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Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water-air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15-20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2-5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm(-2), no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20-30 J cm(-2) range, these polyynes disappeared, while PG and GQDs were found at the water-air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms.

Surface-enhanced Raman scattering (SERS) enables trace-detection for biosensing and environmental monitoring. Optimized enhancement of SERS can be achieved when the energy of the localized surface plasmon resonance (LSPR) is close to the energy of the Raman excitation wavelength. The LSPR can be tuned using a plasmonic superstructure array with controlled periods. In this paper, we develop a new technique based on laser near-field reduction to fabricate a superstructure array, which provides distinct features in the formation of periodic structures with hollow nanoclusters and flexible control of the LSPR in fewer steps than current techniques. Fabrication involves irradiation of a continuous wave laser or femtosecond laser onto a monolayer of self-assembled silica microspheres to grow silver nanoparticles along the silica microsphere surfaces by laser near-field reduction. The LSPR of superstructure array can be flexibly tuned to match the Raman excitation wavelengths from the visible to the infrared regions using different diameters of silica microspheres. The unique nanostructure formed can contribute to an increase in the sensitivity of SERS sensing. The fabricated superstructure array thus offers superior characteristics for the quantitative analysis of fluorescent perfluorooctanoic acid with a wide detection range from 11 ppb to 400 ppm. [ABSTRACT FROM AUTHOR]

Lignin as a renewable natural resource has been the focus of numerical interest in applications ranging from pitch to porous carbon material. Herein, a facile approach is reported to transform lignin into porous conductive carbon structures and interdigitated circuits for supercapacitor devices using femtosecond laser direct writing. Comparative studies revealed that the laser irradiation induced tetrahedral amorphous carbon while only graphitic carbon was obtained through pyrolysis. Meanwhile, the composite membrane was easily prepared to further optimize the capacities by mixing functional materials (MoS2) into the lignin/polyacrylonitrile (PAN) composite polymers. A MoS2 decorated porous carbon network material could be fabricated through focused femtosecond pulsed laser irradiation of the corresponding composite membranes. The microstructure and spectroscopic features of these laser induced hybrid carbon materials have been deeply investigated. The supercapacitor based on lignin/PAN has high areal specific capacitances of 6.7 mF cm−2 (0.9 F cm−3) at 10 mV s−1. Moreover, doped microsupercapacitors with MoS2 demonstrated enhanced areal capacitances up to 16 mF cm−2 (2.2 F cm−3) and at 10 mV s−1, respectively. The relatively high areal capacitances indicate that the proposed method is potential for innovative manufacturing energy storage devices based on natural lignin. [ABSTRACT FROM AUTHOR]

We report on the impact of laser processing on material and device performance characteristics for integrated energy applications. A femtosecond laser was used for development of flexible and transparent supercapacitors, while a nanosecond laser was successfully exploited for high-performance Al-air battery development. A laser direct-write process enabled integration of a three-dimensional-structured micro-supercapacitor on flexible polymer substrate, exhibiting peak specific capacitance of 42.6 mF/cm2 at current density of 0.1 mA/cm2. Femtosecond laser processing was also exploited for development of a novel transparent supercapacitor on silk substrate. The MnO2-coated transparent supercapacitors exhibited high transmittance exceeding 59%. Laser processing in combination with printing technique was used for development of a novel Al-air battery. The nanosecond laser process was effective in sintering the anode printed using Al nanoparticle ink. The efficiency of the laser sintering process was reflected in good battery discharge performance. [ABSTRACT FROM AUTHOR]

• A novel approach to fabricate waterproof sensors inside flexible substrate by laser direct writing. • Silver nanoparticles conductive circuits sealed inside PDMS film form a waterproof sensor. • This process can be developed as a general fabrication method for various waterproof devices. The preparation of stable, reliable and multifunctional sensors requires constant research. This study reports a novel approach to fabricate waterproof sensors inside flexible substrate by laser direct writing. Polydimethylsiloxane (PDMS) films were prepared as flexible substrates. A silver ink composed of silver nitrate, sodium citrate, and polyvinyl pyrrolidone (PVP) were used in this work. The silver ink was first coated on the surface of PDMS film. Then a 405 nm laser was used to reduce silver nanoparticles for conductive circuits on PDMS film. After cleaning the unprocessed silver ink another layer of PDMS film was covered on the silver circuits to form a waterproof sensor. The sensor can be used for detection of bending and elongation of fingers. The response time is 0.3 s, and the recovery time is 0.4 s. The sensor can respond well with high frequency and low frequency bending. It can keep its functions normally after five hundred times of bending. Moreover, the sensor can be operated normally underwater with good waterproof performance and stability. It can be safely used to monitor movement in wet conditions, rainy weather and underwater environments. Based on these experimental results, this facile process is promising for preparation of waterproof wearable sensors. [ABSTRACT FROM AUTHOR]