Inspired by the success of graphene, various two dimensional (2D) structures in free standing (FS) (hypothetical) form and on different substrates have been proposed recently. Silicene, a silicon counterpart of graphene, is predicted to possess massless Dirac fermions and to exhibit an experimentally accessible quantum spin Hall effect. Since the effective spin-orbit interaction is quite significant compared to graphene, buckling in silicene opens a gap of 1.55 meV at the Dirac point. This band gap can be further tailored by applying in plane stress, an external electric field, chemical functionalization and defects. In this topical theoretical review, we would like to explore the electronic, magnetic and optical properties, including Raman spectroscopy of various important derivatives of monolayer and bilayer silicene (BLS) with different adatoms (doping). The magnetic properties can be tailored by chemical functionalization, such as hydrogenation and introducing vacancy into the pristine planar silicene. Apart from some universal features of optical absorption present in all these 2D materials, the study on reflectivity modulation with doping (Al and P) concentration in silicene has indicated the emergence of some strong peaks having the robust characteristic of a doped reflective surface for both polarizations of the electromagnetic (EM) field. Besides this, attempts will be made to understand the electronic properties of silicene from some simple tight-binding Hamiltonian. We also point out the importance of shape dependence and optical anisotropy properties in silicene nanodisks and establish that a zigzag trigonal possesses the maximum magnetic moment. We also suggest future directions to be explored to make the synthesis of silicene and its various derivatives viable for verification of theoretical predictions. Although this is a fairly new route, the results obtained so far from experimental and theoretical studies in understanding silicene have shown enough significant promising features to open a new direction in the silicon industry, silicon based nano-structures in spintronics and in opto-electronic devices.

No abstract

No abstract

Several selenides have been studied as potential thermoelectric materials in the past. Thermoelectric performance improves on reducing the dimension of the system. Following these notions, we studied three hexagonal two-dimensional phases of thallium selenide for promising thermoelectric performance by using first-principles techniques. Their dynamical and mechanical stabilities have been shown. The band gaps using different approximations of calculations have been reported and are in the range that can render these materials to show optimal thermoelectric performance. The lattice thermal conductivity is ultralow between 0.088 and 0.429 W m–1 K–1 at 900 K. High thermoelectric performance has been predicted in the systems with the figure of merit reaching magnitudes of ∼0.5–1.94 between 300 and 900 K. The high thermoelectric performance results from an ultralow thermal conductivity arising due to the strong lattice anharmonicity. These results can have significant impact on the synthesis of high performance thermoelectric materials based on thallium selenide.

Various optical properties of two dimensional buckled silicene have been explored using spin unpolarized density functional theory by incorporating doping with phosphorous and aluminium atoms in the hexagonal network of pristine buckled silicene.