Tsinghua Team Achieves New Breakthroughs in Laser 3D Nanoprint Technology

Quantum dots are the key materials of the next generation display devices.

Smaller luminous unit size and higher device integration density can promote the development of virtual reality technology (VR), near eye display and other fields, and help people travel in the meta universe.

The Tsinghua team has developed a new technology, which uses new printing principles and mechanisms to endow 3D nano printing technology with more magical features. This technology is expected to improve the VR display resolution, so that people can see a high-definition virtual reality world.

Recently, the research team of Professor Sun Hongbo and Associate Professor Lin Linhan from the Department of Precision Instruments of Tsinghua University proposed a new nano particle laser 3D printing technology, which uses photo generated high-energy carriers to control the chemical activity of the surface of nano particles and realize the three-dimensional assembly of chemical bonding between nano particles.

The research team applied the new printing principle for the first time in the world and demonstrated the complex three-dimensional structures and heterostructures of a variety of different nano particles, achieving a new breakthrough in the field of nano particle device. This technology enables high-precision laser micro nano fabrication beyond the optical diffraction limit, and the density of print point array exceeds 20000 ppi, providing a new idea for the preparation of ultra-high resolution functional devices. Professor Dmitri V. Talapin of the University of Chicago also highly recognized and evaluated this technology.

This achievement was recently published in the journal Science, entitled "3D nanoprinting of semiconductor quantum dots by photoexcitation induced chemical bonding".

Nanoscience and technology, as one of the hottest research fields in the 21st century, plays an important role in promoting the current development of integration and intelligence. The application of nanotechnology can be seen everywhere in advanced electronic equipment, biomedical detection and other fields.

Of course, the principle behind these frontier applications is based on a series of strange new physical and chemical effects generated by the reduction of material size to nanometer scale, including quantum confinement effect and quantum tunneling effect in semiconductor materials, surface plasmon resonance in metal materials, etc. The preparation of existing nano devices is mainly based on micro nano manufacturing technologies such as photolithography and electron beam exposure, which is only applicable to a limited variety of nano materials. As a planar preparation process, it is difficult to achieve three-dimensional manufacturing of nano materials. On the other hand, chemical synthesis can be used to achieve the preparation and precise cutting of colorful (different sizes, morphologies, and compositions) nanoparticles, and these nanomaterials have high crystal quality, good surface quality, and superior optical, electrical, and magnetic properties. However, these chemically synthesized nanoparticles lack effective device based preparation technology, which has become the technical bottleneck of their wide application.

In view of the above problems, the research team proposed a new principle of photo induced chemical bonding, realized the laser three-dimensional assembly technology of nanoparticles, and used various nanoparticles as raw materials to assemble three-dimensional nano devices. Taking semiconductor quantum dots with core-shell structure as an example, the laser excited quantum dots are used to generate electron hole pairs. Through energy level matching, the tunneling and surface migration of photogenerated holes are driven, which promotes the desorption of ligands on the surface of quantum dots and the formation of active chemical sites, thereby inducing chemical bonding on the surface of quantum dots and realizing efficient assembly between quantum dots.

Schematic diagram of the principle of photoinduced chemical bonding

What are the refreshing features of this new technology? What areas can it have a profound impact on?

Based on the above principles, the research team further focused and programmed the laser beam, and achieved the precision molding of the complex three-dimensional structure of nanomaterials. Compared with the existing micro nano fabrication technology, this technology has the following distinctive features:

High purity of printing materials: compared with the existing laser 3D nano printing technology, this technology breaks through the principle limitation of photopolymerization, does not require any optical bonding components, and realizes 3D printing of nearly 100% functional nano particle components; Strong 3D processing capability: it can realize nano printing of various 3D structures such as complex linear, bending and volume structures, so as to construct new functional 3D optoelectronic devices; With multi-component printing function: using quantum dots of different sizes as raw materials, this technology demonstrates the multi-component heterogeneous composite printing capability; High printing resolution: nonlinear light excitation is used to make the printing resolution break through the optical diffraction limit. The density of the printing point array exceeds 20000 ppi, and the printing limit resolution reaches 77 nm, which helps to achieve ultra-high resolution display devices and promote the development of VR.

It is worth mentioning that the micro nano manufacturing principle of photoinduced chemical bonding has a wide range of material and structural adaptability. Through energy level design, high-precision micro nano manufacturing of a variety of semiconductors and metal materials can be realized, which opens up a new way to prepare nano devices, and has important application prospects in the fields of on-chip optoelectronic device integration, high-performance sensing materials, etc.

The co first author of this paper is Liu Shaofeng, a 2019 doctoral student in the Department of Precision Instruments of Tsinghua University, and Hou Zhengwei, a 2021 doctoral student in the School of Materials. Tsinghua University is the first author of the paper. The corresponding authors of the paper are Professor Sun Hongbo and Associate Professor Lin Linhan from the Department of Precision Instruments of Tsinghua University. Professor Li Zhengcao of School of Materials, Tsinghua University, Associate Professor Zhang Hao of the Department of Chemistry, Doctor Li Fu, Associate Professor Fang Honghua of the Department of Fine Arts, and 2020 doctoral students Zhao Yao and Li Xiaoze made important contributions to the work of the thesis. In addition, this research was supported by the National Key R&D Program, the National Natural Science Foundation of China, the Tsinghua Foshan Innovation Fund and the National Key Laboratory of Precision Testing Technology and Instruments.

"Different from learning knowledge and applying knowledge, many basic frontier researches from 0 to 1 should be the process of creating knowledge themselves. Facing the new phenomena observed, the students in the research group made bold guesses and assumptions under the condition that the existing literature is relatively scarce, constantly explored the boundary points of knowledge, and constantly verified and eliminated through experiments, finally obtained and confirmed the new mechanism. Now, scientific research projects There are many choices in the direction of research. We will continue to make the most valuable frontier exploration and technological breakthrough to meet the needs of the current country and society. " Lin Linhan said.

Source: Tsinghua University