2-μm single longitudinal mode GaSb-based laterally coupled distributed feedback laser with regrowth-free shallow-etched gratings by interference lithography

We report a type-I Ga Sb-based laterally coupled distributed-feedback（LC-DFB） laser with shallow-etched gratings operating a continuous wave at room temperature without re-growth process. Second-order Bragg gratings are fabricated alongside the ridge waveguide by interference lithography. Index-coupled LC-DFB laser with a cavity of 1500 μm achieves single longitudinal mode continuous-wave operation at 20℃ with side mode suppression ratio（SMSR） as high as 24 dB.The maximum single mode continuous-wave output power is about 10 mW at room temperature（uncoated facet）. A low threshold current density of 230 A/cm^2 is achieved with differential quantum efficiency estimated to be 93 mW/A. The laser shows a good wavelength stability against drive current and working temperature.

The theoretic analysis of maskless surface plasmon resonant interference lithography by prism coupling

The use of an attenuated total reflection-coupling mode of prism coated with metal film to excite the interference of the surface plasmon polaritons （SPPs） was proposed for periodic patterning with a resolution of subwavelength scale. High intensity of electric field can be obtained because of the coupling between SPPs and evanescence under a resonance condition, which can reduce exposure time and improve contrast. In this paper, several critical parameters for maskless surface plasmon resonant lithography are described, and the preliminary simulation based on a finite difference timedomain technique agrees well with the theoretical analysis, which demonstrates this scheme and provides the theoretical basis for further experiments.

Fabrication of 4-Inch Nano Patterned Wafer with High Uniformity by Laser Interference Lithography

We report the fabrication of 4-inch nano patterned wafer by two-beam laser interference lithography and analyze the uniformity in detail. The profile of the dots array with a period of 800 nm divided into five regions is characterized by a scanning electron microscope. The average size in each region ranges from 270 nm to 320 nm,and the deviation is almost 4%, which is approaching the applicable value of 3% in the industrial process. We simulate the two-beam laser interference lithography system with MATLAB software and then calculate the distribution of light intensity around the 4 inch area. The experimental data fit very well with the calculated results. Analysis of the experimental data and calculated data indicates that laser beam quality and space filter play important roles in achieving a periodical nanoscale pattern with high uniformity and large area. There is the potential to obtain more practical applications.

The recent development of soft x-ray interference lithography in SSRF

This paper introduces the recent progress in methodologies and their related applications based on the soft x-ray interference lithography beamline in the Shanghai synchrotron radiation facility.Dual-beam,multibeam interference lithography and Talbot lithography have been adopted as basic methods in the beamline.To improve the experimental performance,a precise real-time vibration evaluation system has been established;and the lithography stability has been greatly improved.In order to meet the demands for higher resolution and practical application,novel experimental methods have been developed,such as high-order diffraction interference exposure,high-aspect-ratio and large-area stitching exposure,and parallel direct writing achromatic Talbot lithography.As of now,a 25 nm half-pitch pattern has been obtained;and a cm2 exposure area has been achieved in practical samples.The above methods have been applied to extreme ultraviolet photoresist evaluation,photonic crystal and surface plasmonic effect research,and so on.

Surface Plasmon Interference Lithography Assisted by a Fabry-Perot Cavity Composed of Subwavelength Metal Grating and Thin Metal Film

A surface plasmon interference lithography assisted by a Fabry-Perot （F-P） cavity composed of subwavelength metal gratings and a thin metal fihn is proposed to fabricate high-quality nanopatterns. The calculated results indicate that uniform straight interference fringes with high contrast and high electric-field intensity are formed in the resist under the F-P cavity. The analyses of spatial frequency spectra illuminate the physical mechanism of the formation for the interference fringes. The influence of the F-P cavity spacing is discussed in detail. Moreover, the error analyses reveal that all parameters except the metal grating period in this scheme can bear large tolerances for the device fabrication.

Response of MG63 Osteoblast Cells to Surface Modification of Ti-6Al-4V Implant Alloy by Laser Interference Lithography

The response of human osteoblast-like osteosarcoma cells （MG63） to surface modification of Ti-6Al-4V implant alloy was investigated by Laser Interference Lithography （LIL）. In this work, laser interference lithography was employed to fabricate the microstructures of grooves, dots and dimples onto the surfaces of Ti-6Al-4V samples. Two and three beam LIL systems were developed to carry out the experiments. The laser treatment resulted in the increases of the roughness and the contact angle of water on the implant alloy surfaces. The proliferation of osteoblasts was analyzed by MTT （3-（4,5-dirnethyl- 2-thiazolyl）-2,5-diphenyl-2-H-tetrazolium bromide） assay for the time periods of 4 hours, 2 days, 3 days, and 6 days. The MTT test results demonstrated that the laser treatment surfaces had a positive impact on the proliferation of os- teoblast cells after 24 hours. The alloy surface morphology and the morphological changes of MG63 cells cultured on the laser textured Ti-6Al-4V surface were observed by Scanning Electron Microscope （SEM）. The SEM results indicated that the os- teoblast cells were aligned on grooved surfaces and they were prolonged with the structures. Enzymatic detachment results showed that the 20 μm grooved structures provided the better cell adhesion to the textured Ti-6Al-4V surfaces.

Laser Interference Lithography for Fabrication of Planar Scale Gratings for Optical Metrology

Laser interference lithography is an attractive method for the fabrication of a large-area two-dimensional planar scale grating,which can be employed as a scale for multi-axis optical encoders or a diffractive optical element in many types of optical sensors.Especially,optical configurations such as Lloyd's mirror interferometer based on the division of wavefront method can generate interference fringe fields for the patterning of grating pattern structures at a single exposure in a stable manner.For the fabrication of a two-dimensional scale grating to be used in a planar/surface encoder,an orthogonal two-axis Lloyd's mirror interferometer,which has been realized through innovation to Lloyd’s mirror interferometer,has been developed.In addition,the concept of the patterning of the two-dimensional orthogonal pattern structure at a single exposure has been extended to the non-orthogonal two-axis Lloyd’s mirror interferometer.Furthermore,the optical setup for the non-orthogonal two-axis Lloyd's mirror interferometer has been optimized for the fabrication of a large-area scale grating.In this review article,principles of generating interference fringe fields for the fabrication of a scale grating based on the interference lithography are reviewed,while focusing on the fabrication of a two-dimensional scale grating for planar/surface encoders.Verification of the pitch of the fabricated pattern structures,whose accuracy strongly affects the performance of planar/surface encoders,is also an important task to be addressed.In this paper,major methods for the evaluation of a grating pitch are also reviewed.

Piecewise Linear Weighted Iterative Algorithm for Beam Alignment in Scanning Beam Interference Lithography

To obtain a good interference fringe contrast and high fidelity,an automated beam iterative alignment is achieved in scanning beam interference lithography(SBIL).To solve the problem of alignment failure caused by a large beam angle(or position)overshoot exceeding the detector range while also speeding up the convergence,a weighted iterative algorithm using a weight parameter that is changed linearly piecewise is proposed.The changes in the beam angle and position deviation during the alignment process based on different iterative algorithms are compared by experiment and simulation.The results show that the proposed iterative algorithm can be used to suppress the beam angle(or position)overshoot,avoiding alignment failure caused by over-ranging.In addition,the convergence speed can be effectively increased.The algorithm proposed can optimize the beam alignment process in SBIL.

Flexible Evanescent Wave Interference Lithography System for Sub-half-Wavelength Complex Relief Structures Fabrication

Surface microstructures impart various useful properties to objects,for example,improving optical characteristics,wettability,and sliding properties.It is well known that biomimicking relief structures are effective in making such properties arise and have been studied to be applied to various devices.Furthermore,they are expected to be utilized not only for improving a particular property but also for adding more complex functions on a device's urface by fabricating different multi-functional structures on a single surface in the future.However,to begin with,artificially fabricating such biomimicking special functional relief is difficult.One typical feature of biomimicking surfaces is the dual-scale structure,the smaller one of which is less than 200 nm.Moreover,in the case of realizing the more complex devices,it is necessary to fabricate various forms as changing process conditions dynamically.In this study,we proposed and developed a flexible evanescent wave interference lithography system as a novel fabrication method,which allows us to realize the fabrication of sub-half-wavelength complex relief structures.Firstly,we theoretically analyzed the fundamental behavior of the fabricated structure and found that the proposed concept has the potential to realize one of the target complex structures.Secondly,we developed the proposed system with high process flexibility,in which the number of beams,the azimuth angles,and the polarization can be simply manipulated.Finally,we validated the concept of the designed system by some experiments,where we fabricated dual-scale structures with 840-nm and 190-nm fringe patterns simultaneously.

Latest developments in EUV photoresist evaluation capability at Shanghai Synchrotron Radiation Facility

Evaluating the comprehensive characteristics of extreme ultraviolet(EUV)photoresists is crucial for their application in EUV lithography,a key process in modern technology.This paper highlights the capabilities of the Shanghai Synchrotron Radiation Facility(SSRF)08U1B beamline in advancing this field.Specifically,it demonstrates how this beamline can create fringe patterns with a 15-nm half-pitch on a resist using synchrotron-based EUV lithography.This achievement is vital for evaluating EUV photoresists at the advanced 5-nm node.We provide a detailed introduction to the methods and experimental setup used at the SSRF 08U1B beamline to assess an EUV photoresist.A significant part of this research involved the fabrication of high-resolution hydrogen silsesquioxane mask gratings.These gratings,with an aspect ratio of approximately 3,were created using electron beam lithography on an innovative mask framework.This framework was crucial in eliminating the impact of zeroth-order light on interference patterns.The proposed framework propose offers a new approach to mask fabrication,particularly beneficial for achromatic Talbot lithography and multicoherent-beam interference applications.

Design and tailoring of patterned ZnO nanostructures for energy conversion applications

ZnO is a typical direct wide-bandgap semiconductor material, which has various morphologies and unique physical and chemical properties, and is widely used in the fields of energy, information technology, biomedicine, and others. The precise design and controllable fabrication of nanostructures have gradually become important avenues to further enhancing the performance of Zn O-based functional nanodevices. This paper introduces the continuous development of patterning technologies, provides a comprehensive review of the optical lithography and laser interference lithography techniques for the controllable fabrication of Zn O nanostructures, and elaborates on the potential applications of such patterned Zn O nanostructures in solar energy, water splitting, light emission devices, and nanogenerators. Patterned Zn O nanostructures with highly controllable morphology and structure possess discrete three-dimensional space structure, enlarged surface area, and improved light capture ability, which realize the efficient carrier regulation,achieve highly efficient energy conversion, and meet the diverse requirements of functional nanodevices. The patterning techniques proposed for the precise design of Zn O nanostructures not only have important guiding significance for the controllable fabrication of complex nanostructures of other materials, but also open up a new route for the further development of functional nanostructures.

Large-area flexible nanostripe electrodes featuring plasmon hybridization engineering

Multifunctional flexible Au electrodes based on one-dimensional(1D)arrays of plasmonic gratings are nanofabricated over large areas with an engineered variant of laser interference lithography optimized for low-cost transparent templates.Au nanostripe(NS)arrays achieve sheet resistance in the order of 20 Ohm/square on large areas(∼cm^(2))and are characterized by a strong and dichroic plasmonic response which can be easily tuned across the visible(VIS)to near-infrared(NIR)spectral range by tailoring their cross-sectional morphology.Stacking vertically a second nanostripe,separated by a nanometer scale dielectric gap,we form near-field coupled Au/SiO_(2)/Au dimers which feature hybridization of their localized plasmon resonances,strong local field-enhancements and a redshift of the resonance towards the NIR range.The possibility to combine excellent transport properties and optical transparency on the same plasmonic metasurface template is appealing in applications where low-energy photon management is mandatory like e.g.,in plasmon enhanced spectroscopies or in photon harvesting for ultrathin photovoltaic devices.The remarkable lateral order of the plasmonic NS gratings provides an additional degree of freedom for tailoring the optical response of the multifunctional electrodes via the excitation of surface lattice resonances,a Fano-like coupling between the broad localised plasmonic resonances and the collective sharp Rayleigh modes.

Fundamental principles and development of proximity-field nanopatterning toward advanced 3D nanofabrication

Three-dimensional(3D)nanoarchitectures have offered unprecedented material performances in diverse applications like energy storages,catalysts,electronic,mechanical,and photonic devices.These outstanding performances are attributed to unusual material properties at the nanoscale,enormous surface areas,a geometrical uniqueness,and comparable feature sizes with optical wavelengths.For the practical use of the unusual nanoscale properties,there have been developments for macroscale fabrications of the 3D nanoarchitectures with process areas over centimeter scales.Among the many fabrication methods for 3D structures at the nanoscale,proximity-field nanopatterning(PnP)is one of the promising techniques that generates 3D optical holographic images and transforms them into material structures through a lithographic process.Using conformal and transparent phase masks as a key factor,the PnP process has advantages in terms of stability,uniformity,and reproducibility for 3D nanostructures with periods from 300 nm to several micrometers.Other merits of realizing precise 3D features with sub-100 nm and rapid processes are attributed to the interference of coherent light diffracted by phase masks.In this review,to report the overall progress of PnP from 2003,we present a comprehensive understanding of PnP,including its brief history,the fundamental principles,symmetry control of 3D nanoarchitectures,material issues for the phase masks,and the process area expansion to the wafer-scale for the target applications.Finally,technical challenges and prospects are discussed for further development and practical applications of the PnP technique.