  Surface roughness is a key factor when it comes to friction and wear, as well
as to other physical properties. These phenomena are controlled by mechanisms
acting at small scales, in which the topography of apparently-flat surfaces is
revealed. Roughness in natural surfaces has been reported to conform to
self-affine statistics in a wide variety of settings (ranging from earthquake
physics to micro-electro-mechanical devices), meaning that the height profile
can be described using a spectrum where the amplitude is proportional to its
wavelength raised to a constant power, which is related to a statistical
parameter named Hurst exponent. We analyze the roughness evolution in atomistic
surfaces during molecular dynamics simulations of wear. Both pairs of
initially-flat and initially-rough surfaces in contact are worn by a third body
formed by particles trapped between them during relative sliding. During the
first sliding stages, the particles trapped between the first bodies scratch
the surfaces. Once the former become coated with atoms from the latter, the
wear process slows down and becomes "adhesive-like". The initial particle sizes
are consistent with the minimum size to be expected for the debris, but tend to
grow by material removal from the surfaces and to agglomerate. We show that,
for the particular configurations under consideration, the surface roughness
seems to converge to a steady state characterized by Hurst exponent close to
0.8, independently of the initial conditions.
