3D simulation of NSOM operation by a nanosphere as a microscope probe using Boundary Element Method.

3D surface topography is simulated using Boundary Element Method (BEM) by computing far field scattered by a metallic or dielectric nanosphere which scans in the near field region of an arbitrary rough surface. Nanosphere is considered as NSOM probe's tip and two scanning modes, Constant Height Mode (CHM) and Constant Distance Mode (CDM) are simulated. Our results show that resolution and image quality are enhanced by decreasing scanning sphere's height or diameter in CHM. Also, image quality in Transverse Magnetic (TM) polarization is higher compared with Transverse Electric (TE) polarization. In TM polarization for both scanning mode CHM and CDM, Aluminum scanner makes a better image quality in comparison to dielectric sphere. However in TE polarization, electric field intensity scattered by a dielectric sphere is higher compared with Aluminum sphere. In spite of higher image quality in CHM, image quality is not satisfactory in CDM and image does not show a perfect match with the surface topography. High precision, speed, and low amount of data during the calculations are advantages of BEM in comparison to other numerical methods. [ABSTRACT FROM AUTHOR]