  Piezoelectric nanowires are promising materials for sensing, actuation and
energy harvesting, due to their enhanced properties at the nanoscale. However,
quantitative characterization of piezoelectricity in nanomaterials is
challenging due to practical limitations and the onset of additional
electromechanical phenomena, such as the triboelectric and piezotronic effects.
Here, we present an open-circuit conductive atomic force microscopy (cAFM)
methodology for quantitative extraction of the axial piezoelectric coefficients
of nanowires. We show, both theoretically and experimentally, that the standard
short-circuit cAFM mode is inadequate for piezoelectric characterization of
nanowires, and that such measurements are governed by competing mechanisms. We
introduce an alternative open-circuit configuration, and employ time-resolved
electromechanical measurements, to extract the piezoelectric coefficients. This
method was applied to GaAs, an important semiconductor, with relatively low
piezoelectric coefficients. The results obtained for GaAs,~0.4-1 pm/V, are in
good agreement with existing knowledge and theory. Our method represents a
significant advance in understanding the coexistence of different
electromechanical effects, and in quantitative piezoelectric nanoscale
characterization. The easy implementation will enable better understanding of
electromechanics at the nanoscale.
