Particle- and phase-selective X-ray spectroscopy with micro- and macrobeams: the case of (SmS)1.19TaS2 nanotubes.

by Azat Khadiev (FS-PETRA-D (FS-PET-D Fachgruppe P23 (Russian/Germ)))

Tuesday 30 Nov 2021, 13:15 → 14:00 Europe/Berlin

Online

The (SmS)1.19TaS2 nanotubes (NT) belongs to the new class of the NT formed by misfit layered compounds (MLCs) and, in particular, chalcogenide-based MLCs of the general formula [(MX)1+y]m[TX2]n (abbreviated here as MX-TX2; M=Pb, Sb, Bi, Sn, rare-earth atom; T = Ta, Nb, Ti, Cr, V; X=S, Se. Here MX stands for one layer of a compound with distorted rocksalt structure, while TX2 is a monolayer of a 2D material with hexagonal (or octahedral) structure. The alternating layers are incommensurate along at least one direction, generally the a-axis, and this incommensuration between the MX slab and TX2 is considered to be a driving force for folding of 2D layers into tube. The stability of the MLC NTs is generally attributed, in addition to the van der Waals force between the layers, also to a partial charge transfer from the MX layer to the TX2 slab, i.e. a polar interaction between the two adjacent layers [1,2]. This charge transfer in NT can potentially be studied by X-ray absorption spectroscopy (XAS).

During (SmS)1.19TaS2 NT synthesis a lot of additional unwanted phases are appearing. The majority of these phases consists of the same elements (like TX2 or MnXm) and some compounds even have similar to NT crystal structure parameters (MLC platelets). Therefore, it is difficult to separate nanotubes’ spectroscopic data from the powder mixture by standard XAS methods.

During this talk I will present the analysis of (SmS)1.19TaS2 nanotube powders achieved at different reaction conditions. I will show how to use Diffraction Anomalous Fine Structure (DAFS) analysis to separate the XAS-like data of pure MLC phases from the powder mixture with X-ray macrobeam. I will use microbeam CRL-based XAS to get spectroscopic data on the single MLC nanotube and compare the results with bulk data. The potentials and challenges of these techniques are discussed, advantages of both methods are also compared.

Proposed work is a joint project with R. Tenne group from Weizman Institute of Science (Rehovot).

1. M. Serra, D. Stolovas, L. Houben, R. Popovitz-Biro, I. Pinkas, F. Kampmann, J. Maultzsch, E. Joselevich, R. Tenne, Chem. Eur. J. 2018, 24, 11354.

2. S.S. Sinha, M.B. Sreedhara, R. Tenne, Nano Today, Vol. 37, 2021, 101060