Band gap expansion, shear inversion phase change behaviour and low-voltage induced crystal oscillation in low-dimensional tin selenide crystals

Abstract

In common with rocksalt-type alkali halide phases and also semiconductors such as GeTe and SnTe, SnSe forms all-surface two atom-thick low dimensional crystals when encapsulated within single walled nanotubes (SWNTs) with diameters below ∼1.4 nm. Whereas previous density functional theory (DFT) studies indicate that optimised low-dimensional trigonal HgTe changes from a semi-metal to a semi-conductor, low-dimensional SnSe crystals typically undergo band-gap expansion. In slightly wider diameter SWNTs (∼1.4-1.6 nm), we observe that three atom thick low dimensional SnSe crystals undergo a previously unobserved form of a shear inversion phase change resulting in two discrete strain states in a section of curved nanotube. Under low-voltage (i.e. 80-100 kV) imaging conditions in a transmission electron microscope, encapsulated SnSe crystals undergo longitudinal and rotational oscillations, possibly as a result of the increase in the inelastic scattering cross-section of the sample at those voltages.

Encapsulated nanowires: Boosting electronic transport in carbon nanotubes

“…Transport is studied by solving the set of parameter-free Boltzmann transport equations (BTE) for coupled dynamics of electrons and phonons, whilst all relevant scattering rates are calculated ab initio with densityfunctional perturbational theory (DFPT). This route to enhanced transport is attractive due to increasingly well-established methods for growth of 1D crystals inside CNTs [15][16][17][18][19] and assembly of nanowires into integrated devices [20,21]. A broad variety of materials have been encapsulated in this manner, allowing for different degrees of phonon-phonon coupling with the encapsulating CNTs.…”

“…The size and colour of the circles relate to the strength of electron-phonon coupling in the Brillouin zone. One of the phonon decay mechanisms available due to Be encapsulation is demonstrated between the highlighted branches: an optical phonon with strong electron-phonon coupling eters [15], more complex structures become energetically favourable in SWCNTs with diameters larger than ∼ 9Å [16][17][18]. We choose Be for this proof-ofconcept study as it possesses a bulk lattice parameter commensurate with armchair CNTs, suggesting that effects of artificial mismatch strain will be small.…”

In Situ Electron Beam Amorphization of Sb2Te3 within Single Walled Carbon Nanotubes

“…86 keV [14]. When SWNTs are filled with PCMs, such as GeTe [8] or SnSe [9], it is therefore possible to rearrange the contained materials selectively either by in situ electron beam heating or by ex situ heating with minimal damage to the templating nanotubes.…”

“…Following related investigations [8,9] we seek here to investigate the in situ phase transformation characteristics of Sb 2 Te 3 , a material which exhibits high crystallinity inside SWNTs under ambient conditions but which undergoes a facile crystalline to glass phase transition at a moderate temperature or under moderate electron beam irradiation. In the bulk, unalloyed Sb 2 Te 3 melts at 580…”

“…Recently, a variety of PCMs, including GeTe [8], SnSe [9] and PbTe [10] have been incorporated into single walled carbon nanotubes (SWNTs) to produce, in effect, "nano-confined" PCMs or nC-PCMs. These confining systems have several significant advantages over many other comparable templated composite systems: (i) the internal van der Waals surface of SWNTs constrains the size of the nC-PCMs to atomically smooth nanopores with confining surfaces as small as ca.…”