Nanomechanical characterization of SU8/ZnO nanocomposite films for applications in energy-harvesting microsystems

Abstract

Integration of piezoelectric zinc oxide (ZnO) nanoparticles with SU8 in the form of photo-patternable nanocomposite films can lead to the development of a new generation of energy-harvesting microdevices. Design of such energy-harvesting micro/nano-systems will require knowledge of the mechanical properties of the SU8/ZnO nanocomposite thin films for various loadings of ZnO. This work presents characterization of mechanical properties of SU8/ZnO nanocomposite films with ZnO concentration varying in the range of 0–25 wt% via quasi-static and dynamic nanoindentation. These films were fabricated using conventional microfabrication steps involving dispersion of ZnO in SU8 by ultrasonication, followed by spin-coating and UV exposure. The elastic modulus obtained via quasi-static nanoindentation varies from ~6.2 GPa for pristine SU8 to ~8.8 GPa for SU8/25 wt% ZnO nanocomposite, while hardness varies from 402 MPa to ~520 MPa for SU8/ZnO nanocomposites in the same range of ZnO wt%. The experimentally-obtained elastic modulus has also been compared with estimates obtained via Eshelby–Mori–Tanaka micromechanics. Storage modulus, loss modulus and loss factor obtained via dynamic nanoindentation tests indicate that the SU8/ZnO nanocomposites exhibit viscoelastic behavior in the studied frequency-range of 10 Hz to 201.5 Hz. Microstructural characterization via scanning electron microscopy and optical characterization via UV–vis spectrometry of the nanocomposites have also been reported.

Quasi-static and dynamic nanomechanical characterization of PMMA/ZnO nanocomposite thick films synthesized by ultrasonication and spin-coating

“…The dynamic nanoindentation tests were performed in the frequency range of 10–201.5 Hz. The evaluation of storage modulus, loss modulus and loss factor from dynamic nanoindentation is based on a simple Kelvin spring-dashpot model, as shown in the study of Krishna et al 15…”

“…The dynamic nanoindentation tests were performed in the frequency range of 10-201.5 Hz. The evaluation of storage modulus, loss modulus and loss factor from dynamic nanoindentation is based on a simple Kelvin springdashpot model, as shown in the study of Krishna et al 15 Cross-sectional scanning electron microscopy (Zeiss, Merlin Compact FE-SEM) was performed to measure the thickness of the spin-coated PMMA and PMMA/ZnO nanocomposite films. Top-view scanning electron micrographs of the nanocomposite films also revealed the nature of the distribution of ZnO nanoparticles in the PMMA matrix.…”

Thin-film conformal fluorescent SU8-phenylenediamine

“…1 Since epoxy groups are crosslinked by being exposed to ultraviolet (UV) light (typically 365–405 nm) and form a stable solid structure, the polymer belongs to the family of negative photoresists. 2,3 After revealing numerous advantages of SU8, it became a technological platform across many disciplines, including microfluidics, 4–7 micromechanics, 8 biomedicine, 9 optoelectronics, 10,11 and many others. 12–15…”

Dual Piezoelectric/Triboelectric Behavior of BTO/SU‐8 Photopatternable Nanocomposites for Highly Efficient Mechanical Energy Harvesting

“…Addition of conductive, non-conductive, and ferroelectric NFs into SU-8 has aroused new research interests by modulating its mechanical and electrical properties. [27][28][29][30] A combined photopatternability and piezoelectric optimization based on the % weight ratio ZnO and BTO in SU-8 has been recently reported. [17,32] However, there are vast unexplored opportunities in SU-8 based nanocomposites in terms of hybrid transduction as the triboelectric properties of SU-8 based nanocomposites have not been explored significantly.…”