The tip-enhanced Raman spectroscopy (TERS) is a modern technique for nano-scale analyses, which combines the excellent spatial resolution of scanning probe microscopy and the chemical sensitivity of surface-enhanced Raman scattering spectroscopy. These unique properties of TERS are achieved via the use of a plasmonic nano-tip positioned only a few nanometers away from the studied sample. However, the tips are prone to mechanical and chemical degradation, which may hinder the achieved spatial resolution and signal enhancement. Therefore, periodic checks of the state of the tip are crucial to maintaining the high quality of TERS experiments. Reference samples are commercially available for these purposes, but they are costly and have a quite short expiration date of several months. For this reason, we have developed a simple procedure for the preparation of reference probe samples for testing TERS tips using copper(II) phthalocyanine on a Au nanolayer, which is prepared by thermal vacuum evaporation of Au on a Si wafer. The analysis of the prepared system by atomic force microscopy and scanning electron microscopy confirmed a relatively smooth surface morphology, which is an important parameter for minimizing the risk of mechanical damage of the tip. TERS experiments proved that the developed system is suitable as a reference sample for TERS at the 785 nm excitation wavelength, enabling a repeated detection of well-resolved TERS spectra. The use of the reference sample for 633 nm excitation is limited because of possible photo-induced processes, which decrease the reproducibility and stability of the collected TERS spectra.

Graphic abstract

中文翻译：

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用于尖端增强拉曼光谱的新型参考样品的开发和表征

尖端增强拉曼光谱 (TERS) 是一种用于纳米级分析的现代技术，它结合了扫描探针显微镜的出色空间分辨率和表面增强拉曼散射光谱的化学敏感性。TERS 的这些独特特性是通过使用距离研究样品仅几纳米的等离子体纳米尖端来实现的。然而，尖端容易发生机械和化学降解，这可能会阻碍实现的空间分辨率和信号增强。因此，定期检查尖端状态对于保持 TERS 实验的高质量至关重要。参考样品可用于这些目的，但它们价格昂贵且有效期很短，只有几个月。为此，我们开发了一种简单的程序，用于在 Au 纳米层上使用铜 (II) 酞菁测试 TERS 尖端的参考探针样品的制备，该纳米层是通过在 Si 晶片上热真空蒸发 Au 制备的。通过原子力显微镜和扫描电子显微镜对制备的系统进行分析，证实了相对光滑的表面形态，这是将尖端机械损坏风险降至最低的重要参数。TERS 实验证明，所开发的系统适合作为 785 nm 激发波长下 TERS 的参考样品，能够重复检测分辨率良好的 TERS 光谱。由于可能的光诱导过程，633 nm 激发的参考样品的使用受到限制，这会降低所收集 TERS 光谱的重现性和稳定性。

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