Search results for "Binding energy"

Positron studies of hydrogen-defect interactions in proton irradiated molybdenum

1985

Molybdenum single crystals are irradiated at 20 K with 6 MeV protons. The radiation damage and lattice defect annealing is studied by positron lifetime spectroscopy in the temperature range from 15 to 720 K. Loss of vacancies due to recombination with mobile interstitials is observed at 40 K (Stage I) in agreement with resistivity measurements. This is the first time Stage I is observed by positrons below 77 K. The implanted hydrogen decorates the vacancies around 100 K, which is consistent with a hydrogen migration energy in molybdenum:E H = 0.3–0.4 eV. Clustering of spatially correlated vacancies takes place in a wide temperature region below the usual vacancy clustering stage (Stage III)…

Dislocation interaction with C in α-Fe: a comparison between atomic simulations and elasticity theory

2008

International audience; The interaction of C atoms with a screw and an edge dislocation is modelled at an atomic scale using an empirical Fe-C interatomic potential based on the Embedded Atom Method (EAM) and molecular statics simulations. Results of atomic simulations are compared with predictions of elasticity theory. It is shown that a quantitative agreement can be obtained between both modelling techniques as long as anisotropic elastic calculations are performed and both the dilatation and the tetragonal distortion induced by the C interstitial are considered. Using isotropic elasticity allows to predict the main trends of the interaction and considering only the interstitial dilatatio…

Changes of lead silicate glasses induced by leaching

1998

Abstract The structural differences in the surface region between freshly fractured and leached silicate glasses containing 16.7, 18.8 and 44.4 mol% PbO, respectively, were investigated by photoelectron spectroscopy (XPS). The optical properties and the thicknesses of leached layers were determined by reflection measurements. The binding energies of the O1s signal components for untreated samples can be ascribed to non-bridging (NBO) and bridging (BO) oxygen and oxygen associated with lead as network former (OPb). The binding energy of OPb was found to be 529.1 ± 0.2 eV. For quantitative conclusions, relative XPS sensitivity factors were determined for oxygen, silicon and lead in these glas…

Metallic evolution of small magnesium clusters

2001

Structural and electronic properties of small magnesium clusters (N≤13) are studied using a first-principles simulation method in conjunction with the density functional theory and generalized gradient correction approximation for the exchange-correlation energy functional. It is observed that the onset of metallization of magnesium clusters is hard to assign since both the s-p hybridization and the energy gap between the valence and conduction bands do not evolve rapidly towards the known bulk properties. Instead these quantities show a slow and nonmonotonic evolution.

Optical and electronic properties of 2H−MoS2 under pressure: Revealing the spin-polarized nature of bulk electronic bands

2018

Monolayers of transition-metal dichalcogenide semiconductors present spin-valley locked electronic bands, a property with applications in valleytronics and spintronics that is usually believed to be absent in their centrosymmetric (as the bilayer or bulk) counterparts. Here we show that bulk $2\mathrm{H}\text{\ensuremath{-}}\mathrm{Mo}{\mathrm{S}}_{2}$ hides a spin-polarized nature of states determining its direct band gap, with the spin sequence of valence and conduction bands expected for its single layer. This relevant finding is attained by investigating the behavior of the binding energy of $A$ and $B$ excitons under high pressure, by means of absorption measurements and density-functi…

Role ofp-dands-dinteractions in the electronic structure and band gap of Zn1−xMxO (M=Cr, Mn, Fe, Co, Ni, and Cu): Photoelectron and optical spectrosc…

2012

We report an investigation on the effect of $p$-$d$ and $s$-$d$ interactions in the electronic structure, and especially in the band-gap value, of wurtzite wide-gap diluted magnetic semiconductors Zn${}_{1\ensuremath{-}x}$${M}_{x}$O ($M=\mathrm{Cr}$, Mn, Fe, Co, Ni, Cu). Thin films prepared by pulsed laser deposition are investigated by means of optical absorption at low-temperature and photoelectron spectroscopy. Pure wurzite phase is shown to be maintained for Co and Mn concentrations up to 25$%$ and for Cr up to 10$%$, while in the case of Fe, Ni, and Cu, other phases are present for concentrations higher than 5, 2, and 1$%$, respectively. The band gap of the Zn${}_{1\ensuremath{-}x}$${M…

2014

Hard x-ray photoelectron spectroscopy (HAXPES) is used to investigate the intrinsic electronic properties of single crystal epitaxial CdO(100) thin films grown by metal organic vapor phase epitaxy (MOVPE). The reduced surface sensitivity of the HAXPES technique relaxes stringent surface preparation requirements, thereby allowing the measurement of as-grown samples with intrinsically higher carrier concentration (n=2.4×1020cm−3). High-resolution HAXPES spectra of the valence band and core levels measured at photon energy of 6054 eV are presented. The effects of conduction band filling and band gap renormalization are discussed to explain the observed binding energy shifts. The measured bandw…

Tuning the hole injection barrier in the intermolecular charge-transfer compoundDTBDT-F4TCNQ at metal interfaces

2014

Molecular monolayers of the charge-transfer salt dithienobenzodithiophene-tetrafluorotetracyanoquinodimethane (DTBDT-F${}_{4}$TCNQ) have been deposited on C(R$15\ifmmode\times\else\texttimes\fi{}3$)/W(110), Co/W(110), and hcp Co(0001) using molecular beam epitaxy in an ultrahigh vacuum. The integrity of the deposited molecules has been confirmed by scanning tunneling microscopy. Scanning tunneling spectroscopy has been used to determine the energetic positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital of acceptor and donor in the pure and in the mixed phase. The mixed charge transfer phase exhibits a new HOMO close to the Fermi edge depicting a charge tra…

3-Chlorotyramine Acting as Ligand of the D2 Dopamine Receptor. Molecular Modeling, Synthesis and D2 Receptor Affinity.

2014

We synthesized and tested 3-chlorotyramine as a ligand of the D2 dopamine receptor. This compound displayed a similar affinity by this receptor to that previously reported for dopamine. In order to understand further the experimental results we performed a molecular modeling study of 3-chlorotyramine and structurally related compounds. By combining molecular dynamics simulations with semiempirical (PM6), ab initio and density functional theory calculations, a simple and generally applicable procedure to evaluate the binding energies of these ligands interacting with the D2 dopamine receptors is reported here. These results provided a clear picture of the binding interactions of these compou…

Carbon nanorings: A challenge to theoretical chemistry

2006

High-level quantum-chemical methods show that the binding in the inclusion complex of hexamethylbenzene (HMB) in 6-cycloparaphenilacetylene (6-CPPA) cannot be explained only in terms of electrostatic interactions - caused by the polarization associated to curved π-conjugated systems - and the inclusion of dispersion forces is definitely needed. The theoretical description of van der Waals interactions is notoriously complicated and in fact some DFT methods cannot even predict the existence of the relatively small supramolecular nanoring studied here. However, ab initio MP2 calculations agree with experimental data and show that, in the considered complex, the HMB fragment is placed at the …