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In scanning tunneling microscopy the lattice mismatch between graphene and Rh(1 1 1) is observed as an additional superstructure. This superstructure is called Moire pattern. Various symmetry sites occur in a Moire pattern. These are distinguished by the arrangement of the graphene lattice over the Rh(1 1 1) lattice. The symmetry sites of the Moire unit cell are investigated by scanning tunneling microscopy and spectroscopy. The observed additional corrugation of the graphene sheet within a Moire cell is the consequence of strain and electronic interactions between graphene and the Rh(1 1 1) substrate. The lattice period of the Moire pattern depends on the in-plane rotation angle of the graphene layer with respect to the Rh(1 1 1) substrate. Scanning tunneling spectroscopy reveals a dependency of the local density of states on the hybridization of the π orbitals of the graphene with the d band of Rh(1 1 1). This results in a characteristic spectroscopic fingerprints of the individual symmetry sites of the Moire pattern.

Passivation and functionalization via atomic hydrogen, hydrogen peroxide (H 2 O 2 ( g )), and trimethylaluminum (TMA) on clean silicon–germanium (Si 0.5 Ge 0.5 (110) and Si 0.47 Ge 0.53 (001)) surfaces were studied and compared at the atomic level using ultra-high vacuum (UHV) scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and X-ray photoelectron spectroscopy (XPS) to understand the topological, electronic, and chemical structures of the surfaces. STM and XPS indicate that a sputter-cleaned SiGe(110) surface is terminated with adatoms, while a SiGe(001) surface is terminated with germanium dimers. STS demonstrates that the Fermi level on a clean SiGe(110) surface is pinned near mid-gap due to surface dangling bonds, while the Fermi level on a clean SiGe(001) surface is consistent with unpinning. A saturation dose of H 2 O 2 ( g ) at 25 °C chemisorbs to SiGe surfaces, leaving the Fermi level at the surface consistent with unpinning, and the surface is functionalized mainly with Si–OH, Ge–OH, and Si–O–Ge bonds on both SiGe(110) and (001). After a subsequent TMA dose at 25 °C, XPS and STM verify that a thermally stable and well-ordered monolayer of Al 2 O 3 is formed on SiGe(110) and (001) surfaces, resulting in the formation of Al–O–Si bonds. The H 2 O 2 ( g ) functionalization provides three times more oxygen sites on the surface and three times as great a TMA nucleation density than does H 2 O( g ) at both 25 °C and 120 °C. STS demonstrates that H 2 O 2 ( g )- and TMA-dosed SiGe surfaces show a Fermi level consistent with unpinning and a local density of states (DOS) without any states between the conduction and valence band edge, indicating an ideal template for further atomic layer deposition (ALD) nucleation of high- k materials on SiGe(110) and (001) surfaces.

We investigate the atom-specific interfacial electronic properties of the epitaxial graphene on Si-terminated SiC substrate using density functional theory (DFT) calculation with van der Waals interaction correction, focusing on the dependency of the local electronic state on the chemical environment. The band structure projected on the respective atomic orbitals of the carbon atoms in the buffer layer and uppermost Si atoms demonstrates that the dangling bonds of these atoms form band structures around the Fermi level. The contribution of each atom to the dangling bond states strongly depends on the chemical environment, i.e., the presence/absence of the interlayer Si-C covalent bond. This difference also affects the atom-specific local density of states of the top-layer graphene through its interaction with the substrate/buffer layer. We demonstrate that the bias voltage dependency of the scanning tunneling spectroscopy (STS) mapping image clearly reflects the presence of the dangling bonds of the buffer layer carbon or uppermost Si atom in the substrate, which would enable the detection of the buried dangling bond with an atomic spatial resolution via STS.

Monolayer hexagonal boron nitride on Rh(111) and graphene on Ru(0001) illustrate a trend of divergence between the density functional theory (DFT) calculated geometric corrugation, and scanning tunneling microscope (STM) measured apparent corrugation, of metal-supported 2D films that feature chemically distinct regions. Notably, the geometric and apparent corrugations differ by up to 2 A for boron nitride/Rh(111), whereas both the DFT-simulated and the experimentally observed STM images agree in the apparent corrugation over a wide range of bias voltages. The disparity is due to unequal contributions of the low/high-lying atoms to the local density of states in the vicinity of the Fermi level. This phenomenon has important implications for the structural characterization of certain supported 2D films, which are being explored for novel electronic and material applications.

Gold nanowire chains are considered a good candidate for nanoelectronic devices since they exhibit remarkable structural and electrical properties. For practical engineering devices, α-wurtzite BeO may be a useful platform for supporting these nanowires, since the atom separation of the BeO (0001) surface is compatible with the Au–Au atom spacing. However, its influence on the nanowire conductivity is unknown. Here, ab initio simulations of adsorption of one gold atom on cleaved BeO (0001) surfaces have been performed to find the most favorable adsorption site. An attractive adsorption was obtained for all the studied sites, but the most favorable site was above the oxygen for the O-terminated surface and above the Be–Be bridge for the Be-terminated surface. A relatively high electron density is observed in the Au O and Au Be bonds, and the local density of states exhibits high peaks in the vicinity of the Fermi energy.

In this paper, we have used low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) to study zigzag or armchair edges of epitaxial graphene on 6H-SiC (0001). The monolayer carbon structures exhibit occasionally one-dimensional ridge (1D) in close vicinity to step edge. This ridge exhibits different edges orientations in armchair–zigzag transition which give rise to different local density of states (LDOS) along this 1D structure. This ridge formation is likely explained by residual compressive in-plane stresses.

The mechanism of H2 dissociative adsorption on Mn-modified Ni(111) surface is investigated and explained using spin-polarized density functional theory (DFT). Potential energy surface (PES) is used to determine the efficient reaction pathway of H2 on the surface. The dissociative adsorption of H2 in the hollow sites with its center-of-mass (CM) positioned on top of Ni atom has low activation barrier. This is lower compared if its CM is on top of the Mn atom. The difference in the reactivity of H2 with Ni and Mn as the CM is corroborated by the positions of the bonding and antibonding orbitals of H2 as it approaches the surface which is verified from local density of states (LDOS). The greater density of states in the region around the Fermi level of the dzz, dxz, and dyz orbitals of the Ni atom explains the low activation barrier obtained for the dissociation of H2 on top of the Ni atom in the Mn-modified Ni(111) surface.

In this study we employ a state-of-the-art pseudopotential method to perform local density of states (LDOS) calculations of n × 1 (n = 5, 7) and (8 × 2) reconstructions induced by the adsorption of rare-earth samarium (RE) in the submonolayer range. We conducted a full comparison between images from scanning tunneling microscopy (STM) and theoretical LDOS. Images taken of both filled and empty states show the effects induced by honeycomb chains and Seiwatz chains. We conclude that LDOS calculations are consistent with the assignment of features observed experimentally by STM.

Large and face dependent neutral fractions have been found recently in the scattering of Li+ by Cu(1 0 0) and Cu(1 1 1) surfaces. These results for high work function surfaces are unexpected within the ‘traditional’ picture of a Li+ ion departing from a jellium surface model. In the present work the Li+/Cu(1 0 0) and Li+/Cu(1 1 1) interacting systems are described by a previously developed bond-pair model based on the localized interactions between the projectile ion and the atoms of the surface, and on the extended features of the electronic band structure through the surface local density of states. By only including the resonant neutralization to the Li atom ground state we explained the face and energy dependences of the measured neutral fractions for large outgoing energy values. We found that the downward shift of the Li ionization level below the Fermi level caused by the short range chemical interactions, is the main responsible of a high neutralization by the resonant mechanism. The remaining differences between theory and experiment values can be explained in terms of the energy gaps and image potential states appearing in these surfaces. The calculated distance behaviours of the energy levels corresponding to the first excited (Li-1s22p) and the negative (Li-1s22s2) atomic configurations indicate that they can also participate in the ion-surface charge exchange process. Fil: García, Evelina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Romero, Marcelo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: González, C.. Czech Academy of Sciences; República Checa Fil: Goldberg, Edith Catalina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina

Recently, an unusual wetting enhancement was observed for the CaF2/(In–Ti) and CaF2/(Cu–Ti) systems. This enhancement cannot be attributed to a chemical reaction between the melt and the substrate, but may occur due to the dissimilarity of the adsorption of the metallic atoms to the substrate. In the present study, ab initio simulations of adsorption of one monolayer of various metal (Me) atoms on the CaF2(1 1 1) surface have been performed for three different atomic sites, in order to understand the nature of the wetting enhancement, to find the reason for the adsorption dissimilarity and to predict other systems that can wet this compound. Each adsorption site was modeled using a periodic two-dimensional slab, a vacuum separation, and a Me layer at a distance of 1–4 A from the surface. An attractive adsorption is obtained only when the Me adsorbs above the terminal F atoms. When transition metals with partly occupied d-states are adsorbed on CaF2, a relatively high electron density is observed in the Me–F bonds, and the local density of states exhibits high peaks in the vicinity of the Fermi energy. This is reflected by the high adsorption energy of these atoms, which may serve as an important detail in understanding the wetting enhancement.

The electronic structure of silicon carbide (SiC) nanowires was studied for the first time using scanning tunneling spectroscopy (STS) and current imaging tunneling spectroscopy (CITS). The STS spectra indicated that the surface of nanowires has an n-type semiconducting behavior which is attributed to nitrogen doping of the sample material. The local density of states (LDOS) showed characteristic peaks in occupied and unoccupied part of the spectra. The origin of the LDOS maxima were discussed in contexts of the dopant-induced states, the subsurface defects, and the surface states related to the local reconstruction process. The work shows the applicability to investigate the SiC nanowires by scanning tunneling microscopy and spectroscopy.

Understanding the electronic changes that take place at the atomic level upon alloying is a key issue in alloy design. The Cu Kα and Al Kα excited XPS and Auger spectroscopy have been used to investigate the role of the major elements in multi component steels from the electronic structure point of view. A combination of the Auger parameter and Core–Core–Valence (CCV) Auger lines were used as the analysis method. The CCV Auger transitions studies, as a probe of the local density of states, revealed that there is some charge transfer between Fe and both Ni and Cr in the steels. However, no significant charge transfer was found between Cr and Ni. The Auger parameter studies of Cr in the steels showed that the charge transfer effect is the main factor affecting the local atomic potential at Cr sites compared to the cohesive energy related factor. It has also been demonstrated that the magnitude of the cohesive energy decreases as the Ni/Cr ratio decreases, which suggests that Ni has a significant role in increasing the cohesive energy of the steels and supports previous quantum mechanical calculations showing that the bulk modulus increases with increasing Ni concentration in Fe 100−( m + n ) Cr m Ni n ternary alloys for the concentration range 13.5 ⩽ m ⩽ 25.5 and 8 ⩽ n ⩽ 24.

Molecular adsorption of formaldehyde on the stoichiometric CeO2(111) and CeO2(110) surfaces was studied using periodic density functional theory. Two adsorption modes (strong chemisorbed and weak physisorbed) were identified on both surfaces. This is consistent with recent experimental observations. On the (111) surface, formaldehyde strongly chemisorbs with an adsorption energy of 0.86 eV to form a dioxymethylene-like structure, in which a surface O lifts from the surface to bind with the C of formaldehyde. A weak physisorbed state with adsorption energy of 0.28 eV was found with the O of formaldehyde interacting with a surface Ce. On the (110) surface, dioxymethyelene formation was also observed, with an adsorption energy of 1.31 eV. The weakly adsorbed state of formaldehyde on the (110) surface was energetically comparable to the weak adsorption state on the (111) surface, but adsorption occurred through a formaldehyde C and surface O interaction. Analysis of the local density of states and charge density differences after adsorption shows that strong covalent bonding occurs between the C of formaldehyde and surface O when dioxymethylene forms. Calculated vibrational frequencies also confirm dioxymethylene formation. Our results also show that as the coverage increases, the adsorption of formaldehyde on the (111) surface becomes weak,more » but is nearly unaffected on the (110) surface. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computations were performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington. Computing time was made under a Computational Grand Challenge “Computational Catalysis”. Part of the computing time was also granted by the National Energy Research Scientific Computing Center (NERSC).« less

We have studied the influence of oxygen pressure during the cyclic annealing used for the cleaning of W(1 1 0) surfaces. For this purpose the surface morphology and electronic properties are measured by means of scanning tunneling microscopy (STM) and spectroscopy (STS), respectively. It is found that the surfaces with impurity atom densities as low as 2 × 10−3 can be obtained by gradually reducing the oxygen pressure between subsequent annealing cycles down to about 2 × 10−8 mbar in the final cycle. Only on the clean surface a bias-dependent spatial modulation of the local density of states (LDOS) is observed at step edges and around impurity sites by STS. In addition, we find a pronounced peak in the occupied states. In combination with density functional theory calculations these features can be traced back to a dispersive pz–dxz-type surface resonance band and the lower band edge of a surface state, respectively.

The adsorption of methylsilane (MeSiH 3 ) on Au(1 1 1) was investigated using density functional theory (DFT) within a generalized gradient approximation (GGA). Two preferred chemisorption sites are identified: the hollow site and an atop site with an ejected gold substrate atom. Both of these configurations result in a tetracoordinate Si with a distorted tetrahedral geometry. The energy of adsorption is calculated allowing an analysis of the preferred binding geometry as a function of coverage. The relation of the supermolecular length scale pattern that emerges from a spinodal decomposition of the two phases arising from the two binding geometries is discussed. The pattern observed in the STM images is shown to be consistent with the local density of states calculated for the two different binding geometries.

We present a theoretical study (within the density functional theory) of the influence of thermal fluctuations of the Ge(0 0 1) structure on its electronic properties, mainly in the context of possible metallization of this surface observed in experiment. Analysis is based on the results of three series of long-time molecular dynamics (MD) simulations performed for p(1 × 2), c(2 × 4) and p(2 × 4) surface unit cells. We have found that for the p(1 × 2) unit cell thermal fluctuations lead to the appearance of a sharp peak in the density-of-states distribution at the Fermi level, and consequently, to metallization of the germanium surface, while the energy structure of the c(2 × 4) reconstructed surface remains non-metallic even at high temperatures. This result is in an agreement with recently published scanning tunneling spectroscopy data. Our MD simulations show that, depending on the translational symmetry of the surface, thermal fluctuations may modify its electronic structure in quite a distinct way. The obtained results also indicate that the observed Ge(0 0 1) surface metallization is an averaged effect of the variations of the local density of states caused by thermal fluctuations.

The adsorption properties of CO on Pt 3 Sn were investigated by utilizing quantum mechanical calculations. The (1 1 1), (1 1 0) and (0 0 1) surfaces of Pt 3 Sn were generated with all possible bulk terminations, and on these terminations all types of active sites were determined. The adsorption energies and the geometries of the CO molecule at those sites were found. Those results were compared with the results obtained from the adsorption of CO on similar sites of Pt(1 1 1), Pt(1 1 0) and Pt(0 0 1) surfaces. The comparison reveals that adsorption of CO is stronger on Pt surfaces; this may be the reason why catalysts with Pt 3 Sn phase do not suffer from CO posioning in experimental works. Aiming to understand the interactions between CO and the metal adsorption sites in detail, the local density of states (LDOS) profiles were produced for atop-Pt adsorption, both for the carbon end of CO for its adsorbed and free states, and for the Pt atom of the binding site. LDOS profiles of C of free and adsorbed CO and Pt for corresponding pure Pt surfaces, Pt(1 1 1), Pt(1 1 0) and Pt(0 0 1) were also obtained. The comparison of the LDOS profiles of Pt atoms of atop adsorption sites on the same faces of bare Pt 3 Sn and Pt surfaces showed the effect of alloying with Sn on the electronic properties of Pt atoms. Comparison of LDOS profiles of the C end of CO in its free and atop adsorbed states on Pt 3 Sn and LDOS of Pt on bare and CO adsorbed Pt 3 Sn surface were used to clear out the electronic changes occurred on CO and Pt upon adsorption. The study showed that (i) inclusion of a Sn atom at the adsorption site structure causes dramatic decrease in stability which limits the number of possible CO adsorption sites on Pt 3 Sn surface, (ii) the presence of Sn causes angles different from 180° for M–C–O orientation, (iii) the presence of Sn in the neighborhood of Pt on which CO is adsorbed causes superposition of the 5σ/1π derived-state peaks at the carbon end of CO and changes in adsorption energy of CO, (iv) Sn present beneath the adsorption site strengthens the CO adsorption, whereas neighboring Sn on the surface weakens it for all Pt 3 Sn surfaces tested and (v) the most stable site for CO adsorption is the atop-Pt site of the mixed atom termination of Pt 3 Sn(1 1 0).

We present a theory to study the temperature-dependent behavior of surface states in a ferromagnetic semi-infinite crystal. Our approach is based on the single-site approximation for the \emph{s-f} model. The effect of the semi-infinite nature of the crystal is taken into account by a localized perturbation method. Using the mean-field theory for the layer-dependent magnetization, the local density of states and the electron-spin polarization are investigated at different temperatures for ordinary and surface transition cases. The results show that the surface magnetic properties may differ strongly from those in the bulk and the coupling constant of atoms plays a decisive role in the degree of spin polarization. In particular, for the case in which the exchange coupling constant on the surface and between atoms in the first and second layer is higher than the corresponding in the bulk, an enhancement of surface Curie temperature and hence the spin polarization can be obtained., 9 pages,8 figures

We present a study of the vibrational properties of the (1 0 0) and (1 1 0) surfaces of nickel oxide. We performed molecular dynamics simulations over a wide temperature range and we calculated the phonon local density of states (LDOS) of the anionic and cationic sublattices as a function of the distance of the atomic planes from the surface. We discuss the differences observed at T = 300 K in the phonon LDOS compared to the bulk as well as the differences observed among the two surfaces due to their specific atomic structure. As far as the temperature behavior of the phonon LDOS is concerned for the (1 0 0) surface we have preservation of its main characteristics up to high temperatures while for the (1 1 0) a modification of the phonon LDOS is observed above T = 1000 K. The difference in behavior of the two surfaces is related to the stability of the (1 0 0) surface and the modification of the atomic structure of the surface planes of the (1 1 0) surface above T = 1000 K.

Density functional theory calculations have been used to study the electronic structure of the O(2 × 1)/Cu(1 1 0) surface. In particular a surface state at the zone boundary Y¯-point of the surface Brillouin zone, that has been experimentally observed in STS spectra at an energy of + 0.56 eV, is also found in our calculations at about the same energy. The energy dependence of the local density of states shows a prominent feature, that is identified with the surface state at the Y¯-point, in agreement with measured dI/dV-spectra. The dI/dV-maps slightly above the surface state energy show a modulation in the [0 0 1] direction with the lattice periodicity (0.36 nm) that reflects the spatial dependence of the charge density. Our results are consistent with the assumption of an added row reconstruction of the Cu(1 1 0) surface after O adsorption.

The adsorption of the two butane isomers on Pt(1 0 0) has been characterised with use of density functional simulations. The adsorption energies corresponding to various adsorption configurations were evaluated in good agreement with experimental values. Limited changes of the molecular structure were evidenced. The C–H bond length increases at a degree depending on the surface-hydrogen distance, while the C–C bond length remains similar to that of the free molecule. The surface on-top Pt sites exert a preferential attraction on the molecule, probably through the interaction with the H atoms. The local density of states curves around H as well as C of the adsorbed molecules show dispersed states below the metal Fermi level indicating a molecule–Pt mixing demonstrating a chemical interaction.

In this paper we simulate STM and STS experiments for CO monomers and dimers on Cu(1 1 1) surface. We show that the contrast of STM images can be attributed to interference effects between tunneling channels, and suggest that functionalizing the microscope tip improves the channel selectivity of STM. Furthermore, we show that voltage and position dependent tunneling spectra also reflect the same interference effects, but adds the energy resolution to the channel analysis. Especially in the case of nonresonant tunneling, STS measures local density of states only indirectly. The present study suggests that STS in constant height mode can be used in investigating the phase and energy sensitivity of tunneling channels in adsorbate molecules and nanostructures.

The adsorption properties of CO on experimentally verified stepped Pt 3 Sn(1 0 2) surface were investigated using quantum mechanical calculations. The two possible terminations of Pt 3 Sn(1 0 2) were generated and on these terminations all types of possible adsorption sites were determined. The adsorption energies and geometries of the CO molecule for all those sites were calculated. The most favorable sites for adsorption were determined as the short bridge site on the terrace of pure-Pt row of the mixed-atom-ending termination, atop site at the step-edge of the pure row of pure-Pt-ending termination and atop site at the step-edge of the pure-Pt row of the mixed-atom-ending termination. The results were compared with those for similar sites on the flat Pt 3 Sn(1 1 0) surface considering the fact that Pt 3 Sn(1 0 2) has terraces with (1 1 0) orientation. The LDOS analysis of bare sites clearly shows that there are significant differences between the electronic properties of Pt atoms at stepped Pt 3 Sn(1 0 2) surface and the electronic properties of Pt atoms at flat (1 1 0) surface, which leads to changes in the CO bonding energies of these Pt atoms. Adsorption on Pt 3 Sn(1 0 2) surface is in general stronger compared to that on Pt 3 Sn(1 1 0) surface. The difference in adsorption strength of similar sites on these two surface terminations is a result of stepped structure of Pt 3 Sn(1 0 2). The local density of states (LDOS) of the adsorbent Pt and C of adsorbed CO was utilized. The LDOS of the surface metal atoms with CO-adsorbed atop and of their bare state were compared to see the effect of CO chemisorption on the electron density distribution of the corresponding Pt atom. The downward shift in energy peak in the LDOS curves as well as changes in the electron densities of the corresponding energy levels indicate the orbital mixing between CO molecular orbitals and metal d-states. The present study showed that the adsorption strength of the sites has a direct relation with their LDOS profiles.

We present results concerning the dynamical behavior of a Ni3+ adsorbate on a NiO(0 0 1) surface obtained by molecular dynamics simulations. In a first place, we examined at low temperature the position of the Ni3+ ion as an adatom on the surface and the corresponding modification of its local environment as reflected on the pair-wise radial distribution function. The calculation of the vibrational properties of the adatom by means of the phonon local density of states (LDOS) shows that there is an anisotropic behavior both in the two principal in-plane directions as well as in the direction normal to the surface in accordance with the structural results. We compare the phonon LDOS of the Ni3+ adatom with the corresponding results for the Ni2+ adatom and the Ni2+ surface cations. Static energetic calculations are indicative that the exchange of the Ni3+ ion with a surface Ni2+ ion could be favorable. Such a behavior is confirmed by results observed at temperatures higher than 700 K where the Ni3+ adsorbate is located on a substitutional position on the surface and not on adatom position. The exchange takes place through simple or double exchange mechanisms. The structural and dynamical behavior of the Ni3+ ion at the substitution position was investigated in the temperature range 700–2000 K through the calculation of the pair distribution function, the relaxed interlayer relative position (RIRP), mean-square displacements (MSDs) and phonon LDOS. Results show that in comparison with the Ni2+ surface ions the Ni3+ ion at substitution position is more tightly bound especially in the direction normal to the surface as is indicated by the local structure and the contraction it presents as well as its phonon LDOS. As temperature increases the binding of the Ni3+ ion becomes less important as reflected on the physical properties mentioned above.

We have investigated the half-metallicity and magnetism at the (1 1 0) surface of CrP by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). From the calculated local density of states (LDOS), we found that the (1 1 0) surface of CrP preserves the half-metallicity, but the band gaps (∼1.1 eV) of the minority states for the surface Cr and P atoms are much reduced from the bulk value (∼1.9 eV). The magnetic moment of the P is coupled antiferromagnetically to that of the Cr. The magnetic moment of surface Cr atom is calculated to be 3.31μB which is increased by 10% compared to the bulk value, 3.00μB.

Intermixing, growth, geometric and electronic structures of gold films grown on antiferromagnetic stacking body-centered-tetragonal manganese (0 0 1) films were studied by means of scanning tunneling microscopy/spectroscopy at room temperature in ultra-high vacuum. We found stable ordered c(2 × 2)-MnAu(0 0 1) alloy layers after depositing Au on pure Mn layers. Since at the fourth layer (5 × 23)-like Au reconstruction appears instead of the c(2 × 2) structure and local density of states peaks obtained on the c(2 × 2)-MnAu surface disappear, pure Au layers likely grow from the fourth layer.

Scanning tunneling microscopy (STM) was used to study the surface structures of dry-prepared and di-chloroethane-treated HOPG samples. Both triangular and honeycomb structures were simultaneously observed with the same tip at room temperature around a strand (grain boundary) on the HOPG surface. This observation did not support the tip effect in STM imaging explanation for HOPG in literature. A general layer-sliding model was utilized to explain the experimental results: sliding of the HOPG topmost layer was used to explain the origins of the triangular and honeycomb structures, and molecule intercalation into inter-layer spacing between the first and second layers of HOPG induced inhomogeneous deformation of the HOPG topmost layer that accordingly generated the Moire patterns of the HOPG sample in di-chloroethane.

The adsorption of vinyl fluoride on the rutile TiO 2 (1 1 0) surface has been simulated, on the basis of a recently proposed experimental model, using hybrid-exchange density functional theory. Different surface coverages have been considered and the lateral interaction between adsorbed vinyl fluoride molecules has been quantified through a simple model of nearest and next nearest neighbouring molecules. The vibrational frequencies of the adsorbed molecule have been calculated and are found to be in excellent agreement with those observed providing support for the proposed adsorption model. The effect of the adsorption on the electronic structure of the molecule and the surface have been characterised by computing electrostatic potential maps and the local density of states.

The potential energy surface and the electronic properties for the migration of an extra Si atom in the Si(1 1 1)(7 × 7) surface are studied by performing tight-binding calculations. Our predicted diffusion region and the lowest energy barrier of an extra Si atom hopping across the cell boundary in the (7 × 7) reconstructed surface match the experimental observations and previous theoretical results very well. Based on our calculated electronic structures of the system, we find that the extra Si atom diffusing along the favored paths in the Si(1 1 1)(7 × 7) surface is driven by decreasing the density of occupied states at/nearby the fermi energy level as much as possible. Furthermore, we point out the fact that the calculated local density of states at/below the fermi energy level can significantly reflect the different local bonding features of the diffused Si atom at different sites in the surface is strongly associated with the covalent bonding character in the system in nature. In addition, we suggest that the observed brighter spot in the STM image from experiment most probably corresponds to the adsorption of an extra Si atom nearby the center adatom in the Si(1 1 1)(7 × 7) surface yet.

Density functional theory with generalised gradient approximation (GGA-PW91) has been used to study the adsorption of CH 4 on Pt(1 0 0) surface at a coverage of 0.25 ML in a (2 × 2) unit cell. In all calculations the CH 4 and the top layer of the metal were allowed to relax. Optimised geometries and adsorption energies for CH 4 on three sites, namely the top, bridge and hollow sites, are presented considering various molecular orientations with respect to the surface. The calculated geometries are in good agreement with the experimental observations. The spread of adsorption energies (from −44 meV to −59 meV) over the three sites is quite small, weakly dependent on the molecular orientation, suggesting a weak interaction between CH 4 and the Pt(1 0 0) surface and a weakly corrugated surface potential of the system. The evolution of C and H local density of states (LDOS) on adsorption of the molecule at top site indicates that the orbitals of H and C become involved in bonding with metal, whereas the analysis of Pt LDOS shows that CH 4 interacts chemically with the Pt surface.

The principle and method of atomic-scale spin-polarized scanning tunneling microscopy is discussed, and its application to the case of the (0 1 0) surface of g-phase Mn3N2 is presented. For this surface, new proofs of the spinpolarized effect are presented, and it is also shown that the spin-polarized effect can turn on and off with small changes to the tip apex which can occur during scanning; this indicates that the tip magnetic density of states can and does change at certain points during the experiment. It is also shown how to model height profile data using spin-polarized local density of states of the sample. As well, it is shown how to relate the equation for the total spin-polarized height profile to those of the separated magnetic and non-magnetic height profiles. Comparison of the experimental height profiles to the simulated height profiles based on spin-polarized local densities of states calculated from first-principles density functional theory is shown. In particular, a comparison is made between the results of using the atom-superposition method vs. a full Tersoff–Hamman simulation method. For the case of the transition metal nitride system here, it is shown that the latter method is crucial for a full understanding due to the directionality of the atomic orbital lobes.

Adsorption of H at a coverage ranging up to 2 monolayers with occupation of fcc and hcp sites and insertion in subsurface sites of Pt(1 1 1) is studied with use of a DFT-based ab initio method. It is shown that no important repulsion between the adatoms grows up to 1 ML, justifying the usual wisdom that 1 H atom adsorbs per Pt surface atom. Beyond this coverage, the surface occupation of both the fcc and the hcp sites become disfavoured and H starts to occupy subsurface sites. Both occupation of octahedral and tetrahedral insertion sites were studied. It is concluded that configurations involving fcc surface sites associated with tetrahedral subsurface sites are favoured. The evolution of the Pt local density of states (LDOS) with the coverage is reported. It is shown that the presence of H in the subsurface decrease the surface Pt chemical reactivity. Finally, stability curves of the Pt–H system as a function of H2 pressure and temperature are given, showing that subsurface H is likely to be present under usual catalytic reaction conditions.

Characteristic features of the bulk band structure of niobium were verified by scanning tunneling spectroscopy (STS). Two different techniques were employed: measurement of standard I–V curves carried out at constant tip–sample separation as well as of Z–V characteristics obtained at constant tunneling current allowing to extend the accessible energy range. Within the range from −5 to +5 eV, the local density of states (LDOS) as determined by STS reveals features which can be attributed to critical points of the theoretically calculated bulk band structure of Nb. The agreement of the STS spectra with the calculated density of states as well as with published photoelectron-spectroscopy data is remarkable.

The spin-resolved electronic states of Na atoms adsorbed on Fe(0 0 1) surfaces have been calculated using full-potential linearized-augmented-plane-wave (FLAPW) method to interpret our spin-polarized metastable-atom deexcitation spectroscopy (SPMDS) measurements reported previously. The spin dependence of the local density of states in the vacuum region calculated for the Fe(0 0 1)-c(2 × 2)-Na and (2 × 2)-Na structures was found to be consistent with the spin asymmetry in the SPMDS spectra and its Na coverage dependence.

The (0 1 0) surface of η-phase Mn3N2 grown on MgO(0 0 1) by molecular beam epitaxy is studied using scanning tunneling microscopy. The images show that the surface is composed of rows with spacing of 6.07 A. Two types of domains with their c-planes perpendicular are observed in which the domain boundary is oriented at ∼45° to the c-planes. In other cases, the angle between the c-planes of the two domains is closer to 87°, consistent with a twin model in which the two domains meet along a (1 0 1) plane. Atomic resolution images vary with the sample bias. At lower sample bias, primarily Mn1 atoms are observed. At higher sample bias, both Mn1 and Mn2 atoms can be resolved. The dependence of the atomic resolution image on sample bias is explained by the ratio of the integrated local density of states of Mn1 to that of Mn2, which are based on first-principles theory. Simulations of the STM atomic-scale height profiles using the integrated local densities of states vs. sample bias voltage are in excellent agreement with the experimental line profiles.

We calculated scanning tunneling microscope images (STM) of Cu atoms adsorbed on a Si(1 1 1)-1 × 1 structure within the Tersoff–Hamann approximation. The following configurations were considered: CuSi substitutional, CuSi 2 interstitial and Cu 2 Si with Cu atoms residing both in H 3 sites and substituting Si in the top layer of the Si(1 1 1) double layer. Our images of the CuSi and Cu 2 Si show hexagonal arrays of deep crater-like features, surrounded by bright protrusions. Their shape depends on the bias voltage, in accordance with experimental findings. Additionally, we found shallow dark spots, whose contrast also changes with applied bias voltage. The interstitial CuSi 2 resembles a pure Si(1 1 1)-1 × 1 structure. Our calculations suggest that the origin of craters observed in the experiments cannot unambiguously be connected solely to the topographic features, but that the local density of states plays an important role in the image formation.

An STM-UHV study of the deposition of titanium bis-phthalocyanine under high vacuum (UHV) conditions on two different substrates such as GaAs(1 0 0)- β 2-(2 × 4) and highly oriented pyrolytic graphite (HOPG) has been carried out. An STM spectroscopic analysis on the local density of states has been also performed. In the case of GaAs as substrate, the STM images show that the molecules align themselves preferentially along the dimer rows, typical of the (2 × 4) reconstruction, thus revealing the fundamental role of the interaction between the molecule and the reconstructed substrate in orienting the adsorbed molecules. In the case of HOPG, the images indicate the formation of irregular channels thus suggesting an auto-assembling of the molecules between themselves rather than a strong interaction with the substrate, as in the GaAs case.

Injection of tunneling electrons and holes from the probe tips of a scanning tunneling microscope was found to enhance the hopping motion of Cl atoms between neighboring dangling-bond sites of Si dimers on Si(1 0 0)-(2 × 1) surfaces, featured by the rate of hopping linearly dependent on the injection current. The hopping rate formed peaks at sample biases of V S ∼+1.25 and −0.85 V, which agree with the peaks in the local density of states spectrum measured by scanning tunneling spectroscopy. The Cl hopping was enhanced at Cl-adsorbed sites even remote from the injection point. The Cl hopping by hole injection was more efficiently enhanced by sweeping the tip along the Si dimer row than by tip-sweeping along the perpendicular direction. Such anisotropy, on the other hand, was insignificant in the electron injection case. All of these findings can be interpreted by the model that the holes injected primarily into a surface band originated from the dangling bonds of Si dimers propagate quite anisotropically along the surface, and become localized at Cl sites somehow to destabilize the Si–Cl bonds causing hopping of the Cl atoms. The electrons injected into a bulk band propagate in an isotropic manner and then get resonantly trapped at Si–Cl antibonding orbitals, resulting in bond destabilization and hopping of the Cl atoms.

We report results of gradient-corrected pseudopotential-based density functional theory calculations on bulk Fe 3 C in the cementite structure and its (0 0 1), (1 1 0), (0 1 1), (1 0 0), (1 0 1), (0 1 0), and (1 1 1) surfaces. Bulk properties are in reasonable agreement with available experimental data. The cementite local density of states shows predominantly metallic character, along with some polar covalent bonding contributions (charge transfer from iron to carbon) for both bulk and surfaces. We predict cementite surface energies in the range of 2.0–2.5 J/m 2 , most of which are lower than all pure Fe surface energies. In particular, we predict the Fe 3 C (0 0 1) surface to be the most stable and the Fe 3 C (1 0 0) surface to be the least stable. We show that greater stability is associated with localized Fe–C bonding at the surface, smoother surfaces created, e.g., by large C atom relaxation into the bulk, and more uniform coordination at the surface. The relatively greater stability of Fe 3 C surfaces is suggested to provide the driving force for cementite to form at the surfaces of bcc iron. Implications for the carburization erosion mechanism for steel, such as cracking and melting, are discussed.

We have performed high temperature tight-binding molecular dynamics simulations as well as 0 K calculations to study the motion of the surface dimers near different types of steps. We compare these results with the corresponding results for dimers in a clean terrace, far from any defect. We have found that the dimers in step A edge flip slower than those in a clean surface, in agreement with STM observations, while those in rebounded step B edge flip faster. These differences in the energy barriers are reflected in the electronic structures, in particular in the local density of states (LDOS) near the energy gap. Finite temperature and 0 K calculations predict the same relevant flipping barriers for dimers near step A edge, but the agreement is not as good for dimers close to rebounded step B edge, where correlated flipping events are important. In this case, finite temperature molecular dynamics simulations are more efficient to estimate the effective barrier. Some similarities in the dynamics are found between dimers close to single dimer vacancies (SDV), steps, and steps with kinks. First neighbours of an SDV, upper step B edge dimers, and dimers close to kinks in step A have similar local environment. Therefore all tend to flip faster, and spend most of the time symmetric. On the other hand, second neighbours of an SDV, upper step A edge dimers, and dimers close to kinks in step B tend to flip slower.

We have analyzed field electron emission from atomically sharp tips on Al(1 0 0) surfaces by using density functional calculations including effects of electric fields and currents. We have obtained a pronounced secondary peak in total energy distribution of emitted electrons in the case of a 30-atom protrusion terminated by a single atom. We have also clarified that the appearance of the secondary peak requires sufficient local barrier reduction in front of the apex atom of protrusions, which is caused by strong electric field and sharp geometry. Further, we have shown that analyses of local density of states are not necessarily sufficient to understand the features of field emission.

Using molecular dynamics and a rigid ion potential we studied the vibrational properties of a Σ5(3 1 0)[0 0 1] tilt grain boundary in NiO. We calculated the local density of states and the mean square displacement (MSD) of the cation and ion sublattice for a wide temperature range. We examined their behaviour in the directions parallel and normal to the boundary as a function from the grain boundary plane. We found that the local phonon density of states of the sites of the boundary are altered with comparison to the bulk presenting in general a shift towards lower frequencies in the direction normal to the boundary and toward higher frequencies in the direction parallel to the grain boundary. This anisotropy, which is conformed by the results of the MSDs, is maintained up to high temperatures. We have also observed that the increase of temperature leads to the gradual loosening of the binding of atoms.

We study the effects of nonmagnetic impurities on the electronic states of CuO 2 planes in copper oxides. We calculate the local density of states at the copper sites and the oxygen sites, around the impurities. The local density of states in the CuO 2 plane with the impurities increases or decreases, depending on the energy ω , as compared with those without the impurities. The spatial distribution of the local density of states has an anisotropic shape in the vicinity of the Fermi energy ω ∼ ω F . At ϵ p (p-level) ω ϵ d (d-level), there is a difference in the spatial distribution of the local density of states between the d- and p-electrons, while at other energies, those of the d- and p-electrons are practically the same.

We present a self-consistent calculation of the electronic structure for the (1 1 0) surface of equiatomic XTi (X=Fe, Co, and Ni) alloys in the B2 (CsCl) structure. The results were obtained using the film linearized augmented-plane-wave method. We have analyzed the change of the local density of states, the valence electronic charge distribution and the calculated work function in the series FeTi, NiTi, and CoTi alloys. It has been found that the bond ionicity at the surface is enhanced and the work function is reduced from FeTi to NiTi. The trend to surface segregation and chemical activity for the (1 1 0) surface of the studied alloys is discussed.

A room-temperature scanning tunneling spectroscopy study has been conducted on single molecules and multilayers of C 60 molecules adsorbed on the Si(1 0 0)-(2×1) surface without any post-annealing. For single isolated molecules, four peaks in the local density of states are observed that can be well attributed to molecular energy levels. Scanning tunneling microscope spectroscopy has also been carried out on molecules that are moved across the silicon surface. Spectroscopy on multilayers of C 60 shows broad, smeared out features for the first monolayer, while the third layer results resemble those of single isolated molecules. We attribute the variations in electronic spectra to differing inter-molecular interactions in the first and upper layers of C 60 .

Employing β-NMR on 8 Li adsorbed on Ru(0 0 1) the local (at the Li nucleus) density of states at the Fermi energy has been determined as function of Li coverage. It is independent of coverage below 0.2 monolayer (ML) and saturates at a twice as large plateau value beyond 1 ML. Calculations employing all electron density functional theory reproduce qualitatively the trend of the data. At low and high coverages, agreement between theory and experiment is almost quantitative. In addition, new terrace diffusion parameters for Li on Ru(0 0 1) have been obtained.

At the surface of the bulk Al 70 Pd 20 Mn 10 quasicrystal, different surface phases can be induced upon changing the chemical composition. Using combined Auger electron and X-ray photoelectron spectroscopy, information was obtained on the local density of states of the alloy components. In the quasicrystalline state the Mn 3d band moves away from the Fermi level thus lowering the density of states and opening the pseudogap.

We found that electron injection from the probe tips of scanning tunneling microscopes enhances the diffusion and desorption of Cl atoms on a Si(1 1 1)-(7×7) surface, featured by a significant peak at a sample bias of ∼+4 V for the diffusion, the linear dependence on the injected current, the spatial spread of the effect laterally over a range of ∼10 nm from the tip position without extending beyond the step edges. The local density of states spectrum in the chlorinated Si surface experimentally measured by scanning tunneling spectroscopy exhibits a peak of Cl origin at +4.1 eV which coincides with the peak in the bias dependence. These facts are well interpreted by the model that electrons primarily injected to empty surface bands propagate until they are resonantly localized at Si–Cl anti-bonding states, which then leads to destabilization or weakening of the bonds resulting in Cl atom diffusion.