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Hybridization of an unoccupied molecular orbital with an image potential state at a lead phthalocyanine/graphite interface
摘要： The interaction of a molecular orbital with a surface state is important to understand the spatial distribution of the wave function at the molecule/substrate interface. In this study, we focus on hybridization of an unoccupied state of lead phthalocyanine (PbPc) with the image potential state (IPS) on a graphite surface. The hybridization modifies the energy-momentum dispersions of the IPS on PbPc films as observed by angle-resolved two-photon photoemission. On the PbPc 1 monolayer film, the IPS band forms a band gap and back-folding appears at the first Brillouin zone boundary due to the periodic potential by the adsorbate lattice. The modification of the dispersion is accompanied by the intensity enhancement of the IPS. We attributed the origin of the modified dispersion and intensity enhancement to a hybridization of the IPS with a molecule-derived unoccupied level. From the photon energy-dependent measurement on multilayer films, we have found the diffuse unoccupied molecular level in the vicinity of the IPS. The tail part of the IPS wave function in the substrate is enhanced by the hybridization with the unoccupied state, and thus strengthens the transition from the occupied substrate band to the hybridized IPS.
关键词： organic ultrathin films,image potential states,two-photon photoemission spectroscopy,unoccupied states,hybridization
更新于2025-09-04 15:30:14
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Growth and surface structural study of tin oxide films on Ag(001)
摘要： Tin oxide was prepared by reactive deposition of Sn in an O2 atmosphere at both room temperature (RT) and high temperature (HT) at 573 K as well from one monolayer to ten monolayer film coverages. The grown films were studied at RT by a combination of x-ray photoemission spectroscopy (XPS), low energy electron diffraction (LEED) and ultraviolet photoemission spectroscopy (UPS). At RT, the coexistence of both SnO and SnO2 was confirmed by XPS and valence band data with more SnO being formed at higher coverage. However, only one oxidised phase of tin oxide mainly due to SnO2 was formed at HT for most of the coverage. Presence of SnO was also confirmed only at the highest coverage studied here for HT. A multidomain LEED pattern having square (1 × 1) domains at 30° to each other was reported for low coverage of tin oxide at RT, which with an increase in coverage, gives rise to diffused background confirming no ordered tin oxide was formed. The similar multi-domain structure was also noticed for HT growth from lower coverage up to 5 monolayer equivalent (MLE) coverage which then transformed into hexagonal multidomain LEED pattern for higher coverage confirming the presence of clear oxide phase, unlike the RT growth case.
关键词： Thin films,Low energy electron diffraction,Photoemission spectroscopy
更新于2025-09-04 15:30:14
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Phase diagram of Bi2Sr2CaCu2O8+δ revisited
摘要： In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level p. In most materials, p cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, Tc, using the assumption that the Tc dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to Tc = 91 K. We show that p can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ0 = (4 ± 1)kBTc.
关键词： cuprate superconductors,Fermi surfaces,superconducting gap,doping,angle-resolved photoemission spectroscopy
更新于2025-09-04 15:30:14
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Study of the Interface of the Early Stages of Growth under Quasi-Equilibrium Conditions of ZnO on Graphene/Cu and Graphite
摘要： The study of the early stages of growth of ZnO on graphene supported on Cu and on highly oriented pyrolytic graphite by means of reactive thermal evaporation of metallic Zn at room temperature is presented. This growth method allows to go in depth in the study of the fundamental interaction between ZnO and graphene at the interface in quasi-equilibrium conditions. Quantitative, chemical, and morphological analysis is performed using photoemission spectroscopy, atomic force, and scanning microscopies as experimental characterization techniques and factor analysis and inelastic peak shape analysis as modeling techniques. The growth of ZnO on a highly oriented pyrolytic graphite substrate is also studied using the same growth method for comparison. The results show that, in spite that the first atomic layer of both substrates is identical, the growth kinetics and morphology of the deposits are completely different. A model for the kinetics of the growth of ZnO on both substrates is proposed.
关键词： X-ray photoemission spectroscopy,early stages of growth,ZnO/graphene interfaces,atomic force microscopy,nanostructured ZnO thin films
更新于2025-09-04 15:30:14
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Electron–phonon coupling in single-layer MoS2
摘要： The electron–phonon coupling strength in the spin–split valence band maximum of single-layer MoS2 is studied using angle-resolved photoemission spectroscopy and density functional theory-based calculations. Values of the electron–phonon coupling parameter λ are obtained by measuring the linewidth of the spin–split bands as a function of temperature and fitting the data points using a Debye model. The experimental values of λ for the upper and lower spin–split bands at K are found to be 0.05 and 0.32, respectively, in excellent agreement with the calculated values for a free-standing single-layer MoS2. The results are discussed in the context of spin and phase-space restricted scattering channels, as reported earlier for single-layer WS2 on Au(111). The fact that the absolute valence band maximum in single-layer MoS2 at K is almost degenerate with the local valence band maximum at Γ can potentially be used to tune the strength of the electron–phonon interaction in this material.
关键词： Density functional theory,Angle-resolved photoemission spectroscopy,Transition metal dichalcogenides,Electron-phonon coupling
更新于2025-09-04 15:30:14
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Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy
摘要： A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy, which significantly limits the accessible momentum space. Using 20.15 eV, 12 fs pulses, we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+d and demonstrate that non-monotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in stark contrast to the monotonic relaxation in the nodal and off-nodal regions.
关键词： electron-phonon interaction,high-temperature superconductors,cuprate,time-resolved ARPES,nodal-antinodal dichotomy,angle-resolved photoemission spectroscopy,quasiparticles
更新于2025-09-04 15:30:14