Electrochemical Stability of n-Si Photoanodes Protected by TiO₂ Thin Layers Grown by Atomic Layer Deposition

Abstract

This work investigates the n-Si photoanodes corrosion protection by Atomic Layer Deposition (ALD) of a TiO 2 film. A specific electrochemical experimental sequence (including successive rest potential measurements and voltammetries under illumination or not) has been established to study the stability of the electrodes in KOH. Depending on the deposition conditions (precursor composition and temperature), the electrochemical properties of the layers are different. The photoanodes coated using titanium tetraisopropoxide (TTIP) at low temperature exhibit a low photocurrent (j ph ) that is progressively enhanced during the electrochemical sequence and their stability decreases. When using tetrakis(dimethylamido)titanium (TDMAT), the j ph is almost constant and the film prevents from corrosion. The characterizations show that the ALD parameters drive the microstructure of the layer that is found critical for the electrochemical response. A hydrogen doping occurring during the open circuit potential measurements under illumination is evidenced by IR spectroscopy. It is mainly localized at the grain boundaries and pores of the layers as well as in the n-Si and it modifies the charge transfer at the electrode/solution junction and the hydrogen diffusion weakens the film causing the Si corrosion. The different charge transfer mechanisms are finally proposed depending on the ALD conditions and the film thickness.

Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO2 Thin Films Grown by Atomic Layer Deposition

“…Based on literature, anatase grains with similar magnitude of size have been fabricated by post deposition annealing of ALD grown amorphous Ti–Nb–O or Ti–Ta–O mixed oxide films . Crystallization of undoped ALD grown am.-TiO 2 into anatase is reported to result in micron-wide grains, instead. , The rutile thin film (PDA-treated TiO 2 grown at 200 °C), by contrast, consists of much smaller grains (<1 μm).…”

“…52 Crystallization of undoped ALD grown am.-TiO 2 into anatase is reported to result in micron-wide grains, instead. 49,53 The rutile thin film (PDA-treated TiO 2 grown at 200 °C), by contrast, consists of much smaller grains (<1 μm).…”

Preventing Corrosion of Aluminum Metal with Nanometer-Thick Films of Al2O3 Capped with TiO2 for Ultraviolet Plasmonics

“…The Al 2 O 3 , HfO 2 , and TiO 2 thin films were grown by ALD in a Fiji 200 reactor (Veeco/Cambridge Nanotech) operating with Ar as the gas carrier. The materials that are commonly used for ALD were used − to ensure that our results can be easily reproduced by others. However, their application in aluminum plasmonics has never been reported so far.…”

“…Atomic layer deposition (ALD) and plasmaenhanced chemical vapor deposition (PECVD) of thin inert layers of metal oxides offer powerful alternative approaches for corrosion protection owing to their ability to deposit dense layers of oxide materials with controlled nanometer thickness and conformal coating at the nanoscale. 50 Alumina (Al2O3), [51][52][53] titania (TiO2) [54][55][56] and hafnia (HfO2) 57,58 are commonly used to protect flat metal surfaces.…”

“…Atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) of thin inert layers of metal oxides offer powerful alternative approaches for corrosion protection owing to their ability to deposit dense layers of oxide materials with controlled nanometer thickness and conformal coating at the nanoscale . Alumina (Al 2 O 3 ), − titania (TiO 2 ), − and hafnia (HfO 2 ) , are commonly used to protect flat metal surfaces. However, the performance of these coatings has never been tested in the newly developing context of UV plasmonics, i.e., in the presence of UV irradiation and the photogenerated radical species and while keeping the constraint of nanoscale features for the plasmonic nanodevices.…”