Giant ultrafast optical nonlinearities of annealed Sb₂Te₃ layers

Abstract

The optimization of a Sb2Te3 thin film structure in order to obtain giant ultrafast nonlinearities is presented.

Thickness-Dependent Optical Nonlinearities of Nanometer-Thick Sb2Te3 Thin Films: Implications for Mode-Locking and Super-resolved Direct Laser Writing

“…44 The higher values obtained here can be attributed to an enhancement of the nonlinear absorption achieved through the thickness optimization that we present in this work and an annealing optimization that has been previously detailed by our group. 16 It has to be mentioned that the nonlinear absorption coefficients found in this work are slightly lower than those that we have previously reported, which is due to the shorter pulse duration of the laser system employed here (400 fs instead of 600 fs used in Reference 16 ). The pulse duration is well-known to have a significant impact on the NLO response of 2D materials.…”

“…16 The crystallization has been obtained by performing a 24 hour annealing at 300°C as previously demonstrated by our group. 16,17 Morphological studies and elemental analysis. The annealed layers have been initially visualized by Scanning Electron Microscopy using a backscatter electron detector that delivers a signal response from deeper subsurface layers of the sample and also shows crystal orientation contrast.…”

“…The XRD peaks obtained belong to the rhombohedral crystalline structure R m with 00l preferred orientation of the Sb 2 Te 3 material, in accordance with the results previously obtained by our group and other scientific groups. 17,16,[27][28][29][30][31] In the case of the 7 nm thick layers and for lower film thicknesses no peaks appeared during the XRD studies. These films are though well crystallized (see Figure S1 in Supporting information for the 7 nm thick layer).…”

“…15 Such materials are currently the most promising candidates for applications requiring significant NLO responses and in several cases it has been shown that they can have superior performances compared to those of graphene. 5,16 Moreover, the broadband character of their optical and nonlinear optical responses enhances their importance for photonic applications. 3,17 The relation between the thickness of 2D materials and their nonlinearities is still unclear, despite their importance for many different fields of photonics and the intense research currently carried out in this scientific domain.…”

“…This has been previously achieved by our group by means of a precise annealing of the Sb 2 Te 3 thin layers. 16 The enhancement of the optical nonlinearities is also expected to depend on the nanocrystal size. Moreover, taking into account that the significant nonlinearities of Sb 2 Te 3 thin films are attributed to their topological insulator character, a high dependence of the NLO response on the thin film thickness can be expected.…”