Scanning tunneling microscopy picture of a zigzag graphene nanoribbon. Credit: Felix Fischer/Berkeley Lab
Method Tunes Into Graphene Nanoribbons Electronic Potential
Since graphene– a thin carbon sheet simply one-atom thick– was found more than 15 years ago, the wonder product ended up being a workhorse in materials science research study. From this body of work, other scientists found out that slicing graphene along the edge of its honeycomb lattice produces one-dimensional zigzag graphene strips or nanoribbons with exotic magnetic residential or commercial properties.
Numerous scientists have looked for to harness nanoribbons unusual magnetic habits into carbon-based, spintronics devices that allow high-speed, low-power information storage and info processing technologies by encoding information through electron spin instead of charge. But due to the fact that zigzag nanoribbons are highly reactive, researchers have actually faced how to observe and carry their exotic residential or commercial properties into a real-world device.
To construct the nanoribbons, the small molecular building blocks are first transferred onto a flat metal surface area, or substrate. Next, the surface is carefully heated, triggering two chemical deals with at either end of each particle. Each time 2 “sticky ends” satisfy while the activated molecules spread out on the surface, the particles integrate to form new carbon-carbon bonds. Eventually, the process constructs 1D daisy chains of molecular building blocks. A 2nd heating step reorganizes the chains internal bonds to form a graphene nanoribbon featuring 2 parallel zigzag edges.
Now, as reported in the journal Nature, researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have actually developed an approach to stabilize the edges of graphene nanoribbons and directly determine their special magnetic homes.
Regional magnetic buying along zigzag edge states (red and blue arrows) in nitrogen-doped graphene nanoribbons induces a splitting in energy of the nitrogen atoms electrons. Credit: Felix Fischer/Berkeley Lab
The team co-led by Felix Fischer and Steven Louie, both faculty researchers in Berkeley Labs Materials Sciences Division, found that by substituting some of the carbon atoms along the ribbons zigzag edges with nitrogen atoms, they could discretely tune the regional electronic structure without interrupting the magnetic properties. This subtle structural change even more enabled the advancement of a scanning probe microscopy method for measuring the materials regional magnetism at the atomic scale.
” Prior attempts to stabilize the zigzag edge inevitably changed the electronic structure of the edge itself,” stated Louie, who is also a professor of physics at UC Berkeley. “This problem has actually doomed efforts to access their magnetic structure with experimental methods, and until now relegated their expedition to computational models,” he included.
Assisted by theoretical models, Fischer and Louie created a personalized molecular structure block featuring a plan of carbon and nitrogen atoms that can be mapped onto the exact structure of the preferred zigzag graphene nanoribbons.
To develop the nanoribbons, the small molecular foundation are first deposited onto a flat metal surface, or substrate. Next, the surface is gently warmed, triggering 2 chemical handles at either end of each particle. This activation step breaks a chemical bond and leaves behind a highly reactive “sticky end.”
Each time 2 “sticky ends” fulfill while the activated molecules expanded on the surface, the molecules integrate to form brand-new carbon-carbon bonds. Eventually, the procedure develops 1D daisy chains of molecular structure blocks. A second heating action rearranges the chains internal bonds to form a graphene nanoribbon featuring 2 parallel zigzag edges.
” The unique advantage of this molecular bottom-up innovation is that any structural feature of the graphene ribbon, such as the precise position of the nitrogen atoms, can be encoded in the molecular structure block,” stated Raymond Blackwell, a graduate student in the Fischer group and co-lead author on the paper together with Fangzhou Zhao, a graduate student in the Louie group.
The next difficulty was to determine the nanoribbons homes.
” We rapidly understood that, to not only measure but in fact quantify the magnetic field caused by the spin-polarized nanoribbon edge states, we would have to deal with two additional problems,” said Fischer, who is also a teacher of chemistry at UC Berkeley.
The group needed to figure out how to separate the electronic structure of the ribbon from its substrate. Fischer fixed the issue by using a scanning tunneling microscope tip to irreversibly break the link in between the graphene nanoribbon and the underlying metal.
The 2nd challenge was to develop a brand-new method to straight determine an electromagnetic field at the nanometer scale. Luckily, the researchers discovered that the nitrogen atoms substituted in the nanoribbons structure actually acted as atomic-scale sensing units.
Measurements at the positions of the nitrogen atoms revealed the characteristic functions of a local magnetic field along the zigzag edge.
Estimations carried out by Louie using computing resources at the National Energy Research Scientific Computing Center (NERSC) yielded quantitative forecasts of the interactions that develop from the spin-polarized edge states of the ribbons. Microscopy measurements of the accurate signatures of magnetic interactions matched those predictions and validated their quantum residential or commercial properties.
” Exploring and ultimately developing the speculative tools that permit logical engineering of these unique magnetic edges opens the door to unprecedented chances of carbon-based spintronics,” said Fischer, referring to next-generation nano-electronic devices that count on intrinsic properties of electrons. Future work will involve checking out phenomena associated with these properties in custom-designed zigzag graphene architectures.
Recommendation: “Spin splitting of dopant edge state in magnetic zigzag graphene nanoribbons” by Raymond E. Blackwell, Fangzhou Zhao, Erin Brooks, Junmian Zhu, Ilya Piskun, Shenkai Wang, Aidan Delgado, Yea-Lee Lee, Steven G. Louie and Felix R. Fischer, 22 December 2021, Nature.DOI: 10.1038/ s41586-021-04201-y.
This research was supported by the DOE Office of Science. NERSC is a DOE Office of Science user facility situated at Berkeley Lab.