Electrochemical Detection of Isolated Nanoscale Defects in 2D Transition Metal Dichalcogenides

Abstract

We show that nanometer and sub-nanometer scale defects in two-dimensional transition metal dichalcogenides can be detected electrochemically using scanning electrochemical cell microscopy (SECCM). We detect isolated anomalous electrochemical responses for the hexaammineruthenium ([Ru­(NH3)6]3+/2+) redox couple on mono-, bi-, and trilayer regions of mechanically exfoliated MoS2. These anomalous sample points display faster electrochemical kinetics, with a diffusion-limited current plateau, compared to the surrounding sample points. The analysis of the electrochemical current suggests that the defects are equivalent to disk-shaped defects with radii of tens of nanometers, or to one-dimensional defects with nanometer to sub-nanometer widths. These results demonstrate that we can effectively isolate and electrochemically amplify the response from individual defects on a sample surface using SECCM, revealing features below the optical diffraction limit that would normally require high-resolution electron microscopy or scanning tunneling microscopy to detect.

First-Principles Study of the Origin of the Distinct Conductivity Type of Monolayer MoSe2 and WSe2

“…Transition metal dichalcogenides (TMDs), such as MoSe 2 and WSe 2 , are promising candidates in novel high-performance nanoelectronic and optoelectronic devices due to their alluring properties. − In general, intrinsic defects and unintentional impurities during the growth of the materials are unavoidable, and they dramatically affect the physical and chemical properties of the materials. − On the other hand, the functionality of semiconductors depends essentially on whether enough free carriers can be introduced by doping. ,− Therefore, the prerequisite for designing and optimizing high-performance devices is to have deep understanding of the properties of defects in materials.…”

The New Era of High-Throughput Nanoelectrochemistry

“…This was already highlighted for graphene on Nafion and films on electrodes in Technical and Theoretical Developments above. When electrochemical activity varies locally across a 2D material, this may be indicative of a key role of defect sites on the basal surface, , and SECCM can be used to estimate the defect size. SECCM revealed that the basal planes of MoS 2 (1H phase and 2H phase) shows catalytic activity.…”

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

“…SECCM was extensively used to acquire high spatial resolution maps to elucidate differences in electrochemical activity between phases and grain boundaries of many polycrystalline materials such as platinum, , palladium, gold, − copper, or boron-doped diamond − surfaces. SECCM in tandem with simulations was used to spatially map electron-transfer kinetics parameters, like the Tafel slope and the heterogeneous electron-transfer rate constant. − The sensitivity of the SECCM for local activity measurement was demonstrated and used to differentiate the surface activities of glassy carbon and graphite. − Two-dimensional materials, such as graphene, − MoS 2 , , and other transition metal dichalcogenides , were also investigated by SECCM. The studies demonstrated the presence of heterogeneous activity at different sites such as defects, edges, and basal planes.…”