Near-field spectroscopy of nanostructures

We report a new near-field Raman imaging technique by trapping and scanning a dielectric microsphere over a sample surface in water. This method has a few critical advantages over both aperture and apertureless near-field Raman techniques, such as strong near-field signal, high reproducibility, high resolution and cheap cost. In this method, the laser is focused to a spot smaller than diffraction limit and only the near-field signal is collected. Using this method, we have achieved spatial resolution of 80 nm. This spatial resolution is extremely useful and powerful for a wide range of applications such as the characterization of nanostructures and nano devices. We show the capability of our technique using a series of nanometer sized samples, e. g. device sample with 45 nm poly-Si gates with SiGe stressors, Au nanopatterns and Au nanobowl structures. Besides of the achievement of high resolution, our near-field technique also provides the opportunity to explore the near-field optical response of surface plasmons of metal nanostructures that cannot be attained by far-field spectroscopy.