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.

Spatially-Resolved Crystallization of Amorphous Silicon Films on the Glass Substrate by Multi-beam Laser Interference

Laser interference induced crystallization of amorphous silicon （a-Si） on the glass substrate was performed using a Q-switched Nd：YAG （yttrium aluminum garnet） laser. White light interferometer （WLI） and atomic force microscope （AFM） were used to characterize the morphology of the structured films, while X-ray diffraction （XRD）, combined with the AFM, was used to analyse the crystalline structure of the film. The experimental results show that the laser energy density above a certain threshold, in the range of 400-500 mJ/cm2,triggers the patterned crystallizations which take the form similar to the laser intensity distribution. For the patterned crystallization under multipulse exposure, a definite polycrystalline structure with individual phases was observed by XRD. The difference in feature form, e.g., deepened craters or heightened lines, is related to the laser energy density relative to the threshold of evaporation of the material.

Nanodot array deposition via single shot laser interference pattern using laser-induced forward transfer

Laser-induced forward transfer(LIFT)is a direct-writing technique capable of depositing a single dot smaller than the laser wavelength at small shot energy through the laser-induced dot transfer(LIDT)technique.To deposit a single nanodot in a single shot of laser irradiation,a liquid nanodrop is transferred from donor to receiver and finally solidified via a solid–liquid–solid(SLS)process.In conventional LIDT experiments,multi-shots with step scanning have been used to form array structures.However,interference laser processing can achieve an arrayed process and generate a periodic structure in a single shot.In this study,a femtosecond laser interference pattern was first applied to LIDT,and an array of nanodots was successfully deposited in a single shot,producing the following unit structures:a single dot,adjoining dots,and stacking dots.The diameter of the smallest nanodot was 355 nm,and the narrowest gap between two adjoining nanodots was 17.2 nm.The LIDT technique produces high-purity,catalyst-free that do not require post-cleaning or alignment processes.Given these significant advantages,LIDT can expand the usability of nanodots in a wide range of fields.

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.

Silver Nano Islands Enhanced Raman Scattering on Large Area Grating Substrates Fabricated by Two Beam Laser Interference

The authors prepared large area surface-enhanced Raman scattering（SERS） active substrates with tunable enhancement. First the large area gratings were fabricated by scanning a photoresist with two-beam laser interference and subsequently they were coated with silver nano islands via vacuum evaporation. SERS active metal island grating substrates with four different periods（300, 400, 515 and 600 nm） and Ag nano islands uniformly coated on an area of 2.5 cm×0.5 cm were obtained. The measured SERS spectra reveal the tuning effect of the period on the Raman sig- nals period. The highest enhancement（ca. 105） for Rhodamine 6G（R6G） as probing molecule is associated with a pe- riod of 515 nm due to the perfect matching of surface plasmons and Raman excitation line. A good reproducibility of SERS signals with almost the same SERS intensity at different spots was observed on all the larger area Ag island grating substrates.

Laser interference fabrication of large-area functional periodic structure surface

Functional periodic structures have attracted significant interest due to their natural capabilities in regulating surface energy, surface effective refractive index, and diffraction. Several technologies are used for the fabrication of these functional structures. The laser interference technique in particular has received attention because of its simplicity, low cost, and high-efficiency fabrication of large-area, micro/nanometer-scale, and periodically patterned structures in air conditions. Here, we reviewed the work on laser interference fabrication of large-area functional periodic structures for antireflection, self-cleaning, and superhydrophobicity based on our past and current research. For the common cases, four-beam interference and multi-exposure of two-beam interference were emphasized for their setup, structure diversity, and various applications for antireflection, self-cleaning, and superhydrophobicity. The relations between multi-beam interference and multi-exposure of two-beam interference were compared theoretically and experimentally. Nanostructures as a template for growing nanocrystals were also shown to present future possible applications in surface chemical control. Perspectives on future directions and applications for laser interference were presented.

Laser self-mixing interference fibre sensor

Fibre sensors exhibit a number of advantages over other sensors such as high sensitivity, electric insulation, corrosion resistance, interference rejection and so on. And laser self-mixing interference can accurately detect the phase difference of feedback light. In this paper, a novel laser self-mixing interference fibre sensor that combines the advantages of fibre sensors with those of laser self-mixing interference is presented. Experimental configurations are set up to study the relationship between laser power output and phase of laser feedback light when the fibre trembles or when the fibre is stretched or pressed. The theoretical analysis of pressure sensors based on laser self-mixing interference is indicated to accord with the experimental results.

Measurement and Analysis of Vibration Effect of Free-falling Corner Cube Driving Mechanism in Free Fall Absolute Gravimeter

The vibration interference of the reference corner cube runs through the free flight process of the free-falling corner cube,which is superimposed on the whole laser interference fringes.Thus,it is necessary to solve the interference fringes with the entire fringe to analyze the quantitative influence of vibration on gravity measurements.

Ultrashort pulsed laser induced complex surface structures generated by tailoring the melt hydrodynamics

We present a novel approach for tailoring the laser induced surface topography upon femtosecond(fs)pulsed laser irradiation.The method employs spatially controlled double fs laser pulses to actively regulate the hydrodynamic microfluidic motion of the melted layer that gives rise to the structures formation.The pulse train used,in particular,consists of a previously unexplored spatiotemporal intensity combination including one pulse with Gaussian and another with periodically modulated intensity distribution created by Direct Laser Interference Patterning(DLIP).The interpulse delay is appropriately chosen to reveal the contribution of the microfluidic melt flow,while it is found that the sequence of the Gaussian and DLIP pulses remarkably influences the surface profile attained.Results also demonstrate that both the spatial intensity of the double pulse and the effective number of pulses per irradiation spot can further be modulated to control the formation of complex surface morphologies.The underlying physical processes behind the complex patterns’generation were interpreted in terms of a multiscale model combining electron excitation with melt hydrodynamics.We believe that this work can constitute a significant step forward towards producing laser induced surface structures on demand by tailoring the melt microfluidic phenomena.

Optimal zero-crossing group selection method of the absolute gravimeter based on improved auto-regressive moving average model

An absolute gravimeter is a precision instrument for measuring gravitational acceleration, which plays an important role in earthquake monitoring, crustal deformation, national defense construction, etc. The frequency of laser interference fringes of an absolute gravimeter gradually increases with the fall time. Data are sparse in the early stage and dense in the late stage. The fitting accuracy of gravitational acceleration will be affected by least-squares fitting according to the fixed number of zero-crossing groups. In response to this problem, a method based on Fourier series fitting is proposed in this paper to calculate the zero-crossing point. The whole falling process is divided into five frequency bands using the Hilbert transformation. The multiplicative auto-regressive moving average model is then trained according to the number of optimal zero-crossing groups obtained by the honey badger algorithm. Through this model, the number of optimal zero-crossing groups determined in each segment is predicted by the least-squares fitting. The mean value of gravitational acceleration in each segment is then obtained. The method can improve the accuracy of gravitational measurement by more than 25% compared to the fixed zero-crossing groups method. It provides a new way to improve the measuring accuracy of an absolute gravimeter.

Influence of structural depth of laser-patterned steel surfaces on the solid lubricity of carbon nanoparticle coatings

Carbon nanoparticle coatings on laser-patterned stainless-steel surfaces present a solid lubrication system where the pattern's recessions act as lubricant-retaining reservoirs.This study investigates the influence of the structural depth of line patterns coated with multi-walled carbon nanotubes(CNTs)and carbon onions(COs)on their respective potential to reduce friction and wear.Direct laser interference patterning(DLIP)with a pulse duration of 12 ps is used to create line patterns with three different structural depths at a periodicity of 3.5μm on AISI 304 steel platelets.Subsequently,electrophoretic deposition(EPD)is applied to form homogeneous carbon nanoparticle coatings on the patterned platelets.Tribological ball-on-disc experiments are conducted on the as-described surfaces with an alumina counter body at a load of 100 mN.The results show that the shallower the coated structure,the lower its coefficient of friction(COF),regardless of the particle type.Thereby,with a minimum of just below 0.20,CNTs reach lower COF values than COs over most of the testing period.The resulting wear tracks are characterized by scanning electron microscopy,transmission electron microscopy,and energy-dispersive X-ray spectroscopy.During friction testing,the CNTs remain in contact,and the immediate proximity,whereas the CO coating is largely removed.Regardless of structural depth,no oxidation occurs on CNT-coated surfaces,whereas minor oxidation is detected on CO-coated wear tracks.

A STUDY OF INTERFACES OF COMPOSITES BY MEANS OF OPTICAL FIBRE SENSING TECHNTIQUE

Fibre stress of glass fibre reinforced polymeric copmosites on load is determined by using optical fibre as model fiber and by means of laser interference method. In addition, the origination of fibre stress during moulding process of composites and the relation between fiber stress of loaded composites and external stress are examined. The experiments show that fibre stress is related to molecular structure of inter facial materials and structure of inter facial layers. When stress is transferred from matrix to fibre, each inter facial layer has different stress gradient and deformability. This property can be characterized by introducing an inter facial stress transfer coefficient k to the two-phase model.

Towards the Mechanism of Mass Transfer of a Single Bubble

This paper focuses on the mechanism of interfacial mass transfer of a single bubble, based on the chemical potential driving force, an approach for calculating interfacial concentration in practical process is proposed. The absorption processes of bubble under both quiescent and mobile conditions are analyzed and discussed respectively. For a stationary absorption, only in the case of liquid bulk concentration near saturated value, the interfacial concentration could close to the equilibrium value ; For a moving bubble, under ordinary operating condition （Yo〉l）, the interfacial concentration is far from its equilibrium. Only under bulk concentration near saturated value or a smaller Yo（Yo〈0.1） which may involve the complication of additional resistance at interface induced by surface contamination or surfactant added, the interfacial concentration could be approximate to equilibrium value. The interfacial concentration close to the interface on liquid side for a single CO2 bubble absorbed by methanol is measured using a modern optical instrumentation in which the laser holographic interference method is adopted with a real-time and amplification technique. Experimental results show that the interfacial concentration decreases significantly with increasing Re and is far from the equilibrium one in a larger Re range. Experiments validate the proposed model.

The Mechanism of Interfacial Mass Transfer in Gas Absorption Process

Based on the method of molecular thermodynamics, the mass transfer mechanism at gas-liquid interface is studied theoretically, and a new mathematical model is proposed. Using laser holographic interference technique, the hydrodynamics and mass transfer characteristics of CO2 absorption are measured. It is shown that the calculated results are in good agreement with the experimental data.

On-chip mode-locked laser diode structure using multimode interference reflectors

We report, for the first time to our knowledge, an on-chip mode-locked laser diode(OCMLLD) that employs multimode interference reflectors to eliminate the need of facet mirrors to form the cavity. The result is an OCMLLD that does not require cleaved facets to operate, enabling us to locate this OCMLLD at any location within the photonic chip. This OCMLLD provides a simple source of optical pulses that can be inserted within a photonic integrated circuit chip for subsequent photonic signal processing operations within the chip(modulation, optical filtering, pulse rate multiplication, and so on). The device was designed using standardized building blocks of a generic active/passive In P technology platform, fabricated in a multi-project wafer run, and achieved mode-locking operation at its fundamental frequency, given the uncertainty at the design step of the optical length of these mirrors, critical to achieve colliding pulse mode-locked operation.

Studies on the Influence of Third Component on Gas-Liquid Mass Transfer

The influence of the third component on gas-liquid mass transfer was studied by use of laser holographic interferometry. Four surfactants were added respectively and experimental results show that the microamount of surfactants can change obviously the concentration near the interface on bubble mass transfer process, which indicated that the third component has a significant effect on the bubble mass transfer process.

Does laser surface texturing really have a negative impact on the fatigue lifetime of mechanical components?

Laser surface texturing(LST)has been proven to improve the tribological performance of machine elements.The micro-scale patterns manufactured by LST may act as lubricant reservoirs,thus supplying oil when encountering insufficient lubrication.However,not many studies have investigated the use of LST in the boundary lubrication regime,likely due to concerns of higher contact stresses that can occur with the increasing surface roughness.This study aims to examine the influence of LST on the fatigue lifetime of thrust rolling bearings under boundary lubrication.A series of periodic patterns were produced on the thrust rolling bearings,using two geometrically different designs,namely cross and dimple patterns.Base oil ISO VG 100 mixed with 0.05 wt%P of zinc dialkyldithiophosphate(ZDDP)was supplied.The bearings with cross patterns reduce the wear loss by two orders of magnitude.The patterns not only retain lubricant in the textured pockets but also enhance the formation of an anti-wear tribofilm.The tribofilm generation may be improved by the higher contact stresses that occur when using the textured surface.Therefore,in contrast to the negative concerns,the ball bearings with cross patterns were instead found to increase the fatigue life by a factor of three.

Generation of micro/nano hybrid surface structures on copper by femtosecond pulsed laser irradiation

The delamination of copper lead frames from epoxy molding compounds(EMC)is a severe problem for microelectronic devices,as it leads to reduced heat dissipation or circuit breakage.The micro/nanoscale surface structuring of copper is a promising method to improve the copper-EMC interfacial adhesion.In this study,the generation of micro/nano hybrid structures on copper surfaces through femtosecond pulsed laser irradiation is proposed to improve interfacial adhesion.The micro/nano hybrid structures were realized by generating nanoscale laser-induced periodic surface structures(LIPSS)on microscale parallel grooves.Several types of hybrid surface structures were generated by changing the laser polarization direction,fluence,and scanning speed.At a specific aspect ratio of microgrooves,a latticed structure was generated on the sides of microgrooves by combining LIPSS formation and direct laser interference patterning.This study provides an efficient method for the micro/nanoscale hybrid surface structure formation for interfacial adhesion improvement between copperand EMC.

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.

Preparation of Large-area Controllable Patterned Silver Nanocrystals for High Sensitive and Stable Surface-enhanced Raman Spectroscopy

A novel and facile method for fabricating large-area pattemed silver nanocrystals was introduced and the investigation on the high sensitive and stable surface-enhanced Raman spectroscopy（SERS） of the nanocrystals was carried out. Nanostructured silicon substrate was processed by laser interference and used as a template for growing silver nanocrystals via galvanic battery reaction method. The substrate with large area for violent chemical reaction was tailored into a nanocell array. The limited reaction area hindered the growth of silver nanocrystals and made their size uniform and controllable. The size and gaps of the nanocrystals could be controlled by template period and ratio, which were easily reproduced by laser interference. Taking 10^-8 to 10^-11 mol/L RhoG for example, the optimized silver arrays exhibited great potential for ultrasensitive molecular sensing in terms of its high SERS enhancement ability, favorable stability, and excellent reproducibility.