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We compare step morphologies on surfaces of Al-rich metallic alloys, both quasicrystalline and crystalline. We present evidence that the large-scale step structure observed on Al-rich quasicrystals after quenching to room temperature reflects equilibrium structure at an elevated temperature. These steps are relatively rough, i.e., have high diffusivity, compared to those on crystalline surfaces. For the fivefold quasicrystal surface, step diffusivity increases as step height decreases, but this trend is not obeyed in a broader comparison between quasicrystals and crystals. On a shorter scale, the steps on Al-rich alloys tend to exhibit local facets (short linear segments), with different facet lengths, a feature which could develop during quenching to room temperature. Facets are shortest and most difficult to identify for the fivefold quasicrystal surface.

The room temperature deposition of PTCDA on hydrogen passivated Si(1 1 1), as a function of evaporation temperature and dosing time, has been studied by STM. At low evaporation temperature, 200 °C, clusters with an average size of 3.5 nm are formed on the surface. The mobility of the small clusters is so high, even at room temperature, that most of the clusters are trapped at surface defects. By increasing the evaporation temperature to 230 °C, larger clusters are formed which have lower mobility. The growth process is identified as a Volmer-Weber mechanism. On increasing the evaporation temperature further to 250 °C, crystals with dendritic shape are formed with an average size of 150 nm. The terraces of the crystal are formed with the (1 0 2) basal plane of the α-phase. Molecular resolution on the terrace also allows us to identify the molecular mechanism involved in the growth of the dendritic crystals.

The adsorption induced surface chirality has been examined with high resolution STM observation of ordered glycine on Cu{1 1 0} surface. Two domains with different internal molecular arrangement have been identified. The homochiral domain shows a pseudo-centered structure while the heterochiral domain presents a clear glide plane symmetry. The lateral relationship between these two domains has also been analysed, which gives the details of the assignment of individual features in the STM images.

High resolution electron energy loss spectroscopy has been used to study the adsorption of water on the clean and Na modified SrTiO 3 (1 0 0)-1×1 surfaces. The vibrational spectrum of clean SrTiO 3 shows three dipole active bands, characteristic of perovskite materials, at 170, 460 and 730 cm −1 . In good agreement with previously published experimental results, we show that water does not adsorb on the clean defect free SrTiO 3 (1 0 0)-1×1 surface. On the other hand, the vibrational spectra of the Na modified SrTiO 3 (1 0 0)-1×1 surface exposed to water shows clearly an OH stretching vibration which indicates the presence of hydroxyl species at the surface. The continuous observation of the 1×1 pattern in low energy electron diffraction indicates that the surface reconstruction is preserved even after exposure of the surface to water.

The adsorption of 4-aminobenzoic acid on the clean and Na modified Si(1 0 0)-2×1 surfaces has been studied by high-resolution electron energy loss spectroscopy (HREELS) and near edge X-ray absorption fine structure. HREELS indicates that adsorption of 4-aminobenzoic acid on Na/Si(1 0 0)-2×1 occurs through cleavage of the OH bond in the carboxylic group. The 4-aminobenzoate species are bonded through the formation of a delocalized bond between the deprotonated carboxylate group and the adsorbed Na atom, leading to species in a bidentate coordination. At room temperature, 4-aminobenzoate saturation is reached at a coverage of one 4-aminobenzoate species per Na or Si dimer. At this coverage, the molecules are tilted in the polar direction by 61±5° to the surface plane. In contrast, we observe monodentate 4-aminobenzoate species following the exposure of Si(1 0 0)-2×1 to 4-aminobenzoic acid.

The adsorption of maleic anhydride on Si(1 0 0)-2×1 has been studied with high resolution electron energy loss spectroscopy and near edge X-ray absorption fine structure (NEXAFS). We observe that at low coverages the adsorption occurs mainly through cycloaddition of the CC bond to the dangling bonds of Si–Si dimers, analogous to the behaviour of cyclopentene. The Si–Si dimer bonds are not cleaved in the chemisorption, process as the continued observation of a 2×1 pattern in low energy electron diffraction shows. In the NEXAFS spectra, the absence of a π * resonance associated with the CC bond, confirms the rehybridisation of the carbon atoms in the olefin bond. The angular dependence of the resonance intensity indicates a molecular plane inclination of 48° to the substrate plane. At higher dosages, chemisorbed maleic anhydride species are bonded to the Si surface atoms via a single Si–C linkage with retention of the CC double bond. In this case, the dissociated hydrogen bonds to one of the neighbouring Si atoms.

The passivation of Si(1 0 0), Si(1 1 3) and Si(1 1 5) with ethanol, isopropanol and tert -butanol has been studied with high resolution electron energy loss spectroscopy (HREELS) and low electron energy diffraction (LEED). The HREEL spectra show clearly that the alcohols chemisorb dissociatively with the formation of a Si–O–C linkage on the three surfaces. We observe a considerable chemisorption of water on the ethoxy and tert -butoxy passivated Si(1 0 0)-2×1 surfaces. From the disappearance of the 2×1 LEED pattern, it can be concluded that the chemisorption of water occurs through a cleavage of the Si–Si dimer bond. In contrast, isopropoxy species on Si(1 0 0)-2×1 reduces dramatically the reactivity towards water. However, Si(1 1 3) and Si(1 1 5) turn out to be much more reactive towards water molecules after the adsorption of any of the alcohols.

The structure of benzoate on Na/Si(100)-2×1 has been studied by high resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and near edge X-ray adsorption fine structure spectroscopy. At room temperature, benzoic acid (C6H5COOH) chemisorbs on Na/Si(100)-2×1 through a cleavage of the OH bond in the carboxylic group. The benzoate molecules formed are bonded exclusively to the sodium atoms in a bidentate coordination, in which the oxygen atoms are equivalent. At room temperature, benzoate saturation on Na/Si(100)-2×1 is reached at a coverage of one benzoate species for each Na atom or silicon dimer. At this coverage, the molecules are tilted in polar direction by 62°±4° to the surface plane and azimuthally rotated by 41°±4° with respect to the [01 1 ] surface azimuth. We propose an adsorbate structure, in which the benzoate molecules are oriented parallel to each other in densely packed rows.

The surface structure of ultra-thin Al 2 O 3 films on NiAl(110) and Ru(0001) was investigated by using high-resolution electron energy loss spectroscopy (HREELS). On a semi-empirical basis, the three phonon loss features, ν 1 (380∼430 cm −1 ), ν 2 (620∼660 cm −1 ), and ν 3 (850∼900 cm −1 ), of crystalline Al 2 O 3 films were assigned to collective excitations of the microscopic vertical stretching motion of in-phase O–Al layers and to the stretching motions of the tetrahedrally and octahedrally coordinated Al–O species, respectively. To a good approximation, the distinct observation of the ν 1 mode in the HREEL spectra of Al 2 O 3 films can be a sign for the synthesis of a vertically well-defined Al 2 O 3 phase. The relative intensity between the ν 2 and the ν 3 loss features has been used to determine the most probable oxide structure, amorphous, transition, or α-like, by using the relative site occupation ratio of Al 3+ cations to hexagonal closely packed O 2− anions.

Exposure of Cu(110) at 90 K to a sub-monolayer amount of benzoic acid gives rise to both benzoate and undissociated acid species. Low coverage STM shows the diffusion and re-arrangement of molecules on the edge of clusters, while higher coverage images show one-dimensional dimeric features, assigned to benzoic acid dimers, growing anisotropically in the 〈001〉 direction. At higher temperature, a different dimer chain along the (±4, 3) directions can be observed. From temperature-dependent FTIR, the deprotonation of the flat-lying species takes place between 120 and 170 K. Further annealing shows crystallization at 183 K, which results in the periodic α-phase. In contrast, for the multilayer surface, the desorption of multilayer starts at 200 K and results in all molecules being upright in the c(8×2) structure.

The hybrid inorganic–organic molecule γ-glycidoxypropyltrimethoxysilane is used as an adhesion promoter because of its ability to act as a molecular bridge between chemically different phases. In this paper we concentrate on the interaction of the organofunctional glycidoxy end chain of this molecule on a γ-Al2O3(111) mimic created by oxidation of NiAl(110). In order to understand better the interaction of this functionality, the glycidoxy moiety was modelled using glycidyl isopropyl ether and epoxyhexane. Reflection–absorption infrared spectroscopy studies of these model compounds demonstrate that monolayer adsorption on the γ-Al2O3 film is non-dissociative, with both molecules being only weakly perturbed, supporting the idea that the organofunctional end group in hybrid inorganic–organic adhesion promoters remains intact, available to react potentially with the adhesive on application.

Azimuthal orientations of 9-anthracene carboxylate (9-AC) on clean and p(2×1)O/Cu(110) surfaces were determined from a reflectance anisotropy spectroscopy (RAS) signal derived from an intramolecular electronic transition. The magnitude of the molecular signal on the p(2×1)O/Cu(110) surface is 4–5 times larger than on the clean surface. We present a complete vibrational assignment of adsorbed 9-AC based on Fourier transform infrared and on- and off-specular high resolution electron energy loss spectroscopy (HREELS) and ab initio calculations. Correlation of the off-specular HREELS on p(2×1)O/Cu(110) with the RAS results demonstrates that the magnitude of the RAS signal depends on the degree of azimuthal orientation.

The adsorption of benzoic acid on Na–Si(100)-2×1 ( Θ Na =0.5) at room temperature leads to benzoate in a bidentate coordination. High-resolution electron energy loss spectroscopy spectra show an intense ν s (OCO) stretching vibration, which is characteristic for benzoate aligned perpendicular to the substrate surface. In contrast, we observe monodentate benzoate species following the exposure of Si(100)-2×1 to benzoic acid at room temperature. On both surfaces, the dissociated hydrogen atom bonds to one of the silicon surface atoms. Removal of benzoate from Na–Si(100)-2×1 is observed after heating the silicon substrate to 300°C for 1 min.

Upon submonolayer deposition of Azure A molecules onto reconstructed Au(1 1 1), two-dimensional quasi-rectangular islands are observed by low-temperature scanning tunneling microscopy. Strikingly, the 22 x root 3 reconstruction with alternating hexagonal close packed (hcp) and face centered cubic (fcc) domains of the native Au(1 1 1) surface layer is found to be strongly modified underneath the self-assembled islands of Azure A molecules. The bridge-hcp-bridge-fcc-bridge period of 63 angstrom on clean Au(1 1 1) is expanded by about 12% and occasionally reaches even 22%. This increase of the unreconstructed fcc areas underneath the molecular islands reflects a partial lifting of the reconstruction caused by the interaction between the adsorbed molecules and the outermost Au atoms at the molecule-metal interface. (C) 2008 Elsevier B.V. All rights reserved.

We show for the first time that, with two coadsorbed periodic structures it is possible to observe in a diffraction condition unique to one structure a relative enhancement of the vibrational losses characteristic of the species contained in the respective periodic structure. A recently developed SPA-LEED instrument equipped with an electron monochromator and analyser was used to distinguish true elastic diffraction from inelastic diffraction in the vibrational losses of coadsorbed (2×3)N/Cu(110) and the α-phase benzoate 4 3 −1 5 structure on Cu(110). Vibrational enhancements by factors of 4–20 were found in energy loss spectra and momentum-resolved spot profiles. Inelastic spot profiles are qualitatively consistent with a kinematic description of the energy–momentum conservation induced broadening from both loss-before-diffraction (L-D) and diffraction-before-loss (D-L) events.

Using reflection absorption infrared spectroscopy (RAIRS), the coverage-dependent reorientation of the benzoate species on the (110) and (111) faces of copper is compared and contrasted. Whereas on Cu(110) benzoate reorients from a flat-lying to an upright orientation with increasing coverage, on Cu(111), at all coverages, benzoate is aligned normal to the surface. The formation of periodic, flat-lying copper–benzoate structures has been attributed to the availability of metal adatoms, which differs dramatically between the (111) and (110) faces. We discuss the face specificity of molecular orientation by comparing calculated formation energies of adatom vacancies from ledges and kink sites on (100), (110) and (111) faces. Further support for this model is given by the evaporation of sodium, either by pre- or post-dosing, onto low-coverage benzoate/Cu(111), which induces benzoate to convert from a perpendicular to a parallel orientation. Likewise, coevaporation of Cu while dosing benzoic acid onto the Cu(111) surface also results in a majority of flat-lying benzoate species. Finally, for adsorption on the p(2×1)O/Cu(110) reconstruction, benzoate occurs only as the upright species, which is consistent with reducing the copper mobility and availability on the (110) face. We therefore suggest the possible role of metal adatoms as a new mechanism in controlling adsorbate orientation and therefore face specificity in surface reactions.

The chemisorption of glycine (NH 2 CH 2 COOH) and its fully deuterated analogue d 5 -glycine, vacuum deposited on a clean Cu{110} surface, have been investigated using reflection absorption infrared spectroscopy (RAIRS). At room temperature (300 K) a saturated monolayer is dissociatively adsorbed producing glycine in its anionic form; a glycinate species. The orientation of the adsorbed species changes as the coverage increases with bonding occurring initially via equivalent oxygen atoms of the carboxylate group, orientated broadly perpendicular to the surface, similar to the bonding found in simple carboxylic acids. At saturation coverage, at 300 K, a different orientation of the carboxylate group is observed with the carboxylate binding in a more unidentate fashion. The IR spectra are then very similar to those of solid copper glycinate. Low energy electron diffraction (LEED) shows a poor (3×2)g pattern. On annealing this fully covered surface to 420 K, there is no significant desorption and the IR spectra show dramatic changes in relative band intensities with the spectra becoming more similar to those obtained at low coverage. The (3×2)g LEED pattern sharpens considerably. At this stage, we suggest that anionic glycine (glycinate) species are adsorbed with the O 2 –C–C–N backbone essentially parallel to the surface with interadsorbate bonding dominated by CH⋯O and N–H⋯O hydrogen bonds similar to those found in bulk glycine. The (3×2) structure is a compromise between optimal adsorbate site, intermolecular hydrogen bonding and maximum adsorbate density. With the substrate held just below room temperature, multilayers of the zwitterionic glycine form which desorb in two stages with the second layer leaving the surface at a higher temperature than the other layers. At liquid nitrogen temperatures (85 K), some of the glycine is present on the surface in its acid form, as evidenced by the presence of a carbonyl (CO) stretch.

The adsorption of benzoic acid on Cu(110) between 300 and 350K results in benzoate species oriented perpendicular to the surface with a c(8 × 2) periodicity at saturation coverage. STM images of the ordered structure and non-dipolar scattering in HREELS demonstrate alignment in the [110] azimuth. We interpret the tunnelling mechanism in STM, negative ion resonance scattering in HREELS, and assign low-frequency vibrational modes utilising ab initio molecular orbital calculations. We propose a model with four molecules per c(8 × 2) unit cell (ϑ = 0.25ML) arranged in two out-of-phase, zig-zag rows along the [001] direction with the car☐ylates bound in short bridge sites alternately three and five lattice constants apart along the [110] direction. Adsorbate-induced dipole-active phonons in the frequency range 65–185 cm −1 in HREELS support the adsorption model.

We have extended the displaced harmonic oscillator model for negative ion resonance (NIR) scattering in high-resolution electron energy loss spectroscopy (HREELS), to interpret the energy transfer processes leading to disordering in STM and LEED, by allowing the curvature of the negative ion PES to be different to that of the ground PES. For the benzoate-Cu(110) system, the results of the extended model are significantly better if the ground and negative ion PESs have frequencies hω = 0.40 and 0.48 eV, respectively, rather than the same frequency. The large resonance width and asymmetry, but not the small overtone to fundamental excitation probability ratio, observed in HREELS can be accounted for with values of the coupling constant, β = 22.2 and inverse lifetime of Г = 0.6 eV (1.1 fs). These parameters, with nD = 7 are simultaneously able to account for the ratio of the STM:LEED disordering cross-sections and, most significantly, predict the large slope observed in the STM disordering cross-section as a function of bias. The properties of the probability distribution, Pn(ϵi, for the NIR process, involving two Franck-Condon transitions, is contrasted with the DIET process and some non-classical behaviour for the case ω0 ≉ ω1 is noted.

The adsorption of ethanol, isopropanol and tert-butanol on clean and H2O pre-dosed Si(100)-2 × 1 has been studied by high resolution electron energy loss spectroscopy (HREELS). We observe that the reactivity of the alcohols towards Si(100)-2 × 1 presaturated with H2O decreases with increasing number of methyl groups in the series (CH3)nCH3 − nOH (n = 1, 2, 3). All alcohols chemisorb on the silicon substrates via a deprotonation of the OH group with the formation of alkoxy and silicon hydride species. In the case of H2O saturated Si(100)-2 × 1, the adsorption involves cleavage of the SiSi bond of the silicon surface dimer.

The chemisorption of benzoic acid (C6H5COOH) and aniline (C6H5NH2) on Si(100)-2 × 1 at room temperature has been studied with high resolution electron energy loss spectroscopy (HREELS) and low electron energy diffraction (LEED). The vibrational data indicate that both aromatic species adsorb dissociatively on Si(100)-2 × 1 via a deprotonation reaction of the functional group. A SiOC or SiNC linkage, respectively, is formed between the silicon substrate, still reconstructed, and the intact phenyl ring. In both cases, the hydrogen atom bonds to a neighbouring silicon atom.

We examine the consequences of multiple scattering in HREELS and propose a new approach to defining the background for the purpose of resolution enhancement when the contribution of broad, continuum excitations interferes with discrete features of interest, e.g. adsorbate features. The method, which should be generally applicable to metals, oxides and semiconductors, is based on the Fourier-log deconvolution procedure for removing the Poisson distribution of multiple losses. The effects of noise and variation in instrumental sensitivity and transmission functions are considered. Statistical testing of the performance of currently available Bayesian resolution enhancement codes has been evaluated with synthetic spectra.

The chemistry of nitro- and amine-substituted aromatic molecules on a Cu(110) surface has been studied using Fourier transform infrared spectroscopy, by comparison of the adsorption of nitrobenzene (NB), p-dinitrobenzene (pDNB) and p-nitroaniline (pNA). When nitrobenzene was adsorbed on a clean Cu(110) surface at room temperature, it decomposed to form a phenyl species with the C2 axis nearer the surface normal than parallel. At 83 K, multilayer nitrobenzene formed with a vibrational spectrum, in good agreement with gas-phase data; upon warming, a phenyl species remained, which was stable to about 350 K. AES of the species present following dosing at 300 K showed carbon and oxygen but no nitrogen. When p-dinitrobenzene was adsorbed it decomposed, losing one NO2, to form a stable nitrophenyl species on Cu(110) orientated with the C2 axis closer to the surface normal than the phenyl species derived from nitrobenzene. In contrast, p-nitroaniline does not decompose on the Cu(110) surface at room temperature. Multilayer and monolayer p-nitroaniline are distinguished by frequency shifts of NO2 and NH2 modes, attributed to intermolecular hydrogen bonding. In the monolayer, the amine group appears to stabilise the ring-nitro group bond, allowing bonding to the surface via the NO2 group in an orientation perpendicular to the surface.

The chemisorption of 3-thiophene carboxylic acid on Cu(110) between 300 and 350 K has been investigated by high resolution electron energy loss spectroscopy (HREELS), scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). Ab initio molecular orbital calculations of the molecular ion aided in vibrational frequency assignments, interpretation of STM images and estimation of intra- and inter-molecular interactions influencing formation of the c(4 × 8) and p(2 × 1) structures. HREELS shows that at low coverage, the molecule lays flat with its π orbitals interacting with the surface. Increasing the coverage induces the molecules to reorient perpendicular to the surface and form a c(4 × 8) intermediate structure. Impact scattering in HREELS demonstrates that the molecules are preferentially aligned with the thiophene ring in the [110] azimuth. STM images suggest that the upright carboxylate species form rows of four adjacent molecules face-to-face along the [001] direction separated by four lattice constants in [110]. Subsequent rows are shifted by two lattice constants along [110], resulting in an overall c(4 × 8) periodicity and a coverage of 0.25 ML. With increasing coverage, the c(4 × 8) structure changes to a p(2 × 1) structure. A model with the carboxylates bound in short bridge sites two lattice constants apart along [110] with a local coverage of 0.5 ML is proposed. Steric repulsion in the p(2 × 1) structure results in rotation of the thiophene ring by an estimated 30° away from the [110] direction, consistent with impact scattering HREELS measurements. Calculated dipole-dipole repulsion between the carboxylate groups is large compared to any dipole-dipole attraction which could result from anti-parallel alignment of the static dipole moments of the thiophene rings.

In light of recent STM measurements of the O/A1(111) system, we reassign the dipole active modes observed at low coverage to resolve discrepancies between the interpretation of Strong, Firey, deWette and Erskine [Phys. Rev. B 26 (1982) 3483], invoking subsurface oxygen, and a variety of other studies which find no evidence for surface oxygen. The STM results, which show that very small island sizes are stabilized over an exposure range up to ∼ 200 L with a total coverage ≤ 0.2 ML, are incompatible with the assumption of long range periodicity required for lattice dynamical modeling. The consequence is that vibrational modes polarized parallel to the surface may become dipole active. Within an Al 3 O cluster model appropriate to exposures ≤ 3 L where most oxygen atoms are isolated species in three-fold hollow sites, the strong feature at 584 cm −1 (72 meV) is still attributed to top-layer oxygen motion perpecdicular to the surface (the symmetric Al 3 O stretch) but the second intense feature at 480 cm −1 (60 meV) is assigned to the umbrella mode involving predominantly Al motion parallel to the surface rather than the motion of two AlO layers moving perpendicular to the surface out of phase with each other. The lowest frequency mode near 224 cm −1 (28 meV) derives from the frustrated translation of the cluster perpendicular to the surface. At higher exposures (> 10 L) where multiple oxygen islands begin to appear, totally symmetric combinations of the E-derived asymmetric Al 3 O stretching motion polarised nominally parallel to the surface become dipole allowed and can be assigned to the loss at 850 cm −1 (105 meV), which was previously attributed to subsurface oxygen.

Scanning tunneling microscopy (STM) has been used to study structures formed by adsorbed formate and benzoate species on Cu(110) surfaces. Partially oxygen-precovered and clean surfaces were exposed to formic and benzoic acids, respectively. STM images show that both adsorbed formate and benzoate result in a tendency for bunched steps to align along 〈1 1 − 2〉 ; directions and to become equidistant: effectively creating small facet planes on the surface. In the case of benzoate, these planes can be described as (11 13 1) and (11 13 1 − ) planes. In the case of formate, ordered arrays of facet planes can form on step edges giving the steps a “sawtooth” appearance. Under some conditions adsorbed formate also appears to stabilize finger-like islands and pits.

Low energy ion-scattering and ion-recoil (LEIS and LEIR) spectroscopies have been used to monitor the structure and composition of an InSb(100) surface during continuous irradiation with argon ions (4.8 keV) directed at grazing incidence. Oscillations in both the scattered and recoil ion intensities have been observed during all bombardment sequences (for doses 2 × 10 16 ions cm 2 ). The periods of these oscillations show some dependence on the experimental geometry, and are close to those predicted for sputter-removal of one or two surface layers. Interestingly, the surface shows no sign of becoming amorphous even following excess ion bombardment. Details of the variations in surface composition are assigned, not only to layer-by-layer depth profiling, but also by rapid diffusion of Sb to the surface from the Sb depleted lattice. These data indicate that LEIS and LEIR can be used to monitor composition profiles with monolayer depth resolution such that different states of the same surface can be achieved simply and controllably by terminating ion bombardment following a pre-determined irradiation dose.

We have studied the effect of deuteration on the adsorption of benzoic acid on a copper (110) surface with RAIRS and HREELS. The resulting benzoate species has been characterized by the assignment of the spectra to modes of A 1 symmetry under the C 2v point group, which shows the carboxylate group and aromatic ring are perpendicular to the surface. Comparison to the non-deuterated species shows some unexpectedly large intensity changes and frequency shifts for several aromatic ring breathing modes due to coupling with modes of the carboxylate group

Metal surfaces can be functionalised by the chemisorption of a bifunctional molecule. One functionality is used to form the chemisorption bond, while the second is directed away from the substrate and available for bonding to a second, potentially different, molecule. The process can be continued to grow an organic film in a layer-by-layer manner using controlled deposition and reaction sequences. These possibilities are demonstrated by the interaction of pyromellitic dianhydride with copper and nickel surfaces and its subsequent reaction with aniline and p-phenylene diamine to form imide links via the intermediate amic acid. The chemisorption behaviour of pyromellitic dianhydride which involves opening one of the anhydride rings, loss of CO and formation of a surface carboxylate link has been characterised by X-ray PES and EELS, and supported by similar measurements on the chemisorption of phthalic anhydride and benzoic acid on a copper surface. The reactions are also followed by these techniques.

Scanning tunneling microscopy (STM) has been used to investigate the structure of the Sb-terminated InSb(100)-c(4 × 4) surface formed by deposition of Sb onto an In-terminated c(8 × 2) surface. Rectangular blocks of three Sb dimers are observed, with the dimer bond aligned along the [011] direction. The images are consistent with a structure based on a missing dimer model, in which a 34 monolayer of Sb atoms in the top layer form dimers on top of a full monolayer Sb-terminated surface. Atomically well resolved filled and empty states images of this surface show identical features and indicate that the same species, namely the Sb dimer, is imaged at both negative and positive sample bias.

The interaction of the polyimide precursor pyromellitic dianhydride (PMDA), and the related compounds benzoic acid and phthalic anhydride, with Cu(110) has been studied by high resolution electron energy loss spectroscopy (HREELS). For benzoic acid, deprotonation of the carboxylic acid group occurs on adsorption leading to the formation of a surface benzoate species (C6H5COO-). Bonding to the surface occurs through a carboxylate linkage via two equivalent oxygen atoms. The HREEL spectrum is characterised by an intense dipole active band, the symmetric OCO stretching vibration, at ∼ 1420 cm −1. The plane of the carboxylate group is aligned perpendicular to the surface as is the plane of the benzene ring. A similar species is found following exposure of Cu(110) to phthalic anhydride. The carboxylate linkage results from disruption of the anhydride ring with loss of the CO character (C6H4COO-). In the case of the dianhydride species PMDA, only one of the anhydride units is used in bonding to the surface; the second unit points away from the surface and is characterised by the symmetric anhydride stretch at 1255 cm−1 and weak OO stretching vibrations at ∼ 1850 cm−1. In both cases, changes in the intensity of some of the bands compared with benzoic acid suggest that the carboxylate group is tilted away from the surface normal due to an interaction between one of the carbons of the aromatic ring and the copper surface. This implies that the plane of the aromatic ring is now twisted out of the plane of the carboxylate group and, although still perpendicular to the surface, the axis is tilted to allow one of the β-carbon atoms to interact with the surface. In all cases, off-specular measurements at a primary electron energy of ∼ 8 eV are dominated by the intense CH stretching vibration. Measurements of the intensity of this mode, in the surface benzoate species, as a function of incident electron energy suggest that excitation of this mode occurs via a resonance scattering mechanism.

The deposition of Au at room temperature onto InSb(100) has been studied by high resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). At low coverages ( 4 ML), screening of the plasmon occurs due to the formation of a thin metallic film and AES results indicate significant segregation of Sb to the surface of the Au film. After annealing the Au-covered (∼ 10 ML) surface to 625 K, a c(4 × 4) structure is observed by LEED. HREEL spectra, recorded after the same treatment, show the re-appearance of the InSb conduction band plasmon. The results are consistent with the migration of the Au into the near-surface region of the InSb, the formation of a sub-surface InAu alloy and an Sb-rich surface due to segregation.

Atomic resolution scanning tunneling microscopy (STM) images of InSb(100) prepared by in situ treatment of several cycles of low energy argon ion bombardment and annealing have been obtained. The STM images demonstrate how the structural quality of the surface improves dramatically with repeated bombardment and annealing cycles. After annealing to 625 K, atomically flat terraces were obtained over areas in excess of 1000 A × 1000 A and low energy electron diffraction (LEED) studies at room temperature revealed a sharp, stable c(8 × 2) pattern. Atomic resolution images indicate (4 × 1) unit cells in which occupied lone pair orbitals of Sb atoms in the second layer are imaged. The data obtained is consistent with the structural model presented for this surface on the basis of high resolution core level photoemission by John et al. [Phys. Rev. B 39 (1989) 1730] in which 3 4 of a monolayer of In dimers are on top of a complete monolayer-Sb-terminated surface.

The phonon and plasmon excitations of both n- and p-type InSb(100) have been studied using high resolution electron energy loss spectroscopy (HREELS). The effects of structural damage, induced by low energy ion bombardment, on the conduction band plasmon energy has been monitored as a function of post-bombardment annealing temperature. In all cases, the plasmon energy reaches a maximum of between 55 and 75 meV after annealing to ~ 500 K. This indicates the presence of a large excess of free-carriers in the near-surface region probably due to the presence of defect states including Sb vacancies which would act as donor states. By monitoring the plasmon energy as a function of incident electron beam energy, we exploit the potential of the HREELS technique to probe the free-carrier concentration in semiconductors over a depth range of about 200–2000 A. The degree and depth of damage induced by the sputtering process is found to be approximately 800–1000 A into the bulk of the material, corresponding to the formation of an n-type layer in this near-surface region.

It is argued that the inverse photoemission features on Au(110)(1 × 2) attributed recently to surface umklapp effects are in fact surface states intrinsic to the unreconstructed (1 × 1) surface.

In their recent paper, concerning the adsorption of a c (2 × 2) overlayer of S on Ni(110), Chesters et al. [1] presented specular HREELS results showing two dipole active modes at 210 and 331 cm −1 , respectively. The higher frequency mode was assigned as a frustrated translation in the surface normal, the S-Ni stretching vibration, while the lower frequency mode was assigned as the surface resonance phonon mode observed at 194 cm −1 on the clean Ni(110) surface [1,2]. Whilst their assignments for the phonon excitation may indeed be correct, their symmetry analysis has major errors. Firstly, an incorrect surface Brillouin zone (SBZ) was drawn for the c (2 × 2) overlayer on the (110) surface and secondly, their symmetry analysis neglects the critical point that the dipole activity of the new phonon modes, which after adsorption appear at \ gG as a consequence of surface Umklapp processes, is crucially dependent on the adsorption site which is occupied [3,4].

Angle resolved photoemission using HeII (40.8 eV) radiation has been applied to a study of the influence of preadsorbed potassium on the adsorption of CO on Cu{100}. Substantial enhancement of the CO-metal bonding is indicated at low temperatures (≈ 80 K) by an increase in the 5σ bonding orbital binding energy of ≈ 0.7 eV. In addition, strong suppression of the characteristic shake-up feature, most noticeable on the 4σ emission is seen. At higher temperatures (≈ 300 K) the preadsorbed potassium induces substantial conversion to a new state which is believed to be dissociated CO. These effects appear pronounced only at rather high coverages indicating that the potassium-CO interaction is highly local and that CO may be adsorbed on top of the preadsorbed potassium rather than at adjacent surface sites.