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While the length and diameter of ZnO NWs were varied by adjusting the flow-rate conditions through different growth regimes limited either by the O2 gas or DEZn reactants, their polarity was consistently Zn-polar, as revealed by #piezoresponseforcemicroscopy ( #PFM ) .*

Moreover, the piezoelectric coefficient of ZnO NWs exhibits a strong correlation with their length and diameter. The highest mean piezoelectric coefficient of 3.7 pm/V was measured on the ZnO NW array with the length above 800 nm and the diameter below 65 nm. These results demonstrate the ability of the PLI-MOCVD system to modify the dimensions of ZnO NWs, as well as their piezoelectric properties.*

NANOSENSORS™ conductive and wear-resistant Platinum-Silicide #AFMprobes of the PtSi-NCH type with a high spring constant (typical value 42 N/m) were used to mitigate the interference of the electrostatic effect during the measurements.*

In the DataCube PFM mode, the #AFMtip was systematically brought into contact with the sample at a determined position, subsequently held in 60 milliseconds for the piezoelectric measurement, and then retracted before proceeding to the next position. This sequential approach and retraction of the AFM tip was employed to avoid tip dragging during the scanning process, which could bend the NWs and cause a contact failure between the AFM tip and the sample. When the AFM tip was in contact with the sample, an AC voltage of 5 V amplitude and 15 kHz frequency of AC voltage was applied across the top and bottom of the sample through the tip and chuck of the AFM system. Due to the piezoelectric properties, the ZnO NWs were deformed in response to the AC voltage. This deformation was measured by the AFM tip to obtain the piezoelectric response amplitude and phase signals. The piezoelectric response amplitude is proportional to the piezoelectric coefficient, while the piezoelectric response phase identifies the polarity of ZnO NWs. Thanks to the small radius of the AFM tip, the piezoelectric response of each individual NW can be measured. By scanning the AFM tip across a 1 × 1 µm2 area, the piezoelectric response of the NWs in the array was mapped. For each sample, the piezoresponse amplitude values were extracted from the piezoresponse amplitude map, and the mean piezoresponse amplitude was evaluated to study the piezoelectric amplitude behavior of ZnO NWs grown at different flow rates.*

Please have a look at the NANOSENSORS blog for the full citation and a direct link to the full article.

#piezoelectricity #nanogenerators #ZincOxideNanowires #PiezoresponseForceMicroscopy #AFM探针 #ピエゾ応答力顕微鏡