The number of dopant atoms is a parameter that can effectively tune the electronic and magnetic properties of graphitic and pyridinic N-doped graphene.

Magnetism of reduced graphene oxide/rGO prepared by a green synthesis method from coconut shells (rGO-s) and the commercial product (rGO-c, ®Graphenea) have been investigated. Similar magnetic feature of a weak ferromagnetism concomitant with diamagnetic nature was observed in both samples. At 300 K, the saturation magnetization (MS) of rGO-s is approximately 14×10-3 emu/g, which is about 3 times of that observed in rGO-c (~5×10-3 emu/g). The noticeable difference in the MS is suggested due to the different concentration of oxygen-functional groups and other defects presented in the rGO sheets. The samples have similar structure and contains similar functional groups, yet rGO-s contains higher concentration of oxygen-functional groups and defects than rGO-c. A paramagnetic behavior was also indicated at low temperature. This study supports an indication of the defect-induced-magnetism in rGO and confirms that various magnetic features, such as ferromagnetic, diamagnetic and paramagnetic, can coexist in rGO.

Cu-Ni alloys are promising catalysts for precisely controlling the number of graphene layers grown by chemical vapor deposition (CVD). However, the theoretical understanding of the effect of the Ni atomic...

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Electrical dan magnetic properties of graphene-derivatives materials are strongly influenced by their physical properties. Here we report a study on physical properties of reduced graphene oxide (rGO) prepared from two different raw materials, namely coconut shell (rGO-s) and graphite mineral (rGO-c, produced by Graphenea Inc.). rGO-s was prepared by carbonization method followed by mechanical exfoliation. While both samples have the same density of about 1.9 g/cm 3 , rGO-c has more porous compared to rGO-s. Specific surface area in rGO-c was also obtained much larger than that of rGO-s. Examinations on particle size and surface morphology show that rGO-c has homogenous particles which consist of transparent thin sheets, while rGO-s has rather heterogenous particles that look like dens stacked sheets. The presence of C and O was confirmed at the observed morphology. The difference in physical features was found to influence the obtained electrical conductivity of the samples. rGO-c has higher conductivity than rGO-s. Estimation on gap energy (Eg) indicates that rGO-c and rGO-s have Eg in the range of semiconducting materials. The study provides a better understanding on physical properties of coconut shell-derived rGO to further revise synthesis method to improve quality of the obtained rGO.

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Modifying the bandgap and magnetic properties of graphene is one of the keys to realizing graphene-based nanodevices. Here, we investigate the effect of nitrogen concentration in the pyrrolic bond configuration on the magnetic properties of graphene using the spin-polarized Density Functional Theory (DFT) method. For a better understanding, we also calculated the electronic and structural properties of the pyrrolic N-doped graphene. This study used three models, i.e., pristine graphene and pyrrolic N-doped graphene with two nitrogen concentrations (N x G1 − x , x=2.000% and 3.125%). We observed that the higher the dopant concentration, the more the deformation of the planar structure in pyrrolic N-doped graphene. This is indicated by the more wrinkled structure that forms. Semi-metal to metal transitions were also observed in both models of pyrrolic N-doped graphene. Asymmetry behavior in the spin-polarized density of states (SPDOS) was also observed in both pyrrolic N-doped graphene models. The total magnetic moment increases with increasing dopant concentration. At a concentration of 2.000%, the resulting total magnetic moment is 1.68 µB/cell, and at a concentration of 3.125%, it is 1.74 µB/cell. We suggest that defects and nitrogen impurities play a crucial role in the transition of the magnetic properties of graphene. Our result shows that nitrogen-doped graphene with pyrrolic configuration is a promising candidate for nanomagnetic devices.

This study investigated the structural and electronic properties of bulk, bilayer, and monolayer SnSe using the density functional theory (DFT) method. We succeeded in calculating the bandgap and identifying accurately the transformation of the band structure from bulk to monolayer systems using generalized gradient approximation. An increase in the lattice parameter a and a decrease in the lattice parameter b were observed when the bulk dimensions were reduced to a monolayer. The reduction of van der Waals interactions when the dimensions of a system are reduced is the main factor that causes changes in lattice parameters. The indirect bandgap of bulk SnSe (0.56 eV, 0.3∆→0.7Σ) becomes wider in the monolayer system (0.94 eV, 0.2∆→0.8Σ). Bandgap widening is predicted due to the emergence of the quantum confinement effect in low-dimensional systems. Furthermore, we found the formation of a quasi-degenerate minimum conduction band in the monolayer SnSe. With the formation of these bands, we predict the monolayer SnSe will have better thermoelectric properties than the bulk or bilayer system. This study provides an in-depth understanding of the electronic structure of SnSe and its correlation to thermoelectric properties.