Abstract:We have developed and demonstrated a highly flexible P(VDF-TrFE) film-based energy harvesting device on a PDMS substrate, avoiding any complex composites and patterned structures. The structural and electrical properties of the P(VDF-TrFE) film was investigated using multiple characterization techniques and an optimized film of 7 µm thickness was used for the energy harvesting application. The device, with Ti/Ni metal contacts, was driven by a shaker providing an acceleration of 1.75 g, and frequencies varying from 5 to 30 Hz. The energy harvesting performance of the final fabricated device was tested using the shaker, and resulted in a maximum output capacitor voltage of 4.4 V, which successfully powered a set of 27 LEDs after several minutes of charging.

We report on a novel graphene/P(VDF-TrFE) heterostructure based highly sensitive, flexible, and biocompatible pressure/strain sensor developed through a facile and low-cost fabrication technique. The high piezoelectric coefficient of P(VDF-TrFE) coupled with outstanding electrical properties of graphene makes the sensor device highly sensitive, with an average sensitivity of 0.76 kPa −1 , a gauge factor of 445, and signal-to-noise ratio of 60.8 dB in the range of pressure up to 45 mmHg. A model was proposed to explain the sensor operation, based on carrier density and mobility changes induced by the piezoelectric charge generated in response to strain, which was supported by Hall measurements and Raman spectroscopy. Potential applications in wearable sensing for human activity monitoring were also demonstrated.

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The structural and optical properties of the ZnO, Al-doped ZnO, Ga-doped ZnO, and In-doped ZnO nanorods were investigated using field-emission scanning electron microscopy, X-ray diffraction, photoluminescence (PL) and ultraviolet-visible spectroscopy. All the nanorods grew with good alignment on the ZnO seed layers and the ZnO nanorod dimensions could be controlled by the addition of the various dopants. For instance, the diameter of the nanorods decreased with increasing atomic number of the dopants. The ratio between the nearband-edge emission (NBE) and the deep-level emission (DLE) intensities (I NBE /I DLE ) obtained by PL gradually decreased because the DLE intensity from the nanorods gradually increased with increase in the atomic number of the dopants. We found that the dopants affected the structural and optical properties of the ZnO nanorods including their dimensions, lattice constants, residual stresses, bond lengths, PL properties, transmittance values, optical band gaps, and Urbach energies.

Boron-doped ZnO (BZO) nanorods were grown on quartz substrates using hydrothermal synthesis, and the temperature-dependence of their photoluminescence (PL) was measured in order to investigate the origins of their PL properties. In the UV range, near-band-edge emission (NBE) was observed from 3.1 to 3.4 eV; this was attributed to various transitions including recombination of free excitons and their longitudinal optical (LO) phonon replicas, and donor-acceptor pair (DAP) recombination, depending on the local lattice configuration and the presence of defects. At a temperature of 12 K, the NBE produces seven peaks at 3.386, 3.368, 3.337, 3.296, 3.258, 3.184, and 3.106 eV. These peaks are, respectively, assigned to free excitons (FX), neutral-donor bound excitons (D o X), and the first LO phonon replicas of D o X, DAP, DAP-1LO, DAP-2LO, and DAP-3LO. The peak position of the FX and DAP were also fitted to Varshni's empirical formula for the variation in the band gap energy with temperature. The activation energy of FX was about ~70 meV, while that of DAP was about ~38 meV. We also discuss the low temperature PL near 2.251 eV, related to structural defects.

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Catalyst-and seed layer-free zinc oxide (ZnO) thin films were grown on porous silicon (PS) by a hydrothermal method. Atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) were carried out to investigate the structural and optical properties of the PS and the ZnO thin films. The ZnO thin films have an extraordinary tendency to grow along the a-axis with a hexagonal wurtzite structure. The growth rate of the ZnO thin films was increased with the increase in the precursor concentration. The crystal quality of the ZnO thin films was improved, and the residual stress was decreased as their thickness increased. Monochromatic indigo and red light emission peaks were observed from the ZnO thin films and the PS, respectively. At an excessively high precursor concentration, a green light emission peak was also observed in the ZnO thin films. The luminescent efficiency of the indigo light emission peak was enhanced with the increase in the precursor concentration.