SnTe microcrystals: Surface cleaning of a topological crystalline insulator

Abstract

Investigating nanometer and micron sized materials thought to exhibit topological surface properties that can present a challenge, as clean surfaces are a prerequisite for band structure measurements when using nano-ARPES or laser-ARPES in ultra-high vacuum. This issue is exacerbated when dealing with nanometer or micron sized materials, which have been prepared ex-situ and so have been exposed to atmosphere. We present the findings of an XPS study where various cleaning methods have been employed to reduce the surface contamination and preserve the surface quality for surface sensitive measurements. Microcrystals of the topological crystalline insulator SnTe were grown ex-situ and transferred into ultra high vacuum (UHV) before being treated with either atomic hydrogen, argon sputtering, annealing, or a combination of treatments. The samples were also characterised using the scanning electron microscopy, both before and after treatment. It was found that atomic hydrogen cleaning with an anneal cycle (200 C) gave the best clean surface results. V

CdTe:Sn thin films deposited by the simultaneous laser ablation of CdTe and Sn targets

“…Saghir et al [24] reported that a binding energy of 485.4 eV corresponds to Sn 2+ in SnTe, thus, for the present results it can be concluded that Sn 2+ are present in the films, which means that Sn substitutes Cd as both have the same oxidation state.…”

Surface oxidation and thermoelectric properties of indium-doped tin telluride nanowires

“…The former corresponds to a 0 state, 74 and the latter is +4 as in TeO 2 . [57][58][59] In contrast to the EDX characterization which has a lower sensitivity, two prominent In peaks are observed in Figure 5d and the binding energies are 453.7 eV (3d 3/2 ) and 446.0 eV (3d 5/2 ) which correspond to a +3 oxidation state. 75 These results suggest that the sample surface is oxidized and forms XPS spectra taken at other spots on the first substrate show similar results ( Figure S5 and Table S1, Supplementary Information).…”

“…The Sn 3d spectrum in Figure 5b shows two peaks at ~ 496.0 eV (3d 3/2 ) and ~ 487.6 eV (3d 5/2 ), indicating a +4 oxidation state in contrast to the nominal +2 in SnTe. [57][58][59] The Te 3d spectrum in Figure 5c has two components with binding energies of 583.9 eV (3d 3/2 ), 573.5 eV (3d 5/2 ) and 587.8 eV (3d 3/2 ), 577.4 eV (3d 5/2 ), respectively. The former corresponds to a 0 state, 74 and the latter is +4 as in TeO 2 .…”

“…[50][51][52][53][54][55] The topological surface could have enhanced thermopower due to its unique energy dispersion and strongly energy-dependent relaxation time. 49,56 In spite of great promise in various aspects, the surfaces of SnTe-based compounds are often prone to contamination or oxidation [57][58][59] . This creates an essential challenge to directly probing topological states of pristine nanostructures using surface sensitive techniques such as scanning tunneling microscopy (STM) and nano angle-resolved photoemission spectroscopy (nano-ARPES), because of the unavoidable exposure to air during sample transfer from the growth reactor to the measurement chamber.…”

Physicochemical Properties of SnTe Thin Films Dependent on Compositional Ratios

“…[11] The peaks of Sn 4þ and Te 4þ were associated with SnO 2 and TeO 2 on the TF surface. [47] The ratio of Sn 4þ species decreased and the ratio of Te 4þ species increased as the Te composition of the STX TFs increased.…”