V. N. Svetlov

Wavelet transform as a method for studying the fractal properties of the surface of amorphous metals under mechanical load

The effect of mechanical tension on the multifractal characteristics of the lateral surface of a Fe77Ni1Si9B13 amorphous alloy is studied by scanning tunneling microscopy (STM). It is established that, at small loads, the surface is smoothed out much as a crumpled sheet of paper is smoothed out under tension. With an increase in the load, there appears a tendency to the formation of a fractal structure on the surface.

Hierarchy of defect ensembles on the surface of loaded copper

The evolution of the distribution of nanodefects formed on the surface of polished copper foils under tensile stresses is investigated. It is found that nanodefects form four ensembles. The energies of formation and the mean sizes of nanodefects in two consecutive ensembles differ, respectively, by a factor of three. When the concentration of nanodefects in a particular ensemble reaches a thermodynamically optimum value (≈5%), some of these nanodefects annihilate and the other nanodefects transform to nanodefects of the following ensemble. The load applied to the sample continuously generates nanodefects comprising the first ensemble, which leads to periodic oscillations of the nanodefect concentration in all four ensembles.

The emission of photons and the dynamics of submicrodefects on the surface of noble metals

The shape and concentration of defects, as well as the intensity of electroluminescence from the back side of Cu, Ag, and Au samples with their front side irradiated by a laser shot, are studied experimentally. It is shown that there exists a correlation between the electroluminescence intensity and the concentration of radiation-induced defects, which is consistent with the dislocation model of luminescence.

Hierarchy of statistical ensembles of nanodefects on the surface of stressed molybdenum

The evolution of the distribution of nanodefects that are formed under the effect of tensile stresses existing at the surface of polished foils of molybdenum was studied. The nanodefects form four statistical ensembles in which the size distribution is determined by the maximum of the configurational entropy. The energy of formation and the average size of nanodefects in adjacent ensembles differ by a factor of three. When the concentration of nanodefects in one of the ensembles reaches a thermodynamically optimum value of ≈5%, part of the nanodefects annihilates and the other part becomes transformed into nanodefects of the next (higher) hierarchical level. The application of a load to the sample studied continuously generates nanodefects that form the first (lowest-level) ensemble, which leads to periodic oscillations in the concentrations of nanodefects in all four ensembles.

Defect ensembles on the surface of loaded metals as a result of their reversible aggregation

The structures of nanodefect ensembles formed on the surfaces of copper, gold, and molybdenum under a load have been investigated. The properties of the defect ensembles are described in the framework of the reversible aggregation model. The size distribution of nanodefects is thermodynamically determined by the maximum “entropy of their mixing” with atoms of the crystal lattice. The entropy of mixing reaches a maximum value at a small concentration of defects due to a considerable difference in the sizes of defects and atoms. This concentration agrees closely with the experimental data. The reduced size distribution of defects is universal.

Mechanoluminescence and submicrorelief of a copper surface

Copper plates are irradiated with pulsed laser light on one side, and the opposite side is investigated with a scanning tunneling microscope. It is found that the submicrorelief of the back surface changes after irradiation. During irradiation it emits a light pulse. It is established that a relation exists between the luminescence intensity and the magnitude of the change in the surface submicrorelief.

Evolution of the surface relief of annealed copper and palladium samples under load

The evolution of submicrodefects on loaded Cu and Pd surfaces annealed after polishing is investigated by tunneling profilometry. The shallowest defects formed in a sample under tension appear in the form of prismatic indentations with a vertex angle ≈70°. On Cu surfaces they have a depth of 15±3 nm and dimensions in the plane of the surface 50×50 nm. On Pd surfaces the defects have a depth of ≈5 nm and dimensions in the plane of the surface 10×20 nm. The defects grow with time, attaining depths ≈1 µm and areal dimensions of a few micrometers before fracture. This process evolves in a stop-go pattern: The defect depth remains approximately constant for a certain time, then changes suddenly, stabilizes again, changes once more, and so on. Defects of depth <100 nm are distributed uniformly over the surface of the sample, while defects of depth ⩾200 nm are clustered at the boundaries of blocks.

Formation mechanism for nanodefects on surfaces of loaded metals

Tunneling profilometry is used to investigate the shape and orientation of defects that form at the surfaces of Cu, Au, Mo and Pd under loading. The defects have the shape of an indented prism. The value of the angles at the tip of the defects coincide with the angles between glide planes, while the orientation of the walls coincide with the orientation of these planes. At the edges of the defects there exist “swellings” caused by expulsion of material at the surface. Based on these results, the creation of these defects is explained by the exit of dislocations as they burst through barriers formed at intersecting glide planes.

Tunneling microscopic study of submicroscopic defects on the surfaces of loaded metals

Load-induced submicroscopic defects of the surfaces metals were studied with a scanning tunnelling microscope. The methodological aspects of microscopy investigation of loaded metal samples in air and nitrogen were examined in detail. Defects shaped like in a print of a triangular prism are observed to form on the surface of polished and annealed samples of Cu, Au, Mo and Pd. Original defects were 5, 15, 22 and 18 nm deep on surfaces of Pd, Cu, Au and Mo and 50 - 100 nm wide and long. The vertex angles of prism were approximately equals 700 in Pd, Au and Cu surfaces and approximately equals 500 or approximately equals 900 on Mo surfaces. Concentrations of the defects grows, reaches a maximum value and decreases. Then there are emerged new defects which depth is 2 - 3 times more than the original one. Their concentration grows, reaches a maximum value and decreases. The following type of defects of larger sizes create on the surface, their concentration grows, reaches a new maximum value and decreases, and so on. All defects have the form much like the original defects and their deep is a multiple the original defect deep.

Dynamics of nanodefects on a loaded gold surface

The dynamics of defects with linear dimensions from ≈1 to ≈100 nm on a Au surface under load have been studied by means of tunnelling microscopy. It is found that the origin, growth, and resorption of the defects is caused by displacements of bands of material from 5 to 50 nm wide, parallel to the {111} slip planes. The defects can be separated into two groups: nonsteady-state defects, whose lifetime does not exceed 15 min, while the depth is ⩽20 nm, and quasi-steady-state defects, with a lifetime three orders of magnitude greater than the first. It is assumed that the nonsteady-state defects are formed when the ensemble of dislocations is being reconstructed, while the quasi-steady-state defects are formed at the instant of formation of dislocation substructures during the creep of the loaded metal.