Zhu Qifeng, Shen Yanting, Chen Zhuo, Chen Binghuang, Dai Enwen, Pan Weiqing
Department of Physics, Zhejiang University of Science and Technology, Hangzhou 310023, China.
Sensors (Basel). 2024 Jun 14;24(12):3851. doi: 10.3390/s24123851.
Few-layer black phosphorus (FLBP) is a highly promising material for high sensitivity label-free surface plasmon resonance (SPR) sensors due to its exceptional electrical, optical, and mechanical properties. FLBP exhibits inherent anisotropy with different refractive indices along its two main crystal orientations, the zigzag and armchair axes. However, this anisotropic property is often overlooked in FLBP-based sensors. In this study, we conducted a comprehensive investigation of the SPR reflectivity and phase in a BK7-Ag-FLBP structure to understand the influence of the stacking sequence and the number of FLBP layers on the sensing performance. Clear resonant angle shifts caused by different stacking sequences of FLBP could be observed both theoretically and experimentally. In the theoretical study, the highest reflective and phase sensitivities were achieved with a 12-layer black phosphorus (BP) structure. The reflectivity sensitivity reached 287.9°/refractive index units (RIU) with the zz stacking 12-layer BP film exhibiting a sensitivity 76°/RIU higher than the ac stacking structure. Similarly, the phase sensitivity reached 1162°/RIU with the zz stacking 12-layer BP structure showing a sensitivity 276.9°/RIU higher than the ac stacking structure. The electric field distribution of the 12-layer BP structure with four different stacking sequences has also been analyzed. In the experiment study, the well-known Attenuated Total Reflection (ATR) θ-2θ SPR setup is utilized to detect the reflectivity and phase of BK7-Ag-FLBP structures. The FLBP samples with the same thickness but different stacking sequences show significant resonant angle shift (0.275°) and maximum phase difference variation (34.6°). The FLBP sample thickness and crystal orientations have been demonstrated using the angular-resolved polarized Raman spectroscopy (ARPRS). These theoretical and experimental results provide strong evidence that the stacking sequences of FLBP have a significant impact on the sensing performance of SPR sensors. By harnessing the anisotropic properties of materials like FLBP, novel structures of anisotropic-2D material-based SPR sensors could open up exciting possibilities for innovative applications.
少层黑磷（FLBP）因其优异的电学、光学和机械性能，是用于高灵敏度无标记表面等离子体共振（SPR）传感器的极具潜力的材料。FLBP沿其两个主要晶体取向（锯齿形和扶手椅形轴）表现出具有不同折射率的固有各向异性。然而，这种各向异性特性在基于FLBP的传感器中常常被忽视。在本研究中，我们对BK7-Ag-FLBP结构中的SPR反射率和相位进行了全面研究，以了解FLBP的堆叠顺序和层数对传感性能的影响。理论和实验均能观察到由FLBP不同堆叠顺序引起的明显共振角偏移。在理论研究中，12层黑磷（BP）结构实现了最高的反射率和相位灵敏度。对于锯齿形堆叠的12层BP薄膜，反射率灵敏度达到287.9°/折射率单位（RIU），比扶手椅形堆叠结构的灵敏度高76°/RIU。同样，对于锯齿形堆叠的12层BP结构，相位灵敏度达到1162°/RIU，比扶手椅形堆叠结构的灵敏度高276.9°/RIU。还分析了具有四种不同堆叠顺序的12层BP结构的电场分布。在实验研究中，利用著名的衰减全反射（ATR）θ-2θ SPR装置检测BK7-Ag-FLBP结构的反射率和相位。具有相同厚度但不同堆叠顺序的FLBP样品显示出明显的共振角偏移（0.275°）和最大相位差变化（34.6°）。使用角分辨偏振拉曼光谱（ARPRS）对FLBP样品的厚度和晶体取向进行了表征。这些理论和实验结果提供了有力证据，证明FLBP的堆叠顺序对SPR传感器的传感性能有重大影响。通过利用FLBP等材料的各向异性特性，基于各向异性二维材料的SPR传感器的新型结构可能为创新应用开辟令人兴奋的可能性。
