Visualization of point defects in ultrathin layered 1T-PtSe ₂

Abstract

Among two-dimensional (2D) transition metal dichalcogenides (TMDs), platinum diselenide (PtSe2) stands at a unique place in the sense that it undergoes a phase transition from type-II Dirac semimetal to indirect-gap semiconductor as thickness decreases. Defects in 2D TMDs are ubiquitous and play crucial roles in understanding and tuning electronic, optical, and magnetic properties. Here we investigate intrinsic point defects in ultrathin 1T-PtSe2 layers grown on mica through the chemical vapor transport (CVT) method, using scanning tunneling microscopy and spectroscopy (STM/STS) and first-principles calculations. We observed five types of distinct defects from STM topography images and obtained the local density of states of the defects. By combining the STM results with the first-principles calculations, we identified the types and characteristics of these defects, which are Pt vacancies at the topmost and next monolayers, Se vacancies in the topmost monolayer, and Se antisites at Pt sites within the topmost monolayer. Our study shows that the Se antisite defects are the most abundant with the lowest formation energy in a Se-rich growth condition, in contrast to cases of 2D molybdenum disulfide (MoS2) family. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in fewlayer 1T-PtSe2 and other related 2D materials.

Probing magnetism in atomically thin semiconducting PtSe2

“…1b. Consistent with early scanning tunneling microscopy investigations 19 , we observe native Se and Pt vacancies in ultra-thin PtSe 2 films. The concentration of Pt vacancy defects is found to be~9 × 10 12 cm −2 (see Supplementary Note 2).…”

“…Motivated by direct observation of Pt vacancies in our transmission electron microscope images shown in Fig. 1b, their indirect inference from our charge transport measurements as well as earlier scanning tunneling microscopy studies 19 , we investigate electronic and magnetic properties of mono-and bilayer models of PtSe 2 with platinum vacancy defects by means of first-principles calculations. For the monolayer case, we find that a Pt vacancy defect in its fully spin-polarized configuration gives rise to a local magnetic moment of 4.00 μ B , which is localized mostly on the six selenium atoms neighboring to the missing Pt atom.…”

“…Recent experimental investigations highlighted a broad variety of intrinsic point defects in PtSe 2 19 . Even though imperfections are often regarded as detrimental to material properties, in many cases their presence has proven successful in introducing functionalities that would otherwise be absent in pristine materials 20 , 21 .…”

Electronic and structural characterisation of polycrystalline platinum disulfide thin films

“…Moreover, recent reports have indicated that damage by the TEM electron beam can be a problematic issue for TMDs. [37][38][39] On the other hand, scanning tunnelling microscopy and spectroscopy (STM/STS) are non-destructive techniques, which can be used to map morphology and probe the electronic structure of samples [40][41][42][43] and, provided a conductive pathway can be established through the sample, do not require a transfer process.…”

Phase transition and thermal stability of epitaxial PtSe2 nanolayer on Pt(111)

“…Similar domains were observed by Zheng et al, and were interpreted as Se-rich antisite defects. 47,48 Aer a further annealing at 750 C, the unit cell of the Pt 2 Se undergoes a rotation of 30 compared with the (O3 Â O3)R30 structure at 600 C, resulting in a (2 Â 2) pattern with respect to the Pt lattice, as seen in Fig. 2e and f. For the (2 Â 2) structure, one observes a large density of defects on the surface which is consistent with the LEED pattern showing high-background and diffusing diffraction spots.…”