Competition between ferroelectric and semiconductor properties in Pb(Zr0.65Ti0.35)O-3 thin films deposited by sol-gel

Asymmetric metal–ferroelectric–metal (MFM) structures were manufactured by sol–gel deposition of a lead zirconate-titanate (PZT with Zr/Ti ratio 65/35) film on Pt-coated Si, with a Au top electrode. The average remnant polarization of 9 µC/cm2 and the coercive field of 39 kV/cm were obtained from the hysteresis loop measurements. A detailed analysis of the polarization–electric field (P–E), capacitance–voltage (C–V), and current–voltage (I–V) measurement results allowed us to estimate the near-electrode space-charge region thickness (roughly half of the film thickness at zero voltage), net doping concentration (around 1018 cm–3), built-in potential (in the 0.4–0.8 V range, depending on the injecting electrode), and dynamic dielectric constant (5.2). The current logarithm–voltage dependence for the field-enhanced Schottky emission obeys a "1/4" law. The spectral distribution of the short circuit current measured under continuous light illumination in the 290–800 nm range exhibits a cutoff wavelength at 370 nm and a maximum sensitivity at about 340 nm. The estimated band-gap energy of the PZT material is 3.35 eV. The MFM structure is discussed in terms of two back-to-back Schottky diodes with a ferroelectric material in between. It is concluded that the semiconductor properties of the films are not negligible and, in certain conditions, are dominating over the ferroelectric one

Current Status of the Open-Circuit Voltage of Kesterite CZTS Absorber Layers for Photovoltaic Applications—Part I, a Review

Herein, based on the reviewed literature, the current marketability challenges faced by kesterite CZTS based-solar cells is addressed. A knowledge update about the attempts to reduce the open circuit voltage deficit of kesterite CZTS solar cells will be addressed, with a focus on the impact of Cu/Zn order/disorder and of Se doping. This review also presents the strengths and weaknesses of the most commercially attractive synthesis methods for synthesizing thin kesterite CZTS films for photovoltaic applications

Scanning polarization force microscopy investigation of contact angle and disjoining pressure of glycerol and sulfuric acid on highly oriented pyrolytic graphite and aluminum

For liquid droplets of sub-micrometer dimensions, the study of wetting properties (quantified by contact angle, disjoining pressure, spreading coefficient, etc.) is possible using the relatively new technique known as scanning polarization force microscopy (SPFM). This non-contact scanning probe microscopy technique was successfully implemented in our laboratory in order to study the wetting properties of glycerol and sulfuric acid on the surface of highly oriented pyrolytic graphite (HOPG) and glycerol on aluminum film deposited on mica. An AC polarization bias of 3 V at 3 kHz frequency was applied between a conductive atomic force microscope tip and the substrate. The resulting polarization force was measured with high accuracy, allowing non-contact topography profile measurements of liquid micro- and nanodroplets. The dependence of the contact angle on droplet height was determined in order to calculate the values of the spreading coefficient and the disjoining pressure between the liquid and substrates. The calculated potential energies give disjoining pressure values of ∼0.4 atm for glycerol on HOPG, ∼0.47 atm for glycerol on aluminum and ∼13 atm for H2SO4 on HOPG. In the case of H2SO4 on HOPG the strength of the force appears to be thirty times bigger than that for glycerol on HOPG and aluminum

Chitosan-Based Materials Featuring Multiscale Anisotropy for Wider Tissue Engineering Applications

We designed graphene oxide composites with increased morphological and structural variability using fatty acid-coupled polysaccharide co-polymer as the continuous phase. The matrix was synthesized by N, O-acylation of chitosan with palmitic and lauric acid. The obtained co-polymer was crosslinked with genipin and composited with graphene oxide. FTIR spectra highlighted the modification and multi-components interaction. DLS, SEM, and contact angle tests demonstrated that the conjugation of hydrophobic molecules to chitosan increased surface roughness and hydrophilicity, since it triggered a core-shell macromolecular structuration. Nanoindentation revealed a notable durotaxis gradient due to chitosan/fatty acid self-organization and graphene sheet embedment. The composited building blocks with graphene oxide were more stable during in vitro enzymatic degradation tests and swelled less. In vitro viability, cytotoxicity, and inflammatory response tests yielded promising results, and the protein adsorption test demonstrated potential antifouling efficacy. The robust and stable substrates with heterogeneous architecture we developed show promise in biomedical applications