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Direct 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. [ABSTRACT FROM AUTHOR]

Abstract: Actuators that can convert environmental stimuli into mechanical work are widely used in intelligent systems, robots, and micromechanics. To produce robust and sensitive actuators of different scales, efforts are devoted to developing effective actuating schemes and functional materials for actuator design. Carbon‐based nanomaterials have emerged as preferred candidates for different actuating systems because of their low cost, ease of processing, mechanical strength, and excellent physical/chemical properties. Especially, due to their excellent photothermal activity, which includes both optical absorption and thermal conductivities, carbon‐based materials have shown great potential for use in photothermal actuators. Herein, the recent advances in photothermal actuators based on various carbon allotropes, including graphite, carbon nanotubes, amorphous carbon, graphene and its derivatives, are reviewed. Different photothermal actuating schemes, including photothermal effect–induced expansion, desorption, phase change, surface tension gradient creation, and actuation under magnetic levitation, are summarized, and the light‐to‐heat and heat‐to‐work conversion mechanisms are discussed. Carbon‐based photothermal actuators that feature high light‐to‐work conversion efficiency, mechanical robustness, and noncontact manipulation hold great promise for future autonomous systems. [ABSTRACT FROM AUTHOR]

We report herein the engineering of the surface/interface properties of graphene oxide (GO) films by controllable photoreduction treatment. In our recent works, typical photoreduction processes, including femtosecond laser direct writing (FsLDW), laser holographic lithography, and controllable UV irradiation, have been employed to make conductive reduced graphene oxide (RGO) microcircuits, hierarchical RGO micro-nanostructures with both superhydrophobicity and structural color, as well as moisture-responsive GO/RGO bilayer structures. Compared with other reduction protocols, for instance, chemical reduction and thermal annealing, the photoreduction strategy shows distinct advantages, such as mask-free patterning, chemical-free modification, controllable reduction degree, and environmentally friendly processing. These works indicate that the surface and interface engineering of GO through controllable photoreduction of GO holds great promise for the development of various graphene-based microdevices. [ABSTRACT FROM AUTHOR]

Inspired from butterfly wings that exhibit unique dewetting properties and brilliant structural color synchronously, we reported here the preparation of biomimetic few-layer graphene films through a template-directed chemical vapor deposition method using laser-structured Cu foil as substrates. Hierarchical micronanostructures, including microscale stripes derived from the laser scanning and nanoscale laser-induced periodic surface structures (LIPSS), formed on Cu foil after a simple femtosecond laser treatment. By tuning the laser power, the surface roughness of the resultant Cu foils can be well controlled. Using the laser structures Cu foil as templates, biomimetic few-layer graphene films with both iridescence and superhydrophobicity have been successfully prepared. The present work may open up a new way to design and prepare structured graphene film in a biomimetic manner, and we deem that the bioinspired few-layer graphene films may find broad applications in the near future. [ABSTRACT FROM AUTHOR]

Inspired by natural autonomous systems that demonstrate controllable shape, appearance, and actuation under external stimuli, a facile preparation of moisture responsive graphene-based smart actuators by unilateral UV irradiation of graphene oxide (GO) papers is reported. UV irradiation of GO is found to be an effective protocol to trigger the reduction of GO; however, due to the limited light transmittance and thermal relaxation, thick GO paper cannot be fully reduced. Consequently, by tuning the photoreduction gradient, anisotropic GO/reduced GO (RGO) bilayer structure can be easily prepared toward actuation application. To get better control over the responsive properties, GO/RGO bilayer paper with a certain curvature and RGO patterns are successfully prepared for actuator design. As representative examples, smart humidity-driven graphene actuators that mimic the cilia of respiratory tract and tendril climber plant are successfully developed for controllable objects transport. [ABSTRACT FROM AUTHOR]

Reported here is a bioinspired fabrication of superhydrophobic graphene surfaces by means of two-beam laser interference (TBLI) treatment of graphene oxide (GO) films. Microscale grating-like structures with tunable periods and additional nanoscale roughness are readily created on graphene films due to laser induced ablation effect. Synchronously, abundant hydrophilic oxygen-containing groups (OCGs) on GO sheets can be drastically removed after TBLI treatment, which lower its surface energy significantly. The synergistic effect of micro-nanostructuring and the OCGs removal endows the resultant graphene films with unique superhydrophobicity. Additionally, dual TBLI treatment with 90° rotation is implemented to fabricate superhydrophobic graphene films with two-dimensional grating-like structures that can effectively avoid the anisotropic hydrophobicity originated from the grooved structures. Moreover, the superhydrophobic graphene films become conductive due to the laser reduction effect. Unique optical characteristics including transmission diffraction and brilliant structural color are also observed due to the presence of periodic microstructures. As a mask-free, chemical-free, and cost-effective method, the TBLI processing of GO may open up a new way to biomimetic graphene surfaces, and thus hold great promise for the development of novel graphene-based microdevices. [ABSTRACT FROM AUTHOR]

Summary: Graphene microcircuits have been successfully created on graphene oxide films via direct femtosecond laser reduction process according to preprogrammed patterns. Atomic force microscopy (AFM) characterization shows that surface height of the micropatterns was lower than the rest of the film due to the loss of oxygen confirmed by XPS and XRD techniques. The electric resistivity and conductivity of as-reduced graphene have strong dependences on output power of femtosecond laser. Moreover, current–voltage curves of graphene microcircuits show typical linear relationship, indicating the stable conductivities. The micro-nanoprocessing of graphene through femtosecond laser technologies might open the door for applications of graphene-based materials in electronic microdevices. [Copyright &y& Elsevier]

Graphene is emerging as one of the most useful electrode materials for various organic optoelectronic devices because of its outstanding properties such as high optical transparency, excellent mechanical flexibility, good electrical conductivity, and environmental stability. Numerous synthesis and transfer techniques used to obtain large‐area and high‐quality graphene materials are demonstrated, aiming at high‐performance graphene‐based organic optoelectronic devices such as solar cells, light‐emitting diodes, and field‐effect transistors. The properties, synthesis, and transfer processes of graphene are first introduced. Recent research progress on organic optoelectronic devices with graphene bottom, top, and full electrodes is then reviewed. Finally, graphene composite electrodes integrated with other conductive materials are also summarized. All these advanced works represent important steps in the evolution of graphene electrodes and indicate a bright future for their application in organic optoelectronic devices. [ABSTRACT FROM AUTHOR]

As the demand for display technology in consumer electronics and lighting panels increases, thin, light, high‐quality, and more cost‐effective light‐emitting devices are required. Organic light‐emitting devices (OLEDs), satisfying the criteria exactly, have been considered the most promising next‐generation display and lighting technique. In particular, an OLED based on flexible substrate enables the device to be applied to curved displays, electronic newspapers, wearable displays, and conceptual lighting panels, has been always in the spotlight both in science and industry. Great advances on flexible OLEDs (FOLEDs) have been made over the past three decades. The fundamental elements of FOLEDs including substrates, electrodes, fabrication and encapsulation techniques, as well as the strategies of efficiency improvement are discussed herein. Moreover, emerging electrodes such as graphene, carbon nanotubes, metal nanowire network and their composite, flexible perovskite light emitting devices, and stretchable light emitting devices are also considered. Finally, the future challenges and prospects for these devices are put forward. The fundamental elements of flexible organic light‐emitting devices including substrates, electrodes, fabrication and encapsulation techniques, as well as the strategies of efficiency improvement are discussed. Moreover, emerging electrodes such as graphene, carbon nanotubes, metal nanowire network and their composites, flexible perovskite light emitting devices, and stretchable light emitting devices are also considered. Finally, the challenges and prospects for the future are put forward. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An ultrathin Au/graphene composite electrode with high transmittance and conductivity has been demonstrated. • The ultrathin Au/graphene composite electrode is applied to supercapacitor. • Flexible and transparent supercapacitor with the composite electrode exhibits high capacitance and mechanical stability. Abstract Large-area monolayer graphene by chemical vapor deposition as electrode in electronic devices always suffers from shortages of low conductivity and high contact resistance. In this work, we demonstrate a composite electrode by depositing a continuous and homogeneous ultrathin 7-nm Au film on monolayer graphene with low average sheet resistance of 24.6 Ω/□ and high transmittance of 74.6% at 520 nm. The excellent properties of the composite electrode are attributed to the suppressed Au Volmer-Weber growth mode of the ultrathin Au film by the organized hexagonal carbon lattices of graphene. Rigid supercapacitor based on the composite electrode exhibits a capacitance of 81.5 μF/cm2 at the scan rate of 0.1 V/s, which is 17 times higher than the device based on monolayer graphene. Flexible supercapacitor based on the composite electrode can be bending at curvature radius of 2 mm and with slight performance decrease over 1800 bending cycles. [ABSTRACT FROM AUTHOR]

The combination of surface-enhanced Raman spectroscopy (SERS) technology with microfluidics makes it possible to diagnose genetic disease through label-free on-chip DNA detection. However, open problems including the integration of SERS substrate with microfluidic devices, controllable trapping and releasing of target molecules are still challenging. Here we demonstrate a facile laser scribing method to fabricate silver nanoparticles (AgNPs) and graphene oxide (GO) based biochips as a reusable SERS sensor for DNA detection. Programmable laser scribing of the AgNPs@GO composite film enables direct patterning of sensitive SERS channels that consist of graphene supported AgNPs by exfoliating the composites into hierarchical porous structures. Integrating the SERS-active patterns with a microfluidic chip forms a biochip for allowing SERS detection of DNA. The noncovalent interactions between DNA and graphene mediated controllable trapping and releasing of DNA sequences, enabling efficient on-chip SERS detection and the regeneration of the biochip. The simple, green and cost-effective fabrication of the SERS-active biochips reveals great potential for biomolecular sensing and genetic engineering applications. [ABSTRACT FROM AUTHOR]

The transferred chemical vapor deposition (CVD)-grown graphene from copper foils to other desired substrates by using poly(methyl methacrylate) (PMMA) as supporter, suffers from problems of rough surface, low conductivity and poor wettability, which hinders its applications in optoelectronic devices. In this work, a combined thermal annealing and HNO 3 doping treatment for graphene electrode has been employed to simultaneously improve its smoothness, conductivity and wettability. The thermal annealing process results in the improved surface smoothness by removing the PMMA residue. HNO 3 doping treatment for the graphene enhances its conductivity and surface wetting to PEDOT:PSS. Furthermore, the work function (WF) of two-step treated graphene increased from ∼4.4 eV to ∼5.1 eV. Small-molecule organic solar cells (OSCs) based on the two-step treated graphene anodes exhibit a power conversion efficiency (PCE) of 2.43%, which is comparable to that of ITO electrode (2.48%). This work demonstrates the bright future of graphene transparent electrodes as a replacement for ITO. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculation identifies elementary processes in the thermal reduction of graphene oxide (GO) and reveals the effects of alkaline-earth metals (AEMs) in recovering the graphene. These metals are highly effective in removing residual oxygen groups resistive to thermal reduction, as well as healing the defects formed during the reduction, such as the carbonyl groups. In the AEM-assisted reduction, the AEMs serve as an electron reservoir of high chemical potential that forces electron transfer to the GO, whereas pristine carbon regions on the GO serve as a “bridge” to facilitate the electron transfer directly to oxidized carbon. This enables fast kinetics for the breaking of both C–O and CComplete reduction is observed in our simulation at T ≤600K within 32ps for a 28%-oxygen-coverage GO model. [Copyright &y& Elsevier]

Abstract: Two-beam-laser interference was used for the simultaneous reduction, patterning and nanostructuring of graphene oxide on flexible polyethylene terephthalate substrates for the production of a high performance humidity sensing device. Hierarchical graphene nanostructures were formed after laser interference treatment of graphene oxide, which holds great promise for gaseous molecular adsorption, and thereby significantly increases their sensing performance. By tuning the laser power, the content of oxygen functional groups, could be changed within a certain range, which contributes not only controllable conductivity but also tunable response/recovery time of the humidity sensor due to the interaction between water molecules and oxygen functional groups on the graphene oxide sheets. The laser interference processing of graphene oxide films is a mask-free, surfactant-free and large-area approach to the production of hierarchical graphene micro-nanostructures, and thus shows great potential for fabrication of future graphene-based microdevices. [Copyright &y& Elsevier]

PH1000/graphene (Gra) composite film with thermally-induced wrinkles has been employed as an electrode in organic solar cells (OSCs) to enhance the device efficiency. The wrinkled PH1000/Gra composite electrode exhibits excellent transmittance of 88.5% at 550 nm, decreased sheet resistance of 147.5 Ω sq−1 and appropriate work function of ~4.9 eV compared to pristine graphene. OSCs with wrinkled composite electrode possess enhanced short circuit current (J SC) compared to that of planar devices due to the wrinkles-induced enhancements in light absorption and charge collection. The power conversion efficiency (PCE) of OSCs with wrinkled composite electrode is 4.67%, which is 60% or 35% higher than that of planar devices based on the pristine graphene (2.93%) or PH1000 (3.45%) electrode, respectively. Corresponding PCE is comparable to that of the conventional ITO-based OSCs (5.08%). Even better, flexible OSCs with PH1000/Gra composite electrode exhibited excellent mechanical stability compared to ITO device. The enhanced efficiency of the OSCs demonstrates that the wrinkled PH1000/Gra composite electrode is a promising candidate for efficient and flexible optoelectronic application. Performance-enhanced organic solar cells with wrinkled PH1000/graphene composite electrodes have been demonstrated. Image 1 • Wrinkled graphene and conducting polymer composite electrode has been fabricated. • Composite electrode exhibits high electrical conductivity and modified work function. • OSCs with composite electrode have realized an enhanced efficiency of 4.67%. • Flexible OSCs based on composite electrode exhibit excellent mechanical stability. • The mechanism of performance-enhanced OSCs has been discussed. [ABSTRACT FROM AUTHOR]