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Experimental X-ray photoelectron spectroscopy (XPS) and theoretical density functional theory (DFT) calculations reveal the electronic and structural properties of CoCu catalysts before and after CO adsorption. DFT calculations show that, prior to CO adsorption, CoCu has a high tendency to self-assemble into a Co@Cu core-shell structure, which is in accordance with previous atom probe tomography (APT) results for CoCu-based systems and the known mutually low miscibility of Co and Cu. We demonstrate that Co and Cu are electronically immiscible using a density of states (DOS) analysis wherein neither metal's electronic structure is greatly perturbed by the other in “mixed” CoCu. However, CO adsorption on Co is in fact weakened in CoCu compared to CO adsorption on pure Co despite being electronically unchanged in the alloy. Differential charge density analysis suggests that this is likely due to a lower electron density made available to Co by Cu. CO adsorption at coverages up to 1.00 ML are then investigated on a Cu/Co(0001) model slab to demonstrate CO-induced segregation effects in CoCu. Accordingly, a large driving force for a Co surface enrichment is found. At high coverages, CO can completely invert the layer sequence of Co and Cu. This result is echoed by XPS evidence, which shows that the surface Co/Cu ratio of CoCu is much larger in the presence of CO than in H 2 .

Methods are developed to describe catalytic reactions on multi-facetted surfaces in high electric fields in the conditions of field emission microscopy. These methods are applied to the hydrogen–oxygen–rhodium system for which a mean-field kinetic model is established. This model is shown to reproduce not only the nonequilibrium regimes of bistability and oscillations and their nanopatterns, but also the temperature-programmed desorption spectra of hydrogen and oxygen on rhodium, as well as the equilibrium phase diagram of oxygen on rhodium with the transition to the trilayer surface oxide ORhO. The dependence of the kinetic constants on the surface orientation of the facets is taken into account by expanding them in kubic harmonics suitable for the fcc rhodium crystal. The electric field modifies the gas pressure as well as the activation energies of the different kinetic processes. The tip of the field emission microscope is shown to behave as a nanoreactor.

The dynamic interaction of pure gold nanocrystals (“tips”) with H 2 O/CO gas mixtures was studied by means of video-field ion microscopy (FIM). While imaging with nano-scale resolution selected areas of the equivalent of ∼200 atomic Au sites were analysed for their chemical composition using short field pulses and injecting respective ions into a time-of-flight mass spectrometer (pulsed field desorption mass spectrometry, PFDMS). At room temperature the exposure of a clean Au sample to water gas at 10 −4 Pa, in the presence of an electric field of ∼10 V/nm, led to water adsorption and formation of bright patterns in FIM. Additional exposure to CO gas at 5 × 10 −3 Pa led to the removal of the water layer. This was associated with the occurrence of bright wave fronts which ignited simultaneously in several regions of the Au surface with no preference for a certain crystallographic surface plane. In some cases wave fronts were seen to collide resulting in more complicated patterns such as concentric rings. Surface areas free of water appeared with low brightness. The phenomena were completely reversible. PFDMS demonstrated water ions to be responsible for image formation. Surface hydroxyl was also detected mass spectrometrically and respective ion intensities decreased during the titration with CO. The results suggest that gold nanocrystals, in the absence of oxidic support materials, may be active in the reaction between water and CO at temperatures as low as 300 K and in the presence of an electric field of ∼10 V/nm.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed as an in situ tool to study the temperature-induced alteration of the surface composition of amorphous Finemet, Fe 73 Si 15.8 B 7.2 Cu 1 Nb 3 . Temperature was changed reversibly by cooling from room temperature to 118 K and warming back to room temperature. As a general result, the ion intensities and, consequently, the surface concentrations of the alloy constituents were found to vary non-monotonously. Therefore segregation processes were in operation the extent of which was element-specific. Most importantly, while cycling the temperature hysteresis behaviour was observed with concentration of Fe developing just opposite to that of the alloying elements. Accordingly, on cooling the alloy, the surface enrichment with B, Si, Nb, Cu attained first a maximum in the range of 248–193 K before the segregation changed the trend to establish appreciable depletion of these elements at 118 K (as compared to room temperature). By contrast, the surface iron content developed inversely and decreased first to a minimum at ∼223 K before reaching enrichment at 118 K. During warming, a maximum segregation of boron and silicon was observed at about 223 K – similar as on cooling – so that this temperature can be considered characteristic of the segregation process. Dissociative adsorption of water from the residual atmosphere occurring at low temperatures was responsible for the formation of surface hydroxides of iron, silicon and niobium; an enhanced adsorption of molecular water was observed at temperatures below 153 K. The temperature-dependent segregation and adsorption–desorption processes were found to be largely reversible, so that the surface composition of Finemet was practically restored after finishing the cooling–warming cycle. The processes and factors governing the non-monotonous temperature dependence of the surface segregation in the amorphous alloy are discussed within the frame of segregation theory and the influence of temperature-induced tensile stress on segregation.

We have studied the interaction of hydrogen with Rh tips under imaging conditions of field ion microscopy. In electric fields of 2.4 V/A, in the presence of hydrogen gas at 10 −5 mbar and at cryogenic temperatures, discrete events of field evaporation were found to form (1×2) patterns on Rh{1 1 0} due to the removal of Rh atoms along [0 1 1 ] the direction of densely packed atomic chains. This is different from the usual field evaporation mechanism which occurs by a shrinkage of layers from the edge to the center. Corroborating evidence for this interpretation is obtained from ab initio cluster calculations based on density functional theory.

Field ion microscopy (FIM) was used to study the reaction of nitric oxide (NO) with silver (Ag) field emitter tips. The clean and almost hemispherical shape of the Ag tip apex was found to undergo restructuring during field-free interaction with 150 L NO (1 L = 1.3 × 10 -4 Pa.s) at 400 K. Imaging at 57 K revealed an enlarged central (111) pole and a smaller number of layers leading to peripheral planes. Thus, crystal coarsening occurred during reaction with NO gas. Moreover, planes lying along the zone lines appeared dark and could only be recovered by field evaporation of a large number of surface layers. Areas of the former {012} planes appeared enlarged. These structural changes are interpreted as being caused by oxygen atoms released during NO decomposition. Cleaning the oxygen-covered tip by field evaporation and heating it to 400 K reproduced this reconstruction form. This finding is explained by the formation of subsurface oxygen and its resegregation to the surface. However, if the sample, either clean or oxygen-covered, was sputter-cleaned and subsequently heated to 400 K, only slight changes of the surface structure were found. These changes involved increased local disorder and somewhat enlarged low-index planes as compared to the field-evaporated clean Ag specimen.

The interaction of oxygen/hydrogen gas mixtures with Rh crystals was studied by means of video-FIM (field ion microscopy) at temperatures between 400 and 500 K and total pressures up to 10 -2 Pa. Rh samples were found to suffer considerable morphological changes during the reaction at 505 K and relative gas amounts of H 2 /O 2 = 0.1…9. Strong faceting of planes lying along the zone lines was seen and interpreted as being oxygen-driven. The surface structures changed while removing hydrogen from the gas mixture. In situ video-FIM allowed us to monitor the time dependence of changes. Accordingly, planes lying along the zone lines transformed first from O ad /H ad into O ad -covered The process started in {011 } planes and finally reached the (001) pole. A cross-like image feature thus appeared and divided the apex surface of the Rh crystal into four equivalent quadrants with {111 } planes in their center. These quadrants reacted subsequently in an independent manner, that is, the transformation from an O ad /H ad mixed layer into an O ad layer occurred with a delay period of up to several minutes while decreasing the hydrogen gas pressure. The structural changes observed were reversible upon increasing the hydrogen gas pressure.

The tribological properties of N-isopropylacrylamide (NIPA) gel surfaces were studied using scanning force microscopy (SFM) in air or in a temperature-controlled liquid cell. Topography and friction were probed with smooth, micrometer-sized glass spheres mounted on V-shaped cantilevers. The friction coefficients, μ, were evaluated from the slope of plots of the lateral force versus load. The respective value for the water-swollen NIPA gel (μ=0.42±0.05) was found to be only slightly smaller than that for the dry gel, but higher by a factor of more than 10 compared with macrotribological measurements in water. The high friction of NIPA in water is most probably influenced by the long-range adhesive forces (ranging up to 13 nN) as observed in measurements of force–displacement curves.

We have used field ion microscopy (FIM) to study the structural changes of Pt crystal tips after adsorption of nitric oxide at 525 K in the presence of an electric field of 8.5 V nm −1 . Imaging of the final tip shape in H 2 gas at cryogenic temperatures resulted in the observation of a top-truncated pyramidal morphology rather than a nearly hemisphere as initially present. The pyramidal form was found to consist of large slopes with {111} symmetry separated from the [001] oriented top by a small number of net planes. Planes other than {111} and (001) did not develop. In a subsequent field evaporation experiment, several ten layers of the (001) plane had to be removed in order to recover the initial form of a hemisphere.

The subject of this investigation was the kinetics of Ni volatilization in form of nickeltetracarbonyl (Ni(CO) 4 ) during the interaction of CO gas with a Ni foil at room temperature (or slightly above). A trap-decomposition technique on an auxiliary Rh surface and posterior Auger spectroscopy were used for the product analysis. The presence of a high step site density (kinks) on an intentionally roughened Ni surface was found to cause a strong rate enhancement. CO pressures as low as 5×10 −5 mbar turned out to be sufficient for the reaction to occur. However, a well-annealed equilibrium Ni surface remained inactive in Ni(CO) 4 formation under these conditions. A reaction model is presented by taking into account the present-day knowledge about Ni-subcarbonyl intermediate formation.

Atomic force microscopy has been employed to study the (010) surface structure of the natural zeolite heulandite. Images on a macroscopic scale exhibit large terraces separated from each other by half of the unit cell length b . Molecular resolution is obtained when measured in 0.1M NaOH. The surface ac unit cell is about 26% larger in area than the bulk unit cell.

The chemisorption of CO on either clean or oxygen containing Rh(210) single crystal surfaces has been investigated by means of temperature programmed static secondary ion mass spectrometry (TPSSIMS), temperature programmed desorption (TPD), ion scattering spectroscopy (ISS), and Auger electron spectroscopy (AES). Part of the CO, molecularly adsorbed on clean Rh(210), undergoes dissociation during heating. This is evidenced by the occurrence of RhnC+ and RhnO+ cluster ions (n = 1, 2) in TPSSIMS. Recombination of Cad and Oad at elevated temperatures is associated with a β-CO peak in TPD and the disappearance of respective features in TPSSIMS. Small amounts of subsurface oxygen obtained by adsorption of 10 L O2 ( PL = 1.3 × 10 −4 Pa s s ) at 1073 K, are not detectable by either ISS or SSIMS but show up in AES in form of KLL transitions shifted towards lower kinetic energies as compared to the respective transitions of chemisorbed oxygen prepared by exposure to 0.5 L O2 at 300 K. Subsurface oxygen is found to prevent dissociation of adsorbed CO. Neither significant amounts of RhnC+ and RhnO+ cluster ions (n = 1, 2) are present in SSIMS, nor does β-CO desorption take place in TPD under these conditions. By contrast, both methods indicate a change in the kinetics of thermal desorption of molecularly adsorbed CO.

Field ion microscopy (FIM) has been employed to study morphological changes of Rh field emitter tips induced by the (field-free) reaction with carbon monoxide at various temperatures between 200 and 420 K and pressures of 10 −4 Pa. The observed changes are dependent on the temperature and range from small lateral displacements of individual atoms to an overall reshaping of the emitter apex. Displacements are found first at 270 K in the (012) region as well as in the neighbouring high-index planes. A reshaping associated with the coarsening of the originally almost hemispherical crystal is observed to occur at higher temperatures. The step density between the central (001) plane and the peripherical low-index planes appears drastically reduced, i.e. facets with extended low-index terraces are formed. This is illustrated by a micrograph obtained after reaction at 420 K. The results can only be understood on the basis of surface diffusion. A model is given, based on earlier measurements by means of pulsed field desorption mass spectrometry (PFDMS), according to which Rh-subcarbonyl species are formed at kink sites and diffuse across the surface until they decompose at favourable sites.

Adsorption, desorption and decomposition of carbon monoxide on a Rh(210) surface have been investigated in the temperature range between 300 and 1100 K by combined temperature programmed static secondary ion mass spectrometry (TPSSIMS), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Following adsorption of CO at 300 K three different molecular binding states, α1, α2 and α3, are formed and identified through TPD. Partial decomposition of COad takes place during heating. Cad and Oad build-up have been followed by monitoring the relative Σ n Rh n X + Rh n + (n = 1, 2; X = O, C ) cluster ion intensities in (TP)SSIMS. At higher temperatures, i.e., above 500 K, Cad and Oad recombine as evidenced by the occurrence of a β-CO feature in TPD. This process is associated with a decrease of the Σ n Rh n X + Rh n + ratios. Further support for partial CO decomposition on Rh(210) is obtained from XPS. Carbon and oxygen show up in C 1s and O 1s features at 283.7 and 530.1 eV, respectively. Their intensities are about 10% of those found for a saturated CO layer at 300 K. Only the α3 state seems to be implicated in the decomposition process as low exposures to CO, for which only the α3 state is occupied, lead to the same amount of carbon and oxygen as high exposures.

The adsorption and decomposition of methanol on a clean and oxygen precovered Pd(111) single crystal surface has been studied by means of static secondary ion mass spectrometry (SSIMS) and X-ray photoelectron spectroscopy (XPS). Besides Pdx+(x=1−3) the SSIM spectra contain a variety of ions, including PdmO+(m=1,2), PdOCH3+, PdCH3+ and PdnCO+(n=1−3 these species are dependent on the oxygen precoverage and follow different trends in relaxation type measurements (uptake-deple- tion) or when the surface is heated in a temperature programmed manner (TPSSIMS). Preadsorbed oxygen (1 L O2 = 1.3 × 10−4 Pa · s) acts as a trapping agent for hydrogen atoms released during methanol decomposition. The occurrence of PdOCH3+ and PdCH3+ ions suggests the formation of adsorbed methoxy and methyl after both O-H and O-C bond activation in CH3OH. This is supported by the C1s XP spectra obtained at 310 K. Within the range of temperatures applied (300–500 K, during TPSSIMS) the formation of COad occurs exclusively through decomposition of the CH3Oad. Substantial amounts of this intermediate build up after accumulation of COad. While CH3Oad undergoes reversible thermal desorption (after recombination with Had) CH3, ad is little inclined to any reaction with coadsorbed species below 500 K. A suppression of methyl formation by the presence of adsorbed oxygen is not found.

The decomposition of methanol on a Pd(111) surface has been investigated under steady reaction conditions and at temperatures T > 300 K by combined static secondary ion mass spectrometry (SSIMS) and X-ray photoelectron spectroscopy (XPS). Pulsed field, desorption mass spectrometry (PFDMS) has been applied in studies of the same reaction at 300 K on a Pd field emitter surface with (111) orientation of the terraces. The major reaction route on both types of surfaces involves O-H bond breaking in CH 3 OH with subsequent formation of a methoxy species. Further decomposition of this methoxy species to CO (and H 2 ) proceeds via stepwise hydrogen abstraction as concluded from the observation of CH 2 O + and CHO + ions in the PFD mass spectra. The detection of PdCH + 3 and PdO + or PdOD + in SSIMS suggests O-C bond scission in CH 3 OH as a side reaction leading to surface methyl- and/or surface oxygen/hydroxyl species. The C1s XP spectra taken at T ⩾ 373 K, i.e. at temperatures well above those necessary for recombination of CH 3 O ad and H ad (with subsequent thermal desorption of methanol) give corroborating evidence for the simultaneous presence of adsorbed CO and CH 3 . The adsorbed methyl, which is present in quite small amounts, is thermally stable up to temperatures of at least 440 K.

The interaction of CO/O2 mixtures with well defined small Pd particles on different support materials (mica, MgO, alumina) has been studied by means of SSIMS. Various ionic species are desorbed from the surface, including those of the type PdnX+ (X = C, O, CO; n = 1, 2). Under catalytic reaction conditions at total pressures below 10−4 Pa the relative intensities PdnX+/Pdn+ depend on the partial pressures of CO and O2, on the surface temperature and on the Pd particle size. Our results indicate the partial decomposition of CO and the formation of surface carbon as an intermediate species during the steady state CO2 production. The intermediate carbon formation is most pronounced for small Pd particles (3 nm) at high CO partial pressures. Minor amounts of carbon are found for continuous films. The observed particle size effect proves the CO oxidation over Pd to be structure sensitive.

The reaction of methanol with stepped single crystal surfaces of Ru and Rh has been studied by pulsed field desorption mass spectrometry (PFDMS) in order to provide insight into the reaction mechanisms of the decomposition reaction. CH 3 OH dissociates easily on Ru and Rh and initially forms adsorbed OCH 3 at temperatures T =300–700 K. At temperatures T >460 K, on Ru(001) the surface coverage of CO ad is limited by thermal desorption during the reaction, time t R . CH 3 OH readily decomposes at, empty sites and, consequently, the amount of detected reaction intermediates is small. For T 3 + (OCH 3 + ) are observed, indicating that the decomposition of adsorbed methoxy, OCH 3 , is inhibited by the product species, CO ad . Thus, here the thermal desorption of CO ad is the rate determining step. This inhibition can be suppressed by field desorption of CO ad . In this way we observe that the decomposition reaction is faster than the shortest measurable time t R =100 μs, even at T =300 K. The influence of the electrical field on the decomposition reaction over Rh has been studied by applying a steady field, F R , during the reaction interval between the pulses. At F R ≈4 V/nm the intensities of COH + , COH 2 + , and CH 3 + increase steeply. This increase is most pronounced for COH 2 + and coincides with a decrease of the CO + and H n + intensities. Thus, the steady electrical field reduces the reaction rate and stabilizes the intermediate stages.