Formation Of Periodic Nanostructures Research Articles

Laser-induced periodic surface nanostructures formation and modification in polyethylene terephthalate (PET)

Polyethylene terephthalate (PET) is a thermoplastic polymer used in a large variety of industries as clothing, packaging and aeronautics among many others. Laser-inducted periodic surface nanostructures presents great potential as long as the modifications of materials are delivered in a controlled manner. However the formation of nanostructures having different morphological properties presents itself a difficult errand. The purpose of this paper is to present how the surface structure of Polyethylene terephthalate (PET) changes at nanoscale levels after irradiation with laser beams of spatially variant polarization. Utilizations of such nanostructures can be seen in a multitude of applications varying from electronics and textiles to aeronautical and military implementations. For the creation of the new nanostructures has been used an YAG solid state laser (Spectra Physics, Quanta Ray) with a pulse duration of 4 ns and a repetition rate of 10 Hz for different spatial periods and at different inclination angles, an Atomic Force Microscope and a Scanning Electron Microscope in order to analyze the newly created nanostructures. Such Polyethylene terephthalate (PET) modified structures have been used as well in combination with fiber glass compounds in order to produce highly resistant engineering resins to heat and impact. The formation of specific controllable surface nanostructures given different functionalities are of major interest as a technique to improve or even produce completely new specific oriented properties. This study reveals how the structure of polyethylene terephthalate surface changes after laser-induced treatment.

Formation of femtosecond laser-induced periodic nanostructures on GaN

The femtosecond laser-induced periodic surface structure (LIPSS) method has attracted considerable interest as a way to form fine structures with dimensions below the laser wavelength. These structures are highly reproducible, demonstrating that this method is suitable for applications such as quantum devices. In this study, we investigated the shape and crystalline state of a LIPSS to clarify the material properties and laser conditions that define its structure. While a LIPSS composed of GaN maintained its crystallinity, disturbances in its local crystalline orientation were generated. The direction and periodicity of the LIPSS did not depend on the in-plane crystal direction of GaN or the scanning direction, but the aspect ratio of each LIPSS depended on the in-plane crystal direction. The LIPSS with exposed {1–100}GaN faces showed high aspect ratios, with narrower widths and deeper depths, than LIPSS with different exposed faces.

Investigating surface morphology of Ag-AgCl thin film by scattering pattern at normal and oblique incident angles.

We study the formation of periodic nanostructures on Ag-AgCl thin films by irradiating s-polarized laser beams at different incident angles. A theoretical model is proposed to describe the formation of the structures based on interference of the incident beam and TE0 mode propagating in an AgCl slab waveguide. The line-space of periodic nanostructures on Ag-AgCl thin film can be manipulated by changing the incident angle and wavelength of the laser beam. The scattering and diffraction pattern of a periodic nanostructure during laser irradiation provides useful information about the structure's surface morphology. The periodic nanostructures formed on Ag-AgCl thin films are anisotropic structures.

Theoretical and Experimental Investigation of the Formation of High Spatial Frequency Periodic Structures on Metal Surfaces Irradiated by Ultrashort Laser Pulses

Experimental results on the formation of small-scale periodic nanostructures during ablation of solids by pico- and femtosecond laser pulses are presented. The period of these nanostructures is in the range of 50 to 100 nm, and they may coexist with known periodic nanostructures, whose period and orientation is determined by the laser wavelength and amounts to several hundreds of nanometers. The formation of high-frequency periodic structures with a period of about 100nm is theoretically analyzed by joint numerical solution of the heat conduction problem and Navier−Stokes equation. It is shown that their orientation is determined by the melt bath geometry.

Nanostructure Formation on Diamond-Like Carbon Films Induced with Few-Cycle Laser Pulses at Low Fluence from a Ti:Sapphire Laser Oscillator.

This study reports the results of experiments on periodic nanostructure formation on diamond-like carbon (DLC) films induced with 800 nm, 7-femtosecond (fs) laser pulses at low fluence from a Ti:sapphire laser oscillator. It was demonstrated that 7-fs laser pulses with a high power density of 0.8–2 TW/cm2 at a low fluence of 5–12 mJ/cm2 can form a periodic nanostructure with a period of 60–80 nm on DLC films. The period decreases with increasing fluence of the laser pulses. The experimental results and calculations for a model target show that 7-fs pulses can produce a thinner metal-like layer on the DLC film through a nonlinear optical absorption process compared with that produced with 100-fs pulses, creating a finer nanostructure via plasmonic near-field ablation.

Periodic nanostructures formed on a poly-methyl methacrylate surface with a femtosecond laser for biocompatibility improvement

Poly(methyl methacrylate) (PMMA) is widely used as a biomaterial. The formation of periodic nanostructures on the surface is necessary to improve the biocompatibility. A method was proposed and developed to form periodic nanostructures on a PMMA surface. A PMMA plate was placed on titanium (Ti) plate, and then the Ti plate was irradiated with a laser through the PMMA plate. We try to effectively produce periodic nanostructures on PMMA with a femtosecond laser at a fundamental wavelength by increasing the contact pressure and using titanium (Ti) plate. The contact pressure between PMMA and Ti required to form a periodic nanostructure is 300 kPa, and for a contact pressure of 2400 kPa, periodic nanostructures are formed in 62% of the laser-irradiated area on the PMMA surface. These results suggest that the formation efficiency of the periodic nanostructure depends on the laser conditions and the contact pressure.

Spontaneous periodic ordering on the surface and in the bulk of dielectrics irradiated by ultrafast laser: a shared electromagnetic origin

Periodic self-organization of matter beyond the diffraction limit is a puzzling phenomenon, typical both for surface and bulk ultrashort laser processing. Here we compare the mechanisms of periodic nanostructure formation on the surface and in the bulk of fused silica. We show that volume nanogratings and surface nanoripples having subwavelength periodicity and oriented perpendicular to the laser polarization share the same electromagnetic origin. The nanostructure orientation is defined by the near-field local enhancement in the vicinity of the inhomogeneous scattering centers. The periodicity is attributed to the coherent superposition of the waves scattered at inhomogeneities. Numerical calculations also support the multipulse accumulation nature of nanogratings formation on the surface and inside fused silica. Laser surface processing by multiple laser pulses promotes the transition from the high spatial frequency perpendicularly oriented nanoripples to the low spatial frequency ripples, parallel or perpendicular to the laser polarization. The latter structures also share the electromagnetic origin, but are related to the incident field interference with the scattered far-field of rough non-metallic or transiently metallic surfaces. The characteristic ripple appearances are predicted by combined electromagnetic and thermo-mechanical approaches and supported by SEM images of the final surface morphology and by time-resolved pump-probe diffraction measurements.

Design of co-existence parallel periodic surface structure induced by picosecond laser pulses on the Al/Ti multilayers

Formation of periodic nanostructures on the Ti/5x(Al/Ti)/Si multilayers induced by picosecond laser pulses is studied in order to better understand the formation of a laser-induced periodic surface structure (LIPSS). At fluence slightly below the ablation threshold, the formation of low spatial frequency-LIPSS (LSFL) oriented perpendicular to the direction of the laser polarization is observed on the irradiated area. Prolonged irradiation while scanning results in the formation of a high spatial frequency-LIPSS (HSFL), on top of the LSFLs, creating a co-existence parallel periodic structure. HSFL was oriented parallel to the incident laser polarization. Intermixing between the Al and Ti layers with the formation of Al-Ti intermetallic compounds was achieved during the irradiation. The intermetallic region was formed mostly within the heat affected zone of the sample. Surface segregation of aluminium with partial ablation of the top layer of titanium was followed by the formation of an ultra-thin Al2O3 film on the surface of the multi-layered structure.

Optical chirality in AgCl-Ag thin films through formation of laser-induced planar crossed-chain nanostructures

Irradiation of AgCl-Ag thin films by a linearly polarized He-Ne laser beam results in the formation of self-organized periodic nanostructures. As a result of secondary irradiation of the initially exposed sample by the same linearly polarized He-Ne laser beam, but with different orientations of polarization, a complex crossed-chain nanostructure forms. We found that such a complex nanostructure has noticeable chirality and increased optical anisotropy, resulting in optical activity of the sample. Double exposure produces two gratings, crossing each other with angle α, which leads to the formation of crossed building blocks with chiroptical effects. It is established that the amount and the sign of the angle between the two laser-induced gratings (±α) determine the amount and the direction of rotation of the linearly polarized probe beam, respectively. We have also observed an induced anisotropy-dependent ellipticity for the probe light, which is passed through the sample. It is shown that the amount of ellipticity depends on the angle α.

Employing refractive beam shaping in a Lloyd's interference lithography system for uniform periodic nanostructure formation

Uniform periodic structure formation over a large sample area has been challenging in laser interference lithography (LIL) mainly due to the Gaussian intensity distribution inherent to a laser beam. In this work, refractive beam shaping devices are applied in a Lloyd's interferometer to create a flat-top light field (2.8% intensity variation over an area of 20 × 20 cm2) for wafer-scale nanopatterning. Around 10−2 variation in fill factors are obtained for all the reported one dimensional and two dimensional periodic structures across a 2-in. wafer, which is 1 order of magnitude lower than the values obtained for the samples exposed to a Gaussian light field. The proposed LIL system also allows gradual light field transitions from the Gaussian, super-Gaussian, and flat-top to the inverse-Gaussian by simply adjusting the spot size of the laser incident to the beam shaper. The authors believe that the proposed LIL system can be applied for a variety of applications that benefit from the nature of periodic nanostructures.

Demonstration of periodic nanostructure formation with less ablation by double-pulse laser irradiation on titanium

By pairing femtosecond laser pulses (duration ∼40 fs and central wavelength ∼810 nm) at an appropriate time interval, a laser-induced periodic surface structure (LIPSS) is formed with much less ablation than one formed with a single pulse. On a titanium plate, a pair of laser pulses with fluences of 70 and 140 mJ/cm2 and a rather large time interval (>10 ps) creates a LIPSS with an interspace of 600 nm, the same as that formed by a single pulse of 210 mJ/cm2, while the double pulse ablates only 4 nm, a quarter of the ablation depth of a single pulse.

Femtosecond laser-induced periodic nanostructure creation on PET surface for controlling of cell spreading

A new method of periodic nanostructure formation on a polyethylene terephthalate (PET) surface has been developed, employing a femtosecond laser with a wavelength of 1045 nm. To generate structured films, the PET was placed in contact with a silicon (Si) wafer, followed by irradiation with the laser focused on the Si wafer, passing through the PET film. In order to evaluate the surface morphology, atomic force microscopy analysis was conducted on both treated and untreated PET surfaces. From the results, nanostructures with a period of 600 nm and height of 100 nm were formed on the PET film surface by laser treatment. A cell cultivation test was carried out on PET films with and without periodic nanostructures, showing that for nanostructured films, the cells (MG-63) were spread along the periodic grooves; in contrast, random cell spreading was observed for cultures grown on the untreated PET film.

Formation of Periodic Nanostructures with Femtosecond Laser for Creation of New Functional Biomaterials

Pure Titanium (Ti) and Ti alloys are the most used biomaterials. However, they have problem for bioactivity because metals have no biofunction. Therefore, adding new function to Ti and Ti alloys are necessary. One method to add new function is the creation of periodic structures on the biomaterial surfaces, which can control cell spreading. Femtosecond laser is one of the useful tools for creating periodic nanostructures, which can be created on metals and semiconductors by self-organizing in the laser focusing spot. In our previous study, the nanostructures could be formed on the Ti plate by using the femtosecond laser with fundamental wavelength of 775nm. The periodicities of the nanostructures on the Ti plate was approximately 590nm, which was shorter than the laser wavelength. Cells tests indicated that cell spreading clearly occurs along the grooves of the nanostructures. However, the influence of the periods of the nanostructure on cell spreading has not yet been investigated. It is expected that the periods can be varied by changing laser parameters, such as pulse widths, laser wavelengths, laser fluences, and number of shots. In this study, the periodic nanostructures are created on the Ti plate surface by using the femtosecond laser with fundamental wavelength of 790nm. Then, influence of the pulse width and number of shots on the periods is investigated. In the experiments, laser beam is focused and scanned on the Ti plate surfaces. The laser irradiated areas are analysed by using a scanning electron microscope (SEM).

Analysis of periodic nanostructures formation on a gold surface under exposure to ultrashort laser pulses near the melting threshold

Analysis of periodic nanostructures formation on a gold surface under exposure to ultrashort laser pulses near the melting threshold

フェムト秒レーザを用いたナノ周期構造形成による新機能生体材料創製

フェムト秒レーザを用いたナノ周期構造形成による新機能生体材料創製

Biocompatibility of Titanium Dioxide Film Modified by Femtosecond Laser Irradiation

Titanium (Ti) is one of the most widely used for biomaterials, because of its excellent anti-corrosion and high mechanical properties. In addion to these properies, the bioactivity of Ti is required. Recently, coating of the titanium dioxide (TiO2) film on Ti plate surface is useful methods to obtain biocompatibility of Ti plate. If periodic nanostructures were formed on the film surface, direction of cell spreading might be controlled due to grooves direction. Then, femtosecond laser is one of the useful tools of periodic nanostructures formation. Peiriod of periodic nanostructures might be varied by changing the laser wavelength. In the experiments, the film was formed on Ti plate with an aerosol beam which was composed of submicron size TiO2 particles and helium gas. The film was irradiated with the femtosecond laser. Laser wavelengths of the laser was at 1044, 775 and 388 nm, respectively. Periodic nanostructures, lying perpendicular to the laser electric field polarization vector, were formed on the film by femtosecond laser irradiation at 1044, 775 and 388 nm, respectively. The period of the periodic nanostructures on the film produced by femtosecond laser irradiation at 1044, 775 and 388 nm was about 350, 230 and 130 nm, respectively. In the cell test, cell spreading along the grooves of the periodic nanostructures was observed although it was not done for the film without the periodic nanostructures. These results suggested that direction of cell spreading could be controlled by the periodic nanostructures formation

Ellipticity-dependent laser-induced optical gyrotropy in AgCl thin films doped by silver nanoparticles

A laser-induced optical gyrotropy is observed in light-sensitive waveguide AgCl–Ag thin films, as a result of spontaneous periodic nanostructure formation, which is the product of interaction of a polarized incident light with the film’s substances. Interference of the incident He–Ne laser beam with the excited TE-modes of the waveguide AgCl–Ag thin film and migration of Ag nanoparticles to minima of the interference pattern results in formation of spontaneous periodic nanostructures. Results of our investigation indicate that, in our case, the strength of induced optical rotation depends on the ellipticity of the polarization state of the incident laser beam. It is found that the induced optical activity is caused by two factors in the film: (1) the induced anisotropy; and (2) formed chiral complex planar nanostructures. The portion of each factor in the induced optical gyrotropy depends on the polarization state of the incident laser beam. We have shown that, under incidence of circular polarized light, the chirality is the most efficient factor to produce gyrotropy, but for elliptical polarized incident light, the induced anisotropy, which increases dissymmetry of the film, plays essential role. In this connection, the induced circular dichroism of the samples and optical rotation of the linear polarized probe beam are measured. In this regard, the induced birefringence (∆n) of the samples is measured. The present study proposes a new candidate for meta-materials and also a simple method for recording the ellipticity and sign of rotation of the polarized incident light.

Mechanism and control of periodic surface nanostructure formation with femtosecond laser pulses

Fundamental mechanism of femtosecond-laser-induced periodic surface nanostructure formation has been investigated under the condition using superimposed multiple shots at lower fluence than the single-pulse ablation threshold. With increasing the shot number of low-fluence fs-laser pulses, the periodic nanostructure develops through the bonding structure change of target material, the nanoscale ablation with optical near-fields induced around the high curvatures, and the excitation of surface plasmon polaritons (SPPs) to create the nano-periodicity in the surface structure. It is confirmed that non-thermal interaction at the surface plays the crucial role in the nanostructure formation. Based on the mechanism, we have demonstrated that the periodic nanostructure formation process can be controlled to fabricate a homogeneous nanograting on the target surface, using a two-step ablation process in air. The experimental results obtained represent exactly the nature of a single spatial standing SPP wave mode that generates periodically enhanced near-fields for the nanograting formation. The calculated results for a model target reproduce well the nanograting period and explain the characteristic properties observed in the experiment.

Cell spreading on titanium dioxide film formed and modified with aerosol beam and femtosecond laser

Titanium (Ti) is widely used in biomaterials because of its excellent anti-corrosion properties and high strength. However, Ti has no biological function, so its bioactivity must be improved. Coating a titanium dioxide (TiO2) film on a Ti plate surface has been shown to improve the biocompatibility of Ti plates. If periodic nanostructures were formed on the film surface, the direction of cell spreading might be controlled by the direction of the grooves. Controlling cell spreading on biomaterials would contribute to the creation of advanced biomaterials. In this paper, a TiO2 film was formed on a Ti plate with an aerosol beam composed of sub micron-sized TiO2 particles and helium gas. Periodic nanostructures, lying perpendicular to the laser electric field polarization vector, were formed on the film by scanning the femtosecond laser focusing spot. The period and height of the periodic nanostructures were about 230nm and 150nm, respectively. In a cell test, cell spreading was observed along the grooves of the periodic nanostructures; in contrast, cell spreading did not show a definite direction on TiO2 a film without periodic nanostructures. These results suggest that the direction of cell spreading on the film can be controlled by periodic nanostructure formation generated using a femtosecond laser.

Nanograting formation through surface plasmon fields induced by femtosecond laser pulses

Ablation of solid surfaces irradiated with superimposed multiple shots of low fluence femtosecond (fs) laser pulses often results in the formation of periodic nanostructures on the target surface. We demonstrate that the self-organization process of nanostructuring can be regulated to fabricate a homogeneous nanograting on the target surface in air. A simple two-step ablation process was used to control the nanoscale energy deposition that should be developed through the excitation of surface plasmon polaritons (SPPs) during the fs laser-surface interaction. The results obtained for crystalline gallium nitride represent exactly the nature of a single spatial standing wave mode of SPPs of which periodically enhanced near-fields ablate the target surface to form the nanograting with a period of ∼200 nm. The calculated results for a model target reproduce well the observed nanograting period and explain the origin of its characteristic properties.