As surface-only materials, freestanding 2D materials are known to have a high level of contamination—mostly in the form of hydrocarbons, water, and residuals from production and exfoliation. For well-designed experiments, it is of particular importance to develop effective cleaning procedures, especially since standard surface science techniques are typically not applicable. We perform ion spectroscopy with highly charged ions transmitted through freestanding atomically thin materials and present two techniques to achieve clean samples, both based on thermal treatment. Ion charge exchange and energy loss are used to analyze the degree of sample contamination. We find that even after cleaning, heavily contaminated spots remain on single layer graphene. The contamination coverage, however, clusters in strand-like structures leaving large clean areas. We present a way to discriminate clean from contaminated areas with our ion beam spectroscopy if the heterogeneity of the surface is increased sufficiently enough. We expect a similar discrimination to be necessary in most other experimental techniques.

中文翻译：

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独立式二维材料在离子束光谱学中污染物的作用：热处理研究。

作为仅表面的材料，独立式2D材料已知污染程度很高，主要是碳氢化合物，水以及生产和剥落后残留的形式。对于精心设计的实验，开发有效的清洁程序尤为重要，特别是因为通常不适用标准的表面科学技术。我们对通过独立原子薄材料传输的高电荷离子进行离子光谱分析，并提出了两种技术来实现清洁样品，这两种技术均基于热处理。离子电荷交换和能量损失用于分析样品污染的程度。我们发现，即使清洁后，单层石墨烯上仍保留着严重污染的斑点。但是，污染覆盖物聚集在类似股线的结构中，留下了较大的清洁区域。如果表面的异质性足够充分地增加，我们将提供一种利用离子束光谱技术将污染区域与清洁区域区分开的方法。我们期望在大多数其他实验技术中也需要类似的区分。