Brookite Formation in TiO2?Ag Nanocomposites and Visible‐Light‐Induced Templated Growth of Ag Nanostructures in TiO2

TiO₂? Ag‐nanocomposites exhibit various desirable properties that make them suitable for a variety of applications, for example in photocatalysis and as bactericidal coatings. In this work, a new method for processing TiO₂? Ag nanocomposites is presented. The nanocomposite films are fabricated from one precursor solution with high silver loading of up to 50%. The resulting films exhibit a microstructure consisting of TiO₂? Ag_xO nanocomposites with a largely XRD‐amorphous TiO₂ matrix containing brookite nanocrystals. This specific microstructure absorbs in the visible range so that photoreduction of Ag ions can be accomplished by using visible light. The thin films can be patterned using simple shadow masks. The illuminated areas show a high density of self‐organized nanoparticles (SNPs) and nanorods (SNRs), which are templated by the TiO₂ porous network. The particle size can be tuned by varying the irradiation time. Most of the SNPs and SNRs form faceted crystals, which are mostly a combination of {111} and {110}. The application of these films as substrates for surface‐enhanced Raman scattering is shown. Enhancement factors as high as 4.6 × 10⁶ could be obtained using rhodamine 6G dye molecules. More applications should involve photocatalytic water purification using visible light.     

Thickness and erbium doping effects on the electrical properties of lead zirconate titanate thin films

Thin films of erbium doped lead zirconate titanate (PZT) of different thickness were deposited by sol–gel technique on Pt/TiO₂/SiO₂/Si substrates. Capacitance–voltage measurements show that the dielectric constant continuously increases with the thickness. This is interpreted in terms of effects due to a low permittivity interfacial layer in series with the ferroelectric bulk. The linear fit of the reciprocal of capacitance vs. thickness leads to a true dielectric constant of the ferroelectric of 774 and interfacial capacitance of 14.6 nF. The leakage current properties also depend on thickness and temperature. The calculated interfacial potential barrier height amounts to 0.81 and 0.74 eV, respectively for erbium doped and pure PZT thin films.     

Microstructure and Properties of Solution Deposited, Nb-Doped PZT Thin Films

Nb doped PZT films with Nb concentrations of 0, 5, 8 and 12 mol% are being processed via chemical solution deposition on platinized Silicon substrates. An original processing route including seed layer and additional PbO coating is presented whereby homogeneous, pyrochlore free microstructures with 111/100 texture are obtained. The temperature dependence of the dielectric constant shows diffuse peaks corresponding to the paraelectric to ferroelectric transition. The transition temperature is found to decrease from 325°C to 220°C with increasing Nb content. Nb is however found to lead to a substantial increase in the dielectric constant in comparison to non-doped PZT. The dependence of the dielectric constant on DC bias field is also reported. Strong asymmetries towards positive values both in the values of the dielectric constant and coercive fields are obtained at room temperature, and become replenished at 100°C. This is interpreted in terms of space charge effects on the pinning of domain walls. Furthermore, the loss tangent shows a relaxation peak which shifts to higher frequencies with increasing Nb content, and suggests that Nb-doping affects the dielectric properties of the interfacial layer. Finally, Nb addition is found to lead to slant hysteresis loops with lower remnant polarization and coercive field.     

Dielectric and pyroelectric properties of PZFNT/PZT bimorph thin films

Pyroelectric Pb_1,1(Zr_0.58Fe_0.2Nb_0.2Ti_0.02)O₃/Pb_1.1(Zr_0.9Ti_0.1)O₃ (PZFNT/PZT) bimorph thin films are processed via a modified sol-gel method on highly textured (1 1 1)Pt/Ti/SiO₂/Si substrates. XRD and SEM investigations show full pyrochlore to perovskite phase transformation after annealing at 750 °C. XPS depth profiling reveals diffusion of Fe leading to a broad transition layer. The PZT 90/10 bottom layer was shown to be effective for dielectric permittivity control of the bimorph structure. The small signal dielectric constant, , was determined as 580 at 10 kHz. The temperature dependence of is shown to exhibit a single maximum at approximately 195 °C. The C–V characteristics of the bimorph structure show the typical behavior of ferroelectric perovskites. These results are attributed to microstructural effects, particularly the presence of a broad transition layer. The pyroelectric properties are reported in the temperature range from 20 to 60 °C and compared to monomorph PZT and PZFNT films. It is shown that the bimorph thin film has higher pyroelectric coefficient and detectivity than the constituent monomorph films.     

Structural and Dielectric Characterization of Sol-Gel Fabricated PbTiO3 Thin Films Doped with Lanthanide Ions

Lanthanide elements doped PbTiO₃ thin films were prepared by a modified sol-gel method via spin-coating on platinized silicon substrates. The films microstructure and phase composition were investigated by means of scanning electron microscopy, X-ray diffractometry and Raman spectroscopy. Small signal dielectric properties of the films were characterized at different temperatures and doping element concentration. It is shown that dielectric constant, loss tangent and Curie transition temperature of lanthanide elements doped thin films correlate with concentration and ionic radii of these elements. The results obtained are discussed from the point of view of substitution type and compared to some extent to the data, reported by other research groups.     

Substrate heterostructure effects on interface composition,microstructure development and functional properties of PZT thin films

Platinum- and (La_0.8,Sr_0.2)MnO₃ (LSMO)-terminated silicon substrates were used for the liquid-phase deposition of Pb(Zr_0.52,Ti_0.48)O₃ (PZT) thin films. Different layer thicknesses ranging from 100 to 600 nm were processed by sequential coating. Characterization of the films involved X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy (XPS) combined with depth profiling to probe the interface composition. The films deposited on Pt exhibit an intermetallic layer, Pt_xPb, after annealing at 500 °C in air. This film has been used to establish the XPS signature of the intermetallic phase which consists of a negative shift of the peak position of Pt(4f) due the electron transfer from Pb to Pt. In all cases pure phase perovskite thin films were obtained after short annealing at 700 °C. XPS depth profiling shows unambiguously the existence of an intermetallic layer, Pt_xPb, of approximately 10 nm at the interface between Pt and PZT, while an interdiffusion layer of ～30 nm was observed between LSMO and PZT. The impacts of interfacial layers on microstructure development and functional properties translate in the formation of specific textures, i.e. a pronounced (1 1 1)-texture on Pt due to lattice matching between (1 1 1)-PZT and (1 1 1)-Pt_xPb, and a random film orientation on LSMO, and a substantial thickness dependence of the dielectric and ferroelectric properties, though specific behaviors were observed for the two different substrate heterostructures.