Academic literature on the topic 'Nano-ripples'

The periodic microstructures on 65Mn plate were induced by the irradiation of the femtosecond laser with the laser wavelength of 800 nm and the pulse length of 130 fs. The parallel periodic ripples structures were observed at the laser fluence of 1 J/cm2 with different pulses number( N=5,50,400,800) which lied parallel to the laser electric polarization field vector. For 400 pulses, the nano-holes arrays were generated to interrupt the consistent ripples structures.For 800 pulses, initial nano-holes evolution to the grooves, which the direction were uncertainly. Further experiments have been made to induce large area consitent ripple structures by scanning, at the laser fluence of 1 J/cm2 with speed v=500μm/s. 2D arrays were induced by accurate processing control

The bioactivity and biocompatibility play key roles in the success of dental and orthopaedic implants. Although most commercial implant systems use various surface microstructures, the ideal multi-scale topographies capable of controlling osteointegration have not yielded conclusive results. Inspired by both the isotropic adhesion of the skin structures in tree frog toe pads and the anisotropic adhesion of the corrugated ridges on the scales of Morpho butterfly wings, composite micro/nano-structures, including the array of micro-hexagons and oriented nano-ripples on titanium alloy implants, were respectively fabricated by microsecond laser direct writing and femtosecond laser-induced periodic surface structures, to improve cell adherence, alignment and proliferation on implants. The main differences in both the bioactivity in simulated body fluid and the biocompatibility in osteoblastic cell MC3T3 proliferation were measured and analyzed among Ti-6Al-4V samples with smooth surface, micro-hexagons and composite micro/nano-structures, respectively. Of note, bioinspired micro/nano-structures displayed the best bioactivity and biocompatibility after in vitro experiments, and meanwhile, the nano-ripples were able to induce cellular alignment within the micro-hexagons. The reasons for these differences were found in the topographical cues. An innovative functionalization strategy of controlling the osteointegration on titanium alloy implants is proposed using the composite micro/nano-structures, which is meaningful in various regenerative medicine applications and implant fields.

Abstract— An Omicron low temperature multi-probe technique is used for manipulation of mechanically exfoliated suspended and attached graphene sheets on SiO2 substrates. Scanning electron microscopy (SEM) and Raman spectroscopy are used to detect the graphene sheets and determine their thicknesses and quality, respectively. The interaction of the etched tungsten tip with the graphene is used to lift and release the sheet and induce artificial ripples. Both suspended and attached sheets onto the substrates show different behaviour in response to bias voltage. IndexTerms: graphene,multi-probe microscopy, ripples.

Physics and potential applications of femtosecond laser pulses interacting with matter have captured interest in various fields, such as nonlinear optics, laser micromachining, integrated optics, and solar cell technologies. On the one hand, such ultrashort intense pulses make them practical elegant tools to be utilized for direct structuring of materials with high accuracy and numerous potential applications. On the other hand, studying the fundamental aspects and nonlinear nature of such interactions opens new remarkable venues for various unique investigations. In recent years, the emerging topic of structured light (also known as twisted or optical vortex light), i.e., a beam of light with a twisted wave-front that can carry orbital angular momentum (OAM), has attracted the attention of many researchers working in the field of light-matter interaction. Such beams offer various applications from classical and quantum communication to imaging, micro/nano-manipulation, and modification of fundamental processes involved in light-matter interactions, e.g., absorption and emission. Nevertheless, the fabrication of complex structures, controlled modification, and achieving a high spatial resolution in material processing still remain in the spotlight. Moreover, the fundamental role of orbital angular momentum in the nonlinear absorption of materials, particularly in solids, has yet remained a subject of debate. Addressing these points was the main motive behind this dissertation. To accomplish this objective and investigate new aspects of structured light-matter interaction, I conducted various experiments, the results of which are presented in this work. The general idea was to study the interaction of femtosecond laser radiation, having a structured phase and polarization, with the matter in two aspects: (i) surface morphology modification and (ii) nonlinear absorption of solids. In this regard, I studied surface processing of crystalline silicon and CVD diamond with femtosecond laser vortex pulses generated by a birefringent phase-plate, known as q-plate, in single and multiple pulse irradiation regimes, respectively. The characterization of the modified region was performed using optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). I demonstrated that upon irradiation of a single vortex pulse on silicon, a nano-cone structure is formed within the ablated crater, whose height was independent of the helicity of the twisted light. However, for a linearly polarized vortex pulse, the height of the nano-cone decreases at higher pulse energies. The dynamics of nano-cone formation and the role of polarization were also investigated by simulating the mass transport function in this process. Moreover, using superimposed vortex beams, we fabricated complex patterns containing several nano-cones, by single-shot irradiation on the silicon surface. My experimental results offer an ability to actively control and manipulate material, in terms of the nanocones position, in two dimensions with an ultra-high resolution. I further proceeded with our experiments in the multiple pulse regime on a diamond target. By irradiation of a high number of superimposed vortex pulses, I was able to imprint complex polarization states of structured light on the target surface in the form of periodic nano-ripples. This procedure enabled us to not only generate spatially varying nano-gratings but also directly visualize and study very complex states of polarization. Besides these surface structuring, I carried out experimental studies to investigate the response of bulk material to an incident circularly polarized vortex beam that carries orbital angular momentum. The experimental results reveal, for the first time, that such an interaction can produce a differential absorption that gives rise to helical dichroism. We demonstrate that this response is sensitive to the handedness and degree of the twist in the incident vortex beam. Such a dichroism effect may be attributed to the excitation of dipole-forbidden atomic transitions, e.g., electric quadrupole transitions. However, this explanation is not absolute and remains open to further research and investigations.

L’appauvrissement en lubrifiant d’un contact élasto-hydrodynamique peut menacer la pérennité du film interfacial séparant les surfaces, entraîner l’augmentation des forces de frottement et l’endommagement rapide du tribosystème. Industriellement, la volonté de réduire les quantités de lubrifiant embarquées et de limiter les opérations de maintenance favorisent la sous-alimentation. L’objectif de cette thèse est de contrôler l’alimentation d’un contact EHD sous-alimenté par une texturation de surface multi-échelle, afin d’assurer une lubrification minimale à l’interface. Une démarche scientifique s’appuyant sur la dissociation des échelles spatiales, temporelles ainsi que sur l’analyse des contributions des écoulements dans les différentes zones du contact a été mise en oeuvre. La compréhension de l’interaction laser/matière en irradiation ultra-brève a permis de générer des texturations nanométriques (ripples) et micrométriques (ondulations et réseaux de cavités) à l’aide d’un laser femtoseconde. La contribution de chaque échelle topographique sur la lubrification d’un contact a été étudiée. Lorsque les forces hydrodynamiques sont faibles (contact statique), l’alimentation d’un contact résulte d’une compétition entre une contribution capillaire et une contribution visqueuse. La macro géométrie des solides déformés ainsi que la viscosité pilotent au premier ordre la propagation du lubrifiant à l’extérieur de la zone haute pression. L’imbibition de la zone de Hertz n’est possible qu’avec l’introduction d’une surface nanotexturée et sa cinétique dépend de l’orientation et de l’amplitude des ripples. Pour des nombres capillaires élevés (contact dynamique), un critère de prédiction de l’apparition de la sous-alimentation a été établi. En présence de réseaux de cavités et sous l’action d’un cisaillement interfacial, les surfaces texturées possédant une capacité de rétention élevée réalimentent la zone de haute pression. Le volume piégé envahit alors le contact puis crée une surépaisseur de lubrifiant qui protège les solides de l’endommagement tout en limitant l’augmentation du frottement. Les texturations nanométriques (ripples) et micrométriques, anisotropes et périodiques, modifient l’équilibre entre les débits de réalimentation et les débits de fuite. Une orientation adaptée des motifs peut contenir le drainage du lubrifiant dans le contact et ainsi empêcher ou retarder l’apparition d’un régime de sous-alimentation totale. Au final, chaque échelle topographique contribue à la réalimentation d’un contact sousalimenté, soit en favorisant l’expansion des réservoirs latéraux, soit en apportant localement du lubrifiant, ou en maintenant un film fluide résiduel sur les surfaces
The lubricant depletion of an elasto-hydrodynamic contact may threaten the sustainability of the interfacial film separating the surfaces, can result in the increase of frictional forces and a rapid damage of the tribosystem. Industrially, the trend to reduce the amount of initial lubricant and to limit maintenance promotes starvation of the lubricated contact. The aim of this work is to control the lubricant feeding of a starved EHL contact by a multi-scale surface texturing, in order to ensure minimal lubrication at the interface. A scientific approach based on the separation of spatial and temporal scales, as well as the analysis of the flow contributions in different zones of the contact has been implemented.The understanding of the laser/matter interaction in ultra-short irradation has helped us to generate both nanoscale texturing (ripples) and microscale texturing such as microwaves and networks of micrometric cavities, using a femtosecond laser. The contribution of each topographic scale on the contact lubrication has been analysed. When the hydrodynamic forces are low (static contact), the feeding of the contact results from a competition between capillary and viscous contributions. The macro geometry of the deformed solids and the lubricant viscosity mainly control the lubricant spread around the high-pressure zone. The imbibition of the Hertz contact area is only possible with the introduction of a nanotextured surface. The imbibition kinetics depends on the orientation and amplitude of the ripples. For high capillary numbers (dynamic contact), a criterion has been established in order to predict the occurrence of starvation. Using a network of micro cavities and the action of an interfacial shear, the high retention capacity textured surfaces brings lubricant to the high-pressure zone. The trapped volume propagates inside the contact and creates a film thickness that protects the solids from damages while limiting the increase in friction. Anisotropic and periodic nanoscale and microscale texturing, like ripples, influences the balance between re-feeding and leakage flow rates. A suitable orientation of the geometries may prevent the lubricant from drainage and thus delay the onset of a starved lubrication regime. In conclusion, each topographic scale contributes to re-feed a starved contact, by promoting lateral reservoir extension, by providing lubricant locally where it is needed, or maintaining a residual fluid film on surfaces