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PLANAR scanning probe microscopy
PLANAR SCANNING PROBE MICROSCOPY – THE ART OF LOW-LEVEL FLIGHT AT THE NANOSCALE
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Friedemann REINHARD 1, 2
1
University of Rostock, Institute of Physics, Rostock, Germany
2
University of Rostock, Department of Life, Light and Matter, Rostock, Germany * friedemann. reinhard @ uni-rostock. de
https:// doi. org / 10.1051 / photon / 202513162
An unorthodox optical approach to scanning probe positioning is opening a realm of novel applications in various fields of research. By using optical interferometry to carefully align a sensor parallel to a sample, even millimeter-sized sensors can be brought into nanometer-scale proximity of samples. Extended circuits and massively parallel arrays of sensors can thus be used as a scanning probe, a feat that would be impossible using established sharp tips.
For decades, scanning probe microscopy has been probing surfaces with various forms of sharp tips. Sharp conductive tips extract a tunnelling current from a sample in scanning tunnelling microscopy( STM). Sharp mechanical tips literally touch and feel the surface of a sample to reveal its topography in atomic force microscopy( AFM), similar to the needle of a vinyl record player. In both techniques the sharpness of the tip is critical for the spatial resolution that can be obtained, so that sharp tips have become considered a strict necessity for any kind of scanning probe approach. Interestingly, this
Figure 1. If an extended( 10 µ m – millimeter)-sized planar sensor is carefully aligned parallel to a planar sample, the sensor and the sample can be brought into nanometer-scale proximity of each other.
paradigm remained unchallenged when a new generation of nano-sensors emerged in the past decades and promised to greatly expand the range of quantities that can be measured with nanoscale resolution. These sensors comprise nitrogen-vacancy colour centers few nanometers beneath the surface of a diamond to measure magnetic fields, plasmonic optical antennas for near-field microscopy and microfabricated microwave cavities to measure electron spin resonance. All these novel sensors share a central challenge. The sensors themselves are natively planar devices, microfabricated circuits on a substrate or defects under a crystal surface, but the established approach to scanning probe positioning requires the sensor to be a tip to provide force-feedback and to approach the sample as close as possible. Much effort has been spent to merge these incompatible worlds and fabricate extended sensors onto tip-like structures, e. g. by anisotropic dry etching of diamond sensors into nanopillars, or sophisticated evaporation of superconducting films onto
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