Atomic Defects and Doping of Monolayer NbSe₂

Abstract

We have investigated the structure of atomic defects within monolayer NbSe encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reveal that adventitious impurities of C, N, and O can substitute into the NbSe lattice stabilizing Se divacancies. We further observe evidence of Pt substitution into both Se and Nb vacancy sites. This knowledge of the character and relative frequency of different atomic defects provides the potential to better understand and control the unusual electronic and magnetic properties of this exciting two-dimensional material.

High-quality monolayer superconductor NbSe2 grown by chemical vapour deposition

“…Since a bare NbSe 2 monolayer film is sensitive to the ambient environment, we transferred the NbSe 2 flakes grown on SiO 2 substrate with graphene encapsulation (see “Methods” section), constructing a graphene/NbSe 2 /graphene sandwich structure for STEM imaging. Such structures have been demonstrated to be effective in protecting sensitive monolayer materials from being oxidized 32 . Figure 2a shows a low magnification ADF-STEM image of a large area of monolayer NbSe 2 sandwiched by graphene (schematic shown in the inset ), where little oxidization is observed.…”

Nonreciprocal superconducting NbSe2 antenna

“…Recent theory has revealed that nonreciprocal charge transport occurs in non-centrosymmetric superconductors when vortices driven by the external charge current move among the asymmetric pinning potentials in the vortex flow regime 15 . In 2D NbSe 2 , the asymmetric pinning potentials naturally appear as a consequence of disorder 15 such as defects [30][31][32] in 2D crystals with inversion symmetry breaking, as shown in Fig. 1c.…”

Phase slip lines in superconducting few-layer NbSe 2 crystals

“…The most studied van der Waals SC is the 2H polytype of NbSe 2 (in the following simply indicated as NbSe 2 ). [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] This material can be easily exfoliated in few-layer-thick flakes and then encapsulated in hBN. 25 Typical devices for transport measurements have a size of several micrometers.…”