Films and photos with ever higher resolutions and better contrast now allow lifelike impressions and virtual worlds. However, current display and projection technologies cannot yet exploit this potential because their individual pixels are too large and therefore do not reach the required resolutions.
Scientists around the world are investigating how to reduce pixel size and increase resolutions. A particularly promising approach can be found in the field of nanoplasmonics. Here, the optical scattering properties of nanometer-sized metallic particles are used - in other words, their ability to produce brilliant and pure colors. By simply varying the size of such particles, colours can be produced across the entire visible spectrum and beyond. These scattered colors can even be manipulated and controlled by using phase transition materials. Combining these ideas, nanometer-sized plasmonic pixels can be realized with colors that can be switched on and off.
Probably the most promising phase transition material is magnesium. This metal, which is found in large quantities on earth, can be switched to a dielectric insulator with the help of hydrogen, i.e. from a coloured to a transparent particle. This extreme optical material contrast makes magnesium an ideal candidate for optically active and switchable systems such as dynamic holography, plasmonic color displays or switchable metamaterials.
So far, however, the use of magnesium in technological applications is hampered by the fact that the processes on the nanoscale are not yet understood. At the phase transition from metallic magnesium to dielectric magnesium hydride, the volume expands considerably and so-called diffusion barriers are formed. These are regions that hinder, slow down or even prevent further switching.
Measuring switching processes with previously unattained nanometer resolution
A team of researchers led by Prof. Harald Gießen at the 4th Institute of Physics at Universität Stuttgart has now succeeded for the first time in measuring these switching processes with previously unattained nanometer resolution. The researchers were thus able to analyse and explain the influence of nanoscale morphology (shape) on the switching process in detail. In his experiment, doctoral student Julian Karst used self-supporting magnesium films in combination with scanning near-field microscopy to map the hydrogen diffusion processes in real time. His measurements with nanometer resolution show a strong influence of material morphology on the optical switching mechanism and reveal strategies to significantly improve the material properties.
Are the 3D holographic VR glasses coming?
"We are convinced that the published work will make a decisive contribution to the development of high-performance optical components with nanometer-sized pixels," emphasizes Prof. Harald Gießen. The head of the study also sees further important implications, because magnesium is used as a hydrogen storage medium. The storage efficiency of these media will benefit from a deeper understanding of diffusion processes on the nanometer scale. This could make visions such as 3D holographic VR glasses a reality in just a few years.
The results of the experiment have been published in the journal Science Advances (issue of May 8, 2020).