Sb₂Te₃ Growth Study Reveals That Formation of Nanoscale Charge Carrier Domains Is an Intrinsic Feature Relevant for Electronic Applications

Abstract

Sb 2 Te 3 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 Sb 2 Te 3 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 Sb 2 Te 3 nanoparticles 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 Sb 2 Te 3 and might strongly influence all of its electronic applications.

Bi2Te3 Nanoplates’ Selective Growth Morphology on Different Interfaces for Enhancing Thermoelectric Properties

“…A QL hexagonal Bi 2 Te 3 grows on the surface of H-terminated Si(111) and then subquintuple steps continuous to growth on the first QL. For thicker films, screw dislocation caused spiral structures, leading to several quintuple-layered terraces. , Finally, the hexagonal Bi 2 Te 3 present a spiral terraces-step NPs similar to Sb 2 Te 3 . While there is a seed layer of 10 nm with discrete islands as a buffer layer, the islands are only weakly bonded to the H-terminated Si(111) by vdW forces and are rather mobile, leading the following growth of slip NPs in the x – y plane and stacked .…”

“…10,14 Finally, the hexagonal Bi 2 Te 3 present a spiral terracesstep NPs similar to Sb 2 Te 3 . 31 While there is a seed layer of 10 nm with discrete islands as a buffer layer, the islands are only weakly bonded to the H-terminated Si(111) by vdW forces and are rather mobile, leading the following growth of slip NPs in the x−y plane and stacked. 16 The SNPs are the reflection of stacked QLs' morphology in the c-axis.…”

Chemical Etching of Screw Dislocated Transition Metal Dichalcogenides

“…In addition to the conventional monolayer or layer-by-layer structures, 2D materials often contain screw dislocations. ,− A screw dislocation is a line defect that shears part of the crystal lattice. In layered materials, it typically shears along the out-of-plane direction, connects layers into one continuous helicoid, and results in a spiral morphology. , Screw dislocation growth has been observed in CVD grown 2D materials, such as graphene, h-BN, MoS 2 , , WS 2 , ,− WSe 2 , , SnS 2 , SnSe 2 , SnS, and GeS, , as well as Bi 2 Se 3 and Sb 2 Te 3 grown via solution synthesis and molecular beam epitaxy. − Screw dislocations drive the growth of layered materials in a different way from the typical layer-by-layer growth and can influence the vertical stacking configurations and overall crystal symmetry to yield complex morphologies as well as varied physical properties. − , Screw dislocations combined with non-Euclidean surfaces also provide a pathway to introduce interlayer twists rationally . Although dislocations are commonly observed in layered materials, the studies on the structures of screw dislocations and their formation process have been limited.…”

Stacking and Twisting of Layered Materials Enabled by Screw Dislocations and Non-Euclidean Surfaces

“…Among these examples, MoS 2 , WS 2 , WSe 2 , graphene, hBN, SnSe 2 , and SnS are synthesized via chemical vapor deposition. Sb 2 Te 3 and Bi 2 Se 3 are grown using solvothermal synthesis. BiOCl, CoAl layered double hydroxide (LDH), zinc hydroxy sulfate (ZHS), Ni­(OH) 2 , gold nanoplates, and l -cystline are made by aqueous solution synthesis.…”