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With the aim of offering advanced and selective catalysis, a series of defect-rich titania (TiO2.40, TiO1.81, TiO1.74, TiO1.72, and TiO1.54) are prepared via scalable, precise pulsed laser deposition technique. Their catalytic performance is compared to stoichiometric Degussa P25 TiO2. On mere decreasing O/Ti ratio, native titania turns from a photoelectrocatalyst to electrocatalyst for improved water splitting. At a stoichiometric composition of TiO1.81, titania acts as an absolute photoanode for an oxygen evolution reaction and generates a photocurrent of 0.62 mA cm–2 at 0 V versus reversible hydrogen electrode under AM1.5 simulated solar illumination while acting as a poor electrocatalyst with high onset potential of 650 mV for a hydrogen evolution reaction. On increasing the oxygen vacancies in titania, relatively higher electrocatalytic hydrogen evolution is observed for defect-rich TiO1.54 and affords a current density of 10 mA cm–2 at just an overpotential of 610 mV, despite its negligible photoelectrocatalytic activity. Since defect concentration in titania is mainly responsible for the trade-off between electrocatalytic and photoelectrocatalytic water-splitting behavior, systematic attempts have also been made to understand the interplay between defects and catalysis of titania. The different intrinsic characteristics of defect-rich titania ranging from microscopic structural evolution (X-ray diffraction and microscopic imaging) to chemical speciation (X-ray photoelectron spectroscopy, electron paramagnetic resonance, and ultraviolet–visible spectroscopy) to kinetics of electro/photoelectrochemical water splitting [intensity-modulated photocurrent/photovoltage spectroscopy, electrochemical impedance spectroscopy, open-circuit photovoltage decay, depth of trap states (DOS) measurement] are extensively studied in this work. Unequivocally, the higher photoelectrocatalytic water-splitting activity of TiO1.81 is due to its large microstrain (1.9%) associated optimum defect-induced lattice distortion index (0.006), which facilitates high charge transfer efficiency (82%) with a low recombination rate constant (1.98 s–1) of photogenerated electron–hole pair by favorable DOS. On the other hand, high density of oxygen vacancy in TiO1.54 induces a magnanimous distortion index (0.035) in TiO6 octahedra with a small microstrain of 0.4%, which provides a high donor density (10.2 × 1018 cm–3) and favors efficient electrocatalytic water-splitting activity. Overall, this work highlights the overlooked and unexploited facets of defect engineering.

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This study investigates the effect of chemical mechanical planarization (CMP) processing parameters such as platen velocity, concentration of the oxidizer and abrasive nanoparticle, slurry pH, and surfactant types on the surface roughness of cadmium zinc telluride (CdZnTe) substrate. It was found that these parameters have a significant effect on the quality of the polished surfaces. It was also found that lower platen velocity, lesser abrasive particles concentration, basic slurry pH, and addition of anionic surfactant into the CMP slurry solution improved surface planarity. Optical surface profiler and atomic force microscopy techniques were used to monitor the surface topography before and after polishing. A notable root-mean-square surface roughness, (Rq), ~0.9 nm, has been obtained on polished CdZnTe (CZT) surface over a scan area of 481×361 µm2 under the optimized conditions of 60 rpm relative velocity, slurry pH of 9, 3.75 vol. % of oxidizer (H2O2) and 1.25 wt. % of abrasive (SiO2 nanoparticle). A probable mechanism of the present CMP surface planarization of CZT substrate has been proposed. Unlike the conventional surface planarization processes, which involve two-step lapping followed by CMP for the CZT surfaces, we have developed a single step CMP process to obtain good surface planarity.

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