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Copper-based catalysts gain activity through the presence of poorly coordinated Cu atoms and incomplete oxidation at the surface. The catalytic mechanisms can in principle be observed by controlled dosing of reactants to single-crystal substrates. However, the interconnected influences of surface defects, partial oxidation, and adsorbate coverage present a large matrix of conditions that have not been fully explored in the literature. We recently characterized oxygen and carbon monoxide coadsorption on Cu(111), a nominally defect-free surface, and now extend our study to the stepped surface Cu(211). Temperature-programmed desorption of CO adsorbed to bare metal surfaces confirms that two sites dominate desorption from a saturated layer: atop terrace atoms of local (111) character and atop step edge atoms with CO bound more strongly to the latter. At low coverage, discrete CO resonances in reflection adsorption infrared spectra can be assigned to these sites: 2077 cm -1 for extended (111) terraces, 2093 cm -1 for step sites, and additional kink-adsorbed molecules at 2110 cm -1 . With increasing coverage, in contrast to Cu(111), the infrared spectral features on Cu(211) evolve and shift as a consequence of dipole-dipole coupling between differentially occupied types of sites. Auger electron spectroscopy shows that exposure to background O 2 oxidizes the (211) surface at a rate nearly 1 order of magnitude greater than (111); we argue that the resulting surface is stoichiometric Cu 2 O, as previously found for Cu(111). This oxide binds CO less strongly than the bare metal and the underlying crystal cut continues to influence the adsorption sites available to CO. On oxidized (111) terraces, broad absorption peaks at 2115-2120 cm -1 ; on oxidized Cu(211), CO adsorbed to step sites appears as a resolved secondary peak at 2144 cm -1 . This suite of spectroscopic signatures, obtained under carefully controlled conditions, will help to determine the origin and fate of adsorbed species in future studies of reaction mechanisms on copper., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

We have studied the adsorption of O 2 on Cu(111) using supersonic molecular beam techniques. For incident energies ranging between 100 and 400 meV, we have determined the sticking probability as a function of angle of incidence, surface temperature, and coverage. Initial sticking probabilities range from near 0 to 0.85 with an onset near 100 meV, making Cu(111) considerably less reactive than Cu(110) and Cu(100). Normal energy scaling applies and reactivity increases appreciably over the entire range of surface temperatures from 90 to 670 K. A strictly linearly decreasing coverage dependence on sticking precludes adsorption and dissociation via an extrinsic or long-lived mobile precursor state. We cannot exclude that sticking also occurs molecularly at the lowest surface temperatures. However, all tell tales from our experiments suggest that sticking is predominantly direct and dissociative. Comparison to earlier data shows implications for the relative reactivity of Cu(111) vs. Cu/Ru(0001) overlayers.

In a study preliminary to investigating CO 2 dissociation, we report our results on oxygen and carbon monoxide coadsorption on Cu(111). We use reflection adsorption infrared spectroscopy and Auger electron spectroscopy to characterize and quantify adsorbed species. On clean Cu(111), the CO internal stretch mode appears initially at 2077 cm -1 for a surface temperature of ∼80 K. We accurately reproduce the previously determined redshift of the absorption band with increasing CO coverage. We subsequently oxidize the surface by exposure to O 2 at 300 K to ensure O 2 dissociation. The band's frequency and line shape of subsequently adsorbed CO at ∼80 K are not affected. However, the maximum absorbance and integrated peak intensities drop with increasing O coverage. The data suggest that CO is not adsorbed near O, likely as a consequence of the mechanism of Cu(111) surface oxidation by O 2 at 300 K. We discuss whether our RAIRS results may be used to quantify CO 2 dissociation in the zero-coverage limit., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Conversion of CO 2 into CO with plasma processing is a potential method to transform intermittent sustainable electricity into storable chemical energy. The main challenges for developing this technology are how to get efficient CO 2 conversion with high energy efficiency and how to prove its feasibility on an industrial scale. In this paper we review the mechanisms and performance of different plasma methodologies used in CO 2 conversion. Mindful of the goals of obtaining efficient conversion and high energy efficiency, as well as industrial feasibility in mind, we emphasize a promising new approach of CO 2 conversion by using a thermal plasma in combination with a carbon co-reactant.

Low coordinated sites on catalytic surfaces often enhance reactivity, but the underlying dynamical processes are poorly understood. Using two independent approaches, we investigate the reactivity of O 2 impinging onto platinum and resolve how step edges on (111) terraces enhance sticking. At low incident energy, the linear dependence on step density, independence of step type, and insensitivity to O 2 's molecular alignment show that trapping into a physisorbed state precedes molecular chemisorption and dissociation. At higher impact energies, direct molecular chemisorption occurs in parallel on steps and terraces. While terraces are insensitive to alignment of the molecule within the (111) plane, steps favor molecules impacting with their internuclear axis parallel to the edge. Stereodynamical filtering thus controls sticking and dissociation of O 2 on Pt with a twofold role of steps., Competing Interests: The authors declare no conflict of interest., (Copyright © 2019 the Author(s). Published by PNAS.)

Rare earth (RE) ions doped in Si-based materials, compatible with Si technology, are promising compounds with regards to optical communication and energy conversion. In this article, we show the emission properties of Nd-doped Si-rich Si oxynitride (Nd-SRSON) films, and their dependence on the dangling bond density and the nature of the sensitizer. These films were prepared by reactive magnetron sputtering and post-annealing. The film composition, microstructure, and emission properties were investigated as a function of deposition parameters and annealing temperatures. Both Fourier transform infrared (FTIR) and ellipsometry spectroscopy measurements have confirmed that the sample composition (Si/N ratio) can be carefully tuned by varying the ratio of reactive nitrogen to argon in the sputtering plasma. Moreover, FTIR and x-ray photoelectron spectroscopy measurements demonstrate the existence of both nitrogen and oxygen dangling bonds (N· and O·) in as-deposited samples. These dangling bonds were passivated during annealing. Under non-resonant excitation at 488 nm, the films exhibit a significant photoluminescence (PL) signal from Nd 3+ ions demonstrating the occurrence of an effective sensitization of Nd 3+ ions in the host matrix. Both PL excitation and ellipsometry results (the energy band gap from new amorphous model) exclude the sensitization by an exciton with energy over the band gap, whereas the presence of Si agglomerates, at the atomic scale, have been identified as effective sensitizers towards Nd 3+ ions. This work not only provides knowledge to optimize Si-based materials for favorable emission properties, but also, presents a universal methodology to investigate the nature of sensitizers for RE emitters. This allows one to find correlations between composition, microstructure, and emission properties.

We present a combined experimental-theoretical study on structural and coverage dependences of the adsorption and desorption of molecular hydrogen on atomically flat Cu(111) and highly stepped Cu(211) surfaces. For molecules with identical incident energy from supersonic molecular beams, we find a reduced dissociative sticking probability for the stepped surface compared to Cu(111). DFT calculations of activation barriers to dissociation for the clean and partially precovered surfaces, as well as quantitative analysis of TPD spectra, support that the A-type step of the (211) surface causes an upward shift in activation barriers to dissociation and lowering of the desorption barrier. The new data allow us to determine low sticking probabilities at conditions where King and Wells measurements fail to determine the reactivity. They are also fully consistent with the unexpected observation that monoatomic steps on a surface lower the reactivity toward the dissociation of a diatomic molecule.

Stepped metal surfaces are usually assumed to exhibit an increased catalytic activity for bond cleavage of small molecules over their flat single-crystal counterparts. We present experimental and theoretical data on the dissociative adsorption of molecular hydrogen on copper that contradicts this notion. We observe hydrogen molecules to be more reactive on the flat Cu(111) than on the stepped Cu(211) surface. We suggest that this exceptional behavior is due to a geometric effect, that is, that bond cleavage on the flat surface does not occur preferentially over a top site.

Eley-Rideal (ER) reactions involving neutral atoms heavier than hydrogen reacting with adsorbed atoms of similar mass were first observed in recent molecular beam experiments by Zaharia et al. [Phys. Rev. Lett. 113, 053201 (2014)]. Through analysis of two types of measurements, they obtained different estimations for the N-O ER reaction cross section, one of which is unexpectedly high. This was qualitatively accounted for by invoking a secondary effect whereby the presence of N adatoms on the surface acted to "shield" O adatoms from prompt recombinative desorption. We apply a rate equation model that includes two ER processes involving different adsorbed species (N-Oad and N-Nad) and an N-adsorption process to the full-beam exposure subset of the experimental data in order to study the reaction kinetics. Values for the individual reaction cross sections are derived. The measured N2 response can be well described by the model, but it is insufficient to completely describe the NO response. Modeling of different exposures is used to evaluate the qualitative picture presented by Zaharia et al.

Forward-directed NO molecules with large translational energies are formed upon exposure of an O-covered Ru(0001) surface to a nitrogen (N+N_{2}) beam. This is an unequivocal experimental demonstration of the Eley-Rideal reaction for a "heavy" (i.e., nonhydrogenated) neutral system. The time dependence of prompt NO formation exhibits an exceptionally fast decay as a consequence of shifting reaction pathways and probabilities over the course of the exposure. Prompt production shuts down as the O coverage decreases due to competition from more favorable Eley-Rideal production of N_{2}.

Radiation-damaged tungsten is exposed to high-flux, low-energy deuterium plasmas at self-bias conditions. We observe that the fraction of deuterium that penetrates is only 10(-5)-10(-7) of the plasma flux and strongly dependent on the local surface temperature. We propose that deuterium does not directly penetrate bulk tungsten but that it thermalizes at the surface, where it forms a protective chemisorbed layer. We find an energy barrier of 1-2 eV between the surface and bulk, causing the influx of deuterium to be low as compared to the number of defects and leading to slow filling of the damaged layer.

We demonstrate the formation of complexes involving attractive interactions between D and CO on Ru(0001) that are stable at significantly higher temperatures than have previously been reported for such intermediate species on this surface. These complexes are evident by the appearance of new desorption features upon heating of the sample. They decompose in stages as the sample temperature is increased, with the most stable component desorbing at >500 K. The D:CO ratio remaining on the surface during the final stages of desorption tends towards 1:1. The new features are populated during normally incident molecular beam dosing of D(2) on to CO pre-covered Ru(0001) surfaces (180 K) when the CO coverage exceeds 50% of the saturation value. The amount of complex formed decreases somewhat with increasing CO pre-coverage. It is almost absent in the case of dosing on to the fully saturated surface. The results are interpreted in terms of both local and long-range rearrangements of the overlayer that give rise to the observed CO coverage dependence and limit the amount of complex that can be formed., (© 2012 American Institute of Physics)

A mixed beam of hyperthermal N atoms and N(2) molecules was scattered from the N-covered Ag(111) surface held at 300 K. The angular distribution of scattered N atoms is very broad. In contrast, N(2) molecules exhibit a sharp angular distribution. Taking into account the relative mass ratio, N loses more energy at the surface than N(2). In terms of energy loss, the atoms approximately follow the binary collision model while the molecules do not. Instead, the energy curves of scattered N(2) are more comparable to the parallel momentum conservation model for near specular outgoing angles (40°-65°). For both atoms and molecules the angle-resolved intensity and final energy curves are very similar to those from the bare surface. However, the N-covered surface yields non-negligible N(2) intensity for a broad range of outgoing angles, including along the surface normal. This was not the case from the clean surface, where the measured intensity distribution was confined to the narrower angular range indicated above. Backscattering and direct abstraction reactions are evaluated as possible origins of this additional N(2) signal. Of these, an abstraction mechanism appears to be the most consistent with the measured data., (© 2011 American Institute of Physics)

Hyperthermal Ar atoms were scattered under grazing incidence (θ(i) = 60°) from a CO-saturated Ru(0001) surface held at 180 K. Collision-induced desorption involving the ejection of fast CO (∼1 eV) occurs. The angularly resolved in-plane CO desorption distribution has a peak along the surface normal. However, the angular distribution varies with the fractional coverage of the surface. As the total CO coverage decreases, the instantaneous desorption maximum shifts to larger outgoing angles. The results are consistent with a CO desorption process that involves lateral interaction with neighboring molecules. Furthermore, the data indicate that the incident Ar cannot readily penetrate the saturated CO overlayer. Time-of-flight measurements of scattered Ar exhibit two components-fast and slow. The slow component is most evident when scattering from the fully covered surface. The ratio and origin of these components vary with the CO coverage.

Hyperthermal Ar atoms were scattered from a Ru(0001) surface held at temperatures of 180, 400 and 600 K, and from a Ru(0001)-(1×1)D surface held at 114 and 180 K. The resultant angular intensity and energy distributions are complex. The in-plane angular distributions have narrow (FWHM ≤ 10°) near-specular peaks and additional off-specular features. The energy distributions show an oscillatory behavior as a function of outgoing angle. In comparison, scattered Ar atoms from a Ag(111) surface exhibit a broad angular intensity distribution and an energy distribution that qualitatively tracks the binary collision model. The features observed for Ru, which are most evident when scattering from the clean surface at 180 K and from the Ru(0001)-(1×1)D surface, are consistent with rainbow scattering. The measured TOF profiles cannot be adequately described with a single shifted Maxwell-Boltzmann distribution. They can be fitted by two components that exhibit complex variations as a function of outgoing angle. This suggests at least two significantly different site and∕or trajectory dependent energy loss processes at the surface. The results are interpreted in terms of the stiffness of the surface and highlight the anomalous nature of the apparently simple hcp(0001) ruthenium surface.

In this study we investigate how the hydrogen flux administered to amorphous hydrogenated carbon (a-C : H) samples influences the sticking probability of hydrocarbon radicals on these samples. We bombard a-C : H samples that were previously subjected to different hydrogen fluxes with hydrocarbon radicals. The energy of the radicals is 10 eV. The sample temperatures are 700 and 1000 K. The results show that the sticking probability is larger on samples pre-irradiated with a higher hydrogen flux caused by the higher sp(2) fraction in the sample. This suggests that redeposition can contribute to the observed flux dependency of the carbon erosion yield.

Measurements on scattering of hyperthermal N atoms from the Ag(111) surface at temperatures of 500, 600, and 730 K are presented. The scattered atoms have a two-component angular distribution. One of the N components is very broad. In contrast, scattered Ar atoms exhibit only a sharp, single-component angular distribution. There are noteworthy features in the angle-resolved energy of the scattered N when compared with Ar. Taking into account the relative masses involved, N atoms lose significantly more energy at the surface than Ar. However, there is a preferential loss mechanism that predominantly affects low-energy N atoms with small total scattering angle trajectories. The results are interpreted in terms of probing of different interaction potentials: strongly attractive and almost purely repulsive, and spin-state changes during the interaction of N with the surface appear probable.

We study the flux dependence of the carbon erosion yield and the hydrogen enrichment of the surface in the high flux regime at 10(28) ions per m(2) s and higher by using molecular dynamics (MD). We simulate an amorphous hydrogenated carbon sample exposed to high flux hydrogen bombardment with a hydrogen energy of 10 eV at surface temperatures of 700 and 1000 K. As interaction potential the reactive empirical bond order potential of Brenner-Beardmore is taken and energy dissipation is simulated with the Berendsen thermostat. The simulation results show that the carbon erosion yield is higher for higher sample temperatures but does not show a strong dependence on the hydrogen flux. Hence, the hydrogen enrichment in the upper surface layer observed in the simulations most likely does not contribute to the erosion yield reduction in the experiments. Furthermore, the composition of the eroded material shows a slight increase in CH, C(2)H and C(2)H(2) for higher fluxes, whereas species with more hydrogen, C atoms and C(2) are decreased. However, the H : C ratio in the eroded material shows no flux dependence.

Hydroxyl (OH) is identified and characterized on the Ni(111) surface by high-resolution electron energy loss spectroscopy. We find clear evidence of stretching, bending, and translational modes that differ significantly from modes observed for H(2)O and O on Ni(111). Hydroxyl may be produced from water by two different methods. Annealing of water co-adsorbed with atomic oxygen at 85 K to above 170 K leads to the formation of OH with simultaneous desorption of excess water. Pure water layers treated in the same fashion show no dissociation. However, the exposure of pure water to 20 eV electrons at temperatures below 120 K produces OH in the presence of adsorbed H(2)O. In combination with temperature-programmed desorption studies, we show that the OH groups recombine between 180 and 240 K to form O and immediately desorbing H(2)O. The lack of influence of co-adsorbed H(2)O at 85 K on the O-H stretching mode indicates that OH does not participate in a hydrogen-bonding network.

We have studied the reactivity of hydrogen on the Pt(211) stepped surface using supersonic molecular beam techniques. We observe an energy dependence that is indicative of indirect adsorption below 9 kJ mol(-1) and direct adsorption between 0 and 37 kJ mol(-1). Comparison of our results to predictions based on six-dimensional quantum dynamics calculations for Pt(211) [R. A. Olsen et al., J. Chem. Phys. 128, 194715 (2008)] yields reasonable agreement. Discrepancies between theory and our experiments at low kinetic energy strongly indicate that the wells in the used potential energy surface are too shallow. Discrepancies at high kinetic energy point toward neglect of degrees of freedom vital to capture the full dynamics.

The influence of pre-adsorbed CO on the dissociative adsorption of D(2) on Ru(0001) is studied by molecular-beam techniques. We determine the initial dissociation probability of D(2) as a function of its kinetic energy for various CO pre-coverages between 0.00 and 0.67 monolayers (ML) at a surface temperature of 180 K. The results indicate that CO blocks D(2) dissociation and perturbs the local surface reactivity up to the nearest-neighbour Ru atoms. Non-activated sticking and dissociation become less important with increasing CO coverage, and vanish at theta(CO) approximately 0.33 ML. In addition, at high D(2) kinetic energy (>35 kJ mol(-1)) the site-blocking capability of CO decreases rapidly. These observations are attributed to a CO-induced activation barrier for D(2) dissociation in the vicinity of CO molecules.

We have studied the surface coverage dependence of the co-adsorption of D and D(2)O on the Ni(111) surface under UHV conditions. We use detailed temperature-programmed desorption studies and high resolution electron energy loss spectroscopy to show how pre-covering the surface with various amounts of D affects adsorption and desorption of D(2)O. Our results show that the effects of co-adsorption are strongly dependent on D-coverage. In the deuterium pre-coverage range of 0-0.3 ML, adsorption of deuterium leaves a fraction of the available surface area bare for D(2)O adsorption, which shows no significant changes compared to adsorption on the bare surface. Our data indicate phase segregation of hydrogen and water into islands. At low post-coverages, D(2)O forms a two-phase system on the remaining bare surface that shows zero-order desorption kinetics. This two phase system likely consists of a 2-D solid phase of extended islands of hexamer rings and a 2-D water gas phase. Increasing the water post-dose leads at first to 'freezing' of the 2-D gas and is followed by formation of ordered, multilayered water islands in-between the deuterium islands. For deuterium pre-coverages between 0.3 and 0.5 ML, our data may be interpreted that the water hexamer ring structure, (D(2)O)(6), required for the formation of an ordered multilayer, does not form anymore. Instead, more disordered linear and branched chains of water molecules grow in-between the extended, hydrophobic deuterium islands. These deuterium islands have a D-atom density in agreement with a (2x2)-2D structure. The disordered water structures adsorbed in-between form nucleation sites for growth of 3-D water structures. Loss of regular lateral hydrogen bonding and weakened interaction with the substrate reduces the binding energy of water significantly in this regime and results in lowering of the desorption temperature. At deuterium pre-coverages greater than 0.5 ML, the saturated (2x2)-2D structure mixes with (1x1)-1D patches. The mixed structures are also hydrophobic. On such surfaces, submonolayer doses of water lead to formation of 3-D water structures well before wetting the entire hydrogen-covered surface.

We have used temperature-programmed desorption in combination with specular and off-specular high resolution electron energy loss spectroscopy to study the interaction of H(2)O and D(2)O with the bare and hydrogen-covered Ni(111) surface. Our results for the bare metal surface agree with previous reports and we are able to relate two prominent features in vibrational spectra to nuclear motions at the surface. Pre-covering Ni(111) with hydrogen alters both adsorption and desorption of water significantly. The strong H-Ni bond does not allow for isotopic exchange with co-adsorbed D(2)O. Strong resemblance of desorption traces and vibrational spectra of submonolayer coverages on H-covered Ni(111) and multilayers on bare Ni(111) suggests that adsorption of hydrogen makes this nickel surface hydrophobic.

A highly sensitive imaging Thomson scattering system was developed for low temperature (0.1-10 eV) plasma applications at the Pilot-PSI linear plasma generator. The essential parts of the diagnostic are a neodymium doped yttrium aluminum garnet laser operating at the second harmonic (532 nm), a laser beam line with a unique stray light suppression system and a detection branch consisting of a Littrow spectrometer equipped with an efficient detector based on a "Generation III" image intensifier combined with an intensified charged coupled device camera. The system is capable of measuring electron density and temperature profiles of a plasma column of 30 mm in diameter with a spatial resolution of 0.6 mm and an observational error of 3% in the electron density (n(e)) and 6% in the electron temperature (T(e)) at n(e) = 4 x 10(19) m(-3). This is achievable at an accumulated laser input energy of 11 J (from 30 laser pulses at 10 Hz repetition frequency). The stray light contribution is below 9 x 10(17) m(-3) in electron density equivalents by the application of a unique stray light suppression system. The amount of laser energy that is required for a n(e) and T(e) measurement is 7 x 10(20)n(e) J, which means that single shot measurements are possible for n(e)>2 x 10(21) m(-3).

We examined reactivity of H(2) on Ru(0001) using molecular beam techniques and we compared our results to experimental results for similar systems. The dissociative adsorption of H(2) on Ru(0001) is similar to that on Pt(111) and Ni(111), although on ruthenium nonactivated adsorption is strongly suggested. However, we find no clear signature of a steering- or precursor-based mechanism that favors nonactivated reaction paths at low kinetic energy. In comparison to Pd(111) and Rh(111) our results indicate that a universal mechanism enhancing reactivity at low energy does not have a mass dependence. In addition, we have compared our results to predictions of reactivity for H(2) on Ru(0001) from six-dimensional dynamical calculations using two different generalized gradient approximation functionals. It leads us to conclude that the PW91 functional yields a more accurate value for the minimum energy path but does not impose enough corrugation in the potential. The revised-Perdew-Burke-Ernzerhof (RPBE) functional appears to behave slightly better at higher energies, but we find significant quantitative disagreement. We show that the difference is not due to different energy resolutions between experiment and theory. However, it may be due to a dependence of the reactivity on rotational state or on omission of relevant dimensions in the theoretical description.

Laser-induced desorption of water molecules from nanometer amorphous solid water films supported on a single-crystal platinum substrate is reported. A femtosecond laser pulse creates hot substrate electrons, which are injected into the water layer, resulting in significant desorption at the water-vacuum interface. The dependence of the desorption yield on film thickness and results for isotopic spacer and capping layers reveal that the desorbing water originates from relatively deep down into the water layer, i.e., from several nanometers below the surface. This is proposed to be the result of cooperative electronic effects resulting from the high electron densities in the thin water film, which cause a transient destabilization of the water H-bonded network. Motion of excited water molecules through the layer is enabled by mixing within the layer on ultrafast timescales during the desorption process.

We have simulated CF scattering from Si(100) using the molecular dynamics method. Translational energy loss spectra are presented. The shape of the energy loss distribution as a result of internal energy release is analyzed. At the classical turning point, the internal energy of the molecule is mainly in the form of rotational energy. The strong rotational excitation results in additional molecule-surfaces interactions during the latter half of the collision. These additional collisions permit some molecules that initially gain internal energy exceeding the bond strength to ultimately survive the collision process via rotational de-excitation. The rotational motion exhibited by surviving molecules is determined by the combination of the molecular axis orientation and the local surface structure during the collision process. The rotation planes of the surviving molecules are preferentially aligned with the surface normal (cartwheel-like and propeller-like motions). In this study, propeller-like motion of the surviving molecules is predicted. The majority of surviving molecules exhibit a cartwheel-like motion. However, molecules that gain a propeller-like rotation exhibit a much better alignment of their planes-of-rotation compared with molecules exhibiting cartwheel-like motion.

The decreasing availability of energy and concern about climate change necessitate the development of novel sustainable energy sources. Fusion energy is such a source. Although it will take several decades to develop it into routinely operated power sources, the ultimate potential of fusion energy is very high and badly needed. A major step forward in the development of fusion energy is the decision to construct the experimental test reactor ITER. ITER will stimulate research in many areas of science. This article serves as an introduction to some of those areas. In particular, we discuss research opportunities in the context of plasma-surface interactions. The fusion plasma, with a typical temperature of 10 keV, has to be brought into contact with a physical wall in order to remove the helium produced and drain the excess energy in the fusion plasma. The fusion plasma is far too hot to be brought into direct contact with a physical wall. It would degrade the wall and the debris from the wall would extinguish the plasma. Therefore, schemes are developed to cool down the plasma locally before it impacts on a physical surface. The resulting plasma-surface interaction in ITER is facing several challenges including surface erosion, material redeposition and tritium retention. In this article we introduce how the plasma-surface interaction relevant for ITER can be studied in small scale experiments. The various requirements for such experiments are introduced and examples of present and future experiments will be given. The emphasis in this article will be on the experimental studies of plasma-surface interactions.

The laser-induced movement of CO molecules over a platinum surface was followed in real time by means of ultrafast vibrational spectroscopy. Because the CO molecules bound on different surface sites exhibit different C-O stretch vibrational frequencies, the site-to-site hopping, triggered by excitation with a laser pulse, can be determined from subpicosecond changes in the vibrational spectra. The unexpectedly fast motion--characterized by a 500-femtosecond time constant--reveals that a rotational motion of the CO molecules, rather than pure translation, is required for this diffusion process. This conclusion is corroborated by density functional theory calculations.

The 266 nm photodissociation of bromoform adsorbed on an amorphous solid water (ASW) layer has been investigated for the first time under well-defined ultrahigh vacuum conditions. Time-of-flight (TOF) measurements indicate direct release of gas-phase Br, CHBr2, Br2, and CHBr species, with potential implications for stratospheric chemistry. Furthermore, new, ice-surface-mediated C-C (C2H2Br2) and C-O (CHBrO, CO) species are revealed in postirradiation temperature programmed desorption (TPD) and reflection absorption infrared (RAIR) spectra. A cross section of approximately 5 x 10(-20) cm2 is determined for bromoform photodissociation at 266 nm based on the integrated area of both the TOF spectra of Br and Br2 and the postirradiation TPD curves of CHBr3. The involvement of the free, non-hydrogen-bonded water groups at the ASW surface in the formation of the photoproducts is evident from the RAIRS results.

We present an experimental and theoretical investigation of the adsorption, desorption, and dissociation of NO on the stepped Pt (533) surface. By combining temperature programmed desorption and reflection absorption infrared spectroscopy, information about the adsorption sites at different temperatures is obtained. Surprisingly, metastable adsorption structures of NO can be produced through variation of the dosing temperature. We also show that part of the NO molecules adsorbed on the step sites dissociates around 450 K. After dissociation the N atoms can desorb either by combining with an O fragment, or with another N atom, resulting in NO and N(2). The N(2) production can be enhanced by coadsorbing CO on the surface: CO scavenges the oxygen atom, thereby suppressing associative recombinative desorption of N and O atoms. Density functional theory calculations are used to reveal the adsorption energies and vibrational frequencies of adsorbed NO as well as barriers for dissociation of NO and for diffusion of N atoms. The combined experimental results and theoretical calculations reveal that dissociation of NO is the rate limiting step in the formation of N(2)., ((c) 2004 American Institute of Physics.)

We demonstrate that the crystallization of thin, supported amorphous solid water layers is initiated at the water surface. This is concluded from the observation of sequential crystallization of amorphous water at the surface, in the bulk, and at the water-support interface. A surface nucleation model quantitatively reproduces the observed transformation kinetics at the three sites.

A novel application of vibrational sum frequency generation (VSFG) is developed to study the molecular properties of the surface of submicron particles in suspension. The Rayleigh-Gans-Debye scattering theory is extended to extract the local molecular response from the macroscopic nonlinearly scattered spectral intensity. These results demonstrate the use of VSFG to investigate quantitatively the surface molecular properties of submicron particles, dispersed in solution. It provides information on the order and density of alkane chains and allows us to determine the elements of the local second-order surface susceptibility.

The use of molecular beams to study chemical dynamics at surfaces is outlined. The techniques is briefly introduced and its applications are given in a few areas. Scattering experiments give detailed information about the first steps toward a chemical reaction at a surface. Beams with enhanced population of specific quantum states make an even more detailed analysis possible. Adsorption at surfaces can be studied very well using beam methods, especially in the case of activated processes. Beams can be used to grow novel structures. Beams allow the study of chemical reactions at surfaces, and in particular those where product are directly ejected into the gas phase, or where reactions take place upon impact. Finally the study of liquid surfaces is briefly introduced.