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Direct growth of large-area uniform graphene films on insulating materials could facilitate the applications of graphene in optoelectronic devices. The ultrafast photocarrier relaxation and saturable absorption of direct chemical vapor deposition-grown graphene glasses, with lots of defects, are studied by using femtosecond time-resolved pump–probe and Z-scan techniques at 800 nm. We find that both the relaxation times associated with hot carrier cooling and the hot phonon effect are greatly suppressed in these defect-rich graphene glasses, which further leads to the increase of both saturation intensity and anisotropy in transient optical response for graphene glasses as compared with defect-free graphene. And, both the suppression effect and saturation intensity increase with the thickness of graphene film. The dominance of defect-assisted carrier-acoustic phonon scattering (i.e., supercollision, the collision of a carrier with both an acoustic phonon and defects) in the cooling process of hot carriers is responsible for the suppression of relaxation time. [ABSTRACT FROM AUTHOR]

In recent years, two‐dimensional (2D) atomic crystals represented by graphene have opened up new fields of 2D physics. Layered materials with atomic layer thickness are self‐assembled into van der Waals heterostructures by weak van der Waals forces without considering lattice matching. Van der Waals heterostructures can not only enhance the performance of its constituent materials but also show new characteristics. High‐quality heterostructures require mechanically cleaved intrinsic 2D materials and flexible 2D material stacking techniques. Here, we summarize in detail the reliable exfoliation methods for large‐area single‐layer 2D materials and the dry and wet stacking techniques with high success rates. The twisted bilayer graphene is used as an example to briefly introduce the single‐crystal tearing method, which is currently the most practical method for preparing isotropic twisted heterostructures with high‐precision rotation angles. We hope to provide a valuable reference for researchers of 2D materials. [ABSTRACT FROM AUTHOR]

Based on the polarization-sensitive absorption effect, we have proposed a method to accurately count the number of carbon atomic layers for both exfoliated and chemical vapor deposition graphene sheets on transparent substrate. With spatial scanning, the three-dimensional imaging of graphene sample can be achieved to test the uniformity of the sample. In addition, our method serves for graphene test on transparent substrate, which is different from the commonly used SiO2/Si substrate. Moreover, this method is also applicable to layers counting of other two-dimensional materials. Therefore, it paves the way for applications of two-dimensional materials on transparent medium. [ABSTRACT FROM AUTHOR]

Based on the polarization-sensitive absorption of graphene under conditions of total internal reflection, we demonstrate the fabrication and reading of transparent and flexible multi-layer-film optical data storage media based on graphene recording layers. We report a realization of the process of data writing-transferring-reading by repeatedly transferring recorded graphene and its strong polarization effect. The reading results show a high signal-to-noise ratio and stability and low crosstalk interference between the layers. In addition, the graphene-based multi-layer-film optical data storage medium has a high transparency and flexibility. The high signal-to-noise ratio remains stable after the structure is bent 1000 times. [ABSTRACT FROM AUTHOR]

Abstract: We used a two-layer structure consisting of polyethylene terephthalate (PET) and silicone to transfer graphene grown by chemical vapor deposition onto various rigid and flexible substrates through dispersive adhesion. It only takes a few seconds to transfer graphene from PET/silicone to the target substrates at ambient conditions. And the recycling of the PET/silicone decreases the production cost greatly. The transferred graphene films were characterized by optical and atomic force microscopy, Raman spectroscopy, electrical analyses, and optical transmittance measurements, and the results show that the graphenes transferred by PET/silicone have a cleaner and more continuous surface, lower doping level, and higher optical transmittance and conductivity than those transferred by thermal release tape. Considering its high efficiency, low cost, large area and high quality, the PET/silicone transfer method would be particularly useful for graphene’s electronic applications such as field-effect transistors and transparent conducting electrodes. [Copyright &y& Elsevier]

Many novel transport phenomena are observed in graphene nanochannels with ultrahigh surface flatness and nano‐ or sub‐nanoscale constraints. Two critical physical parameters, surface slip length, and surface charge, play a vital role in the channel transport process. However, effectively controlling these parameters under such tight constraints remains a significant challenge. Here, it is developed a novel method that combines oxygen ion etching and layer‐by‐layer assembly of 2D material, to prepare graphene nanochannels. During the assembly process, defects are introduced into the graphene surface via oxygen ion etching. A significantly higher conductivity is observed for the pristine graphene channels compared to those with defects on both the upper and lower surfaces. Consistent with this observation, the conductivity of graphene channels with defects on only one surface falls between the two aforementioned values. Combined with theoretical analysis, the conductivity difference is attributed to the surface slip inhibition due to the introduced defects, and the change of surface charge, both caused by oxygen ion etching. By introducing defects, a new method is uncovered for fine‐tuning ion transport in graphene nanochannels. [ABSTRACT FROM AUTHOR]

A polarization-dependent saturable absorber is developed by the use of graphene-polymer film covered microfiber. The evanescent field of the guided mode propagating along the microfiber can effectively interact with graphene. Polarization analysis shows that the single-layer graphene-based saturable absorber is more sensitive to polarization and has larger modulation depth than that of multi-layer graphene. Such a saturable absorber exhibits large saturable absorption power of >56.03~mW, and is easy to fabricate and compatible with optical fiber system. It has high potential in wide range of photonics applications. [ABSTRACT FROM PUBLISHER]

Ultrafast carrier dynamics and saturable absorption of few-layered graphene oxide, well-dispersed in organic solvent, are studied using femtosecond pump-probe and Z-scan techniques. The results demonstrate that few-layered graphene oxide has a fast energy relaxation of hot carriers and strong saturable absorption, which is comparable with that of reduced graphene oxide. Fast carrier relaxation combined with well solution processing capability arises from the large fraction of sp2 carbon atom inside the few-layered graphene oxide sheet together with oxidation mainly existing at the edge areas. This superiority of few-layered graphene oxide will facilitate potential applications of graphene for ultrafast photonics. [ABSTRACT FROM AUTHOR]

Onthe basis of the polarization-dependent absorption of graphene undertotal internal reflection, we designed a graphene-based optical refractiveindex sensor with high resolution of 1.7 × 10–8and sensitivity of 4.3 × 107mV/RIU, as well asan extensive dynamic range. This highly sensitive graphene opticalsensor enables label-free, live-cell, and highly accurate detectionof a small quantity of cancer cells among normal cells at the single-celllevel and the simultaneous detection and distinction of two cell lineswithout separation. It provides an accurate statistical distributionof normal and cancer cells with fewer cells. This facile and highlysensitive sensing refractive index may expand the practical applicationsof the biosensor. [ABSTRACT FROM AUTHOR]

Highlights: [•] The nonlinear optical properties of three graphene hybrid materials are studied. [•] In nanosecond regime, RGO–ZnPc shows better optical limiting properties. [•] In femtosecond regime, GO–ZnPc shows better nonlinear optical properties. [•] The interaction between graphene and ZnPc causes optical nonlinearity enhancement. [ABSTRACT FROM AUTHOR]