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Atomic and electronic structure of the Si(331)-(12 × 1) surface
摘要： We report on the investigation of the atomic and electronic structures of a clean Si(331)-(12 × 1) surface using a first-principles approach with both plane wave and strictly localized basis sets. Starting from the surface structure proposed by Zhachuk and Teys [Phys. Rev. B 95, 041412(R) (2017)], we develop significant improvements to the atomic model and localized basis set which are critical for the correct description of the observed bias dependence of scanning tunneling microscopy (STM) images. The size mismatch between the Si pentamers from the surface model and those seen by STM is explained within the context of the Tersoff-Hamann model. The energy barriers that separate different Si(331) buckled configurations were estimated, showing that the surface structure is prone to dynamic buckling at room temperature. It is found that empty electronic states on Si(331) are essentially localized on the pentamers with interstitials and under-coordinated Si sp2-like atoms between them, while filled electronic states are localized on under-coordinated Si sp3-like atoms and dimers on trenches. The calculated electronic density of states exhibits two broad peaks in the fundamental bandgap of Si: one near the valence band top and the other near the conduction band bottom. The resulting surface bandgap of 0.58 eV is in an excellent agreement with spectroscopy studies.
关键词： scanning tunneling microscopy,Si(331)-(12 × 1) surface,first-principles approach,electronic density of states,Tersoff-Hamann model,atomic and electronic structures,dynamic buckling
更新于2025-09-10 09:29:36
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Driving chemical interactions at graphene-germanium van der Waals interfaces via thermal annealing
摘要： Despite its extraordinary charge carrier mobility, the lack of an electronic bandgap in graphene limits its utilization in electronic devices. To overcome this issue, researchers have attempted to chemically modify the pristine graphene lattice in order to engineer its electronic bandstructure. While significant progress has been achieved, aggressive chemistries are often employed which are difficult to pattern and control. In an effort to overcome this issue, here we utilize the well-defined van der Waals interface between crystalline Ge(110) and epitaxial graphene to template covalent chemistry. In particular, by annealing atomically pristine graphene-germanium interfaces synthesized by chemical vapor deposition under ultra-high vacuum conditions, chemical bonding is driven between the germanium surface and the graphene lattice. The resulting bonds act as charge scattering centers that are identified by scanning tunneling microscopy. The generation of atomic-scale defects is independently confirmed by Raman spectroscopy, revealing significant densities within the graphene lattice. The resulting chemically modified graphene has the potential to impact next-generation nanoelectronic applications.
关键词： graphene,van der Waals interfaces,germanium,Raman spectroscopy,chemical bonding,scanning tunneling microscopy,thermal annealing
更新于2025-09-10 09:29:36
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Surface structures of tellurium on Si(111)–(7?×?7) studied by low-energy electron diffraction and scanning tunneling microscopy
摘要： The Te-covered Si(111) surface has received recent interest as a template for the epitaxy of van der Waals (vdW) materials, e.g. Bi2Te3. Here, we report the formation of a Te buffer layer on Si(111)–(7×7) by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While deposition of several monolayer (ML) of Te on the Si(111)–(7×7) surface at room temperature results in an amorphous Te layer, increasing the substrate temperature to 770 K results in a weak (7×7) electron diffraction pattern. Scanning tunneling microscopy of this surface shows remaining corner holes from the Si(111)–(7×7) surface reconstruction and clusters in the faulted and unfaulted halves of the (7×7) unit cells. Increasing the substrate temperature further to 920 K leads to a Te/Si(111)–(2√3×2√3)R30° surface reconstruction. We find that this surface configuration has an atomically flat structure with threefold symmetry.
关键词： scanning tunneling microscopy,surface reconstruction,Si(111),tellurium,low-energy electron diffraction
更新于2025-09-10 09:29:36
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Competitive metal-coordination of hexaaminotriphenylene on Cu(111) by intrinsic copper versus extrinsic nickel adatoms
摘要： The interplay between self-assembly and surface chemistry of 2,3,6,7,10,11-hexaaminotriphenylene (HATP) on Cu(111) was complementarily studied by high-resolution Scanning-Tunneling-Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS) under ultra-high vacuum conditions. To shed light on competitive metal-coordination, comparative experiments were carried out on pristine and nickel-covered Cu(111). Directly after room temperature deposition of HATP onto pristine Cu(111) self-assembled aggregates were observed by STM, while XPS indicated non-deprotonated amino groups. Annealing up to 200 °C activated the progressive single deprotonation of all amino groups as indicated by chemical shifts of both N 1s and C 1s core levels in the XP spectra. This enabled the formation of topologically diverse π-d conjugated coordination networks with intrinsic copper adatoms. The basic motif of these networks was a metal-organic trimer, where three HATP molecules were coordinated by Cu3 clusters, as corroborated by accompanying Density Functional Theory (DFT) simulations. Additional deposition of more reactive nickel atoms resulted in both chemical and structural changes with deprotonation and formation of bis(diimino)-Ni bonded networks already at room temperature. Even though fused hexagonal metal-coordinated pores were observed, extended honeycomb networks remained elusive, as tentatively explained by a restricted reversibility of these metal-organic bonds.
关键词： Scanning Tunneling Microscopy,Cu(111),metal-coordination,hexaaminotriphenylene,X-ray Photoelectron Spectroscopy
更新于2025-09-10 09:29:36
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-II
摘要： The basic and the charge density wave (CDW) structures of the monoclinic NbS3-II polymorph were studied by synchrotron x-ray diffraction, ab initio calculations, simulation of electron diffraction patterns, and by atomic-resolution transmission electron and low-temperature scanning tunneling microscopies. It is con?rmed that the basic structure belongs to the space group P 21/m and is described with a unit cell, formed of four pairs of symmetry-related trigonal prismatic (TP) columns [a0 = 0.96509(8) nm, b0 = 0.33459(2) nm, c0 = 1.9850(1) nm, and β0 = 110.695(4)?]. The incommensurate components of the two CDWs, (cid:3)q1 = (0, 0.298, 0) and (cid:3)q2 = (0, 0.352, 0), are related as q1b + 2q2b ≈ 1. Both CDWs form their own modulation patterns with unit cells (am = 2a0, bm = b0/qjb, cm = c0, βm = β0) and are ordered along adjacent isosceles TP columns either pairwise or with both columns modulated by either the (cid:3)q1 or (cid:3)q2 CDW only. The CDWs are ordered according to one of the two possible modulation pattern space groups, Cm or C2/m. If considered as long-period commensurate, the entire modulated structure with both CDWs included is described within experimental error with an enlarged unit cell (a = 2a0, b = 37b0, c = c0, and β = β0) and with all atoms displaced from their average positions in accord with the speci?ed modulation pattern.
关键词： synchrotron x-ray diffraction,ab initio calculations,charge density wave,scanning tunneling microscopy,transmission electron microscopy,NbS3-II
更新于2025-09-09 09:28:46
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Electronic properties of Pb islands on graphene: Consequences of a weak interface coupling from a combined STM and <i>ab initio</i> study
摘要： By means of scanning tunneling microscopy and spectroscopy, we investigate the electronic properties of lead islands (width 5–100 nm, thickness 5–25 monolayers) deposited by molecular beam epitaxy on twisted graphene layers grown on SiC(000-1). We ?nd that elastic scattering processes govern the local density of states probed at the surface of the Pb islands, inducing (i) the well-known quantum well states due to electron con?nement in the direction perpendicular to the surface and (ii) spatial in-plane periodic modulations related to quasiparticle interferences off the island edges. Through a quantitative analysis of these effects, compared with ab initio calculations for a two-dimensional Pb slab, we conclude that the lead islands grown on the surface of graphene can be considered as freestanding from the point of view of their electronic structure, leaving the surrounding graphene layer unperturbed. Accordingly, low bias tunneling spectra show evidence of a sizable interface resistance. Nevertheless, we suggest that the transparency of the interface, which can be estimated from its resistance, is good enough to induce superconductivity within the underlying graphene layer by proximity effect with the Pb islands.
关键词： lead islands,graphene,quantum well states,quasiparticle interferences,interface resistance,superconductivity,scanning tunneling microscopy,proximity effect,spectroscopy
更新于2025-09-09 09:28:46
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A Scanning Tunneling Microscopy Study of Monolayer and Bilayer Transition-Metal Dichalcogenides Grown by Molecular-Beam Epitaxy
摘要： This review presents an account of some recent scanning tunneling microscopy and spectroscopy (STM/S) studies of monolayer and bilayer transition-metal dichalcogenide (TMD) films grown by molecular-beam epitaxy (MBE). In addition to some intrinsic properties revealed by STM/S, defects such as inversion domain boundaries and point defects, their properties and induced effects, are presented. More specifically, the quantum confinement and moiré potential effects, charge state transition, quasi-particle interference and structural phase transition as revealed by STM/S are described.
关键词： transition-metal dichalcogenides,quantum confinement,structural phase transition,molecular-beam epitaxy,moiré potential,quasi-particle interference,scanning tunneling microscopy,charge state transition
更新于2025-09-09 09:28:46
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Local Electronic Structure of Molecular Heterojunctions in a Single-Layer 2D Covalent Organic Framework
摘要： The synthesis of a single-layer covalent organic framework (COF) with spatially modulated internal potentials provides new opportunities for manipulating the electronic structure of molecularly defined materials. Here, the fabrication and electronic characterization of COF-420: a single-layer porphyrin-based square-lattice COF containing a periodic array of oriented, type II electronic heterojunctions is reported. In contrast to previous donor–acceptor COFs, COF-420 is constructed from building blocks that yield identical cores upon reticulation, but that are bridged by electrically asymmetric linkers supporting oriented electronic dipoles. Scanning tunneling spectroscopy reveals staggered gap (type II) band alignment between adjacent molecular cores in COF-420, in agreement with first-principles calculations. Hirshfeld charge analysis indicates that dipole fields from oriented imine linkages within COF-420 are the main cause of the staggered electronic structure in this square grid of atomically–precise heterojunctions.
关键词： type II heterojunctions,covalent organic frameworks,density functional theory,scanning tunneling microscopy and spectroscopy,electronic structure
更新于2025-09-09 09:28:46
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Analyzing the Influence of Substituents on Proton Tautomerization - a Comparison of tetra- <i>tert</i> -Butyl Phthalocyanine Isomers
摘要： We present a comparative study of tetra-tert-butyl phthalocyanine (ttbPc) isomers on a Ag(111) surface by means of low temperature scanning tunneling microscopy to analyze the influence of substituents on the tautomerization, a proton transfer reaction, in single molecules. By comparing ttbPc with the well studied phthalocyanine (H2Pc) molecule, we demonstrate a decoupling from the surface by the tert-butyl substituents. A comparison between the four ttbPc isomers, which naturally exist due to different bonding positions of the tert-butyl groups on the macrocycle, reveals a significant influence of the structural differences on their tautomerization behavior, as evidenced by a switching rate which varies by up to a factor of four between ttbPc isomers. These findings can be understood by an energetic landscape of the proton switch which links the binding distance of tert-butyl groups with the height of potential barriers. This model is supported by the analysis of two types of deprotonated ttbPc molecules with the molecular nanoprobe (MONA) technique.
关键词： tetra-tert-butyl phthalocyanine,proton transfer,scanning tunneling microscopy,tautomerization,isomers
更新于2025-09-09 09:28:46
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Visualizing topological edge states of single and double bilayer Bi supported on multibilayer Bi(111) films
摘要： Freestanding single bilayer Bi(111) is a two-dimensional topological insulator with edge states propagating along its perimeter. Given the interlayer coupling experimentally, the topological nature of Bi(111) thin films and the impact of the supporting substrate on the topmost Bi bilayer are still under debate. Here, combined with scanning tunneling microscopy and first-principles calculations, we systematically study the electronic properties of Bi(111) thin films grown on a NbSe2 substrate. Two types of nonmagnetic edge structures, i.e., a conventional zigzag edge and a 2 × 1 reconstructed edge, coexist alternately at the boundaries of single bilayer islands, the topological edge states of which exhibit remarkably different energy and spatial distributions. Prominent edge states are persistently visualized at the edges of both single and double bilayer Bi islands, regardless of the underlying thickness of Bi(111) thin films. We provide an explanation for the topological origin of the observed edge states that is verified with first-principles calculations. Our paper clarifies the long-standing controversy regarding the topology of Bi(111) thin films and reveals the tunability of topological edge states via edge modifications.
关键词： topological insulator,scanning tunneling microscopy,edge states,first-principles calculations,Bi(111) thin films
更新于2025-09-09 09:28:46