SU-8 Photoresist Research Articles

Generation of arbitrarily patterned polarizers using 2-photon polymerization

Patterned polarizers are prepared using liquid crystals (LC) doped with a black dichroic dye and in combination with a linear polarizer. The pattern is achieved with a nanostructured LC alignment surface, that is generated using a two-photon polymerization direct laser write (2PP-DLW). This technique creates a pattern of high-resolution grooves in the photoresist at any arbitrary angle. The angle governs the LC orientation at any substrate surface point, determining the transmitted light linear polarization angle. This paper presents the first use of a 2PP-DLW cured positive tone photoresist for dichroic dye-doped LC alignment. Two complementary photoresists have been employed: conventional negative tone SU-8 photoresist and, in this context novel, positive tone S1805 photoresist. The alignment quality of the polarizers has been assessed by analyzing the transmission using an additional polarizer. For SU-8, the resulting grayscale pattern and a contrast ratio (CR) of 14 has measured. The uniformity of the alignment has been measured to be 65% using normalized Shannon entropy (H). For S1805, a CR of 37 was measured, and a uniformity of 63% was obtained. 2PP-DLW allows for shaping complex patterns in submicron dimensions and for the fabrication of arbitrarily patterned polarizers and other LC devices.

Inkjet-Assisted Electroforming of Magnetically Guidable Devices for Interfacial Microfluidic Manipulation

In the last few decades, inkjet printing (IJP) evolved into a versatile manufacturing technique able to find application in a great number of industrial fields (e.g. electronics, display production, flexible devices). Thanks to its scalability and efficiency, IJP proved to be one of the most promising technologies to pattern materials on a wide variety of rigid and flexible substrates. Recently, it also found application in the field of microfabrication. It was employed, for example, to manufacture microelectromechanical systems (MEMS) [1] or microelectronic components and sensors [2]. Another possible application of IJP, still not developed in the existing literature, is the production of magnetically guidable microrobots [3]. These can find application in a wide variety of fields, including for example micromanipulation, cell transport and drug delivery applications.Many applications of IJP in microfabrication, and microrobots production in particular, require the presence of conductive or magnetic layers to allow actuation or sensing. By directly employing IJP, however, it is difficult to obtain highly conductive and mechanically stable layers. From this point of view, the variety and the performances of IJP printed conductive and magnetic materials are in many cases limited. To expand IJP applicability to micromanufacturing, we developed a novel approach to indirectly pattern bulk metallic microstructures by combining IJP printing and electroforming. Initially, a layer of SU-8 photoresist is IJP printed [4] on a conductive substrate to form a negative of the final pattern. The positive pattern is then growth by means of electrodeposition inside this negative SU-8 pattern. SU-8 is finally removed, leaving an indirectly printed metal pattern. It is also possible to dissolve the substrate in a suitable aggressive solution, leaving thus freestanding electroformed planar structures.In the present work, the technique described is applied to the microfabrication of untethered functional microdevices inspired to the shape and behavior of water-striders (Gerridae) [5]. These insects exploit water surface tension to walk on the surface of shallow lakes and ponds. Taking inspiration from Gerridae, micromachined devices able to move on the air-water interface were developed. A stack of three metallic layers (Cu, NiFe, Cu) was electrodeposited inside a SU-8 pattern. The substrate was subsequently dissolved, releasing thus the electroformed microdevices. These were actuated by applying a controlled magnetic field gradient and they proved able to manipulate droplets of fluids floating at the air-water interface. Moreover, the possibility to carry out microreactions by merging droplets in a controlled way was demonstrated as well.[1] R. Bernasconi et al., Micromachines 14, 2082 (2023)[2] N. K. Mani et al., “Bioelectrochemical Interface Engineering”, chapter 19, John Wiley & Sons (2020)[3] S. Palagi et al., Nat. Rev. Mater. 3(6), 113 (2018)[4] R. Bernasconi et al., Polymer 185, 121933 (2019)[5] R. Bernasconi et al., ACS Appl. Mater. Interfaces 15, 2396-2408 (2023)

High Q factor of photonic cavity with SU-8 photoresist micro-disk for electromagnetic wave control

How to control electromagnetic wave effectively is the key to the realization of applicable filters in many optics technologies. In our work, a SU-8 photoresist micro-disk is written onto a photonic crystal waveguide to control electromagnetic wave. Corresponding simulation and experiment shows that, the quality Q increases as the thickness of SU-8 smaller. When the thickness exceeds 400 nm, the change of thickness has little influence on electromagnetic waves. Besides, the increase of the radius of disc-shaped SU-8 can also increase the Q value. By optimizing the simulation and experimental data, we can successfully create a SU-8 photoresist micro-disk cavity with the thickness of 5 µm and height of 20 nm, the quality factor of Q can reach 8200. However, longer exposure time and more stable experimental equipment is needed if we want to get a larger radius. The method in our work by using SU-8 photoresist micro-disk on photonic crystals to control electromagnetic wave is more practical and flexible, which can provide new significance for research into optical filter.

Efficient fabrication of high quality SU-8 photoresist based microsphere lasers via emulsion

SU-8 photoresist is a highly important material in the field of microfabrication and photonics owing to its low cost, excellent chemical and mechanical durability, high refractive index and transparency in the visible range. As a result, SU-8 photoresist has been employed as a cavity matrix for microsphere lasers. However, the current fabrication technique of SU-8 based microsphere lasers is complex and time-consuming. Here, we demonstrate a novel, cost-effective fabrication method for dye-doped SU-8 microspheres with diameters ranging from about 15–100 µm. These microspheres exhibit efficient lasing emission under optical pulse excitation. Lasing thresholds of 20–30 µJ mm−2 and quality factors ranging from 1500 to 3000 are achieved. The size dependence of lasing characteristics indicates that the lasing mechanism is due to whispering gallery mode. Interestingly, these microsphere lasers can work in water, presenting promising application prospects in the fields of biological and chemical sensors.

Fabrication of pyrolytic carbon interdigitated microelectrodes by maskless UV photolithography with epoxy-based photoresists SU-8 and mr-DWL

Maskless UV photolithography is increasingly used, especially in research environments where low turn-around time for new designs improves productivity. Here, we fabricate pyrolytic carbon interdigitated microelectrodes with small interelectrode gaps, good adhesion to the carrier substrate, high surface area and excellent electrochemical properties using maskless UV photolithography with two negative epoxy-based photoresists, namely the commonly used SU-8 and the recently developed mr-DWL. The minimum realizable trench width in 15 μm thick photoresist films is 2.4 ± 0.15 μm for mr-DWL 5 and 3.1 ± 0.10 μm for SU-8 2035. After pyrolysis, the two resulting pyrolytic carbon materials show similar electrochemical properties. However, shrinkage during pyrolysis is significantly lower for mr-DWL compared to SU-8, which is beneficial for the fabrication of interdigitated microelectrodes. Furthermore, delamination of the electrodes during processing and operation is prevented due to the introduction of poly silicon adhesion structures. This work provides valuable insights into maskless UV lithography as well as into the pyrolytic carbon process to increase the yield, performance and productivity for fabrication of microelectrodes.

Design of a multi-physics coupling MEMS pressure sensor

The pressure measurement of explosion shock wave puts forward high requirements on the temperature resistance and response speed of the sensor. In this paper, a multi-physics coupling pressure sensor is designed to meet requirements. The sensor mainly consists of a Fabry-Perot cavity optical fiber sensing unit, a piezoelectric pressure sensing unit and a thermometric resistance temperature measurement module. Firstly, the structure of the sensor is designed. The top and bottom surfaces of the Fabry-Perot cavity are composed of a silicon diaphragm and a quartz glass. The piezoelectric pressure sensing unit is an AlN film including its electrodes. Pt thermometric resistance is developed to realize real-time temperature monitoring. Secondly, the fabrication process of the sensor is discussed, especially three key technologies. An Al film is sputtered to increase the reflectivity of the quartz glass. The SU-8 photoresist is applied to accurately control the thickness of Fabry-Perot cavity. Etching is adopted to work out the graphics of the AlN piezoelectric film. At last, a complete fabrication process of the sensor is described. The fabrication of multilayer films begins with a double-sided polishing silicon wafer, while Fabry-Perot cavity was from a double-sided polishing quartz glass. Then two parts of the sensor are combined to ensure the multi-physics coupling sensor to achieve complete function.

Fabrication of NdFeB micromagnets based on vacuum negative pressure injection

Micromagnets integrated into microelectromechanical systems devices are widely used in the fields of micro-energy harvesters, micro-actuators, and speakers. A novel method for fabricating NdFeB micromagnets based on vacuum negative pressure injection is presented. The influence of array element shape, size, and injection channel on the surface magnetic field was studied by Maxwell finite element analysis. A circle array of 600 µm diameter and 150 µm spacing could generate a stronger magnetic field at the edge of the magnet array. Micron-sized magnetic powders with a diameter of 5 µm mixed with the SU8 T2010 photoresist were filled into the microcavity on a PDMS (polydimethylsiloxane) elastomer, which was prepared by the SU8 positive membrane. The PDMS elastomer was bonded to the glass substrate and degassed by a vacuum pump to form negative pressure for rapid injection and uniform filling. By selecting a suitable binder and optimizing the mixing ratio of the magnetic powder, a 165 µm thick micromagnet with homogeneous dispersion of magnetic powder particles was achieved, and the weight percentage of magnetic powder in the SU8 photoresist was 41.8%. The remanent magnetization of micromagnets was 42 emu/g, the coercivity was 6895 Oe, and the maximum surface magnetic field strength was 1.3 mT after magnetization in a 2 T uniform magnetic field. Finally, the micromagnet array was utilized in a cantilever beam micro-actuator, which could drive the cantilever beam and exhibit an excellent linearity.

Exposure and post-bake thermal treatment in one step for SU8 photoresist

This work demonstrates an effect which would allow a reduction in the number of baking steps in a post-development process for a system consisting of the SU8 photoresist with nanoparticles, in which up-conversion luminescence can be excited. Traditionally, writing structures in photoresists involves several steps, e.g. the I-line method requires a UV light source as the writing element, and several bake procedures (post-bake and hard-bake) in the post-development process. Photoresist mixed with nanoparticles (e.g. NaYF4 doped with Tm3+ and Yb3+) makes it possible to use up-conversion luminescence, which opens up new opportunities in photolithography. One opportunity includes recording structures by means of up-conversion luminescence using nanoparticles mixed into the photoresist as a UV light source. However, this work is related to another possibility: the reduction of the number of bake procedures in the post-development process when the structures in the SU8 photoresist are mixed with nanoparticles (NaYF4:Tm3+:Yb3+) that emit visible and ultraviolet light under infrared excitation. It will be shown that NaYF4:Tm3+:Yb3+ nanoparticles act not only as a UV light source, but also as local heaters. Such a double application allows to record structures and thermally fix them simultaneously while retaining the physical properties, which were evaluated using structure hardness measurements and dissolution experiments with two type of solvents (2-propanol and acetone)

An optoelectronic Coupler based on graphene patterns and SU-8 photoresist

PurposeThe purpose of this research is to efficiently separate incident terahertz (THz) waves into distinct transmission and reflection channels by minimizing the absorption ratio. So, the optical systems operating within the THz frequency range can developed. To achieve a multi-band response, four different periodic arrays of graphene patterns are used. These arrays are strategically stacked on both sides of three SU-8 photoresists, serving as dielectric materials. Consequently, each layer exhibits a unique influence on the device's response, and by applying four external bias voltages, the behavior of the device can be precisely controlled and adjusted.Design/methodology/approachA novel optoelectronic device operating in the THz frequency range is introduced, using periodic arrays of graphene patterns and SU-8 photoresist dielectrics. The design of this device is based on meta-surface principles, using both the equivalent circuit model (ECM) and transmission line concept. The output of the device is a THz coupler implemented by analyzing the reflection and transmission channels. The structure is characterized using the ECM and validated through comprehensive full-wave simulations. By representing the electromagnetic phenomenon with passive circuit elements, enabling the calculation of absorption, reflection and transmission through the application of the theory of maximum power transfer.FindingsBased on simulation results and theoretical analysis, the proposed device exhibits sensitivity to gate biasing, enabling efficient reflection and transmission of THz waves. The device achieves reflection and transmission peaks exceeding across the five distinct THz bands 90%, and its behavior can be tuned by external gate biasing. Moreover, the device's sensitivity to variations in geometrical parameters and chemical potentials demonstrates its reliable performance. With its outstanding performance, this high-performance meta-surface emerges as an ideal candidate for fundamental building blocks in larger optical systems, including sensors and detectors, operating within the THz frequency band.Originality/valueThe proposed device covers a significant portion of the THz gap through the provision of five adjustable peaks for reflection and transmission channels. Additionally, the ECM and impedance matching concept offers a simplified and time-efficient approach to designing the meta-surface. Leveraging this approach, the proposed device is effectively represented using passive circuit elements such as inductors, capacitors and resistors, while its performance is validated through the utilization of the finite element method (FEM) as a full-wave simulation tool. This combination of circuit modeling and FEM simulation contributes to the robustness and accuracy of the device's performance evaluation.

Fabrication and Characterization of 2D Nonlinear Structures Based on DAST Nanocrystals and SU-8 Photoresist for Terahertz Application.

We demonstrate a method for the realization of highly nonlinear optical 4-(4-dimethylaminostyryl)- 1-methylpyridinium tosylate (DAST) two-dimensional structures by a double-step technique. The desired polymeric structures were first fabricated by using the multiple exposure of the two-beam interference technique, and the DAST nanoscrystals were then prepared inside the air-voids of these photoresist templates, resulting in nonlinear periodic structures. The nonlinear properties were characterized by optical and scanning microscopies, as well as by second-harmonic generation technique. This nonlinear modulation is very promising for the enhancement of nonlinear conversion rates, such as terahertz generation, by using the quasi-phase matching technique.

Novel Method for Development of Nanobubbles with Consistent Size Distribution

Background/Objective:Ultrasound is a versatile non-invasive clinical tool that can be used for monitoring, diagnosis, and management of disease. Contrast-Enhanced Ultrasound (CEUS) takes advantage of microbubbles which are small gas filled bubbles made of lipids to image and evaluate functioning of organs such as the heart, liver, and kidneys. CEUS is better for assessing vascularization of tissues compared to US. However, ultrasound contrast agents have been limited by their size and cannot extravasate blood vessels easily. Current methods also have high polydispersity. We hypothesize that a microfluidic device could deliver nanobubbles with improved size distribution by mixing through micro sized pores.
 Methods:The microfluidic device was fabricated using 3D printing for a proof of concept and photolithography for functional use and was done in a class 1-10-100-1000 cleanroom. SU-8 photoresist was spun onto a 4” silicon wafer at 3000 rpm for 30 seconds. The silicon wafer was then baked and exposed under UV with a photomask designed on AutoCAD. The wafer was then developed, hard baked, and was cross linked with Polydimethylsiloxane (PDMS).
 Results:Dynamic light scattering data of a shaken formulation shows a monodisperse distribution. Further work will have to be done to determine if this can be delivered by microfluidic device and the parameters that affect size and polydispersity.
 Conclusion and Potential Impact:This study will determine the parameters needed for the microfluidic device to efficiently create microbubbles for contrast enhanced ultrasound.

(Invited) Fabriations and Applications Using Liquid Metal Towards Stretchable Electronics

Highly deformable devices have many potential applications, including wearable electronics, robotics and health monitoring. Mechanically deformable devices and sensors can conformally cover electronic systems on curved or soft surfaces. Liquids deform more easily than solids, so sensors and actuators that utilise liquids trapped in soft templates as sensing components are ideal platforms for such applications. Such highly deformable electronics using ultra-flexible conductive materials are called stretchable electronics. Liquid metals (LMs) are one of the leading materials. In the last few years, liquid metals have steadily gained interest, especially in the field of flexible soft electronics and related applications. The term liquid metal has several definitions and many research efforts are underway to utilise liquid metals in various fields. The simplest definition can be given as 'a composite of low-melting alloys that retain their liquid state at room temperature, are easily deformable and have high electrical conductivity'. Here, an overview of liquid metals, new processing methods, sensors and actuators, batteries and smart devices are reported in focus.To date, we have adopted a patterned method using microfluidic channels with regard to processing methods for liquid metals such as EGaIn and Galinstan. Microfluidic channels are one of the most accurate and reliable method of producing electrode patterns among the three processing methods, although they are limited by the substrate material and pattern design for pattern fabrication. The creation of microfluidic channels follows the method used in Micro Electro Mechanical Systems (MEMS) and micro Total Analysis Systems (microTAS). In practice, the molds are fabricated by photolithography using SU-8 photoresist. Rubber materials such as polydimethylsiloxane (PDMS) are poured into the mold and allowed to cure. Microfluidic channels are fabricated by chemically bonding the flat PDMS with the PDMS to which the pattern has been transferred. We have succeeded in fabricating a two-dimensional pattern of liquid metal by the method described above. Furthermore, we have successfully fabricated microfluidic channels by 3D printing of rubber materials and constructed 3D circuits by using liquid metal. As liquid metal is a liquid material, processing methods centred on "printing" processing can be used, and the most suitable processing method can be selected according to the device and application.Physical sensors such as strain sensors and chemical sensors such as oxygen gas sensors have been reported using liquid metal wiring. By optimising the wiring of the liquid metal, capacitor structures and resistors can be fabricated. By encapsulating these in a flexible material, PDMS, it is possible to realize sensors that can measure displacements such as strain. Indeed, by optimising three sensor structures, we have reported a physical sensor capable of sensing three sensing modes: two-dimensional tension and vertical compression. However, taking into account the actual application in wearable devices for healthcare applications such as pulse rate, a detection sensitivity below 1 k Pa is required. The authors realized a high-sensitivity pressure sensor by using a Wheatstone bridge circuit structure for the liquid metal wiring in the PDMS to form a Diaphragm sensor. In fact, a pulse rate sensing device was realized based on the developed device. Furthermore, a PDMS glove capable of measuring 16 points simultaneously was realized by attaching the developed pressure sensor to a hand mold using 3D printing5).Such physical sensors are very easy to construct and can be realized with one type of liquid metal. While there are many different types of liquid metals as described above, liquid metals easily mix when they come into contact with each other. Therefore, the authors proposed a "liquid" state heterojunction using ionic liquids and liquid metals with extremely low vapor pressure. By using ionic liquids [EMIM][Otf], [EMIM][PF6] and [EMPYR][NTf2], sensors for temperature, humidity and oxygen gas were realized. Furthermore, with regard to their sensitivity, the detection sensitivity was 10 times higher than that of normal metal temperature and humidity sensors for temperature and humidity sensors. In this study, heterojunctions were realized using microfluidics. Due to the low Reynolds number of the microfluidics, the robustness of the liquid state heterojunction with respect to deformation was also very high due to the high viscosity effect, making the configuration suitable for stretchable sensors. In addition to electrodes and sensors, development of batteries and smart devices has also been initiated and will be reported in this presentation.

Fabrication of High Aspect Ratio Nano-Channels by Thermal Nano-Imprinting and Parylene Deposition.

A low-cost method of fabrication of high aspect ratio nano-channels by thermal nano-imprinting and Parylene deposition is proposed. SU-8 photoresist nano-channels were first manufactured by thermal nano-imprinting, and Parylene deposition was carried out to reduce the width of the nano-channels and increase the aspect ratio. During the process, the side walls of the SU-8 nano-channels were covered with the Parylene film, reducing the width of the nano-channels, and the depth of the channels increased due to the thickness of the Parylene film deposited on the surface of the SU-8 nano-channels, more so than that at the bottom. The influence of Parylene mass on the size of nano-channels was studied by theoretical analysis and experiments, and the deposition pressure of Parylene was optimized. The final high aspect ratio nano-channels are 46 nm in width and 746 nm in depth, of which the aspect ratio is 16. This simple and efficient method paves the way for the production of high aspect ratio nano-channels.

Digital LIGA: exploitation of droplet-on-demand inkjet printing to fabricate complex mechanical structures by electroforming

A novel 3D fabrication technique called digital LIGA is proposed, integrating functional digital printing with 3D microfabrication via electrodeposition. This allows for the realization of complex multilevel metallic structures without problems associated with merging growth fronts. To achieve this, we developed a gold nanoparticle ink, compatible with a SU-8 photoresist, for printing the digitally-defined seed layers. Using this ink, selective printing of a conductive seed layer on a multi-level photoresist was used along with subsequent electrodeposition. Defect-free complex multilevel metallic 3D structures were successfully prepared via this method.

Ether cleavage and chemical removal of SU-8

The high chemical stability of SU-8 makes it irreplaceable for a wide range of applications, most notably as a lithography photoresist for micro and nanotechnology. This advantage becomes a problem when there is a need to remove SU-8 from the fabricated devices. Researchers have been struggling for two decades with this problem, and although a number of partial solutions have been found, this difficulty has limited the applications of SU-8. Here we demonstrate a fast, reproducible, and comparatively gentle method to chemically remove SU-8 photoresist. An ether cleavage mechanism for the observed reaction is proposed, and the hypothesis is tested with ab initio quantum chemical calculations. We also describe a complementary removal method based on atomic hydrogen inductively coupled plasma.

Identification of Unknown Nanofabrication Chemicals Using Raman Spectroscopy and Deep Learning

Raman spectroscopy is a common identification and analysis technique used in research and manufacturing industries. This study investigates the use of Raman spectroscopy and deep learning techniques for identifying various nanofabrication chemicals. Four solvents and SU-8 developer were identified inside common chemical storage and distribution containers. The containers attenuated the spectra and contributed varying amounts of background fluorescence, making manual identification difficult. Two varieties of SU-8 photoresist were differentiated inside amber glass jars, and cured samples of three ratios of polydimethylsiloxane (PDMS) were differentiated using Raman microscopy. The neural network accurately identified the nanofabrication chemicals 100% of the time, without additional preprocessing. This investigation demonstrates the use of Raman spectroscopy and neural networks for the identification of nanofabrication chemicals and makes recommendations for use in other challenging identification applications.

Preparation of Highly Stable Polymer Microstructure with Enhanced Adhesion Strength by Pushpin-like Nano/Microstructure Array.

This polymer microstructure expands more available application, which is a milestone for the development of micro-electro-mechanical system devices towards intelligence and multifunction. Poor interface bonding between the polymer and Si or metal is a particular problem, which restricts the application and promotion of polymer materials. In this study, a transition strengthening layer is proposed to obtain a highly stable polymer microstructure by enhancing the interfacial adhesion strength. The transition strengthening layer is activated by a pushpin-like nano/microstructure array with micromachining technology. Given its good graphical qualities and compatibility, epoxy negative photoresist SU-8 is applied to evaluate the strengthened capabilities of the pushpin-like nano/microstructure array. The microstructure of SU-8 is prepared by the same processes, and then the adhesion strength between the SU-8 microstructure and various activated substrates is tested by the thrust tester. It was determined that SU-8 with an activated pushpin-like microstructure array possessed a highly stable adhesion ability, and its adhesion strength increased from 6.51 MPa to 15.42 MPa. With its ultrahigh stable adhesion ability, it has been applied in fabricating three typical microstructures (hollow square microstructure, gradually increasing adjacent periodic microstructure, and slender strip microstructures) and large-area SU-8 microstructures to evaluate the feasibility of the transition strengthening layer and repeatability and universality of the microfabrication processes. The drifting and gluing phenomenon are avoided by this method compared with the traditional design. The proposed pushpin-like nano/microstructure array is promising in enhancing the stability of polymer microstructures with a substrate.

Self-aligned multi-layer X-ray absorption grating using large-area fabrication methods for X-ray phase-contrast imaging

X-ray phase-contrast (XPCi) imaging methods are an emerging medical imaging approach that provide significantly better soft tissue contrast and could function as a viable extension to conventional X-ray, CT, and even some MRI. Absorption gratings play a central role in grating-based XPCi systems, especially because they enable the acquisition of three images in a single exposure: transmission, refraction, and dark-field. An impediment to commercial development and adoption of XPCi imaging systems is the lack of large area, high aspect ratio absorption gratings. Grating technology development, primarily due to technological limitations, has lagged system development and today prevents the scaling up of XPCi system into a footprint and price point acceptable to the medical market. In this work, we report on a self-aligned multi-layer grating fabrication process that can enable large-area X-ray absorption gratings with micron-scale feature sizes. We leverage large-area fabrication techniques commonly employed by the thin-film transistor (TFT) display industry. Conventional ITO-on-glass substrates are used with a patterned film of Cr/Au/Cr that serves as a self-aligned lithography mask for backside exposure. Commonly available SU-8 photoresist is patterned using the backside exposure mask followed by an electroplating step to fill the gaps in the SU-8 with X-ray attenuating material. Consequently, the electroplated patterned material acts as a self-aligned photomask for subsequent SU-8 layer patterning and so forth. The repeatability of the reported process makes it suitable for achieving higher aspect ratio structures and is advantageous over previously reported X-ray LIGA approaches. A prototype three-layer grating, with a thickness of around 40,upmu text{m}, having a visibility of 0.28 at 60,text{kV}_p with a 70,text{mm}times 70,text{mm} active area was fabricated on a 4-inch glass substrate and demonstrated by modifying a commercially available 3D propagation-based XPCi Microscope. The scalable and cost-effective approach to build larger area X-ray gratings reported in this work can help expedite the commercial development and adoption of previously reported Talbot-Lau, speckle-tracking, as well as coded-aperture XPCi systems for large-area clinical and industrial applications.

Fabricating SU-8 Photoresist Microstructures with Controlled Convexity–Concavity and Curvature through Thermally Manipulating Capillary Action in Poly(dimethylsiloxane) Microholes

We present a simple, robust, and cheap microfabrication method, based on thermally manipulating capillary action in poly(dimethylsiloxane) (PDMS) microholes, for preparing SU-8 curved microstructures. The microstructure morphology including convexity-concavity and curvature can be controlled via tuning the formation temperature. The convex SU-8 microspherical crowns with a height of 40 μm were formed at 10 °C, whereas the concave SU-8 microspherical crowns with a height of 90 μm were formed at 100 °C. The morphology of the microstructures is dictated by the thermally controlled combination of the pressure difference across the interface, contact angle, and surface tension. The fabricated microstructures with a spherical surface can be used as a microlens array or a mold for producing a microlens array. The clear and uniform images were observed using the generated microlens arrays. The equilibrium morphology of the microstructures can be predicted by numerical simulation, which can lessen the number of experiments and thus the design cost. The proposed method has the potential to find applications in industrial fields.

Direct laser-writing of glass-based planar waveguide for fluorescence imaging

Fluorescent microscopic imaging technology has the characteristics of strong labeling capability, high signal strength, low experimental cost, simple imaging process, and imaging from living to in vitro, which is widely used in biological analysis imaging research such as tumor cell imaging, drug distribution in vivo detection, but how to simultaneously have both a wide field of view and a high resolution is a major difficulty in the current field of fluorescence microscopic imaging. Planar silicon waveguides have been found to be able to achieve a wide range of imaging of ultra-thin samples. However, they require sputtering deposition or ion beam etching and other preparation processes. The related processes are complex and equipment required is expensive. In this work, a planar-waveguide-type fluorescence microscope device based on direct picosecond-laser-writing is designed, in which picosecond laser is used to etch the glass surface to rapidly prepare micron sized grooves, and the low-cost and batch-preparation of glass based planar waveguides is further realized by spinning SU-8 photoresist. The waveguide diameter and depth can be customized by adjusting laser processing power, frequency, scanning speed and other parameters. The microscopic detection experiment with using Rhodamine B fluorescent molecule verifies that the direct laser-writing glass based planar waveguide fully meets the requirements for biological imaging with high resolution and large field of view. This simple and rapid processing method can effectively improve the the fluorescence imaging.