Simulation of an electromagnetic wave propagating down a coaxial cable and interacting with a sample through and STM-tipped probe. The probe is 20 nm above the perfectly conducting sample. Shown is the magnitude of the electric field (red is large, blue is small) in a cross section view. We use simulations such as these to interpret the images obtained with our scanning near-field microwave microscopes. We acknowledge Agilent Technologies for donating the High Frequency Structure Simulator software used to perform these calculations.



We have developed a near-field scanning microwave microscope (NSMM), capable of imaging many types of samples with spatial resolutions from below 1 μm to 1 mm, at frequencies from 0.1 MHz to 50 GHz. In materials imaging mode, we have demonstrated quantitative imaging of the sheet resistance of conducting thin films, the linear and nonlinear permittivity of dielectric thin films and crystals, and magnetic permeability and ferromagnetic resonance.

In field imaging mode, we can image electricand magnetic fields above operating microwave devices, including high-temperature superconducting devices. In this mode, we can also image nonlinearity and intermodulation in superconductors. This technique also could be applied in the design of microwave components, so that one could image the fields and currents in a device and compare them to numerical models.

The NSMM consists of an open-ended coaxial probe connected to a resonant length of transmission line. The probe is coupled to a sample in the near-field limit.

1. Materials Imaging Mode
2. Electromagnetic Field Imaging Mode

A commercial version of the NSMM is being developed by Neocera, Inc. Neocera also has an informative tutorial on microwave microscopy

Electrodynamic Measurements

Electrodynamic measurements tell us how a material reacts to stimulation by electromagnetic radiation. This type of measurement is important because the material's response often depends on its fundamental physical properties. These measurements are performed on many different materials in our lab, including cuprate superconductors, oxide ferromagnetic materials, and dielectrics. In all of these measurements, we illuminate the sample of interest with rf, microwave, and millimeter wave radiation, and examine the response of the sample.

In general, we can vary the frequency and power of the electromagnetic wave, the temperature of the sample, and the applied magnetic field. Some of these techniques (parallel plate resonator and Nb cavity) are resonant, which means that they excite an electromagnetic resonance of a geometrical structure, typically a box. The Corbino reflection technique is broad-band (i.e. non-resonant), and is simply a measurement of the reflectivity of the sample at microwave frequencies. Below we give links to pictures and schematic diagrams of these experiments, and give some description of how they work. Also included is a brief description of one of our thin film deposition systems and additional links to related areas of research.

1. Parralell Plate Resonator
2. Nb Cavity
3. Corbino Reflector
4. Thin Film Depostion
 
Additional Links
1. Electrodynamics of Superconductors
2. Wave Chaos

Center for Superconductivity Research, University of Maryland, College Park, MD 20742-4111
Phone: 301.405.6129 Fax: 301.405.3779
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