| Research Abstract |
We applied the near-field scanning optical microscope (NSOM) using a metallic probe tip to biological samples. In testing with murine embryonal myocardial cell as a sample, we can observe the fine structure (the variance of refractive index) in our NSOM images. This structure cannnot be observed by a scanning electrontunneling microscope (STM). In addition, we clarify that 1) NSOM images are different to the surface profile of samples, and that 2) their contasts vary with the polarizing state of illumination, and that 3) the interference of the evanescent wave is localized on the sample surface of periodical structure.
We developed our metal-tip NSOM to a reflecting-mode system. Therefore, we can apply it to apply the nontransparent samples, such as semi-conductor or metallic samples, which cannot be observed by a former transparent mode system. To estimate resolving performance of this system, we use the semi-conducting materials as a sample, whose surface has periodical structure with a period of 240 nm. In experiments, we can observe the localization of the electromagnetic field with a spatial resolution of 60nm.
Electromagnetic simulations of the metal-tip NSOM have carried out in 3D model using realistic size and materials. A results of calculation confirmes that there is high electric intensity at the apex of the metallic tip, which is about 40 times greater than the incident light. This result shows that the metal-tip NSOM system can extract the nanometric optical information at the vicinity of the tip apex, and that new imaging system will be available, if it is combined with nonlinear optics such as two photon absorption or SHG.This may make effective use of field enhancement of the tip.
|
