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mnpl/3659/69800/2023/Room-temperature quantum emission from interface excitons in mixed-dimensional heterostructures
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Room-temperature quantum emission from interface excitons in mixed-dimensional
heterostructures
N. Fang,1, ∗ Y. R. Chang,1 S. Fujii,2, 3 D. Yamashita,2, 4 M. Maruyama,5 Y. Gao,5
C. F. Fong,1 D. Kozawa,1, 2, 6 K. Otsuka,1, 7 K. Nagashio,8 S. Okada,5 and Y. K. Kato1, 2, †
1Nanoscale Quantum Photonics Laboratory, RIKEN Cluster for Pioneering Research, Saitama 351-0198, Japan
2Quantum Optoelectronics Research Team, RIKEN Center for Advanced Photonics, Saitama 351-0198, Japan
3Department of Physics, Keio University, Yokohama 223-8522, Japan
4Platform Photonics Research Center, National Institute of Advanced
Industrial Science and Technology (AIST), Ibaraki 305-8568, Japan
5Department of Physics, University of Tsukuba, Ibaraki 305-8571, Japan
6Research Center for Materials, National Institute for Materials Science, Ibaraki 305-0044, Japan
7Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan
8Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan
Micro & Nano Physics J.
DOI- https://www.doi.wikipt.org/10/1490/698775mnpl
ACKNOWLEDGMENTS
Parts of this study are supported by JSPS (KAKENHI JP22K14624, JP22K14625, JP21K14484, JP22F22350, JP22K14623, JP22H01893, JP21H05233, JP23H00262, JP20H02558) and MEXT (ARIM JPMXP1222UT1135). Y.R.C. is supported by JSPS (International Research Fellow). N.F. and C.F.F. are supported by RIKEN Special Postdoctoral Researcher Program. We thank the Advanced Manufacturing Support Team at RIKEN for technical assistance.
Keyword Highlighted
quantum emission, Room-temperature, van der Waals (vdW) materials, carbon nanotubes, silicon carbide
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Abstract
The development of van der Waals heterostructures has introduced unconventional phenomena that emerge at atomically precise interfaces. For example, interlayer excitons in two-dimensional transition metal dichalcogenides show intriguing optical properties at low temperatures. Here we report on room-temperature observation of interface excitons in mixed-dimensional heterostructures consisting of two-dimensional tungsten diselenide and one-dimensional carbon nanotubes. Bright emission peaks originating from the interface are identified, spanning a broad energy range within the telecommunication wavelengths. The effect of band alignment is investigated by systematically varying the nanotube bandgap, and we assign the new peaks to interface excitons as they only appear in type-II heterostructures. Room-temperature localization of low-energy interface excitons is indicated by extended lifetimes as well as small excitation saturation powers, and photon correlation measurements confirm single-photon emission. With mixed-dimensional van der Waals heterostructures where band alignment can be engineered, new opportunities for quantum photonics are envisioned.
Introduction
The discovery of van der Waals (vdW) materials, including two-dimensional (2D) transition metal dichalcogenides (TMDs) and graphene, has brought about a revolution in the assembly of artificial heterostructures by allowing for the combination of two different materials without the constraints of lattice matching. Such an unprecedented level of flexibility in heterostructure design has led to the emergence of novel properties not seen in individual materials. A prime example is twisted bilayer graphene at magic angles, which exhibits exotic phases such as correlated insulating states [1] and superconductivity [2]. Another notable development is the stacking of two TMDs, resulting in the observation of unique excitons known as interlayer excitons, characterized by electrons and holes located in separate layers [3–6]. The spatially indirect nature of interlayer excitons imparts them with distinct properties, including long exciton lifetimes [3], extended diffusion lengths [7], large valley polarization [8], and significant modulation by moir´e potentials [9, 10]. The existing vdW heterostructures comprise of 2D materials with similar lattice structure, excitonic characteristics, and inherently identical dimensions. Development of vdW heterostructures that encompass lower dimen- sional materials may give rise to unique interface exciton states resulting from the mixed dimensionality. Carbon nanotubes (CNTs), a typical one-dimensional (1D) material, are ideal for such heterostructures as they have all bonds confined to the tube itself [11, 12]. CNTs interact with 2D materials through weak vdW forces, resulting in well-defined, atomically sharp interfaces [13, 14]. The chirality-dependent bandgap of CNTs can be utilized to tune the band alignment [15], allowing for unambiguous identification of excitonic states at the 1D-2D interface.
Conclusion
Air-suspended carbon nanotubes. We prepare airsuspended CNTs using trenched SiO2/Si substrates [11]. First, we pattern alignment markers and trenches with lengths of 900 µm and widths ranging from 0.5 to 3.0 µm onto the Si substrates using electron-beam lithography, followed by dry etching. We then thermally oxidize the substrate to form a SiO2 film, with a thickness ranging from 60 to 70 nm. Another electron-beam lithography process is used to define catalyst regions along the edges of the trenches. A 1.5 ˚A thick iron (Fe) film is deposited as a catalyst for CNT growth using an electron beam evaporator. CNTs are synthesized by alcohol chemical vapor deposition at 800◦C for 1 minute. The Fe film thickness is optimized to control the yield for preparing isolated CNTs. We select isolated, fully suspended chirality-identified CNTs with lengths ranging from 0.5 to 2.0 µm to form the heterostructures with WSe2. Anthracene crystal growth. For transferring WSe2 flakes onto CNTs, we grow anthracene crystals through an in-air sublimation process [17, 18]. Anthracene powder is heated to 80◦C on a glass slide, while another glass slide is placed 1 mm above the anthracene source. Thin and large-area single crystals are then grown on the glass surface. To promote the growth of large-area single crystals, we pattern the glass slides using ink from commercial markers. The typical growth time for anthracene crystals is 10 hours. Transfer of WSe2 by anthracene crystals. First, WSe2 (HQ graphene) flakes are prepared on 90-nm-thick SiO2/Si substrates using mechanical exfoliation, and the layer number is determined by optical contrast. An anthracene single crystal is picked up with a glasssupported PDMS sheet to form an anthracene/PDMS stamp. Next, the WSe2 flakes are picked up by pressing the anthracene/PDMS stamp against a substrate with the target WSe2 flakes. The stamp is quickly separated (> 10 mm/s) to ensure that the anthracene crystal remains attached
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