Numerical Analysis Of PSTM Imaging By Standard/nonstandard FDTD Methods

Photon Scanning Tunneling Microscope (PSTM) is one kind of Scanning Probe Microscope (SPM), which obtains the various optical images of the sample's nanometer surface, transcended the diffraction of conventional optical microscope, by using a optical-fiber tip probing ultra-high frequency optical information consist in evanescent wave. It can detect the sample harmless, study the biology alive, even the translucent materials. So it is applied widely in lots of fields such as biology and medicine.The resolution and sensitivity of PSTM are influenced by several parameters. Optical-fiber probe is the key component as a part of obtaining information of sample. The polarization of incident wave also can influence the result definitely. Furthermore, probe-sample distance and incident angle are the parameters too. So, numerical simulation is necessary and effective which can clarify near-field imaging process.The thesis mainly includes the following contents and results:Firstly, based on the result of our group, fiber probe with Al-coated was applied to PSTM for improving the resolution and sensitivity. Using 2D finite-difference time-domain method (FDTD), bare fiber probe, fiber probe with Al particle, Al-coated aperture fiber probe and total Al-coated fiber probe were analyzed. The result shows that: metal nano-particle or nano-film could produce surface field enhancement;the sensitivity of fiber probe tip with Al-coated can be one hundred times compared with bare fiber probes;the resolution of fiber probe with Al particle is superior to 20nm;the resolution of total Al-coated fiber probe and Al-coated aperture fiber probe are 20nm and 20nm respectively.Secondly, the near-field imaging on dielectric and silver metal sample with different mode of polarization in system of PSTM was simulated using 3D FDTD method. Field distribution can be calculated in the plain of 5nm above the sample of "PSTM". The results are: to dielectric sample, p polarized can reflect the profile better than s polarized incident wave and the direction of the incident field determines the pattern of near-field intensity distribution;silver metal can enhance the near field intensity, both p and s polarized incident wave can reflect the profile in a way.Finally, for the sake of reducing the dispersion of FDTD, we attempt to use nonstandard FDTD algorithm, with a solution error less than 10^-4 that of the conventional one. This thesisincludes the formulae for scatter in space and in PSTM, and pilot study the scatter in near-field and PSTM system.