Raman spectroscopic investigation of polycrystalline structures of CVD-grown graphene by isotope labeling

One-year post-exposure assessment of 14C-few-layer graphene biodistribution in mice: single versus repeated intratracheal administration

Research on graphene-based nanomaterials has experienced exponential growth in the last few decades, driven by their unique properties and their future potential impact on our everyday life. With the increasing production and commercialization of these materials, there is significant interest in understanding their fate in vivo. Herein, we investigated the distribution of 14C-few-layer graphene (14C-FLG) flakes (lat. dim. ∼ 500 nm) in mice over a period of one year. Furthermore, we compared the effects of repeated low-dose and acute high-dose exposure by tracheal administration. The results showed that most of the radioactivity was found in the lungs in both cases, with longer elimination times in the case of acute high-dose administration. In order to gain deeper insights into the distribution pattern, we conducted ex vivo investigations using μ-autoradiography on tissue sections, revealing the heterogeneous distribution of the material following administration. For the first time, μ-autoradiography was used to conduct a comprehensive investigation into the distribution and potential presence of FLG within lung cells isolated from the exposed lungs. The presence of radioactivity in lung cells strongly suggests internalization of the 14C-FLG particles. Overall these results show the long-term accumulation of the material in the lungs over one year, regardless of the administration protocol, and the higher biopersistence of FLG in the case of an acute exposure. These findings highlight the importance of the exposure scenario in the context of intratracheal administration, which is of interest in the evaluation of the potential health risks of graphene-based nanomaterials.

Easy and Versatile Synthesis of Bulk Quantities of Highly Enriched 13C-Graphene Materials for Biological and Safety Applications

The preparation of bulk quantities of ¹³C-labeled graphene materials is relevant for basic investigations and for practical applications. In addition, ¹³C-labeled graphene materials can be very useful in biological and environmental studies, as they may allow the detection of graphene or its derivatives in cells or organs. In this paper, we describe the synthesis of ¹³C-labeled graphene materials (few-layer graphene, FLG, and graphene oxide, GO) on a tens of mg scale, starting from ¹³C-labeled methane to afford carbon fibers, followed by liquid-phase exfoliation (FLG) or oxidation (GO). The materials have been characterized by several analytical and microscopic techniques, including Raman and nuclear magnetic resonance spectroscopies, thermogravimetric analysis, X-ray photoelectron spectroscopy, and X-ray powder diffraction. As a proof of concept, the distribution of the title compounds in cells has been investigated. In fact, the analysis of the ¹³C/¹²C ratio with isotope ratio mass spectrometry (IRMS) allows the detection and quantification of very small amounts of material in cells or biological compartments with high selectivity, even when the material has been degraded. During the treatment of ¹³C-labeled FLG with HepG2 cells, 4.1% of the applied dose was found in the mitochondrial fraction, while 4.9% ended up in the nuclear fraction. The rest of the dose did not enter into the cell and remained in the plasma membrane or in the culture media.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

Strain-inducing photochemical chlorination of graphene nanoribbons on SiC (0001)

As different low-dimensional materials are sought to be incorporated into microelectronic devices, graphene integration is dependent on the development of band gap opening strategies. Amidst the different methods currently investigated, application of strain and use of electronic quantum confinement have shown promising results. In the present work, epitaxial graphene nanoribbons (GNR), formed by surface graphitization of SiC (0001) on crystalline step edges, were submitted to photochemical chlorination. The incorporation of Cl into the buffer layer underlying graphene increased the compressive uniaxial strain in the ribbons. Such method is a promising tool for tuning the band gap of GNRs.

In situ chemical probing of hole defects and cracks in graphene at room temperature

Chemical vapor deposition (CVD) has emerged as the most promising technique towards manufacturing of large area, high quality graphene. Characterization, understanding, and controlling of various structural defects in CVD-grown graphene are essential to realize its true potential for real-world applications. We report a new method for in situ chemical probing of vacancy defects in CVD-grown graphene at room temperature. Our approach is based on a solid-gas phase reaction that occurs selectively in graphene vacancy defect regions such as holes and cracks. Our new probing technique has a unique combination of the following advantages: (1) no exposure to liquids; (2) non-damaging in situ probing; (3) high selectivity, sensitivity, and reliability towards vacancy defects; (4) simplicity and scalability. By focusing on hexagonal graphene domains, we have made the following findings: (1) the nucleation centers of graphene domains are favorable locations of hole defects. (2) The lengthy electron-beam irradiation at very low energy (3.5 keV) could etch the graphene. (3) Graphene cracks often kink at the angle of primarily 150° or 120°. (4) There exist complex graphene cracks such as cracks with clock-hands patterns, and cracks with snowflake-like branched structures. (5) There exist discontinuous cracks in some graphene domains, where hole defects are oriented along a straight or curved line. Such discontinuous cracks may arise from the ductile fracture of graphene. In addition, we have shown that our method is also applicable to chemical probing of vacancy defects such as holes, continuous and discontinuous cracks in CVD-grown monolayer polycrystalline graphene films on copper. Our study also suggests that the copper grain and copper grain boundary play significant roles in formation and distribution of graphene vacancy defects.

Carbon Nanotubes versus Graphene as Flexible Transparent Electrodes in Inverted Perovskite Solar Cells

Transparent carbon electrodes, carbon nanotubes, and graphene were used as the bottom electrode in flexible inverted perovskite solar cells. Their photovoltaic performance and mechanical resilience were compared and analyzed using various techniques. Whereas a conventional inverted perovskite solar cells using indium tin oxide showed a power conversion efficiency of 17.8%, the carbon nanotube- and graphene-based cells showed efficiencies of 12.8% and 14.2%, respectively. An established MoO₃ doping was used for  carbon electrode-based devices. The difference in the photovoltaic performance between the carbon nanotube- and graphene-based cells was due to the difference in morphology and transmittance. Raman spectroscopy, and cyclic flexural testing revealed that the graphene-based cells were more susceptible to strain than the carbon nanotube-based cells, though the difference was marginal. Overall, despite higher performance, the transfer step for graphene has lower reproducibility. Thus, the development of better graphene transfer methods would help maximize the current capacity of graphene-based cells.

Toward fast growth of large area high quality graphene using a cold-wall CVD reactor

In this work we provide a detailed analysis on graphene synthesis by Chemical Vapor Deposition (CVD) using a cold wall CVD reactor to achieve fast production of large area high quality graphene.

Nondestructive optical visualisation of graphene domains and boundaries

The domain boundaries of polycrystalline graphene produced by chemical vapor deposition (CVD) adversely influence the graphene transporting properties. The existing domain visualisation methods for large area graphene always cause detrimental damage or contamination. Here we report a nondestructive method for spatial visualisation of the domains and boundaries of large area continuous graphene grown on Cu foils (Gr/Cu) by CVD. Using a rationally modified optical microscope, we can directly observe novel star-like bright line sets of Gr/Cu in an enhanced dark field mode. Each set of the bright lines is identified as the ridges of one Cu surface pyramid which arises beneath one enlarging graphene domain due to slower evaporation of graphene-covered Cu than that of graphene-free Cu. This one to one correspondence thereby enables nondestructive visualisation. This method offers an advantageous pathway for monitoring the spatial distribution of the graphene domains and boundaries. We have further discovered for the first time various types of star-like ridge structures which are governed by the underlying Cu crystallographic orientations. This gives rise to a new phenomenon for research on the complex 2D material-metal interfacing.

Tracking airborne CO2 mitigation and low cost transformation into valuable carbon nanotubes

Primary evidence of the direct uptake of atmospheric CO2 and direct transformation into carbon nanotubes, CNTs, is demonstrated through isotopic labeling, and provides a new high yield route to mitigate this greenhouse gas. CO2 is converted directly to CNTs and does not require pre-concentration of the airbone CO2. This C2CNT (CO2 to carbon nanotube) synthesis transforms CO2-gas dissolved in a 750 °C molten Li2CO3, by electrolysis, into O2-gas at a nickel electrode, and at a steel cathode into CNTs or carbon or nanofibers, CNFs. CNTs are synthesized at a 100-fold price reduction compared to conventional chemical vapour deposition, CVD, synthesis. The low cost conversion to a stable, value-added commodity incentivizes CO2 removal to mitigate climate change. The synthesis allows morphology control at the liquid/solid interface that is not available through conventional CVD synthesis at the gas/solid interface. Natural abundance (12)CO2 forms hollow CNTs, while equivalent synthetic conditions with heavier (13)CO2 favours closed core CNFs, as characterized by Raman, SEM and TEM. Production ease is demonstrated by the first synthesis of a pure (13)C multiwalled carbon nanofiber.

Etchant-free graphene transfer using facile intercalation of alkanethiol self-assembled molecules at graphene/metal interfaces

We report a novel etchant-free transfer method of graphene using the intercalation of alkanethiol self-assembled monolayers (SAMs) at the graphene/Cu interfaces. The early stage of intercalation proceeds through graphene grain boundaries or defects within a few seconds at room temperature until stable SAMs are formed after a few hours. The formation of SAMs releases the compressive strain of graphene induced by Cu substrates and make graphene slightly n-doped due to the formation of interface dipoles of the SAMs on metal surfaces. After SAM formation, the graphene is easily delaminated off from the metal substrates and transferred onto insulating substrates. The etchant-free process enables us to decrease the density of charged impurities and the magnitude of potential fluctuation in the transferred graphene, which suppress scattering of carriers. We also demonstrate the removal of alkanethiol SAMs and reuse the substrate. This method will dramatically reduce the cost of graphene transfer, which will benefit industrial applications such as of graphene transparent electrodes.