Morphological change during crystallization of thin amorphous solid water films on Ru(0001)

The isothermal crystallization process of thin amorphous solid water (ASW) films on Ru(0001) has been investigated in real time by simultaneously employing helium atom scattering, infrared reflection absorption spectroscopy, and isothermal temperature-programmed desorption. The measurements reveal that the crystallization mechanism consists of random nucleation events in the bulk of the ASW films, followed by homogeneous growth. Morphological changes of the solid water film during crystallization expose the water monolayer just above the substrate to the vacuum during the crystallization process.     

Structure of Oxygen and CO Adsorption on Ru(0001) Electrode

It is important to understand the chemisorption of oxygen and CO on Ru(0001) surface. CO oxidation at oxygen precovered Ru(0001) surface at low oxygen coverages gave an extremely low CO oxidation rate, and it was also observed that, with a nominal oxygen coverage exceeding ca. 3 mL, rather high CO/CO2 conversion probabilities were achieved1. In the case of coadsorption of CO and oxygen on Ru(0001) surface under UHV conditions, a model comprising two CO molecules in an (22)-O unit cel…     

Initial growth of the water layer on (1 x 1)-oxygen-covered Ru(0001) in comparison with that on bare Ru(0001)

The initial growth of a water (D2O) layer on (1 x 1)-oxygen-covered Ru(0001) has been studied in comparison with that on bare Ru(0001) by means of temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Although water molecules adsorbed on both bare and (1 x 1)-oxygen-covered Ru(0001) commonly tend to form hydrogen bonds with each other when mobility occurs upon heating, the TPD and IRAS measurements for the two surfaces exhibit distinct differences. On (1 x 1)-oxygen-covered Ru(0001), most of the D2O molecules were desorbed with a peak at 160 K, even at submonolayer coverage, as condensed water desorption. The vibration spectra of adsorbed D2O also showed broad peaks such as a condensed water phase, from the beginning of low coverage. For submonolayer coverage, in addition, we found a characteristic O-D stretching mode at around 2650 cm(-1), which is never clearly observed for D2O on bare Ru(0001). Thus, we propose a distinctive water adsorption structure on (1 x 1)-oxygen-covered Ru(0001) and discuss its influence on water layer growth in comparison with the case of D2O on bare Ru(0001).     

Evidence of stable high-temperature D(x)-CO intermediates on the Ru(0001) surface

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.     

Interaction of CO and deuterium with bimetallic, monolayer Pt-island/film covered Ru(0001) surfaces

The adsorption properties of structurally well defined bimetallic Pt/Ru(0001) surfaces, consisting of a Ru(0001) substrate partly or fully covered by monolayer Pt islands or a monolayer Pt film, were studied by temperature programmed desorption (TPD) using CO and deuterium as probe molecules. Additionally, the adsorption of CO was investigated by infrared reflection absorption spectroscopy (IRAS). The presence of the pseudomorphic platinum islands or monolayer film leads to considerable modifications of the adsorption properties for both adsorbates, both on the Pt covered and, to a smaller extent, on the bare Ru part of the surfaces. In addition to distinct weakly bound adspecies, which are adsorbed on the monolayer Pt islands, we find unique contributions from island edge desorption, from spill-over processes during the desorption run, and a general down-shift of the peak related to desorption from Pt-free Ru(0001) areas with increasing Pt coverage. These effects, which we consider as characteristic for adsorption on bimetallic surfaces with large contiguous areas of the respective types, are discussed in detail.     

Oxygen adsorption on Pt/Ru(0001) layers

Chemical properties of epitaxially grown bimetallic layers may deviate substantially from the behavior of their constituents. Strain in conjunction with electronic effects due to the nearby interface represent the dominant contribution to this modification. One of the simplest surface processes to characterize reactivity of these substrates is the dissociative adsorption of an incoming homo-nuclear diatomic molecule. In this study, the adsorption of O(2) on various epitaxially grown Pt films on Ru(0001) has been investigated using infrared absorption spectroscopy and thermal desorption spectroscopy. Pt/Ru(0001) has been chosen as a model system to analyze the individual influences of lateral strain and of the residual substrate interaction on the energetics of a dissociative adsorption system. It is found that adsorption and dissociative sticking depends dramatically on Pt film thickness. Even though oxygen adsorption proceeds in a straightforward manner on Pt(111) and Ru(0001), molecular chemisorption of oxygen on Pt/Ru(0001) is entirely suppressed for the Pt/Ru(0001) monolayer. For two Pt layers chemisorbed molecular oxygen on Pt terraces is produced, albeit at a very slow rate; however, no (thermally induced) dissociation occurs. Only for Pt layer thicknesses N(Pt) ≥ 3 sticking gradually speeds up and annealing leads to dissociation of O(2), thereby approaching the behavior for oxygen adsorption on genuine Pt(111). For Pt monolayer films a novel state of chemisorbed O(2), most likely located at step edges of Pt monolayer islands is identified. This state is readily populated which precludes an activation barrier towards adsorption, in contrast to adsorption on terrace sites of the Pt/Ru(0001) monolayer.     

CO诱导的FeO(111)/Ru(0001)负载Au原子吸附位和电荷的改变

采用密度泛函理论研究了CO气氛对FeO(111)/Ru(0001)负载Au原子吸附位、电荷及其稳定性的影响. 首先考察了FeO(111)单层薄膜在Ru(0001)表面上的界面结构. 研究发现,表面莫尔超晶胞内的HCP区域有最小的Fe-O层间距(rumpling),且Fe和O原子均与衬底Ru形成化学键. Au原子在FeO/Ru(0001)上最稳定的吸附在HCP区域的Fe-bridge位. 其中,Au原子诱导两个Fe原子从O原子层的下面翻转到其上面,形成两个Au-Fe键,且Au带负电. 当把体系暴露在CO气氛下后,CO能诱导Au原子从原来最稳定的Fe-bridge位转移到其邻近的O-top位,伴随着Au的电荷从负变到正,形成非常稳定的Au⁺-CO羰基物. 结果表明,反应气氛对负载金属催化剂的化学状态及其稳定性的影响很大; 同时也强调了反应条件下催化剂原位表征的重要性.     

The growth of perylene on Ru(0001)

The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4x4) structure is observed from a monolayer (about 4 A thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 degrees C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 degrees C.     

Electrooxidation of CO on Ru（0001） and RuO2（ 100） Electrode Surfaces

The electrooxidation of CO on Ru(0001) and RuO2(100) electrode surfaces were characterized by cyclic voltammetry,AES and RHEED,The CO adlayer was first partially oxidized at 0.8 V, which is controlled by the attack of oxygen species toward the Ru(0001) surface. The remaining CO aldayer oxidation at 0.55 V is related to the combination of CO molecules with oxygen species already located on the surface,In contrast,successive peaks on RuO2(100) at 0.4 V and 0.72 V are observed ,which shows that CO molecules can directly react with two different lattice-oxygen on the surface to carbon dioxide.     

Synergistic interactions in three-center metal---metal bonding. Cu---Zn on Ru(0001)

Cu and Zn alloy when co-adsorbed on top of Ru(0001). The properties of these alloy films have been examined using thermal desorption mass spectroscopy, core-level photoemission, and CO chemisorption. For submonolayer coverages of Cu and Zn, the interaction among the Ru---Zn, Ru---Cu and Zn---Cu bonds produces a system that has electronic and chemical properties significantly different from those of Cu/Ru(0001), Zn/Ru(0001) and thick copper zinc alloys. Two-dimensional copper zinc alloys supported on Ru(0001) show Zn---Ru and Zn---Cu bonds more stable than the corresponding bonds in Zn/Ru(0001) or thick CuZn alloys. We propose that this phenomenon is caused by synergistic interactions in three-center metal---metal bonding.     

Thin silica films on Ru(0001): monolayer, bilayer and three-dimensional networks of [SiO4] tetrahedra

The atomic structure of thin silica films grown over a Ru(0001) substrate was studied by X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, low energy electron diffraction, helium ion scattering spectroscopy, CO temperature programmed desorption, and scanning tunneling microscopy in combination with density functional theory calculations. The films were prepared by Si vapor deposition and subsequent oxidation at high temperatures. The silica film first grows as a monolayer of corner-sharing [SiO(4)] tetrahedra strongly bonded to the Ru(0001) surface through the Si-O-Ru linkages. At increasing amounts of Si, the film forms a bilayer of corner-sharing [SiO(4)] tetrahedra which is weakly bonded to Ru(0001). The bilayer film can be grown in either the crystalline or vitreous state, or both coexisting. Further increasing the film thickness leads to the formation of vitreous silica exhibiting a three-dimensional network of [SiO(4)]. The principal structure of the films can be monitored by infrared spectroscopy, as each structure shows a characteristic vibrational band, i.e., ～1135 cm(-1) for a monolayer film, ～1300 cm(-1) for the bilayer structures, and ～1250 cm(-1) for the bulk-like vitreous silica.     

氢原子在Ru(0001)表面的化学吸附

用密度泛函理论研究了氢原子的污染对于Ru(0001)表面结构的影响. 通过PAW(projector-augmented wave)总能计算研究了p(1×1)、p(1×2)、(3^(1/2)×3^(1/2))R30°和p(2×2)等几种氢原子覆盖度下的吸附结构, 以及在上述结构下Ru(0001)面fcc(面心立方)格点和hcp(六方密堆)格点的氢原子吸附. 所得结果表明, 在p(1×1)-H、p(1×2)-H、(3^(1/2)×3^(1/2))R30°-H和p(2×2)-H几种H原子覆盖度下, 以p(1×1)-H结构单个氢原子吸附能为最大. 在p(1×1)-H吸附结构下,由于氢原子吸附导致的Ru(0001) 表面第一层Ru 原子收缩的理论计算数值分别为-1.11%(hcp 吸附)和-1.55%(fcc 吸附), 因此实际上最有可能的情况是两种吸附方式都有一定的几率. 而实验中观察到的“清洁”Ru(0001)表面实际上是有少量氢原子污染的表面. 不同覆盖度和氢分压下氢原子吸附的污染对Ru(0001)表面结构有极大的影响,其表面的各种特性都会随覆盖度的不同而产生相应的变化.     

Modification of Surface Reactivity by CO: Effects on Decomposition and Polymerization of Acetaldehyde on Ru(0001)

The adsorption and reaction of acetaldehyde on the clean and CO pre-covered Ru(0001) surfaces have been investigated using temperature programmed desorption method. On the clean Ru(0001) surface, the decomposition of acetaldehyde is the main reaction channel, with little polymerization occurring. However, on the CO pre-covered Ru(0001) surface, the decomposition of acetaldehyde is inhibited considerably with increasing CO coverage. Whereas, the polymerization occurs efficiently, especially at high CO coverage (θ_CO>0.5 ML), which is strongly CO coverage dependent. Combined with previous studies, the well-ordered hexagonal structure of CO layer formed on the Ru(0001) surface at high CO coverage that matches the configuration of paraldehyde is likely to be the origin of this remarkable phenomenon.     

Ultrathin Rh films on Ru(0001): oxidation in confinement

Ultrathin rhodium films with a thickness ranging from 1 to a few monolayers were deposited on a single-crystal Ru(0001) surface in order to investigate the oxidation behavior of ultrathin epitaxial films on a dissimilar substrate. It is found that rhodium grows on Ru(0001) initially layer by layer, adapting the in-plane lattice parameters of Ru(0001). When exposing Rh films to oxygen environment (approximately 4.8 x 10(6) L O2 exposure) at 660 K, 2-4 ML Rh films form a surface oxide composed of (9 x 9) O-Rh-O trilayers. Quite in contrast, oxidation of the 1 ML RhRu(0001) film leads to a poorly ordered oxide with a rutile structure reminiscent of RuO2(110) on Ru(0001). The oxidized 1 ML RhRu(0001) film contains much more oxygen than the oxidized thicker Rh films. Lower temperatures (535 K) and high doses of oxygen lead to a (1 x 1)-O overlayer on the 1 ML RhRu(0001) surface, whose atomic geometry resembles closely that of the (1 x 1)-O phase on clean Ru(0001).     

In situ FTIR studies on the effect of temperature on the electro-oxidation of small organic molecules at the Ru(0001) electrode

The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(000 1) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials < 900 mV vs. Ag/AgCl, and at all three temperatures employed, 10, 25 and 50 degrees C. However, both formaldehyde and formic acid did undergo dissociative adsorption, even at -200 mV, to form linear (CO(L)) and 3-fold-hollow (COH) binding CO adsorbates. In contrast to the adsorption of CO, it was found that increasing the temperature to 50 degrees C markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of both formaldehyde and formic acid. On increasing the potential, the electro-oxidation of the CO adsorbates to CO2 took place via reaction with the active (1 x 1)-O oxide. Formic acid was detected as a partial oxidation product during formaldehyde electro-oxidation. At all three temperatures employed, it was found that adsorbed CO species were formed from the adsorption of both formic acid and formaldehyde, and were oxidised to CO2 faster than was observed in the experiments involving CO adsorbed from CO(g), suggesting a higher mobility of the CO adsorbates formed from the adsorption of the HCOOH and HCHO. At potentials > 1000 mV, both the oxidation of formic acid to CO2 and the oxidation of formaldehyde to both CO2 and formic acid were significantly increased, and the oxidation of methanol to CO2 and methyl formate was observed, all of which were attributed to the formation of an active RuO2 phase on the Ru(0001) surface.     

Reactivity of oxide precursor states on Ru(0001)

Smooth and defect-rich Ru(0001) surfaces prepared under ultrahigh-vacuum (UHV) conditions have been loaded with oxygen under high-pressure (p 相似文献   

Growth of PtRu Clusters on Ru(0001)‐Supported Monolayer Graphene Films

We report on results of a detailed scanning tunnelling microscopy study on the formation, size and size distribution, and internal structure of small bimetallic PtRu clusters on a graphene monolayer film supported on a Ru(0001) substrate. These clusters, with sizes around ～15 (Ru) or ～40 (Pt) atoms per cluster at the lowest coverage, are interesting model systems for the catalytic behaviour of small metal PtRu particles, for example for application in electrocatalytic oxidation reactions. The clusters were generated by sequential deposition of the two metals at room temperature. The data reveal a distinct influence of the deposition sequence on the cluster formation process, with Ru pre‐deposition followed by Pt deposition leading to predominantly bimetallic clusters, possibly with a core–shell‐type structure, while the reverse sequence results in co‐existent mono‐ and bimetallic clusters, where the latter are likely to intermix at the interface. The observations are related to the nucleation process of the respective metals on the templated surface, and the 2D growth behaviour of the two metals.     

Surface Structure and Electrocatalytic Activity of Ru(0001) and Ru/Pt(111) Single Crystal Electrodes:In-situ FTIR and ex-situ LEED,RHEED and AES Studies

In-situ FTIR spectroscopic and electrochemical data, and ex-situ (emersion) electron diffraction (LEED and RHEED) and Auger electron spectroscopic (AES) data are presented on the structure and reactivity, with respect to the electro-oxidation of CO, of the Ru(0001) single crystal surfaces in perchloric acid solution. In both the absence and presence of adsorbed CO, the Ru(0001) electrode shows the potential-dependent formation of well-defined and ordered oxygen-containing adlayers. At low potentials (eg. from -80 to +200 mV vs Ag/AgCl), a (2 x 2)-O phase is formed, which is unreactive toward CO oxidation, in agreement with UHV studies; increasing the potential results in the formation of (3 x 1) and (1 x 1) phases at 410 mV and 1100 mV, respectively, with a concomitant increase in the reactivity of the surface toward CO oxidation. Both linear (CO_L) and threefold-hollow (CO_H) binding CO adsorbates (bands at 2000-2040 cm^-1 and 1770-1800 cm^-1, respectively) were observed on the Ru(0001) electrode. The in-situ FTIR data show that the adsorbed CO species still remain in compact islands as CO oxidation proceeds, suggesting that the oxidation occurs at the boundaries between the CO_ad and active O_ad domains via the Langmuir-Hinshelwood mechanism. At low CO coverages,reversible relaxation, (at lower potentials), and compression, (at higher potentials), of the CO_L adlayer were observed and rationalised in terms of the reduction and formation of surface O-adlayers, The data obtained from the Ru(0001) electrode are in marked contrast to those observed at polycrystalline Ru, where only linear CO is observed.     

Morphology and crystallization kinetics of compact (HGW) and porous (ASW) amorphous water ice

An investigation of porosity and isothermal crystallization kinetics of amorphous ice produced either by background water vapour deposition (ASW) or by hyperquenching of liquid droplets (HGW) is presented. These two types of ice are relevant for astronomical ice research (Gálvez et al., Astrophys. J., 2010, 724, 539) and are studied here for the first time under comparable experimental conditions. From CH(4) isothermal adsorption experiments at 40 K, surface areas of 280 ± 30 m(2) g(-1) for the ASW deposits and of 40 ± 12 m(2) g(-1) for comparable HGW samples were obtained. The crystallization kinetics was studied at 150 K by following the evolution of the band shape of the OD stretching vibration in HDO doped ASW and HGW samples generated at 14 K, 40 K and 90 K. Comparable rate constants of ～7 × 10(-4) s(-1) were obtained in all cases. However a significant difference was found between the n Avrami parameter of the samples generated at 14 K (n～ 1) and that of the rest (n > 2). This result hints at the possible existence of a structurally different form of amorphous ice for very low generation temperatures, already suggested in previous literature works.     

Oxide-free oxygen incorporation into Ru(0001)

A smooth Ru(0001) surface prepared under ultra-high vacuum conditions has been loaded with oxygen under high-pressure (p approximately 1 bar) and low-temperature (T < 600 K) conditions. Oxygen phases created in this way have been investigated by means of thermal desorption spectroscopy, low-energy electron diffraction, and ultraviolet photoelectron spectroscopy. The exposure procedures applied lead to oxygen incorporation into the subsurface region without creation of RuO2 domains. For oxygen exposures ranging from 10(11) to 10(14) L oxygen contents up to about 4 monolayer equivalent could be achieved. The oxygen incorporation is thermally activated. The CO oxidation reaction conducted at mild temperatures (T < 500 K) at a sample loaded with subsurface oxygen reaches CO --> CO2 conversion probabilities of 10(-3).