Synnatschke Kevin, Moses Badlyan Narine, Wrzesińska Angelika, Lozano Onrubia Guillermo, Hansen Anna-Lena, Wolff Stefan, Tornatzky Hans, Bensch Wolfgang, Vaynzof Yana, Maultzsch Janina, Backes Claudia
Institute of Physical Chemistry, Heidelberg University, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany; School of Physics, University of Dublin, Trinity College, Dublin 2, Ireland.
Institute for Solid-State Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany; Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen, Germany.
Ultrason Sonochem. 2023 Aug;98:106528. doi: 10.1016/j.ultsonch.2023.106528. Epub 2023 Jul 19.
Liquid phase exfoliation (LPE) has been used for the successful fabrication of nanosheets from a large number of van der Waals materials. While this allows to study fundamental changes of material properties' associated with reduced dimensions, it also changes the chemistry of many materials due to a significant increase of the effective surface area, often accompanied with enhanced reactivity and accelerated oxidation. To prevent material decomposition, LPE and processing in inert atmosphere have been developed, which enables the preparation of pristine nanomaterials, and to systematically study compositional changes over time for different storage conditions. Here, we demonstrate the inert exfoliation of the oxidation-sensitive van der Waals crystal, CrTe. The pristine nanomaterial was purified and size-selected by centrifugation, nanosheet dimensions in the fractions quantified by atomic force microscopy and studied by Raman, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and photo spectroscopic measurements. We find a dependence of the relative intensities of the CrTe Raman modes on the propagation direction of the incident light, which prevents a correlation of the Raman spectral profile to the nanosheet dimensions. XPS and EDX reveal that the contribution of surface oxides to the spectra is reduced after exfoliation compared to the bulk material. Further, the decomposition mechanism of the nanosheets was studied by time-dependent extinction measurements after water titration experiments to initially dry solvents, which suggest that water plays a significant role in the material decomposition.
液相剥离法（LPE）已成功用于从大量范德华材料制备纳米片。虽然这有助于研究与尺寸减小相关的材料特性的基本变化，但由于有效表面积显著增加，这也会改变许多材料的化学性质，通常伴随着反应活性增强和氧化加速。为防止材料分解，已开发出在惰性气氛中进行液相剥离和加工的方法，这能够制备原始纳米材料，并系统研究不同储存条件下随时间的成分变化。在此，我们展示了对氧化敏感的范德华晶体CrTe的惰性剥离。通过离心对原始纳米材料进行纯化和尺寸选择，通过原子力显微镜对各部分中的纳米片尺寸进行量化，并通过拉曼光谱、X射线光电子能谱（XPS）、能量色散X射线光谱（EDX）和光光谱测量进行研究。我们发现CrTe拉曼模式的相对强度与入射光的传播方向有关，这使得拉曼光谱轮廓与纳米片尺寸之间无法建立关联。XPS和EDX表明，与块状材料相比，剥离后表面氧化物对光谱的贡献减少。此外，在对初始干燥溶剂进行水滴定实验后，通过随时间变化的消光测量研究了纳米片的分解机制，结果表明水在材料分解中起重要作用。
