Layer-by-Layer Oxidation Induced Electronic Properties in Transition-Metal Dichalcogenides

Recent progress in transition-metal dichalcogenides has opened up new possibilities for atomically thin nanomaterial based electronic device applications. Here we investigate atomic-scale self-assembled heterojunction modulated by layer-by-layer controlled oxidation in monolayer and few-layer dichalcogenide systems and their electronic properties within a first-principles framework. Pristine dichalcogenide systems exhibit semiconducting behavior. We observe reduction of the band gap for partial oxidation of the top layer. However, complete oxidation of the top layer makes the system metallic, owing to the charge transfer from the pristine to the oxidized layer, as observed in recent experiments. When the bottom layer gets partially oxidized with fully oxidized top layers, the system shows unprecedented semimetallic behavior. The appearance of valence band maximum and conduction band minimum at different k-points can introduce valley polarization. Therefore, our study shows controlled oxidation induced varying electronic properties in dichalcogenide based heterojunctions that can be exploited for advanced electronic, optoelectronic, and valleytronic device applications

Self-Limiting Layer-by-Layer Oxidation of Atomically Thin WSe₂

Growth of a uniform oxide film with a tunable thickness on two-dimensional transition metal dichalcogenides is of great importance for electronic and optoelectronic applications. Here we demonstrate homogeneous surface oxidation of atomically thin WSe₂ with a self-limiting thickness from single- to trilayers. Exposure to ozone (O₃) below 100 °C leads to the lateral growth of tungsten oxide selectively along selenium zigzag-edge orientations on WSe₂. With further O₃ exposure, the oxide regions coalesce and oxidation terminates leaving a uniform thickness oxide film on top of unoxidized WSe₂. At higher temperatures, oxidation evolves in the layer-by-layer regime up to trilayers. The oxide films formed on WSe₂ are nearly atomically flat. Using photoluminescence and Raman spectroscopy, we find that the underlying single-layer WSe₂ is decoupled from the top oxide but hole-doped. Our findings offer a new strategy for creating atomically thin heterostructures of semiconductors and insulating oxides with potential for applications in electronic devices

Commissioning engineers compendium Revision 3: 2000

First edition published 1991, ISBN 1-873623-00-3SIGLEAvailable from British Library Document Supply Centre-DSC:m01/15145 / BLDSC - British Library Document Supply Centre3. rev. ed.GBUnited Kingdo