Second harmonic generation spectroscopy on two-dimensional materials [Invited]

Abstract

The discovery of atomically thin layered materials such as graphene and transition metal dichalcogenides has unveiled the unique exploration of novel fundamental physics and device applications in two-dimensions. Characterization of their crystal symmetry and subsequent electronic properties are prominent to realize the full potential of these reduced dimensional systems, which fundamentally determine the topology, chirality and rich interfacial physics. Second harmonic generation (SHG), a nonlinear optical effect, is sensitive to crystal symmetry and electronic structures, which proves to be one of the most powerful yet simple technique to capture the essence physics. On the other hand, the 2D nature of layered materials enables large tunability in its physical properties with a number of external stimuli, which in turn paves the way for the development of 2D nonlinear optoelectronic applications. In this review, we overview recent efforts employing second harmonic generation spectroscopy and microscopy to probe lattice structures and dipole polarizations in two-dimensional transition metal dichalcogenide and polar materials. In addition, multiple external stimuli used to control SHG as potential optoelectronic devices are covered. We conclude with a perspective on the future directions of exploration on emerging 2D magnetic and topological materials based on SHG spectroscopy.

Tuning Excitonic Properties of Monolayer MoS2 with Microsphere Cavity by High‐Throughput Chemical Vapor Deposition Method

“…and Eversole et al . Each WGM mode of a spherical cavity can be identified by using (1) azimuthal mode number m attributed to oscillation periods number per cycle propagating around microsphere circumference, and (2) radial mode number r corresponds to the number of radial modes . Through substituting reflective index of SiO 2 ( n = 1.48) into above algorithm, the resonant modes (Figure d, red) of monolayer MoS 2 on SiO 2 microsphere (see Figure a) can be assigned to the first ( r = 1) and the second ( r = 2) order transverse magnetic (TM) modes (Figure d, blue).…”

Large Out‐of‐Plane Second Harmonic Generation Susceptibility in Penta‐ZnS2 Sheet

“…In recent years, with the rapid development of 2D materials, large SHG responses have been experimentally observed in many 2D non‐centrosymmetric materials including 2H‐MoS 2 , [ 7 ] h‐BN, [ 8 ] 2D perovskite, [ 9 ] and CrI 3 , [ 10 ] which are much stronger than those of their bulk and few‐layered counterparts. [ 11 ] For instance, the SHG susceptibility of 2H‐MoS 2 is three orders of magnitude larger than that of bulk MoS 2 . [ 7 ] Theoretically, the numerical method for calculating SHG has been well developed by applying the density matrix method within the framework of perturbation theory, [ 12,13 ] which makes it possible to find more 2D materials with SHG effect.…”

Nanoscale imaging of photocurrent enhancement by resonator array photovoltaic coatings

“…Close-packed arrays of nanospheres required for high surface coverage can potentially enable better coupling of the resonators. 21–24,32,33,35–40 To construct monolayer close-packed nanosphere arrays, many approaches have been used including the Langmuir-Blodgett method, 23,41 sedimentation, 42,43 evaporation, 44,45 and the Meyer rod rolling technique. 24,46 For practical application as an antireflective coating for commercial photovoltaics, the deposition process has to be inexpensive and compatible with continuous production.…”