Active Tunable Nanogaps: Revolutionizing Wafer-Scale Metallic Structures for Gap Control, Dynamic Light-Matter Interaction, and Advanced Sensing Applications

Abstract

Recent advances in nanofabrication technology have led to the development of metallic gap structures with sub-nanometer widths. These structures provide exceptional confinement and enhancement of electromagnetic fields, enabling a range of innovative applications in ultrasensitive detection systems. The transition from traditional nanometer gaps to flexible structures represents a significant development in this field and opens the door to dynamic 'Gaptronics', a concept that could revolutionize many areas of nanotechnology. This work provides a comprehensive overview of wafer-scale metallic nanogap structures on flexible substrate. Various fabrication methods are explored, highlighting their applicability and versatility in creating these advanced structures. A key aspect of this research is the active control of gap widths achieved by applying mechanical stress to flexible substrates. This innovative approach enables real- time manipulation of light transmission properties and demonstrates sub-wavelength nanogap closure at microwave (12-18 GHz) and terahertz (0.2-2 THz) frequencies. In addition, the development of tunable plasmonic nanostructures on flexible substrates using thermally sensitive materials is described in detail. This technology enables real-time control of gap width tailored to specific molecule sizes and improves surface-enhanced Raman scattering (SERS) signals. The tunable nanogaps showed an amplification factor of over 10⁷ and a detection limit as low as 10-¹² M, positioning these structures as powerful tools for the precise detection of molecules. Another application presented is a new type of strain sensor technology called Zerogap Strain Sensor (ZSS). This sensor utilizes lithography to overcome the limitations of conventional resistance-based strain sensors, which suffer from randomness and variability in crack formation. By creating uniform gaps with short periodicity and smooth sidewall contacts, the ZSS operates over an unprecedented range of strains while maintaining high sensitivity. The sensor achieves a remarkable gage factor of over 15,000 at an external strain of 18%, demonstrating its potential for various applications. Overall, this research highlights the transformative potential of tunable metallic nanogaps for advancing the fields of photochemistry, quantum optics and next-generation communications. By creating a versatile platform for dynamic light-matter interactions and enhanced sensing capabilities, this work paves the way for future innovations in nanotechnology and its myriad applications in science and industry.