Electronic Transport of MoS₂ Monolayered Flakes Investigated by Scanning Electrochemical Microscopy

Abstract

The amazing properties of 2D materials are envisioned to revolutionize several domains such as flexible electronics, electrocatalysis, or biosensing. Herein we introduce scanning electrochemical microscopy (SECM) as a tool to investigate molybdenum disulfide in a straightforward fashion, providing localized information regarding the electronic transport within chemical vapor deposition (CVD)‐grown crystalline MoS2 single layers having micrometric sizes. Our investigations show that within flakes assemblies some flakes are well electrically interconnected, with no detectable contact resistance, whereas others are not electrically connected at all, independent of the size of the physical contact between them. Overall, the work shows how the complex electronic behavior of MoS2 flake assemblies (semiconducting nature, contact quality between flakes) can be investigated with SECM.

Nanoscale Selective Passivation of Electrodes Contacting a 2D Semiconductor

“…The reason for this blockage is that during the anodic polarization of the MoS 2 the number of available charge carriers in the material (electrons), is reduced, which results in lower exchange currents. High contact resistance, which is a general problem in device fabrication, also plays a role by limiting the charge carrier injection and subsequently the electron transport through the 2D material . This might also be the reason why we have not observed any deposition at the sites which could potentially become electrochemically active, particularly, the edges and defective sites where molybdenum atoms are exposed to the solution .…”

“…There are two main reasons why the PPO deposition does not occur on the MoS 2 : the semiconducting nature of MoS 2 (in this case n‐type semiconductor), and the nonefficient charge injection into the 2D material due to the high contact resistance at the electrode–2D material interface. It has been observed that in n‐type MoS 2 the heterogeneous electron transfer (HET) rate decreases with more positive potentials . For redox couples that have relatively positive redox potentials, such as Fe 3+/2+ , the HET readily occurs only in the cathodic direction (reduction), while the anodic reaction (oxidation) gets partially or completely blocked .…”

“…The potential range in which the MoS 2 crystal is electrochemically stable is between −1.2 and 1.3 V toward the Ag|AgCl electrode . Since the rate of electron transfer between the n‐type semiconductor and the species in solution is extremely slow at positive potentials, this anodic window before the threshold potential for material oxidation could be utilized for the selective coating of electrodes contacting MoS 2 . One of the polymers which can be electrochemically deposited in this anodic region, and shows excellent insulating properties, is poly(phenylene oxide) (PPO) .…”

Compound‐Specific Imaging of Methanol Fuel Cell for Performance and Degradation Studies Using a Mini Positron Emission Tomograph

“…The small detector ring (MiniPET) camera (also known as small animal PET camera) is applied for imaging of the positron-emitter labeled compounds with high 1.2 mm spatial resolution compared to bigger, human PET camera with 4-5 mm resolution. [35] In the previous works the PET imaging was already effectively used in molecular imaging of liquid chromatography and heterogeneous catalysis processes. [36][37][38] In the present work the 11 C-radiolabeled methanol as a tracing fuel compound (labeled by 11 C-positronemitter isotope) and its 11 C-derivatives (their collective name 11 C-adsorbates) were determined in terms of chemical property on the reactive surface area along the layers of the fuel cell.…”

Mapping Electron Transfer at MoS2 Using Scanning Electrochemical Microscopy

“…7,11,20 Scanning electrochemical microscopy (SECM) 27 showed that strain enhances the hydrogen evolution reaction (HER) at MoS 2 28 and that the conductivity of MoS 2 flakes varies widely depending on the nature of the contact. 29 Other applications of SECM include measuring the HER kinetics and hydrogen adsorption at amorphous MoS 2 on gold 30 and mapping the HER at MoS 2 /graphene oxide composites 31 although spatial differences in the active MoS 2 areas is unclear due to the high probe currents in the SECM images. Likewise, scanning electrochemical cell microscopy (SECCM) demonstrated that the HER at MoS 2 proceeds at the basal planes albeit at much lower rates than edge sites.…”