High-Resolution Laser-Induced Graphene from Photoresist

Carbon Micro/Nano Machining toward Miniaturized Device: Structural Engineering, Large-Scale Fabrication, and Performance Optimization

With the rapid development of micro/nano machining, there is an elevated demand for high-performance microdevices with high reliability and low cost. Due to their outstanding electrochemical, optical, electrical, and mechanical performance, carbon materials are extensively utilized in constructing microdevices for energy storage, sensing, and optoelectronics. Carbon micro/nano machining is fundamental in carbon-based intelligent microelectronics, multifunctional integrated microsystems, high-reliability portable/wearable consumer electronics, and portable medical diagnostic systems. Despite numerous reviews on carbon materials, a comprehensive overview is lacking that systematically encapsulates the development of high-performance microdevices based on carbon micro/nano structures, from structural design to manufacturing strategies and specific applications. This review focuses on the latest progress in carbon micro/nano machining toward miniaturized device, including structural engineering, large-scale fabrication, and performance optimization. Especially, the review targets an in-depth evaluation of carbon-based micro energy storage devices, microsensors, microactuators, miniaturized photoresponsive and electromagnetic interference shielding devices. Moreover, it highlights the challenges and opportunities in the large-scale manufacturing of carbon-based microdevices, aiming to spark further exciting research directions and application prospectives.

Laser-Driven Rapid Synthesis of Metal-Organic Frameworks and Investigation of UV-NIR Optical Absorption, Luminescence, Photocatalytic Degradation, and Gas and Ion Adsorption Properties

In this study, we designed a platform based on a laser-driven approach for fast, efficient, and controllable MOF synthesis. The laser irradiation method was performed for the first time to synthesize Zn-based MOFs in record production time (approximately one hour) compared to all known MOF production methods with comparable morphology. In addition to well-known structural properties, we revealed that the obtained ZnMOFs have a novel optical response, including photoluminescence behavior in the visible range with nanosecond relaxation time, which is also supported by first-principles calculations. Additionally, photocatalytic degradation of methylene blue with ZnMOF was achieved, degrading the 10 ppm methylene blue (MB) solution 83% during 1 min of irradiation time. The application of laser technology can inspire the development of a novel and competent platform for a fast MOF fabrication process and extend the possible applications of MOFs to miniaturized optoelectronic and photonic devices.

Recent Advances in Laser-Induced Synthesis of MOF Derivatives

Metal-organic frameworks (MOFs) are crystalline materials with permanent pores constructed by the self-assembly of organic ligands and metal clusters through coordination bonds. Due to their diversity and tunability, MOFs are used as precursors to be converted into other types of functional materials by pyrolytic recrystallization. Laser-induced synthesis is proven to be a powerful pyrolytic processing technique with fast and accurate laser irradiation, low loss, high efficiency, selectivity, and programmability, which endow MOF derivatives with new features. Laser-induced MOF derivatives exhibit high versatility in multidisciplinary research fields. In this review, first, the basic principles of laser smelting and the types of materials for laser preparation of MOF derivatives are briefly introduced. Subsequently, it is focused on the peculiarity of the engineering of structural defects and their applications in catalysis, environmental protection, and energy fields. Finally, the challenges and opportunities at the current stage are highlighted with the aim of elucidating the future direction of the rapidly growing field of laser-induced synthesis of MOF derivatives.

Semiconducting MOFs on ultraviolet laser-induced graphene with a hierarchical pore architecture for NO2 monitoring

Due to rapid urbanization worldwide, monitoring the concentration of nitrogen dioxide (NO₂), which causes cardiovascular and respiratory diseases, has attracted considerable attention. Developing real-time sensors to detect parts-per-billion (ppb)-level NO₂ remains challenging due to limited sensitivity, response, and recovery characteristics. Herein, we report a hybrid structure of Cu₃HHTP₂, 2D semiconducting metal-organic frameworks (MOFs), and laser-induced graphene (LIG) for high-performance NO₂ sensing. The unique hierarchical pore architecture of LIG@Cu₃HHTP₂ promotes mass transport of gas molecules and takes full advantage of the large surface area and porosity of MOFs, enabling highly rapid and sensitive responses to NO₂. Consequently, LIG@Cu₃HHTP₂ shows one of the fastest responses and lowest limit of detection at room temperature compared with state-of-the-art NO₂ sensors. Additionally, by employing LIG as a growth platform, flexibility and patterning strategies are achieved, which are the main challenges for MOF-based electronic devices. These results provide key insight into applying MOFtronics as high-performance healthcare devices.

Direct Conversion of Liquid Organic Precursor into 3D Laser-Induced Graphene Materials

Among the different states of matter, liquids have particular advantages in terms of easy handling and recycling, which has been manifested in various chemosynthetic reactions, but remains underexplored in graphene synthesis. This work reports the direct conversion of liquid organic precursor into versatile 3D graphene materials using rapid laser irradiation. The liquid precursor allows for easy fabrication of graphene with significant 3D architectures, including powders, patterned composite structures, and substrate-free films. Taking advantage of the high compatibility of liquid precursor with a wide range of dopants, the 3D graphene can be further engineered together with various functional components, especially the high loading (≈15 wt.%) and well-dispersed (an average diameter of less than 50 nm) high-entropy alloy nanoparticles. Furthermore, combined with the 3D printing strategy, the rapid construction of graphene with complex and accurate 3D shapes is demonstrated via a selective in situ laser transforming (SLT) strategy. With the high structural integrity unachievable by traditional 3D printing methods, the obtained objects show an electrical conductivity of 4380 S m^-1 and a compressive modulus of 31.8 MPa. The results reported in this work will open up a new way for the fabrication of functional carbon materials with customizable shapes and components.

Effect of Laser Parameters on Laser-Induced Graphene Filter Fabrication and Its Performance for Desalination and Water Purification

Laser-induced graphene (LIG) is a low-cost, chemical-free single-step fabrication process and has shown its potential in water treatment, electronics, and sensing. LIG fabrication optimization is mostly explored for dense polyimide (PI) polymers. However, LIG-based filters and membranes for water treatment need to be porous, and additional steps are required to get porous surfaces from PI-based surfaces. Polyethersulfone (PES) porous membranes are cost-effective and are common in water purification as compared to PI; further, the optimization of LIG fabrication on PES-based porous membranes is not explored. So, this study demonstrated the fabrication, optimization, and characterization of LIG with different laser parameters such as power, speed, image density (ID), focusing, laser platforms, and membrane support layer effect on porous PES commercial (UP010) and lab-casted 15% PES (PES15) membranes. The performance of optimized LIG filters was tested for interfacial evaporation (IE)-based desalination in single and stacked layer configuration and water purification applications such as dye removal and disinfection. IE was done in Joule heating (JH) and solar heating (SH) modes, and the UP010-ID7 LIG filter showed the highest JH evaporation rates of ∼1.1, 1.8, and 2.82 kg m^-2 h^-1 in single, double, and triple stacked configurations, respectively. Using a JH IE setup, the best-performing UP010-ID7 LIG filters have also shown ∼100% removal of methylene blue dye from the contaminated water. Furthermore, all LIG filters showed a complete 6-log bacterial inhibition at the 5 V filtration experiments; at 2.5 V, the optimized LIG filters showed a higher removal than the non-optimized filters. Additionally, the LIGs obtained with the aluminum platform were the best quality. This work demonstrates that laser power, ID, platform, and membrane support are critical parameters for the best-performing PES-LIG filters, and they can be effectively utilized to fabricate PES-based LIG porous surfaces for various energy, environmental, and catalysis applications.

Highly Robust Laser-Induced Graphene (LIG) Ultrafiltration Membrane with a Stable Microporous Structure

Laser-induced graphene (LIG) materials have great potential in water treatment applications. Herein, we report the fabrication of a mechanically robust electroconductive LIG membrane with tailored separation properties for ultrafiltration (UF) applications. These LIG membranes are facilely fabricated by directly lasing poly(ether sulfone) (PES) membrane support. Control PES membranes were fabricated through a nonsolvent-induced phase separation (NIPS) technique. A major finding was that when PES UF membranes were treated with glycerol, the membrane porous structure remained almost unchanged upon drying, which also assisted with protecting the membrane's nanoscale features after lasing. Compared to the control PES membrane, the membrane fabricated with 8% laser power on the bottom layer of PES (PES (B)-LIG-HP) demonstrated 4 times higher flux (865 LMH) and 90.9% bovine serum albumin (BSA) rejection. Moreover, LIG membranes were found to be highly hydrophilic and exhibited excellent mechanical and chemical stability. Owing to their excellent permeance and separation efficiency, these highly robust electroconductive LIG membranes have a great potential to be used for designing functional membranes.

In Situ Synthesis and Microfabrication of High Entropy Alloy and Oxide Compounds by Femtosecond Laser Direct Writing under Ambient Conditions

Synthesis and coating of multi-metal oxides (MMOs) and alloys on conductive substrates are indispensable to electrochemical applications, yet demand multiple, resource-intensive, and time-consuming processes. Herein, an alternative approach to the synthesis and coating of alloys and MMOs by femtosecond laser direct writing (FsLDW) is reported. A solution-based precursor ink is deposited and dried on the substrate and illuminated by a femtosecond laser. During the illumination, dried precursor ink is transformed to MMO/alloys and is simultaneously bonded to the substrate. The formulation of the alloy and MMO precursor ink for laser processing is universally applicable to a large family of oxides and alloys. The process is conducted at room temperature and in an open atmosphere. To demonstrate, a large family of 57 MMOs and alloys are synthesized from a group of 13 elements. As a proof of concept, Ni_0.24 Co_0.23 Cu_0.24 Fe_0.15 Cr_0.14 high entropy alloy synthesized on stainless-steel foil by FsLDW is used for the oxygen evolution reaction, which achieves a current density of 10 mA cm^-2 at a significantly low overpotential of 213 mV. Further, FsLDW can also achieve microfabrication of alloys/MMO with feature sizes down to 20 µm.

Research Progress on the Preparation and Applications of Laser-Induced Graphene Technology

Graphene has been regarded as a potential application material in the field of new energy conversion and storage because of its unique two-dimensional structure and excellent physical and chemical properties. However, traditional graphene preparation methods are complicated in-process and difficult to form patterned structures. In recent years, laser-induced graphene (LIG) technology has received a large amount of attention from scholars and has a wide range of applications in supercapacitors, batteries, sensors, air filters, water treatment, etc. In this paper, we summarized a variety of preparation methods for graphene. The effects of laser processing parameters, laser type, precursor materials, and process atmosphere on the properties of the prepared LIG were reviewed. Then, two strategies for large-scale production of LIG were briefly described. We also discussed the wide applications of LIG in the fields of signal sensing, environmental protection, and energy storage. Finally, we briefly outlined the future trends of this research direction.

Carbon Dots Embedded in Cellulose Film: Programmable, Performance-Tunable, and Large-Scale Subtle Fluorescent Patterning by in Situ Laser Writing

Fluorescent patterns with multiple functions enable high-security anti-counterfeiting labels. Complex material synthesis and patterning processes limit the application of multifunctional fluorescent patterns, so the technology of in situ fluorescent patterning with tunable multimodal capabilities is becoming more necessary. In this work, an in situ fluorescent patterning technology was developed using laser direct writing on solid cellulose film at ambient conditions without masks. The fluorescent intensity and surface microstructure of the patterns could be adjusted by programmable varying of the laser parameters simultaneously. During laser direct writing, carbon dots are generated in situ in a cellulose ester polymer matrix, which significantly simplifies the fluorescent patterning process and reduces the manufacturing cost. Interestingly, the tunable fluorescent intensity empowers the fabrication of visual stereoscopic fluorescent patterns with excitation dependence, further improving its anti-counterfeiting performance. The obtained fluorescent patterns still show ultrahigh optical properties after being immersed in an acid/base solution (pH 5-12) over one month. In addition, the anti-UV performance of the obtained laser-patterned film with transmittance around 90% is comparable to that of commercial UV-resistant films. This work provided an advanced and feasible approach to fabricating programmable, performance-tunable, subtle fluorescent patterns in large-scale for industrial application.

Laser-Induced Graphene (LIG) as a Smart and Sustainable Material to Restrain Pandemics and Endemics: A Perspective

A healthy environment is necessary for a human being to survive. The contagious COVID-19 virus has disastrously contaminated the environment, leading to direct or indirect transmission. Therefore, the environment demands adequate prevention and control strategies at the beginning of the viral spread. Laser-induced graphene (LIG) is a three-dimensional carbon-based nanomaterial fabricated in a single step on a wide variety of low-cost to high-quality carbonaceous materials without using any additional chemicals potentially used for antiviral, antibacterial, and sensing applications. LIG has extraordinary properties, including high surface area, electrical and thermal conductivity, environmental-friendliness, easy fabrication, and patterning, making it a sustainable material for controlling SARS-CoV-2 or similar pandemic transmission through different sources. LIG's antiviral, antibacterial, and antibiofouling properties were mainly due to the thermal and electrical properties and texture derived from nanofibers and micropores. This perspective will highlight the conducted research and the future possibilities on LIG for its antimicrobial, antiviral, antibiofouling, and sensing applications. It will also manifest the idea of incorporating this sustainable material into different technologies like air purifiers, antiviral surfaces, wearable sensors, water filters, sludge treatment, and biosensing. It will pave a roadmap to explore this single-step fabrication technique of graphene to deal with pandemics and endemics in the coming future.

Electrothermal Performance of Heaters Based on Laser-Induced Graphene on Aramid Fabric

Nanostructured heaters based on laser-induced graphene (LIG) are promising for heat generation and temperature control in a variety of applications due to their high efficiency as well as a fast, facile, and highly scalable fabrication process. While recent studies have shown that LIG can be written on a wide range of precursors, the reports on LIG-based heaters are mainly limited to polyimide film substrates. Here, we develop and characterize nanostructured heaters by direct writing of laser-induced graphene on nonuniform and structurally porous aramid woven fabric. The synthesis and writing of graphene on aramid fabric is conducted using a 10.6 μm CO₂ laser. The quality of laser-induced graphene and electrical properties of the heater fabric is tuned by controlling the lasing process parameters. Produced heaters exhibit good electrothermal efficiency with steady-state temperatures up to 170 °C when subjected to an input power density of 1.5 W cm^-2. In addition, the permeable texture of LIG-aramid fabric heaters allows for easy impregnation with thermosetting resins. We demonstrate the encapsulation of fabric heaters with two different types of thermosetting resins to develop both flexible and stiff composites. A flexible heater is produced by the impregnation of LIG-aramid fabric by silicone rubber. While the flexible composite heater exhibits inferior electrothermal performance compared to neat LIG-aramid fabric, it shows consistent electrothermal performance under various electrical and mechanical loading conditions. A multifunctional fiber-reinforced composite panel with integrated de-icing functionality is also manufactured using one ply of LIG-aramid fabric heater as part of the composite layup. The results of de-icing experiments show excellent de-icing capability, where a 5 mm thick piece of ice is completely melted away within 2 min using an input power of 12.8 W.

Large-Scale Syntheses of 2D Materials: Flash Joule Heating and Other Methods

In the past 17 years, the larger-scale production of graphene and graphene family materials has proven difficult and costly, thus slowing wider-scale commercial applications. The quality of the graphene that is prepared on larger scales has often been poor, demonstrating a need for improved quality controls. Here, current industrial graphene synthetic and analytical methods, as well as recent academic advancements in larger-scale or sustainable synthesis of graphene, defined here as weights more than 200 mg or films larger than 200 cm² , are compiled and reviewed. There is a specific emphasis on recent research in the use of flash Joule heating as a rapid, efficient, and scalable method to produce graphene and other 2D nanomaterials. Reactor design, synthetic strategies, safety considerations, feedstock selection, Raman spectroscopy, and future outlooks for flash Joule heating syntheses are presented. To conclude, the remaining challenges and opportunities in the larger-scale synthesis of graphene and a perspective on the broader use of flash Joule heating for larger-scale 2D materials synthesis are discussed.

Hierarchically Porous, Laser-Pyrolyzed Carbon Electrode from Black Photoresist for On-Chip Microsupercapacitors

We report a laser-pyrolyzed carbon (LPC) electrode prepared from a black photoresist for an on-chip microsupercapacitor (MSC). An interdigitated LPC electrode was fabricated by direct laser writing using a high-power carbon dioxide (CO₂) laser to simultaneously carbonize and pattern a spin-coated black SU-8 film. Due to the high absorption of carbon blacks in black SU-8, the laser-irradiated SU-8 surface was directly exfoliated and carbonized by a fast photo-thermal reaction. Facile laser pyrolysis of black SU-8 provides a hierarchically macroporous, graphitic carbon structure with fewer defects (I_D/I_G = 0.19). The experimental conditions of CO₂ direct laser writing were optimized to fabricate high-quality LPCs for MSC electrodes with low sheet resistance and good porosity. A typical MSC based on an LPC electrode showed a large areal capacitance of 1.26 mF cm^-2 at a scan rate of 5 mV/s, outperforming most MSCs based on thermally pyrolyzed carbon. In addition, the results revealed that the high-resolution electrode pattern in the same footprint as that of the LPC-MSCs significantly affected the rate performance of the MSCs. Consequently, the proposed laser pyrolysis technique using black SU-8 provided simple and facile fabrication of porous, graphitic carbon electrodes for high-performance on-chip MSCs without high-temperature thermal pyrolysis.