Scanning force microscopy was used in the contact mode to determine the adhesion force between a mica surface and a silicon nitride tip. The measurements were performed in an aqueous solution of sodium and calcium chlorides. The adhesion force according to the Derjaguin-Landau-Verwey- Overbeek theory depends on the competition between two kinds of forces: van der Waals and electrostatic "double layer". Two different curves of adhesion force versus salt concentration were obtained from the experiment with monovalent and divalent ions. The tip-surface adhesion force was determined from a statistical analysis of data obtained from the force vs. distance retracting curves.
The application to surface problems of X-ray spectroscopy has started almost at the same time as in materials science. While the theoretical basis is obviously the same, SEXAFS has some experimental peculiarities which are reviewed here. Some examples will then be given.
The aim of this investigation was to determine the adhesion force as a function of calcium dichloride concentration in water. The studies were performed with two surfaces carrying opposite charge in water solution: mica - as a negatively charged surface and glass covered with poly-L-lysine - as a positively charged surface, the latter due to the presence of amino groups. The surfaces were immersed in a CaCl_2 solution in the range of concentration varied from 0 to 100 mM. The scanning force microscopy was applied to determine the adhesion force by measurements of the pull-off force. Additionally, the values of the single bond force were estimated basing on the Poisson distribution of the number of binding sites.
Mechanics of metal surface layers deals with a description of the following objects, quantities and processes: structures and mechanical properties of metal surface layers after a heat, chemical, electro-chemical or physical treatment; evolution of these structures and properties during mechanical treatments; mechanical behaviour of the layers during exploitation processes. This branch of mechanics is based on the results of physical investigations, but it uses a mechanical approach. In the paper, descriptions of metal surface layers within the classical anisotropic plasticity, large strain plasticity, and finally, the crystal and polycrystal plasticity are recalled. Problems connected with a formulation of laws governing a surface layer behaviour are comprehensively discussed.
Technological surface layers, most often met in practice, received by the methods of heat, thermo-diffusion, mechanical and chemical treatment have been described. The range of application of surface layers received as a result of various technological treatments have been presented. Improvement of mechanical properties of the machine elements and constructions after surface treatment is the subject of this paper. The changes of mechanical, static and fatigue properties as well as impact strength, crack resistance and friction properties, such as wear resistance, seizing resistance and friction factor have been discussed. It has been found that the efficiency of the improvement of mechanical properties is a function of technological parameters and of a type of destruction being a result of the mechanical external loads. We claim that it is possible to design surface layers in dependence on the parameters of processing, or on the structure of the layers (determined by hardening, residual stresses) and on the mechanical external loads of machine parts and constructions. Methods of designing surface layers, useful in practice, have been presented. Examples of changes of the mechanical properties after surface treatment have been given.
An atomic force microscope is a useful tool to study the interaction forces at molecular level. In particular the atomic force microscope can measure an unbinding force needed to separate the two single molecule complexes. Recent studies have shown that such unbinding force depends linearly on the logarithm of the applied loading rate, defined as a product of scanning velocity and the spring constant characterizing the investigated system (cantilever vs. surface). This dependence can be used to study the energy landscape shape of a molecular complex by the estimation of energy barrier locations and the related dissociation rates. In the present work the complex consisting of ethylene(di)aminetetraacetic acid and the bovine serum albumin was measured. The dependence between the unbinding force and the logarithm of the loading rate was linear. Using the Bell model describing the dissociation of the above molecules caused by the action of the external bond breaking force, two parameters were estimated: the dissociation rate and the position of the energy barrier needed to overcome during a transition from a bound to unbound state. The obtained results are similar to those obtained for a typical ligand-receptor interaction.
Micrographs of metal surface layers after the roller burnishing process show that while about 90% of surface layer thickness is displaced forwards of a roller motion, a thin contact zone undergoes a backward displacement. This seizing effect is caused by a softening of the contact zone due to overheating of the material, during high speed rolling, or due to the plastic strain cumulation in the layer after multiple rolling repetition. The effect is responsible for a peeling and cracking of surface layers during the burnishing process. The plastic analysis of the process taking into account the above effect is presented in the paper. The proposed slip-line field and corresponding velocity field are modification of the simplified solution for the rolling of the rigid-plastic half-space given by Collins.
A notion of natural surface layer of metals as a reference state for a mechanical description of technological surface layers is introduced. According to experimental observations it is assumed that the yield stress of metal surface layer without any technological treatment is lower than in the bulk material. A simple mechanical model that enables one to find a yield stress distribution in the natural surface layer is proposed. As an example the natural surface layer of aluminium specimen is examined. According to the model and experimental observations, a layer thickness is equal 2-3 grains' diameters, and the yield stress in the layer may be 30% lower than in the bulk material.
Diamond-like carbon (DLC), in particular hydrogenated amorphous carbon (a-C:H) films have been formed on various conductive and dielectric materials by plasma immersion ion implantation and deposition (PI^{3}D) processing. Effect of pulse voltage and other process parameters on the film properties was investigated. It was found that for conductive substrates, a low-voltage ( ≈1 kV), high repetition rate pulsing provides better overall film performance comparing to that obtained by applying higher voltages, which is also favourable for conformal treatment of 3D workpieces. However, short 1-2 μs, high-voltage 5-20 kV pulses are required for dielectric workpieces several millimeter thick. Good film adhesion was achieved by forming a Si-containing buffer layer using hexamethyldisiloxane (HMDSO) as a precursor and a low-voltage pulsing. Roughness and wettability of DLC coatings was found to be controlled by varying the bias specs and sample temperature. Very smooth films with average roughness less than 1 Å were prepared at optimised process parameters.
The influence of the Laser Shock Processing (LSP) on the morphology, microstructure and surface layer properties of a Ti6Al4V alloy has been studied. Residual stresses were assessed as well. For the Laser Shock Processing a 1 KW, high-power Q-switched Nd:YAG laser was used. During the process the surface of the investigated material was covered by series of single, partially overlapping impulses. The laser power density was a 1 GW/cm^{2} and a pulse duration of 18 ns. The microstructure and the phases presented in the surface layer of the treated material were analysed by optical, scanning and transmisssion electron microscopy as well as by X-ray diffractometry. The X-ray diffractometry was also use to determine the residual stresses. It has been found that the laser shock processing can cause plastic deformation and generate the compressive residual stresses into the treated surface of a Ti6Al4V alloy.
In this work we report on the atomic structures, elemental distribution, defects and dislocations of three types of semiconductor nanowires: ZnTe, CdTe, and complex ZnTe/(Cd,Zn)Te core/shell hetero-nanowires grown by a molecular beam epitaxy on (111) Si substrate using a vapor-liquid-solid mechanism. The structural properties and the chemical gradients were measured by transmission electron microscopy methods. The nanowires reveal mainly sphalerite structure, however wurtzite nanowires were also observed.
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