A detailed understanding of micelle formation that occurs above a critical micelle concentration (cmc) is a crucial point for the surfactant-assisted preparation of porous materials such as molecular sieves. However, the role of the cmc in the surfactant-assisted electrodeposition of porous oxides is widely unknown. In this study, we investigated the electrodeposition of ZnO films under utilization of alkyl sulfates and alkyl sulfonates with different chain lengths. Cmc values of the surfactants were measured directly in the electrodeposition bath by surface tension measurements. Subsequently, we performed electrodeposition with surfactant concentrations from above the cmc down to concentrations well below the cmc. Beside a lamellar ZnO phase already known from earlier studies, a second nanoparticular ZnO phase was found at concentrations below the cmc.
Electrodeposited nanoporous ZnO/eosin Y hybrid films have been investigated in view of their potential applications in dye-sensitized solar cells and supercapacitors. Intensity-modulated photocurrent spectra were measured at different electrode potentials at films of different thicknesses. It was found that the results represent either the RC constant of the cell and surface recombination of photogenerated holes with electrons or the diffusion of photogenerated electrons and are dependent on the electron concentration in the ZnO, which is influenced by the film thickness, the electrode potential, and the light intensity. The results suggest that the porosity of the electrodeposited ZnO increases with the film thickness and the films therefore consist of two parts, a less porous part deposited in the first few minutes that exhibits field-driven electron transport and a more porous outer part where electron transport is by diffusion. The results are supported by frequency-dependent capacitance measurements, which also show that the material is suitable for supercapacitors.
that the TSPcMe could act as photosensitizers in photoelectrochemical measurements. More recently, Pauporte el al. [7] extended this work by using other metals (Me = Ni, Co, Fe) and the use of O 2 instead of NO 3 as oxidant for the formation of ZnO. In all these studies, however, the TSPcMe were added to the electrodeposition bath in relatively low concentrations of typically 25 or 50 lM and a systematic variation of the dye concentration has not been carried out at all. In fact, the use of 3864
1 Introduction Nanostructured thin films of inorganic wide-bandgap semiconductors are an interesting field of research due to the numerous applications e.g. in photocatalysis [1] and optoelectronic devices [2,3]. Fabrication of semiconductor thin films presently often relies on gas phase methods like vacuum evaporation, sputtering and chemical vapour deposition, which are of high cost because of the need for high energy, high temperatures or expensive vacuum facilities. Our approach is the electrochemical deposition of porous semiconductor thin films, a method which promises to be cost-effective and convenient since usually no high temperatures, vacuum conditions or other expensive equipment is needed. Moreover, nanostructuring of the films and the formation of inorganic/organic hybrid films can easily be achieved in situ just by the presence of the organic substances to be codeposited in the electrodeposition bath.
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