Hanyang University ERICA Campus Department of Mechanical Engineering Professor Hong Seok-jun’s research team developed various structural colors on metal substrates and metal insulators through selective growth of iron oxide thin film using lasers.

The structural colors, which are not unique colors of objects but appear from diffraction or interference of light according to the geometric structure of the object, can incarnate various colors without various dyes, so research in the field of optoelectronics is especially active. A typical example of structural color is the rainbow shown on the back of a CD, which appears when the light that meets the microgrooves of the surface is broken at different angles and dispersed into many wavelength lights.

Previously, there were attempts to shape structural colors by investigating beams or gases on the surface of matter in a vacuum and forming deposition, geometric microstructure, or adjusting the surface height of microstructure. However, the deposition process in a vacuum was complex and costly.

Professor Hong's research team first examined continuous wave lasers on platinum substrates in solutions such as iron chloride and sodium nitrate, and developed iron oxide on the surface of substrates. Then, they have succeeded in implementing various colors due to interference of light that touches the iron oxide by controlling the energy and exposure time of the laser. It was possible to remove the formed iron oxide thin film or modify the colors already incarnated through crystal changes of the iron oxide. It showed the possibility of tuning optoelectronic devices like the methods of programming.

The structural colors shown on the surface are related to the absorption and reflection of light, so that they can be used to improve photoelectricity efficiency. It has provided a clue that can make color composition more simplified than in current deposition-based process.

The findings were carried out by the promotion from the Ministry of Science and ICT and the Korea Research Foundation’s support projects for mid-sized research and up-and-coming research support projects and were published in the September 28th issue of the international academic journal "Advanced Financial Materials."

Meanwhile, Professor Hong won the 2018 ERICA Award for New Researcher and the International Paper Award for the 2019 Excellent Teacher's Award.