N-doped TiO2 coatings grown by atmospheric pressure MOCVD for visible light-induced photocatalytic activity

N-doped TiO2 films were deposited by atmospheric pressure CVD from titanium tetra-isopropoxide (TTIP) and N2H4 as reactive gas in the temperature range 400–500 °C on various substrates. The films grown at 400 °C are amorphous and exhibit a compact structure and a smooth surface morphology. Increasing the deposition temperature first leads to the crystallization in the anatase structure (temperature range 410–450 °C) and then to the formation of rutile, so that an anatase-rutile mixture is observed in the temperature range 450–500 °C. Correlation between the structure, the morphology, optical properties, hydrophilicity and photocatalytic activity of the thin films both under UVand VIS light are presented and discussed in relation with deposition conditions

Effect of H2 on the microstructure and properties of TiO2 films grown by atmospheric pressure MOCVD on steel substrates

TiO2 thin films were deposited under atmospheric pressure by MOCVD in the range 400-600 °C on various steel substrates under hydrogen ambiance. It is unusual to study the growth of functional oxide layers under H2 partial pressure, i.e. a reactive gas generally used as reductive atmosphere in CVD. Titanium tetra-isopropoxide was used as single source precursor of Ti and O. The growth rate of TiO2 layers grown under nitrogen increases with the temperature and reaches a maximum in the range 500-550 °C. At these temperatures the diffusion of substrate ions enhances the formation of rutile leading to a lower UV photocatalytic activity. Addition of H2 in the input gas phase during the deposition (i) reduces the formation of interface oxide layer, (ii) prevents the diffusion of cations from the steel substrate toward the TiO2 layer and (iii) favors the growth of anatase. This leads to an increase of photocatalytic efficiency under UV irradiation

Growth of TiO2 thin films by AP-MOCVD on stainless steel substrates for photocatalytic applications

TiO2 thin films were deposited under atmospheric pressure by MOCVD in the temperature range 400–600 °C on stainless steel and Si(100) substrates. Titanium tetraisopropoxide (TTIP) was used as Ti and O source. Single-phased anatase and bi-phased (anatase/rutile) coatings with controlled composition have been deposited depending on the temperature and the TTIP mole fraction. The films grown on stainless steel at low temperature (b420 °C) and low TTIP mole fraction (b10−4) are constituted of pure anatase and they exhibit a high photocatalytic activity under UV light and a high hydrophilicity. In the temperature range 430–600 °C the rutile starts growing leading to anatase/rutile mixtures and subsequently to a progressive decrease of both photocatalytic activity and wettability. Correlations between functional properties and microstructure of the films are discussed

A surface science approach to cathode electrolyte interfaces in Li ion batteries Contact properties, charge transfer and reactions

Reactions and charge transfer at cathode/electrolyte interfaces affect the performance and the stability of Li-ion cells. Corrosion of active electrode material and decomposition of electrolyte are intimately coupled to charge transfer reactions at the electrode/electrolyte interfaces, which in turn depend on energy barriers for electrons and ions. Principally, energy barriers arise from energy level alignment at the interface and space charge layers near the interface, caused by changes of inner electric (Galvani) potential due to interfacial dipoles and concentration profiles of electronic and ionic charge carriers. In this contribution, we introduce our surface science oriented approach using photoemission (XPS, UPS) to investigate cathode/electrolyte interfaces in Li-ion batteries. After an overview of the processes at cathode/electrolyte interfaces as well as currently employed analysis methods, we present the fundamentals of contact potential formation and energy level alignment (electrons and ions) at interfaces and their analysis with photoemission. Subsequently, we demonstrate how interface analysis can be employed in Li-ion battery research, yielding new and valuable insights, and discuss future benefits