First principles second harmonic generation of transition metal dichalcogenides and boron nitride alloys: from monolayers and nanotubes to Haeckelites and Schwarzites

TL;DR

This study uses first principles calculations to explore second harmonic generation in various 2D layered alloys, nanotubes, Haeckelites, and Schwarzites, revealing structures with notably high nonlinear optical responses.

Contribution

It provides the first comprehensive theoretical analysis of SHG in diverse 2D and porous BN structures, identifying new materials with exceptional  responses.

Findings

Tungsten-based alloys have higher  at high photon energies.

Hypothetical NbSSe and Nb0.5Ta0.5S2 Haeckelites show the highest  among studied structures.

Decreasing nanotube diameter enhances , approaching monolayer levels.

Abstract

In order to shed light on the second harmonic generation (SHG) of new 2-D systems, first principles methods are used to calculate the second order susceptibility \chi(2) for different types of layered alloys such as monolayers of transition metal dichalcogenide (TMD) alloys, TMD Haeckelite alloys, nanotubes of TMD alloys, hexagonal boron nitride (h-BN) systems which include BxNyCz alloys, BN and BNC2 nanotubes, BxNxCy Haeckelites and BN Schwarzites (porous BN). It is found that the tungsten based alloys possess higher \chi(2) than Mo based at high photon energies, but at low energies, one type of MoSSe dominates. The hypothetical TMD Haeckelites NbSSe and Nb0.5Ta0.5S2 reveal the highest \chi(2) of all the calculated structures. Zigzag TMD alloy nanotubes show higher \chi(2) as the diameter is reduced and approximate to the monolayer for big diameters. BNC alloys exhibit a higher \chi(2) than the h-BN monolayer and are comparable to TMD alloys, except for one case which doubles its intensity. The BN tubes show an increase of \chi(2) as the diameter decreases, similarly to the TMD nanotubes. BxNxCy Haeckelites possess a very high \chi(2) and may shed light on the role of extended defects in nonlinear optical properties. One of the BN Schwarzites exhibits a higher \chi(2) than already known 3-D materials.