Artificial graphene will redefine the highest level of nanofabrication

At the beginning of this century, the discovery of graphene caused great repercussions in the physics community. As the first two-dimensional material to appear in the real world, it quickly became the darling of scientists. But as a natural substance, graphene has only one fixed atomic arrangement, so all experiments on graphene must adapt to these constraints. However, recently Columbia University experts have made a better performance semiconductor "man-made graphene" device, which perfectly solves this problem.

The unique arrangement of carbon atoms in graphene provides a platform for testing new quantum phenomena that are difficult to observe in traditional materials. With its unusual electronic properties: its electrons can travel a long distance before scattering, and graphene is a superior conductor. These properties also show other unique properties that make electrons appear to be close to the speed of light. Like particles, it has the singular properties that non-relativistic electrons do not have. However, the position of the atoms in the graphene lattice is fixed. In contrast, the spacing and configuration of the lattice in the artificial graphene can be freely set in a large interval. This powerful versatility makes artificial graphene a treasure in the eyes of researchers in the field of condensed matter.

The study was led by experts from Columbia University's Department of Engineering specializing in nanoscale material handling. Through collaboration with colleagues at Princeton University, Purdue University and the Italian University of Science and Technology, the team redesigned the electronic structure of graphene in semiconductor devices for the first time. Thus, a new type of "artificial graphene" was produced.

Figure | Etching pillars refer to the position of quantum dots (red pits) in a hexagonal lattice arrangement. When the spacing between quantum dots is small enough, electrons can move between them. (Source: Diego Scarabelli / Department of Engineering, Columbia University)

Aron Pinczuk, a professor of applied physics and physics at the University of Columbia's Department of Engineering, said: "This milestone has redefined the highest level of condensed matter science and nanofabrication. Although artificial graphene has been applied to optics other systems, such as molecules and photons, but these platforms lack the versatility that semiconductor processing technology can provide. Semiconductor artificial graphene devices may become a platform for exploring new electronic switches, high-performance transistors, and even new methods of quantum state information storage.

Shalom Wind, a co-author of the Applied Physics and Applied Mathematics department, said: "This is a rapidly growing field of research. Many new phenomena that were previously unattainable have now been discovered. As we continue to explore the use of electrically controlled artificial graphene with the new devices, we can unearth more potential for graphene in the field of optoelectronics and data processing."

"This work is actually a major advancement in artificial graphene technology. Previous theories have predicted that graphene-based electronic systems were created manually and tuned with graphical 2D electron gas. But until this time at Columbia University's research. No one has successfully observed these features in engineered semiconductor nanostructures," said Steven G. Louie, a professor of physics at the University of California, Berkeley. “Previous molecular, atomic and photonic structure experiments can only represent systems with poor versatility and stability. This nano-semiconductor structure offers new opportunities for exploring new sciences and their practical applications.

Researchers use tools in traditional chip technology to develop artificial graphene in standard gallium arsenide semiconductors. They designed a layered structure so that electrons can only move within a very narrow layer, effectively creating a 2D plane. They used nanolithography and etching to characterize gallium arsenide: after characterization, gallium arsenide produced a hexagonal lattice that confines electrons in the lateral direction. By placing these so-called "artificial atoms" close enough to each other (about 50 nanometers apart), these artificial atoms can interact in a quantum mechanical manner, similar to the way atoms share their electrons in solids.

Nanolithography and etching form small pillars, and the quantum dots underneath are arranged in a hexagonal lattice. Scanning the electron micrograph at the bottom shows a hexagonal array with a perimeter of only 50 nanometers from the top. (Source: Diego Scarabelli / Columbia Engineering)

The group detects the electronic state of the artificial lattice by irradiating the laser and measures the scattered light. Scattered light can show the energy lost when an electron transitions from one state to another. When they mapped these state transitions, the team found that they were approaching zero in a linear fashion close to the "Dirac point", a characteristic of graphene at which electron density would disappear.

This artificial graphene has many advantages over natural graphene: for example, researchers can adjust the electronic behavior by adjusting the cellular lattice. And because the spacing between quantum dots is much larger than the spacing of atoms in natural graphene, researchers can observe more exotic quantum phenomena under the action of magnetic fields.

The discovery of graphene and other new low-dimensional materials (such as ultra-thin layered van der Waals films) laid the foundation for this research. Pinczuk pointed out: "Previous advances in nanofabrication technology are critical to this research. These previous studies have provided us with an ever-expanding 'toolbox' that we can use to portray high-quality patterns on countless nanoscale scales. It is no exaggeration to say that this discovery has inspired our physicists in this field."

The Nobel Prize in Physics in 2010 brought graphene into the people's attention. Since its discovery, graphene has received extensive attention and has been continuously developed, but it is facing many challenges in the current research and development of technology, but these challenges are also the fertile ground for our future research. If the 20th century is the century of silicon, graphene will create a new material era in the 21st century, which will bring substantial changes to the world. We believe that the future of graphene and related technologies is bright.

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