Using vertically grown hydrothermal ZnO nanowires, we demonstrate the assembly of fully functional piezoelectric energy harvesters on plastics substrates. A seedless hydrothermal process is employed for the growth of single crystalline vertically orientated ZnO NWs at around 100oC. Flexible NG are assembled using ∼7μm thick PDMS polymer matrix on a 3x3cm substrate. A representative device with an active area of 4cm2 is characterised revealing average output voltage generation of ∼22mV (±1.2) and -32mV (±0.16) in the positive and negative cycles after 3-4mm periodic deflection at 20Hz. A power density of ∼288nW/cm3 is estimated for the device. It is envisaged that such energy scavengers may find potential applications targeting self-powered systems, sensors and on-body charging of electronics

We separate localization and interaction effects in epitaxial graphene devices grown on the C face of an $8^{°}$-off-axis 4$H$-SiC substrate by analyzing the low-temperature conductivities. Weak localization and antilocalization are extracted at low magnetic fields, after elimination of a geometric magnetoresistance and subtraction of the magnetic-field-dependent Drude conductivity. The electron-electron interaction correction is extracted at higher magnetic fields, where localization effects disappear. Both phenomena are weak but sizable and of the same order of magnitude. If compared to graphene on silicon dioxide, the electron-electron interactions on epitaxial graphene are not significantly reduced by the larger dielectric constant of the SiC substrate.

We present a method of selective epitaxial growth of few layers graphene (FLG) on a “prepatterned” silicon carbide (SiC) substrate. The methods involves, successively, the sputtering of a thin aluminium nitride (AlN) layer on top of a monocrystalline SiC substrate and, then, patterning it with $e$ -beam lithography and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman $G$ -band at $\sim 1582{\mathrm{cm}}^{-1}$ in the AlN-free areas is used to validate the concept. It gives absolute evidence of selective FLG growth.

The present work demonstrates the production of single crystalline ZnO nanowires (NWs) using the low temperature hydrothermal process and their integration as the active channel material and piezoelectric elements in single NW field-effect transistors (FETs) and functional nanogenerators (NGs), respectively. Even though hydrothermally grown ZnO NWs show high levels of excess free carriers ≫10¹⁸ cm⁻³, we show that an optimized thermal annealing process at just 450 °C in atmospheric air sufficiently reduces this level to around ∼3.7 × 10¹⁷ cm⁻³. The excess free carrier suppression is verified by assessing the field-effect transport behaviour in a single NW FET. The single device is found to exhibit good performance metrics, including low off-state current (pA range), high on-state current (in the 10 s of μA range) and moderate effective mobility (∼10 cm² V⁻¹ s⁻¹). The functional NGs are based on vertically grown ZnO NWs with ∼7 μm thick polydimethylsiloxane (PDMS) polymer matrix. We show that a NG incorporating annealed ZnO NWs can continuously generate higher output voltages and power compared to a reference device based on as-grown ZnO NWs. This included peak output voltage of ∼109 mV and an output power density of ∼16 μW cm⁻³. We envisage that this approach of thermal annealing may find practical applications in other areas of hydrothermal ZnO NW research, including high performance NW FETs and piezoelectric energy harvesters.

The present work investigates the possibility to charge a Lithium micro-battery (LiB) via direct conversion of ambient mechanical energy into electricity using piezoelectric ZnO nanowire (NW) based microgenerators (PGs). An estimate is provided for the power levels at the different stages of mechanical-to-electrical energy conversion chain, in the following areas: (1) PG output, (2) power management block and (3) LiB storage unit. Also covered in this work is the synthesis, which is a prerequisite for realising such PGs. ZnO NWs of 2μm in length and 200nm in diameter have been grown using a low temperature (<150°C) hydrothermal process on 100μm thick PET substrates (25 × 25 mm2). Substrates containing bi-layer metal layers with dissimilar electro-negativities functioned as a galvanic cell in the growth nutrients, which acted as an electrolyte medium. This necessitated ZnO NWs growth on conductive surfaces, even in the absence of seed layers and/or substrate with specific lattice parameters. Finally, the assembly steps undertaken to realise the fully functional PGs are discussed, and the performances of the final PG are described thereafter. Subjecting such devices to a 10Hz sinusoidal bending force resulted in a measured PG output of ∼56mV peak to peak, on 1 MΩ resistive load