Kim, Yong-Jae Kim, Seon Joon Seo, Darae Chae, Yoonjeong Anayee, Mark Lee, Yonghee Gogotsi, Yury Ahn, Chi Won Jung, Hee-Tae 2024-01-19T14:02:12Z 2024-01-19T14:02:12Z 2021-10-21 2021-08 0897-4756 https://pubs.kist.re.kr/handle/201004/116581 Understanding the etching mechanisms of MXene and obtaining direct insights into the influence of etchants on structural features and defects are of critical importance for improving MXene properties, optimization of etching protocols, and exploring new MXene compositions. Despite their importance, such studies have been challenging because of the monoatomic thickness of the A-element layers being etched and aggressive etchants that hinder in situ studies. Here, we visualize the etching behavior of the Ti3AlC2 MAX phase in different etchants at the atomic scale using focused ion beam and electron microscopy. We also report on the structural changes in the Ti3AlC2 phase as a function of etching time and etchant type (LiF/HCl, HF, or NH4HF2) to reveal the etching mechanism for the first time. Interestingly, direct visualization reveals an unexpected stepwise etching where the edge Al atoms at the middle layers of the MAX particle are not etched despite contact with the acidic etchant counterintuitively. Also, while the propagation of the etching front occurs in the direction normal to the inner basal plane for all etchants, we reveal that HF and NH4HF2 etch the grain boundaries of polycrystal MAX particles to expose more edge sites to the etchant, which is not observed for LiF/HCl. English AMER CHEMICAL SOC Etching Mechanism of Monoatomic Aluminum Layers during MXene Synthesis Article 10.1021/acs.chemmater.1c01263 1 CHEMISTRY OF MATERIALS, v.33, no.16, pp.6346 - 6355 CHEMISTRY OF MATERIALS 33 16 6346 6355 N scie scopus 000691302400010 2-s2.0-85113986033 Chemistry, Physical Materials Science, Multidisciplinary Chemistry Materials Science Article TI3C2 EXFOLIATION CAPACITANCE TI3ALC2