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Author: search.filters.author.Rao, V. RamgopalSubject: search.filters.subject.Nanocomposites

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    A Novel Photoplastic Piezoelectric Nanocomposite for MEMS Applications
    (IEEE, 2012-04) Rao, V. Ramgopal
    This letter reports a photoplastic (SU-8) piezoelectric (ZnO) nanocomposite route for realization of simple and low-cost piezoelectric microelectromechanical systems (MEMS). Integrating the ZnO nanoparticles into a photosensitive SU-8 polymer matrix not only retains the highly desired piezoelectric properties of ZnO but also combines the photopatternability and the optical transparency of the SU-8 polymer. These two aspects, therefore, lead to exciting MEMS applications with simple photolithography-based microfabrication. This approach opens up many new applications in the field of both sensor and energy harvesting
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    Vibtrational energy harvesting using photo-patternable piezoelectric nanocomposite cantilevers
    (Elsevier, 2013-09) Rao, V. Ramgopal
    Here we report on fabricating photo-patternable polymer nanocomposite cantilevers for harvesting electrical energy from mechanical vibrations. The optimized piezoelectric polymer nanocomposite enables direct photo patterning and, therefore, easy fabrication of microcantilevers eliminating expensive etching steps. Integrating piezoelectric zinc oxide (ZnO) nanoparticles (NPs) with optimum weight fraction into a photosensitive SU-8 polymer matrix not only retains the highly desired piezoelectric and semiconducting properties of the ZnO, but also combines the photo-patternability and the optical transparency of the SU-8. The maximum output power produced by nanocomposite cantilevers was 0.025 μW across a resistive load of 100 kΩ with peak to peak voltage of ∼140 mV at a resonance frequency of 4 kHz. This inexpensive platform offers design flexibility and ease of fabrication for harvesting mechanical vibrations.
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    Spin-coatable, photopatternable magnetic nanocomposite thin films for MEMS device applications
    (RSC, 2015) Rao, V. Ramgopal
    Magnetic nanomaterials' (especially metals) air stability and compatibility with standard micro-fabrication technologies are often a concern for development of MEMS-based magnetic devices. In this paper, we report an air-stable, photo-patternable and spin-coatable magnetic thin film preparation process for MEMS applications. This magnetic nanocomposite thin film was prepared by incorporating carbon capped ferromagnetic cobalt nanoparticles of dimension 20–80 nm into the SU-8 matrix. TEM, XRD and EDAX analyses were done, to investigate the crystal structure, dispersion and phase stability of the films. The SQUID magnetometry and MFM measurements of the film confirmed its magnetic response at room temperature and the retention of its magnetic properties over a period of time. The material compatibility for MEMS device applications was demonstrated through fabrication of a suspended circular membrane of radius ∼250 μm, having four U-shaped beams, of dimension ∼270 × 50 μm each. Three conventional lithography steps and a sacrificial release layer of ∼1 μm thick oxide was used for the fabrication. The membrane was characterized by evaluating its spring constant and resonant frequency. The spring constant and resonant frequencies were estimated to be ∼4.2 N m−1 and ∼29 kHz respectively. Finally, we demonstrated the actuation of the magnetic membrane by an off-chip generated magnetic field, for its possible use as a MEMS device
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    Microscopic Origin of Piezoelectricity in Lead-Free Halide Perovskite: Application in Nanogenerator Design
    (ACS, 2019-03) Rao, V. Ramgopal
    In this work, we report a lead-free hybrid halide perovskite system with a very high piezoelectric charge density for applications in nanogenerators. We use materials engineering by incorporation of formamidinium tin iodide, FASnI3, in a soft polymer (polyvinylidene fluoride, PVDF) matrix and demonstrate high-performance large-area flexible piezoelectric nanogenerators. This is achieved by using self-poled thin films of a FASnI3:PVDF nanocomposite. The fabricated devices show an output voltage up to ∼23 V and power density of 35.05 mW cm–2 across a 1 MΩ resistor, under a periodic vertical compression, with a release pressure of ∼0.1 MPa. Measured values of the local piezoelectric coefficient (d33) of these films reach up to 73 pm/V. We provide the microscopic mechanism using first-principles calculations, which suggest that a soft elastic nature and soft polar optic phonons are responsible for the high piezoelectric response of FASnI3. Our studies open up a route to high-performance nanogenerators using a lead-free organic–inorganic halide perovskite family of materials.