Chapters authored
Pulsed Laser-Deposited TiO2-based Films: Synthesis, Electronic Structure and Photocatalytic Activity
Active under visible light, photocatalysts based on doped titania were obtained via pulsed laser deposition (PLD) method. To find out the crystalline structure, optical properties, and electronic structure, the following techniques such as X-ray diffraction, electronic spectroscopy, electrical conductivity measurements, and X-ray photoelectron spectroscopy (XPS) are used. Photocatalytic activity is monitored by applying the photoreduction of dichromate ions under UV and visible light. The influence of zirconium ions and its content and synthesis conditions on the efficiency of nitrogen incorporation into titania structure that, in turn, determines the electronic structure and photocatalytic ability of the semiconductive materials are discussed. A substitutional nitrogen (Ti–N) rather than an interstitial one (Ti–O–N) is mainly responsible for the observed photoactivity. It is pointed that substitutional nitrogen is responsible for bandgap narrowing or formation of intragap localized states within semiconductor bandgap. The bandgap energy values are sharply decreased, while the relative intensity of substitutional nitrogen XPS peaks is increased. Pulsed laser synthesis of TiO2 films in N2/CH4 atmosphere not only leads to nitrogen incorporation but also to the formation of defects including oxygen vacancies and Ti3+ states which are all contributing to light absorption. An appropriate ratio of gas mixture, optimum zirconia content, suitable pressure, and temperature during synthesis was found for the synthesis of highly active semiconductive films. The highest photocatalytic conversion yields are obtained for nitrogen-doped 10% ZrO2/TiO2 synthesized in N2:CH4 = 5:1 at 100 Pa and at 450°C under both UV and visible light.
Part of the book: Semiconductor Photocatalysis
Heterostructures Based on Porphyrin/Phthalocyanine Thin Films for Organic Device Applications
Multilayer or blend heterostructures based on porphyrins and phthalocyanines were obtained on different substrates using VTE and MAPLE methods. Stacked structures based on ZnPc and C60 with NTCDA were prepared by VTE on ITO/glass, their current value being increased by the deposition of the materials in an inverted configuration or by using ITO/PEDOT:PSS as a substrate. Multilayer structures comprising ZnPc and NTCDA were fabricated by MAPLE on an AZO/glass. Treating the AZO in oxygen plasma, a higher current value was obtained for the deposited heterostructures. The oxygen plasma treatment can increase the work function of the AZO resulting in a decrease of the energetic barrier from AZO/organic interface and finally improving the charge transport. Stacked layers or blend heterostructures having ZnPc, MgPc and TPyP were deposited by MAPLE on ITO/PET. In the case of those containing MgPc and TPyP, an increase in the current value (in dark) was obtained for the blend compared to the stacked layer configuration. For those with ZnPc and TPyP, under illumination, a photovoltaic effect was observed for the blend structure. All heterostructures are featured by a large absorption in the visible domain of the solar spectrum and suitable electrical properties for their use in OPV applications.
Part of the book: Phthalocyanines and Some Current Applications
Laser Prepared Thin Films for Optoelectronic Applications
Laser techniques such as pulsed laser deposition, combinatorial pulsed laser deposition, and matrix-assisted pulsed laser evaporation were used to deposit thin films for optoelectronic applications. High-quality transparent conductor oxide films ITO, AZO, and IZO were deposited on polyethylene terephthalate by PLD, an important experimental parameter being the target-substrate distance. The TCO films present a high transparency (>95%) and a reduced electrical resistivity (5 × 10−4 Ωcm) characteristics very useful for their integration in the flexible electronics. InxZn1−xO films with a compositional library were obtained by CPLD. These films are featured by a high optical transmission (>95%), the lowest resistivity (8.6 × 10−4 Ωcm) being observed for an indium content of about 44–49 at.%. Organic heterostructures based on arylenevinylene oligomers (P78 and P13) or arylene polymers (AMC16 and AMC22) were obtained by MAPLE. In the case of ITO/P78/Alq3/Al heterostructures, a higher current value is obtained when the film thickness increases. Also, a photovoltaic effect was observed for heterostructures based on AMC16 or AMC22 deposited on ITO covered by a thin layer of PEDOT:PSS. Due to their optical and electrical properties, such organic heterostructures can be interesting for the organic photovoltaic cells (OPV) applications.
Part of the book: Nanoscaled Films and Layers