| Currently, near-field scanning optical microscopes are becoming increasingly popular analytical instruments. This can be attributed to their ability to resolve images beyond the diffraction limit of conventional optical microscopes while maintaining such important nondestructive characteristics of their conventional counterparts as the ability to gather spectral information of the sample. Therefore, the construction of a near-infrared near-field scanning optical microscope (NSOM) will allow spectrometric images to be obtained on a nanometric level. For this microscope, an optical fiber is pulled to a subwavelength tip. Typically, the fiber is then coated with metal in order to contain the near-IR light. This small aperture light source by itself, however, is not enough to achieve the desired resolution. The sample must also be within the near-field of the source. Once this is achieved, transmission images can be obtained point-by-point by scanning the probe across the sample.;The transmission near-field microscope has been numerically modeled using computational electromagnetics techniques. Specifically, both moment method and finite-difference time-domain simulations have been utilized. In both cases, the computational models differ from the near-IR NSOM instrument described above. Specifically, due to the difficulty involved in modeling the actual fiber probe, the aperture is modeled as a subwavelength circular aperture within an infinite perfectly electrically conducting plane. The main specimen of interest is a number of thin perfectly conducting wires with a finite length. In this manner, specific capabilities and behavior of the microwave microscope can be studied as well as compared to real NSOM data. This in turn will provide a better understanding of the physical phenomena involved in NSOM instruments. Furthermore, this new knowledge can be utilized to better interpret NSOM imaging data.;In addition to the numerical models, an X-band NSOM or a near-field scanning microwave microscope (NSMM) has been developed. Specifically, the NSMM provides a transition between experimental and theoretical work. Because the NSOM effect is independent of wavelength, the X-band instrument can be utilized to study such samples as subwavelength. thin-wires that would otherwise be difficult to analyze in an optical system. To this end, the NSMM has been utilized as a reference system to compare the data generated by the computational models. Therefore, by combining all of these topics, the understanding of NSOM phenomena will be greatly enhanced. |
