Stresses in Si as small as 10 MPa have been measured using electron backscattered diffraction (EBSD) and confocal Raman microscopy (CRM) with spatial resolutions of 10 nm and 100 nm, respectively. In both techniques, data were collected across wedge indentations in (001) Si. EBSD measured the stress and strain tensors and CRM measured the uniaxial stress. The results agreed very well except close to the indentation, where the surface-sensitive EBSD results indicated larger stresses. Results converged when the CRM laser excitation wavelength was reduced, probing smaller depths. The stress profiles are consistent with the inverse-square power law predicted by Eshelby analysis.
Laser technique is employed to improve substantially the tribological behavior of microstructured stainless steel surfaces. The laser-generated patterns consisting of precisely ablated microcraters were produced using a flash lamp pumped, Q-switched Nd:YAG laser. The rims of resolidified melt around the craters are typical features of laser-produced microstructures and the laser parameters were established where their extent was notably reduced. The remaining rims could easily be removed by gentle polishing. The laserstructured substrates were tribologically tested by a sliding tribometer under standard conditions. The test results show clearly that the microstructures improve the lifetime of the samples.
PACS: 42.65.Cs; 79.60.DsThe microstructuring of solid surfaces modifies their friction and wear properties. At the present moment, experimental works [1,2] are focused on finding the effects of predetermined induced structures, while theoretical efforts [3,4] are beeing made to understand the mechanisms of this modification.For instance, an array of microholes induced on a friction surface can act like a lubricant reservoir and as a trap for abrasive particles -both effects improve the friction and wear properties -but the microholes can also generate hydrodynamic perturbations of the lubricating fluid -increasing the dynamic friction forces. The sizes and the distribution of the microholes are the key factors for determining which behavior will be dominant. Mainly depending on the target material and on efficiency considerations, several ways to generate such microstructures can be used, e.g. laser devices with various wavelengths, electronic guns, and chemical etching. The tool of choice for our purpose is the laser, which with its versatility can easily be adapted to a wide range of desired structure morphologies.A laser beam can either be focused on a solid surface producing removal of target material, or it can be expanded and an ablation mask used. The incident energy and the time of interaction between the laser radiation and the target surface determine [5] the phenomena that occur: a wide area of processes can be induced, from local heating to a very accurate removal of material without affecting the surrounding zones when ultrashort laser pulses are used. The use of ultrashort laser pulses in the femtosecond range was reported [6] to generate sharp microstructures in different materials; but these lasers, at the moment, lack the efficiency for the production of surface patterns consisting of millions of craters. Furthermore, they are expensive and not very suitable for an industrial environment as envisaged by a possible application resulting from this work.
Use of the laser beamIn the presented work, a Q-switched Nd:YAG laser was used to induce microstructures on stainless steel samples (AISI 440C).The thermal diffusion length, L = (kτ p )/( c), is a significant parameter to describe in a first approximation the amplitude of the thermal phenomena that occur when a laser beam is focused on a solid surf...
In a statistical nanoindentation study using a spherical probe, the effect of crystallographic orientation on the phase transformation of silicon (Si) was investigated. The occurrence and the contact pressures at which events associated with phase transformation occur, for an indentation force range from 20 to 200 mN, were analyzed and compared for the orientations Si (001), Si (110), and Si (111). It was found that plastic deformation combined with phase transformation during loading was initiated at lower forces (contact pressures) for Si(110) and Si(111) than for Si(001). Also, the contact pressure at which the phase transformation occurred during unloading was strongly influenced by the crystallographic orientation, with up to 38% greater values for Si (110) and Si(111) compared to Si(001). Mapping the residual stress field around indentations by confocal Raman microscopy revealed significant differences in the stress pattern for the three orientations.
We demonstrate the use of copolymer micelle lithography using polystyrene-block-poly(2-vinylpyridine) reverse micelle thin films in their as-coated form to create nanopillars with tunable dimensions and spacing, on different substrates such as silicon, silicon oxide, silicon nitride and quartz. The promise of the approach as a versatile application oriented platform is highlighted by demonstrating its utility for creating super-hydrophobic surfaces, fabrication of nanoporous polymeric membranes, and controlling the areal density of physical vapor deposition derived titanium nitride nanostructures.
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