Numerical Simulation Of The Scanning Imaging Photon Scanning Tunneling Microscope

Photon scanning tunneling microscope(PSTM),using optical probes to detect the ultra-high frequency information carried by surface evanescent wave of the sample,is a newly developed scanning probe microscope(SPM),it can detect the sample harmless with high resolution beyond the diffraction limit,so it is applied widely in lots of fields such as studies in translucent materials,biology and medicine.The resolution and sensitivity of PSTM are influenced by several parameters,and the physical model is a multi-body scattering electromagnetieul system,a strict theory and analytical expression is very difficult to achieve.Therefore,numerical simulation method occupies an important position in the near-field optics.Optical-fiber probe is the key component as a part of obtaining information of sample.In this paper,the image of PSTM,using fiber probe coated by metal with a nano-rod at the edge of the aperture,is analyzed with 3-D finite difference time domain(FDTD).The results show that the obtained images by the probe with a nano-rod,mainly determined by the parameters of the nano-rod,has higher resolution and sensitivity,while its stability is better.Simulating structures often contain small parts which strongly influence the local field behaviour in near-field calculation.However,the usage of graded meshes can help to model structure details but often the stable time step becomes very small and the total number of mesh cells becomes too large.The improvements of common algorithms are needed to improve com putation efficiency:1.A stable subgridding algorithm,which is to introduce locally refined meshes into the base mesh for the computation,is very useful for an FDTD code,since it can refine the mesh locally and improve the accuracy of the result without significantly increasing the computational efforts.The method based on interpolation of electric and magnetic current densities have better stability and can be applied to the situation that the material surface traverses the coarse-fine boundary conveniently.In this paper,this method is applied to the analysis of near-field distribution of probe coated by metal with a nano-rod.2.The multiresolution time-domain(MRTD) algorithm based on wavelet is presented by introducing a field expansion in terms of biorthogonal scaling and wavelet functions.We employ the Cohen-Daubechies-Feauveau(CDF) biorthogonal wavelet basis,characterized by compact support,continuity.The better resolution can be obtained by MRTD based on CDF biorthogonal wavelet basis.It can get high efficiency to apply wavelets only in the regions where the targets reside.This thesis includes the 2-D formulae for scatter,and pilot study the scatter in near-field.