金刚石延(111)面生长的第一性原理研究

利用密度泛函理论(DFT)对碳原子在镍(111)表面吸附结构进行了计算，得到了吸附能以及态密度 (density of state, DOS)分布，分析了吸附在镍(111)面的碳原子和金刚石(111)面的碳原子的分波态密度(PDOS)，结果表明吸附在镍表面的碳原子具有与金刚石表面碳原子相类似的电子结构特点，即两者都存在孤对的和成键的sp³杂化电子,进而发现吸附在镍表面的碳原子极易与金刚石表面相互作用形成稳定的类金刚石几何结构. 关键词： 密度泛函理论 化学吸附 电子结构 金刚石生长     

Femtosecond evolution of electronic interactions at the Ni(111) surface

We used time-resolved photoemission spectroscopy to measure the changes in electron self energy for the occupied surface resonance near the surface Brillouin zone center of Ni/W(110) single crystalline films following optical excitations with a fs laser pulse. Binding energy and lifetime display pronounced variations on a 100 fs time scale. We provide evidence that this is directly linked to the laser induced population of electronic levels. PACS 73.20.-r; 73.50.Gr; 78.47.+p; 79.60.Bm     

The structure and bonding of furan on Pd(111)

The structure and bonding of molecular furan, C₄H₄O, on Pd(111) has been investigated using density functional theory (DFT) calculations and the results compared with those of a recent experimental investigation using scanned-energy mode photoelectron diffraction (PhD). The DFT results confirm the orientation of the molecular plane to be essentially parallel to the surface and show a clear energetic preference for one of the two possible structures identified in the PhD study, namely that with the molecule centred over the hollow sites of the surface. Two slightly different geometries at the hollow sites are found to be essentially energetically equivalent; in both cases, one Pd surface atom bonds to two C atoms, while two other Pd atoms each bond to one C atom. These structures differ in that in one case the pair of C atoms bonding to a single Pd atom are both β-C (C atoms not bonded to O in the furan molecule), whereas in the second case this pair of C atoms comprises one β-C and one α-C (adjacent to the O atom in furan). In both structures the C–Pd bonding is accompanied by displacements of the H and O atoms away from the surface and out of the molecular plane and local C–Pd coordination consistent with a rehybridisation of the C bonding to sp³ character.     

Magnetic properties of Co clusters deposited on Pt(111)

Using the fully relativistic version of the Korringa–Kohn–Rostoker method for electronic structure calculations within local spin density functional theory, the magnetic and spectroscopic properties of Co clusters deposited on Pt(111) have been investigated. Of central interest was the role of spin–orbit coupling, since it influences the spontaneous formation and orientation of magnetic moments and gives rise among other things to the occurrence of orbital magnetic moments, magnetic anisotropy energy and magnetic circular dichroism in X-ray absorption. The results have been complemented by calculations of the exchange coupling parameters J_ij used within Monte Carlo simulations on the basis of the extended classical Heisenberg Hamiltonian. This allowed us to simulate the magnetic properties at finite temperatures, which are of central importance for applications. PACS 73.20.-r; 71.15.Rf; 73.22.-f; 87.64.Ni     

Origin of unusual work function change upon forming Tl nanoclusters on Si(111)-7x7 surface

We report an unusual behavior of the work function that remains unchanged while increasing the coverage (θ) of thallium (Tl) nanoclusters regularly arranged on a Si(111)-7×7 surface. Such a constant work function with increasing θ is understood in terms of a θ-dependent inter-cluster interaction that cancels the change induced by dipoles due to Tl nanoclusters. The spectral changes of Si 2p and Tl 5d_5/2 core-levels as a function of θ strongly indicates the presence of such an inter-clusters interaction, which is further supported by our theoretical calculation revealing a significant charge redistribution. PACS 73.20.-r; 73.30.+y; 68.47.Fg; 79.60.-i; 73.20.Hb     

Lifetimes of electrons in the Shockley surface state band of Ag(111)

We present a theoretical many-body analysis of the electron–electron (e–e) inelastic damping rate Γ of electron-like excitations in the Shockley surface state band of Ag(111). It takes into account ab initio band structures for both bulk and surface states. Γ is found to increase more rapidly as a function of surface state energy E than previously reported, thus leading to an improved agreement with experimental data. PACS 73.20.At; 68.37.Ef; 72.15.Lh     

Surface interactions of Au(I) cyclo-trimer with Au(111) and Al(111) surfaces: A computational study

A plane-wave density functional theory (DFT) study on surface interactions of a cyclo-[Au(μ-Pz)]₃ monolayer (denoted as T), Pz = pyrazolate, with Au(111) and Al(111) surfaces (denoted as M′) has been performed. Structural and electronic properties at the M′–T interfaces are determined from individually optimized structures of M′, T and M′–T. Results show that the gold pyrazolate trimer (T) binds more strongly on the Au(111) surface than on Al(111). Charge redistribution has been observed at both M′–T interfaces, where charge is “pushed” back towards the Au(111) surface from the trimer monolayer in Au(111)–T system, while the opposite happens in the Al(111)–T system where the charge is being pushed toward the trimer monolayer from the Al(111) surface. Considerable changes to the work function of Au(111) and Al(111) surfaces upon the trimer adsorption which arise from monolayer vacuum level shifts and dipole formation at the interfaces are calculated. The interaction between cyclo-[Au(μ-Pz)]₃ with metal surfaces causes band broadening of the gold pyrazolate trimer in M′–T systems. The present study aids better understanding of the role of intermolecular interactions, bond dipoles, energy-level alignment and electronic coupling at the interface of metal electrodes and organometallic semiconductor to help design metal–organic field effect transistors (MOFETs) and other organometallic electronic devices.     

Atmospheric effects on the adhesion and friction between non-hydrogenated diamond-like carbon (DLC) coating and aluminum - A first principles investigation

Experimentally, non-hydrogenated DLC coatings were tested against 319 Al alloy in the nitrogen, hydrogen, dry air (0% RH), and ambient air (40% RH) environments using a vacuum pin-on-disc tribometer. The average coefficient of friction (COF) and the material transfer changed dramatically depending on the test environment. Density functional theory (DFT) calculations were performed to investigate the interaction of diamond surface, to represent non-hydrogenated DLC, with N₂, H₂, and H₂O molecules. These calculations suggested that hydrogen and water would dissociate and be chemically adsorbed at a diamond surface whereas the dissociation of nitrogen is very unlikely to happen. Therefore, the diamond/DLC surface is passivated by -H termination in hydrogen and by -OH termination in water vapor, but not passivated in nitrogen. The calculated work of separation for Al with non-passivated and reacted diamond surfaces indicated the same tendency of adhesive transfer as observed in the pin-on-disc tests. The calculated work of separation at the interfaces formed after material transfer has the same trend with the measured COF. Therefore, DFT calculations successfully explained the atmospheric dependency of the tribological behavior of non-hydrogenated DLC coatings.     

Further study of the difference in nitrogen aggregation among (111) and (100) growth sectors of synthetic diamonds

Abstract

Single nitrogen atoms in synthetic diamond crystals aggregate in pairs by heat treatment under high pressure after electron irradiations. We find that the rate constants of nitrogen aggregation in the (111) growth sectors grown by the various solvents are about ten times greater than those of the (100) growth sectors. Furthermore the rate constant of nitrogen aggregation of the same sector is almost the same value. (shown Table-1). We have considered a few reasons for this fact. It may be accurate that a form of nitrogen atoms contained in (111) growth sectors of an as-grown diamond differs from that in (100) grown sectors and that the former accelerates nitrogen aggregation. Consequently we propose one nitrogen migration and aggregation model.     

Ag(111)和Au(111)上铋的初始生长行为

半金属铋(Bi)的表面合金具有的Rashba效应,和其具体结构性质有重要关联.本文结合扫描隧道显微镜(STM)和密度泛函理论(DFT),系统地研究了Bi原子在Ag(111)和Au(111)上的不同初始生长行为.在室温Ag(111)上,连续的Ag2Bi合金薄膜会优先在Ag台阶边缘形成;在570 K Ag(111)上,随着...     

Laser-induced graphitization on a diamond (111) surface

We report an atomistic simulation study of laser-induced graphitization on the diamond (111) surface. Our simulation results show that the diamond to graphite transition occurs along different pathways depending on the length of the laser pulse being used. Under nanosecond or longer laser pulses, graphitization propagates vertically into bulk layers, leading to the formation of diamond-graphite interfaces after the laser treatment. By contrast, with femtosecond (0.2-0.5 ps) laser pulses, graphitization of the surface occurs layer by layer, resulting in a clean diamond surface after the ablation. This atomistic picture provides an explanation of recent experimental observations.     

GaAs(111)A/B surface orientation effects on electron density in normal and inverted pseudomorphic HEMTs

We present calculations of the two-dimensional electron density in a Si -doped AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (P-HEMT), at low temperature, for three different growth directions (001) and (111)A/B. The calculations are made using a self-consistent resolution of Schrödinger and Poisson equations. The presence of a strong built-in piezoelectric field in (111)A/B growth directions causes changes of the confining potential shape and the carrier distribution in the InGaAs channel. We discuss the influence of GaAs substrate orientation on the conduction-band structure and thereafter on the two-dimensional electron gas (2DEG) concentration in the channel. Our results show that the calculated 2DEG concentration in the normal P-HEMT structure grown on a (111)A GaAs substrate is significantly higher than those grown on (001) and (111)B GaAs substrates. We also note an increase of the average separation between the ionized donors and the carriers. On the other hand, the GaAs (111)B substrate orientation appears as inadequate for the type of structure (normal P-HEMT) on account of the charge-transfer reduction in the channel compared with the (001) orientation. In contrast, we demonstrate that the calculated 2DEG Si -doped GaAs/InGaAs/AlGaAs pseudomorphic inverted high electron mobility transistor (PI-HEMT) grown on aGaAs (111)B substrate is appreciably higher than that grown on (001) and afterwards an enhancement of the spatial separation between confined electrons in the channel and ionized dopants occurs. These effects might result in considerably improved devices of great interest regarding high electron mobility. PACS 73.20.Dx; 73.20.At; 73.90.+f; 73.63.Hs; 72.20.Dp     

Phonon spectra of clean and Ni-terminated diamond (111) surfaces: An ab-initio study

The phonon densities of states (ph-DOSs) of clean and Ni-terminated C(111) surfaces with 1 × 1 and 2 × 1 surface structures were investigated using ab-initio density functional perturbation theory. The ph-DOSs showed vibrational spectra associated with the surface structures of C(111) and Ni/C(111). Further analyses of various surface phonon modes were performed to identify vibrational features involving the surface atoms of C(111) and Ni/C(111). These features provide important information for experimentally verifying the formation of a diamond bulk-like structure at Ni/C(111), as suggested in a previous study.     

Influence of the herringbone reconstruction on the surface electronic structure of Au(111)

We present angular-resolved photoemission investigations of the Shockley-type surface state on the reconstructed (111) surface of gold. The so-called herringbone reconstruction, with three different 22×3^1/2domain orientations, forms a super-lattice that has a clearly observable influence on the surface electronic structure. In the L gap of the projected bulk states, there appears a non-uniform photoemission intensity distribution due to the back-folding of the Shockley state at the Bragg planes of the reduced surface Brillouin zone. Furthermore, there is a clear indication of the existence of surface-state band gaps in the electronic density of states of the Shockley state. PACS 73.20.At; 68.35.Bs; 79.60.Bm     

Quantum confinement in monatomic Cu chains on Cu(111)

The existence of one-dimensional (1D) electronic states in Cu/Cu(111) chains assembled by atomic manipulation is revealed by low-temperature scanning tunneling spectroscopy and density functional theory (DFT) calculations. Our experimental analysis of the chain-localized electron dynamics shows that the dispersion is fully described within a 1D tight-binding approach. DFT calculations confirm the confinement of unoccupied states to the chain in the relevant energy range, along with a significant extension of these states into the vacuum region.     

Theoretical investigation of the structure and properties of the VN(111) monolayer on the MgO(111) surface

The VN(111) monolayer on the MgO(111) surface has been simulated and optimized in terms of the density functional theory (DFT) calculations. The most favorable arrangement of vanadium nitride on the surface of the magnesium oxide plate has been found. The band structure and densities of states for the VN(111) monolayer have been calculated. It has been concluded based on the densities of states for the VN monolayer on the MgO surface that this structure exhibits properties of a diluted magnetic semiconductor.     

Atomic and molecular adsorption on Pd(111)

The adsorption properties of a variety of atomic species (H, O, N, S, and C), molecular species (N₂, HCN, CO, NO, and NH₃) and molecular fragments (CN, NH₂, NH, CH₃, CH₂, CH, HNO, NOH, and OH) are calculated on the (111) facet of palladium using periodic self-consistent density functional theory (DFT–GGA) calculations at ¼ ML coverage. For each species, we determine the optimal binding geometry and corresponding binding energy. The vibrational frequencies of these adsorbed species are calculated and are found to be in good agreement with experimental values that have been reported in literature. From the binding energies, we calculate potential energy surfaces for the decomposition of NO, CO, N₂, NH₃, and CH₄ on Pd(111), showing that only the decomposition of NO is thermochemically preferred to its molecular desorption.     

Morphological modifications of Ag/Cu(111) probed by photoemission spectroscopy of quantum well states and the Shockley surface state

Epitaxial ultra-thin Ag films grown on Cu(111) have been investigated by angle-resolved photoemission spectroscopy. The thickness dependence of the binding energy for the Shockley surface state at 300 K could be determined accurately in films up to 5 ML thick. Furthermore, we observe drastic changes in the film morphology after annealing to 450 K. Spectral modifications in the shape of the quantum-well states (QWS), characteristic for these ultra-thin silver films, prove that the surface morphology is homogeneous. The photoemission spectra also indicate that the silver film bifurcates to form a film exhibiting two distinct film thicknesses. For all levels of silver coverage, we identify surface regions that are 2 ML thick, while the thickness of the remaining surface depends on the amount of deposited silver. The almost purely Lorentzian line-shape of the spectral features corresponding to the two different surface regions show that both surface areas are atomically flat. PACS 68.55.Jk; 73.20.At; 73.21.Fg; 79.60.Dp     

MD study on high-energy reactive cluster impact on diamond (111) and (100) surfaces

Molecular dynamics (MD) simulations of single argon, CO₂ and O₂ cluster impacts on diamond (100) and (111) surfaces are performed in order to investigate the surface erosion process. The transient crater on the (100) surface seems rather unpherical and skew compared to the typical hemispherical crater appeared on the (111) surface due to the orientation-dependent hardness. Argon cluster impacts on the diamond (100) surface resulted in a slightly higher erosion rate than on the (111) surface while it is lowered on the (111) surface for CO₂ cluster impacts. The difference in the susceptibility to the physical erosion appears in the rim or the crater.