Identification of aggregated 2D cobalt tellurides using a spatial self-phase modulation technique

Abstract

We report a previously unreported application of the spatial self-phase modulation (SSPM) technique for recognizing solute-solvent interaction in a suspension of 2D material. Broadband optical absorption of the 2D Co2Te3 leads to a nonlinear optical (NLO) susceptibility for the monolayer, i.e., χ M o n o ( 3 ) of 1.5 ×10−9 (3.3 ×10−9) esu at 532 (632) nm, which is 1–2 orders higher than for the 2D CoTe and CoTe2. The fine structure of the SSPM patterns is analyzed to explore the foundations of the observed NLO effects. With increasing polarity of the liquid media, a change of 2D Co2Te3 from homophonous dispersion to aggregation occurs, as confirmed from in situ optical microscopy and UV-vis absorption spectroscopy. As a result, type-I (thickest outer ring) SSPM ring patterns are converted to type-II (thinnest outer ring) SSPM ring patterns. Therefore, using SSPM with a CW laser as an optical tool to identify solvent-polarity-induced aggregation in 2D materials is possible.