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.

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We report on the chemically stabilized epitaxial w-BN thin film grown on c-plane sapphire by pulsed laser deposition under slow kinetic condition. Traces of no other allotropes such as cubic (c) or hexagonal (h) BN phases are present. Sapphire substrate plays a significant role in stabilizing the metastable w-BN from h-BN target under unusual PLD growth condition involving low temperature and pressure and is explained based on density functional theory calculation. The hardness and the elastic modulus of the w-BN film are 37 & 339 GPa, respectively measured by indentation along <0001> direction. The results are extremely promising in advancing the microelectronic and mechanical tooling industry. 2 Boron Nitride (BN) exhibits numerous allotropes e.g., hexagonal (h-BN, P63/mmc), rhombohedral (r-BN, R3m), cubic (c-BN, Fd3m) and wurtzite (w-BN, P63mc) which are analogous to Carbon (C) allotropes. Among these, h-BN is the most stable form found at room temperature and pressure. c-BN and metastable w-BN can be stabilized, but require extreme temperature (1730-3230 °C) and pressure (5-18 GPa) condition. 1 The equilibrium phase diagram of BN depicts that the stabilization of w-BN requires either c-BN or h-BN as the starting phase and may be difficult to synthesize in pure form. 2 Observation of synthetic w-BN, converted from h-BN at pressure of 11.5 GPa and temperature of 2000K, was first reported in 1963 by Bundy and Wentorf Jr. 3 Subsequently, Various methods e.g., static high-pressure, shock-wave compression method, direct conversion from h-BN have been reported. 4-8 Experimental investigation into the properties of w-BN are scarce because of the difficulty in synthesizing sufficiently large and pure crystals of it. Recently, synthesis of 2 mm diameter and 350 µm thick w-BN crystals with 98% purity (h-BN is the residue phase) under direct conversion method involving high temperature (1500 °C) and pressure (4 GPa) was reported. 7 There are reports on the formation of w-BN and c-BN by thin film growth procedure. 9-13 Polycrystalline (2-20 µm grain size) w-BN film is deposited on amorphous C film by pulsed laser deposition. 11 Only c-BN thin film is deposited on Si (100) substrate by ion assisted pulse laser deposition at 400 °C and 10 -5 Torr. 12 Mixture of c-BN and w-BN has also been reported by PLD on WS2 and ReS2 template. 14 Two-dimensional (2D) layered h-BN (also called white graphene) has recently attracted considerable attention to improve the performance of graphene, other 2D materials such as MoS2and also being explored as an active material for the optoelectronic and energy applications. [15][16] On the other hand, c-BN and w-BN are attractive due to high hardness and the potential in electronic applications remains unexplored. 14,17 In the w-BN structure each atom is tetrahedrally

Hexagonal boron nitride (h-BN) as a filler has significantly improved the mechanical properties of various polymers composites. Among them, polyvinyl alcohol (PVA) is particularly important for its wide range of industrial applications and biocompatibility nature. However, preparing a homogenous composite of h-BN and PVA in water is troublesome as the aqueous processing of h-BN without any additives is challenging. In this context, a pre-processing technique is used to produce an additive-free aqueous dispersion of h-BN. The uniformly dispersed composites are then prepared with different concentrations of h-BN. Free-standing thin films are fabricated using the doctor blade technique, and nanoindentation is employed to understand their deformation behaviour at smaller length scale for better understanding of micro-mechanism involved. Reduced elastic modulus and hardness of 10 wt% h-BN/PVA composite film are enhanced by ∼93% and ∼159%, respectively, compared to pristine PVA. Frequency sweep dynamic mechanical analysis is performed between 1 and 50 Hz, and the elastic properties of composite materials are found to improve significantly upon addition of h-BN nanosheets. Besides, the impact of h-BN incorporation in stress relaxation behaviour and hardness depth profiling are also investigated. The observed improvement in mechanical properties of the composites may be attributed to the uniform distribution of the nanosheets and the strong interfacial interaction between h-BN and PVA, which ensures efficient mechanical stress transfer at the interface.

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