Microscopes are powerful tools that provide visual access to much of what is otherwise unseen by the naked eye, from cells of living organisms to microorganisms and more. The technology, however, remains limited in areas such as materials research and data processing, which would benefit from the ability to observe structures and processes down to the nanoscale level and below.

Researchers in Germany have developed a way to display, study and even see inside the tiny, complex structures of electronic components, computer chips and circuits without destroying them. Their method, Coherence Tomography with extreme ultraviolet light (XCT) advanced by scientists from Friedrich Schiller University Jena, Helmholtz Institute Jena, Technical University of Darmstadt, Fraunhofer Institute for Applied Optics and Precision Engineering and Leibniz Institute of Photonic Technology is described in the scientific journal Optica.

The procedure is based on optical coherence tomography (OCT), a well-established imaging test in Extreme ultraviolet coherence tomography enables material-specific characterization of nanoscopic buried structures.ophthalmology that uses infrared light to illuminate the retina and non-invasively create 3D images. OCT uses long-wave infrared light. The radiation is selected so that the tissue being examined absorbs a minimal amount and it is reflected by the inner structures. The research physicists used extremely short-wave UV light instead to accommodate the size of the structures they were imaging.

Extremely short-wave UV light (XUV) was generated, previously possible mainly in large-scale research facilities, using high harmonics, radiation produced by a laser light. It has a frequency many times that of the original light. "In this way, we generate light with a wavelength of between 10 and 80 nm using infrared lasers," explained Gerhard Paulus, Professor of Nonlinear Optics at the University of Jena. "Like the irradiated laser light, the resulting broadband XUV light is also coherent, which means that it has laser-like properties."

Nanoscopic layer structures in silicon were exposed to the coherent XUC radiation, after which the reflected light was analyzed. Thin layers of titanium, silver or other metals were observed within the sample. The reflective properties of these metals, which are different from the silicon, allowed for their detection in the reflected radiation. The extremely precise method can display the deep structure of the tiny samples with nanometer accuracy, and the chemical composition of the samples can also be precisely determined without destroying the sample.

"This makes coherence tomography an interesting application for inspecting semiconductors, solar cells or multilayer optical components," said Paulus. XCT, therefore, has potential use in quality control, for detection of internal defects or chemical impurities during the manufacturing process of these types of nanomaterials.