is studied by a combination of fluorescence miscroscopy and scanning Kelvin probe microscopy (SKPM). Applying a bias to the LECs leads to the quenching of the photoluminescence (PL) in between the electrodes and to a sharp drop of the electrostatic potential in the middle of the device, far away from the contacts. The results shed light on the operational mechanism of iTMC-LECs and demonstrate that these devices work essentially the same as LECs based on conjugated polymers do, i.e., according to an electrochemical doping mechan…