This paper reports an exhaustive review of recent research progress in the development of millimeter-wave absorbers. With the advancement in technologies, microwave absorbers have shown their evolution in several applications such as defense, security identification, stealth technology, and several more. The importance of these absorbers is increasing due to electromagnetic interference (EMI) effects. Primarily, an abundant amount of absorbers has been developed in lower frequency bands and with the increasing demand for 5G technology, the usage of millimeter-wave bands has gained attention. This in turn requires the development of millimeter-wave absorbers to provide EMI shielding in several applications. Out of several materials, polymers have grabbed attention in the mitigation of EMI. An absorber that combines carbonaceous elements with polymers offers large design flexibility and tunability per the filler concentration. This paper focuses on the classification of these absorbers based on geometry as well as that by using polymers with their design challenges, merits, and demerits with their industrial applications. Comparative studies of geometrically based absorbers and polymeric-based absorbers are also shown.

In this study, the problem of backward heating in microwave ablation technique is examined and an electromagnetic solution based on the use of high impedance graphene material is presented for its mitigation. In this context, a one-atom-thick graphene layer is added on the coaxial double slot antenna. In addition to the electromagnetic behavior, thermal effects caused by the graphene-covered antenna are emphasized. The graphene's conductivity being highly dependent on its chemical potential and the relaxation time, a parametric study is performed to determine a range of tolerances within which the graphene-coated antenna outperform a typical graphene-free antenna. The range of values is found to be 0 < μc < 0.5 eV and τ < 0.4 ps, for the chemical potential and the relaxation time, respectively. The backward heating problem being prevented, the ablation region is ensured to be spherical around the tip of the antenna. Effects of the graphene layer to the heat dissipation in the tissue, the necrotic tissue ratio (damage to the cancerous tissue of the caused by electromagnetic energy), and the treatment time using the coaxial double slot antenna were examined. The results show that the heat dissipation is concentrated around the slots (region of cancerous tissue) and a higher necrotic tissue ratio can be achieved with a graphene-covered double slot antenna in a shorter time.

This work is focused on determining whether two graphene derivatives: graphene oxide (GO) and reduced graphene oxide (RGO) can be used alone as a component of anticancer therapy. In this paper, we present the synthesis GO and RGO, their physicochemical characterization as well as an evaluation of their cytotoxic properties on cancer (HepG2 and MCF-7) and non-malignant (clone-9 and HMF) cells. We demonstrated that both tested graphene derivatives have a high affinity to cancer cells. We showed that cytotoxic properties of GO and RGO were different depending on the type of solvent in which they were prepared. Additionally, we observed that cytotoxic properties of GO and RGO were different depending on the origin of the cells (liver and breast) and the form of graphene material (GO and RGO). We showed that GO and RGO can be potential, selectively materials which in future can found application in anticancer therapy.

Developing easy and effective surface functionalization approaches has required to facilitate the processability of graphene while seeking novel application areas. Herein, an in situ single-step reductive covalent bromination of graphene has been reported for the first time. Highly brominated graphene flakes (>3% Br) were prepared by only subjecting the bromine-intercalated graphite flakes to a reduction reaction with reactive lithium naphthalide. The bromine-functionalized graphene was characterized by X-ray photoelectron spectroscopy and thermogravimetric analysis. Results revealed that Br2 molecules acted as both an intercalating agent for the graphite and a reactant for the surface functionalization of the graphene. After brominating, the remaining negative charges on the reduced graphene surface were further used for the dual surface functionalization of graphene with a long-chain alkyl group (~1% dodecyl group addition). The functionalized graphenes were also characterized by Fourier transform infrared and Raman spectroscopy.

Polymer nanocomposites possess unique sets of properties that make them suitable for different applications, including structural and flame-retardant material, electromagnetic wave reflector, sensors, thin film transistor, flexible display, and many more. The properties of these nanocomposite are dependent on nanofiller dispersion and bonding with polymer matrix (i.e. particle-matrix interaction). Thermography is a non-destructive method that may be used to gain insight into dispersion and particle-matrix interaction. Infrared (IR) radiation emitted from these nanomaterial polymer composite depends on the emissivity of the individual components. In addition, during flash heating and cooling, different thermal conductivity of components in the nanocomposite can influence pixel intensity differently in the IR image or video being captured. We have used an economical mid wavelength IR camera Fluke RSE600 equipped with a close-up macro lens and algorithm based on MATLAB image processing toolbox to analyse dispersion, voids and thermal diffusivity of patented graphene polymer nanocomposite materials (G-PMC) in micro-scale. These G-PMCs can act as a standard material to determine the potential of our IR thermography technique due to their homogeneity and lack of impurity due to unique fabrication process. Thermal diffusivity and dispersion of nanoparticles in our G-PMCs was estimated after irradiation with a xenon flash lamp by spatially mapping transient IR radiations from different G-PMCs using the Fluke RSE600 thermal imager. Results from thermography experiments were compared with scanning electron microscope (SEM) and Raman spectroscopy results. Micro-scale thermography was able to detect millimetre scale thermal diffusivity variation in the injection molded G-PMC samples and relate it to change in dispersion of nanofillers, unlike SEM and Raman, where micro-scale measurements could not determine the reason behind millimetre scale property variation. We believe this low cost, fast, micro-scale, non-destructive technique will provide valuable insight into functional polymer nanocomposite fabrication and corresponding electrical and thermal properties.

The contact angle is a material property determined by the surface tensions between substrate, liquid and the air. In this study, the surface wettability of vertical graphene nanosheets (VGNs) which are carbon nanostructures consisting of a few layers of graphene sheets vertically standing on the substrates, were developed by applying different voltages on the substrate. The contact angle of the water droplet on VGNs/Cu decreased from 123° to 16° with increasing the applied voltage which indicated the hydrophobic and hydrophilic transition of VGNs surfaces. It is anticipated that this member of the carbon material family (VGNs) could serve as a tunable wettability coting for future improvements in electronic devices and open a new perspective to the construction of smart material surfaces.

Sarin gas is a dangerous chemical warfare agent (CWA). It is a nerve agent capable of bringing a person to death in about 15 minutes. A lethal concentration of sarin molecules in air is about 30 mg/m3. Experimental research on this gas requires very careful safety protocols for handling and storage. Therefore, theoretical and computational studies on sarin gas are very welcome and might provide important safe guides towards the management of this lethal substance. In this work, we investigated the interactions between sarin, air and nanoporous graphene, using tools of classical molecular dynamics simulations. Aiming to cast some light in the possible sarin selective filtration by graphene, we designed a bipartite simulation box with a porous graphene nanosheet placed at the middle. Sarin and air molecules were initially placed only on one side of the box so as to create an initial pressure towards the passage of both to the other side. The box dimensions were chosen so that the hole in the graphene was the only possible way through which sarin and air molecules can get to the other side of the box. The number of molecules that passed through the hole in graphene was monitored during 10 ns of simulation and the results for different temperatures were compared. The results show that, as far as the size of the holes are small, van der Waals forces between graphene and the molecules play a significant role on keeping sarin near graphene, at room temperature.

Dental pulp derived cells are pluripotent stem cells which can be differentiated along odontogenic, osteogenic, adipogenic, or neurogenic lineages. Odontogenic and osteogenic differentiation, in the absence of dexamethasone, have been shown to be highly dependent on substrate morphology and mechanics. Here we focus on neurogenic differentiation, using the protocol described by A. Arthur et al., and its dependence on substrate nature. DPSCs were cultured on PLA, a biodegradable polymer approved for internal use. The upregulation of genetic markers was compared with that of cells plated on standard TCP. The role of substrate morphology was investigated by plating on electrospun fibers approximately 2.0 ± 1.0 μm in diameter and on spin-cast thin films. The influence of graphene was investigated through the addition of 3% and 10% graphene nanoparticles to the films and fibers respectively.

The aspect ratio of the cells was measured using confocal microscopy. Cells grown on graphene containing substrates had larger aspect ratios than their non-graphene counterparts, and cells grown on microfibers were longer than their counterparts on the flat films. But the cell aspect ratio did not necessarily correlate with genetic differentiation. The results after 21 days of incubation indicated that early markers (TBP, β-III tubulin), decreased uniformly on all substrates relative to day 0, with the largest decrease occurring on the PLA flat film with graphene. The late stage marker, NEFM, which indicates differentiation, was upregulated to a significantly larger extent on all PLA substrates. No difference was observed between the fibers and the flat film in the absence of graphene, thus morphology did not play a significant role on this polymer. Addition of graphene did not affect the outcome on the fibers, but significantly suppressed the gene expression on the flat films. These results indicate that PLA is a promising scaffold material for neurogenic differentiation.

Graphene has been publicized as the game changing material of this millennium. As research continues to expand our knowledge of this 2D semimetal, the properties at the interface have become an increasingly important characteristic. Translating graphene’s strength at the nanoscale to the macroscale is suggested by functionalizing the graphene, creating a favourable interfacial morphology to adhere. An interfacial morphology that is able to form primary chemical bonds is ideal, providing the best mechanical property performance. We proposed a method of creating a graphene reinforced polymer matrix composite from flake mineral graphite in-situ, using high shear elongational flow to produces these conditions. In our process we were able to identify chemical bonding at graphene’s surface, which developed into newly created interfacial morphologies. These morphologies lead to an increase in mechanical properties while providing an improved stress transfer between graphene and its containing matrix. Our work sheds light on a solvent free route to scalable high strength graphene composites.

We consider the scattering and absorption of the H-polarized plane wave by finite and semi-infinite systems of layers in the THz range. Every layer consists of an infinite graphene strip grating embedded into a dielectric slab. The solution of the problem we obtain in several steps. First, with the use of the method of singular integral equations we obtain scattering matrices of a single layer. Then, we present equations for the finite and semi-infinite systems of layers relatively the Fourier amplitudes of the scattered field. The frequency dependences of the reflection, transmission, and absorption coefficients demonstrate the variety of resonances: plasmon, slab-mode, grating-mode resonances, and resonances of the multilayer structure.

Flexible electrode is an indispensable component of emerging portable, flexible, and wearable electronic devices. Although various flexible electrodes with different dimensions and functions have been explored, developing a new electrode material with excellent mechanical reliability and superior electrical performance remains a challenge. Here, a graphene-covered Cu composite electrode film with a total thickness of ∼100 nm is successfully fabricated onto a flexible polyimide substrate by means of a series of assembly methods including physical vapor deposition, chemical vapor deposition, and transfer technique. The composite electrode film on the flexible substrate exhibits evidently enhanced tensile strength, monotonic bending, and repeatedly bending fatigue reliability as well as electrical performance compared with that of the bared Cu film electrode. Such excellent mechanical performances are attributed to the role of the graphene coating in suppressing fatigue damage formation and preventing crack advance. It is expected that the chemical vapor-deposited graphene-covered Cu composite electrode would extend the potential ultrathin metal film electrode as the innovative electrode material for the next-generation flexible electronic devices.

Three-dimensional graphene (3D-GN)/Cu/Fe3O4 composite support materials were synthesized by a modified chemical reduction method using graphene oxide precursor. A 3D-GN/Cu/Fe3O4 biosensor was prepared by coating the electrode with laccase. The electrochemical properties of the biosensor were investigated by cyclic voltammetry (CV) and differential pulse voltammetry using potassium ferricyanide, phosphate-buffered saline (PBS) solution, and bisphenol A (BPA) solution. The current response of 3D-GN/Cu/Fe3O4 biosensors presents a remarkable sensitivity based on CV. The linear range of BPA is 7.2–18 μM using differential pulse voltammetry in PBS solution (pH = 4.0). A linear fitting equation of the laccase biosensor was observed for the current response as a function of BPA concentration. The detection limit was decreased to 1.7 μM. The detection approach herein turns out to be highly sensitive, has a wide linear range, and exhibits excellent stability.

The physicochemical properties and broad applications of graphene have been extensively studied, but its preparation method is still a bottleneck, and it cannot simultaneously meet the requirements of low process cost and high quality of products in the time being. In this article, the redox potential was employed to control the quality of graphene prepared from graphene oxide by chemical reduction. The effects of the initial redox potential on the productivity, microscopic morphology, and structural and intrinsic properties of graphene were investigated. Results showed that there was an optimum initial redox potential range between −1200 and −1180 mV. In such a range could the graphene with a high yield be obtained, and layers of graphene products could be stabilized at 1 or 2 layers. Therefore, the redox potential could be used as an effective parameter instead of trying to design orthogonal tests to determine the optimal conditions and control the synthesis of graphene.

Raman spectroscopy is a fundamental tool for the characterization of two-dimensional materials. It provides insights into the electronic and vibrational properties of these materials and is particularly rich in features when the incident laser energy approaches the electronic energy transition of the material. Among these features, the double resonance Raman process provides important information on the electron, phonon, and electron–phonon properties. It was on the study of carbon-related materials that the double resonance bands sparkled showing their potential and, since then, have been deeply searched in the study of novel 2D materials. Here, the authors review the double resonance Raman process in 2D materials focusing on graphene and semiconducting MoS2 highlighting the origin of the bands mediated by the two-phonon and phonon–defect processes. The authors discuss the observed properties of the double resonance bands and compare the processes for graphene and MoS2 to find guiding principles for the appearance of double resonance bands. The authors also discuss the new findings of the intervalley scattering process in transition metal dichalcogenides. A brief discussion of the defect-induced bands in both materials is also presented.

In this report, bulk graphene–reinforced titanium (Ti–Gr) nanocomposite with millimeter thickness was fabricated by selective laser melting process. Demonstrated by the characterizations of scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectra, graphene nanoplatelets were successfully embedded into the titanium matrix with a uniform dispersion due to a fast heating–cooling process. High-resolution transmission electron microscopy was used to investigate the interface between titanium and graphene, where a certain amount of carbide was formed attribute to the chemical reaction between them during multilayer laser melting. A high density of dislocations was observed surrounding the graphene nanoplatelets in titanium matrix. The strength and elastic modulus of the nanocomposites were significantly improved, which has been demonstrated by nano-indentation tests. The hardness of the bulk Ti–Gr nanocomposites was approximately 1.27 times higher than pristine Ti counterpart. The strengthening mechanisms were discussed in detail.