Transition Metal Dichalcogenides Interfacing Photoactive Molecular Components for Managing Energy Conversion Processes

Abstract

Transition metal dichalcogenides (TMDs) are materials with the generalized formula MX 2 , where M refers to a transition metal from groups 4-7 of the periodic table and X is a chalcogen atom such as S, Se, or Te. [1] The metal cation is bonded to four chalcogenide anions in a honeycomb lattice. This structure forms a three-atom thick layer, where the metals are sandwiched between the chalcogens. Markedly, the chalcogens do not have high reactivity due to chemical saturation by bonding to the transition metal atoms. These three-atom thick layers are held together with multiple van der Waals forces. [2] However, they can be easily exfoliated by splitting these weak interlayer interactions upon use of a variety of techniques, forming 2D nanosheets with extraordinary physical and chemical properties. In addition, TMDs exist in different lattice structures, which influence the materials' electronic character. Monolayer TMDs have a trigonal prismatic phase (2H phase), that belongs to the D 3h symmetry group and corresponds to a trigonal prismatic coordination for the metal atoms, or an octahedral phase (1T phase), that belongs to the D 3d symmetry group and corresponds to an octahedral coordination of the metal atoms. [3,4] The 1T phase is metastable and tends to convert to the thermodynamically stable 2H phase at room temperature via intralayer atomic gliding. [5] The realization of TMD monolayers leads to the confinement of charge carriers in 2D. Thus, due to quantum confinement effects, the transition from indirect bandgap at bulk TMDs, to direct bandgap at few layers and monolayers, occurs, [6] leading to enhanced photoluminescence. [7] Consequently, this is a straightforward approach for tuning the material's photophysical properties. In addition to the aforementioned strategy for obtaining and manipulating the electronic characteristics of TMDs, tuning the materials' properties can be further achieved through doping methods [8] or heterojunctions creation. [9][10][11] However, due to their atomically thin layers' nature, it becomes impossible to dope TMDs using common techniques that are widely used in semiconductors. [12] In contrast, chemical exfoliation and processing have the advantage of simultaneous modification of the electronic nature of TMDs [13] and in parallel offer the benefit of enhancing dispersibility, allowing surface modification. [14,15] Thus, another way to manipulate the electronic properties of TMDs is by edge or surface functionalization, especially upon incorporation of photoactive molecular species. The latter is a process that has recently emerged for TMDs and considering the advancement already brought in graphene, by the development of numerous functional graphene-based hybrid materials performing in energy conversion schemes under illumination, it certainly deserves further boost. [16][17][18][19] Moreover, among various approaches and

Field-effect transistor antigen/antibody-TMDs sensors for the detection of COVID-19 samples

“…More importantly, the intensities of 2LA(M) of MoS 2 bands decrease after functionalization, which is associated with covalent functionalization. [21][22][23][24][25][28][29][30][31][32][33] Further, XPS suggests reducing the number of sulphur defects, in agreement with Raman. 28,30 Finally, we could not detach the antibodies from MoS 2 without breaking the devices.…”

“…Basically, the thiols in our antibodies (calculate as 3% of cysteines in weight by Ellman's reagent vs. 1% in antigens) 34,37 react with bare metals at sulphur vacancies of MoS 2 and WS 2 . [21][22][23][24][25][26][27][28][29][30][31][32][33] Maldi-fingerprint before and after the reaction are identical, showing that antibodies do not degrade after the reaction (see ESI Fig. S2a †).…”

“…Covalent functionalization has been widely studied in graphene, 20 whereas the studies in TMDs are still under development. 21,22 Focusing on TMDs, the best method for functionalizing semiconducting MoS 2 or WS 2 is undoubtedly the addition of organic compounds with sulphur derivatives such as thiol, dithiolanes, or dithiolenes 21,22 because it prevents disruption of the TMDs basal plane. For example, thiols covalently interact with Mo or W metals through the S vacancy on the basal plane of TMDs.…”