For the first time, scientists have prepared isolated microstructures based on “folds”

Rolling hills, shriveled peels, cracked painted walls and wrinkled skin… These “folds” can be seen everywhere in daily life. In recent years, scientists have been committed to obtaining the microstructure of controllable “folds” through artificial induction, which has become one of the research hotspots in the field of micro-nano processing.

Recently, a research team led by Liu Qian, a researcher at the National Center for Nanoscience and Wang Cong, associate professor of the School of Mathematics and Physics, Beijing University of Chemical Technology, proposed a new strain processing technology using electron beam-assisted laser, which overcame the great limitation of the intrinsic wavelength of the fold on the designability of strain structures, and prepared an isolated controllable and designable folded submicron strain structure for the first time. The results were recently published in Laser & Photonics Reviews.

A fold is a surface strain structure caused by mechanical instability. In recent years, scientists have used laser-induced wrinkling methods to effectively solve the problems of disorder and defects encountered in wrinkle micromachining, realize the periodic controllable wrinkle and the designable processing of periodic structure, and make fold as a new micro-nano processing method a big step forward. However, due to the transitive and periodic nature of the fold strain, the isolated fold structure has not been realized. In the eyes of scientists, this is mainly due to the existence of “intrinsic wavelengths”, and laser-induced methods can only prepare periodic micro-nanostructures close to eigenwavelengths.

In the newly published paper, the researchers realized for the first time an arbitrary isolated fold structure without any secondary structure and disordered folds on a polystyrene-silicon (PS-Si) double-layer membrane system supplemented by electron beam irradiation. This technique successfully breaks through the limitation of the intrinsic wavelength of folds in the double-layer membrane system, and demonstrates the designability and controllability of arbitrarily isolated micro/nano strain structures.

The paper shows that the convex array structure fabricated by the new method can ensure that the spacing (5 microns) of each convex structure is greater than the intrinsic wavelength of the fold, ensuring the relative independence of each convex structure. The results of various characterizations show that the lateral dimensions of such raised basic units are in the sub-micron range and the longitudinal size is in the order of 100 nanometers, which can meet the requirements of surface micro/nanostructure in practical applications.

Schematic diagram of the manufacture of the raised array (Photo courtesy of the research team)

Electron beam irradiation is the key to controllable fabrication that enables arbitrary design of isolated structures. In this paper, the mechanism of polystyrene (PS) glass transition temperature increase through the electron beam irradiation region is proposed, and the effect of the electron beam under different accelerating voltages is quantitatively studied, and the optimal strength of the electron beam to inhibit disordered fold structures is specified.

Subsequently, researchers proposed a new method for generating pre-strain structure, that is, by laser induced lower PS decomposition and gasification, the upper silicon (Si) film produces a certain amount of expansion, so as to pave the way for the subsequent pre-strain conversion into a highly controllable raised basic unit. The intrinsic mechanism of this process is fully supported by relevant experiments and simulations. A variety of foundations and complex isolated structures constructed with raised structures as the basic units were also manufactured, demonstrating the high designability of the method.

The researchers believe that by combining the two methods of laser-induced pre-strain and electron beam irradiation, this new method pioneers the realization of arbitrary strain structure, making isolated strain microstructures that could not be processed before, and making “laser path induction” truly develop into a universal micro/nano manufacturing technology.

Qu Yusong, doctoral student of the National Center for Nanoscience, Chen Shengyao, a doctoral student of Nankai University, He Juxing, a doctoral student of the Shanghai Institute of Microsystems and Information Technology, Chinese Academy of Sciences, are the co-first authors of the paper, Liu Qian, a researcher of the National Center for Nanoscience and Chemistry, and Wang Cong, associate professor of the School of Mathematics and Physics, Beijing University of Chemical Technology, are co-corresponding authors. The project has been funded by the National Natural Science Foundation of China, the National Key Research and Development Program, the Seventh Framework Plan of the European Union, the Strategic Pilot A Project of the Chinese Academy of Sciences, and the Basic Research Business Fund of Central Universities. (Source: China Science News Gan Xiao)

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