January 26, 2023

Layered Graphene with a Twist Displays Unique Quantum Confinement Effects in 2-D

Comprehending how electrons relocate 2-D layered material systems might cause advances in quantum computing and interaction.
Researchers studying two different setups of bilayer graphene– the two-dimensional (2-D), atom-thin type of carbon– have actually found electronic and optical interlayer resonances. In these resonant states, electrons get better and forth in between the two atomic planes in the 2-D interface at the same frequency. By characterizing these states, they found that twisting one of the graphene layers by 30 degrees relative to the other, instead of stacking the layers directly on top of each other, shifts the resonance to a lower energy.

If we can understand how electrons move at the little scale of a couple of nanometers in the decreased measurements of 2-D materials, we might be able to unlock another way to utilize electrons for quantum details science.”
These quantum confinement impacts are the outcome of quantum mechanical wave-like movement rather than classical mechanical movement, in which electrons move through a material and are scattered by random flaws.
For this research study, the team chose a simple material model– graphene– to investigate quantum confinement results, applying two various probes: electrons and photons (particles of light). Dai and Sadowski designed and brought out experiments in which they shot electrons into the product with a low-energy electron microscopic lense (LEEM) and detected the reflected electrons. The LEEM microscopic lense is part of the x-ray photoemission electron microscopy (XPEEM)/ LEEM endstation of the Electron Spectro-Microscopy beamline at NSLS-II; the CFN operates this endstation through a partner user contract with NSLS-II.

From this result, just released in Physical Review Letters, they deduced that the distance in between the 2 layers increased significantly in the twisted setup, compared to the stacked one. When this distance changes, so do the interlayer interactions, affecting how electrons move in the bilayer system. An understanding of this electron motion might notify the design of future quantum technologies for more powerful computing and more safe interaction.
The complete QPress system, still under advancement, will automate the stacking of 2-D products into layered structures with exotic homes for quantum applications. Credit: Brookhaven National Laboratory.
” Todays computer system chips are based upon our understanding of how electrons relocate semiconductors, specifically silicon,” stated first and co-corresponding author Zhongwei Dai, a postdoc in the Interface Science and Catalysis Group at the Center for Functional Nanomaterials (CFN) at the U.S. Department of Energy (DOE)s Brookhaven National Laboratory. “But the physical residential or commercial properties of silicon are reaching a physical limit in regards to how little transistors can be made and how many can fit on a chip. If we can understand how electrons move at the small scale of a few nanometers in the reduced measurements of 2-D materials, we may have the ability to open another method to utilize electrons for quantum information science.”
At a few nanometers, or billionths of a meter, the size of a product system is equivalent to that of the wavelength of electrons. The products electronic and optical homes change when electrons are confined in a space with measurements of their wavelength. These quantum confinement impacts are the outcome of quantum mechanical wave-like movement rather than classical mechanical movement, in which electrons move through a product and are spread by random problems.
( Clockwise from left to right) Team members Chang-Yong Nam, Jurek Sadowski, Zhongwei Dai, Samuel Tenney, Nikhil Tiwale, and Ashwanth Subramanian outside the Center for Functional Nanomaterials. Credit: Brookhaven National Laboratory
For this research, the group picked a simple product design– graphene– to examine quantum confinement effects, using 2 various probes: electrons and photons (particles of light). Co-corresponding author and CFN Interface Science and Catalysis Group researcher Jurek Sadowski had actually formerly designed this substrate for the Quantum Material Press (QPress). Traditionally, researchers exfoliate 2-D product “flakes” from 3-D parent crystals (e.g., graphene from graphite) on a silicon dioxide substrate a number of hundred nanometers thick.
” This layer is transparent enough for optical characterization and decision of the density of exfoliated flakes and stacked monolayers while conductive adequate for electron microscopy or synchrotron-based spectroscopy techniques,” described Sadowski.
In the Charlie Johnson Group at the University of Pennsylvania– Rebecca W. Bushnell Professor of Physics and Astronomy Charlie Johnson, postdoc Qicheng Zhang, and former postdoc Zhaoli Gao (now an assistant teacher at the Chinese University of Hong Kong)– grew the graphene on metal foils and moved it onto the titanium oxide/silicon dioxide substrate. When graphene is grown in this way, all three domains (single layer, stacked, and twisted) exist.
( a) Schematics of the experimental setup for electron and photon scattering. (b) An atomic model of the pattern formed by the twisted bilayer graphene (30 °- tBLG )crystal structure. (c) A low-energy electron microscopic lense picture of a common sample location containing 30 °- tBLG, stacked bilayer graphene (AB-BLG), and single-layer graphene (SLG). (d) A low-energy electron diffraction pattern on a 30 °- tBLG area. Credit: Brookhaven National Laboratory
Then, Dai and Sadowski developed and brought out experiments in which they shot electrons into the material with a low-energy electron microscope (LEEM) and spotted the reflected electrons. They also fired photons from a laser-based optical microscopic lense with a spectrometer into the material and evaluated the spectrum of light scattered back. This confocal Raman microscope becomes part of the QPress cataloger, which together with image-analysis software application, can pinpoint the areas of sample locations of interest.
” The QPress Raman microscope allowed us to quickly recognize the target sample area, accelerating our research,” said Dai.
Their outcomes recommended that the spacing between layers in the twisted graphene configuration increased by about 6 percent relative to the non-twisted setup. Estimations by theorists at the University of New Hampshire validated the distinct resonant electronic habits in the twisted setup.
” Devices constructed out of turned graphene may have extremely fascinating and unexpected residential or commercial properties since of the increased interlayer spacing in which electrons can move,” said Sadowski.
Next, the team will make gadgets with the twisted graphene. The group will also build on preliminary experiments performed by CFN staff researcher Samuel Tenney and CFN postdocs Calley Eads and Nikhil Tiwale to check out how adding various materials to the layered structure impacts its optical and electronic properties.
” In this initial research, we selected the most basic 2-D material system we can synthesize and manage to understand how electrons act,” said Dai. “We plan to continue these kinds of basic studies, ideally clarifying how to manipulate products for quantum computing and interactions.”
This research was supported by the DOE Office of Science and utilized resources of the CFN and National Synchrotron Light Source II (NSLS-II), both DOE Office of Science User Facilities at Brookhaven. The LEEM microscopic lense belongs to the x-ray photoemission electron microscopy (XPEEM)/ LEEM endstation of the Electron Spectro-Microscopy beamline at NSLS-II; the CFN operates this endstation through a partner user arrangement with NSLS-II. The other financing companies are the National Science Foundation, Research Grant Council of Hong Kong Special Administrative Region, and the Chinese University of Hong Kong.
For more on this research study, read Atomically-Thin, Twisted Graphene Has Unique Properties That Could Advance Quantum Computing.
Reference: “Quantum-Well Bound States in Graphene Heterostructure Interfaces” by Zhongwei Dai, Zhaoli Gao, Sergey S. Pershoguba, Nikhil Tiwale, Ashwanth Subramanian, Qicheng Zhang, Calley Eads, Samuel A. Tenney, Richard M. Osgood, Chang-Yong Nam, Jiadong Zang, A. T. Charlie Johnson and Jerzy T. Sadowski, 20 August 2021, Physical Review Letters.DOI: 10.1103/ PhysRevLett.127.086805.

Leave a Reply

Your email address will not be published. Required fields are marked *