  This manuscript demonstrates the theory, design, and simulation of scattering
scanning near field microscopy (s-SNOM) in 0.5THz. A comprehensive simulation
model of nanotips' geometry, sample materials, and incident field is
established to significantly improve the scattering efficiency and spatial
resolution to achieve optimal performance. The theoretical model is based on
full-wave simulation and dipole moment analysis which can describe the overall
nanotip's geometry information to screen the optimal parameters corresponding
to the 0.5THz, which is the center frequency of most THz sources. The
customized nanotip can achieve 40 nm $(\lambda / 15000)$ spatial resolution
while maintaining an excellent scattering efficiency. This nanotip design
method doesn't depend on the homogenization commercial AFM tips, providing an
approach for customized nanotip design of THz wave scattering near field
microscopy.
