A near-field scanning microwave microscope in a scanning electron microscope: design and challenges

International audienc

The Shapes of Flux Domains in the Intermediate State of Type-I Superconductors

In the intermediate state of a thin type-I superconductor magnetic flux penetrates in a disordered set of highly branched and fingered macroscopic domains. To understand these shapes, we study in detail a recently proposed "current-loop" (CL) model that models the intermediate state as a collection of tense current ribbons flowing along the superconducting-normal interfaces and subject to the constraint of global flux conservation. The validity of this model is tested through a detailed reanalysis of Landau's original conformal mapping treatment of the laminar state, in which the superconductor-normal interfaces are flared within the slab, and of a closely-related straight-lamina model. A simplified dynamical model is described that elucidates the nature of possible shape instabilities of flux stripes and stripe arrays, and numerical studies of the highly nonlinear regime of those instabilities demonstrate patterns like those seen experimentally. Of particular interest is the buckling instability commonly seen in the intermediate state. The free-boundary approach further allows for a calculation of the elastic properties of the laminar state, which closely resembles that of smectic liquid crystals. We suggest several new experiments to explore of flux domain shape instabilities, including an Eckhaus instability induced by changing the out-of-plane magnetic field, and an analog of the Helfrich-Hurault instability of smectics induced by an in-plane field.Comment: 23 pages, 22 bitmapped postscript figures, RevTex 3.0, submitted to Phys. Rev. B. Higher resolution figures may be obtained by contacting the author

Memristor Device Characterization by Scanning Microwave Microscopy

International audienceWe report memristive device characterization using near-field scanning microwave microscopy. Atomic force microscopy, magnitude and phase-shift images of the complex reflection coefficient of TiO2 devices can be acquired simultaneously in the range 1-20 GHz. In particular, measurement of the complex reflection coefficient of a 200 by 200 nm 2 TiO2 device is exemplary demonstrated. These results are beneficial for electrical modeling and optimization of memristor devices to address OxRAM applications

Electromagnetic Modeling in Near-Field Scanning Microwave Microscopy Highlighting Limitations in Spatial and Electrical Resolutions

International audienceNear-field scanning microwave microscopy (NSMM) is a scanning probe microscopy (SPM) technique that measures the local interaction of evanescent microwaves with a sample using a sharp tip probe. The traceability in NSMM is still challenging as the distribution of the electrical fields is affected by several parameters. In this effort, finite element method (FEM) based electromagnetic modeling methods are used to study the effects of the wavelength of operation and the humidity on the spatial and electrical resolutions respectively. From the simulated data, it is demonstrated that the lateral resolution is improved with increasing the frequency of operation. Furthermore, the existence and influence of a water meniscus is highlighted by fine comparison between simulated and measured data. To face these issues, an alternative near-field scanning millimeter-wave microscopy working in a controlled environment is proposed. Keywords-near-field scanning microwave microscopy (NSMM); finite element method (FEM); electromagnetic modeling; vector network analyzer (VNA); scanning electron microscope (SEM)