Vibrational dynamics of extreme 2×2 and 3×3 potassium iodide nanowires encapsulated in single-walled carbon nanotubes

Unprecedented New Crystalline Forms of SnSe in Narrow to Medium Diameter Carbon Nanotubes

“…The van der Waals forces at the internal surfaces of the SWCNTs constrain the encapsulated material to cross sections as small as ≃1 nm 2 , resulting in structures that are completely different to the bulk form of the material, , producing unprecedented new nanostructured crystalline forms. These can be observed experimentally but also anticipated by predictive modeling methods including molecular dynamics (MD), − density functional theory (DFT), , and ab initio random structure searching (AIRSS). − Both experimentation and theoretical modeling are making significant headway in terms of measuring and predicting new functionality of novel nanostructured crystalline forms including modified phonon optics, anticipated band gap modification but, most recently, potentiation of thermoelectric properties in the smallest crystalline forms, prompting new studies into similar materials and other phenomena on a similar scale including electrochemical reactivity …”

“…Nanowires, sometimes referred to as extreme nanowires, formed at as small as one to three atoms in cross section are being formed by a variety of single elements including S, P, As, and Te and, increasingly, from binary systems including CsI, HgTe, KI, SnTe, and now SnSe. ,,,,− In all cases, profound effects are noted in both fundamental changes in crystal growth and phase formation with polymerization being noted in the case of S, P, and As, and continuous chain or coil formation being noted in the case of Te, and unprecedented new crystalline single, zigzag, and double zigzag chain forms being reported for semiconductors including SnTe and SnSe. Even between these dramatic low-dimensional forms and more conventionally observed bulk-like nanowire forms of these same materials, there exists a size domain in which new crystalline forms are possible, which exhibit novel coordination and novel symmetry and which produce profound changes in physical properties which is true of all of the extreme nanowires formed at or below this size domain.…”

“…For the ultimate scale (i.e., single atomic chain) these include novel metallicity in S, P 4 , and As 4 polymerization, , realization of Peierls distortions in Te, and enhancement of the Seebeck coefficient in SnTe . When the atomic thickness reaches 2–3 atoms, novel rod symmetries arise ,, which give rise to Raman measurable optical phonons that cannot be reproduced in the bulk structure. Similar enhancements to semiconducting band gap , and related improvements to thermoelectric characteristics are also anticipated by theory but are in common with several of the characteristics mentioned above, and these need to be separated from or incorporated with the properties of the embedding nanotubes.…”

Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties

“…23 Binary 1D chain filling in narrow SWCNTs was also demonstrated for chalcogenides SnTe 21 and SnSe, 22 for which computations with density-dunctional theory (DFT) indicated enhanced thermoelectric properties in isolated nanowires of the former. 1D properties have been investigated by Raman spectroscopy for I 3 − , I 5 − , 24−26 KI, 29 and HgTe. 30 True 1D physical phenomena such as Peierls distortions (e.g., Te x ) 18 and Charge Density Waves (e.g., I x − ) can potentially also be addressed.…”

Vibrational and electronic structures of tin selenide nanowires confined inside carbon nanotubes

“…In order to assess the last two questions, we studied experimentally the Raman spectra of SnSe@SWCNT composites. Raman spectroscopy has proven to be a very efficient tool for characterizing SWCNTs embedding 1D atom-sized crystalline HgTe and KI nanowires [23,24]. In both cases it has been demonstrated that it is possible to identify several intrinsic vibrational modes of the nanowires superimposed with the Raman spectrum of SWCNTs.…”