Novel method produces large, high-quality crystals

With unique electronic and optical properties, gallium selenide crystals are used in semi-conductors, ultra-thin nanomaterials and more. Layered and soft, the GaSe crystals take days to grow — a hindrance in readily exploring its full applications and advancing future technologies, according to an international research team. To overcome this time delay, the researchers developed a solution that produces crystals of equal quality in just five minutes.

 

They published their approach on Dec. 26, 2021, in Nano Research.

 

“In this paper, we propose an ultrafast crystal growth process with low energy consumption and capability of producing crystals of excellent quality,” said co-corresponding author Yumeng Shi, professor in the Engineering Technology Research Center for 2D Material Information Function Devices and Systems of Guangdong Province, International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, Institute of Microscale Optoelectronics at Shenzhen University in China. “We also demonstrate that large-sized GaSe crystals — half to one centimeter long — can be obtained within the short period of five minutes.”

 

GaSe crystals are traditionally grown via chemical vapor transport, where the starting chemical components react with a solution, reconfiguring their constituents into gas, liquid and solid phases that settle out as crystals once properly separated, typically by temperature. They can also be grown via another technique called the vertical Bridgman, which uses the same temperature controls, but involves a seed crystal that shares the geometry of the crystal to be grown. As the material is created, it grows on the seed into its own crystal formation.  

 

“Although these growth techniques are well established, the growth of such high-quality large-scale crystals is often a time-consuming, expensive and complicated process,” said co-corresponding author Zhongchang Wang, principal investigator of the Atomic Manipulation for Quantum Nanotechnology group at the International Iberian Nanotechnology Laboratory in Portugal.

 

The key to crystal growth, according to the researchers, is nucleation. This is the first step in molecules assembling themselves into a new structure, such as the point at which water begins to turn to ice.

 

“The traditional processes adopt the strategy of suppressing nucleation by lowering the concentration of the feedstock, which inevitably results in a much lower growth rate,” said co-corresponding author Jingbo Li, professor at the Institute of Semiconductors, South China Normal University. But, he noted, while increasing the feedstock concentration increases the growth rate, it also lowers the quality of the crystals. “The growth kinetics change and can result in dendrite crystals or cracks. Therefore, an ultra-fast crystal synthesis process, which suppresses nucleation events without the necessity to reduce feedstock supply, is urgently required.”

 

To reduce the nucleation density — or number of molecules self-assembling into varied or low-quality crystals — while maintaining a high growth rate, the researchers used liquid metal to enhance an approach called atmospheric pressure chemical vapor deposition (CVD). This synthesis method uses atmospheric pressure and consists of a substrate reacting with another chemical. The reaction produces a chemical vapor that deposits onto the substrate. In this case, liquid gallium serves as the substrate, resulting in a high-quality crystal of a suitable size in five minutes.

 

To test the crystals, the researchers used them to fabricate a photodetector, which uses light to make electrical signals, and found that it was comparable to photodetectors made with slow-growth GaSe crystals.

 

“Our proposed technique could be further extended to other metals with low-melting points, opening a new avenue to potential optoelectronic applications of 2D crystals,” Shi said. “Next, we plan to further study the microscopic mechanism of this new method at the atomic level and promote the industrialization of this method. We look forward to cooperation with the companies to promote the single crystal growth processing technology and its resultant single crystal products.”

 

Other contributors include Zuxin Chen, Quan Chen and Zebing Chai, Institute of Semiconductors, South China Normal University; Bin Wei, School of Materials, Sun Yat-Sen University; Jun Wang, School of Electrical Engineering and Automation, Wuhan University; and Yanping Liu, School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University. Zuxin Chen is also affiliated with the Shenzen University’s Engineering Technology Research Center for 2D Material Information Function Devices and Systems of Guangdong Province and the International Iberian Nanotechnology Laboratory.

 

The National Natural Science Foundation of China, the Postdoctoral Science Foundation, the Key Project of Department of Education of Guangdong Province and the Shenzhen Peacock Plan supported this research.

 

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About Nano Research 

 

Nano Research is a peer-reviewed, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society. It offers readers an attractive mix of authoritative and comprehensive reviews and original cutting-edge research papers. After more than 10 years of development, it has become one of the most influential academic journals in the nano field. Rapid review to ensure quick publication is a key feature of Nano Research. In 2020 InCites Journal Citation Reports, Nano Research has an Impact Factor of 8.897 (8.696, 5 years), the total cites reached 23150, and the number of highly cited papers reached 129, ranked among the top 2.5% of over 9000 academic journals, ranking first in China's international academic journals.

 

About Tsinghua University Press

 

Established in 1980, belonging to Tsinghua University, Tsinghua University Press (TUP) is a leading comprehensive higher education and professional publisher in China. Committed to building a top-level global cultural brand, after 41 years of development, TUP has established an outstanding managerial system and enterprise structure, and delivered multimedia and multi-dimensional publications covering books, audio, video, electronic products, journals and digital publications. In addition, TUP actively carries out its strategic transformation from educational publishing to content development and service for teaching & learning and was named First-class National Publisher for achieving remarkable results.

 

 

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