br Results and discussions Fig a b c show SEM

Results and discussions Fig. 1(a,b,c) show SEM images of ZnO nanowires grown on a PET substrate, and a hexagonal wurtzite structure is evidenced in Fig. 1(c). Fig. 1(a,b,c)are taken at an elevation of 90°, 80° and 60° respectively. Images have shown well oriented nanostructures having a diameter of around 150nm and the narrow spacing between them was also achieved by controlling the concentration of the nutrient solution. In Fig. 2 EDS images are obtained from ESEM Philips XL30 and tranylcypromine Supplier (KeV) is represented along x-axis and the arbitrary no. of counts are taken along the y-axis. The image has shown the elemental composition of nanowires, i.e. Zn and O, and most importantly no other elemental peaks are visible showing contamination of free structure. Fig. 3(a) represents the output piezoelectric potential generated by ZnO nanowires having a 2.5nm top electrode thickness; obtained voltage peaks were not as periodic as in the case of a 7.5nm thick sputtered electrode. We have acquired periodic voltage peaks with a maximum voltage of 1.858V. In Fig. 3(b) the upper half (scope 1) represents voltage and the lower part (spectrum 1) represents an output power density of 215.4mW/cm2. Time is taken along the x-axis and voltage along the y-axis. Novelty of research work is that by reducing the diameter of nanowires from 350nm [17] to 150nm we have acquired high voltage values; the reason for high voltage values is that by a decrement in the diameter of nanowires, a more pronounced edge effects phenomenon is caused within nanowires which caused enhanced scattering within nanowires and due to this increase in scattering, reverse leakage current through nanowires has been reduced considerably and all piezoelectric potential has appeared in the output stages of the device. Output power density for a 2.5nm thick Pt sputtered electrode has been recorded but not included due to an insignificant value however in the case of a 7.5nm thick Pt electrode we have acquired a high output power density of 215.4mW/cm2. We have already shown in our earlier work [13] that a 7.5nm thick gold electrode has produced the maximum possible value of voltage with periodic voltage peaks. We sputtered a Pt electrode for 1min and 3min to obtain 2.5nm and 7.5nm thick layers respectively. A 7.5nm thick layer of an electrode has previously shown the ideal Schottky contact. A Schottky contact is essential for piezoelectric potential and electron affinity of a semiconductor which should be less than the work function of sputtering metal [14]. Earlier we have reported 1.34V with a 7.5nm sputtered gold electrode and now we have obtained 1.858V with a Pt sputtered electrode of the same thickness of 7.5nm. It clearly indicates that a sputtered electrode with a high work function has produced high output voltage. Gold has a work function of 5.1eV while Pt has 6.1eV [15], and low output values in the case of gold are due to a reverse leakage current that has been reduced in the case Pt. Not only has a sputtered electrode played a role in producing high voltage but also a decrement in diameter of nanowires also has a vital role in the reduction of reverse leakage current that is due to “Edge effects” present in nanowires. Electrons suffer huge scattering due to these edge effects which cause poor conductivity through nanowires [16]. Earlier with 350nm ZnO nanowires we have reported voltage values of 1.65V and now voltage has been enhanced up to 1.858V with 150nm diameter which shows a reduction in reverse leakage current hence an increase in output voltage. An external force of ~50nN was applied by using an extremely light roller on top of the Pt electrode. As we have discussed in our earlier work, such external force could not deform nanowires permanently because once the force is removed they will regain their original position due to the high elasticity [17–18].
Conclusion High voltage values (1.858V) have been obtained with a 7.5nm thick Pt electrode. The values have been improved by our previously reported voltage values. We have obtained improved results by reducing the diameter up to 150nm and by substituting the top Gold electrode by a Pt electrode. We have also achieved a high output power density of 215.4mW/cm2 with low noise values.