An international multi-institutional team of scientists used atomically precise methods to synthesize graphene nanoribbons (ultra-thin ribbons of carbon atoms) on the surface of titanium dioxide, which eliminated the barriers to custom-designed carbon nanostructures required by quantum information science.
Graphene is composed of a carbon layer with a thickness of one atom. It has ultra-light, conductive and extremely strong mechanical properties. Due to its highly adjustable electronic, optical and transmission properties, it is a material that has been extensively studied and is expected to change electronics and information science.
When graphene is made into nanoribbons, it can be applied to nanoscale devices. However, when using the most advanced "top-down" synthesis method, that is, cutting graphene sheets into atomic narrow strips, the lack of atomic-level precision limits the practical use of graphene.
Researchers at the Center for Nanophase Materials Science (CNMS) in California, USA, conceived and implemented a "bottom-up" approach, that is, directly constructing graphene nanoribbons at the atomic level so that they can be used for specific applications. As shown in the picture, the scientist shows the graphene nanoribbons shown in yellow in blue on the titanium dioxide substrate. The lighter end of the ribbon shows a magnetic state. The illustration shows how the ends are rotated up and down, suitable for creating qubits.
As graphene segments become smaller and smaller, this absolutely precise method helps preserve the valuable properties of graphene monolayers. The difference in the width of only one or two atoms can significantly change the characteristics of the system, thereby turning a semiconductor ribbon into a metal ribbon. The research results were published in the journal Science.
The researchers processed the precursor materials and verified the results through scanning tunneling microscopes. The researchers said, "These microscopes can directly image and process matter at the atomic scale." "The tip is so thin that it is essentially the size of a single atom. The microscope moves row by row, continuously measuring the interaction between the needle and the surface, and drawing an atomically accurate surface structure map."
In past experiments on graphene nanoribbons, materials were synthesized on metal substrates, which inevitably inhibited the electronic properties of nanoribbons. "The electronic characteristics of these ribbons work as designed. From an application point of view, the use of a metal substrate is useless because it can shield these characteristics." "This is a huge challenge, how do we effectively To separate molecular networks to transfer to transistors?"
Current decoupling methods involve removing the system from ultra-high vacuum conditions and subjecting it to a multi-step wet chemical process, which requires etching away the metal substrate. This process contradicts the careful and clean precision used when creating the system.
In order to find a suitable process for non-metallic substrates, researchers began to experiment with oxide surfaces to mimic the strategy used for metals. In the end, it turned to a group of European chemists who specialized in the chemistry of fluoroaromatic hydrocarbons and began to study the design of a chemical precursor that could be synthesized directly on the surface of rutile titanium dioxide.
Dr. Li Anping, one of the leading research papers, said: "Surface synthesis allows us to produce very high precision and achieve this goal. We started with molecular precursors." "We get what we need for certain properties. The reaction has basically been programmed into the precursor. We know the temperature at which the reaction occurs, and by adjusting the temperature, we can control the sequence of the reaction." "Another advantage of surface synthesis is that there are many types of candidate materials that can be used as precursors. Achieve high programmability."
An-Ping Li, received his Ph.D. degree in condensed matter physics from Peking University in 1997, and became a professor at Oak Ridge National Laboratory and the Department of Physics and Astronomy at the University of Tennessee in 2002. He is the research team at the Center for Nanophase Materials Science (CNMS) The department's scanning tunneling microscope group leader and quantum material heterogeneity leader.
The precise application of chemical substances decouples the system and helps maintain the open-shell structure, allowing researchers to construct and study molecules with unique quantum properties at the atomic level. Li said: "It is particularly pleasing to find that these graphene ribbons have coupled magnetic states (also called quantum spin states) at the ends." "These states provide us with a platform for studying magnetic interactions and hopefully provide quantum information. Applications in science create qubits.” Since there is little interference with magnetic interactions in carbon-based molecular materials, this method allows the programming of a durable magnetic state from within the material.
This research method creates a high-precision color band separated from the substrate, which is an ideal application for spintronics and quantum information science. The final system is very suitable for further research and construction because it has a wide band gap that may cross The space between the electronic states required to transmit on/off signals can be used as nanoscale transistors.