Browsing by Author "Xiang, Rong"

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Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures
(2022-03-09) Burdanova, Maria G.; Liu, Ming; Staniforth, Michael; Zheng, Yongjia; Xiang, Rong; Chiashi, Shohei; Anisimov, Anton; Kauppinen, Esko I.; Maruyama, Shigeo; Lloyd-Hughes, James
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Strong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examining the ultrafast response of radial C/BN/MoS2 core/shell/skin nanotubes to femtosecond infrared light pulses. Remarkably, infrared excitation of excitons in the semiconducting carbon nanotubes (CNTs) creates a prominent excitonic response in the visible range from the MoS2 skin, even with infrared photons at energies well below the bandgap of MoS2. Via classical analogies and a quantum model of the light–matter interaction these findings are assigned to intertube excitonic correlations. Dipole–dipole Coulomb interactions in the coherent regime produce intertube biexcitons, which persist for tens of femtoseconds, while on longer timescales (>100 ps) hole tunneling—from the CNT core, through the BN tunnel barrier, to the MoS2 skin—creates intertube excitons. Charge transfer and dipole–dipole interactions thus play prominent roles on different timescales, and establish new possibilities for the multi-functional use of these new nanoscale coaxial cables.
One-dimensional van der Waals heterostructures: Growth mechanism and handedness correlation revealed by nondestructive TEM
(2021-09-14) Zheng, Yongjia; Kumamoto, Akihito; Hisama, Kaoru; Otsuka, Keigo; Wickerson, Grace; Sato, Yuta; Liu, Ming; Inoue, Taiki; Chiashi, Shohei; Tang, Dai Ming; Zhang, Qiang; Anisimov, Anton; Kauppinen, Esko I.; Li, Yan; Suenaga, Kazu; Ikuhara, Yuichi; Maruyama, Shigeo; Xiang, Rong
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We recently synthesized one-dimensional (1D) van der Waals heterostructures in which different atomic layers (e.g., boron nitride or molybdenum disulfide) seamlessly wrap around a single-walled carbon nanotube (SWCNT) and form a coaxial, crystalized heteronanotube. The growth process of 1D heterostructure is unconventional-different crystals need to nucleate on a highly curved surface and extend nanotubes shell by shell-so understanding the formation mechanism is of fundamental research interest. In this work, we perform a follow-up and comprehensive study on the structural details and formation mechanism of chemical vapor deposition (CVD)-synthesized 1D heterostructures. Edge structures, nucleation sites, and crystal epitaxial relationships are clearly revealed using transmission electron microscopy (TEM). This is achieved by the direct synthesis of heteronanotubes on a CVD-compatible Si/SiO2 TEM grid, which enabled a transfer-free and nondestructive access to many intrinsic structural details. In particular, we have distinguished different-shaped boron nitride nanotube (BNNT) edges, which are confirmed by electron diffraction at the same location to be strictly associated with its own chiral angle and polarity. We also demonstrate the importance of surface cleanness and isolation for the formation of perfect 1D heterostructures. Furthermore, we elucidate the handedness correlation between the SWCNT template and BNNT crystals. This work not only provides an in-depth understanding of this 1D heterostructure material group but also, in a more general perspective, serves as an interesting investigation on crystal growth on highly curved (radius of a couple of nanometers) atomic substrates.