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arXiv 2403.19263physics.opticscond-mat.mtrl-sciphysics.ins-det
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用于非金属表面、具备入射角选择功能的红外反射吸收光谱装置

Infrared Reflection Absorption Spectroscopy Setup with Incidence Angle Selection for Surfaces of Non-Metals

David Rath, Vojtěch Mikerásek, Chunlei Wang, Moritz Eder, Michael Schmid, Ulrike Diebold, Gareth S. Parkinson, Jiří Pavelec

AI总结:

针对介电单晶 IRAS 中最佳作用角与低反射率区重合的问题,本文提出带高数值孔径镜组和可调入射角光阑的 UHV FTIR 装置,并在 CO/TiO2(110) 与 D2O/TiO2(110) 上验证了高信噪比。

摘要:

在介电单晶上开展红外反射吸收光谱(IRAS)研究颇具挑战性,因为光与吸附质相互作用的最佳入射角恰好位于红外反射率较低的区域。在此,我们介绍一种优化的 IRAS 装置,可使非金属测量的信噪比最大化。这是通过最大化光通量,并选择会直接影响光谱峰高的最佳入射角来实现的。该装置使用商用 FTIR 光谱仪,并可在超高真空(UHV)环境中使用。具体而言,其设计特点是在 UHV 系统内部设置具有高数值孔径的样品照明和收集反射镜,并用一个可调光阑来选择样品上的入射角范围。这对于介电材料上的 p 偏振测量非常重要,因为光谱中的峰会在布儒斯特角处发生方向反转(谱带反转)。系统各部件通过单个法兰精确连接,确保了长期稳定性。我们研究了 TiO2(110) 上一个单层 CO 的 p 偏振 IRAS 光谱中信噪比(SNR)随入射角范围的变化,在 4 cm-1 分辨率、五分钟测量时间下获得了 70 的最大信噪比。s 偏振能力则通过测量吸附在 TiO2(110) 表面上的一个单层 D2O 得到验证:在二十分钟内,当 delta_R/R0 峰高为 1.4×10-4 时,获得了 65 的 SNR。

英文摘要:

Infrared Reflection Absorption Spectroscopy (IRAS) on dielectric single crystals is challenging because the optimal incidence angles for light-adsorbate interaction coincide with regions of low IR reflectivity. Here, we introduce an optimized IRAS setup that maximizes the signal-to-noise ratio for non-metals. This is achieved by maximizing light throughput, and by selecting optimal incidence angles that directly impact the peak heights in the spectra. The setup uses a commercial FTIR spectrometer and is usable in ultra-high vacuum (UHV). Specifically, the design features sample illumination and collection mirrors with a high numerical aperture inside the UHV system, and an adjustable aperture to select the incidence angle range on the sample. This is important for p-polarized measurements on dielectrics, because the peaks in the spectra reverse direction at the Brewster angle (band inversion). The system components are connected precisely via a single flange, ensuring long-term stability. We studied the signal-to-noise (SNR) variation in p-polarized IRAS spectra for one monolayer of CO on TiO2(110) as a function of incidence angle range, where a maximum signal-to-noise ratio of 70 was achieved at 4 cm-1 resolution in five minutes measurement time. The capabilities for s-polarization are demonstrated by measuring one monolayer D2O adsorbed on a TiO2(110) surface, where a SNR of 65 was achieved at a delta_R/R0 peak height of 1.4x10-4 in twenty minutes.

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