Single Quasi-1D Chains of Sb2Se3 Encapsulated Within Carbon Nanotubes

Abstract

The realization of stable monolayers from 2D van der Waals (vdW) solids has fueled the search for exfoliable crystals that possess even lower dimensionalities. To this end, 1D and quasi-1D (q-1D) vdW crystals comprised of weakly-bound chains with sub-nanometer thicknesses have been discovered and demonstrated to exhibit nascent physics in the bulk. Although established micromechanical and liquid phase exfoliation methods have been applied to access single isolated chains from bulk 1D and q-1D vdW crystals, the existence of interchain vdW interactions with non-equivalent strengths has greatly hindered the ability to achieve uniform single isolated chains. Here, we report that encapsulation of the model q-1D vdW crystal, Sb2Se3, within single-walled carbon nanotubes (CNTs) circumvents the relatively stronger vdW interactions between the chains and allows for the isolation of single chains with structural integrity. Comprehensive high-resolution transmission electron microscopy and selected area electron diffraction studies of the Sb2Se3@CNT heterostructure revealed that the structure of the [Sb4Se6]n chain is preserved, enabling us to systematically probe the size-dependent properties of Sb2Se3 from the bulk down to a single chain. We then show that ensembles of the [Sb4Se6]n chains within CNTs display Raman confinement effects and an emergent band-like absorption onset around 600 nm, suggesting a strong blue shift of the near-infrared band gap of Sb2Se3 into the visible range upon encapsulation. First-principles density functional theory calculations further provided a qualitative insight on the structures and interactions that could manifest in the Sb2Se3@CNT heterostructure. From these calculations, spatial visualization of the electron density difference map of the heterostructure indicated the possibility of electron donation from the host CNT to the guest [Sb4Se6]n chain. Altogether, this model system demonstrates that 1D and q-1D vdW crystals with strongly anisotropic vdW interactions can be precisely studied by encapsulation within carbon nanotubes with suitable diameters, thereby opening opportunities in understanding dimension-dependent properties of a plethora of emergent vdW solids at or approaching the sub-nanometer regime.

Encapsulation of Crystalline and Amorphous Sb2S3 within Carbon and Boron Nitride Nanotubes

“…23 We, however, did not observe any apparent difference between empty and filled SWCNTs in the region we surveyed, with only broadband CNT absorbance visible. This contrasts with our work on Sb2Se3@SWCNT, where we saw the onset of a distinct edge in the heterostructure not present in empty SWCNTs 72 and is likely due to the lower absorption coefficient of Sb2S3 compared to Sb2Se3. 31 From these measurements, it became clear that the observation of confined optical properties of Sb2S3 down to the single chain regime in encapsulated heterostructures requires a transparent nanotube as a host material.…”

“…1B). As we saw previously with our work on Sb2Se3, 72 this method of confinement within SWCNTs accessed ultrathin nanowires of Sb2S3 within nanotubes of fewer than 2 nm, meaning that only 1-2 covalent chains with 1.04 nm distance between terminal sulfur atoms could occupy a given nanotube. We performed Raman spectroscopy to further verify that minimal structural modulation had occurred as was 15 observed by HRTEM imaging (Fig.…”

Encapsulation of crystalline and amorphous Sb2S3 within carbon and boron nitride nanotubes

“… 23 We, however, did not observe any apparent difference between empty and filled SWCNTs in the region we surveyed, with only broadband CNT absorbance visible. This contrasts with our work on Sb 2 Se 3 @SWCNT, where we saw the onset of a distinct edge in the heterostructure not present in empty SWCNTs 72 and is likely due to the lower absorption coefficient of Sb 2 S 3 compared to Sb 2 Se 3 . 31 From these measurements, it became clear that the observation of confined optical properties of Sb 2 S 3 down to the single chain regime in encapsulated heterostructures requires a transparent nanotube as a host material.…”

“…1B ). As we saw previously with our work on Sb 2 Se 3 , 72 this method of confinement within SWCNTs accessed ultrathin nanowires of Sb 2 S 3 within nanotubes of fewer than 2 nm, meaning that only 1–2 covalent chains with 1.04 nm distance between terminal sulfur atoms could occupy a given nanotube.…”