  Low-frequency noise with the spectral density S(f)~1/f^g (f is the frequency
and g~1) is a ubiquitous phenomenon, which hampers operation of many devices
and circuits. A long-standing question of particular importance for electronics
is whether 1/f noise is generated on the surface of electrical conductors or
inside their volumes. Using high-quality graphene multilayers we were able to
directly address this fundamental problem of the noise origin. Unlike the
thickness of metal or semiconductor films, the thickness of graphene
multilayers can be continuously and uniformly varied all the way down to a
single atomic layer of graphene - the actual surface. We found that 1/f noise
becomes dominated by the volume noise when the thickness exceeds ~7 atomic
layers (~2.5 nm). The 1/f noise is the surface phenomenon below this thickness.
The obtained results are important for continuous downscaling of conventional
electronics and for the proposed graphene applications in sensors and
communications.
