Ultra-narrow Linewidth Symmetry-breaking Silicon Metasurface for Trace Biomolecules Sensing报告人:
蔡暻煊，博士，中山大学生物医学工程学院助理教授，硕士生导师。于2012年在清华大学精密仪器与机械学系获得工学学士学位，2017年在香港大学获得博士学位。在Advanced Materials、Advanced Functional Materials、Advanced Drug Delivery Reviews等国际著名期刊发表学术研究论文20余篇，申请多项中国及美国发明专利。参与国家自然科学基金、香港创新科技署ITF基金、香港研究资助局RGC项目等课题研究研究方向包括微纳米制造技术；柔性器件；纳米光学；纳米等离子体生物传感。
The silicon-based all-dielectric metasurface, based on the Mie scattering theory, improves the interaction between light and matter by enhancing the local electromagnetic field intensity of the metasurface. Compared with their metallic counterpart, the silicon-based dielectric metasurface has lower optical loss while retaining a stronger optical resonance response, resulting a narrower linewidth optical response. The optical response of the silicon-based metasurface is determined by many factors, such as period, shape, and thickness of silicon. Recent studies reveal that utilizing structural symmetry-breaking dielectric metasurfaces, an ultra-narrow linewidth (<1 nm) optical absorption (or transparency/reflection) will arise, which is induced by the quasi-BIC of the asymmetric structure.1 Such unique property of symmetric-breaking dielectric metasurface makes it a promising candidate as a high quality factor (Q-factor) biosensor for highly-reliable detection of the tiny spectral shift of resonance caused by the attached trace biomolecules. Many efforts have been devoted to optimizing structural design for excellent optical responses, such as disk-bar structure and tilted silicon nanobars.2, 3 However, resonances in most of the structures are strongly depends on the geometry of the dielectric nanostructures and requires costly high-precision nanofabrication techniques. Therefore, a symmetry-breaking dielectric metasurface with ultra-narrow linewidth optical response and robust nanofabrication is of importance to its real-life applications.
In this research, we propose a robust structural symmetry-breaking silicon metasurface with ultra-narrow transparency. Figure 1 shows the dielectric metasurface fabrication process flow. Polycrystalline silicon is first deposited on a fused silica substrate by a low-pressure chemical vapor deposition (LPCVD) process. Then a thin layer of e-beam resist (AR-P 6200) is spin coated on the substrate. A dual-trapezoidal nanostructure array is fabricated in ARP through electron beam lithography (EBL). Finally, dual-trapezoidal nanopatterns are transferred into silicon by inductive coupled plasma (ICP) and complete the whole fabrication. Figure 2a shows the metaunit of the metasurface, which is composed of two centrosymmetric silicon trapezoids on the fused silica substrate. Figure 2b-f show the finite-difference time-domain (FDTD) simulation results. As shown in Fig. 2b, the FWHM of the resonance on the reflectance spectrum of the metasurface can be as narrow as 1.5 nm. The electric field are mainly concentrated on the waists of the trapezoids (Fig. 2c), thus results a relatively large detection depth for biomolecules. The refractometric sensitivity of the metasurface is 209.6 nm/RIU (Fig. 2d, e). Moreover, the FWHM and resonance suppression efficiency are not significantly influenced by the fillet radius (Fig. 2f), indicating that the metasurface is robust against fabrication errors.