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

Abstract

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.

Antenna Enhanced Infrared Photoinduced Force Imaging in Aqueous Environment with Super-Resolution and Hypersensitivity

“…(d) and (i): Corresponding spatio-spectral transection along the red arrows. Spectra were obtained in 5 s with 1 cm -1 spectral resolution, with 100 nm separation.To demonstrate the possibility of the proposed strategy, the PDMS layer on a commercial PtIr AFM tip is firstly used as probe, which is naturally coated on the tip in the packaging box with the thickness ~1-2 nm 27,28. Such sampling strategy has several advantages: (1) Sample variation on different detection region could be eliminated, making it reliable to compare the signal enhancement at different positions and different antennas; (2) PDMS has four characteristic IR peaks at 1266 cm -1 , 1100 cm -1 , 1025 cm -1 and 816 cm -1 (dielectric function shown in FigureS4), which overlap well with the resonance of the applied antenna arrays; (3) PDMS has relatively high absorption coefficient and large thermal expansion coefficient which are expected to induce strong photoinduced thermodynamic force 26.…”

Embedding an Amphiphilic 4-Hydroxy Thiazole Dye in Langmuir Matrices: Studying Miscibilities with Arylic and Alkylic Matrix Amphiphiles via Langmuir Isotherms and Photo-induced Force Microscopy

“…To investigate the Π-dependent transition from ideal miscibility to phase separation for the 10:SA blend and the transition from real to ideal miscibility to phase separation for the 10:TPCA blend, the Langmuir layers are deposited via the LB technique at surface pressures causing minimum and maximum excess areas. These LB films are characterized via atomic force microscopy (AFM) and photo-induced force microscopy (PiFM). , PiFM enables to assign different morphological domains to the individual molecular species via their IR absorption spectroscopic signatures at nanometer spatial resolution. , …”

Nanoscale spectroscopic origins of photoinduced tip–sample force in the midinfrared

“…The induced dipole contrast can be enhanced with the help of the tip-enhanced thermal expansion of a functionalized tip (30). It is well known that some commercial cantilevers may have a thin layer of polydimethylsiloxane (PDMS) contamination (1∼2 nm) on their surface, which can be traced to the packaging and shipping container (31, 32).…”