Jaeyeon Pyo’s team at the Korea Electrotechnology Research Institute (KERI) has become the first in the world to reveal light emission patterns from 3D-printed nanowires. As the size of light-emitting devices shrinks to hundreds of nanometers, peculiar changes occur in the light-matter interaction, resulting in significantly different emission pattern compared to macro structures. Therefore, understanding of light emission from nanostructures is an essential prerequisite for the practical application of nanoscale light-emitting devices.

The research team, dedicated in display research using nano­photonic 3D printing technology for years, revealed highly directional light emission patterns from the 3D-printed nanowires for the first time in the world. The technology is used for imple­menting photonic devices with a nanoscale high-resolution 3D printing method. Fabri­cation of nanoscale photonic structures in 3D archi­tecture is achieved by direct writing of functional inks formulated from various optical materials. 

Typically, it is challenging to uniformly fabricate light-emitting materials of desired sizes at specific locations using conven­tional chemical or physical vapor deposition methods. However, the 3D printing technology allows precise control of the diameter through the restriction by the printing nozzle’s aperture, enabling the reliable fabri­cation of light-emitting materials at desired locations with a wide range of sizes. 

The team experi­mentally observed and measured light emission patterns from specimens precisely fabricated using the nano­photonic 3D printing technology, ranging in size from the nanometer- to micrometer-scale. The team also conducted electro­magnetic wave simulations for in-depth analysis and cross-validation of their arguments. As a result, when the size of light-emitting materials becomes as small as 300 nanometers in diameter, internal reflection of light vanishes due to spatial confine­ment, leading to one-directional straight propagation of light.

Consequently, the light emission pattern becomes highly directional. Typically, light propagates through diverse paths within a given internal structure, resulting in broad emission patterns as their super­position. However, in nanowire structures, only a single path exists, leading to the observed highly directional emission pattern. The observed highly directional attribute can signi­ficantly enhance the performance of displays, optical storage media, encryption devices, and more.

Macro-structures with broad emission patterns can suffer from optical crosstalk when densely integrated, causing signals to overlap or blur. In contrast, nanowires with highly directional emission patterns allow clear separation between signals from each structure at high densities, elimina­ting distortions in represen­tation or inter­pretation. The highly directional emission of nanowires makes them suitable for high-perfor­mance devices, as experi­mentally demonstrated now.

Jaeyeon Pyo stated, “Research on optical physics at the nanoscale is challenging, especially due to the difficulty in specimen preparation, which is often high-cost and time-consuming. Our contri­bution demonstrates that the 3D printing method can be a versatile platform for studying optical physics owing to its simple, flexible, and low-cost charac­teristics.” He added, “This research will signi­ficantly contribute to the cutting-edge display techno­logies, and quantum physics, which are part of South Korea’s ‘National Strategic Techno­logy Nurture Plan.”

The research team anticipates that their contri­bution will attract significant interest in the fields of virtual reality (AR, VR), beam projectors, optical storage media, photonic integrated circuits, encryption techno­logies, and security printing, where ultra-small light-emitting materials can be utilized. They aim to continue inves­tigating various optical phenomena occurring at the nanoscale using the 3D printing method, leveraging its capa­bility for free-form fabrication. (Source: KERI)

Reference: J. Bae et al.: Emission Directionality of 3D-Printed Photonic Nanowires, ACS Nano 18, 16265 (2024); DOI: 10.1021/acsnano.4c02820

Link: Smart 3D Printing Research Team, Korea Electrotechnology Research Institute (KERI), Changwon, Korea