  Ferroelectric materials possess spontaneous polarization that can be used for
multiple applications. Owing to a long term development for reducing the sizes
of devices, the preparation of ferroelectric materials and devices are entering
nanometer-scale regime. Accordingly, to evaluate the ferroelectricity, there is
a need to investigate the polarization charge at the nanoscale. Nonetheless, it
has been generally accepted that the detection of polarization charges using a
conventional conductive atomic force microscopy (CAFM) without a top electrode
is not feasible because the nanometer-scale radius of an atomic force
microscopy (AFM) tip yields a very low signal-to-noise ratio. However, the
detection is unrelated to the radius of an AFM tip, and in fact, a matter of
the switched area. In this work, we demonstrate the direct probing of the
polarization charge at the nanoscale using the Positive-Up-Negative-Down method
based on the conventional CAFM approach without additional corrections or
circuits to reduce the parasitic capacitance. We successfully probed the
polarization charge densities of 73.7 and 119.0 uC/cm2 in ferroelectric
nanocapacitors and thin films, respectively. The obtained results show the
feasibility of the evaluation of the polarization charge at the nanoscale and
provide a new guideline for evaluating the ferroelectricity at the nanoscale.
