Researchers from China's Tianjin University, Fudan University, University of Chinese Academy of Sciences, National Center for Nanoscience and Technology and Tsinghua University have introduces a new technique, called the "Wax-aided immersion method," to produce controllable chiral graphene rolls. This advancement provides a novel approach to chirality modulation in two-dimensional materials and their potential applications in spintronics, laying a foundation for future developments in quantum computing and spintronic devices.
Chirality refers to the property of objects whose mirror images cannot be perfectly superimposed, much like the relationship between a person's left and right hands. Chirality is omnipresent in nature, from molecules to materials, and chiral structures often exhibit unique optical, electronic, and chemical properties. For example, the biological activity of many drug molecules differs significantly based on their chirality. In materials science, the development of chiral materials is crucial for advancing frontier technologies such as optical devices, spintronics, and quantum computing.
Graphene, a two-dimensional material known for its high electrical conductivity, excellent mechanical strength, and chemical stability, has long been a focal point of material science research. However, graphene itself is achiral. In recent years, scientists have attempted to introduce chirality into graphene and other two-dimensional materials by rolling them up, exploring their potential new characteristics and applications. Nonetheless, the challenge of precisely introducing chirality into two-dimensional materials has remained formidable. Currently, few two-dimensional materials possess chirality-based spintronics functionality, and there is a lack of universal methods for fabrication. This challenge is what the team aimed to address in it latest work.
The scientists developed the "Wax-aided immersion method," which allows for the controlled rolling of graphene at specific angles to create chiral graphene rolls. This technique is not only applicable to graphene but can also be extended to other two-dimensional materials for large-scale production. In the method, a thin layer of paraffin is applied to the surface of a monolayer graphene and transferred to a silicon substrate. The sample is then vertically immersed in isopropanol, using the surface tension of the solvent to curl the graphene into a tubular structure. By adjusting the immersion speed and solvent polarity, the researchers can precisely control the chiral angle of the graphene rolls, thus tuning their optical and electronic properties.
Experimental results demonstrated that the left- handed and right-handed graphene rolls exhibited significant optical activity and remarkable spin-selectivity effects. At room temperature, these graphene rolls showed a spin polarization rate exceeding 90%, far surpassing other carbon-based materials. Through precise control of the chiral angle, the team also achieved control on chiral-induced spin-selectivity, which holds unique application potential for spintronics. Furthermore, the researchers observed that electrons primarily moved along one side of the graphene roll, leading to preferential spin polarization. This chiral-induced spin-selectivity effect opens new possibilities for developing efficient spin filters and spintronic devices.
"This research not only offers a universal method for chirality control in non-chiral two-dimensional materials, but also paves new avenues for exploring quantum behavior and developing room-temperature spintronic technologies," said Tianjin University's Professor Lei Shengbin. "In the future, this technique is expected to enable unique functionalities that surpass traditional carbon materials in fields such as spintronics, quantum computing, optical devices, and material science, injecting new vitality into the development of spintronics and quantum technologies."