Laser-induced Graphene Patterns Research Articles

Optimization of dry laser-induced graphene (LIG) electrodes for electrocardiography (ECG) signals monitoring

This work presents the optimization of the fabrication procedure for laser-induced graphene (LIG) electrodes intended for biopotentials acquisition. The results presented in this study demonstrate a significant improvement with respect to the performance obtained for other LIG-based electrodes previously reported in the literature. In particular, we propose the use of a galvanometric laser instead of a CNC laser to improve the engraving resolution and the LIG synthesis process, thus enhancing the surface area of the interface skin–electrode. For that, we have studied the resistance of the resulting LIG patterns as a function of the laser parameters (engraving power and scan speed) seeking their optimization. After tunning the laser fabrication process, we have fabricated and characterized electrocardiogram (ECG) electrodes with different surface areas using a commercial silver-based electrode as a reference. Thus, circular electrodes with a diameter of 15 mm, 10 mm and 6.5 mm were used to acquire the ECG on different volunteers using a commercial equipment. The signals acquired were processed afterwards with cutting edge processing techniques to perform a statistical analysis in terms of sensitivity, specificity, positive prediction and accuracy for the detection of QRS complexes. The results demonstrate that the proposed electrodes improve the signal acquisition with respect to the previously reported LIG-based electrodes in terms of noise and do present comparable or even better results than commercial electrodes (even with a smaller surface area) with the additional advantage of not requiring the use of an electrolyte gel.

Study and fabrication of rain triboelectric nanogenerator based on laser-induced graphene interdigital electrode

In this work, a rain triboelectric nanogenerator (R-TENG) based on a laser-induced graphene (LIG) interdigital electrode was developed to harvest rain energy. The R-TENG comprises a LIG interdigital electrode on a polymer substrate with a hydrophobic Polydimethylsiloxane (PDMS) layer as a protective layer. When raindrops fall onto the surface of the PDMS layer and move between two adjacent interdigital electrodes, the accumulated charges move back and forth, resulting in the generation of alternating current. The LIG pattern design and the energy collection efficiency were studied by altering the production parameters of the LIG electrode and measuring the droplet diameter on the PDMS surface. A R-TENG with an electrode width of 3 mm produces a laser power of 2.1 W, and an output voltage of 2.46 V is generated. The R-TENG could be applied as an additional energy source to harvest rain energy for agricultural IoT sensors.

Optimization of structural and electrical properties of graphene-based TiO2 thin film device using Bayesian machine-learning approach

The optimization of laser-induced graphene (LIG) patterning is crucial for achieving desirable electronic properties in flexible electronic devices. In this study, we applied state-of-the-art automated parameter optimization techniques, specifically Bayesian optimization, to enhance the electrical resistance of LIG patterns. By iteratively optimizing the laser power, irradiation time, pressure, and gas type, we achieved minimum LIG resistance within eight batch configurations suggested by the Bayesian optimization (BO) approach. Our method eliminates the reliance on skilled operators, as the initial surrogate models were trained with random parameter evaluations. Notably, our system enables the optimization of material properties even when characterizations are only available outside the experiment loop. Furthermore, the surrogate model provided insights into the underlying mechanisms of LIG growth on quartz substrates. Through partial dependence analysis, we identified relevant physical domains for further investigation, leading to the discovery of negative capacitance and a correlation between structural and electrical properties in LIG. These findings were supported by XPS, Raman, and optical characterizations. Our approach streamlines the experimental design, reducing time and cost while accelerating materials research, and offers human-interpretable conclusions for a deeper understanding of LIG patterning processes.

Laser-Induced Graphene Stretchable Strain Sensor with Vertical and Parallel Patterns.

In intelligent manufacturing and robotic technology, various sensors must be integrated with equipment. In addition to traditional sensors, stretchable sensors are particularly attractive for applications in robotics and wearable devices. In this study, a piezoresistive stretchable strain sensor based on laser-induced graphene (LIG) was proposed and developed. A three-dimensional, porous LIG structure fabricated from polyimide (PI) film using laser scanning was used as the sensing layer of the strain sensor. Two LIG pattern structures (parallel and vertical) were fabricated and integrated within the LIG strain sensors. Scanning electron microscopy, an X-ray energy dispersive spectrometer, and Raman scattering spectroscopy were used to examine the microstructure of the LIG sensing layer. The performance and strain sensing properties of the parallel and vertical stretchable LIG strain sensors were investigated in tensile tests. The relative resistance changes and the gauge factors of the parallel and vertical LIG strain sensors were quantified. The parallel strain sensor achieved a high gauge factor of 15.79 in the applied strain range of 10% to 20%. It also had high sensitivity, excellent repeatability, good durability, and fast response times during the tensile experiments. The developed LIG strain sensor can be used for the real-time monitoring of human motions such like finger bending, wrist bending, and throat swallowing.

Darkening of Laser‐Induced Graphene in Wet for Readable In Situ Real Time Sweating Rate Analysis

AbstractDeveloping a simple technique for in situ monitoring of sweating rate can provide real time feedback of individual's dehydration status and further assist in human health management. This work demonstrates the visible darkening of laser‐induced graphene (LIG) after wetting and its wearable practicability in monitoring sweating rate. LIGs with various porous morphologies are generated and their color differences are quantitatively assessed with hue‐saturation‐value model, correlated with the sheet resistance and the porous architecture. Embedding LIG pattern within microchannel enables the direct readout of water‐filled region and arranging length scale marks along microchannel allows direct readout of fluid volume with human eye for more simple measurements. Flexible design of length scale resolution can balance the detection frequency (i.e., real time ability) and its accuracy. The in situ and real time flow rate monitoring performance is successfully adopted on‐body for sweating rate analysis with reasonable accuracy. Apart from the simplicity and low cost, compared to other flow rate sensing methods, the proposed platform is reusable with no special cleaning needed for the microchannel but just drying, and no visible decline of the performance occurs. LIG's darkening strategy endows an avenue for the development of powerful in situ and real time sweating analytical platform.

Integrated Sensing and Warning Multifunctional Devices Based on the Combined Mechanical and Thermal Effect of Porous Graphene.

Wearable devices with integrated alarm functions play a vital role in daily life and can help people prevent potential hazards. Although many wearable sensors have been extensively studied and proposed to monitor various physiological signals, most of them are needed to integrate with the external alarm elements to realize warning, such as light-emitting diodes and buzzers, resulting in the system complexity and poor flexibility. In this paper, an integrated sensing and warning multifunctional device based on the mechanical and thermal effect of porous graphene is proposed on a bilayer asymmetrical pattern of laser-induced graphene (LIG). Compared with the strain sensor with nonpatterned LIG, the mechanical performance is greatly improved with the highest gauge factor value of up to 950 for the strain sensor with mesh-patterned LIG. On the contrary, the heating performance of the heater with nonpatterned LIG is better than that with mesh-patterned LIG. Combining the performance differences of different LIG patterns, the integrated wearable device with a bilayer asymmetrical LIG pattern is demonstrated. It can generate enough heating energy to warn the person when the detected signal meets the threshold condition measured in real time by the ultrasensitive strain sensor. This work will provide a new way to construct an integrated wearable device for realizing multifunctional applications. This integrated multifunctional device shows great potential toward the applications in healthcare monitoring and timely warning.

Laser‐Induced Graphene Tapes as Origami and Stick‐On Labels for Photothermal Manipulation via Marangoni Effect

AbstractDirect light‐to‐work conversion enables remote actuation through a non‐contact manner, among which the photothermal Marangoni effect is significant for developing light‐driven robots because of the diversity of applicable photothermal materials and light sources, as well as the high energy conversion efficiency. However, the lack of nanotechnologies that enable flexible integration of advanced photothermal materials with actuators of complex configurations significantly restricts their practical applications. In this paper, laser‐induced graphene (LIG) tape is reported as stick‐on photothermal labels for developing light‐driven actuators based on the Marangoni effect. With the help of direct laser writing technology, graphene patterns with superior photothermal properties are prepared on the PI tape. The patterned LIG tape can be stuck on any desired objects and generates an asymmetric photothermal field under light irradiation, forming a photothermal Marangoni actuator. Additionally, the PI tape with LIG patterns can be folded into 3D origami actuators that permit photothermal Marangoni actuation including both translation and rotation. The graphene‐based photothermal Marangoni actuators feature biocompatibility, which is confirmed by MDA‐MB‐231 cells proliferation experiments. Owing to the excellent photothermal property of LIG patterns, the as‐produced photothermal actuators can be manipulated by a variety of light sources, holding great promise for developing light‐driven soft robots.

Scalable fabrication of inkless, transfer-printed graphene-based textile microsupercapacitors with high rate capabilities

We have demonstrated the use of thermal transfer printing for scalable, inkless fabrication of a graphene-based textile microsupercapacitor (MSC). An adhesive film of a heat transfer paper was employed as a flat, buffer adhesive layer on a rough textile substrate. Laser-induced graphene (LIG) directly laser-written on polyimide (PI) films was transferred onto the adhesive film area of the textile substrates at elevated temperature and pressure. A thermally transfer-printed LIG pattern preserved porous structure with 3D interconnected pores and high electrical conductivity of LIG formed on PI films. The developed textile LIG-MSCs exhibit electrical double layer capacitive characteristics with areal capacitance of 0.76mFcm−2 and excellent capacitance retention of 96% after 1000 cycles of large bending (180°) deformation. Furthermore, scalable transfer of a large-area LIG pattern provided various array configurations of MSCs in series and in parallel to adjust the voltage and current for practical applications. Moreover, LIG-MSCs with a LIG-metal composite exhibit fast ion transport at a high scan rates of up to 20Vs-1, suggesting outstanding rate capability among graphene-based textile MSCs. In this regard, the proposed inkless transfer strategy provided low cost and scalable fabrication of a LIG composite electrode on a textile substrate without preparing costly graphene-based ink materials.

Stretchable, ultrasensitive, and low-temperature NO2 sensors based on MoS2@rGO nanocomposites

The recent development of 3D highly porous laser-induced graphene (LIG) has drawn significant attention for numerous sensing applications. In particular, novel gas sensing platforms based on stretchable LIG patterns with self-heating capabilities have been demonstrated as a simple alternative to interdigitated electrodes (IDEs) for integrating gas-sensitive nanomaterials. However, their direct performance comparison with the IDEs is unclear. In this paper, the sensing performance of nanomaterials with various specific surface areas between the LIG patterns and IDEs are compared directly. Molybdenum disulfide (MoS2) @ reduced graphene oxide (rGO) was synthesized with controllable size and morphology for nitrogen dioxide (NO2) sensing. When dispersing MoS2@rGO on an IDE integrated on a soft silicone polymeric substrate, the stretchable gas sensor exhibited mechanical robustness upon stretching and a significantly large signal-to-noise ratio (SNR) for rapid detection of 10 ppb NO2. The MoS2@rGO nanocomposite was integrated on a stretchable 3D porous LIG pattern yielding an extraordinarily high SNR of 1026.9 to NO2 of 2 ppm. Considering the high SNR of over 60 to NO2 of 10 ppb, the novel LIG gas sensing platform with a simple fabrication process shows a great promise to test nanomaterials and enable stretchable bio-integrated gas sensors for monitoring of the health and environment.

Machine-learning-assisted fabrication: Bayesian optimization of laser-induced graphene patterning using in-situ Raman analysis

The control of the physical, chemical, and electronic properties of laser-induced graphene (LIG) is crucial in the fabrication of flexible electronic devices. However, the optimization of LIG production is time-consuming and costly. Here, we demonstrate state-of-the-art automated parameter tuning techniques using Bayesian optimization to advance rapid single-step laser patterning and structuring capabilities with a view to fabricate graphene-based electronic devices. In particular, a large search space of parameters for LIG explored efficiently. As a result, high-quality LIG patterns exhibiting high Raman G/D ratios at least a factor of four larger than those found in the literature were achieved within 50 optimization iterations in which the laser power, irradiation time, pressure and type of gas were optimized. Human-interpretable conclusions may be derived from our machine learning model to aid our understanding of the underlying mechanism for substrate-dependent LIG growth, e.g. high-quality graphene patterns are obtained at low and high gas pressures for quartz and polyimide, respectively. Our Bayesian optimization search method allows for an efficient experimental design that is independent of the experience and skills of individual researchers, while reducing experimental time and cost and accelerating materials research.

Direct Fabrication of Ultra-Sensitive Humidity Sensor Based on Hair-Like Laser-Induced Graphene Patterns.

Three-dimensional (3-D) porous graphitic structures have great potential for sensing applications due to their conductive carbon networks and large surface area. In this work, we present a method for facile fabrication of hair-like laser induced graphene (LIG) patterns using a laser scribing system equipped with a 355 nm pulsed laser. The polyimide (PI) film was positioned on a defocused plane and irradiated at a slow scanning speed using a misaligned laser beam. These patterns have the advantages of a large surface area and abundant oxidation groups. We have applied the hair-like LIG patterns to a humidity sensor. The humidity sensor showed good sensitivity characteristics and a large amount of electronic carriers can be stored.

Stable and durable laser-induced graphene patterns embedded in polymer substrates

The stability and durability of laser-induced graphene (LIG) patterns embedded in polymer substrates are significant for their practical application. However, most of currently reported LIG precursors are facing the dilemma of weak structural controllability, poor resistance to acid/base, or bad processability. In this work, we efficiently converted the synthesized poly (Ph-ddm) into LIG using a straightforward CO2 laser, aiming to find a potential LIG precursor with excellent durability under harsh conditions. The graphene structure of obtained LIG was confirmed by Raman spectra, scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Results indicated that the poly (Ph-ddm)-based LIG showed a low sheet resistance of 35 Ω/sq as well as a high specific surface area of 883 m2/g. And due to the superior properties of poly (Ph-ddm), the LIG patterns exhibited excellent resistance to strong acid/base solutions and high adhesion on the substrate, which ensured their stable application under severe conditions. Besides, potential application of as-prepared LIG was demonstrated in well-performed supercapacitors and electrode for water splitting in an alkaline medium. Based on the results in this work, polybenzoxazine could be a promising precursor for stable and durable LIG preparation.

Novel gas sensing platform based on a stretchable laser-induced graphene pattern with self-heating capabilities

Laser-induced graphene based gas sensor conformable to skin with low detection limit at low temperature.

Flexible and Highly Sensitive Strain Sensor Based on Laser-Induced Graphene Pattern Fabricated by 355 nm Pulsed Laser.

A laser-induced-graphene (LIG) pattern fabricated using a 355 nm pulsed laser was applied to a strain sensor. Structural analysis and functional evaluation of the LIG strain sensor were performed by Raman spectroscopy, scanning electron microscopy (SEM) imaging, and electrical–mechanical coupled testing. The electrical characteristics of the sensor with respect to laser fluence and focal length were evaluated. The sensor responded sensitively to small deformations, had a high gauge factor of ~160, and underwent mechanical fracture at 30% tensile strain. In addition, we have applied the LIG sensor, which has high sensitivity, a simple manufacturing process, and good durability, to human finger motion monitoring.

One‐Step Scalable Fabrication of Graphene‐Integrated Micro‐Supercapacitors with Remarkable Flexibility and Exceptional Performance Uniformity

AbstractThe rapid development of miniature electronics has accelerated the demand for simplified and scalable production of micro‐supercapacitors (MSCs); however, the preparation of active materials, patterning microelectrodes, and subsequent modular integration of the reported MSCs are normally separated and are involved in multiple complex steps. Herein, a one‐step, cost‐effective strategy for fast and scalable fabrication of patterned laser‐induced graphene (LIG) for all‐solid‐state planar integrated MSCs (LIG‐MSCs) with various form factors of designable shape, exceptional flexibility, performance uniformity, superior modularization, and high‐temperature stability is demonstrated. Notably, using the conductive and porous LIG patterns composed of randomly stacked graphene nanosheets simultaneously acting as both microelectrodes and interconnects, the resulting LIG‐MSCs represent typical electrical double capacitive behavior, having an impressive areal capacitance of 0.62 mF cm−2 and long‐term stability without capacitance degeneration after 10 000 cycles. Furthermore, LIG‐MSCs display exceptional mechanical flexibility and adjustable voltage and capacitance output through arbitrary arrangement of cells connected in series and in parallel, indicative of exceptional performance customization. Moreover, all‐solid‐state LIG‐MSCs working at ionogel electrolyte exhibit highly stable performance even at high temperature of 100 °C, with 90% capacitance retention over 3000 cycles, suggestive of outstanding reliability. Therefore, the LIG‐MSCs offer tremendous opportunities for miniature power source‐integrated microelectronics.