Scattering-type scanning near-field optical microscopy (s-SNOM) has emerged as one of the key technologies to study the optical properties of physical, chemical and biological materials on the 20-nm length scale – far beyond the ubiquitous diffraction limit of light. s-SNOM combines the best of two worlds, the nano-scale spatial resolution of Atomic Force Microscopy (AFM) and the analytical power of infrared spectroscopy (nano-FTIR). It employs the strong confinement of infrared light at the apex of a sharp metallic AFM tip to create a nanoscale optical hot-spot. Analyzing the tip-scattered light interferometrically enables the measurement of the complex dielectric function (absorption, reflectivity) of the sample directly below the tip and yields nanoscale resolved images simultaneous to topography. Measuring and analyzing the material specific optical near-fields that are confined at the surface of materials, nano-FTIR is a true surface sensitive optical spectroscopy technique with a probing depth of only a few tens of nanometers.<br/>nano-FTIR imaging and spectroscopy provides information regarding the local chemical composition, crystal structure, molecular orientation as well as local free-carrier concentration and conductivity for a wide range of different nanomaterials. Applications show analysis of the secondary structure in individual protein nanofibers and membranes, chemical characterization of embedded structural phases in biominerals and polymer blends, quantification of free-carrier concentration and carrier mobility in doped semiconductor nanowires and direct visualizing of the effect of chemical doping on the carrier concentration in graphene by plasmon interference mapping.<br/>Recently, nano-FTIR has been extended towards ultrafast experiments with up to 10-femtosecond temporal resolution. Carrier-relaxation dynamics in semiconductor nanowires, graphene, or intricate materials like vanadium dioxide can now directly be observed on their natural time and length-scale, revealing key insights into the role of surface potentials, the number of layers, and local strain on the electron dynamics in such materials.<br/>In this presentation we will introduce the basic principle of s-SNOM microscopy and nano-FTIR and address their impact and key applications for characterization for complex nanomaterials.

nano-FTIR: Infrared imaging and spectroscopy with 20nm spatial resolution

255th National Meeting (2018)

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