Suppression of stripe-ordered structural phases in monolayer IrTe$_2$ by a gold substrate

Abstract

Metal-assisted exfoliation of two-dimensional (2D) materials has emerged as an efficient route to isolating large-area monolayer crystals, yet the influence of the supporting metal substrate on their intrinsic properties remains poorly understood. Here, we demonstrate successful gold-assisted exfoliation of monolayer IrTe$_2$ up to the millimeter scale. Angle-resolved photoemission spectroscopy (ARPES), combined with first-principles calculations, reveals that the low-energy electronic structure closely resembles that of a freestanding monolayer 1T-IrTe$_2$. We find that quasi-covalent hybridization together with substrate-induced strain leads to only modest modifications of the electronic bands. Although strain contributes to phase stability, it is essentially hybridization that drives the stabilization of the 1T-phase of the monolayer IrTe$_2$ by suppressing stripe-ordered phase transitions. These results establish gold-assisted exfoliation as a robust route to prepare a large-area monolayer IrTe$_2$ and highlight the role of metal-substrate interaction in engineering 2D materials with tailored structural phases.

Figures (4)

• Figure 1: Crystal structure and characterization of IrTe2 monolayers:a Optical image of IrTe2 monolayer flake (outlined by dashed yellow line) on a polycrystalline Au substrate. b Large-scale STM topograpy image ($200 \times 200\ \mathrm{nm}{}^2$, I=0.2 nA, V=$-0.3$ V, plane correction, flattened), with step edges and terraces highlighted with a dashed black circle. c STM topography image with atomic resolution ($6.172 \times 6.172\ \mathrm{nm}{}^2$, I=1.3 nA, V=$-0.005$ V, plane correction, flattened, Gaussian smoothed). The region marked by a dotted rectangle is enlarged in d. Black solid and dashed rhombuses indicate the (1 $\times$ 1) unit cell of monolayer IrTe2 and (2 $\times$ 2) modulation, respectively. e Side and top views of the optimized IrTe2-Au structure. f DFT-simulated STM image of IrTe2-Au, with $-0.3$ bias voltage, extracted 4 Å above the monolayer surface, predicting the observed (2 $\times$ 2) modulation, consistent with d.
• Figure 2: Electronic structure of bulk and monolayer IrTe2: (a, c) ARPES intensity maps of bulk IrTe2 along L-A-L high symmetry direction and monolayer IrTe2 along M-$\Gamma$-M, respectively. Panel b shows the corresponding EDCs of three phases of bulk IrTe2 while panel d displays EDCs of monolayer IrTe2 at different temperatures. The Fermi level is indicated with a dashed line in panels b and d. The EDCs were obtained by integrating over $\pm 0.07$ Å$^{-1}$ around A in the bulk and $\Gamma$ in the monolayer.
• Figure 3: DFT-calculated electronic properties of monolayer IrTe2:a DFT band structure of freestanding monolayer IrTe2 with and without SOC. b ARPES intensity map at 34 K overlaid with DFT band structure for the undistorted case (from a) and 1.5% biaxially strained monolayer IrTe2, both calculated including SOC. c Density of states (DOS) of Ir and Au d orbitals in the IrTe2-Au model, calculated with SOC. d Charge density difference plot for the IrTe2-Au model, with an isosurface value of 0.003 e/ų. Red refers to electron accumulation, and green to electron depletion.
• Figure 4: Phonon calculations: Phonon band structure of a) unstrained and b) 1.5% biaxially strained monolayer IrTe2, and c) the IrTe2-Au model, computed with SOC.