Third-order optical nonlinearity of the CuCo0.5Ti0.5O2 nanostructure under 120 fs laser irradiation.

Recently, titanium-based nanostructures with high nonlinear optical properties have found use in ultrafast photonic system applications. Here, we report a study of the third-order nonlinear optical property of the ${{\rm CuCo}_{0.5}}{{\rm Ti}_{0.5}}{{\rm O}_2}$CuCo0.5Ti0.5O2 (CCoTO) nanostructure synthesized via a simple chemical route. The 40-70 nm CCoTO nanoparticles with centrosymmetric crystalline structure show strong absorption in the 325-850 nm wavelength range due to the presence of different crystalline phases and surface vacancies. A Z-scan technique is used to study the electronic third-order nonlinearity of the synthesized nanoparticles, where a low-repetition-rate 120 fs laser source is employed to minimize thermal agitation-related nonlinearity. The CCoTO nanoparticles possess high surface defects due to oxygen- and copper-related vacancies, which are able to enhance the exciton oscillator strength resulting from the high value of third-order optical nonlinearity. The estimated values of nonlinear refractive index (${n_2}$n2) and nonlinear absorption coefficient ($\beta $ß) of the CCoTO are $ - {1.24}\; \times \;{{10}^{ - 15}}$-1.24×10-15 and ${3.79} \times {{10}^{ - 11}}$3.79×10-11, respectively, under ${188}\,\,{{\rm GW/cm}^2}$188GW/cm2 incident intensity. The intensity-dependent nonlinear optical property of the synthesized nanoparticles is also studied under different incident laser irradiation (62.7, 93, and ${188}\,\,{{\rm GW/cm}^2}$188GW/cm2). In the two-photon absorption (TPA)-dominated third-order nonlinear optical process, the values of ${n_2}$n2 and $\beta $ß of CCoTO are increased with intensifying the incident laser irradiation. The obtained high value of third-order optical nonlinearity of the synthesized nanostructure can be exploited in optical power limiters, pulse power reshaping, and optical switching applications.

Ultraviolet- and Microwave-Protecting, Self-Cleaning e-Skin for Efficient Energy Harvesting and Tactile Mechanosensing.

Smart, self-powered, and wearable e-skin that mimics the pressure sensing property of the human skin is indispensable to boost up cutting edge robotics, artificial intelligence, prosthesis, and health-care monitoring technologies. Here, fabrication of a facile and flexible hybrid piezoelectric e-skin (HPES) with multifunctions of tactile mechanosensing, energy harvesting, self-cleaning, ultraviolet (UV)-protecting, and microwave shielding properties is reported. The principal block of the HPES is an SnO2 nanosheets@SiO2 (silica-encapsulated tin oxide nanosheets)/poly(vinylidene fluoride) (PVDF) nanocomposite (SS)-based PES acting as a single unit for simultaneous energy harvesting and tactile mechanosensing. Gentle human finger imparting onto the PES showed outstanding energy conversion efficiency (16.7%) with high power density (550 W·m-3) and current density (0.40 µA·cm-2). This device can generate high enough electrical power to directly drive portable electronics like a light-emitting diode (LED) panel (consisting of 85 commercial LEDs) and to charge up capacitors very rapidly. Thin PES mechanosensors demonstrated promising performance for quantitatively detecting static and dynamic pressure stimuli with a high sensitivity of 0.99 V·kPa-1 and a short response time of 1 ms. PES was also integrated to a health-data glove for precisely monitoring and discriminating fine motions of proximal interphalangeal, metacarpophalangeal, and distal interphalangeal joints of a human finger and bending motion of different human fingers. A (4 × 4) sensing matrix of PES was successfully employed to detect the spatial distribution of static pressure stimuli. The sensing matrix can precisely record the shape and size of an object placed onto it. PES was encapsulated with a nanocomposite film for providing self-cleaning and UV and microwave protection capability to the HPES. The hydrophobic SS film wrapping (water drop contact angle ∼85.6°) of the HPES enables the self-cleaning feature and makes HPES resistive against water and dirt. The HPES was integrated with in-house-made robotic hands, and the responses of the sensors due to grabbing of an object were evaluated. This work explores new prospects for UV- and microwave-protective, self-cleaning e-skin for energy harvesting and mechanosensation, which can eventually boost up the self-powered electronics, robotics, real-time health-care monitoring, and artificial intelligence technologies.

Enhancement of electroactive ß phase crystallization and dielectric constant of PVDF by incorporating GeO2 and SiO2 nanoparticles.

Poly(vinylidene fluoride) (PVDF) nanocomposites are recently gaining importance due to their unique dielectric and electroactive responses. In this study, GeO2 nanoparticles/PVDF and SiO2 nanoparticles/PVDF nanocomposite films were prepared by a simple solution casting technique. The surface morphology and structural properties of the as-prepared films were studied by X-ray diffraction, scanning electron microscopy, and FT-IR spectroscopy techniques. The studies reveal that the incorporation of GeO2 or SiO2 nanoparticles leads to an enhancement in the electroactive ß phase fraction of PVDF due to the strong interactions between the negatively charged nanoparticle surface and polymer. Analysis of the thermal properties of the as-prepared samples also supports the increment of the ß phase fraction in PVDF. Variation of dielectric constant, dielectric loss, and ac conductivity with frequency and loading fraction of the nanoparticles were also studied for all the as-prepared films. Dielectric constant of the nanocomposite films increases with increasing nanofiller concentration in PVDF. 15 mass% SiO2-loaded PVDF film shows the highest dielectric constant, which can be attributed to the smaller size of SiO2 nanoparticles and the homogeneous and discrete dispersion of SiO2 nanoparticles in PVDF matrix.