Correlation of Structural and Electronic Properties in a New Low-Dimensional Form of Mercury Telluride

Using high resolution electron microscopy and first principles quantum mechanical calculations we have explored the fundamental physics and chemistry of the semiconductor, HgTe grown inside single wall carbon nanotubes. This material forms a low-dimensional structure based on a repeating ${\mathrm{Hg}}_2{\mathrm{Te}}_2$ motif in which both atom species adopt new coordination geometries not seen in the bulk. Density-functional theory calculations confirm the stability of this structure and demonstrate conclusively that it arises solely as a consequence of constrained low dimensionality. This change is directly correlated with a modified electronic structure in which the low-dimensional form of HgTe is transformed from a bulk semimetal to a semiconductor.

Figure 1

(a), (b) Composite restorations of the phase of the exit plane wave function of two separate SWCNTs with diameters of 1.36 and 1.49 nm, respectively, containing crystalline HgTe. The boxes indicate individually restored subregions as described in the text which were also used for establishing relative focus levels along the SWCNT axis.

Figure 2

(a) Generalized ${\mathrm{Hg}}_4{\mathrm{Te}}_4$ motif with both ${\mathrm{Hg}}_2{\mathrm{Te}}_2$ dimers delineated. This motif is shown with a local rotation angle $(\varphi )=0$, intralayer Hg-Te-Hg angle $(\gamma )=70°$, and relative tilt angle $(\theta )=0$. (b) Subsets of optimized simulations of the phase of the specimen exit plane wave with $(\theta )=0$ and 25°, respectively, for fixed $(\gamma )=70°$ and for values of $(\varphi )$ as indicated. (c) Detail from Fig. 1a. (d) Simulation matching (c). (e) Structure model corresponding to the indicated region in (d). (f) Detail from Fig. 1b. (g) Simulation matching (f). (h) Structure model corresponding to the indicated region in (f).

Figure 3

Optimized geometry of the low-dimensional form of HgTe showing local bond lengths and angles calculated from DFT. The equivalent experimentally determined bond lengths and angles are given in the text.