Nanoscopic friction under electrochemical control.

We propose a theoretical model of friction under electrochemical conditions focusing on the interaction of a force microscope tip with adsorbed polar molecules whose orientation depends on the applied electric field. We demonstrate that the dependence of friction force on the electric field is determined by the interplay of two channels of energy dissipation: (i) the rotation of dipoles and (ii) slips of the tip over potential barriers. We suggest a promising strategy to achieve a strong dependence of nanoscopic friction on the external field based on the competition between long-range electrostatic interactions and short-range chemical interactions between tip and adsorbed polar molecules.

Mechanism of wear and ripple formation induced by the mechanical action of an atomic force microscope tip.

We propose a model for a description of formation of quasiperiodic nanoscale patterns induced by scratching a surface with an atomic force microscope tip. The simulations demonstrate that the interplay between the developing surface corrugation and the frictional stress produced by the moving tip plays a decisive role in the formation of the regular ripples. Our model reveals the size and shape of the tip as the main factors that determine periodicity and amplitudes of the patterns, and it allows experimental observations to be explained.

Multi-minimum adiabatic potential in the single crystal normal spinel ZnAl(2)O(4), doped by Cu(2+) ions.

Spectroscopic investigations of a ZnAl(2)O(4) spinel doped with bivalent copper ions of 0.05% concentration have been carried out in the temperature range 4.2-290 K using a 3 cm(-1) range electron paramagnetic resonance (EPR) spectrometer having an operational frequency f = (9.

Origin of friction anisotropy on a quasicrystal surface.

Wearless friction force experiments [Science 309, 1354 (2005)10.1126/science.1113239] have recently demonstrated that tribological response in quasicrystals could be related to the exotic atomic structure of the bulk material.

Rotary motors sliding along surfaces.

We introduce a family of molecular rotors that may convert light or chemical energy into directed translational motion along surfaces. The dependencies of diffusion coefficient and drift velocity of the rotating molecule on the magnitude of external torque, symmetry of surface potential, and temperature have been investigated. Our simulations show that the rotation-translation coupling could be very effective, and the molecule may move by approximately one surface lattice spacing per complete rotation.

Spectroscopic evidence of spinel phase clustering in solid solutions Hg(1-x)Cr(x)Se (0.03 ≤ x ≤ 0.1).

The diluted magnetic semiconductors Hg(1-x)Cr(x)Se (0.03≤x≤0.1) were prepared by the solid state recrystallization method.

Torque and twist against superlubricity.

Superlubricity between incommensurate surfaces provides a desired low-friction state essential for the function of small-scale machines. Here we demonstrate experimentally and theoretically that superlubricity in contacts lubricated by lamellar solids might be eliminated due to torque-induced reorientation coupled to lateral motion. We find that the possibility of reorientation always leads to stabilization of a high frictional state which corresponds to a commensurate configuration.

Actin-based motility: cooperative symmetry-breaking and phases of motion.

A microscopic model is proposed for the motility of a bead driven by the polymerization of actin filaments. The model exhibits a rich spectrum of behaviours similar to those observed in biomimetic experiments, which include spontaneous symmetry-breaking, various regimes of the bead's motion and correlations between the structure of the actin tail which propels the bead and the bead dynamics. The dependences of the dynamical properties (such as symmetry-breaking time, regimes of motion, mean velocity, and tail asymmetry) on the physical parameters (the bead radius and viscosity) agree well with the experimental observations.

Friction through dynamical formation and rupture of molecular bonds.

We introduce a model for friction in a system of two rigid plates connected by bonds (springs) and experiencing an external drive. The macroscopic frictional properties of the system are shown to be directly related to the rupture and formation dynamics of the microscopic bonds. Different regimes of motion are characterized by different rates of rupture and formation relative to the driving velocity.

Confined molecules under shear: from a microscopic description to phenomenology.

A coarse grained two-state model is derived starting from a molecular dynamics description of a molecular system under shear. This model captures the main features of the response of a confined system under shear, and generalizes the phenomenological Tomlinson model for the response of a driven system. The derivation is based on the solution of coupled microscopic equations using a mean field approximation.