Near-field microwave microscopy for nanoscience and nanotechnology

Abstract

We have demonstrated the possibility of near-field microwave imaging of physical structures, such as thin films, bulk material, fluids, etc. by using a near-field microwave microscopy (NFMM). We have developed theoretical models for the microwave reflection coefficient S11 and resonant frequency shift Δf/f0 dependence on electromagnetic characteristics, in particular, electrical conductivity, dielectric permittivity, magnetic permeability to distinguish the spatial changes of these parameters in materials under various preparation and measurement conditions. The models are based on standard transmission line theory, material perturbation concept as well as finite-element numerical simulation methods. The NFMM is a noncontact, nondestructive and label-free evaluation tool to obtain material properties with high contrast and with high spatial resolution. The smallest detectable change in solvent (glucose) concentration is about 0.5mg/ml at SNR = 20 dB, the smallest detectable change in permittivity (dielectrics) is about 0.2 at SNR = 30 dB, the smallest detectable change in conductivity (semiconductors and perfect metals) is about 0.01 S/m at SNR = 60 dB, the smallest detectable change in permeability (Permalloy) is about 10 at SNR = 40 dB, and the smallest detectable change in thickness (self-assembled monolayers, SAMs) is 2 nm at SNR = 50 dB. The results clearly show the sensitivity and the usefulness of NFMM for many device applications at microwave frequency such as 3D surface mapping and topography, material characteristics (permittivity, permeability, conductivity, carriers density, etc.) pointby-point distribution, and label-free biosensing (DNA, SAM, aqueous solution of glucose, NaCl, etc.).