Toward Defect-Free Nanoimprinting.

Nanoimprinting large-area structures, especially high-density features like meta lenses, poses challenges in achieving defect-free nanopatterns. Conventional high-resolution molds for nanoimprinting are often expensive, typically constructed from inorganic materials such as silicon, nickel (Ni), or quartz. Unfortunately, replicated nanostructures frequently suffer from breakage or a lack of definition during demolding due to the high adhesion and friction at the polymer-mold interface. Moreover, mold degradation after a limited number of imprinting cycles, attributed to contamination and damaged features, is a common issue. In this study, a disruptive approach is presented to address these challenges by successfully developing an anti-sticking nanocomposite mold. This nanocomposite mold is created through the co-deposition of nickel atoms and low surface tension polytetrafluoroethylene (PTFE) nanoparticles via electroforming. The incorporation of PTFE enhances the ease of polymer release from the mold. The resulting Ni-PTFE nanocomposite mold exhibits exceptional lubrication properties and a significantly reduced surface energy. This robust nanocomposite mold proves effective in imprinting fine, densely packed nanostructures down to 100 nm using thermal nanoimprinting for at least 20 cycles. Additionally, UV nanoimprint lithography (UV-NIL) is successfully performed with this nanocomposite mold. This work introduces a novel and cost-effective approach to reusable high-resolution molds, ensuring defect-reduction production in nanoimprinting.

Study on magnetohydrodynamic internal cooling mechanism within an aluminium oxide cutting tool.

One of the challenges in the transfer of heat during the mechanical machining process is the coolant substance used in the internal cooling method which is generally liquid water or a water-based coolant. This limits the heat transfer capacity insofar as the thermal conductivity of liquid water is concerned. The other difficulty is the requirement for an external mechanical system to pump the coolant around the internal channel, providing efficient transfer of the accumulated thermal energy. This study proposes a novel method to address this issue by using liquid gallium which provides the means to transfer the excess heat generated during the cutting process by integrating the design into an aluminium oxide insert. Combining this with a magnetohydrodynamic drive, the coolant system operates without the need for mechanical input. Liquid gallium is nontoxic and has a much higher thermal conductivity over liquid water. Investigations of the novel cooling system is performance compared against liquid water through numerical modelling, followed by an experimental machining test to ascertain the difference in heat transfer effectiveness, tool wear rates and workpiece surface finish when compared to dry machining and external cooling conditions on stainless steel 316L. Without cooling, experimental machining tests employing a cutting speed of Vc = 250 m min-1 resulted in a corner wear VBc rate of 75 µm, and with the magnetohydrodynamic-based coolant on, produced a VBc rate of 48 µm, indicating a difference of 36% in relative tool wear under the same cutting conditions. Increasing the cutting speed Vc to 900 m min-1, produced a corner wear VBc rate of 357 µm without the active coolant and a VBc rate of 246 µm with the magnetohydrodynamic-based coolant on, representing a decrease of 31% in relative tool wear. Further tests comparing external liquid water cooling against the liquid gallium coolant showed at Vc = 250 m min-1, a difference of 29% in relative tool wear rate reduction was obtained with the internal liquid gallium coolant. Increasing the cutting speed to Vc = 900 m min-1, the data indicated a difference of 16% relative tool wear reduction with the internal liquid gallium. The results support the feasibility of using liquid gallium as an internal coolant in cutting inserts to effectively remove thermal energy.

Defect-Mediated Atomic Layer Etching Processes on Cl-Si(100): An Atomistic Insight.

Defects play a significant role in atomic layer etching (ALE) processes; however, a fundamental understanding at the atomic level is still lacking. To bridge this knowledge gap, this study investigated the role of point defects in the laser-induced ALE of Cl-Si(100) using density functional theory (DFT) and real-time time-dependent DFT calculations. In the calculations, both the pristine surface and the defective surface were considered for comparative analysis. The key finding is the enhanced desorption of SiCl molecules, facilitated by point defects under laser pulse irradiation. The presence of point defects was found to effectively reduce both the desorption energy barrier and the laser intensity threshold required for desorption. Additionally, extra defective levels within the band gap were observed through the density-of-state diagram. Based on these findings, a defect-mediated etching regime was proposed to elucidate the layer-by-layer etching process. This study provides atomistic insight into understanding the role of defects in laser-induced ALE processes. The presence of point defects can enhance the etching selectivity between the topmost layer and the underlying layers, thereby contributing to highly efficient and damage-free etching processes through the defect-mediated etching mechanism.

Pre-Compensation of Thermal Error for Laser-Assisted Diamond Turning.

The laser-assisted diamond turning (LADT) method can effectively improve the machinability of hard and brittle materials based on the laser heating effect, resulting in prolonged diamond tool life and better surface integrity. However, due to the incomplete absorption of laser beam energy within the workpiece cutting zone, simultaneous heating of the tool holder occurs, resulting in a structural thermal expansion that affects the workpiece form accuracy. In this article, the form accuracy of a LADT-machined workpiece was systematically studied. Accurate calculations of the tool shank and tool holder thermal fields and thermal expansion were performed using thermodynamic coupled finite element analysis. In addition, the LADT tool path was precisely pre-compensated by taking into account the structure expansion. The experimental results demonstrate that the form accuracy can be significantly improved with a pre-compensated tool path, which provides crucial technical support for achieving a high-precision finish on optical elements using the LADT method.

Optimized design and experimental study of a macroscopic mirror to achieve linear amplification of optical force-induced displacement.

A new thin plane mirror with an Archimedes spiral structure (Archimedes-structure thin plane mirror - ATPM) that implements an elastic support boundary is proposed in this study. An optimal structure of ATPM is developed to achieve a linear displacement response with respect to optical forces. The displacement response of the optimized ATPM is analyzed by considering the combined effects of optical force and gravity. The distribution of the optical force density is calculated based on a tilted Gaussian laser beam. Experimental results demonstrate that the optimized ATPM can produce a steady-state displacement of 24.18 nm on average in a normal-gravity environment when subjected to an average optical force of 132.17 nN. When the optical force exceeds 133 nN, the nonlinearity of the displacement response of the optimized ATPM is less than 6.28%. An amplification of the optical force-induced displacement is achieved by more than 15 times compared with that for an unstructured mirror of the same size. The results of this study can assist the development of a miniaturized macroscale optical force platform based on an ATPM for practical applications including the in-situ laser power measurement and nN level force source in the atomic and close-to-atomic scale manufacturing.

Poster Session: Dynamic optomechanical eye model for the validation of peripheral aberration measurement.

Many myopia control products based on the peripheral defocus theory have emerged on the market in the past five years. However, efficient measurement of peripheral aberrations is still not a well-addressed problem. To validate the aberrometer for peripheral aberration measurement, a dynamic wide field optomechanical eye model is designed and fabricated. This model consists of a plano-convex lens representing cornea (f'=30mm), a double-convex lens representing crystalline lens (f'=100mm), and a spherical retinal screen with a 12mm radius. To optimize the quality of spot-field images get from the Hartman-Shack sensor, the materials and surface treatment for the retina are studied. The model has a movable retina to achieve Zernike 4th item (Z4 focus) ranging from -6.28-＋6.84 µm. As for M (Mean sphere equivalent), it can achieve -11.85D-+10.88D at 0° visual field and -6.97D-+5.88D at 30° visual field with a 4mm pupil size. To allow a changing pupil size, a slot at the back of the cornea mount and a series of thin metal sheets with 2, 3, 4, and 6 mm holes are manufactured. Both on-axis aberrations and peripheral aberrations of the eye model are verified by commercial aberrometer VX130 (Luneau Technology, France) and the feasibility of the eye model to mimic a human eye in a peripheral aberration measuring system is illustrated.

Magnetohydrodynamic-based Internal Cooling System for a Ceramic Cutting Tool: Concept Design, Numerical Study, and Experimental Evalidation.

The effective removal of the heat generated during mechanical cutting processes is crucial to enhancing tool life and producing workpieces with superior surface finish. The internal cooling systems used in cutting inserts employ a liquid water-based solvent as the primary medium to transport the excess thermal energy generated during the cutting process. The limitations of this approach are the low thermal conductivity of water and the need for a mechanical input to circulate the coolant around the inner chamber of the cutting tool. In this context, this paper proposes an alternative method in which liquid gallium is used as the coolant in combination with a magnetohydrodynamic (MHD) pump, which avoids the need for an external power source. Using computational fluid dynamics, we created a numerical model of an internal cooling system and then solved it under conditions in which a magnetic field was applied to the liquid metal. This was followed by a simulation study performed to evaluate the effectiveness of liquid gallium over liquid water. The results of experiments conducted under non-cooling and liquid gallium cooling conditions were analyzed and compared in terms of the tool wear rate. The results showed that after six machining cycles at a cutting speed Vc = 250 m min -1, the corner wear VBc rate was 75 µm with the coolant off and 48 µm with the MHD-based coolant on, representing a decrease of 36% in tool wear. At Vc = 900 m min-1, the corner wear VBc rate was 75 µm with the coolant off and 246 µm with the MHD-based coolant on, representing a decrease of 31% in tool wear. When external cooling using liquid water was added, the results showed at Vc = 250 m min-1, the difference between the tool wear rate reduction with the internal liquid gallium coolant relative to the external coolant was 29%. When the cutting speed was increased to Vc = 900 m min-1, the difference observed between the internal liquid gallium coolant relative to the external coolant was 16%. The study proves the feasibility of using liquid gallium as a coolant to effectively remove thermal energy through internally fabricated cooling channels in cutting inserts.

Measurement Technologies of Light Field Camera: An Overview.

Visual measurement methods are extensively used in various fields, such as aerospace, biomedicine, agricultural production, and social life, owing to their advantages of high speed, high accuracy, and non-contact. However, traditional camera-based measurement systems, relying on the pinhole imaging model, face challenges in achieving three-dimensional measurements using a single camera by one shot. Moreover, traditional visual systems struggle to meet the requirements of high precision, efficiency, and compact size simultaneously. With the development of light field theory, the light field camera has garnered significant attention as a novel measurement method. Due to its special structure, the light field camera enables high-precision three-dimensional measurements with a single camera through only one shot. This paper presents a comprehensive overview of light field camera measurement technologies, including the imaging principles, calibration methods, reconstruction algorithms, and measurement applications. Additionally, we explored future research directions and the potential application prospects of the light field camera.

Ab initio simulations of ultrashort laser pulse interaction with Cl-Si(100): implications for atomic layer etching.

Due to the remarkable resistance of SiCl against photo-induced desorption, achieving atomic layer etching (ALE) of Cl-Si(100) through a laser-based method has remained a formidable challenge. In this study, we investigate the interaction between ultrashort laser pulses and the Cl-Si(100) surface via ab initio simulations that combine real-time time-dependent density functional theory and molecular dynamics. Our results demonstrate the direct desorption of the stubborn SiCl layer through the application of appropriate femtosecond laser pulses. Notably, the desorption process is enhanced by pulses with higher laser intensity, shorter wavelength, and longer pulse duration. There is a threshold intensity beyond which the SiCl can be directly desorbed under laser pulses with a wavelength of 488 nm and a pulse duration of 40 ℏ eV-1 (26.3 fs). Analysis of electron localization function reveals a critical bond breaking length of 2.98 Šbetween Si-Si, connecting SiCl to the bulk material. The time evolution of bond lengths and forces reveals that the desorption of SiCl is primarily driven by repulsive forces generated within the Si-Si bond. Furthermore, electron density difference analysis and Keldysh factor calculations indicate that these repulsive forces arise from multiphoton ionization. This study provides crucial atomic-level insights into the interaction of ultrashort laser pulses with Cl-Si(100), thereby propelling the advancement of laser-induced atomic layer etching techniques.

Vision-Based Contact Adhesion Measurement Method on Soft Matter Surfaces.

Adhesion property measurements contribute to a comprehensive understanding of the mechanical properties of soft matters. Indentation tests are a common method for measuring the adhesion force. However, indenters generally have a large volume and a small sensing angle and, thus, are not conducive to local detection in high-precision environments. Here, we propose a vision-based contact adhesion measurement (VisCAM) method to achieve the contact image and adhesion force on soft matter surfaces from the perspective of indentation direction. The coupling of the 7.6 mm diameter probe and a flexible fiber makes the system similar to a miniaturized endoscope. Classical contact theories and finite element models are used for the contact mechanics analysis of silicone rubber. The image grayscale-load mathematical model is constructed based on the change in contact light spot. Finally, the uncertainty of the system is less than 4%, and the measurement error is 0.04 N. In-vitro kidney indentation experiments showed that the local adhesion force measurement of soft tissues can be completed. Our method provides better solutions for understanding the adhesion properties of soft matters.

Optimal tool design in micro-milling of difficult-to-machine materials.

The limitations of significant tool wear and tool breakage of commercially available fluted micro-end mill tools often lead to ineffective and inefficient manufacturing, while surface quality and geometric dimensions remain unacceptably poor. This is especially true for machining of difficult-to-machine (DTM) materials, such as super alloys and ceramics. Such conventional fluted micro-tool designs are generally down scaled from the macro-milling tool designs. However, simply scaling such designs from the macro to micro domain leads to inherent design flaws, such as poor tool rigidity, poor tool strength and weak cutting edges, ultimately ending in tool failure. Therefore, in this article a design process is first established to determine optimal micro-end mill tool designs for machining some typical DTM materials commonly used in manufacturing orthopaedic implants and micro-feature moulds. The design process focuses on achieving robust stiffness and mechanical strength to reduce tool wear, avoid tool chipping and tool breakage in order to efficiently machine very hard materials. Then, static stress and deflection finite element analysis (FEA) is carried out to identify stiffness and rigidity of the tool design in relation to the maximum deformations, as well as the Von Mises stress distribution at the cutting edge of the designed tools. Following analysis and further optimisation of the FEA results, a verified optimum tool design is established for micro-milling DTM materials. An experimental study is then carried out to compare the optimum tool design to commercial tools, in regards to cutting forces, tool wear and surface quality.

Dynamic opto-mechanical eye model with peripheral refractions.

Many myopia control methods based on the peripheral defocus theory have emerged towards applications in recent years. However, peripheral aberration is a critical issue, which is still not well-addressed. To validate the aberrometer for peripheral aberration measurement, a dynamic opto-mechanical eye model with a wide visual field is developed in this study. This model consists of a plano-convex lens representing cornea (f' = 30 mm), a double-convex lens representing crystalline lens (f' = 100 mm), and a spherical retinal screen with a radius of 12 mm. To optimize the quality of spot-field images from the Hartman-Shack sensor, the materials and surface topography for the retina are studied. The model has an adjustable retina to achieve Zernike 4th item (Z4 focus) ranging from -6.28 µm to +6.84 µm. As for mean sphere equivalent, it can achieve -10.52 D to +9.16 D at 0° visual field and -6.97 D to +5.88 D at 30° visual field with a pupil size of 3 mm. To realize a changing pupil size, a slot at the back of the cornea mount and a series of thin metal sheets with 2, 3, 4, and 6 mm holes are generated. Both on-axis aberrations and peripheral aberrations of the eye model are verified by a well-used aberrometer and the eye model to mimic a human eye in a peripheral aberration measurement system is illustrated.

Periodic surface structure of 4H-SiC by 46.9†nm laser.

This paper presents an experimental study on the laser-induced atomic and close-to-atomic scale (ACS) structure of 4H-SiC using a capillary-discharged extreme ultraviolet (EUV) pulse of 46.9 nm wavelength. The modification mechanism at the ACS is investigated through molecular dynamics (MD) simulations. The irradiated surface is measured via scanning electron microscopy and atomic force microscopy. The possible changes in the crystalline structure are investigated using Raman spectroscopy and scanning transmission electron microscopy. The results show that the stripe-like structure is formed due to the uneven energy distribution of a beam. The laser-induced periodic surface structure at the ACS is first presented. The detected periodic surface structures with a peak-to-peak height of only 0.4 nm show periods of 190, 380, and 760 nm, which are approximately 4, 8, and 16 times the wavelength. In addition, no lattice damage is detected in the laser-affected zone. The study shows that the EUV pulse is a potential approach for the ACS manufacturing of semiconductors.

Scaling up the fabrication of wafer-scale Ni-MoS2/WS2 nanocomposite moulds using novel intermittent ultrasonic-assisted dual-bath micro-electroforming.

In the scale-up fabrication process for electroformed Ni-MoS2/WS2 composite moulds, the formulation of nanosheets is critical, since the size, charge, and their distribution can largely affect the hardness, surface morphology and tribological properties of the moulds. Additionally, the long-term dispersion of hydrophobic MoS2/WS2 nanosheets in a nickel sulphamate solution is problematic. In this work, we studied the effect of ultrasonic power, processing time, surfactant types and concentrations on the properties of nanosheets to elaborate their dispersion mechanism and control their size and surface charge in divalent nickel electrolyte. The formulation of MoS2/WS2 nanosheets was optimized for effective electrodeposition along with nickel ions. A novel strategy of intermittent ultrasonication in the dual bath was proposed to resolve the problem of long-term dispersion, overheating, and deterioration of 2D material deposition under direct ultrasonication. Such strategy was then validated by electroforming 4-inch wafer-scale Ni-MoS2/WS2 nanocomposite moulds. The results indicated that the 2D materials were successfully co-deposited into composite moulds without any defects, along with the mould microhardness increasing by ∼2.8 times, the coefficient of friction reducing by two times against polymer materials, and the tool life increasing up to 8 times. This novel strategy will contribute to the industrial manufacturing of 2D material nanocomposites under ultrasonication process.

Study on surface thermal oxidation of silicon carbide irradiated by pulsed laser using reactive molecular dynamics.

Pulsed lasers are a powerful tool for fabricating silicon carbide (SiC) that has a hard and brittle nature, but oxidation is usually unavoidable. This study presents an exploration of the oxidation mechanism of 4H-SiC in oxygen and water under different temperatures via reactive force field molecular dynamics. Single pulse irradiation experiments were conducted to study the oxygen content of the laser-affected zone through energy dispersive x-ray spectrometry. The results show that laser-induced thermal oxidation is a complex dynamic process with the interactions among H, C, O, and Si atoms. The oxidation zone includes an oxide layer, a graphite layer, and a C-rich layer. With an increase in oxygen concentration, the amorphous oxide layer changes from silicon oxide to silicon dioxide. In addition, the formation of carbon clusters at the interface between SiOx and C-rich layers promotes the desorption of the oxide layer. The mechanism revealed in this study provides theoretical guidance for high-quality processing of 4H-SiC at atomic and close-to-atomic scales.

Polishing Approaches at Atomic and Close-to-Atomic Scale.

Roughness down to atomic and close-to-atomic scale is receiving an increasing attention in recent studies of manufacturing development, which can be realized by high-precision polishing processes. This review presents polishing approaches at atomic and close-to-atomic scale on planar and curved surfaces, including chemical mechanical polishing, plasma-assisted polishing, catalyst-referred etching, bonnet polishing, elastic emission machining, ion beam figuring, magnetorheological finishing, and fluid jet polishing. These polishing approaches are discussed in detail in terms of removal mechanisms, polishing systems, and industrial applications. The authors also offer perspectives for future studies to address existing and potential challenges and promote technological progress.

Solid-State Nanopore Array: Manufacturing and Applications.

Nanopore brings extraordinary properties for a variety of potential applications in various industrial sectors. Since manufacturing of solid-state nanopore is first reported in 2001, solid-state nanopore has become a hot topic in the recent years. An increasing number of manufacturing methods have been reported, with continuously decreased sizes from hundreds of nanometers at the beginning to ≈1 nm until recently. To enable more robust, sensitive, and reliable devices required by the industry, researchers have started to explore the possible methods to manufacture nanopore array which presents unprecedented challenges on the fabrication efficiency, accuracy and repeatability, applicable materials, and cost. As a result, the exploration of fabrication of nanopore array is still in the fledging period with various bottlenecks. In this article, a wide range of methods of manufacturing nanopores are summarized along with their achievable morphologies, sizes, inner structures for characterizing the main features, based on which the manufacturing of nanopore array is further addressed. To give a more specific idea on the potential applications of nanopore array, some representative practices are introduced such as DNA/RNA sequencing, energy conversion and storage, water desalination, nanosensors, nanoreactors, and dialysis.

Numerical Analysis of Microchannels Designed for Heat Sinks.

Conjugate heat transfer is numerically investigated using a three-dimensional computational fluid dynamics approach in various microchannel geometries to identify a high-performance cooling method for piezoelectric ceramic stacks and spindle units in high-precision machines. Straight microchannels with rectangular cross sections are first considered, showing the performance limitations of decreasing the size of the microchannels, so other solutions are needed for high applied heat fluxes. Next, many microchannel designs, focusing on streamwise geometric variation, are compared to straight channels to assess their performances. Sinusoidally varying channels produce the highest heat transfer rates of those studied. Thus, their optimization is considered at a channel width and height of 35 and 100 µm, respectively. Heat transfer increases as the amplitude and spatial frequencies of the channels increase due to increased interfacial surface area and enhanced Dean flow. The highest performance efficiencies are observed at intermediate levels of amplitude and frequency, with efficiency decreasing as these geometric parameters are increased further at the onset of flow separation. The sinusoidal channel geometries are then optimized with respect to minimizing the system's pressure drop for all applied heat fluxes between 5690 and 6510 kW/m2. Doing so created an optimal geometry curve and showed that all geometries in this region had amplitudes close to 40 µm. Therefore, imposing a fixed heat flux requirement for a case study of cooling piezoelectric ceramics, the optimized sinusoidal geometry decreases the system pressure drop by 79% relative to a straight channel while maintaining a larger minimum feature size.

Manufacturing of Soft Contact Lenses Using Reusable and Reliable Cyclic Olefin Copolymer Moulds.

We present experimental evidence of reusable, reliable cyclic olefin copolymer (COC) moulds in soft contact lens manufacturing. The moulds showed high performance surface roughness characteristics despite >20 kW exposure to 365 nm ultraviolet (UV) light from repeated use. Ultra-precision manufacturing techniques were used to fabricate transparent COC mould inserts and to produce soft contact lenses from liquid monomer compositions. Both polymer and silicone hydrogels were fabricated with more than 60 individual uses of the moulds. White light interferometry measured the surface roughness (Sa) of the COC moulds to be almost unchanged before and after repeated use (Sa 16.3 nm before vs. 16.6 nm after). The surface roughness of the prototyped lenses and that of commercially available soft contact lenses were then compared by white light interferometry. The surface roughness of the lenses was also nearly unchanged, despite undergoing more than 60 uses of the COC moulds (lens Sa 24.4 nm before vs. after Sa 26.5 nm). By comparison the roughness of the commercial lenses ranged from 9.3−28.5 nm, including conventional and silicone lenses, indicating that the reusable COC moulds produced competitive surface properties. In summary, COC moulds have potential as reusable and reliable mould inserts in the manufacturing of soft contact lenses, yet maintain high quality optical surfaces even after sustained exposure to UV light.

Intelligent evaluation for lens optical performance based on machine vision.

Optical performance evaluation is a critical process in the production of collimating lenses. However, the current visual inspection of lens light-spot images is inefficient and prone to fatigue. Intelligent detection based on machine vision and deep learning can improve evaluation efficiency and accuracy. In this study, a dual-branch structure light-spot evaluation model based on deep learning is proposed for collimating lens optical performance evaluation, and a lens light-spot image dataset is built, containing 9000 images with corresponding labels. Experimental results show that the proposed model achieves accurate classification of lens optical performance evaluation. Combined with the proposed weighted multi-model voting strategy, the performance of the model is further improved, and the classification accuracy successfully reaches 98.89%. Through the developed application software, the proposed model can be well applied to the quality inspection in collimating lens production.