Tip-enhanced Raman spectroscopy with a spatial resolution of $25\mathrm{nm}$ is conducted on a sample of graphite that has been exposed to a $50\mathrm{keV}$ focused Ga ion beam with a diameter of $20\mathrm{nm}$ . The G mode located at $1579{\mathrm{cm}}^{-1}$ does not exhibit a measurable tip enhancement, while the D mode at $1364{\mathrm{cm}}^{-1}$ is significantly enhanced. A method is proposed to calculate the enhancement factor of anisotropic materials due to the electromagnetic field using the measured signal enhancement induced by the tip.