Unraveling the Growth Mechanism Forming Stable γ-In₂S₃ and β-In₂S₃ Colloidal Nanoplatelets

Abstract

Inorganic two-dimensional semiconductor nanostructures intrigue the scientific community because of their tunable and sparse electronic states and their high conductivity. The current work deals with colloidal nanoplatelets (NPLs) based on In2S3 compound, focusing on the growth mechanism that leads to the formation of two different phases, trigonal γ-In2S3 and defect spinel β-In2S3, both stabilized at room temperature and characterized by ordered metal voids. In particular, we substantiate the experimental factors (e.g., temperature, reaction duration, and surface ligands) that control the growth progress. The results indicated the formation of hexagonal NPLs of the γ-phase at an elevated temperature and dodecagon NPLs of the γ-phase at a lower temperature. A long-reaction duration time transformed the hexagons/dodecagons into truncated triangular shapes. Furthermore, the analysis of thermodynamic and kinetic factors indicated a phase transformation from the γ-phase to the β-phase. All phases were produced by a new colloidal procedure based on a single precursor. The structures created were verified by X-ray diffraction, high-resolution transmission electron microscopy analyses, and Raman measurements. Elementary optical properties were identified by absorption and emission measurements. The nanoplatelets discussed offer low toxicity and optical activity in the UV and visible spectral regimes and an option for electrical or magnetic doping, enabled by the existing voids.

Prediction of intermediate band in Ti/V doped γ-In2S3

“…Usually the HSE functional gives E g close to that of experimental values; however, the experimental E g value is not available for γ-In 2 S 3 for comparison. 41 A broad shift in the band gap from 2.15 to 2.50 eV is observed upon the structural phase change from β to γ-In 2 S 3 . This shows that a small difference in total energy of the β and γ phases induces a huge distinction within the band gap and band features.…”

“…Recently, the thermodynamic and kinetic factors analyzed by Horani and Lifshitz, 41 showed the structural transition of the γ to β phase. They exposed the less stable γ-phase as a room temperature polymorph in addition to the β-phase.…”

β-In2S3 as Water Splitting Photoanodes: Promise and Challenges

“…In 2 S 3 exists in three stable phases: α-In 2 S 3 with defective cubic structure, β-In 2 S 3 with defective spinel structure, and γ-In 2 S 3 with layered hexagonal structure, where other two phases (εand Th 3 P 4 -In 2 S 3 ) are instable in an ambient pressure [38,45,61,62]. β-In 2 S 3 can be further divided into cubic or tetragonal phase [63].…”

“…In β-In 2 S 3 crystal, indium ion (In 3+ ) centers are surrounded by six sulfur anions (S 2− ) in the octahedral sites and four S 2− anions in the tetrahedral sites. The octahedral sites are fully occupied with cation centers while the 2/3 of tetrahedral sites are occupied and 1/3 of them are empty forming the In 3+ vacancies [38]. The neighboring sulfur atoms would be bonded to three indium atoms rather than four as usual [64].…”

“…As a typical n-type III-VI group chalcogenide semiconductor, In 2 S 3 with narrow band gap of 2.0-2.3 eV has attracted great interest for various applications recently [35]. Owing to its high photoelectric sensitivity, high photoconductivity, large photoelectric conversion yield, low toxicity, and high absorption coefficient [36][37][38], In 2 S 3 shows superior properties in optical-absorption applications such as photoanodes [35,[39][40][41][42][43][44][45], photocatalysts [36,[46][47][48][49][50][51][52][53], solar cells [54], photocatalytic conversion of carbon dioxide (CO 2 ) reduction [55,56], electrochemical storage cells [57], and photodetectors [37,58,59].…”