Laser-assisted Chemical Etching Research Articles

Six million Q factor micro fused silica shell resonator with teeth-like tines released by femtosecond laser-assisted chemical etching

Six million Q factor micro fused silica shell resonator with teeth-like tines released by femtosecond laser-assisted chemical etching

Bubble dynamics and speed of jets for needle-free injections produced by thermocavitation.

The number of injections administered has increased dramatically worldwide due to vaccination campaigns following the COVID-19 pandemic, creating a problem of disposing of syringes and needles. Accidental needle sticks occur among medical and cleaning staff, exposing them to highly contagious diseases, such as hepatitis and human immunodeficiency virus. In addition, needle phobia may prevent adequate treatment. To overcome these problems, we propose a needle-free injector based on thermocavitation. Experimentally study the dynamics of vapor bubbles produced by thermocavitation inside a fully buried 3D fused silica chamber and the resulting high-speed jets emerging through a small nozzle made at the top of it. The injected volume can range from to per shot. We also demonstrate that these jets have the ability to penetrate agar skin phantoms and ex-vivo porcine skin. Through the use of a high-speed camera, the dynamics of liquid jets ejected from a microfluidic device were studied. Thermocavitation bubbles are generated by a continuous wave laser (1064nm). The 3D chamber was fabricated by ultra-short pulse laser-assisted chemical etching. Penetration tests are conducted using agar gels (1%, 1.25%, 1.5%, 1.75%, and 2% concentrations) and porcine tissue as a model for human skin. High-speed camera video analysis showed that the average maximum bubble wall speed is about 10 to 25m/s for almost any combination of pump laser parameters; however, a clever design of the chamber and nozzle enables one to obtain jets with an average speed of . The expelled volume per shot (0.1 to ) can be controlled by the pump laser intensity. Our injector can deliver up to 20 shots before chamber refill. Penetration of jets into agar of different concentrations and ex-vivo porcine skin is demonstrated. The needle-free injectors based on thermocavitation may hold promise for commercial development, due to their cost and compactness.

Optimization of fs + ps double-pulse sequence parameters for laser-assisted chemical etching of microchannels in fused silica

Developing laser fabricating technology to improve the etching rate of microchannels is of great significance for the development of microfluidic devices. In this paper, the laser processing parameters of the fs + ps double-pulse sequence, including temporal delay and pulse energy ratio, have been investigated to optimize the fabrication of microchannels, in order to obtain a high etching rate. As a result, the optimal energy ratio could be obtained at Efs:Eps = 2:1 in negative delays. Furthermore, the etching rate of microchannels was significantly improved by 40.8% compared with those written by fs + fs double-pulse sequence with an energy ratio of 1:1. This improvement is possibly because fs sub-pulse excited seed electron may trigger impact ionization via an efficient energy absorption process within the following ps sub-pulse, this energy accumulation and subsequent thermal diffusion lead to an increase of the modified area. The aforementioned results possibly offer an effective route to improve the etching rate of microchannels which is in favor of accelerating the fabrication of three-dimensional microfluidic devices.

Hyperdoping-regulated room-temperature NO2 gas sensing performances of black silicon based on lateral photovoltaic effect

Black silicon co-hyperdoped with sulfur and nitrogen in different ratios is prepared by femtosecond laser-assisted chemical etching in the mixed atmosphere of SF6 and NF3 with varying gas pressure ratios. Their room-temperature NO2 gas sensing capability is studied systematically, in which the photocurrent as a readout signal is generated by the lateral photovoltaic effect of black silicon under an asymmetrical light illumination. These co-hyperdoped black silicon exhibits high response, fast response/recovery, ultrawide detection range from 29 ppb to 2000 ppm, excellent selectivity and acceptable long-term durability over 3 months. Moreover, NO2 gas sensing performances are effectively tuned or optimized by deliberately changing the co-doping ratio of sulfur and nitrogen, as different photovoltaic characteristics are induced by changes in morphology and structural defects resulting from different hyperdoping. Specifically, ultra-high relative gas response (∼3955%@20 ppm NO2) and superior selectivity are obtained at the SF6/NF3 pressure ratio of 56/14, while faster response/recovery time (17 s/ 47 s @ 20 ppm NO2) and response photocurrent with a weaker disturbance by humidity are given by the samples with SF6/NF3 of 7/63 and 63/7, respectively. Therefore, such black silicon material has good potential to meet different application needs.

Polarization-independent microchannel in a high-speed-scan femtosecond laser-assisted etching of fused silica.

Microchannels fabricated by femtosecond laser-assisted chemical etching are of great use in biochemical analysis. In this paper, we study the morphology change of etched microchannels in fused silica by controlling the laser scan speed, and we find a significant difference between the chemical etched length and volume. The fabricated microchannels would gradually become tapered along the scan direction, which influences the flow of the hydrofluoric (HF) reagent and the etching rate. As a result, the difference ratios of the etched length and volume, respectively, reach -5.56% and -41.83% followed by the scan speed increasing from 5 to 200µm/s. Microchannels with polarization independence and better aspect ratio could be obtained in a high-speed-scan mode. We suggest that laser-induced structural transformation from interconnected microcracks to nanogratings could be responsible for this change. Aforementioned results offer a feasible approach to achieve polarization-independent microchannels, which is in favor of accelerating the fabrication of three-dimensional microfluidic devices.

Manufacture of Three-Dimensional Optofluidic Spot-Size Converters in Fused Silica Using Hybrid Laser Microfabrication

We propose a hybrid laser microfabrication approach for the manufacture of three-dimensional (3D) optofluidic spot-size converters in fused silica glass by a combination of femtosecond (fs) laser microfabrication and carbon dioxide laser irradiation. Spatially shaped fs laser-assisted chemical etching was first performed to form 3D hollow microchannels in glass, which were composed of embedded straight channels, tapered channels, and vertical channels connected to the glass surface. Then, carbon dioxide laser-induced thermal reflow was carried out for the internal polishing of the whole microchannels and sealing parts of the vertical channels. Finally, 3D optofluidic spot-size converters (SSC) were formed by filling a liquid-core waveguide solution into laser-polished microchannels. With a fabricated SSC structure, the mode spot size of the optofluidic waveguide was expanded from ~8 μm to ~23 μm with a conversion efficiency of ~84.1%. Further measurement of the waveguide-to-waveguide coupling devices in the glass showed that the total insertion loss of two symmetric SSC structures through two ~50 μm-diameter coupling ports was ~6.73 dB at 1310 nm, which was only about half that of non-SSC structures with diameters of ~9 μm at the same coupling distance. The proposed approach holds great potential for developing novel 3D fluid-based photonic devices for mode conversion, optical manipulation, and lab-on-a-chip sensing.

Low-loss optofluidic waveguides in fused silica enabled by spatially shaped femtosecond laser assisted etching combined with carbon dioxide laser irradiation

We demonstrate the fabrication of low-loss optofluidic waveguides encapsulated in fused silica glass using femtosecond laser microfabrication followed by carbon dioxide laser irradiation. Spatially-shaped femtosecond laser-assisted chemical etching is first used to fabricate microchannels with circular cross-sections and a string of open extra-access ports in the glass. Further, the carbon dioxide laser direct writing on the glass surface is used to create a thermal reflow effect of etched glass microstructures for simultaneously polishing all internal surfaces of channels and sealing the extra-access ports. With this effect, the inner surface roughness of the etched microchannels can be reduced to ∼ 40 nm. Finally, a single-mode microfluidic optical waveguide with a propagation loss of ∼ 0.78 dB/cm at 1310 nm is obtained inside the glass by filling a mixture solution of decane and liquid paraffin into a laser-polished microchannel.

A micro gas chromatography column fabricated by ultrafast laser-assisted chemical etching

A novel micro gas chromatography column (μGCC) with straight-sided elliptic microchannel cross sections was prepared by ultrafast laser-assisted chemical etching inside a glass substrate. The straight-sided elliptic cross sections resulted in a uniform distribution of the flow velocity field. This uniform distribution and the use of a microchannel with a consistent composition led to a uniform stationary phase coating. Upon the separation of a test mixture of C7–C11 alkanes, highly symmetrical chromatographic peaks were obtained. The tailing factors of the chromatographic peaks ranged from 0.95 to 1.05, which satisfies the relevant provisions of Pharmacopoeia of the People's Republic of China (ChP). The test results show that the improvement of the tailing factors is mainly due to the optimization of the cross-section structure rather than the optimization of the test conditions. Notably, due to the simple preparation processes and the low cost of the glass substrate, the total manufacturing cost of this novel μGCC is low.

A Volume-Tuning Capillary Gripper That Enhances Handling Capabilities and Enables Testing of Micro-Components.

Capillary forces are shown to be extremely effective for micro-assembly and pick-and-place processes, especially for their ability to self-align the handled objects. However, in today’s machines, micro-objects are submitted to high loads, such as compressions for the electrical testing of the micro-components, or inertial forces coming from the high accelerations of the machines. There, capillary grippers may show some limits. These issues, as well as the difficulty to perform precise visual inspections (due to the tilt of the handled micro-object that can occur after a perturbation, such as the displacement of the gripper), can all be solved by temporarily removing the liquid meniscus. Therefore, we present a novel volume-tuning capillary gripper that provides a solution to these limitations without adding additional significant complexities or changes to the existing pick-and-place machines. A multi-scale prototype was dimensioned and produced by using fast prototyping methods, such as a femtosecond laser-assisted chemical etching process for fused silica. Models bringing a deeper understanding of the subsystems are presented. The proof of concept was extensively tested. Its picking capabilities and enhancements of the handling capabilities during horizontal motions, as well as the repeatability of the tuning of the volume of liquid, are presented.

Glass Surface Modification Was Induced by the Combination of Coating Technology and Femtosecond Laser Assisted Chemical Etching

Due to its high hardness and high transmittance, ultra-white glass has a strong application prospect in the fields of optoelectronics industry and experimental instruments. However, because of its brittleness, it was still a difficult problem in the machining industry. Surface modification provides a basic research idea for ultra-white glass microstructure processing. An effective method to obtain surface modified area on ultra-white glass was presented. The modified zone on the surface of ultra-white glass was induced by the technique of coating and femtosecond laser-assisted chemical etching. The method combines vacuum coating with femtosecond laser irradiation. Next, the modified glass was processed with highly selective potassium hydroxide solution. In order to control the surface size more efficiently, the optimization experiment of laser parameters and chemical parameters on the machining process was carried out. The experimental results show that the method made the surface modification of ultra-white glass more easily and provides basic research for fabricating microchannels on the material.

Etch the borosilicate glass to form a straight through-glass-via based on the FLACE technology

Interposers will become in demand for advanced electronic systems and through the substrate, vias are essential for 3D integration. A straight via is necessary because a tapered hole is accompanied by large signal loss. This article reports a straight through-glass-via (TGV) fabricated by femtosecond laser-assisted chemical etching (FLACE). The femtosecond laser was used to modify the glass substrates, and the modified glass samples were etched with hydrofluoric acid (HF) solution to form TGV. The effects of key processing parameters, including laser pulse energy, the number of burst pulses, and the HF solution concentration, on the TGV taper profile, were systematically investigated. It was found that The TGV taper sidewall angle decreases with increasing laser pulse energy and increases with increasing HF solution concentration. The number of bursts should be optimized because more than 10 bursts would prevent TGV formation. The study shows via etched in 3 wt% HF after irradiation with 3 bursts of 60 μJ can become approximately vertical. Among the three processing parameters, HF concentration was found to be the most crucial parameter. This work can serve as a critical reference for applications of TGV in high-performance 3D integrated circuits.

Glass-in-glass infiltration for 3D micro-optical composite components.

Chalcogenide glass exhibits a wide transmission window in the infrared range, a high refractive index, and nonlinear optical properties; however, due to its poor mechanical properties and low chemical and environmental stability, producing three-dimensional microstructures of chalcogenide glass remains a challenge. Here, we combine the fabrication of arbitrarily shaped three-dimensional cavities within fused silica molds by means of femtosecond laser-assisted chemical etching with the pressure-assisted infiltration of a chalcogenide glass into the resulting carved silica mold structures. This process enables the fabrication of 3D, geometrically complex, chalcogenide-silica micro-glass composites. The resulting products feature a high refractive index contrast that enables total-internal-reflection guiding and an optical quality roughness level suited for applications in the infrared.

High-Uniformity Submicron Gratings with Tunable Periods Fabricated through Femtosecond Laser-Assisted Molding Technology for Deformation Detection.

As one of the important diffractive optical elements, the submicron gratings on flexible substrates can actively and precisely control the dispersion and steering characteristics of beams and have been widely applied in deformation detection technologies. Herein, we propose a spatially modulated femtosecond laser-assisted molding technology for efficiently fabricating high-uniformity large-area submicron gratings with tunable periods on flexible substrates. The technology first uses a cylindrically focused femtosecond laser-assisted chemical etching method to form a regular submicron grating on silicon; subsequently, the structure is cast with polydimethylsiloxane, a useful flexible substrate with a small Young's modulus, and cured to obtain a high-uniformity large-area submicron grating with a tunable period. The grating exhibits high mechanical stability and sensitivity and favorable optical properties. In the present study, as the deformation of the grating increased from 0 to 10%, the diffraction angle changed by 6.5°. Under illumination by a broad-band white-light source, distinguishable multicolor diffraction patterns were clearly observed. Drawing on this characteristic, we fabricated a deformation sensor. The grating fabricated by using the proposed technology also has potential applications in optical sensors and soft robots.

Three-Dimensional Large-Scale Fused Silica Microfluidic Chips Enabled by Hybrid Laser Microfabrication for Continuous-Flow UV Photochemical Synthesis.

We demonstrate a hybrid laser microfabrication approach, which combines the technical merits of ultrafast laser-assisted chemical etching and carbon dioxide laser-induced in situ melting for centimeter-scale and bonding-free fabrication of 3D complex hollow microstructures in fused silica glass. With the developed approach, large-scale fused silica microfluidic chips with integrated 3D cascaded micromixing units can be reliably manufactured. High-performance on-chip mixing and continuous-flow photochemical synthesis under UV irradiation at ~280 nm were demonstrated using the manufactured chip, indicating a powerful capability for versatile fabrication of highly transparent all-glass microfluidic reactors for on-chip photochemical synthesis.

High-Throughput Continuous-Flow Separation in a Micro Free-Flow Electrophoresis Glass Chip Based on Laser Microfabrication.

Micro free-flow electrophoresis (μFFE) provides a rapid and straightforward route for the high-performance online separation and purification of targeted liquid samples in a mild manner. However, the facile fabrication of a μFFE device with high throughput and high stability remains a challenge due to the technical barriers of electrode integration and structural design for the removal of bubbles for conventional methods. To address this, the design and fabrication of a high-throughput μFFE chip are proposed using laser-assisted chemical etching of glass followed by electrode integration and subsequent low-temperature bonding. The careful design of the height ratio of the separation chamber and electrode channels combined with a high flow rate of buffer solution allows the efficient removal of electrolysis-generated bubbles along the deep electrode channels during continuous-flow separation. The introduction of microchannel arrays further enhances the stability of on-chip high-throughput separation. As a proof-of-concept, high-performance purification of fluorescein sodium solution with a separation purity of ~97.9% at a voltage of 250 V from the mixture sample solution of fluorescein sodium and rhodamine 6G solution is demonstrated.

Fabrication of a Chalcogenide Glass Microlens Array for Infrared Laser Beam Homogenization.

Infrared (IR) microlens arrays (MLA) have attracted increasing interest for use in infrared micro-optical devices and systems. However, the beam homogenization of IR laser light is relatively difficult to achieve because most materials absorb strongly in the IR wavelength band. In this paper, we present a new method for the application of double-sided quasi-periodic chalcogenide glass (ChG) MLAs to infrared laser homogenization systems. These are non-regular arrays of closely spaced MLAs. The double-sided MLAs were successfully prepared on the ChG surface using a single-pulse femtosecond laser-assisted chemical etching technique and a precision glass molding technique. More than two million close-packed microlenses on the ChG surface were successfully fabricated within 200 min. By taking advantage of ChG’s good optical performance and transmittance (60%) in the infrared wavelength band (1~11 μm), the homogenization of the IR beam was successfully achieved using the ChG quasi-periodic MLA.

Laser multifunctional fabrication of metallic microthermal components embedded in fused silica for microfluidic applications

Microheaters as tiny in-situ heating elements are of great importance for developing many thermal-sensitive microdevice applications. A facile technique for the fabrication of embedded metallic microheaters, microheater arrays, and microthermal sensors based on the combination of femtosecond laser-assisted chemical etching, electroless plating, and mechanical polishing has been proposed. With the proposed technique, uniform and controllable temperature distributions in the central area of fabricated microheaters have been achieved. Moreover, flexible manipulation of localized temperature in a microheater array as well as precise calibration of microheaters based on a simultaneously integrated microthermal sensor has been demonstrated. Furthermore, precise control of temperature in glass channels and acceleration of a chemical reaction in microfluidics using monolithically integrated microheaters have been realized, showing great potential for developing laser manufacturing of multifunctional thermal-control microfluidic devices.

Microscale patterning of semiconductor c-Si by selective laser-heating induced KOH etching

Laser patterning has been used for the micro-scale fabrication of semiconductor devices like solar cells, photodetectors, LEDs, and also for modification of surfaces for wettability, reflected colors, initial bacterial adhesion, etc, due to its several advantages of patterning flexibility, spatial resolution, and mask-free operation over complex conventional lithography. Currently, laser-induced ablation is a promising patterning method in silicon solar cell fabrication; however, laser-induced defects, and thermal stresses remain a significant concern. In this paper, we demonstrate a laser ablation-free method for patterning c-Si based on the observation that the anisotropic etching of c-Si by KOH is highly temperature-dependent as the etching rate is about 100 times faster at 80 °C compared to room temperature. The laser heating-induced chemical etching (LHICE) of crystalline silicon can help alleviate such laser-induced damage by providing the necessary low temperature on the localized area(s) on the silicon substrate. We investigated the micro-second pulsed laser-assisted chemical etching of c-Si substrate for microscale patterning and showed that laser-induced damage could be eliminated as indicated by the minority carrier lifetime preservation. We also present results of the effect of laser processing parameters such as laser power, scan speed, and duty cycle on etching depth and surface morphology. The optical, surface morphology, depth profile, and LCPSim simulation results are also presented to optimize and understand the LHICE process. This versatile methodology of temperature-selective chemical etching could be applied to various thin-film and bulk materials used in diverse device fabrication.

Elliptical Microlens Fabrication by Spatially Shaped Femtosecond Laser-assisted Chemical Etching

We proposed a promising method for fabricating elliptical microlens and microlens array with controlling morphology by slit-based spatially shaped femtosecond laser-assisted chemical etching on fused silica (SiO2). The major axis length and the ratio of major and minor axis were controlled by changing the slit width. The minor axis length was controlled by changing the energy. This method had good flexibility and high efficiency. The convex elliptical microlens and microlens array were also realized by mold replication.

Attomolar Sensing Based on Liquid Interface-Assisted Surface-Enhanced Raman Scattering in Microfluidic Chip by Femtosecond Laser Processing.

Surface-enhanced Raman scattering (SERS) is a multidisciplinary trace analysis technique based on plasmonic effects. The development of SERS microfluidic chips has been exploited extensively in recent times impacting on applications in diverse fields. However, despite much progress, the excitation of label-free molecules is extremely challenging when analyte concentrations are lower than 1 nM because of the blinking SERS effect. In this paper, a novel analytical strategy which can achieve detection limits at an attomolar level is proposed. This performance improvement is due to the use of a glass microfluidic chip that features an analyte air-solution interface which forms on the SERS substrate in the microfluidic channel, whereby the analyte molecules aggregate locally at the interface during the measurement, hence the term liquid interface-assisted SERS (LI-SERS). The microfluidic chips are fabricated using hybrid femtosecond (fs) laser processing consisting of fs laser-assisted chemical etching, selective metallization, and metal surface nanostructuring. The novel LI-SERS technique can achieve an analytical enhancement factor of 1.5 × 1014, providing a detection limit below 10-17 M (<10 aM). The mechanism for the extraordinary enhancement afforded by LI-SERS is attributed to Marangoni convection induced by the photothermal effect.