Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAtomic oxygen adsorption and incipient oxidation of the Pb(111) surface: A density-functional theory study
175
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the atomic oxygen adsorption on Pb(111) surface by using density-functional theory within the generalized gradient approximation and a supercell approach. The atomic and energetic properties of purely on-surface and subsurface oxygen structures at the Pb(111) surface are systematically investigated for a wide range of coverages and adsorption sites. The fcc and tetra-II sites (see the text for definition) are found to be energetically preferred for the on-surface and subsurface adsorption, respectively, in the whole range of coverage considered. The on-surface and subsurface oxygen binding energies monotonically increase with the coverage, and the latter is always higher than the former, thus indicating the tendency to the formation of oxygen islands (clusters) and the higher stability of subsurface adsorption. The on-surface and subsurface diffusion-path energetics of atomic oxygen, and the activation barriers for the O penetration from the on-surface to the subsurface sites are presented at low and high coverages. In particular, it is shown that the penetration barrier from the on-surface hcp to the subsurface tetra-I site is as small as 65 meV at low coverage ($Theta $=0.25). The other properties of the O/Pb(111) system, including the charge distribution, the lattice relaxation, the work function, and the electronic density of states, are also studied and discussed in detail, which consistently show the gradually stabilizing ionic O-Pb bond with increase of the oxygen coverage.
rate research
Read More
A nanorod structure has been observed on the Ho/Ge(111) surface using scanning tunneling microscopy (STM). The rods do not require patterning of the surface or defects such as step edges in order to grow as is the case for nanorods on Si(111). At low holmium coverage the nanorods exist as isolated nanostructures while at high coverage they form a periodic 5x1 structure. We propose a structural model for the 5x1 unit cell and show using an ab initio calculation that the STM profile of our model structure compares favorably to that obtained experimentally for both filled and empty states sampling. The calculated local density of states shows that the nanorod is metallic in character.
Chemisorption of CO on the stepped Cu(211) surface is studied within ab-initio density functional theory (DFT) and scanning tunneling microscopy (STM) imaging as well as manipulation experiments. Theoretically we focus on the experimentally observed ordered (2x1) and (3x1) CO-phases at coverages 1/3, 1/2 and 2/3 monolayer (ML). To obtain also information for isolated CO molecules found randomly distributed at low coverages, we also performed calculations for a hypothetical (3x1) phase with 1/3 ML. The adsorption geometry, the stretching frequencies, the work functions and adsorption energies of the CO molecules in the different phases are presented and compared to experimental data. Initially and up to a coverage of 1/2 ML CO adsorbs upright on the on-top sites at step edge atoms. Determining the most favorable adsorption geometry for the 2/3 ML ordered phase turned out to be nontrivial both from the experimental and the theoretical point of view. Experimentally, both top-bridge and top-top configurations were reported, whereby only the top-top arrangement was firmly established. The calculated adsorption energies and the stretching frequencies favor the top-bridge configuration. The possible existence of both configurations at 2/3 ML is critically discussed on the basis of the presently accessible experimental and theoretical data. In addition, we present observations of STM manipulation experiments and corresponding theoretical results, which show that CO adsorbed on-top of a single Cu-adatom, which is manipulated to a location close to the lower step edge, is stronger bound than CO on-top of a step edge atom.
We discuss the structural and electronic properties of tetragonal CuO grown on SrTiO3(100) by means of hybrid density functional theory. Our analysis explains the anomalously large Cu-O vertical distance observed in the experiments (~2.7 A) in terms of a peculiar frustration between two competing local Cu-O environments characterized by different in-plane and out-of-plane bond lengths and Cu electronic populations. The proper inclusion of substrate effects is crucial to understand the tetragonal expansion and to reproduce correctly the measured valence band spectrum for a CuO thickness of 3-3.5 unit cells, in agreement with the experimentally estimated thickness.
A magnetic skyrmion observed experimentally in chiral magnets is a topologically protected spin texture. For their unique properties, such as high mobility under current drive, skyrmions have huge potential for applications in next-generation spintronic devices. Defects naturally occurring in magnets have profound effects on the static and dynamical properties of skyrmions. In this work, we study the effect of an atomic defect on a skyrmion using the first-principles calculations within the density functional theory, taking MnSi as an example. By substituting one site of Mn or Si with different elements, we can tune the pinning energy. The effects of pinning by an atomic defect can be understood qualitatively within a phenomenological model.
We study the electronic structure and magnetism of 25% Mn substituted cubic Zirconia (ZrO2) with several homogeneous and heterogeneous doping profiles using density-functional theory calculations. We find that all doping profiles show half-metallic ferromagnetism (HMF), and delta-doping is most energy favorable while homogeneous doping has largest ferromagnetic stabilization energy. Using crystal field theory, we discuss the formation scheme of HMF. Finally, we speculate the potential spintronics applications for Mn doped ZrO2, especially as spin direction controllment.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
