Towards Ultra-High-Resolution Displays

Visualization of the topography of magnesium with nanometer resolution covered with an optical scattering phase map showing hydrogenated and unhydrogenated areas. (Source: PI 4, U. Stuttgart)

Future display techno­logies such as virtual and aug­mented reality require higher pixel resolutions and optical contrast. However, the potential of state-of-the-art displays is limited by the indi­vidual pixel size to achieve necessary reso­lution. Researchers at the Uni­versity of Stuttgart have now succeeded to observe switching processes at previously unattained nanometer reso­lution. It opens the door towards new and innovative ultra-high-reso­lution displays of the future.

The size of pixels in state-of-the-art switchable optical devices is intrin­sically limited by the fabri­cation of micrometer-sized transistors and spatial light modu­lators. To further decrease their size, several approaches are currently under debate and inves­tigated in research labs all over the world. One promising route can be found in the field of nano­plasmonics. A plasmonic nano­particle typically has sizes of only several tens of nanometers and can focus light into sub-wavelength dimensions with an extreme locali­zation of electro­magnetic fields. By adjusting the size of such particles, their color appearance can be shifted through the entire visible spectral range. In combination with phase-tran­sition materials their optical properties and their appearance can be tuned, colors can be turned on and off, and one can realize switchable colored plasmonic pixels with nano­meters size.

One promising material for this purpose is magnesium. The metal can, under external stimulus, hydrogenate to a dielectric insulator with an extreme optical material contrast. This makes it an ideal candidate for opti­cally active and switchable systems such as dynamic holo­graphy, plasmonic color displays, or switchable meta­materials. So far, the optical switching from metallic mag­nesium to dielectric magnesium hydride with hydrogen is strongly limited by intrinsic material factors and obstacles such as the volume expansion of the material, poor cycla­bility, and limited diffusion coeffi­cients.

Researchers from the 4th Physics Institute at the Uni­versity of Stuttgart have succeeded for the first time to image and watch the switching process of this smart material with the required nanometer resolution to under­stand and analyze the influence of nanoscale morpho­logy on the hydro­genation. In his experiment, Julian Karst from the group of Harald Giessen uses free-standing magnesium to image in-situ its nano­scale optical and morpho­logical properties. The measure­ments reveal an extreme influence of morphology on the nanoscale optical switching mechanism and highlight the possibility for significant future improve­ments of the optical switching performance.

Giessen believes that their work will help in the future to develop, design, and analyze high-perfor­mance pixelated smart material optical devices with nanometer-sized pixels. Further­more, as magnesium is also a very promising candidate for hydrogen storage, he believes that the results on the diffusion processes on the nanometer scale will aid the improve­ment of the hydrogen storage effi­ciency. It might pave the way to realize 3D holo­graphic virtual reality glasses in a few years. (Source: U. Stuttgart)

Reference: J. Karst et al.: Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale, Sci. Adv. 6, eaaz0566 (2020); DOI: 10.1126/sciadv.aaz0566

Link: Ultrafast Nanooptics (H. Gießen), 4th Physics Institute, University of Stuttgart, Stuttgart, Germany

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