Trion confinement in monolayer MoSe2 by carbon nanotube local gating

We have successfully confined trions into a one-dimensional restricted space of a MoSe2 device with CNT gate electrodes. The dry transfer process, including deterministic dry transfer of aligned CNTs, has led to an hBN-encapsulated MoSe2 device with CNT back gate electrodes. In contrast to a location without CNT gate electrodes, applying voltage via CNT gate electrodes significantly alters PL spectra at a location with CNT gate electrodes. PL imaging has revealed that image contrast from trions is linear along the CNT electrode underneath, consistent with 1D confinement of trions in response to the CNT local gating. The confinement width obtained from the PL image is 5.5 x 10^2 nm, consistent with nanoscale 1D confined trions with the diffraction limit broadening. This work has demonstrated electrical control of excitonic states at the nanoscale, leading to novel optoelectronic properties and exciton devices in the future

Atomic-scale structural identification and evolution of Co-W-C ternary SWCNT catalytic nanoparticles: High-resolution STEM imaging on SiO 2

International audienceRecently, W-based catalysts have provided a promising route to synthesize single-walled carbon nanotubes (SWCNTs) with specific chirality, but the mechanism of the growth selectivity is vaguely understood. We propose a strategy to identify the atomic structure as well as the structure evolution of the CoW -C ternary SWCNT catalyst. The key is to use a thin SiO 2 film as the catalyst support and observation window. As the catalyst is uniformly prepared on this SiO 2 film and directly used for the SWCNT synthesis, this method has an advantage over conventional methods: it creates an opportunity to obtain original, statistical, and dynamic understanding of the catalyst. As a technique, atomic-scale imaging directly on SiO 2 serves as a powerful and versatile tool to investigate nanocrystals and high-temperature reactions; for the synthesis of SWCNTs, this work successfully visualizes the structure and evolution of the catalyst and illuminates the possible nucleation sites of the chirality-specific growth

Intertube excitonic coupling in nanotube van der Waals heterostructures

Strong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examining the ultrafast response of radial C/BN/MoS$_2$ core/shell/skin nanotubes to femtosecond infrared light pulses. Remarkably, infrared excitation of excitons in the semiconducting CNTs creates a prominent excitonic response in the visible range from the MoS$_2$ skin, even with infrared photons at energies well below the bandgap of MoS$_2$. Via classical analogies and a quantum model of the light-matter interaction we assign these findings 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 MoS$_2$ 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 nano-scale coaxial cables