  In the past few years, phase-change materials have become increasingly
important in nano-photonics and optoelectronics. The advantages of sizeable
optical contrast between phases and the additional degree of freedom from phase
switching have been the driving force. From multilevel reflectance to dynamic
nanoprinting and structural colors, phase-change materials have achieved
outstanding results with prospects for real-world applications. The local
crystallization/amorphization of phase-change materials and the corresponding
reflectance tunning by the crystallized/amorphized region size have potential
applications for future dynamic display devices. Although the resolution is
much higher than current display devices, the pixel sizes in those devices are
limited by the locally switchable structure size. Here, we reduce the spot
sizes further by using ion beams instead of laser beams and dramatically
increase the pixel density, demonstrating the capability of having superior
resolution. In addition, the power to sputter away materials can be utilized in
creating nanostructures with relative height differences and local contrast.
Our experiment focuses on one archetypal phase-change material, Sb$_2$Se$_3$,
prepared by pulsed-laser deposition on a reflective gold substrate. We
demonstrate that we can produce structural colors and achieve reflectance
tunning by focused ion beam milling/sputtering of phase change materials at the
nanoscale. Furthermore, we show that the local structuring of phase-change
materials by focused ion beam can be used to produce high pixel density display
devices with superior resolutions.
