37 research outputs found
Thermal effects on atomic friction
We model friction acting on the tip of an atomic force microscope as it is
dragged across a surface at non-zero temperatures. We find that stick-slip
motion occurs and that the average frictional force follows ,
where is the tip velocity. This compares well to recent experimental work
(Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all
microscopic parameters. We calculate the scaled form of the average frictional
force's dependence on both temperature and tip speed as well as the form of the
friction-force distribution function.Comment: Accepted for publication, Physical Review Letter
Mode-locking of incommensurate phase by quantum zero point energy in the Frenkel-Kontorova model
In this paper, it is shown that a configuration modulated system described by
the Frenkel-Kontorova model can be locked at an incommensurate phase when the
quantum zero point energy is taken into account. It is also found that the
specific heat for an incommensurate phase shows different parameter-dependence
in sliding phase and pinning phase. These findings provide a possible way for
experimentalists to verify the phase transition by breaking of analyticity.Comment: 6 pages in Europhys style, 3 eps figure
A simple variational approach to the quantum Frenkel-Kontorova model
We present a simple and complete variational approach to the one-dimensional
quantum Frenkel-Kontorova model. Dirac's time-dependent variational principle
is adopted together with a Hatree-type many-body trial wavefunction for the
atoms. The single-particle state is assumed to have the Jackiw-Kerman form. We
obtain an effective classical Hamiltonian for the system which is simple enough
for a complete numerical solution for the static ground state of the model.
Numerical results show that our simple approach captures the essence of the
quantum effects first observed in quantum Monte Carlo studies.Comment: 12 pages, 2 figure
Defect-induced perturbations of atomic monolayers on solid surfaces
We study long-range morphological changes in atomic monolayers on solid
substrates induced by different types of defects; e.g., by monoatomic steps in
the surface, or by the tip of an atomic force microscope (AFM), placed at some
distance above the substrate. Representing the monolayer in terms of a suitably
extended Frenkel-Kontorova-type model, we calculate the defect-induced density
profiles for several possible geometries. In case of an AFM tip, we also
determine the extra force exerted on the tip due to the tip-induced
de-homogenization of the monolayer.Comment: 4 pages, 2 figure
Friction between atomically flat surfaces
We investigate the mechanism of atomic friction between two infinitely
extended atomically
flat surfaces within a two-dimensional Frenkel-Kontorova-Tomlinson
model. The surfaces are identical but are rotated with respect to each
other through an arbitrary misfit angle.
The misfit gives rise to the formation of domains where every potential
valley contains exactly one particle. They are separated by two sets of
shift lines, crossing each other in topological defects.
During quasistatic sliding, the whole domain pattern moves perpendicular
to the driving force. Dissipation and friction hysteresis in the
quasistatic limit are caused by irreversible jumps of these topological
defects, which are the two-dimensional analogues of discommensurations
occurring in the one-dimensional case of friction between chains with
different lattice constants.
Critical spring constants for the occurrence of instabilities can be
derived. Friction shows strong dependence on both the misfit angle
and the pulling direction. The relevance of the theoretical study for
friction experiments on the nanoscale is discussed
Friction experiments on the nanometre scale
In this review, we present various results obtained by friction force microscopy in the last decade. Starting with material-specific contrast, commonly observed in friction force maps, we discuss how the load dependence of friction and the area of contact have been estimated and compared to elasticity theories. The features observed in a sliding process on the atomic scale can be, interpreted within the Tomlinson model. An extension of the model, including thermal effects, predicts a smooth velocity dependence of friction, which recent experiments have confirmed. Other subjects like anisotropy of friction, role of environment, topographical effects, electronic friction and tip modifications are also discussed. The growing importance of molecular dynamics simulations in the study of tribological processes on the atomic scale is outlined