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Semiconductor properties of a-Fe2O3 (hematite) thin films prepared on FTO electrodes by hydrogen peroxide electroreduction. Influence of the E/t perturbation program used during electrosynthesis of iron oxyhydroxide precursor.

Ricardo S. Schrebler 1Eduardo C. Muñoz 1,2Cynthia A. Llewelyn 1Francisco Herrera 1Claudio A. Suárez 1Ricardo A. Córdova 1

1. Pontificia Universidad Católica de Valparaíso (PUCV), Avda Brasil 2950, Valparaíso Chile, Valparaíso xxxx, Chile
2. Universidad de Viña del Mar (UVM), Agua Santa 7255, Viña del Mar xxxx, Chile

Abstract

In this work the semiconductor properties of a-Fe2O3 (hematite) with differents carriers density, ND, were studied. This oxide was obtained from iron oxyhydroxide thin films (FeOOH) prepared using the H2O2 reduction reaction on a conductor glass FTO (SnO2:F). This reaction takes place in the interface: FTO / 0.1 M H2O2 + 0.05 M FeCl3 + 0.05 M NaF at 50ºC. To obtain a-Fe2O3 with differents ND, the oxy–hydroxide precursor was synthesized by the repetitive potential pulses technique. This E/t program consisted to apply a cathodic potential EC = -0.9 V during a time 0.5 s ≤ tC ≤ 5 s and after, an anodic potential 0.0 V ≤ EA ≤ 0.5 V was aplied during a time tA = 5 s. At EC, onto surface the OH- electrogeneration and iron oxy–hydroxide precipitation take place. At EA, it is procured that Fe(III) deposited maintains its oxidation state. The electrodeposition process was stopped when the total time at EC was 30 min. Then, FeOOH thin film was transformed into a-Fe2O3 upon heat treatment at 525ºC by 30 min. This phase was characterized morphological and estructurally by SEM and XRD, respectivelly. By Orange II method, a roughness factor 17 ± 2 was determinated. This is in agree with dendritic structure observed by SEM. From Mott-Schottky plot obtained at 10 kHz in 0.1 M NaOH, the flat band potential (EFB = -0.63 V vs HNE) and the donors density, ND, were determined. ND was dependent of anodic potential, EA, that was used during the oxyhydroxide precursor formation. In general, ND decreased from 1.2 1019 cm-3 at EA = 0.0 V until 2,2 1017 cm-3 at EA = 0.5 V. Photocurrent transients (PCT) and cyclic photovoltammetry in an 0.05 M NaI + 0.1 M NaOH solution were measured. These results are discussed considering the processes associated to the electron-hole pair generation, charge transfer in the interface, hole diffusion and electron-hole pair recombination.

 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium B, by Ricardo S. Schrebler
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-10 20:01
Revised:   2009-06-07 00:44