  We review a new implementation of Kelvin probe force microscopy (KPFM) in
which the dissipation signal of frequency modulation atomic force microscopy
(FM-AFM) is used for dc bias voltage feedback (D-KPFM). The dissipation arises
from an oscillating electrostatic force that is coherent with the tip
oscillation, which is caused by applying the ac voltage between the tip and
sample. The magnitude of the externally induced dissipation is found to be
proportional to the effective dc bias voltage, which is the difference between
the applied dc voltage and the contact potential difference. Two different
implementations of D-KPFM are presented. In the first implementation, the
frequency of the applied ac voltage, $f_\mathrm{el}$, is chosen to be the same
as the tip oscillation ($f_\mathrm{el} = f_\mathrm{m}$: $1\omega$D-KPFM). In
the second one, the ac voltage frequency, $f_\mathrm{el}$, is chosen to be
twice the tip oscillation frequency ($f_\mathrm{el}= 2 f_\mathrm{m}$:
$2\omega$D-KPFM). In $1\omega$D-KPFM, the dissipation is proportional to the
electrostatic force, which enables the use of a small ac voltage amplitude even
down to $\approx 10$\,mV. In $2\omega$D-KPFM, the dissipation is proportional
to the electrostatic force gradient, which results in the same potential
contrast as that obtained by FM-KPFM. D-KPFM features a simple implementation
with no lock-in amplifier and faster scanning as it requires no low frequency
modulation. The use of a small ac voltage amplitude in $1\omega$D-KPFM is of
great importance in characterizing of technically relevant materials in which
their electrical properties can be disturbed by the applied electric field.
$2\omega$D-KPFM is useful when more accurate potential measurement is required.
The operations in $1\omega$ and $2\omega$D-KPFM can be switched easily to take
advantage of both features at the same location on a sample.
