The self-assembled wire structure features a core and outer shell composed of different materials, representing a key characteristic that future advanced electronic devices should possess. Nanowires, as nano-scale conductive wires made from semiconductor materials, hold great promise for applications in transistors, solar cells, and sensors. Their unique properties make them ideal candidates for next-generation nanoelectronics.
Nanowires are considered essential building blocks for future nanodevices. Depending on the substrate used for their growth, various types of nanowires can be tailored to suit specific functions in electronic products. Recently, Professor Xiuling Li’s research team developed a novel method called "Van der Waals extension" to grow nanowires from the bottom up on semiconductor substrates like silicon. These nanowires are made from III-V materials, which are widely used in optical devices such as solar cells and lasers.
Previously, growing III-V nanowires on silicon was challenging due to defects in the silicon material, leading to inconsistent results. To overcome this, the researchers turned to graphene — a single-layer carbon material known for its exceptional mechanical strength, flexibility, and electrical conductivity. By using graphene as a substrate, they were able to grow high-quality indium gallium arsenide (InGaAs) nanowires with improved performance.
Graphene is not only thinner and more flexible than silicon but also significantly cheaper. It can be easily obtained through exfoliation from graphite or synthesized via chemical vapor deposition. This makes it an attractive alternative to traditional substrates, especially in cost-sensitive applications like solar cells.
Mohseni, a member of the research team, explained that one major advantage of using graphene is reducing reliance on expensive and thick substrates. In conventional solar cells, up to 80% of the manufacturing cost comes from the substrate. With graphene, scientists can achieve better performance at a lower cost. Additionally, graphene allows for new functionalities that are not possible with traditional materials.
In their experiments, the researchers placed a mixture of indium, gallium, and arsenic onto graphene sheets. The graphene surface began to self-assemble vertically, forming a dense, carpet-like structure. Using a similar method, they also grew nanowires using only two gases. The results showed that InGaAs nanowires grown on graphene could separate into distinct core and shell structures — a process that was previously unexpected.
“This is something we didn’t anticipate,†said Professor Li. “Normally, growing a core-shell structure requires multiple steps, changing conditions after the initial growth. But with graphene, the entire process happens in one step, resulting in a perfect interface between the core and shell.â€
Further investigation revealed that the atomic spacing in the indium arsenide crystal matched that of graphene. This compatibility allowed for seamless nucleation and growth of the nanowires on the graphene surface. Surprisingly, gallium deposited on the nanowire surface rather than the graphene itself, a phenomenon that had not been observed before.
By adjusting the ratio of indium to gallium during fabrication, the researchers could fine-tune the optical and electrical properties of the nanowires. This opens up new possibilities for customizing nanowires for specific applications.
Looking ahead, Professor Li’s team plans to use these graphene-grown nanowires to develop next-generation solar cells and other electronic devices. The study, supported by the National Science Foundation and the U.S. Department of Energy, was published in *Nano Letters*. (Based on the article “Nanowires Grown On Graphene Have Surprising Structure†translated by Wang Xian.)
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