Revealing Microscopic Marvels: Carbon-Focused Quantum Technologies

Attribution: Researchers at Empa, along with their global partners, have effectively integrated carbon nanotube electrodes with atomically accurate nanoribbons. Source: Empa

Researchers engage with individual graphene nanoribbons.

The field of quantum technology is fraught with intricacies, yet it brims with extraordinary potential. Foreseen to catalyze a range of technological breakthroughs in the forthcoming years, it is poised to provide us with more refined and miniature sensors, resiliently secure data transmission channels, and high-performance computing systems. These innovations are expected to surpass current computational technology, facilitating the accelerated discovery of novel pharmaceuticals and materials, optimizing financial markets, and improving meteorological predictions.

For the actualization of these advantages, specific materials demonstrating notable quantum physical properties are essential. One such material is graphene, a two-dimensional carbon arrangement with unique physical attributes such as extraordinary tensile strength and high thermal and electrical conductivity, in addition to specific quantum phenomena. Further constraining this already two-dimensional material, for example by shaping it into a ribbon-like structure, engenders a variety of tunable quantum behaviors.

This is exactly the focus of research led by Mickael Perrin. For several years, the Empa’s Transport at Nanoscale Interfaces laboratory, managed by Michel Calame, has been exploring graphene nanoribbons under the guidance of Perrin. “Graphene nanoribbons offer even more captivating properties than graphene itself,” states Perrin. “Modulating their dimensions, edge geometries, and the inclusion of additional atoms allows us to tailor a myriad of electrical, magnetic, and optical attributes.”

Nanoribbon characteristics diverge depending on their dimensions and edge shapes. Source: Empa

Unmatched Accuracy – Down to Individual Atoms

Conducting research on these promising ribbons is far from straightforward. The slimmer the ribbon, the more evident its quantum characteristics become—however, this also complicates the isolation of a single ribbon for study. This exacting work is essential to discern the singular features and potential applications of this quantum material, differentiating them from aggregate phenomena.

In a newly published paper in the journal Nature Electronics, Perrin, Empa researcher Jian Zhang, and their international colleagues have for the first time successfully made contact with individual, atomically precise graphene nanoribbons. This accomplishment is far from trivial: “A nanoribbon that is merely nine carbon atoms wide has a width of just about 1 nanometer,” notes Zhang. To ensure interaction with only one nanoribbon, the researchers utilized electrodes of similar dimensions—carbon nanotubes measuring approximately 1 nanometer in diameter.

For an experiment of such delicacy, precision is paramount, beginning with the source materials. These were obtained through a robust, long-standing partnership with Empa’s nanotech@surfaces laboratory, led by Roman Fasel. “Roman Fasel and his team have extensive experience with graphene nanoribbons, and they can produce various kinds with atomic precision starting from singular precursor molecules,” clarifies Perrin. These precursor molecules were sourced from the Max Planck Institute for Polymer Research in Mainz.

Interdisciplinary Collaboration

Progress in this cutting-edge area necessitates cross-disciplinary efforts, and diverse international research teams contributed their distinct expertise: Carbon nanotubes were cultivated by a research group at Peking University, and to decode the study’s outcomes, Empa researchers collaborated with computational experts at the University of Warwick. “Such a project would be infeasible without a collaborative approach,” asserts Zhang.

Engaging with individual ribbons using nanotubes presented a significant challenge. “Carbon nanotubes and graphene nanoribbons are synthesized on separate substrates,” Zhang elaborates. “First, nanotubes must be transferred to the device substrate and connected with metal electrodes. Then they are segmented into two electrodes via high-resolution electron-beam lithography.” Following this, the ribbons are relocated onto the same substrate. Extreme accuracy is crucial: Even the smallest rotational misalignment can notably diminish the chances of a successful connection. “Access to the superior infrastructure at the Binnig and Roher Nanotechnology Center at IBM Research in Rüschlikon was indispensable for testing and executing this technology,” states Perrin.

Applications Ranging from Computing to Energy Conversion

The team verified their experimental achievements through charge transport measurements. “Quantum effects tend to be more conspicuous at low temperatures, so we conducted tests close to absolute zero in a high vacuum,” explains Perrin. However, he is prompt to highlight another particularly encouraging feature of graphene nanoribbons: “Given the extremely small dimensions, we anticipate their quantum effects to be sufficiently robust to be observable even at room temperature.” According to Perrin, this could facilitate the design and operation of semiconductor components that capitalize on quantum effects without necessitating elaborate cooling systems.

“This initiative paves the way for devices based on single nanoribbon configurations, not merely to study essential quantum effects like electron and phonon interactions at the microscopic level, but also to exploit such phenomena for applications in quantum switching, quantum sensing, and quantum energy conversion,” adds Hatef Sadeghi, a professor at the University of Warwick involved in the project.

While graphene nanoribbons are not yet prepared for commercial deployment, significant research is still underway. In a subsequent study, Zhang and Perrin aim to manipulate varying quantum states within a single nanoribbon. Additionally, they intend to develop devices comprising two connected nanoribbons, thus forming a dual quantum dot. Such a configuration could function as a qubit—the fundamental information unit in a quantum computer. Furthermore, in the context of his recently awarded ERC Starting Grant and an SNSF Eccellenza Professorial Fellowship, Perrin intends to investigate the nanoribbons as highly efficient energy converters. In his inaugural address at ETH Zurich, he envisions a future where electricity could be derived from temperature differences with minimal energy loss, signifying a true quantum revolution.

International Contributions

Several research teams played pivotal roles in this endeavor. The graphene nanoribbons were synthesized by Empa’s nanotech@surfaces laboratory, managed by Roman Fasel, based on precursor molecules contributed by the Klaus Müllen team at the Max Planck Institute for Polymer Research in Mainz. The nanoribbons were incorporated into nanodevices by the Transport at Nanoscale Interfaces laboratory at Empa, overseen by Michel Calame, where Mickael Perrin’s group operates. High-quality carbon nanotubes essential for this specific research were provided by the research group of Jin Zhang at Peking University. To decipher the study’s outcomes, Empa collaborated with computational scientists at the University of Warwick, supervised by Hatef Sadeghi.

Reference: “Engaging with Individual Graphene Nanoribbons via Carbon Nanotube Electrodes” by Jian Zhang, Liu Qian, Gabriela Borin Barin, Abdalghani H. S. Daaoub, Peipei Chen, Klaus Müllen, Sara Sangtarash, Pascal Ruffieux, Roman Fasel, Hatef Sadeghi, Jin Zhang, Michel Calame, and Mickael L. Perrin, published on 14 August 2023, in Nature Electronics.
DOI: 10.1038/s41928-023-00991-3

Frequently Asked Questions (FAQs) about Carbon-Based Quantum Technology

More about Carbon-Based Quantum Technology

• Empa Research Overview
• Introduction to Quantum Technology
• What are Graphene Nanoribbons?
• Challenges in Quantum Computing
• Importance of International Collaboration in Scientific Research
• Potential Applications of Quantum Technology
• Carbon Nanotubes in Nanotechnology
• Understanding Quantum Effects