78 research outputs found
Multiple scattering investigation of the 1T-TaS2 surface termination
Abstract.: Multiple scattering theory based on a cluster model is used to simulate full hemispherical X-ray photoelectron diffraction measurements on a 1T-TaS2(0001) surface. Key points to determine the surface termination are discussed. As the commonly applied single scattering simulations do not give satisfying results, a multiple scattering approach has to be used to accurately simulate the full hemispherical photoelectron diffraction patterns. Differences and similarities between calculations of Ta and S terminated surfaces are presented along with experimental results at room temperature using both, the single and the multiple scattering approaches. We find that the surface is S terminated and that the quantitative difference between the calculations for both terminations permits to show the limits of the single scattering approach for solving surface termination problems. Moreover, by generalizing the results obtained using the multiple scattering approach, we discuss the application of this method to other similar system
Non-uniform doping across the Fermi surface of NbS2 intercalates
Abstract.: Magnetic ordering of the first row transition metal intercalates of NbS2 due to coupling between the conduction electrons and the intercalated ions has been explained in terms of Fermi surface nesting. We use angle-resolved photoelectron spectroscopy to investigate the Fermi surface topology and the valence band structure of the quasi-two-dimensional layer compounds Mn1/3NbS2 and Ni1/3NbS2. Charge transfer from the intercalant species to the host layer leads to non-uniform, pocket selective doping of the Fermi surface. The implication of our results on the nesting properties are discusse
Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films
X-ray photoelectron diffraction is used to directly probe the intra-cell
polar atomic distortion and tetragonality associated with ferroelectricity in
ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab-initio
calculations, unambiguously demonstrate non-centro-symmetry in films a few unit
cells thick, imply that films as thin as 3 unit cells still preserve a
ferroelectric polar distortion, and also show that there is no thick
paraelectric dead layer at the surface
Non-uniform doping across the Fermi surface of NbS intercalates
Magnetic ordering of the first row transition metal intercalates of NbS
due to coupling between the conduction electrons and the intercalated ions has
been explained in terms of Fermi surface nesting. We use angle-resolved
photoelectron spectroscopy to investigate the Fermi surface topology and the
valence band structure of the quasi-two-dimensional layer compounds
MnNbS and NiNbS. Charge transfer from the intercalant
species to the host layer leads to non-uniform, pocket selective doping of the
Fermi surface. The implication of our results on the nesting properties are
discussed
X-ray photoelectron diffraction study of ultrathin PbTiO3 films
Abstract.: Full hemispherical X-ray photoelectron diffraction (XPD) experiments have been performed to investigate at the atomic level ultrathin epitaxial c-axis oriented PbTiO3 (PTO) films grown on Nb-doped SrTiO3 substrates. Comparison between experiment and theory allows us to identify a preferential ferroelectric polarization state in a 60 Ã… -thick PTO film. Multiple scattering theory based on a cluster-model [ Phys. Rev. B , 075404 (2001)] is used to simulate the experiment
Fermi surface induced lattice distortion in NbTe
The origin of the monoclinic distortion and domain formation in the quasi
two-dimensional layer compound NbTe is investigated. Angle-resolved
photoemission shows that the Fermi surface is pseudogapped over large portions
of the Brillouin zone. Ab initio calculation of the electron and phonon
bandstructure as well as the static RPA susceptibility lead us to conclude that
Fermi surface nesting and electron-phonon coupling play a key role in the
lowering of the crystal symmetry and in the formation of the charge density
wave phase
Automatic medical encoding with SNOMED categories
BACKGROUND: In this paper, we describe the design and preliminary evaluation of a new type of tools to speed up the encoding of episodes of care using the SNOMED CT terminology. METHODS: The proposed system can be used either as a search tool to browse the terminology or as a categorization tool to support automatic annotation of textual contents with SNOMED concepts. The general strategy is similar for both tools and is based on the fusion of two complementary retrieval strategies with thesaural resources. The first classification module uses a traditional vector-space retrieval engine which has been fine-tuned for the task, while the second classifier is based on regular variations of the term list. For evaluating the system, we use a sample of MEDLINE. SNOMED CT categories have been restricted to Medical Subject Headings (MeSH) using the SNOMED-MeSH mapping provided by the UMLS (version 2006). RESULTS: Consistent with previous investigations applied on biomedical terminologies, our results show that performances of the hybrid system are significantly improved as compared to each single module. For top returned concepts, a precision at high ranks (P0) of more than 80% is observed. In addition, a manual and qualitative evaluation on a dozen of MEDLINE abstracts suggests that SNOMED CT could represent an improvement compared to existing medical terminologies such as MeSH. CONCLUSION: Although the precision of the SNOMED categorizer seems sufficient to help professional encoders, it is concluded that clinical benchmarks as well as usability studies are needed to assess the impact of our SNOMED encoding method in real settings. AVAILABILITIES : The system is available for research purposes on: http://eagl.unige.ch/SNOCat
- …