11:15 AM - 11:30 AM
▼ [14a-C302-7] Near-field absorption imaging by two color nano-light source
Keywords:nano-imaging
Aperture-less near-field scanning optical microscopy (NSOM) is a promising spectroscopic technique for nano-scale imaging which provides high spatial resolution beyond the diffraction limit of light. Due to its advantages, aperture-less NSOM has been employed for various spectroscopic applications, for example, absorption and scattering for electron state analysis by monitoring the Rayleigh scattering efficiency; or vibrational state analysis by measuring Raman scattering from molecules. However, absorption analysis via monitoring Rayleigh scattering is not straightforward since the origin of Rayleigh scattering is a complex problem. This is because the background signal of Rayleigh scattering from the substrate and the optics cannot be distinguished from the signal coming from the sample. In this study, we propose a novel method for absorption imaging based on aperture-less NSOM using Raman-nano-light, whose origin, unlike Rayleigh scattering, is clearly known. We utilized an uncoated silicon nano-tip as the near-field probe, which creates a strong Raman signal of silicon at the tip apex . When the nano-tip is placed on the sample and is illuminated, it generates silicon Raman signal of nanometer size, which, while passing through the sample, can be partially absorbed by the sample. Therefore, one can measure the absorption of the silicon Raman signal by measuring the intensity of transmitted light through the sample at nano-scale resolution. Further, we employed two excitation lasers with wavelengths of 488nm and 594nm, in order to observe the absorption property of the sample independent of the sample topography. To verify the success of absorption imaging, we observed two types of carbon nanotubes (CNTs) that have different absorption properties. An absorption ratio image allowed us to distinguish the two kinds of CNTs due to the difference of their absorption coefficients.