2D platinum telluride as SERS substrate: Unique layer-dependent Raman enhanced effect

Two-dimensional (2D) materials have drawn ever-increasing interest for the application of surface-enhanced Raman scattering (SERS) because of their low-cost synthesis, non-toxic characteristics, flat surface and outstanding optical properties. The unique thickness-dependent SERS of 2D materials is intriguing, however, the underlying mechanism of this phenomenon is not fully understood. In this work, the few-layer platinum telluride (PtTe₂), an emerging 2D type-II Dirac semimetal with strong interlayer interaction, is explored as a potential SERS substrate. The Raman enhancement on 2D PtTe₂ is confirmed experimentally to be originated from the predominant charge transfer mechanism. The unique thickness-dependent SERS effect reveals that four-layer (4 L) PtTe₂ exhibits the strongest Raman intensity of probe molecule Rhodamine 6 G (R6G). Combined with the theoretical investigation by density functional theory (DFT), the ultrasensitive SERS effect of 4 L PtTe₂ is found to be attributed to its high density of states (DOS) near the Fermi level and strongest built-in electric field at the interface of molecule/PtTe₂. R6G, crystal violet (CV) and rhodamine B (RhB) on 4 L PtTe₂ all reach a detection limit as low as 10⁻¹⁰ M. The uniformity, stability and photobleaching effect of PtTe₂ as SERS substrate is also studied. Our findings reveal that the charge transfer between molecule and 2D materials is a complex process that is influenced by multiple factors, which might deepen our understanding of the unique chemical mechanism (CM) of SERS in 2D materials.