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Oxidation of Epitaxial Silicene on Ag(111)
摘要： The high chemical reactivity of epitaxial silicene on Ag(111) still remains a debated subject in the literature. In particular results on the oxidation of epitaxial silicene and its related lifetime under ambient conditions are controversially discussed. Here, a detailed investigation of the oxygen exposure to epitaxial silicene layers investigated by means of X-ray photoemission and in situ Raman spectroscopy is reported. The results should clearly cease the discussion on the stability of epitaxial silicene against oxygen as it becomes completely oxidized after an exposure to only 100 L of oxygen. Such a small dose sets strict limits for ex situ studies of epitaxial silicene. Besides the formation of silicon oxide also the silver substrate surface oxidizes, suggesting that the silicene layer can hardly protect it, probably owing to the high number of domain boundaries within the silicene layer.
关键词： epitaxial silicene,2D materials,oxidation,in situ Raman spectroscopy,photoemission spectroscopy
更新于2025-09-10 09:29:36
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Synchrotron-based Spectroscopy In On-Surface Polymerization of Covalent Networks
摘要： Synchrotron radiation is a powerful tool to probe physical properties of materials on the nanoscopic scale. It can provide a chemical fingerprint of a nanomaterial with unrivalled resolution, it can measure the geometric structure down to thousands of a nanometer with not only elemental sensitivity but also chemical sensitivity, and it can study charge transfer dynamics in the sub-nanosecond regime. Within this article the application of synchrotron radiation to studying on-surface catalysis, to the view of forming two-dimensional covalent networks, will be explored.
关键词： covalent networks,on-surface polymerization,Normal Incidence X-ray Standing Waves,Synchrotron radiation,X-ray Photoemission Spectroscopy,Near Edge X-ray Absorption Fine Structure
更新于2025-09-10 09:29:36
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In-Plane Optical Anisotropy of Low-Symmetry 2D GeSe
摘要： As a new member of 2D materials, GeSe has attracted considerable attention recently due to its fascinating in-plane anisotropic vibrational, electrical, and optical properties originating from the low-symmetry crystal structure. Among these anisotropic properties, the anisotropic optical property, as a new degree of freedom to manipulate optoelectronic properties in 2D materials, is of great importance for practical applications. However, the fundamental understanding of the optical anisotropy of GeSe is still under exploration, severely restricting its utility in polarization-sensitive optical systems. Here, a systematic study about the in-plane optical anisotropy of GeSe is reported, including its anisotropic optical absorption, reflection, extinction, and refraction. The anisotropic band structure of GeSe is experimentally observed for the first time through angle-resolved photoemission spectroscopy, explaining the origin of the optical anisotropy. The anisotropic reflection and refraction of GeSe are further directly visualized through the angle-dependent optical contrast of GeSe flakes by azimuth-dependent reflectance difference microscopy and polarization-resolved optical microscopy, respectively. Finally, GeSe-based photodetectors exhibit a polarization-sensitive photoresponsivity due to the intrinsic linear dichroism. This study provides fundamental information for the optical anisotropy of GeSe, forcefully stimulating the exploration of novel GeSe-based optical and optoelectronic applications.
关键词： polarization-resolved optical microscopy,azimuth-dependent reflectance difference microscopy,birefringence,angle-resolved photoemission spectroscopy,germanium monoselenide
更新于2025-09-10 09:29:36
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European Microscopy Congress 2016: Proceedings || Is the electronic structure of few layer transition metal dichalcogenides always two dimensional ?
摘要： The electronic structure of the transition metal dichalcogenides (TMDs) is investigated using angle-resolved photoemission spectroscopy (ARPES). We observe a new class of layered materials that can be prepared in various thicknesses down to single layers. Compared with the more well-known graphene, the TMDs are semiconductors and can be more useful in applications where an energy gap is essential. Our results show that the electronic structure of the TMDs is highly dependent on the number of layers, with a transition from indirect to direct bandgap as the thickness is reduced to a single layer. This transition is accompanied by a significant enhancement in photoluminescence intensity, making monolayer TMDs promising candidates for optoelectronic applications.
关键词： Angle-resolved photoemission spectroscopy,Bandgap engineering,Electronic structure,Optoelectronic applications,Transition metal dichalcogenides
更新于2025-09-10 09:29:36
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surface alloy
摘要： We have investigated the atomic and electronic structure of the (√3×√3)R30? SnAu2/Au(111) surface alloy. Low-energy electron diffraction and scanning tunneling microscopy measurements show that the native herringbone reconstruction of bare Au(111) surface remains intact after formation of a long-range ordered (√3×√3)R30? SnAu2/Au(111) surface alloy. Angle-resolved photoemission and two-photon photoemission spectroscopy techniques reveal Rashba-type spin-split bands in the occupied valence band with comparable momentum space splitting as observed for the Au(111) surface state, but with a hole-like parabolic dispersion. Our experimental findings are compared with density functional theory (DFT) calculation that fully support our experimental findings. Taking advantage of the good agreement between our DFT calculations and the experimental results, we are able to extract that the occupied Sn-Au hybrid band is of (s, d )-orbital character, while the unoccupied Sn-Au hybrid bands are of (p, d )-orbital character. Hence we can conclude that the Rashba-type spin splitting of the hole-like Sn-Au hybrid surface state is caused by the significant mixing of Au d with Sn s states in conjunction with the strong atomic spin-orbit coupling of Au, i.e., of the substrate.
关键词： angle-resolved photoemission spectroscopy,density functional theory,SnAu2/Au(111) surface alloy,Rashba-type spin splitting,two-photon photoemission spectroscopy
更新于2025-09-09 09:28:46
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Growth, Morphology and Stability of Au in Contact with the Bi2Se3(0001) Surface
摘要： We report a combined microscopy and spectroscopy study of Au deposited on the Bi2Se3(0001) single crystal surface. At room temperature Au forms islands, according to the Volmer–Weber growth mode. Upon annealing to 100° C the Au deposits are not stable and assemble into larger and thicker islands. The topological surface state of Bi2Se3 is weakly affected by the presence of Au. Contrary to other metals, such as Ag or Cr, a strong chemical instability at the Au/Bi2Se3 interface is ruled out. Core level analysis highlights Bi diffusion toward the surface of Au islands, in agreement with previous findings, while chemical interaction between Au and atomic Se is limited at the interfacial region. For the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10-8 mbar) regime.
关键词： metal to topological insulator contact,chemical properties,photoemission spectroscopy,growth mode,electronic properties,microscopy
更新于2025-09-09 09:28:46
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across the quantum phase transition from topological to trivial insulator
摘要： Using spin- and angle-resolved photoemission spectroscopy and relativistic many-body calculations, we investigate the evolution of the electronic structure of (Bi1?xInx )2Se3 bulk single crystals around the critical point of the trivial to topological insulator quantum-phase transition. By increasing x, we observe how a surface gap opens at the Dirac point of the initially gapless topological surface state of Bi2Se3, leading to the existence of massive fermions. The surface gap monotonically increases for a wide range of x values across the topological and trivial sides of the quantum-phase transition. By means of photon-energy-dependent measurements, we demonstrate that the gapped surface state survives the inversion of the bulk bands which occurs at a critical point near x = 0.055. The surface state exhibits a nonzero in-plane spin polarization which decays exponentially with increasing x, and which persists in both the topological and trivial insulator phases. Our calculations reveal qualitative agreement with the experimental results all across the quantum-phase transition upon the systematic variation of the spin-orbit coupling strength. A non-time-reversal symmetry-breaking mechanism of bulk-mediated scattering processes that increase with decreasing spin-orbit coupling strength is proposed as explanation.
关键词： quantum-phase transition,topological insulator,electronic structure,photoemission spectroscopy,spin-orbit coupling
更新于2025-09-09 09:28:46
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Dirac nodal lines and flat-band surface state in the functional oxide
摘要： The efficiency and stability of RuO2 in electrocatalysis has made this material a subject of intense fundamental and industrial interest. The surface functionality is rooted in its electronic and magnetic properties, determined by a complex interplay of lattice-, spin-rotational, and time-reversal symmetries, as well as the competition between Coulomb and kinetic energies. This interplay was predicted to produce a network of Dirac nodal lines (DNLs), where the valence and conduction bands touch along continuous lines in momentum space. Here we uncover direct evidence for three DNLs in RuO2 by angle-resolved photoemission spectroscopy. These DNLs give rise to a flat-band surface state that is readily tuned by the electrostatic environment, and that presents an intriguing platform for exotic correlation phenomena. Our findings support high spin-Hall conductivities and bulk magnetism in RuO2, and are likely related to its catalytic properties.
关键词： RuO2,angle-resolved photoemission spectroscopy,electrocatalysis,flat-band surface state,Dirac nodal lines
更新于2025-09-09 09:28:46
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Accurate and efficient data acquisition methods for high-resolution angle-resolved photoemission microscopy
摘要： Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique in materials science, as it can directly probe electronic states inside solids in energy (E) and momentum (k) space. As an advanced technique, spatially-resolved ARPES using a well-focused light source (high-resolution ARPES microscopy) has recently attracted growing interests because of its capability to obtain local electronic information at micro- or nano-metric length scales. However, there exist several technical challenges to guarantee high precision in determining translational and rotational positions in reasonable measurement time. Here we present two methods of obtaining k-space mapping and real-space imaging in high-resolution ARPES microscopy. One method is for k-space mapping measurements that enables us to keep a target position on a sample surface during sample rotation by compensating rotation-induced displacements (tracing acquisition method). Another method is for real-space imaging measurements that significantly reduces total acquisition time (scanning acquisition method). We provide several examples of these methods that clearly indicate higher accuracy in k-space mapping as well as higher efficiency in real-space imaging, and thus improved throughput of high-resolution APRES microscopy.
关键词： k-space mapping,ARPES,real-space imaging,Angle-resolved photoemission spectroscopy,high-resolution ARPES microscopy
更新于2025-09-09 09:28:46
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Electrical properties of α-Ir <sub/>2</sub> O <sub/>3</sub> /α-Ga <sub/>2</sub> O <sub/>3</sub> pn heterojunction diode and band alignment of the heterostructure
摘要： Corundum-structured iridium oxide (a-Ir2O3), showing p-type conductivity, is a strong candidate to form high-quality pn heterojunctions with a-Ga2O3. We fabricated a-Ir2O3/a-Ga2O3 pn heterojunction diodes and they showed well-defined rectifying current-voltage (I-V) characteristics with the turn-on voltage of about 2.0 V. The band alignment at the a-Ir2O3/a-Ga2O3 interface was investigated by X-ray photoemission spectroscopy, revealing a staggered-gap (type-II) with the valence- and conduction-band offsets of 3.34 eV and 1.04 eV, respectively. The total barrier height for electrons was about 2.4 eV, which reasonably agreed with the turn-on voltage in the I-V characteristics. This means that electrons are mainly attributed to electrical conduction around the turn-on voltage.
关键词： pn heterojunction,a-Ir2O3,X-ray photoemission spectroscopy,a-Ga2O3,band alignment
更新于2025-09-09 09:28:46