ACS Appl. Nano Mater, Article ASAP

M. Lewin, L. Mester, T. Saltzmann, S.-J. Chong, M. Kaminski, B. Hauer, M. Pohlmann, A. M. Mio, M. Wirtssohn, P. Jost, M. Wuttig, U. Simon and T. Taubner

ACS Appl. Nano Mater, Article ASAP (2018)

Sb₂Te₃ exhibits a plethora of fundamentally relevant electronic phenomena enabling electronic phase change memory cells, thermoelectric devices, and three-dimensional topological insulator structures. Thus, the controlled growth of nanostructures and thin films with well-defined electronic properties is of utmost importance. Previously, our group observed symmetric infrared domains in hexagonal Sb₂Te₃ nanoplatelets from a solvothermal chemical synthesis. The relative optical contrast observed was indirectly linked to the formation of regions with different defect densities (charge carrier concentrations). This raises two major questions, which we answer in this study: Is the domain formation restricted to the specific platelet growth process? No! Do the infrared spectra of both domains really follow a “Drude-like” free charge carrier response? Yes! By controlling the initial water concentration, we promote the growth of the nanoplatelets in the c-direction and tune the morphology from platelet-like to octahedra-like. Although the growth mode changes from spiral growth to layer-by-layer, similar infrared domains are identified using scattering-type scanning near-field optical microscopy (s-SNOM). Furthermore, we also reproduced the formation of symmetric infrared domains in thin, high quality crystalline films grown using molecular beam epitaxy (MBE). Normalized infrared near-field spectra of smaller Sb₂Te₃nanoparticles reveal a relative shift of the plasma frequency in both domains. These findings demonstrate that the formation of domains with different charge carrier properties is an intrinsic material property of Sb₂Te₃ and might strongly influence all of its electronic applications.

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