Single-layer PtSe2 adsorbed with non-metallic atoms: geometrical, mechanical, electronic and optical properties and strain effects.

Recently, single-layer PtSe2, possessing high carrier mobility and optical response, has been successfully fabricated. To further expand its application scope and find new physics, in this work, we functionalized it via the adsorption of non-metallic atoms X (X = H, B, C, N, O, and F) to form hybrid systems X-PtSe2, and their geometrical, mechanical, electronic, and optical properties as well as strain tuning effects were studied deeply. Calculations show that the energy stability of X-PtSe2 systems is significantly enhanced, and they also hold higher thermal and mechanical stability. Particularly, X-PtSe2 systems present excellent in-plane tenacity and out-of plane stiffness against deformations, which make them more applicable for designing nanodevices. Intrinsic PtSe2 is a semiconductor, while the X-PtSe2 system can be a band-gap narrowed semiconductor or metal, thus expanding the application scope for PtSe2, and the odd-even effect of electronic phase variation related to the atomic number is found. Besides, the wavelength range of optical adsorption is increased in X-PtSe2 systems, implying that its optical response region is wide, providing more options for developing optoelectronic devices. Moreover, it is shown that strain can flexibly tune the electronic property of X-PtSe2 systems, especially enhancing the optical absorption ability substantially, beneficial for their applications in solar devices.

Inducing abundant magnetic phases and enhancing magnetic stability by edge modifications and physical regulations for NiI2 nanoribbons.

Recently, a magnetic semiconducting NiI2 monolayer was successfully fabricated. To obtain richer magneto-electronic properties and find new physics for NiI2, we studied the zigzag-type NiI2 nanoribbon (ZNiI2NR) with edges modified by different concentrations of H and/or O atoms. Results show that these ribbons hold a higher energy stability, thermal stability, and magnetic stability, and the Curie temperature can be increased to 143 from 15 K for the bare-edged ribbons. They feature a half-semiconductor, bipolar magnetic semiconductor, or half-metal, depending on the edge-terminated atomic species and concentrations, and are closely related to the ribbon edge states, impurity bands or hybridized bands. By applying strain or an electric field, ribbons can achieve a reversible multi-magnetic phase transition among a bipolar magnetic semiconductor, half-semiconductor, half-metal, and magnetic metal. This is because strain changes the Ni-I bond length, resulting in a variation of bond configurations (weight of ionic and covalent bonds) and the number of unpaired electrons. The compressive strain can increase the Curie temperature because it makes the edged Ni-I-Ni bond angle closer to 90°, leading to the FM d-p-d superexchange interaction being increased. The electric field varies the magnetic phase because it alters the electrostatic potential of the ribbon edges, and the Curie temperature is enhanced under the electric field because the ribbon is changed to a metallic state (half-metal or magnetic metal), in which the magnetic Ni atoms satisfy the Stoner criterion and hold a large magnetic exchange coefficient and electron state density at the Fermi surface.