*Correspondence to: a.khajetoorians@science.ru.nlWe report on the structural and electronic properties of a single bismuth layer intercalated underneath a graphene layer grown on an Ir(111) single crystal. Scanning tunneling microscopy (STM) reveals a hexagonal surface structure and a dislocation network upon Bi intercalation, which we attribute to a √3 × √3 R30 ∘ Bi structure on the underlying Ir(111) surface. Ab-initio calculations show that this Bi structure is the most energetically favorable, and also illustrate that STM measurements are most sensitive to C atoms in close proximity to intercalated Bi atoms.Additionally, Bi intercalation induces a band gap ( g = 0.42 eV) at the Dirac point of graphene 2 and an overall n-doping (~0.39 eV), as seen in angular-resolved photoemission spectroscopy.We attribute the emergence of the band gap to the dislocation network which forms favorably along certain parts of the moiré structure induced by the graphene/Ir(111) interface. by the structural confinement in graphene nanoribbons 9 10 ; by the stacking of multiple graphene layers 11,12 ; by the periodic modulation of the graphene lattice (breaking the sub-lattice symmetry), which can be achieved by using patterned substrates 13 , or through the patterned adsorption of other elements such as hydrogen 5 .Pristine graphene shows weak spin-orbit interactions 14 , but increasing the strength of these interactions could give rise to new interesting possibilities in spin-based nanoelectronics. One route toward manipulation of graphene's electronic structure is intercalation of defined The Ir(111) surface was cleaned in ultra-high vacuum (UHV) by repeated cycles of Ar sputtering, followed by annealing to 1470 K. Additionally, carbon contamination was removed, when necessary, by intermittent annealing in O 2 . A monolayer (ML) of high quality graphene was grown by exposing the clean Ir(111) surface to ethylene gas at a surface temperature of 1075 K. The growth process was followed by a short (< 30 ) rapid heating to max = 1455 K.This step increases the quality of the resulting graphene ML. Bismuth was subsequently deposited on the G/Ir(111) surface at a sample temperature of 715 K. After the deposition, the 5 sample was heated to a temperature of 1273 K for 60 s. This step leads to intercalated bismuth underneath the graphene. These surface regions where this intercalation structure is present are referred to as G/Bi/Ir throughout the text.Scanning tunneling microscopy (STM) was performed using a home-built variable temperature STM in a UHV system with a base pressure below 1 × 10 −10 mbar 20 21 . Tip and sample were cooled to = 30 K. Electrochemically etched and flashed W tips were used for all STM measurements. STM topography was recorded in constant current mode ( t ) with the bias applied to the sample ( S ). Differential conductance maps (short I/ V maps) were recorded by applying a modulation voltage ( mod ) using lock-in detection at a modulation frequency of = 5.477 kHz.ARPES data were acquired at the SGM3 beamline at ...

The experimental realization of large-scale, homogeneous semiconducting films with a single-layer thickness is of major importance for next-generation devices. Especially in view of the compatibility with state-of-the-art semiconductor technology, Si-based monolayer crystals are of particular interest. Here, the successful epitaxial growth of monolayer Si 2 Te 2 (MLSi 2 Te 2 ) films on semiconducting Sb 2 Te 3 thin film substrates is reported. High-quality (1 × 1) ML-Si 2 Te 2 films with a coverage as high as 95% are obtained as revealed by scanning tunneling microscopy. X-ray photoelectron spectroscopy confirms the existence of the SiTe bonds in the obtained films. By combining scanning tunneling spectroscopy with density functional theory calculations, the existence of a semiconducting bandgap is demonstrated on the order of 370 meV for the MLSi 2 Te 2 films which reside in an important mid-infrared spectral range. The results pave the way for practical applications of this novel artificial two-dimensional material.

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The investigation of the magnetic phase transitions in the parent compounds of Fe-based superconductors is regarded essential for an understanding of the pairing mechanism in the related superconducting compounds 1-4 . Even though the chemical and electronic properties of these materials are often strongly inhomogeneous on a nanometer length scale 5-7 , studies of the magnetic phase transitions using spatially resolved experimental techniques are still scarce 8,9 . Here, we present a real space spin-resolved scanning tunneling microscopy investigation of the surface of Fe 1+y Te single crystals with different excess Fe content, y, which are continuously driven through the magnetic phase transition. For Fe 1.08 Te, the transition into the low-temperature monoclinic commensurate antiferromagnetic phase 10 is accompanied by the sudden emergence of ordering into four rotational domains with different orientations of the monoclinic lattice and of the antiferromagnetic order, showing how structural and magnetic order are intertwined. In the low-temperature phase of Fe 1.12 Te one type of the domain boundaries disappears, and the transition into the paramagnetic phase gets rather broad, which is assigned to the formation of a mixture of orthorhombic and monoclinic phases 11 .

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