Conductivity Enhancement in Transition Metal Dichalcogenides: A Complex Water Intercalation and Desorption Mechanism

Area of Science:

• Materials Science
• Surface Science
• Condensed Matter Physics

Background:

• The water adsorption-desorption mechanism at transition metal dichalcogenides (TMDs) interfaces and its effect on current transport remain unclear.
• Understanding these interfacial phenomena is crucial for optimizing TMD-based electronic devices.

Purpose of the Study:

• To investigate the rapid intercalation of atmospheric adsorbates at TMD interfaces and between TMD layers.
• To probe the influence of this intercalation on the electrical properties of TMDs.
• To elucidate the role of water intercalation in TMD degradation.

Main Methods:

• Time-of-flight-secondary ion mass spectrometry (ToF-SIMS) to identify adsorbates.
• Scanning tunneling microscopy (STM) to visualize intercalation and defects.
• Scanning probe microscopy (SPM)-based conductivity measurements to assess electrical properties.
• Ultrahigh vacuum (UHV) conditions to study reversibility.

Main Results:

• Persistent water intercalation, primarily hydroxyl species, occurs rapidly (minutes) at TMD interfaces and between layers, even under vacuum.
• Intercalation is partly reversible under UHV.
• Complete desorption of intercalated water enhances electronic properties due to a pressure-induced melting effect.
• Water intercalation significantly affects TMD characterization in air, inert environments, and vacuum.
• A correlation between water intercalation, defects, and material degradation was observed.

Conclusions:

• Atmospheric water intercalation is a rapid and significant factor influencing TMD electrical properties and characterization.
• Defect-mediated water intercalation contributes to the long-term degradation of TMD materials.
• Controlling water intercalation is essential for reliable TMD device performance and accurate material assessment.