An Insight into the Phase Transformation of WS₂ upon Fluorination

Abstract

reduces the TMDs and the gliding of the S planes results in the transformation from 2H to 1T. Functionalization by other electron donating species such as Re, Tc, and Mn can also induce the transformation. [7][8][9][10][11] The electron donated by the alkali metals alters the d electron count of the metal (Mo or W), and it splits in the octahedral coordination to have three unpaired electrons in the valence band d orbitals. However, the 1T phase is highly unstable and converts back into 2H phase with time and temperature. [12] Apart from alkali metals, several attempts have been made on the covalent functionalization of 2H and 1T phases by organic functional groups. [13][14][15][16] Sarkar et al. decorated the 2D layers with metal nanoparticles which changed the transfer characteristics of the 2D devices and demonstrated its capability as a gas sensor. [17] Theoretically, hydrogenation also converts the 2H semiconducting phase into the metallic phase. [18] A transformation from an n-type to a p-type semiconductor, a nonmagnetic to a magnetic material and a boost in the catalytic activity was achieved through controlled and selective doping of TMDs by transition metals. [19] An interesting deviation from extrinsic doping was intrinsic doping by the incorporation of islands of 1T in a lattice of 2H semiconducting nanosheets, where the The transformation from semiconducting to metallic phase, accompanied by a structural transition in 2D transition metal dichalcogenides has attracted the attention of the researchers worldwide. The unconventional structural transformation of fluorinated WS 2 (FWS 2 ) into the 1T phase is described. The energy difference between the two phases debugs this transition, as fluorination enhances the stability of 1T FWS 2 and makes it energetically favorable at higher F concentration. Investigation of the electronic and optical nature of FWS 2 is supplemented by possible band structures and bandgap calculations. Magnetic centers in the 1T phase appear in FWS 2 possibly due to the introduction of defect sites. A direct consequence of the phase transition and associated increase in interlayer spacing is a change in friction behavior. Friction force microscopy is used to determine this effect of functionalization accompanied phase transformation. FluorinationThe unique properties found in graphene and later in monolayers of other materials thrust the research on transition metal dichalcogenides (TMDs) as evidenced from the publications on TMDs in the past decade. [1][2][3][4][5] A distinctive property of TMDs is their polymorphic structural and electronic characteristics. For instance, in group 6 chalcogenides such as MoS 2 and WS 2 , when the sulfur (S) atoms occur on top of each other, it results in trigonal prismatic symmetry in the commonly called 2H semiconducting phase and the displaced S atoms results in octahedral symmetry in the 1T metallic phase. [6] Li or K functionalization

Electroactive 1T-MoS2 Fluoroelastomer Ink for Intrinsically Stretchable Solid-State In-Plane Supercapacitors

“…27 The article revealed that fluorine radicals (F • ) generated by the hydrothermal decomposition of Nafion at 200 °C intercalated the WS 2 without creating the W−F or S−F bonds. 27 The high electronegativity of the intercalated F • stabilized the 1T-WS 2 crystal structure and led to spectral shifts. It is reported that a high-power ultrasonication degrades hydrocarbon polymers and generates radicals.…”

Gas‐Phase Fluorination of Hexagonal Boron Nitride

“…[53,54] Instead, this reduction is similar to the reduced friction effect noted by the fluorination of WS 2 . [55] To understand the mechanism for friction improvement of hBN caused by fluorination, we further analyzed the structural modifications on hBN lattice caused by fluorination using previous simulations executed utilizing DFT/PAW technique. In Figures 4f,g, we displayed the optimized geometry structure of hBN and F-hBN.…”

“…[ 53,54 ] Instead, this reduction is similar to the reduced friction effect noted by the fluorination of WS 2 . [ 55 ]…”

Revisiting Intercalation‐Induced Phase Transitions in 2D Group VI Transition Metal Dichalcogenides

“…The activation energy barrier between the two phases for phase transition, denoted as E b in Figure A, determines the kinetics of the phase transition, which can be described using the Arrhenius equation. Both the energy difference (Δ E ) and energy barrier ( E b ) are tunable via various material controls, such as chemical alloying of transition metals or chalcogen elements, [ 10,11 ] strain, [ 12 ] charge doping, [ 13 ] and intercalation. The energetics during the phase transition in monolayer MoS 2 by Li intercalation have been studied experimentally and corroborated by density functional theory (DFT) calculations.…”