arXiv subjects

Seeram Ramakrishna

Publications and source records attributed to Seeram Ramakrishna.

4 recordsLinked to original sources

arXiv2026

Cladding Layer Enhanced GHz Bulk Acoustic Wave Resonance in Sodium Niobate Thin Films on Silicon

Bulk acoustic wave resonators (BAWR) and bandpass filters operating at GHz frequency are the workhorse of (Vo-)LTE telecommunication and broadband internet. In line with the Singapore Green Plan 2030 for innovating environmentally friendly products, we fabricated lead-free BAWR with sodium niobate (NaNbO3) piezoelectric on silicon with a high electromechanical coupling factor up to 31.3% operating at ~4 GHz. We disclose our crucial strategy where the NaNbO3 layer is cladded between two thin layers of high band gap insulators, which satisfies two primary objectives, i.e. leakage current mitigation and crack avoidance. In addition, we also verified the efficacy of reducing lattice parameters of the cladding layers in promoting vertically distorted tetragonal phase NaNbO3 and producing stronger BAWR signals.

cond-mat.mtrl-sci↗

arXiv2025

ZnO@C/PVDF Electrospun Membrane as Piezoelectric Nanogenerator for Wearable Applications

The rapid growth of wearable technology demands sustainable, flexible, and lightweight energy sources for various applications ranging from health monitoring to electronic textiles. Although wearable devices based on the piezoelectric effect are widespread, achieving simultaneous breathability, waterproof, and enhanced piezoelectric performance remains challenging. Herein, this study aims to develop a piezoelectric nanogenerator (PENG) using ZnO nanofillers in two morphologies (nanoparticles and nanorods), with a carbon coating (ZnO@C) core-cell structure to enhance piezoelectric performance. Electrospinning technique was employed to fabricate a lightweight, breathable, and water-resistant ZnO@C/PVDF membrane, enabling in situ electrical poling and mechanical stretching to enhance electroactive \b{eta}-phase formation and thus improve piezoelectric performance. A maximum power density of 384.83 μW/cm3 was obtained at RL = 104 kΩ, with a maximum Vout = 19.9 V for ZnO@C nanorod-incorporated PVDF samples. The results demonstrate that ZnO@C nanorods exhibit superior voltage output due to their larger surface-to-volume ratio, leading to enhanced interaction with PVDF chains compared to nanoparticles. The fabricated membrane showed promising results with a water vapor transmission rate (WVTR) of ~0.5 kg/m2/day, indicating excellent breathability, and a water contact angle of ~116°, demonstrating significant waterproofness. These findings highlight the potential of the ZnO@C/PVDF electrospun membrane as an effective piezoelectric nanogenerator and energy harvester for wearable applications.

physics.app-ph↗

arXiv2020

Machine Learning in Materials Modeling -- Fundamentals and the Opportunities in 2D Materials

The application of machine learning in materials presents a unique challenge of dealing with scarce and varied materials data - both experimental and theoretical. Nevertheless, several state-of-the-art machine learning models for materials have been successfully developed to predict material properties for various applications such as materials for photovoltaic cells, thermoelectric materials, dielectrics, materials for batteries, fuel cells, etc. The setup of comprehensive materials databases, and openly accessible algorithm frameworks have also spurred the usage of machine learning for solving some of the most pressing problems in materials science. Some such recent implementations are discussed in this book chapter. A multitude of two-dimensional (2D) materials exist with the potential to replace the conventional materials for energy storage and nanodevices. The challenges faced in designing batteries and how machine learning tools can help in screening and narrowing down on the best composition, as well as the synthesis of air-stable 2D materials, are also discussed.

cond-mat.mtrl-sci↗

arXiv2018

Exceed Improved Efficient Perovskite Solar Cells Under Dual-Irradiation System

In general, perovskite solar cells (PSC) with a sensitized or thin film architecture absorb light from a single illumination. This paper reported a PSC architecture with a semitransparent Au/ITO counter electrode, which allows light to pass it partially. When the device was illuminated simultaneously from both the FTO and Au/ITO sides, the PSC has achieved an overall power conversion efficiency (PCE) as high as 20.1% under high light intensity (1.4 sun), which is much higher than that of the single-irradiation system.

physics.app-ph↗