Two-Dimensional Magnetic Semiconducting Heterostructures of Single-Layer CrI₃–CrI₂

Abstract

Single-layer heterostructures of magnetic materials are unique platforms for studying spin-related phenomena in two dimensions (2D) and have promising applications in spintronics and magnonics. Here, we report the fabrication of 2D magnetic lateral heterostructures consisting of single-layer chromium triiodide (CrI 3 ) and chromium diiodide (CrI 2 ). By carefully adjusting the abundance of iodine based on molecular beam epitaxy, single-layer CrI 3 −CrI 2 heterostructures were grown on Au(111) surfaces with nearly atomic-level seamless boundaries. Two distinct types of interfaces, i.e., zigzag and armchair interfaces, have been identified by means of scanning tunneling microscopy. Our scanning tunneling spectroscopy study combined with density functional theory calculations indicates the existence of spin-polarized ground states below and above the Fermi energy localized at the boundary. Both the armchair and zigzag interfaces exhibit semiconducting nanowire behaviors with different spatial distributions of density of states. Our work presents a novel low-dimensional magnetic system for studying spin-related physics with reduced dimensions and designing advanced spintronic devices.

Observation of In-Gap States in a Two-Dimensional CrI2/NbSe2 Heterostructure

“…The vdW gap between CrI 2 and NbSe 2 is 3.28 Å. Compared to the lattice constant in a previous study, the lattice of CrI 2 in CrI 2 /NbSe 2 heterostructures exhibits a tensile strain (∼4%). To investigate the effect of strain, we further performed calculations on the magnetic ground state of monolayer CrI 2 under strain.…”

“…Figure e shows an atomic-resolved STM image of monolayer CrI 2 on the NbSe 2 surface. Compared with the case on Au(111) surfaces, the lattice constants of monolayer CrI 2 on NbSe 2 surfaces are slightly enlarged ( a 1 = 4.16 Å, a 2 = 4.33 Å and a 3 = 4.31 Å), implying the existence of tensile strain. The large bias range of the differential conductance (d I/ d V ) spectrum on CrI 2 grown on NbSe 2 exhibits occupied and unoccupied states at −1.35 and 1.8 eV, respectively, corresponding to a gap of about 3.15 eV, demonstrating its insulating nature (Figure S3).…”

“…Single-layer CrI 2 was grown on NbSe 2 surfaces with a submonolayer coverage by codeposition of chromium and iodine under ultrahigh vacuum conditions, as described in previous works , (Figure a). Discrete flat CrI 2 nanosheets with an approximately round shape and a size in the range from several tens to a hundred nanometers were formed on the surface, as shown in Figure b.…”

“…Inverse FFT of the blue-circled spots can reproduce the incommensurate Moiré pattern (Figure S2). It is known that the Jahn–Teller effect in the monolayer CrI 2 , induces lattice distortion and breaks the C 3 symmetry, which may promote the formation of the incommensurate Moiré pattern with the underlying NbSe 2 . Figure e shows an atomic-resolved STM image of monolayer CrI 2 on the NbSe 2 surface.…”

Scanning tunneling microscope studies on low-dimensional transition-metal halides

“…22) Besides the coexistence of the mixed isomers, Fig. 2(c) shows the 2D lateral heterostructure composed of the neighboring CrI 2 and CrI 3 , 24) with two edges of the armchair-or zigzag-type demarcating the stoichiometrical domains.…”