In this work, carbonaceous structures composed of graphitic nanocrystals, namely electrically conductive turbostratic graphite or fluorescent graphene quantum dots (GQDs), were patterned on polydimethylsiloxane (PDMS) by laser-induced graphitization. By exploiting the electrical conductivity of the turbostratic graphite and the elasticity of PDMS, a small and sensitive piezoresistive pressure sensor was realized. On the other hand, by exploiting the fluorescence of GQDs and the transparency of PDMS, an anticounterfeiting security tag containing hidden information was realized. This work indicates the implications of using laser-induced graphitization towards the fabrication of novel polymer-based electrical and optical devices.
In this study, we patterned structures composed of graphitic and silicon carbide nanocrystals by the laser-induced carbonization of polydimethylsiloxane. The average size of the observed silicon carbide nanocrystals varied depending on the energy per laser pulse, or pulse energy, used for patterning, where larger crystals were observed for structures patterned with higher pulse energies. Moreover, the electrical property of the patterned structure shifted from conductive to semiconductive, as the pulse energy for patterning increased. To the best of our knowledge, this is the first demonstration of the patterning of structures exhibiting measurable semiconducting properties by the laser-induced carbonization of polymers.
We demonstrate the direct fabrication of graphitic carbon on a biodegradable polymer composite by laser-induced graphitization and applied the structures for the electrode of metal-free biodegradable triboelectric nanogenerators (TENGs). The laser-induced graphitization of fully biodegradable composite sheets composed of alkaline lignin powder and poly(L-lactic acid) (PLLA) was realized. The fabricated TENGs generated electricity by contact with synthetic polymers and natural materials such as water and plant leaves, indicating their applicability for on-site power generation in the natural environment. The proposed method provides the facile fabrication of biodegradable devices and the development of sustainable power generation.
A novel method capable of the rapid fabrication of cellulose nanofiber (CNF)-based supercapacitors using a femtosecond laser is demonstrated. When high-repetition femtosecond laser pulses were scanned onto the surface of a CNF film, a black-colored double-tracked structure was fabricated in the vicinity of the laser ablated groove. The black structure exhibited electrical conductivity, and was composed of graphitic carbon. By utilizing the electrically conductive graphitic carbon as electrodes with an electrolyte solution between the groove, the fabricated double-tracked structure exhibited capacitive properties.
The scope of utilizing soft materials is expanding further in recent years because of the flexibility and the good biocompatibility. In this presentation, laser direct writing of microstructures that exhibits optical and/or electrical properties in and on soft materials by means of photoreduction and graphitization will be described. The fabrication of metal microstructures by multi-photon photoreduction within PEGDA and pNIPAM hydrogels will be reviewed in addition to recent results on applications toward soft actuators. Femtosecond laser direct writing of highly crystalline graphene from native PDMS as well as cellulose nanofiber films, a sustainable biomass, and its application for a highly sensitive piezoresistive sensor will also be presented.
Electrically-conductive-porous carbon was fabricated by the laser carbonization of bamboo and applied as the electrodes of a supercapacitor. Scanning electron microscopy revealed that the porosity of the formed structures was higher when slower scanning speeds were used. We fabricated an all-biomass-derived supercapacitor by covering the patterned porous carbon with agarose gel, which functioned as an electrolyte. Supercapacitors that show relatively higher capacitance were fabricated using slower scanning speeds, which could be attributable to a higher porosity of the electrodes. The proposed method is promising for the realization of sustainable energy-storage devices.
We report the simultaneous synthesis and patterning of graphene quantum dots (GQDs) on and inside a transparent polymer, polydimethylsiloxane (PDMS), using a femtosecond laser. The irradiation of high repetition femtosecond laser pulses induces the formation of GQDs, which is attributable to the laser-induced pyrolysis of graphitic carbon sheets and/or silicon carbide nanocrystals. Furthermore, the patterning of a two-dimensional security tag with a concealed QR code, and a fluorescent three-dimensional design is demonstrated by adjusting the laser irradiation conditions. This work expands the possibilities of GQDs for applications in novel flexible three-dimensional optoelectrical devices.
The surface of native polydimethylsiloxane (PDMS) was modified into black structures by irradiation of femtosecond laser pulses. Material analysis conducted on the modified areas revealed the formation of silicon carbide (SiC) nanocrystals, as well as multilayer graphitic carbon. Furthermore, electrical conductivity measurements of structures fabricated using various fabrication parameters, suggest that the amount of defect in the formed graphitic carbon affects the electrical conductivity of the fabricated structures. A preliminary demonstration of strain sensing was performed using the structures fabricated, indicating the potential of the structures fabricated by the femtosecond-laser-based modification of PDMS for flexible device applications.
By femtosecond-laser-based modification of polydimethylsiloxane (PDMS), we fabricated an electrically conductive structure composed of β-silicon carbide (β-SiC) on a PDMS thin film for strain sensing. With an increase in applied strain, i.e. smaller bend radii of the conductive structures, the conductivity of the structure decreased significantly. The result indicates that the resistance of the conductive structure has high sensitivity to strain, leading to potential applications such as real-time monitoring of human motion.
We experimentally demonstrated formation of electrically conductive structures by modifying native polydimethylsiloxane (PDMS) with femtosecond laser. By irradiating femtosecond laser pulses to native PDMS, black structures with electrical conductivity were formed. Analyses using X-ray diffraction (XRD) show that the formed structures were composed of β-silicon carbide (β-SiC). Our technique enables the spatially selective formation of β-SiC on the surface of PDMS, leading to open a novel route to develop a simple method to fabricate flexible or stretchable MEMS devices with SiC microstructures.
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