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.
We show a different approach to perform near-field Raman imaging with sub-diffraction limit spatial resolution. In this
approach, a dielectric microsphere is trapped by the excitation laser through optical tweezers technique. The microsphere
is used to focus the laser to the sample, and also to collect the scattered Raman signals. We show the capability of this
method in imaging various types of samples, such as device sample with 45 nm poly-Si gates with SiGe stressors and
gold nanopatterns. This method is easy to perform, has better repeatability, and generates stronger signal as compared to
the conventional near-field Raman techniques.