engleski

Reflections on Optics in Monoelemental 2D Materials

Two-dimensional materials inspired a large number of studies, both experimental and theoretical, regarding their beneficial properties and possible applications in various technologies [1, 2]. Using monolayer materials can have many advantages over their bulk counterparts. Monolayers and their respective properties are readily modified by strains, electric fields, surface functionalization and doping. Additionally, they possess flexibility which can be exploited on free-shape surfaces, like vehicles, buildings, clothes and skin. Going beyond graphene, in our studies we concentrate on single layer structures – monolayers – composed of indium (indiene) and antimony (antimonene) atoms. Based on density functional theory we propose stable allotropic modifications of those monolayers. Stable monolayer structures are allocated among planar, buckled and puckered geometries. Full phonon dispersion curves across the whole Brillouin zone reveal the lattice dynamical stability. These allotropic modifications show tunable electronic band structures which leads to diverse polarization dependent optical properties. Modifications of the optical properties can be achieved using the external electric field imposed on the crystal lattice. Proposed applications in optical nano-devices are based on predicted optical properties ranging from relatively high refraction coefficient to very high selective reflectivity [3, 4]. Our results suggest application in the UV part of the electromagnetic spectrum for antimonene and in the Vis and IR parts for indiene. In antimonene allotropes, a high refractive index of up to 3.6 is found in the UV spectrum allowing applications as an inner layer coating under UV absorbers. The dielectric function and electron loss spectra (EELS) reveal the plasmon energies of around 9 eV and, thus, the parts of the electromagnetic spectrum where antimonene reflects like a metallic surface. Although the absorption process starts in the IR part of the spectrum, it peaks in the UV spectrum having a steady fall toward the high energy UV. Large optical anisotropy is observed in indiene for in-plane and out-of-plane light polarizations. This could be very useful in ultra-thin optical polarizers based on indium, for infra-red, visible and ultra-violet light. Very high reflectivity in the visible spectrum of planar indiene is distinguished. Reflectivity in the buckled indiene is characterized by the almost equally spaced reflectance peaks, which span the segment from the infra-red to the ultra-violet wavelengths. Equalizing their separation and reflectance percentage could introduce indiene to applications in wavelength selective reflectors. We have also shown that planar structure remains metallic, while the band gap in the buckled structure can be changed by applying external electric field. An overview of their advantages and disadvantages will be compared to other monolayer materials, like graphene, silicene and transition metal dichalcogenides.

2D materials ; optics ; indium ; antimony ; density functional theory

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