Epitaxial Growth of Diamond-Shaped Au1/2Ag1/2CN Nanocrystals on Graphene

Epitaxial synthesis of inorganic nanomaterials on pristine 2D materials is of interest in the development of nanostructured devices and nanocomposite materials, but is quite difficult because pristine surfaces of 2D materials are chemically inert. Previous studies found a few exceptions including AuCN, AgCN, CuCN, and Cu0.5Au0.5CN, which can be preferentially synthesized and epitaxially aligned onto various 2D materials. Here, we discover that Au1/2Ag1/2CN forms diamond-shaped nanocrystals epitaxially grown on pristine graphene surfaces. The nanocrystals synthesized by a simple drop-casting method are crystallographically aligned to lattice structures of the underlying graphene. Our experimental investigations on 3D structures and the synthesis conditions of the nanocrystals imply that the rhombic 2D geometries originate from different growth rates depending on orientations along and perpendicular to 1D molecular chains of Au1/2Ag1/2CN. We also perform in situ TEM observations showing that Au1/2Ag1/2CN nanocrystals are decomposed to Au and Ag alloy nanocrystals under electron beam irradiation. Our experimental results provide an additional example of 1D cyanide chain families that form ordered nanocrystals epitaxially aligned on 2D materials, and reveal basic physical characteristics of this rarely investigated nanomaterial.

Investigation of the Effect of 3d TM-TM Atom Co-Doped in Graphene Nanosheet: DFT Based Calculations

Graphene, an interesting 2D system has a rare electronic structure of two inverted Dirac cones touching at a single point, with great electron mobility and promising microelectronics applications. In the present article, a theoretical investigation has been performed on the structural, electronic, and magnetic properties of pristine graphene nanosheet and also the effect of 3d transition metal (TM) co-doped in graphene nanosheet within the density functional theory framework. 3d TM is categorized into two groups: Cr- group (Cr-Cr, Cr-Mn, and Cr-Fe) and Ni-group (Ni-Cr, Ni-Ti, Ni-Mn). After co-doping TM atoms on graphene, it still holds its planar shape which refers to the stability of these co-doped graphene nanosheets. This is also confirmed by the increasing bond length of carbon and TM atoms on graphene nanosheets. Highest zero-point energies have been found of -12049.24eV and -10936.87eV respectively for Cr-Cr and Ni-Cr co-doped graphene nanosheet. According to Mulliken's charge and electron density differences, all the TM atoms can act as electron donors while the graphene nanosheet is electron acceptor. All the TMs co-doped graphene nanosheet show metallic behavior in terms of band structures and DOS plots except Ti-Ni which has shown a little band gap. In terms of electronic properties, Cr-Cr and Ni-Cr co-doped graphene nanosheets are found most stable among the other studied systems and they can exhibit magnetic behavior as there is a variation in their up and down spin as shown in spin polarized DOS. That’s why they are beneficial to the application of various magnetic devices as well as sectors. Besides Cr-group co-doped graphene nanosheet can exhibit better magnetic properties than Ni-group.

Graphene Family Nanomaterials (GFN)-TiO2 for the Photocatalytic Removal of Water and Air Pollutants: Synthesis, Characterization, and Applications

Given the industrial revolutions and resource scarcity, the development of green technologies which aims to conserve resources and reduce the negative impacts of technology on the environment has become a critical issue of concern. One example is heterogeneous photocatalytic degradation. Titanium dioxide (TiO2) has been intensively researched given its low toxicity and photocatalytic effects under ultraviolet (UV) light irradiation. The advantages conferred by the physical and electrochemical properties of graphene family nanomaterials (GFN) have contributed to the combination of GFN and TiO2 as well as the current variety of GFN-TiO2 catalysts that have exhibited improved characteristics such as greater electron transfer and narrower bandgaps for more potential applications, including those under visible light irradiation. In this review, points of view on the intrinsic properties of TiO2, GFNs (pristine graphene, graphene oxide (GO), reduced GO, and graphene quantum dots (GQDs)), and GFN-TiO2 are presented. This review also explains practical synthesis techniques along with perspective characteristics of these TiO2- and/or graphene-based materials. The enhancement of the photocatalytic activity by using GFN-TiO2 and its improved photocatalytic reactions for the treatment of organic, inorganic, and biological pollutants in water and air phases are reported. It is expected that this review can provide insights into the key to optimizing the photocatalytic activity of GFN-TiO2 and possible directions for future development in these fields.

Reliability of spin-to-charge conversion measurements in graphene-based lateral spin valves

Understanding spin physics in graphene is crucial for developing future two- dimensional spintronic devices. Recent studies show that efficient spin-to-charge conversions via either the inverse spin Hall effect or the inverse Rashba-Edelstein effect can be achieved in graphene by proximity with an adjacent spin-orbit coupling material. Lateral spin valve devices, made up of a graphene Hall bar and ferromagnets, are best suited for such studies. Here, we report that signals mimicking the inverse Rashba-Edelstein effect can be measured in pristine graphene possessing negligible spin-orbit coupling, confirming that these signals are unrelated to spin-to-charge conversion. We identify either the anomalous Hall effect in the ferromagnet or the ordinary Hall effect in graphene induced by stray fields as the possible sources of this artefact. By quantitatively comparing these options with finite-element-method simulations, we conclude the latter better explains our results. Our study deepens the understanding of spin-to-charge conversion measurement schemes in graphene, which should be taken into account when designing future experiments.