Substructure imaging of heterogeneous nanomaterials with enhanced refractive index contrast by using a functionalized tip in photoinduced force microscopy

• 来源期刊: 光：科学与应用（英文版）
• 年，卷（期）: 2018,（6）
• 页码范围: 749-757
• 页数: 9页
• 语种: 英文
• DOI: 10.1038/s41377-018-0069-y

摘要

The opto-mechanical force response from light-illuminated nanoscale materials has been exploited in many tip-based imaging applications to characterize various heterogeneous nanostructures.Such a force can have two origins:thermal expansion and induced dipoles.The thermal expansion reflects the absorption of the material,which enables one to chemically characterize a material at the absorption resonance.The induced dipole interaction reflects the local refractive indices of the material underneath the tip,which is useful to characterize a material in the spectral region where no absorption resonance occurs,as in the infrared (IR)-inactive region.Unfortunately,the dipole force is relatively small,and the contrast is rarely discernible for most organic materials and biomaterials,which only show a small difference in refractive indices for their components.In this letter,we demonstrate that refractive index contrast can be greatly enhanced with the assistance of a functionalized tip.With the enhanced contrast,we can visualize the substructure of heterogeneous biomaterials,such as a polyacrylonitrile-nanocrystalline cellulose (PAN-NCC) nanofiber.From substructural visualization,we address the issue of the tensile strength of PAN-NCC fibers fabricated by several different mixing methods.Our understanding from the present study will open up a new opportunity to provide enhanced sensitivity for substructure mapping of nanobiomaterials,as well as local field mapping of photonic devices,such as surface polaritons on semiconductors,metals and van der Waals materials.