Formation Of Periodic Nanostructures Research Articles

Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates

Photoreduction on a periodically proton exchanged ferroelectric crystal leads to the formation of periodic metallic nanostructures on the surface. By varying the depth of the proton exchange (PE) from 0.59 to 3.10 μm in congruent lithium niobate crystals, the width of the lateral diffusion region formed by protons diffusing under the mask layer can be controlled. The resulting deposition occurs in the PE region with the shallowest PE depth and preferentially in the lateral diffusion region for greater PE depths. PE depth-control provides a route for the fabrication of complex metallic nanostructures with controlled dimensions on chemically patterned ferroelectric templates.

Periodic Nano-Structure Formation with Femtosecond Laser Ablation and Patterning of Silicon

Regular micro-apparatus which covered with periodic nano-hole, nano-ridge and ripple structures on silicon bulk were formed by laser micro-machining with tightly focused beam of the femtosecond laser with wavelength of 800 nm, repetition rate of 1 kHz and the pulse length of 130 fs in air. The periodic nano-hole structures which focus with a 20× focusing objective lens (NA = 0.4) is reported. Investigating the relationship between the width of structures and the speed of processing.

Ultrafast Dynamic Processes for Periodic Surface Nanostructure Formation Induced with Femtosecond Laser Pulses

Ultrafast Dynamic Processes for Periodic Surface Nanostructure Formation Induced with Femtosecond Laser Pulses

Nanopatterning of metallic features over uniformed arrays of microbowl structures

► An efficient nanofabrication technique based on nanosphere lithography and soft lithography is developed. ► Smaller interstitial spaces between spheres are achievable by self assembly of colloidal spheres over PDMS microbowls mould. ► Size of metallic patterns over PDMS can be tuned by either controlling metal deposition or using different spheres in size. ► Gold nanoparticles with perpendicular bisector of 210 nm and height of 50 nm were obtained in curvilinear triangular shape. ► The proposed nanofabrication process is suitable for volume nanopattern production at low costs. There is a growing interest for formation of periodic nanostructures in high-throughput and low-cost processes, due to their wide range of applications. This paper demonstrates a facile and efficient method to fabricate ordered gold nanopatterns over uniformed arrays of poly (dimethylsiloxane) (PDMS) microbowl structures by combining nanosphere lithography (NSL) and soft lithography. A monolayer of self-assembled polystyrene (PS) spheres is used as a template to create the PDMS microbowl structures. Another self assembly is processed on the PDMS mould followed by gold deposition, resulting in periodic pillars on the surface of microbowl structure. After removal of the microspheres, an array of highly ordered gold nanopatterns over hexagonal distributed pillars with perpendicular bisector of 210 nm and height of 50 nm in average are achieved. The geometry of the nanopillars with curvilinear triangle surface can be tuned by changing the size of spheres. This approach can be also extended to fabricate ordered periodic nanostructures of a wide range of metals (Pt, Ag, Cu, etc.) with controlled size.

Mechanism of femtosecond-laser-induced periodic nanostructure formation on crystalline silicon surface immersed in water

Focused on silicon surface in water, superimposed multiple shots of linearly polarized 800-nm, 100-fs, 10-Hz laser pulses at lower fluence than the single-pulse ablation threshold are shown to produce two kinds of periodic nanostructures with almost constant periods of 150 nm and 400 nm. Surface plasmon polaritons excited in the surface layer illustrates well the formation of nanostructures and its dynamic properties observed. Pump and probe measurements of the ultrafast change in surface reflectivity during the interaction have demonstrated that the multiple low-fluence fs pulses are crucial to the nanostructuring through the accumulation of non-thermal bonding structure change and the subsequent nanoscale ablation.

Periodic Nanostructure Formation on Silicon Irradiated with Multiple Low-fluence Femtosecond Laser Pulses in Water

It is shown that superimposed multiple shots of linearly polarized 800-nm, 100-fs laser pulses at lower fluence than the single-pulse ablation threshold produce periodic nanostructures with almost constant periods of 150 nm and 400 nm on silicon surface immersed in water. The nanostructure formation and its characteristic properties observed are illustrated well with the excitation of surface plasmon polaritons in the newly created surface layer. Pump and probe measurements of surface reflectivity during the ultrafast interaction demonstrate that multiple shots of low-fluence fs pulses are crucial to the accumulation of non-thermal bonding structure change and subsequent ablation for the periodic nanostructure formation.

Modeling the Formation of Periodic Nanostructures on Solid Surface Induced by Femtosecond Laser Ablation by Particle-in-Cell Method

In this paper, we simulate by the particle-in-cell method (PIC) the mechanisms of femtoseconde (fs) laser interactions with a metallic or semiconductor target. Our aim is to identify the mechanisms that are responsible for surface nanostructure formation when laser fluences are close to the ablation threshold. For this purpose, we use a theoretical approach, which considers the solid as a gas of free electrons in a lattice of immobile ions. As a result, the simulations shown that those nanostructures occur during the first moments of the interaction and are due to the inhomogeneous distribution of the density of the electrons

Formation of periodic nanostructures on aluminum surface by femtosecond laser pulses

One-dimensional periodic nanostructures have been produced on the surface of an aluminum specimen using femtosecond laser pulses at wavelengths of 744 and 248 nm. The nanostructurization of the specimen has been conducted in water and in air in the preablation regime. We investigate the dependence that the surface topology has on the parameters of laser radiation (wavelength, fluence, and number of pulses), as well as on the medium in contact with the specimen surface. A calculation of the optical characteristics of aluminum as they depend on the electron temperature is performed that is good at describing the dependence that the reflection of the p-polarized infrared femtosecond pulses of pumping has on the fluence. Using these optical characteristics of the photoexcited aluminum within the interferential model, periods of the aluminum surface nanogratings are estimated which are in good agreement with the periods measured experimentally.

Spontaneous Formation of Periodic Nanostructures by Localized Dynamic Wrinkling

Micro/nanoscale periodic structures are widely used in display, optics and bio industries as key functional elements. We present a novel nanopatterning method, localized dynamic wrinkling (LDW), which creates micro/nanoscale metal gratings continuously by simply sliding a flat edge of a hard material over a thin metal surface coated on a polymer layer. The LDW process presented in this paper is an etching- and template-free nanopatterning technology based on nanoscale wrinkling phenomenon. This simple process enables spontaneous formation of large-area metal gratings with controllable periodicity from micrometer down to 120 nm.

Ultrafast Excitation and Dynamics Measurements with Intense Ultrashort Laser Pulses —High-Order Harmonic Generation from Aligning Molecules and Surface Nanostructuring—

This paper reviews our recent studies on ultrafast, strong-ˆeld interactions with atoms, molecules and solid surfaces. The major in- terest in atomic and molecular processes is concerned with nonperturbative nonlinear processes induced with intense ultrashort laser pulses, especially, high-order harmonic generation from nonadiabatically aligned molecules and its dynamics measurements. Ex- perimental and theoretical results demonstrate characteristic properties of the harmonic generation from coherently rotating mole- cules, depending on molecular structures. Concerning the interaction with solid surfaces, the periodic nanostructure formation observed in femtosecond laser ablation of thinlm surfaces has been the subject for the purpose of potential applications of ultrashort laser pulses to nanoprocessing. It is found that the nano-scale ablation is initiated with laser-induced near-ˆeld on solid surfaces, and the nano-periodicity is attributed to the excitation of surface plasmon polaritons. The results obtained show that the intense ultrashort- pulse laser is a promising tool for investigating new and/or latent dynamics and functions of matter.

Formation of different periodic nanostructures on semiconductors

The interaction of femtosecond pulses with surfaces of semiconductors accompanied by the appearance of different nanostructures and nanoholes is studied. The formation of nanostructures was observed for semiconductors placed into different media. The effect of different parameters (angle of incidence, light polarization, number of shots, pulse duration, etc.) on the formation of the structures is analyzed. The period of the arising ordered structures could be either on the order of the light wavelength (700–800 nm) or much smaller (180 nm).

Origin of periodicity in nanostructuring on thin film surfaces ablated with femtosecond laser pulses

We report physical processes responsible for the periodic nanostructure formation in femtosecond-laser ablation of thin film surfaces. It has been found that an initial random distribution of nanoscale ablation traces is periodically structured with an increase in superimposed laser pulses or fluence on diamond-like carbon film used as the target. The results show that the formation of periodicity can be attributed to the excitation of surface plasmon polaritons to induce the periodic enhancement of local fields in the surface layer. The estimated field period is in good agreement with the observed size of nanostructures.

Mechanism of the formation and evolution of periodic surface relief nanostructures under the scanning laser-induced inelastic photodeformation of semiconductors

A defect-deformational (DD) mechanism is proposed for the self-organization of laser-induced point defects (vacancies and interstitials) under low-threshold (far from the melting point) local (10–100 μm) light-induced heating with the scanning periodic pulsed laser irradiation of a semiconductor resulting in an inelastic deformation of micron-sized regions of Ge. A linear theory of DD instability is developed within the model of a biaxially stressed defective film. This model describes the main experimental data on the formation of two-and one-dimensional periodic nanostructures on a semiconductor surface relief.

Application of Femtosecond-Laser Induced Nanostructures in Optical Memory

The femtosecond laser induced micro- and nanostructures for the application to the three-dimensional optical data storage are investigated. We have observed the increase of refractive index due to local densification and atomic defect generation, and demonstrated the real time observation of photothermal effect after the femtosecond laser irradiation inside a glass by the transient lens (TrL) method. The TrL signal showed a damped oscillation with about an 800 ps period. The essential feature of the oscillation can be reproduced by the pressure wave creation and propagation to the outward direction from the irradiated region. The simulation based on elastodynamics has shown that a large thermoelastic stress is relaxed by the generation of the pressure wave. In the case of soda-lime glass, the velocity of the pressure wave is almost same as the longitudinal sound velocity at room temperature (5.8 microm/ns). We have also observed the localized photo-reduction of Sm3+ to Sm2+ inside a transparent and colorless Sm(3+)-doped borate glass. Photoluminescence spectra showed that some the Sm3+ ions in the focal spot within the glass sample were reduced to Sm2+ ions after femtosecond laser irradiation. A photo-reduction bit of 200 nm in three-dimensions can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence excited by Ar+ laser (lambda = 488 nm). A photo-reduction bit can be also erased by photo-oxidation with a cw Ar+ laser (lambda = 514.5 nm). Since photo-reduction bits can be spaced 150 nm apart in a layer within glass, a memory capacity of as high as 1 Tbit can be achieved in a glass piece with dimensions of 10 mm x 10 mm x 1 mm. We have also demonstrated the first observation of the polarization-dependent periodic nanostructure formation by the interference between femtosecond laser light and electron acoustic waves. The observed nanostructures are the smallest embedded structures ever created by light. The period of self-organized nanostructures can be controlled from approximately 140 to 320 nm by the pulse energy and the number of irradiated pulses. Furthermore, we have also observed the self-assembled sub-wavelength periodic structures created in silica glass by femtosecond pulses on the plane of the propagation of light.

Formation mechanisms of uniform arrays of periodic nanoparticles and nanoripples on 6H-SiC crystal surface induced by femtosecond laser ablation

Uniform arrays of periodic nanoparticles with 80-nm period are formed on 6H-SiC crystal irradiated by circularly polarized 400-nm femtosecond laser pulses. In order to understand the formation mechanism, the morphology evolvement as a function of laser pulse energy and number is studied. Periodic nanoripples are also formed on the sample surface irradiated by linearly polarized 400-, 510- and 800-nm femtosecond laser pulses. All these results support well the mechanism that second-harmonic generation plays an important role in the formation of periodic nanostructures.

Broad band light-emitting nanostructured substrates by ion beam irradiation of lithium fluoride crystals

We present experimental results on simultaneous surface nanostructuring and optical activation of lithium fluoride crystals by 800 eV off-normal Ar + sputtering. Our data demonstrate that the formation of periodic nanostructures is accompanied by the efficient production of stable electronic defects, optically active in the green and red parts of the visible spectra, thus providing the possibility to conceive and fabricate advanced insulating substrates.

Ultrafast dynamics of periodic nanostructure formation on diamondlike carbon films irradiated with femtosecond laser pulses

Using a pump-probe technique the authors have measured reflectivity of diamondlike carbon (DLC) film irradiated with femtosecond laser pulses to understand dynamic processes responsible for periodic nanostructure formation. The results have shown that characteristic reflectivity change observed as a function of superimposed laser shots is closely associated with the nanostructure formation and the bonding structure change to induce surface swelling, leading to a conclusion that the nanostructure formation on the DLC surface is certainly preceded by the bonding structure change. The nanoscale ablation to produce the nanostructure is discussed based on the local field generation on the surface.

P-191: Out Coupling Efficiency Enhancement of Organic Light Emitting Devices with Novel Periodic Nanostructures using Nanoimprint Lithography

Novel periodic nanostructures at the air-glass interface are proposed to cope with the low out-coupling efficiency of OLEDs. Nanoimprint lithography using sol-gel material including glass components has been applied to periodic nanostructure formation. Luminance characteristics with new structures are improved more than 60 % compared to those without nanostructures.

Laser induced formation of periodic nanostructures in silicon covered by SiO2

Three-dimensional (3D) and two-dimensional (2D) periodic silicon nanostructures formed by polarized focused Nd:YAG laser irradiation (532 nm) with spot size less than 3 μm on Si covered by SiO2 are presented in this paper. We observed that at a low laser intensity I range, from I=0.9 to 1.08 W, 2D periodic coexisting of liquid and solid exists, while for 1.08 1.44 W). The periodicity of these periodic structures is 359 nm related to the wavelength of frequency doubledNd:YAG laser and the index of refraction of SiO2. We propose a model based on the fact that as the oxygen is diffusing locally from SiO2 into the melted Si, thus forming SiOβ with a lower melting point, successive pulses melt preferentially these regions giving rise to a positive feedback. This dynamic nanoscale modeling, based on variations of melting points of Si and dielectric and reflection coefficient, confirms the experimental results.

Silicon periodic nano-structures obtained by laser exposure of nano-wires

Silicon nano-wires were fabricated using thin Silicon on Insulator (SOI) wafers and a combination of anisotropic wet etching by Tetra-Methyl Ammonium Hydroxide (TMAH) and Local Oxidation of Silicon (LOCOS). These nano-wires were submitted to laser exposure using gas immersion laser doping (GILD). The result was the formation of either periodic nano-structures or silicon balls. Since the process uses very short laser pulses, it involves rapid melting and solidification of silicon. Hence, the observed periodicity is ascribed to Rayleigh instability, which involves surface tension effects in melted silicon.