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p-CuSCN/n-Fe 2 O 3 heterojunctions were electrochemically prepared by sequentially depositing α-Fe 2 O 3 and CuSCN films on FTO (SnO 2 :F) substrates. The α-Fe 2 O 3 and CuSCN films and the α-Fe 2 O 3 /CuSCN heterojunctions were characterized by Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), and X-Ray Diffraction (XRD). Pure crystalline CuSCN films were electrochemically deposited on α-Fe 2 O 3 films by fixing the SCN/Cu molar ratio in the electrolytic bath to 1:1.5 at 60 °C and at a potential of-0.4 V. The photocurrent measurements showed an increase of the intrinsic surface states or defects at the α-Fe 2 O 3 /CuSCN interface. The photoelectrochemical performance of the α-Fe 2 O 3 /CuSCN heterojunction was examined by chronoamperometry and linear sweep voltammetry techniques. It was found that the α-Fe 2 O 3 /CuSCN structure exhibits a higher photoelectrochemical activity when compared to α-Fe 2 O 3 thin films. The highest photocurrent density was obtained for α-Fe 2 O 3 /CuSCN films in 1 M NaOH electrolyte. This high photoactivity was attributed to the high active surface area and to the external applied bias;, which favors the transfer and the separation of the photogenerated charge carriers in α-Fe 2 O 3 /CuSCN heterojunction devices. The flat band potential and the donor density were found to be maximal for the heterojunction. These results suggest a substantial potential to achieve heterojunction thin films in photoelectrochemical water splitting applications.

Electrodeposition of gold into porous silicon was investigated. In the present study, porous silicon with ~100 nm in pore diameter, so-called medium-sized pores, was used as template electrode for gold electrodeposition. The growth behavior of gold deposits was studied by scanning electron microscope observation of the gold deposited porous silicon. Gold nanorod arrays with different rod lengths were prepared, and their surface-enhanced Raman scattering properties were investigated. We found that the absorption peak due to the surface plasmon resonance can be tuned by changing the length of the nanorods. The optimum length of the gold nanorods was ~600 nm for surface-enhanced Raman spectroscopy using a He–Ne laser. The reason why the optimum length of the gold nanorods was 600 nm was discussed by considering the relationship between the absorption peak of surface plasmon resonance and the wavelength of the incident laser for Raman scattering.

Using the easily applicable hydrothermal method Cr-doped hematite thin films have been deposited polycrystalline on conductive glass substrates. The hydrothermal bath consisted of an aqueous solution containing a mixture of FeCl3.6H2O and NaNO3 at pH = 1.5. The samples were introduced in an autoclave and heated for a fixed time at a fixed temperature and then annealed in air at 550ºC. The concentration of the incorporated Cr atoms (Cr 4+ ions) was controlled by varying the concentration of the Cr(ClO4)3 precursor solution, varied from 0 % to 20 %. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Cr-doped hematite films exhibited higher photoelectrochemical activity than the undoped films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 16 at.% Cr-doped films. This high photoactivity can be attributed to both the large active surface area and increased donor density caused by Cr-doping in the α-Fe2O3 films. All samples reached their best IPCE at 400 nm. IPCE values for 16 at.% Cr-doped hematite films were thirty times higher than that of undoped samples. This high photoelectrochemical performance of Cr-doped hematite films is mainly attributed to an improvement in charge carrier properties.

A model of metal electrodeposition within mesoporous silicon is proposed. The model is based on the coupled map lattice model, which includes diffusion of metal ions, electrode shape, equivalent circuit of electrochemical cell, and potential drop in porous silicon wall. Continuous filling from the pore bottom to the opening and plugging at the pore opening were successfully reproduced using the present model. By analyzing the concentration profile of cupric ions in solution, the mechanism of plugging at the pore opening and discontinuous filling by electrodeposition is discussed.

We report the fabrication and characterization of porous Si templates for electrodeposition of Au high aspect ratio nanostructures. The templates with ordered and controlled pore size, 4 µm and 50 nm in diameter, were created through Si etching. Electrodeposition of Au into macroporous Si and into mesoporous Si was investigated. The different morphologies of deposits depending on the Si type and pore size were compared and discussed. The morphology and structural characteristic of the fabricated nanostructures were analyzed using scanning electron microscopy. The micrographs confirm that the deposition parameters have a strong influence on morphology of the structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Homogeneous decoration of TiO nanotubes (NTs) by Ag metallic nanoparticles (NPs) was carried out by a relatively simple photoreduction process. This Ag-NPs decoration was found to improve the photoconversion efficiency of the TiO-NTs based photoanodes. The x-ray photoelectron spectroscopy and x-ray diffraction analyses confirmed that all the Ag-NPs are metallic and the underlying TiO-NTs crystallize in the anatase phase after their annealing at 400 °C, respectively. Transmission electron microscopy observations have confirmed the effective decoration of the TiO-NTs' surface by Ag-NPs, and allowed to measure the average Ag-NPs size, which was found to increase linearly from (4 ± 2) nm to (16 ± 4) nm when the photoreduction time is increased from 5 to 20 min. The diffuse reflectivity of the Ag-NPs decorated TiO-NTs was found to decrease significantly as compared to the undecorated TiO-NTs. Interestingly, the Ag-NPs decorated TiO-NTs exhibited a significantly enhanced photochemical response, under visible radiation, with regards to the undecorated NTs. This enhancement was found to reach its maximum for the TiO-NTs decorated with Ag-NPs having the optimal average diameter of ∼8.5 nm. The maximum photoconversion efficiency of Ag-NPs decorated TiO-NTs was about two times greater than for the undecorated ones. This improved photo-electro-chemical response is believed to be associated with the additional absorption of visible light of Ag-NPs through the localized surface plasmon resonance phenomenon. This interpretation is supported by the fact that the photoluminescence intensity of the Ag-NPs decorated TiO-NTs was found to decrease significantly as compared to undecorated NTs, due to charge carriers trapping in the Ag NPs. This demonstrates that Ag-NPs decoration promotes photogenerated charges separation in the TiO-NTs, increasing thereby their capacity for current photogeneration. The surface decoration of TiO NTs by noble metals NPs is expected to impact positively the use of TiO-NTs based photoanodes in some energetic applications such as hydrogen generation and photo-electrochemical solar cells.