Diamond cubic Sn-rich nanocrystals were fabricated with radii less than 20 nm by post-growth annealing at T=750°C of SnxGe1-x alloys grown on Ge(001) by molecular beam epitaxy. The crystal phase of the Sn-rich nanocrystals was determined to be diamond cubic from Fourier transform analysis of high-resolution transmission electron microscopy images. Optical transmittance of these SnxGe1-x/Ge (001) films demonstrated changes in optical absorption that can be attributed to absorption from the nanocrystals. The energy bandgap was measured to be 0.45 eV for nanocrystals arrays in Ge with a mean diameter of 32 nm. © Springer-Verlag 2005.

The void mediated formation mechanism of Sn quantum dots in an Si matrix was analyzed. It was found that the diffusion of Sn atoms into these voids leads to an initial rapid coarsening of the quantum dots during annealing. However, as this process is not restricted to Sn, the quantum dots could be grown by controlling the formation of voids and the diffusion of materials in these voids during molecular beam epitaxy.

Trigonal tellurium, a small-gap semiconductor with pronounced magneto-electric and magneto-optical responses, is among the simplest realizations of a chiral crystal. We have studied by spin- and angle-resolved photoelectron spectroscopy its unconventional electronic structure and unique spin texture. We identify Kramers-Weyl, composite, and accordionlike Weyl fermions, so far only predicted by theory, and show that the spin polarization is parallel to the wave vector along the lines in k space connecting high-symmetry points. Our results clarify the symmetries that enforce such spin texture in a chiral crystal, thus bringing new insight in the formation of a spin vectorial field more complex than the previously proposed hedgehog configuration. Our findings thus pave the way to a classification scheme for these exotic spin textures and their search in chiral crystals.