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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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Band Structure Effects on the Charge Exchange Processes in H <sup>+</sup> Colliding with a Cu(111) Surface
摘要： The low-energy ion scattering (LEIS) technique was used to experimentally determine the formation of positive and negative ions in the scattering of protons by a Cu(111) surface for a large scattering angle in the backscattering configuration and a wide range of incoming energies (2?8 keV). Two different collisional geometries were analyzed for a 135° fixed scattering angle: 45°/90° and 67.5°/67.5° incoming/exit angles measured with respect to the target surface. The total fraction of backscattered ions ranges from 10% to 25%, and a peculiarly high yield of negative ions, which always exceeds that of positive ions, was detected for the whole energy range analyzed. A strong dependence of the measured ion fractions with the geometrical conditions was experimentally found. On the theoretical side, a first-principles quantum-mechanical formalism that takes into account the three possible final charge states of the H+ in a correlated way and the fine details of the band structure of the Cu(111) surface was applied to describe the charge transfer processes involved in the experimental situation. The theoretical calculation leads to a nonmonotonous dependence with the incoming energy that properly describes the experimental results, especially the negative ion fraction in the specular collisional geometry. The oscillatory behavior predicted by the theory in the range of low energies is clear evidence of the charge exchange between localized states, that is, the situation related with the presence of the surface state immersed in the L-gap present in the Cu(111) surface. The positive ion fraction is discussed for the first time for this collisional system. The differences found between the measurements and the theory seem to indicate that the neutralization to excited states and also the formation of excited negative hydrogen ions are possible charge exchange channels in the dynamic process analyzed.
关键词： negative ion formation,quantum-mechanical formalism,low-energy ion scattering,Cu(111) surface,charge transfer
更新于2025-09-10 09:29:36
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STM and DFT Study of Chlorine Adsorption on the Ag(111)- <i>p</i> (4x4)-O Surface
摘要： Coadsorption of chlorine and oxygen on the Ag(111) surface has been studied with low-temperature scanning tunneling microscopy (LT-STM) in a combination with density functional theory (DFT) calculations. Room temperature adsorption of chlorine onto the Ag(111)-p(4×4)-O surface leads to the appearance of new bright objects located between protrusions of the 4×4 reconstruction. As chlorine adsorbs, objects form "rosettes" around corner holes. This configuration coincides with the configuration of the chlorine atoms in the Ag(111)-(3×3)-Cl reconstruction structure. We conclude that the adsorption of chlorine on the Ag(111)-p(4×4)-O surface occurs dissociatively, with chlorine atoms displacing oxygen atoms from the fourfold positions. Adsorption of chlorine at 77 K results in the formation of the mixed Cl–O species on the Ag6 triangles of the p(4×4) reconstruction. Both scenarios of chlorine adsorption are unexpected and cannot be explained within a commonly accepted Ag6 model of the p(4×4) reconstruction.
关键词： STM,DFT,Chlorine adsorption,Ag6 model,Ag(111)-p(4×4)-O surface
更新于2025-09-10 09:29:36
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Electric-field-controllable nonvolatile multilevel resistance switching of Bi <sub/>0.93</sub> Sb <sub/>0.07</sub> /PMN-0.29PT(111) heterostructures
摘要： Electric-field switchable multilevel nonvolatile resistance states are achieved at room temperature in Bi0.93Sb0.07/0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3(111) (PMN-0.29PT) heterostructures. During the initial poling of the PMN-0.29PT, the variation of the resistance of the Bi0.93Sb0.07 film with the electric field tracks the variation of the electric-field-induced in-plane strain of the PMN-0.29PT effectively, revealing that the resistance switching is dominated by the ferroelectric-domain-switching-induced lattice strain but not the domain-switching-induced polarization charges. A relative resistance change DR/R ≈ 7% at 300 K and up to ≈10% at 180 K were achieved near the coercive field EC of the PMN-0.29PT(111) substrate. At least five stable resistance states with good endurance properties could be obtained at room temperature by precisely controlling the electric-field pulse sequence as a result of the nonvolatile remnant strain transferring from the PMN-0.29PT to the film, providing a simple and energy efficient way to construct multistate resistive memory.
关键词： Bi0.93Sb0.07/PMN-0.29PT(111) heterostructures,nonvolatile,multilevel resistance switching,ferroelectric-domain-switching-induced lattice strain,electric-field
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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Growth of tr6-CaSi <sub/>2</sub> thin films on Si(111) substrates
摘要： Uniform and high-quality tr6-CaSi2 films were successfully grown via the co-deposition of Ca and Si on a Si(111) substrate. Using reactive Ca deposition, the films tended to form mixed phases of orthorhombic CaSi and two trigonal CaSi2 (three-layer repeat: tr3-CaSi2; six-layer repeat: tr6-CaSi2) structures at low substrate temperatures below 580 °C. A tr6-CaSi2 film was formed when the substrate temperature and thickness of the deposited Ca were controlled. By supplying an external source of Si along with Ca deposition, the formation of CaSi and tr3-CaSi2 was suppressed, and single-phase tr6-CaSi2 was obtained.
关键词： co-deposition,thin films,molecular beam epitaxy,Si(111) substrates,tr6-CaSi2
更新于2025-09-09 09:28:46
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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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X-ray structural analysis of an epitaxially grown Ag film/Si(111)$\sqrt{3} \times \sqrt{3} $-B substrate interface
摘要： We investigated the structure of the Si(111)√3×√3-B surface and epitaxially grown Ag(111) film/Si(111)√3×√3-B substrate interface using surface X-ray diffraction. An analysis of their crystal truncation rod and fractional order rod scatterings revealed a good agreement between the structure of the Si(111)√3×√3-B surface and previous theoretical studies when taking into account structural inhomogeneity caused by subsurface defects. At the Ag film/Si(111)√3×√3-B substrate interface, the Si(111)√3×√3-B surface reconstruction was maintained intact. The experimentally determined positions of Ag atoms were displaced from the ideal Ag(111) bulk sites, and a 3×3 periodicity was introduced to the bottom layer of the Ag film at the interface. The 3×3 periodic corrugation was transferred, albeit damped, to the upper layer. This transfer was considered to be the origin of the 3×3 periodic pattern at the Ag film surface on the Si(111)√3×√3-B substrate, a pattern observed in our previous scanning tunneling microscope study.
关键词： crystal truncation rod,3×3 periodicity,surface X-ray diffraction,Si(111)√3×√3-B substrate,epitaxial growth,Ag film,fractional order rod,X-ray structural analysis
更新于2025-09-09 09:28:46
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Stark effect or coverage dependence? Disentangling the EC-SEIRAS vibrational shift of sulfate on Au(111)
摘要： Infrared spectroscopy is a widely employed analytical tool in (electrochemical) surface science as the spectra contain a wealth of information about the interaction of interfacial adsorbates with their environment. Separating and quantifying individual contributions, for example, of co-adsorbates, the substrate or electric field effects, on the overall spectral response, however, is often non-trivial as the various interactions manifest themselves in similar spectral behavior. Here, we present an experimental approach to differentiate between and quantify potential-induced coverage dependence and field-related Stark effects observed in a sulfate band shift of 93.5 ± 1.5 cm?1/V in electrochemical infrared spectra of the showcase sulfate/Au(111) interface. In combination with a simple linear model equation used to describe the potential-induced peak shift of the sulfate stretch vibration, we determine the coverage dependence contribution to be 15.6 ± 1.2 cm?1/θSO and the Stark effect to amount to 75.6 ± 2.7 cm?1/V. Our work provides a novel route to gain fundamental insight into interfacial adsorbate interactions in electrochemical surface science.
关键词： Stark effect,Infrared spectroscopy,sulfate/Au(111) interface,electrochemical surface science,coverage dependence
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