Substitutional doping of MoTe2/ZrS2 heterostructures for sustainable energy related applications.

Stacking and/or substitutional doping are effective strategies to tune two-dimensional materials with desired properties, greatly extending the applications of the pristine materials. Here, by employing first-principles calculations, we propose that a pristine MoTe2/ZrS2 heterostructure is a distinguished lithium-ion battery anode material with a low Li diffusion barrier (∼0.26 eV), and it has a high maximum Li storage capacity (476.36 mA h g-1) and a relatively low open-circuit voltage (0.16 V) at Li4/MoTe2/Li/ZrS2/Li4. The other heterostructures with different types can be achieved by substitutional doping and their potential applications in sustainable energy related areas are further unraveled. For instance, a type-II TeMoSe/ZrS2 heterostructure could be a potential direct Z-scheme photocatalyst for water splitting with a high solar-to-hydrogen conversion efficiency of 17.62%. The TeMoSe/SZrO heterostructure is predicted to be a potential candidate for application in highly efficient solar cells. Its maximum power conversion efficiency can be as high as 19.21%, which is quite promising for commercial applications. The present results will shed light on the sustainable energy applications of pristine or doped MoTe2/ZrS2 heterostructures in the future.

Strain-Tunable Electronic Properties and Band Alignments in GaTe/C2N Heterostructure: a First-Principles Calculation.

Recently, GaTe and C2N monolayers have been successfully synthesized and show fascinating electronic and optical properties. Such hybrid of GaTe with C2N may induce new novel physical properties. In this work, we perform ab initio simulations on the structural, electronic, and optical properties of the GaTe/C2N van der Waals (vdW) heterostructure. Our calculations show that the GaTe/C2N vdW heterostructure is an indirect-gap semiconductor with type-II band alignment, facilitating an effective separation of photogenerated carriers. Intriguingly, it also presents enhanced visible-UV light absorption compared to its components and can be tailored to be a good photocatalyst for water splitting at certain pH by applying vertical strains. Further, we explore specifically the adsorption and decomposition of water molecules on the surface of C2N layer in the heterostructure and the subsequent formation of hydrogen, which reveals the mechanism of photocatalytic hydrogen production on the 2D GaTe/C2N heterostructure. Moreover, it is found that in-plane biaxial strains can induce indirect-direct-indirect, semiconductor-metal, and type II to type I or type III transitions. These interesting results make the GaTe/C2N vdW heterostructure a promising candidate for applications in next generation of multifunctional optoelectronic devices.

Highly tunable spin-dependent electron transport through carbon atomic chains connecting two zigzag graphene nanoribbons.

Motivated by recent experiments of successfully carving out stable carbon atomic chains from graphene, we investigate a device structure of a carbon chain connecting two zigzag graphene nanoribbons with highly tunable spin-dependent transport properties. Our calculation based on the non-equilibrium Green's function approach combined with the density functional theory shows that the transport behavior is sensitive to the spin configuration of the leads and the bridge position in the gap. A bridge in the middle gives an overall good coupling except for around the Fermi energy where the leads with anti-parallel spins create a small transport gap, while the leads with parallel spins give a finite density of states and induce an even-odd oscillation in conductance in terms of the number of atoms in the carbon chain. On the other hand, a bridge at the edge shows a transport behavior associated with the spin-polarized edge states, presenting sharp pure α-spin and ß-spin peaks beside the Fermi energy in the transmission function. This makes it possible to realize on-chip interconnects or spintronic devices by tuning the spin state of the leads and the bridge position.

Plasmon excitations in sodium atomic planes: a time-dependent density functional theory study.

The collective electronic excitation in planar sodium clusters is studied by time-dependent density functional theory calculations. The formation and development of the resonances in photoabsorption spectra are investigated in terms of the shape and size of the two-dimensional (2D) systems. The nature of these resonances is revealed by the frequency-resolved induced charge densities present on a real-space grid. For long double chains, the excitation is similar to that in long single atomic chains, showing longitudinal modes, end and central transverse modes. However, for 2D planes consisting of (n × n) atoms with n being up to 16, new 2D characteristic modes emerge regardless of the symmetries considered. For in-plane excitations, besides the equivalent end mode, mixed modes with contrary polarity occur. The relation between the frequency of the primary modes and the system size is similar to the case of a 2D electron gas but with a correction due to the realistic atomic structure. For excitations perpendicular to the plane there are corner, side center, bulk center, and circuit modes. Our calculation reveals the importance of dimensionality for plasmon excitation and how it evolves from 1D to 2D.