Laser Interference Lithography Research Articles

Competition of Magnetic Anisotropies in Permalloy Antidot Lattices

Antidot lattices made of magnetic thin films are good candidates to be employed in future magnetic recording media. In this manuscript we present a study on the effect of shape and field-induced magnetic anisotropies on the magnetization reversal of 10 nm and 50 nm thick permalloy antidot lattices. Rounded antidot square lattices were fabricated using a combination of electron beam evaporation and laser interference lithography, covering surfaces of a few cm2. We demonstrate that a magnetic anisotropy induced in the samples, as a consequence of an applied magnetic field during growth, competes with the shape anisotropy that dominates the response of the patterned thin films, and that the effect of the field-induced magnetic anisotropy scales with the thickness of the antidot thin films. Finally, we have quantified the anisotropy constant attributable to the uniaxial field-induced magnetic anisotropy in our antidot lattices. These findings are supported by micromagnetic simulations performed using MuMax3.

Interdisciplinary Methods for Zoonotic Tissue Acellularization for Natural Heart Valve Substitute of Biomimetic Materials.

The goal of this work was to create a bioactive tissue-based scaffold using multi-disciplinary engineering materials and tissue engineering techniques. Materials & methods: Physical techniques such as direct laser interference lithography and proton radiation were selected as alternative methods of enzymatic and chemical decellularization to remove cells from a tissue without degradation of the extracellular matrix nor its protein structure. This study was an attempt to prepare a functional scaffold for cell culture from tissue of animal origin using new physical methods that have not been considered before. The work was carried out under full control of the histological and molecular analysis. Results & conclusions: The most important finding was that the physical methods used to obtain the decellularized tissue scaffold differed in the efficiency of cell removal from the tissue in favour of the laser method. Both the laser method and the proton method exhibited a destructive effect on tissue structure and the genetic material in cell nuclei. This effect was visible on histology images as blurred areas within the cell nucleus. The finite element 3D simulation of decellularization process of the three-layer tissue of animal origin sample reflected well the mechanical response of tissue described by hyperelastic material models and provided results comparable to the experimental ones.

Predictive Biophysical Cue Mapping for Direct Cell Reprogramming Using Combinatorial Nanoarrays.

Biophysical cues, such as nanotopographies of extracellular matrix (ECM), are key cell regulators for direct cell reprogramming. Therefore, high-throughput methods capable of systematically screening a wide range of biophysical cue-regulated cell reprogramming are increasingly needed for tissue engineering and regenerative medicine. Here, we report the development of a dynamic laser interference lithography (DIL) to generate large-scale combinatorial biophysical cue (CBC) arrays with diverse micro/nanostructures at higher complexities than most current arrays. Using CBC arrays, a high-throughput cell mapping method is further demonstrated for the systematic investigation of biophysical cue-mediated direct cell reprogramming. This CBC array-based high-throughput cell screening approach facilitates the rapid identification of unconventional hierarchical nanopatterns that induce the direct reprogramming of human fibroblasts into neurons through epigenetic modulation mechanisms. In this way, we successfully demonstrate DIL for generating highly complex CBC arrays and establish CBC array-based cell screening as a valuable strategy for systematically investigating the role of biophysical cues in cell reprogramming.

Comprehensive theoretical analysis of the period chirp in laser interference lithography.

We present a theoretical investigation on laser interference lithography used for the exposure of linear gratings. The focus is on the geometry of the arising interference lines on the substrate, in particular on their period and orientation, depending on the illumination geometry as determined by the setup. The common approach with point sources emitting spherical wavefronts is considered for the illumination. Three different cases are discussed, namely the interference between two point sources with either two convex, two concave or mixed, i.e., convex and concave wavefronts. General equations focusing mainly on the calculation of the period and the orientation of the grating lines are derived for each of the three exposure cases considering arbitrarily positioned point sources and arbitrarily shaped substrates. Additionally, the interference of symmetrically positioned point sources illuminating plane substrates is investigated, as these boundary conditions significantly simplify the derived equations.

Exploring SERS from two-dimensional symmetric gold array fabricated by double exposure laser interference lithography

In this paper, the electric field enhancement of a two-dimensional symmetric gold array (2DSGA) fabricated by laser interference lithography (LIL), as a surface-enhanced Raman scattering (SERS) substrate, is thoroughly discussed and analyzed. The structure of 2DSGA is closely related to the exposure time and the thickness of the photoresist. 2DSGA, insensitive to the polarization of incident light, has a high enhancement factor (EF) with a lithography depth of 40∼60 nm. The pattern fabricated by LIL will change and the EF will decrease when the theoretical lithography depth exceeds the photoresist thickness due to different exposure times. To obtain a high EF for 2DSGA, it is necessary to control the thickness of the photoresist and exposure time, which contributes to the actual preparation of SERS substrate.

Fabrication System for Large-Area Seamless Nanopatterned Cylinder Mold Using the Spiral Laser Interference Exposure Method

With the advancement in the field of nanotechnology, nanopatterning finds extensive application not only in high value-added products but also in inexpensive products. In addition, the technology required for the mass production of inexpensive products, such as the continuous roll-to-roll (R2R) process, is rapidly emerging. Extensive research has been conducted on the manufacture of submicron- and nano- molds. In this study, we have proposed a laser interference exposure for fabricating nanopatterned cylindrical molds that can be used in continuous roll-to-roll patterning. Additionally, we have demonstrated spiral exposure process to fabricate a seamless patterning on a cylinder (length of 300 mm and diameter of 100 mm) using a prism. The pattern was transferred to the flat mold using UV resin and measured using a field emission scanning electron microscope; the pattern was measured to have a uniform with nano pattern line width (75 nm) and a sub-micron period (286 nm). It was observed that the proposed method for fabrication of the roll mold using laser interference lithography is a fast and reliable seamless patterning.

Enhanced sensing performance from trapezoidal metallic gratings fabricated by laser interference lithography.

Nanograting-based plasmonic sensors are widely regarded as promising platforms due to their real-time label-free detection and ease of integration. However, many reported grating structures are too complicated to fabricate, which limits their application. We propose a 1D bilayer metallic grating with trapezoidal profile as a near-infrared plasmonic sensor in the spectral interrogation. Trapezoidal gratings tend to perform better than rectangular gratings as sensors, particularly as they can detect at oblique incidence to obtain higher performance. Furthermore, we have successfully fabricated such a grating with a period of 633 nm over a 2.25 cm2 area using a two-step approach based on laser interference lithography. Glucose detection has been conducted to experimentally validate the sensing performance of the as-prepared grating. The measured sensitivity and figure-of-merit can reach up to 786 nm/RIU and 30, respectively. Our research sheds new light on the development of cost-effective sensing devices.

Solution-Driven Imprinting Lithography of Sol-Gel ZnO Thin Films for Liquid Crystal Display.

We present a simple and economically convenient method to fabricate nanopatterned ZnO films by imprinting lithography and use them for the layer alignment of liquid crystal (LC) displays. First, a one-dimensional nanopattern was obtained by laser interference lithography on a silicon wafer, and the silicon mold replica was transferred onto a flexible polydimethylsiloxane (PDMS) sheet for conformal patterning. The so-obtained PDMS mold was then applied on a ZnO film spin-coated on a glass substrate. During the imprinting process, the temperature was controlled from 100 to 250 °C to observe the transferring morphologies of the ZnO film; the nanopattern was successfully transferred at annealing temperatures of 200 and 250 °C because the ZnO film at the sol state filled the cavities of the PDMS nanopattern and solidified, forming a negative replica of the nanopattern. The direction of the nanopatterned ZnO film served as a guide for aligning the LC molecules on the LC surface at the centimeter scale and, due to their elastic characteristics and group behavior, propagating their directional states in the LC bulk. The resulting LC cell exhibited an enhanced electro-optical performance and high thermal endurance above 180 °C. The geometry of the alignment layer increased the electric field on the ZnO film and showed reduced threshold voltage. In addition, since flexible devices are generally based on polyimide, which imidized at around 200 °C, the relatively low annealing temperatures of our fabricated nanopatterned ZnO film allow it to be mounted on such devices without any deterioration of the underlying thermoplastic substrate. Therefore, nanopatterned ZnO has a considerable potential for advanced LC displays.

Self-packaged high-resolution liquid metal nano-patterns

•Laser interference lithography is invented for nano-patterning liquid metal (LM) •The resolution in LM patterns breaks the optical limit of laser beams •Pulsed-laser-induced compression enables uniform ∼500-nm LM nanolayers •The robust oxide shell on LM boosts the mechanical properties and reliability High-resolution self-packaged conductive patterns are important in integrated electronics used in harsh environments. One of the most promising candidates is gallium-based liquid due to its unique properties. Here, we introduce an advanced liquid metal nano-patterning technique based on pulsed laser lithography (PLL) to create self-packaged, high-resolution liquid metal patterns. The method described here, for the first time, can directly generate liquid metal nano-patterns with ∼500-nm line width without being limited by laser beam size. Line-scanning pulsed-laser-induced shock and thermal effects could generate compression on the liquid metal to extrude ∼200-nm particles to an ∼30-nm layer covered by an ∼20-nm oxide shell with boosted mechanical properties. When subjected to external damage, the electrical functionality of the nano-patterns is well maintained due to the protective self-packaged shell and its 3D structure. The electrically self-packaged material with high resolution is a promising candidate to serve in demanding applications with high integration densities. High-resolution self-packaged conductive patterns are important in integrated electronics used in harsh environments. One of the most promising candidates is gallium-based liquid due to its unique properties. Here, we introduce an advanced liquid metal nano-patterning technique based on pulsed laser lithography (PLL) to create self-packaged, high-resolution liquid metal patterns. The method described here, for the first time, can directly generate liquid metal nano-patterns with ∼500-nm line width without being limited by laser beam size. Line-scanning pulsed-laser-induced shock and thermal effects could generate compression on the liquid metal to extrude ∼200-nm particles to an ∼30-nm layer covered by an ∼20-nm oxide shell with boosted mechanical properties. When subjected to external damage, the electrical functionality of the nano-patterns is well maintained due to the protective self-packaged shell and its 3D structure. The electrically self-packaged material with high resolution is a promising candidate to serve in demanding applications with high integration densities.

Fabrication of Lead-Free Two-Dimensional Organic-Inorganic Hybrid Perovskite Metamaterials by Laser Interference Lithography

Fabrication of Lead-Free Two-Dimensional Organic-Inorganic Hybrid Perovskite Metamaterials by Laser Interference Lithography

Superior nanopatterns via adjustable nanoimprint lithography on aluminum oxide in high-K thin films with ultraviolet curable polymer.

The present study substantiate that ultraviolet-nanoimprint lithography (UV-NIL) can be used to transfer a one-dimensional nano-pattern onto a high-k thin film of aluminum oxide mixed with a UV photocuring agent. Polydimethylsiloxane (PDMS) molds fabricated on silicon wafers were made using deep ultraviolet laser interference lithography in order to investigate one-dimension nanopatterns. These imprinted nano-patterns induce geometric deformations in the liquid crystal (LC), creating collective and elastic properties, which act as a guide for homogeneous alignment. The nanoimprint method can process a large area, so it can be processed much easier, faster, and more accurately than the conventional rubbing method. Moreover, the optical properties of the nano-imprinted aluminum oxide (AlO) thin-film are about 1.5p% superior to that of conventional commercialized cells, so it has a high effect on the luminance and color gamut of the display. After pattern imprinting, atomic force microscope (AFM) was performed to confirm the result. We can compared the cycle of AlO mixed with UV photocuring agent PDMS pattern cycle, the period is 776 and 750 nm, the width is 468 and 450 nm, the spacing is 292 and 300 nm, and the height is 40 and 30 nm. The nano-imprinted film appears to replicate the width, amplitude, and spacing of the PDMS template. In addition, X-ray photoelectron spectroscopy was performed to determine the chemical properties of the thin film and it was confirmed that UV irradiation induces oxidation, thus increases the intensity significantly. The binding energies of Al 2p and C–O spectra were situated at 74.27 ± 0.5 eV and 531.78 ± 0.5 eV, respectively.

Nano-sized graphene oxide coated nanopillars on microgroove polymer arrays that enhance skeletal muscle cell differentiation

The degeneration or loss of skeletal muscles, which can be caused by traumatic injury or disease, impacts most aspects of human activity. Among various techniques reported to regenerate skeletal muscle tissue, controlling the external cellular environment has been proven effective in guiding muscle differentiation. In this study, we report a nano-sized graphene oxide (sGO)-modified nanopillars on microgroove hybrid polymer array (NMPA) that effectively controls skeletal muscle cell differentiation. sGO-coated NMPA (sG-NMPA) were first fabricated by sequential laser interference lithography and microcontact printing methods. To compensate for the low adhesion property of polydimethylsiloxane (PDMS) used in this study, graphene oxide (GO), a proven cytophilic nanomaterial, was further modified. Among various sizes of GO, sGO (< 10 nm) was found to be the most effective not only for coating the surface of the NM structure but also for enhancing the cell adhesion and spreading on the fabricated substrates. Remarkably, owing to the micro-sized line patterns that guide cellular morphology to an elongated shape and because of the presence of sGO-modified nanostructures, mouse myoblast cells (C2C12) were efficiently differentiated into skeletal muscle cells on the hybrid patterns, based on the myosin heavy chain expression levels. Therefore, the developed sGO coated polymeric hybrid pattern arrays can serve as a potential platform for rapid and highly efficient in vitro muscle cell generation.

Cell spreading behaviors on hybrid nanopillar and nanohole arrays

Although nanopillars (NPs) provide a promising tool for capturing tumor cells, the effect of mixing NPs with other nanopatterns on cell behavior remains to be further studied. In this paper, a method of fabricating silicon nanoscale topographies by combining laser interference lithography with metal assisted chemical etching was introduced to investigate the behaviors and pseudopodia of A549 cells on the topologies. It was found that cells had a limited manner in spreading with small cell areas on the silicon nanopillar (SiNP) arrays, but a good manner in spreading with large cell areas on the silicon nanohole (SiNH) arrays. When on the hybrid SiNP/SiNH arrays, cells had medium cell areas and they arranged orderly along the boundaries of SiNPs and SiNHs, as well as 80% of cells displayed a preference for SiNPs over SiNHs. Furthermore, the lamellipodia and filopodia are dominant in the hybrid SiNP/SiNH and SiNP arrays, respectively, both of them are dominant in the SiNH arrays. In addition, the atomic force acoustic microscopy was also employed to detect the subsurface features of samples. The results suggest that the hybrid SiNP/SiNH arrays have a targeted trap and elongation effect on cells. The findings provide a promising method in designing hybrid nanostructures for efficient tumor cell traps, as well as regulating the cell behaviors and pseudopodia.

Fabrication of uniform diffraction gratings using laser interference lithography for simultaneous measurement of refractive index

sThe refractive index is one of the important optical properties. Many researchers have studied various methods of measuring refractive index. In this paper, we can easily measure the refractive index of liquids by using diffraction gratings fabricated by flat-top laser interference lithography. Using the diffraction grating for the measurement of the refractive index has the advantage of a wide measurement range. To fabricate the diffraction gratings, we suggest a special laser manufacturing method named flat-top laser interference lithography. The reason which we have chosen Flat-top laser interference lithography is that it can fabricate uniformly and large area micro/nanostructures on the substrate, using a 360 nm continuous-wave(C.W) laser. This optical system is an experiment in which micro/nanopatterning is performed by converting the Gaussian beam shape into a Flat-top shape and causing laser interference. We fabricated transmission diffraction grating on a glass wafer by flat-top laser interference lithography. The transmission diffraction grating is set to measure the refractive index of several liquids. When the laser is normally incident to the transmission diffraction grating, diffraction occurs then we set the beam-profiler, which can sense several optical properties, at 1st diffraction order. Depending on the type of liquid, 1st diffraction order may be displaced. We can easily measure this displacement and calculate the refractive index of liquids including water, benzene, and ethyl alcogol each value of 1.310, 1.501, and 1.3677. The calculated refractive index corresponds to the true values.

Composite Structure of Ag Colloidal Particles and Au Sinusoidal Nanograting with Large-Scale Ultra-High Field Enhancement for SERS Detection

In this study, a novel composite Surface-Enhanced Raman Scattering (SERS) substrate is proposed for ultrasensitive detection. Consisting of gold sinusoidal nanograting and silver colloidal nanoparticles (AgNPs-AuSG), this type of SERS substrate is easy for fabrication by maskless laser interference lithography, and capable of providing large-scale ultra-high field enhancement, attributed to localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs). The enhancement factor (EF) of this composite substrate is as high as up to 10 orders of magnitude in the simulation experiment. Experimental results show that this large-area, productive SERS substrate of AgNPs-AuSG has realized sensitive TNT and RDX detection with the limit of detection (LOD) of 10−10 M, which may be a potential candidate for trace explosives detection.

Theoretical study of micro-structure fabrication by multi-beam laser interference lithography with different polarization combinations

In this study, we systematically and comprehensively investigated the influence of polarization angle on the fabrication of micro-structures by multi-beam laser interference lithography. Using theoretical analysis and simulation, we studied the effect of different polarization combinations, i.e. transverse electric (TE) and transverse magnetic (TM) polarization combinations, on the characteristics of the micro-structures fabricated by three-, four-, and six-beam laser interference lithography. We successfully obtained micro-structures with different periodic patterns such as honeycomb dots, quasi-elliptic dots, different square dots, and quasi-triangular dots. The simulation results illustrate that polarization affects the formation of interference patterns, pattern contrasts, and periods. The methods discussed herein are simple, low cost, and allow excellent control over structural parameters, and hence are useful for the micro-structure manufacturing industry.

Creating Two-Dimensional Quasicrystal, Supercell, and Moiré Lattices with Laser Interference Lithography: Implications for Photonic Bandgap Materials

Creating Two-Dimensional Quasicrystal, Supercell, and Moiré Lattices with Laser Interference Lithography: Implications for Photonic Bandgap Materials

Sub- μ m features patterned with laser interference lithography for the epitaxial lateral overgrowth of α-Ga2O3 via mist chemical vapor deposition

The low growth rate of mist chemical vapor deposition normally requires a long growth time to achieve coalescence in the epitaxial lateral overgrowth of α-Ga2O3 thin films on sapphire substrates. To address this issue, sub-μm features were patterned using laser interference lithography. Periodical stripes with a ∼590-nm pitch allowed the overgrowth of crack-free, void-free, and continuous thin films, while typical growth conditions using a low carrier gas flow rate and a low Ga precursor concentration were maintained. Coalescence was achieved even with a short growth time of &amp;lt;30 min and a low film thickness of &amp;lt;500 nm. Transmittance and x-ray diffraction spectra show that the film was predominantly in α-phase. Transmission electron microscopy (TEM) images reveal cup-top-like α-Ga2O3 regions of low dislocation density on the SiOx mask. Selected area electron diffraction and high-resolution TEM analyses confirm that an α-Ga2O3 layer was formed even on the top of the SiOx mask. Interestingly, the dislocations formed on the window areas did not bend toward the center of the masks; rather, a dislocation bending outward from the center was observed. This suggests the occurrence of early coalescence and/or atomic rearrangement.

Interference system for high pressure environment

Laser interference patterning or lithography has been used in variety of the applications using, patterning, masking and processing structures at top of material. It offers fast processing over as large areas can be processed simultaneously. Additionally, fine patterns are possible to achieve both in micro and sub-micro scale. In this manuscript is presented novel concept to combine interference patterning and high-pressure processing environment. With aid of high-pressure system, it is possible to control processing environment and add co-solvents in desired state (liquid, gas, supercritical) and use developed system as controlled reactive environment in the future studies. Two systems were developed and assembled for testing and proofing the concept. The results of the two 4-beam interference systems (lens- and mirror-based) are presented and compared.

The distribution of O and N in the surface region of laser-patterned titanium revealed by atom probe tomography

Direct Laser Interference Lithography (DLIL) has shown to be a promising technique to chemically and physically alter the surface of titanium. In this work, atom probe tomography analysis was performed on DLIL-treated titanium to obtain the chemical composition of the surface in maxima and minima interference positions. The analysis revealed that a multilayer structure consisting of oxide/oxynitride is formed at both positions; however, the chemical composition is altered differently between the two. The observed difference is believed to be due to an uneven heating and temperature distribution, which is demonstrated by thermal simulations.