Monolayer PtTe2 is a narrow gap semiconductor
while
Pt2Te2 is a metal. Here we show that the former
can be transformed into the latter by reaction with vapor-deposited
Pt atoms. The transformation occurs by nucleating the Pt2Te2 phase within PtTe2 islands, so that a metal–semiconductor
junction is formed. A flat band structure is found with the Fermi
level of the metal aligning with that of the intrinsically p-doped
PtTe2. This is achieved by an interface dipole that accommodates
the ∼0.2 eV shift in the work functions of the two materials.
First-principles calculations indicate that the origin of the interface
dipole is the atomic scale charge redistributions at the heterojunction.
The demonstrated compositional phase transformation of a 2D semiconductor
into a 2D metal is a promising approach for making in-plane metal
contacts that are required for efficient charge injection and is of
particular interest for semiconductors with large spin–orbit
coupling, like PtTe2.
An electrochemical micro‐reactor sealed with a single‐layer graphene (SLG) membrane is demonstrated that allows straightforward measurement with established scanning probe microscopies. SLG serves as a working electrode which separates the liquid electrochemical environment from the ambient to enable direct energy‐level determination. Kelvin probe force microscopy (KPFM) thereby reveals the shifts in Fermi‐level of suspended SLG under electrochemical reaction conditions in aqueous alkaline media. Polymer‐free transfer to create suspended SLG minimizes contributions to doping related to any support or contaminants, such that changes in work function (WF) relate predominantly to the electrochemical system under study. These WF changes are rationalized in the context of a simple model of electrochemical gating, providing insight into the interplay between electronic and electrochemical doping (through redox of water) of suspended graphene. Further changes in WF are attributable to the reversible functionalization of graphene during the oxygen evolution reaction. Mechanical changes in the suspended graphene in the form of bulging also occur, which are attributed to electro‐wetting of graphene induced by charge‐carrier doping.
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