In this article we describe evanescent field imaging of material nonuniformities with a record resolution of 0.4 μm at 1 GHz (λg/750 000), using a resonant stripline scanning microwave probe. A chemically etched tip is used as a point-like evanescent field emitter and a probe–sample distance modulation is employed to improve the signal-to-noise ratio. Images obtained by evanescent microwave probe, by optical microscope, and by scanning tunneling microscope are presented for comparison. Probe was calibrated to perform quantitative conductivity measurements. The principal factors affecting the ultimate resolution of evanescent microwave probe are also discussed.

Mechanical properties of self-welded [111] single-crystal silicon nanowire bridges grown between two silicon posts using metal-catalyzed chemical vapor deposition were determined using both dynamic and static measurements. The static tests were carried out using atomic force microscopy (AFM) to measure the nanowires’ Young’s modulus and the strength of the self-welded junctions. The AFM-measured Young’s modulus ranged from 93 to 250 GPa (compared to 185 GPa for bulk silicon in the [111] direction) depending on the nanowire diameter, which ranged from 140 to 200 nm. The self-welded wire could withstand a maximum bending stress in the range of 210–830 MPa (larger than bulk silicon), which also depended on the nanowire diameter and loading conditions. The beam broke close to the loading point, rather than at the self-welded junction, indicating the excellent bond strength of the self-welded junction. The vibration spectra measured with a network analyzer and a dc magnetic field indicated a dynamic Young’s modulus of 140 GPa, in good agreement (within the experimental error) with the static measurement results.

Design, fabrication, and characterization of near-field microwave scanning probes compatible with an atomic force microscope (AFM) for imaging of embedded nanostructures are discussed. The microwave probe discussed here bridges the frequency gap between the existing local probe microscopy systems, and enables localized microwave spectroscopy and imaging of molecules and nanostructures. The probe consists of a coaxially shielded heavily doped silicon tip, and an aluminum (Al) coplanar waveguide. The coaxial tip structure was formed by a thick photoresist and plasma etching process, enabling the silicon apex to protrude through a well-defined aperture in the Al layer. Using this technique, probes with 10-/spl mu/m-high coaxial tips of 5-nm apex radius and 500-nm aperture radius were realized. The aperture confines the electromagnetic fields in the exposed tip region, allowing microwave measurements with high spatial resolution. The mechanical and electrical characterizations of the microwave probes were performed to ensure their compliance with the requirement of an AFM, as well as that of the microwave measurements. Finally, simultaneous AFM and microwave imaging of standard AFM samples with grid structures was performed for the first time. The lateral spatial resolution of the microwave scans was approximately 50 nm at 2.8 GHz, compared to 100 nm for the AFM scans. The ability of the microwave signal to penetrate inside the sample opens new possibilities in hyperspectral and multimodal imaging of nanostructures. Correlations between AFM images and the microwave images enable proper registration and referencing of the microwave properties to landmarks in the topographic AFM images.

We have imaged and mapped material nonuniformities and defects using microwaves generated at the end of a microstripline resonator with 0.4 μm lateral spatial resolution at 1 GHz. Here we experimentally examine the effect of microstripline substrate permittivity, the feedline-to-resonator coupling strength, and probe tip geometry on the spatial resolution of the probe. Carbon composites, dielectrics, semiconductors, metals, and botanical samples were scanned for defects, residual stresses, subsurface features, areas of different film thickness, and moisture content. The resulting evanescent microwave probe (EMP) images are discussed. The main objective of this work is to demonstrate the overall capabilities of the EMP imaging technique as well as to discuss various probe parameters that can be used to design EMPs for different applications.