Anomalous photoemission threshold in high-T c oxide superconductor with Cs and K submonolayers

The photoemission threshold and photocurrent spectra were investigated for Bi₂Sr₂CaCu₂O₈ crystals with K or Cs submonolayer films. The different films of K or Cs were deposited on the Bi-O surface in the temperature range 80–250 K. We observed an appreciable (up to 0.3 eV) energy shift of the threshold and a strong modification of the photocurrent spectra for different temperatures and submonolayer coverages. The appropriate model of such a phenomena is based on a quasimetallic K or Cs clusters effect and additional 2D-polaronic effect.     

The C 1<Emphasis Type="Italic">s</Emphasis> core level spectroscopy of carbon atoms at the surface SiC/Si(111)-4° layer and Cs/SiC/Si(111)-4° interface

Photoemission studies of the electronic structure of the Cs/nano-SiC/Si(111)-4° nanointerface are for the first time carried out with the use of synchrotron radiation in the photon energy range 120–450 eV. The in situ experiments are conducted in the case of submonolayer Cs coating of the surface of an epitaxial SiC layer grown on the vicinal surface Si(111)-4° by a new method of substrate-atom substitution. Modification of the valence-band spectra and the C 1s and Si 2p core levels is studied. The appearance of Cs-induced surface states, with binding energies of 1.2 and 7.4 eV, and a sharp change in the spectrum of the C 1s core level with the appearance of two additional modes are found. The evolution of the spectra shows that the Cs/nano-SiC/Si(111)-4° interface is formed due to charge transfer from Cs adatoms to surface atoms at terraces and steps of the vicinal surface. It is found that the structure of the C layer is nontrivial and involves energetically different carbon states.     

The Electronic Structure of the Cs/<Emphasis Type="Italic">n</Emphasis>-GaN(0001) Nano-Interface

Electronic structures of the n-GaN(0001) surface and Cs/n-GaN(0001) interface with submonolayer Cs coverages were studied for the first time in situ by the photoelectron spectroscopy (PES) method. The spectra of photoemission from the valence band, surface electron states, and core levels (Ga 3d, Cs 4d, Cs 5p) under synchrotron excitation were measured in a range of photon energies within 50–150 eV. Evolution of the spectrum of surface states near the valence-band maximum was revealed by PES during the adsorption of Cs atoms. A metallic character of the Cs/n-GaN(0001) nano-interface is demonstrated.     

A New Type of Carbon Nanostructure on a Vicinal SiС(111)-8° Surface

Technical Physics Letters - The electronic properties of the Ba/SiC/Si(111)-8° nanointerface have been studied for the first time by photoelectron spectroscopy using synchrotron radiation. The...     

Anomalous photoemission threshold in high-Tc oxide superconductor with Cs and K submonolayers

The photoemission threshold and photocurrent spectra were investigated for Bi₂Sr₂CaCu₂O₈ crystals with K or Cs submonolayer films. The different films of K or Cs were deposited on the Bi-O surface in the temperature range 80–250 K. We observed an appreciable (up to 0.3 eV) energy shift of the threshold and a strong modification of the photocurrent spectra for different temperatures and submonolayer coverages. The appropriate model of such a phenomena is based on a quasimetallic K or Cs clusters effect and additional 2D-polaronic effect.     

Induced surface states of the ultrathin Ba/3<Emphasis Type="Italic">C</Emphasis>-SiC(111) interface

The electronic properties of the Ba/3C-SiC(111) nanointerface are for the first time studied by photoelectron spectroscopy with the use of synchrotron radiation in the energy range 80–450 eV. The experiments are performed in situ in ultrahigh vacuum for ultrathin Ba coatings on 3C-SiC(111) samples grown by a new method of substituting substrate atoms. It is found that the adsorption of Ba brings about the appearance of induced surface states with the binding energies 1.9, 6.2, and 7.5 eV. Evolution of the surface states and the spectra of the Si 2p and C 1s core levels shows that the Ba/3C-SiC(111) interface is formed due to charge transfer from Ba adatoms to surface Si atoms and underlying C atoms.     

Photoemission studies of the vicinal SiC(100) 4° surface and the Cs/SiC(100) 4° interface

Photoemission studies of the electronic structure of the vicinal SiC(100) 4° surface, which was grown using a new substrate atom substitution method, and the Cs/SiC(100) 4° interface have been performed for the first time. The modification of spectra of the valence band and C 1s and Si 2p core levels in the process of formation of the Cs/SiC(100) 4° interface was analyzed. The suppression of the surface SiC state with a binding energy of 2.8 eV and the formation of a cesium-induced state with a binding energy of 10.5 eV were observed. The modification of the complex component structure in the spectrum of C 1s core level has been detected and examined for the first time. It was found that Cs adsorption on the vicinal SiC(100) 4° surface results in intercalation of graphene islands on SiC(100) 4° with Cs atoms.